Origin and dynamics of a hybrid zone between Ramphocelus tanagers (Thraupidae) in Colombia
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(2) ABSTRACT. Characterizations of hybrid zones are of importance in evolutionary biology because they can give insights about the characters and processes implied in population divergence. Here, we characterize a hybrid zone between tanagers in the genus Ramphocelus (Thraupidae) located in Western Colombia. We tested whether this hybrid zone originated as a result of secondary contact or of primary differentiation, and described its dynamics across time using molecular, morphological, and plumage coloration data in combination with palaeodistribution modeling. Models of potential historical distributions based on climate data and genetic signatures of population expansion suggest that the hybrid zone originated following secondary contact between two populations that expanded their ranges out of isolated areas in the Quaternary. Concordant patterns of variation in phenotypic characters across the hybrid zone and its narrow extent are suggestive of a tension zone, maintained by a balance between dispersal and selection against hybrids. Comparisons between historical and current specimens suggest the zone has moved towards the east, possibly as a result of sexual selection or of asymmetric gene flow.. KEY WORDS: hybrid zone, Ramphocelus, palaeodistribution modeling, clines. Studies on hybrid zones allow making inferences about the characters and processes implied in the origin and maintenance of differences between populations and species;. 2.
(3) thus, characterizations of hybrid zones are of major importance to evolutionary biology (Barton and Hewitt 1985, Coyne and Orr 2004). A classic question about hybrid zones is how are they formed, with previous studies proposing two alternative hypotheses. First, the hypothesis of secondary contact suggests that hybrid zones result from expansion of populations that were previously isolated geographically and that interbreed in contact zones because complete reproductive isolation between them was not reached during the allopatric phase (Mayr, 1942). A second hypothesis proposes that hybrid zones form in parapatry, by primary differentiation across ecological gradients (Harrison, 1990). Secondary contact is likely to arise if environments that presently allow the distributions of hybridizing populations to overlap were disjunct in the past, a scenario that predicts one should observe genetic signatures of population expansions, some times it is difficult to found. Alternatively, primary differentiation would occur if the extent of suitable environments for the hybridizing populations has been stable over time; this predicts that populations have not expanded their ranges historically, and that the position of the hybrid zone (as indicated by the position of clines in molecular and morphological traits) is coincident with an environmental transition (Barton and Hewitt 1985, Vines et al. 2003). However, we might expect that in a primary differentiation hybrid zone, natural selection on different loci or characters would result in clines with different geographic positions, and that selectively neutral variation would not display a clinal pattern. In contrast, the hybrids between populations that meet at secondary hybrid zones often have low intrinsic fitness due to heterozygote disadvantage or breakdown of coadapted gene complexes (such hybrid zones are often referred to as tension zones) (Futuyma 2005).. Tests of hypotheses posed to account for the origin of hybrid zones can be conducted by examining the historical distribution of hybridizing taxa using paleodistributional 3.
(4) modeling, i.e. projecting ecological niche models, which predict the current distribution of species, onto models of historical climatic conditions to infer potential distributions in the past (Peterson et al. 2004, Carstens and Richards 2007). Such models of historical distributions represent hypotheses that can be tested by using molecular data to evaluate their population genetic predictions, such as signatures of population growth for presumably expanding populations and of stable population size and isolation by distance within populations occurring within climatically stable areas (Richards et al. 2007, Carnaval et al. 2009). This approach has revealed that several vertebrate hybrid zones in different areas of the world likely originated following range expansions leading to secondary contact (Ruegg et al. 2006, Swenson 2006, 2008, Moritz et al. 2009).. Another research focus of studies on hybrid zones is the analysis of their dynamics in time, which can allow understanding the role played by different evolutionary forces in such scenarios. When recombinant hybrid genotypes are less fit than parental genotypes, ‘tension zones’ are formed, which are maintained by a balance between the homogenizing effect of dispersal into the hybrid zone and the diversifying effect of selection against hybrids (Key 1968; Barton and Hewitt 1985; Barton 2001). If there is endogenous selection against hybrids, there should be coincidence in location and concordance in width of clines describing the variation in different characters across a hybrid zone, and such clines should remain stable over time (Moore and Price 1993; Kruuk et al. 1999). However, hybrid zones are often dynamic in time (i.e. they may shift or change in width) and because clines for different characters may change in different ways, one can make inferences about the action of particular processes (e.g. natural selection, sexual selection, competition, asymmetric hybridization, dominance drive) based on dynamics observed for different characters (Buggs 2007). For example, discordant patterns of plumage and. 4.
(5) mitochondrial DNA variation across a hybrid zone between Dendroica warblers, coupled with behavioral experiments showing aggressive superiority of males of one species over the other, indicate movement of this zone has been driven by competition-mediated asymmetric hybridization (Rohwer et al. 2001, Krosby and Rohwer 2009).. There is ample evidence of hybridization between many members of the tanager genus Ramphocelus (Aves, Thraupidae; Griscom, 1932, Sibley, 1958, Hackett 1996, Olson and Violani 1995, McCarthy 2006). In this study, we characterize a hybrid zone between members of this genus located in Western Colombia that has received little study although its existence was noted nearly a century ago (Chapman 1917) and was described in some detail by Sibley (1958). In the Cauca River Valley above 915 m elevation, one finds the large form flammigerus (whose males are black with a scarlet rump), whereas the smaller and yellow-rumped form icteronotus occurs along the costal plain west of the Andes extending into Costa Rica and northern Peru. Females and immatures are similar to their respective males, but are less strongly colored. Along a c. 140 km transect ranging approximately northwest from the city of Cali downslope along the western flank of the Cordillera Occidental, the two forms hybridize, forming a gradient in coloration and body mass (Sibley 1958). Currently, these forms are considered subspecies of R. flammigerus (Remsen et al. 2009), largely because gene exchange between them appears to be unrestricted and there is apparently no selection against hybrids (Sibley 1958).. The Ramphocelus system is particularly well suited to studying the role of different evolutionary forces at work in hybrid zones owing to the existence of variation in characters with different modes of inheritance, and presumably under different forms of selection. Variation in rump coloration across the hybrid zone likely reflects variation in. 5.
(6) the concentration of a single carotenoid pigment and is influenced by the environment because carotenoids are obtained from the diet (Plath 1945; Sibley 1958, Brush 1970). Furthermore, as a result of the strong sexual dichromatism in this species, and the likelihood that its mating system involves some degree of polygamy (Krueger et al. 2008), it appears likely that plumage coloration is influenced by sexual selection. In contrast, morphometric variation likely has a strong genetic basis (i.e. high heritability; Grant 1986, Rasner et al. 2004, Bears et al. 2008) and could be subject to natural selection (Schluter and Smith 1986, Grant and Grant 1994, Benkman 2003, Mila et al. 2009). The value of considering traits with different modes of inheritance and under different selective pressures to understand hybrid zone dynamics is illustrated by studies showing that clines for plumage traits involved in courtship are displaced with respect to clines for presumably neutral traits, suggesting a role for sexual selection driving introgression (Parsons et al. 1993, Brumfield et al. 2001), or that sex-linked molecular markers introgress over smaller distances than autosomal markers suggesting a role for sex chromosomes maintaining reproductive isolation (Carling and Brumfield 2009).. Here, we sought to evaluate whether the Ramphocelus hybrid zone originated as a result of secondary contact or of primary differentiation, and to examine the zone's dynamics over nearly a century to make inferences about the action of different evolutionary processes. To accomplish this, we (1) reconstructed the biogeographic and demographic history of these populations based on ecological niche modeling and coalescent analyses of mtDNA sequence data, (2) characterized genetic, morphological and plumage variation across the hybrid zone, and (3) compared spatial patterns of variation in morphometrics and plumage between specimens collected at different times to assess changes in the hybrid zone in terms of the position, shape, and width of clines.. 6.
(7) METHODS Samples We characterized the Ramphocelus hybrid zone historically by examining specimens collected from 1894 to 1986 in the ornithological collections of the American Museum of Natural History, the Cornell University Museum of Vertebrates, Universidad del Valle, and the Instituto de Ciencias Naturales at Universidad Nacional de Colombia. In order to describe current patterns of variation, one of us (AMR) collected 61 new specimens in 2007-2009. Of these new specimens, 48 are from localities ranging across the hybrid zone from Cali to Buenaventura over a distance of 140 kilometers by road (Sibley 1958); the remaining six are from localities distant from the hybrid zone in Departments Antioquia (2) and Cauca (4). Voucher specimens are deposited in the Museo de Historia Natural de la Universidad de los Andes (ANDES) and tissue samples in the ANDES and Instituto de Investigación de Recursos Biológicos Alexander von Humboldt (IAvH) collections. All localities (historical and current) were plotted and their position along a transect line that best adjusted to points (estimated using a linear regression between latitude and longitude) was recorded. To construct character clines (see below), we grouped sites into 11 sampling localities along the hybrid zone transect (Fig.1; Table 1).. Biogeographic history To model potential distributions of the study taxa, we used 343 georeferenced localities obtained from museum specimens (Darwin Database 2007, Global Biodiversity Facility (http://www.gbif.org) and reliable field observations from Costa Rica, Panama, Colombia, Ecuador, and Peru (Dataves, GBIF Data Portal, C. Sánchez, pers. comm., our observations). We associated localities with GIS layers for 19 climate variables at a c. 1. 7.
(8) km resolution developed for the present obtained from WorldClim (Hijmans et al. 2005). With these data, we used a maximum entropy approach (Phillips et al. 2006) based on current climate layers to generate models of the ecological niche and potential distribution of flammigerus and icteronotus at present (localities of both forms and presumed hybrids were considered together). Model performance in predicting present distributions, as evaluated using receiver operating characteristic curves (Fielding and Bell 1997) in Maxent, was satisfactory, validating the use of this approach to infer potential distributions in the past.. Models based on current climate data were projected onto historical climate surfaces for 6,000 years ago and for the Last Glacial Maximum (LGM; 21,000 years ago) to determine if the distributions of these taxa were likely disjunct in the past as predicted by the secondary contact hypothesis, or have likely been continuous as predicted by the primary intergradation hypothesis. This approach requires assuming ecological niche conservatism and that climate represents a long-term stable constraint on the potential distribution of populations (Peterson et al. 1999, Martínez-Meyer et al. 2004, Graham et al. 2004, Carnaval et al. 2009). Because ecological niche models are based only on climate data, they tend to overpredict potential distributions into areas where the study species do not occur owing to historical limitations to dispersal (e.g. the Amazon region in Ramphocelus). To reduce overprediction, we cropped maps of current and historical distributions to include only areas within the Andes EcoRegion as defined by WWF (Dinerstein et al. 1995). Although cropping potential distributions to this region probably did not remove all areas of model overprediction, it allowed for a semi-quantitative comparison of potential distributions across different time periods by calculating the extent of presence areas within the ecoregion. Maxent produces a continuous variable ranging from zero to one that. 8.
(9) relates to the probability of species presence at different sites. We considered a threshold of 10% omission to categorize pixels as suitable or unsuitable for each of the time periods.. Genetic characterization and demographic history We analyzed variation in DNA sequences of the cytochrome b mitochondrial gene for 54 individuals collected from 2007 to 2009. DNA was extracted from tissue samples or toe pad samples taken from specimens using a Qiagen DNeasy Tissue Kit or a phenolchloroform method as described by Sambrook and Russell (2001). For toe pad tissue samples, lysis time was extended up to five days and the final elution volume was set to 30 µl.. PCR reactions used primers H16064 and L14996 (Sorenson et al 1999) in 26 µl amplification reactions using the following conditions: 2 µl of template extract (~50 ng of DNA), 1 µl of 10 mM dNTPs, 1.2 µl of each primer (10 mM), 2.5 µl of 10X buffer with 1.5 µl of MgCl2, 0.125 µl Taq (5 units/ml AmpliTaq DNA polymerase, Applied Biosystems, Foster City, CA), and 16.5 µl of sterile ddH2O. Reactions were ran in a PTC200 Thermal Cycler (MJ Research), beginning with an initial denaturation at 94°C for two minutes, followed by 34 cycles of denaturation at 94°Cfor 30 s, annealing at 52°Cfor 30 s, and extension at 72°C for one minute, with a final extension phase at 72°C for 7 minutes. PCR products were purified with Exosap-IT (USB corporation), and sequenced in both directions. Sequences were edited, assembled and aligned using Geneious Pro 3.6.1. (http://www.geneious.com). We combined our data with two sequences of flammigerus available in GenBank, one from Ecuador (U15719-1) and one from Panamá (FJ799882.1), and with sequences of Piranga rubra (AY955196.1), Ramphocelus carbo (AF310048.1) and R. passerinii (EF529965.1) as outgroups.. 9.
(10) To describe genealogical relationships among haplotypes observed in flammigerus and icteronotus, we first reduced sequences in the sample to unique haplotypes using the program DNAsp 5.0 (Rozas 2009) and then conducted a maximum likelihood (ML) phylogenetic analysis. The analysis employed the GTR I G model and we evaluated nodal support using 1000 boostrap replicates in RAxML (Stamatakis et al. 2005), run from the CIPRES portal (http://www.phylo.org). Because divergence between sequences was limited, we also examined relationships using a median-joining haplotype network constructed in the program Network v.4.5.1 (Bendelt et al. 1999). We calculated uncorrected pairwise genetic distances using MEGA 4.1 (Tamura et al. 2007).. To determine whether flammigerus and icteronotus have experienced demographic expansions as expected if the Ramphocelus hybrid zone originated following secondary contact, or if these taxa have exhibited historically stable population sizes as expected if the zone originated by primary differentiation, we examined trends in effective population size through time using the Bayesian skyline plot method (Drummond et al. 2005) implemented in the program BEAST v1.4.8 (Drummond and Rambaut 2007). Analyses used the HKY+G model, which was selected as the best fit to the data according to the Akaike Information Criterion in ModelTest v 3.7 (Posada and Crandall, 1998). The number of groups was set to 10 and chains were run for 25,000,000 iterations, of which the first 1% was discarded as burn-in; genealogies and model parameters were sampled every 1,000 iterations.. Phenotypic Characterization To characterize the hybrid zone phenotypically, we measured six morphological characters. 10.
(11) on specimens (n=134 males, 85 females) with dial calipers to the nearest 0.1 mm: wing length (chord of unflattened wing from bend of wing to longest primary), exposed culmen, bill depth (at the base), bill width (at the base), tail length (from point of insertion of central rectrices to tip of longest rectrix), and tarsus length (from the joint of tarsusmetatarsus and tibiotarsus to the lateral edge of last undivided scute). We reduced variation in these characters using a principal components analysis (PCA) in the program SPSS v. 16.. We characterized plumage coloration based on reflectance spectra from 400 to 700 nm (the human visible spectrum) measured on the rump of adult museum specimens (n=155 males, 99 females) using an Ocean Optics USB4F00243 Spectrometer with the SpectraSuite software (Ocean Optics 2007). Three color measurements were estimated for each reflectance spectrum based on segment classification analysis (Endler 1990): brightness, an index of how much light is reflected from the sample relative to a white standard; chroma, the saturation of the color; and hue, which relates to the wavelength of maximum slope. These measurements were calculated using code for the R statistical software written by Parra (2009).. Phenotypic Characterization Based on Clines and Temporal Dynamics To compare patterns of morphometric and plumage reflectance between adult specimens collected at different times in a geographical context, we defined three different time periods based on temporal sampling gaps: prior to 1911, 1956-1986, and 2002-2009. Because our sample sizes were insufficient to allow accurate estimation of cline parameters, we did not use methods based on population genetics (e.g. Barton and Baird 1999, Gay et al 2008) to fit clines describing phenotypic variation in the hybrid zone.. 11.
(12) Rather, we described variation in morphometric and plumage reflectance data across the hybrid zone in different time periods using nonlinear least-squares regression based on a sigmoidal dose-response (variable slope) model, as implemented in the GraphPad Prism software (Motulsky and Christopolus 2004). This model describes a response variable y (i.e. character value in our study) as a function of an independent variable x (i.e. distance from one extreme of the hybrid zone in our case) based on a four-parameter logistic equation:. Here, bottom and top are the y values at the plateau's extremes (i.e. character values at each end of the hybrid zone in our case), LogEC50 is the x (distance) value associated with the midpoint between bottom and top in y, and HillSlope describes the steepness of the curve (Motulsky and Christopolus 2004). Curve fitting using this model allowed us to construct clines and to estimate their center (LogEC50) and width (1/HillSlope) (Szymura and Barton 1986). However, the curve-fitting algorithm did not converge to a solution for some traits and time periods. In those cases, we simply describe variation across the hybrid zone using scatter plots.. RESULTS Biogeographic history A niche model developed under current climatic conditions in Maxent (annual temperature range contributed most, i.e. 23%, to the model) accurately predicted the distributions of flammigerus+icteronotus, with an area under the ROC curve score of 0.987. This suggests that the assumption that climate limits distributions in these taxa is reasonable, so we. 12.
(13) projected models onto past climatic conditions to estimate their potential historical distributions at 6,000 and 21,000 years ago.. Although our models evidently overpredict potential distributions, it is clear that the extent of suitable environments for flammigerus+icteronotus has not been stable over time. The modelled current range of these taxa in the Northern Andes Ecoregion extends for c. 420,000 km2. The predicted potential distribution based on climate for 6,000 years ago was of similar size, with c. 460,000 km2 (Fig. 2). This indicates that current climate conditions and those from 6,000 years ago were similarly suitable for the presence of these taxa at several sites. Indeed, models suggest that the two forms could have been in contact at that time in the current location of the hybrid zone (Fig. 2). In contrast, the predicted range during the LGM was smaller than the predicted current range (c. 280,000 km2; Fig. 3). Moreover, suitable conditions for flammigerus+icteronotus at 21,000 years before present were not continuous along the Pacific slope of the Cordillera Occidental, suggesting that these two forms were possibly disjunct during the LGM. Thus, the hybrid zone may have originated following population expansions and secondary contact as a result of climate change since the LGM, a possibility we address below based on patterns of genetic variation.. Genetic Characterization Overall, there was low genetic divergence between samples and genetic structure across the hybrid zone and among other localities was limited. In 61 individuals analyzed, there were 30 haplotypes with a total of 50 segregating sites. Mean sequence divergence within Colombia was only 0.425% (0-1.385%), but a sample from Ecuador, was 2.57% divergent from the rest of the haplotypes. Relationships among haplotypes were not clearly resolved by the ML phylogenetic analysis (Fig. 4) and genetic variation was not consistent with 13.
(14) position along the hybrid zone as shown by the haplotype network (Fig. 5).. Although confidence intervals for population size in the Bayesian skyline plot are wide (Fig. 6), this analysis suggests that populations show a genetic signature of expansion. This result is also consistent with the hypothesis that the hybrid zone originated as a result of secondary contact following expansion of populations from formerly disjunct areas.. Phenotypic Characterization Reduction of morphometric variation using PCA resulted in a first component (PC1) describing body size in both males and females. In both sexes, variables loading most heavily on this axis (which accounted for 24.5% of the variation in males and 28.9% in females) were tail length and wing chord. Thus, in the following we use PC1 as a general measurement of body size. We did not consider other principal component axes (e.g. PC2, on which bill dimensions loaded heavily) in additional analyses because they did not vary clinally across the hybrid zone.. Morphological data for historical and current male specimens provide evidence of clinal variation in body size (i.e. PC1) along the hybrid zone, with icteronotus being smaller than flammigerus (Fig. 7A). The sigmoidal dose-response model estimated that the center of the morphometric cline is currently located at c. 84 km. In contrast, the center of the cline in the pre-1911 and 1956-1986 samples was estimated at c. 74 and 75 km, respectively, suggesting the zone has moved some 10 km. However, our curve-fitting analysis was unable to estimate confidence intervals for cline centers, so these results must be interpreted with care. The estimated width was very narrow at all times (between 1.4 and 3.8 km), but a confidence interval could only be estimated for the 1956-1986 samples and. 14.
(15) was very wide (Table 2). Data for females could not be fit to the model so we were unable to estimate cline parameters, but pre-1911 and 1956-1986 specimens show clinal trends similar to those observed in males (Fig. 7B). Present-day data for females were concentrated in the center of the hybrid zone, so we were unable to adequately describe the relationship between distance and PC1 for this time period (Fig. 7B).. Plumage brightness of males also varies clinallly, with icteronotus being brighter than flammigerus (Fig. 8A). The brightness cline for current data could not be fit to the model so we were unable to estimate cline parameters, but the center for the pre-1911 and 19561986 samples was estimated at 73 km (95% CI: 67-78.82, estimated for the pre-1911). The estimated width in the pre-1911 sample (12.2 km) was wider than the estimated width in 1956 (0.8 km), but no confidence intervals could be estimated (Table 2). Data for females for the pre-1911 and 1956-1986 samples could not be fit to the model, but for current specimens the estimated center was 96.2 km, with a width of 1.3 km (no CI could be estimated; Fig. 8B, Table 2).. Finally, the rump color of males (as measured by chroma and hue) varied clinally in historical and current specimens, ranging from the yellow icteronotus to the redder flammigerus (Fig. 9A and 10A). The estimated center of the chroma cline is currently located at 84 km, contrasting with the center for the pre-1911 specimens, which was estimated at 73 km (95% CI: 73.6-74.3 km). Data from 1956-1986 could not be fit to the model so we were unable to estimate cline parameters. The estimated width was very narrow in both the pre-1911 (0.86 km) and current (1.17 km) data, but a confidence interval could only be estimated for the pre-1911 samples and it was very wide (Table 2). Data for females also showed clinal variation. The center of the chroma cline is currently. 15.
(16) located at 84 km (no CI could be estimated), whereas it was estimated at 79 km (95% CI: 67.8-92.1 km) in the pre-1911 sample and at 74 km in the 1956-1986 data (no CI estimated). The estimated width in the pre-1911 sample was 14.6 km, much wider than in 1956-1986 (1.1 km) and in the current sample (1.2 km) (Table 2). The estimated center of the hue cline in males is currently located at 84 km (i.e. locality 8). The cline-fitting algorithm was unable to converge on a confidence interval for this parameter, but its point estimate lies outside confidence intervals estimated for historical specimens (pre-1911: 73 km, 95% CI 73.2-74.6 km; 1956-1986: 78 km, 95% CI: 74.6-82.4 km; Fig. 10A), suggesting some degree of zone movement. The estimated widths are very narrow currently (1.2 km) and in the pre-1911 data (1.1 km), in contrast with the estimated width in 1956-1986, which was 10 km (Table 2). Data for females vary clinally in the pre-1911 sample (Fig. 10B) and the center was estimated at 80 km (95% CI: 67.6-93.0 km) with a 16 km width (Table 2). Data for the 1956-1986 samples and current samples could not be fit to the model.. In sum, our data consistently indicate that for each time period, clines for different traits seem to be coincident. In addition, cline centers do not seem to be coincident across time periods, suggesting the zone has moved some 10 km towards Cali. However, confidence intervals (when available) are very wide so interpretation of this pattern must be careful.. DISCUSSION. Biogeography and demographic history Niche models indicate that potential distributions of R. f. icteronotus and R. f. flammigerus were likely disjunct at the LGM (21,000 ya), but were potentially in contact by 6,000 ya.. 16.
(17) This scenario is supported by the historical demography analysis based on mtDNA sequence data, which indicates populations have experienced significant range expansions. This suggests that these forms likely diverged while isolated in each flank of the Cordillera Occidental (icteronotus in the Pacific and flammigerus in the Cauca Valley) and then expanded their distributions, presumably tracking the influence of Pleistocene climate change on vegetation (van der Hammen and Gonzalez 1960; van der Hammen 1961). Thus, our results support the hypothesis that the hybrid zone originated as a result of secondary contact between two populations that did not develop complete reproductive isolation during an allopatric phase (Mayr 1942, Haffer 1967, Hewitt 2001), but are inconsistent with the hypothesis of primary differentiation.. Based on patterns of genetic variation (Hewitt 2000), pollen fossil data (Jackson and Overpeck 2000), and ecological niche modeling (Ruegg et al. 2006, Swenson 2006), several studies in the north temperate zone indicate that the origin of many hybrid zones can be explained as a result of population expansions from isolated refugia since the Last Glacial Maximum. A similar hypothesis was proposed to account for the origin of contact zones in tropical rainforest organisms (Haffer 1967, Haffer 1974, Haffer 1985, Endler 1982), but with the exception of studies in Australia (e.g. Moritz et al. 2009), research on the origin of hybrid zones in the tropics has been limited (Brumfield 2005). By combining ecological niche modeling of paleodistributions with coalescent analyses of population dynamics, this study found evidence consistent with the hypothesis that hybrid zones in Neotropical forest birds resulted from expansion of populations out of isolated areas in the Quaternary. Moreover, the divergence between icteronotus and flammigerus likely took place in the Pleistocene, as indicated by low levels of mtDNA divergence suggesting recent differentiation. However, low divergence across the hybrid zone might also be. 17.
(18) explained by introgression.. Our models based on climate data indicate that the origin of the hybrid zone between R. f. ictenotus and R. f. flammigerus could date from at least 6,000 years ago, when suitable environments for the presence of these forms occurred across the area where the hybrid zone is currently located. In contrast, Sibley (1958) proposed that contact between these forms resulted from recent deforestation that created scrub and second-growth habitats, which are favored by these tanagers over dense rain forest. Although our analyses suggest that climatic conditions were suitable for contact between R. f. icteronotus and R. f. flammigerus thousands of years prior to human alterations in the area, it is likely that anthropogenic activities have facilitated contact between the two forms, possibly leading to an increased incidence of hybridization in recent times.. Characterization and dynamics of the hybrid zone Our analyses are consistent with Sibley's (1958) characterization of the Ramphocelus hybrid zone, showing there is clinal variation in coloration and body size, with males showing more clear trends than females. In addition, we documented that three different measures of coloration (brightness, chroma, and hue) vary clinally across the hybrid zone. Two main patterns are apparent in our data: (1) at each of the three time periods, clines for different traits (e.g. body size, chroma and hue in 2007-2009) appear to be coincident (i.e. they have approximately equal centers) and are similarly narrow, and (2) cline centers do not appear to be coincident across different time periods. Specifically, the center is currently located around 84 km, whereas in the pre-1911 and 1956-1986 data sets, centers were located c. 10 km to the west, suggesting a possible displacement in the position of the hybrid zone.. 18.
(19) The coincidence of cline centers for different characters and their apparent concordance in width (despite uncertainty in the estimation of these parameters) in each of the three time periods is consistent with a tension zone model. This is further supported by the width estimated for character clines. Assuming that the hybrid zone originated at least 6,000 ya according to climate-based models, that generation time in Ramphocelus is 1-2 years, and that dispersal distances per generation lie somewhere between 1 and 20 km, the expected width of clines under a neutral diffusion model (equations in Endler 1977 and Barton and Gale 1993) would be between c. 25 km and more than 500 km. This is much wider than what we observed (Table 2), which requires invoking some form of selection. Alternatively, narrow clines may be a result of a more recent origin of the hybrid zone than implied by climate data. However, even if one assumes that the hybrid zone is as young as proposed by Sibley (1958), the observed clines appear narrower than expected under neutral diffusion (c. 4-75 km). In sum, our results suggest that the Ramphocelus hybrid zone might be a tension zone, maintained by a balance between dispersal and a genomewide barrier to gene flow (Key 1968; Barton & Hewitt 1985; Barton 2001; Ruegg 2008, Mettler and Spellman. 2009). This interpretation contrasts with Sibley´s (1958) conclusion that ¨there is no genetic barrier between of coastal plain and those of the Cauca Valley¨.. That cline centers do not appear to be coincident across different time periods for each of the characters suggests movement of the hybrid zone, but this interpretation needs to be tempered because samples were not taken at exactly the same localities at each time period and because the centers estimated with the sigmoidal dose-response model in some cases had very wide confidence intervals. However, our field observations indicate that the current patterns of variation are, in fact, different from those described by Sibley (1958).. 19.
(20) Specifically, we frequently observed yellow-rumped individuals at Salado and Queremal (locality 8), where Sibley did not report any, and we also have occasional records of yellow-rumped females near Cali, the eastern extreme of the transect. Thus, our quantitative analyses and field observations suggest that the icteronotus phenotype (yellow rump and smaller body size) has extended to the east.. A possible explanation for the concurrent movement of clines for different characters along hybrid zones is competitive advantage of one phenotype mediated by aggression or by sexual selection (Buggs 2007). Thus, movement of the Ramphocelus hybrid zone may have been driven by competition or sexual selection favoring the icteronotus phenotype. We believe it is unlikely that aggressive superiority of icteronotus explains this pattern as shown in other studies of hybrid zones (McDonald et al. 2001, Rohwer et al. 2001) owing to its smaller body size, however in Manacus hybrid zone, M.vitellinus is much more aggressive than M. candei and the latter is much larger but less aggressive bird. Thus, it would be of interest to study mating patterns in the field and to conduct mate choice experiments to determine whether the icteronotus phenotype has increased reproductive success as a result of sexual selection (Stein and Uy 2006).. If sexual selection is based on carotenoid plumage color, which presumably is strongly influenced by the environment (Brush 1970), it is somewhat puzzling that coloration seems to have moved across the hybrid zone in concert with morphometric variation, which presumably has a high heritability and is not involved in mate choice. It is possible, however, that the ability to obtain and accumulate carotenoids is heritable and the fitness advantages it confers may be linked to genes involved in reproductive isolation (Blount and McGraw 2008). If this is the case in R. flammigerus it would represent a plausible. 20.
(21) explanation for the movement of coloration in concert with others traits.. An alternative explanation for zone movement was proposed by Sibley (1958), who predicted that the icteronotus phenotype would introgress across the hybrid zone as a consequence of increased gene flow from coastal to interior populations resulting from presumably larger populations sizes in the former. This could be studied in the future with more samples, using neutral markers to estimate the magnitude of gene flow in both directions (Hey and Nielsen 2004).. In conclusion, this study demonstrates that 1) Models of potential historical distributions based on climate data and genetic signatures of population expansion suggest that the R. flammigerus hybrid zone was originated following secondary contact between two populations that expanded their ranges out of isolated areas in the Quaternary, 2) Concordant patterns of variation in phenotypic characters across the hybrid zone and its narrow extent are suggestive of a tension zone, maintained by a balance between dispersal and selection against hybrids, 3) Comparisons between historical and current specimens suggest the zone has moved towards the east, possibly as a result of sexual selection or of asymmetric gene flow. Future studies on this system should focus on behavioral analyses and would benefit from assessing patterns of variation in molecular markers with different modes of inheritance (i.e. sex-linked nuclear introns, nuclear microsatellites), with the ultimate goal of obtaining a better understanding of the evolutionary forces at work in the hybrid zone.. ACKNOWLEDGMENTS. 21.
(22) Funding for this study was provided by the Facultad de Ciencias at Universidad de los Andes, an American Ornithologists’ Union Research Award, and a Collection Study Grant from the Department of Ornithology at the American Museum of Natural History. The Ministerio de Ambiente, Vivienda y Desarrollo Territorial provided permits for research, collecting, and accessing genetics resources (Expedient RGE0014). F. Ayerbe, J.P. Lopéz, J.P.Goméz, N. Gutiérrez, S. Gonzalez, P. Tovar, F. Gonzalez, C. Wagner, the Luna Family, and the Castaño Family provided assistance in the field, C. Pedraza provided assistance in GIS analyses. We thank the Instituto de Génetica at Universidad de Los Andes (M. Linares) for access to facilities, and the curators and collection managers at institutions who allowed us to examine specimens or provided information: American Museum of Natural History (J. Cracraft, P. Sweet), Cornell University Museum of Vertebrates (K. Botswick, I. Lovette), Universidad del Pacífico (A. Quintero), Universidad del Valle (H. Alvarez and A. Giraldo), Universidad del Cauca (Maria Del Pilar Rivas), and the Insituto de Ciencias Naturales (F. G. Stiles).. LITEREATURE CITED. Barton, N. H., and G. M. Hewitt. 1985. Analysis of hybrid zones. Annual Reviews of Ecology and Systematics 16:113-148.. Barton, N. H., and K. S. Gale. 1993. Genetic analysis of hybrid zones. Pages 13-45 in Hybrid zones and the evolutionary process (R. G. Harrison, Ed.) Oxford Univ. Press, New York.. 22.
(23) Barton, N. H., and S. J. E. Baird. 1999. Analyse: Software for Analysis of Geographic Variation and Hybrid Zones (version 1.0.3). [Online.] Available at http://www.biology.ed.ac.uk/research/institutes/evolution/software/Mac/Analyse/index.ht ml. Barton, N. H. 2001. The role of hybridization in evolution. Molecular Ecology 10:551– 568.. Bears, H., M. C. Drever, and M. K. 2008. Comparative morphology of dark-eyed juncos Junco hyemalis breeding at two elevations: a common aviary experiment. Journal of Avian Biology 39:152–162.. Benkman 2003. Divergent selection drives the adaptive radiation of crossbills. Evolution 57:1176-1181.. Blount, J. D., and K. J. McGraw. 2008. Signal functions of carotenoid coloration. Pages 213-236 in: Carotenoids. Volume 4: Natural Functions (G. Britton, S. Liaaen-Jensen, and H. Pfander, eds.). Birkhauser Basel.. Buggs, R. J. A. 2007. Empirical study of hybrid zone movement. Heredity 99:301–312.. Brumfield, R. T., R. W. Jernigan, D. B. McDonald, and M. J. Braun. 2001. Evolutionary implications of divergent clines in an avian (Manacus; Aves) hybrid zone. Evolution 55:2070-2087.. 23.
(24) Brumfield, R.T. 2005. Mitochondrial variation in Bolivian populations of the variable antshrike (Thamnophilus caerulescens). The Auk, 122; 414-432.. Brush, A. 1970. Pigments in hybrid, variant and melanic tanagers (birds). Comparative Biochemistry and Physiology 36:785-793.. Carling, M. D., and R. T. Brumfield. 2009. Speciation in Passerina buntings: introgression patterns of sex-linked loci identify a candidate gene region for reproductive isolation. Molecular Ecology 18:834-847.. Carnaval, A. C., M. J. Hickerson, C. F. B. Haddad, M. T. Rodrigues, and C. Moritz. 2009. Stability predicts genetic diversity in the Brazilian Atlantic Forest Hotspot. Science 323:785-789.. Carstens, B. C., and C. L. Richards. 2007. Integrating coalescent and ecological niche modeling in comparative phylogeography. Evolution 61:1439-1454.. Chapman, F. M. 1917. The distribution of bird-life in Colombia; a contribution to a biological survey of South America. Bulletin American Museum of Natural History 36:1729.. Coyne, J. A., and H. A. Orr. 2004. Allopatric and Parapatric Speciation. Pages 83-123 in Speciation. Sunderland, Massachusetts.. 24.
(25) Darwin Database. 2007. BIOMAP alliance partners. [Online.] Available at http://www.biomap.net/BioMAP/login_en.php. Dinerstein, E., D. M. Olson, D. Graham, A. Websler, S. Primm, M. Bookbinder, and G. Ledec. 1995. A conservation assessment of the terrestrial EcoRegions of Latin America and Caribbean. World Bant. Washington, D.C.. Drummond, A. J., A. Rambaut, B. Shapiro, and O. G. Pybus. 2005. Bayesian coalescent inference of past population dynamics from molecular sequences. Molecular Biology and Evolution 22:1185-1192.. Drummond, A. J, and A. Rambaut. 2007. BEAST: Bayesian evolutionary analysis by sampling trees. BMC Evolutionary Biology 7:214.. Endler, J. A.1977. Geographic Variation, Speciation, and Clines. Princeton University Press, Princeton, New Jersey.. Endler, J. A.1982. Problems in distinguishing historical from ecological factors in biogeography. American Zoologist 22:441-452.. Endler, J. A. 1990. On the Measurement and classification of color in studies of animal color patterns. Biological Journal of the Linnean Society 41:315-352.. Fielding, A. H., and J. F. Bell. 1997. A review of methods for the assessment of prediction errors in conservation presence/ absence models. Environmental Conservation 24:38-49.. 25.
(26) Futuyma, D. 2005. Evolution. State University of New York at Stony Brook. New York.. Gay, L., P. Crochet, D. Bell, and T. Lenormand. 2008. Comparing clines on molecular and phenotypic traits in hybrid zones: a window on tension zone models. Evolution 62:27892806.. Graham, C. H., S. R. Ron, J. C. Santos, C. J. Schneider, and C. Moritz. 2004. Integrating phylogenetics and environmental niche models to explore speciation mechanisms in dendrobatid frogs. Evolution 58:1781-1793.. Grant, P. R. 1986. Ecology and Evolution of Darwin´s Finches. Princeton University Press, Princeton, New Jersey.. Grant, P. R., and B. R. Grant. 1994. Phenotypic and genetic consequences of hybridization in Darwin's Finches. Evolution 48:297-316.. Griscom, L. 1932. Notes on imaginary species of Ramphocelus. Auk 49:199-210.. Hackett, S. J. 1996. Molecular phylogenetics and biogeography of tanagers in the genus Ramphocelus (Aves). Molecular Phylogenetics and Evolution 5:368-382.. Haffer, J. 1967. Speciation in Colombian forest birds west of the Andes. American Museum Novitates 2294:1-57.. 26.
(27) Haffer, J. 1974. Avian speciation in Tropical South America. Nuttal Ornithological Club. Cambridge, Massachusetts.. Haffer, J. 1985. Avian Zoogeography of the Neotropical Lowlands. Ornithological Monographs 36:113-146.. Harrison, R. G. 1990. Hybrid zones: Windows on evolutionary process. Pages 69-128 in Oxford surveys in evolutionary biology (Futuyma D. and J. Antonovics Eds.). Oxford University Press, London.. Hey, J., and R. Nielsen. 2004. Multilocus methods for estimating population sizes, migration rates and divergence time, with applications to the divergence of Drosophila pseudoobscura and D. persimilis. Genetics 167:747-760.. Hewitt, G. M. 2000. The genetic legacy of the Quaternary ice ages. Nature 405:907-913.. Hewitt, G. M. 2001. Speciation, hybrid zones and phylogeography -or seeing genes in space and time. Molecular Ecology 10:537-549.. Hijmans, R., S. Cameron, J. L. Parra, P. Jones and A. Jarvis. 2005. Very high resolution interpolated climate surfaces for Global land areas. International Journal of Climatology 25:1965–1978.. Jackson, S. T., and J. T. Overpeck. 2000. Responses of plant populations and communities to environmental changes of the late Quaternary. Paleobiology 26:194-220.. 27.
(28) Key, K. H. L. 1968. The concept of stasipatric speciation. Systematic Zoology 17:14-22.. Krosby, M., and S. Rohwer. 2009. A 2000 km genetic wake yields evidence for northern glacial refugia and hybrid zone movement in a pair of songbirds. Proceedings of The Royal Society Biological Sciences 276:615-621.. Krueger, T. R., D. A. Williams and W. A. Searcy 2008. The Genetic Mating Systemof a Tropical Tanager. The Condor 110:559-562. Kruuk, L. E. B., S. J. E. Baird, K. S. Gale, and N. H. Barton. 1999. A comparison of multilocus clines maintained by environmental adaptation or by selection against hybrids. Genetics 153:1959-1971.. Martínez-Meyer, E., A. T. Peterson, and W. Hargrove. 2004. Ecological niches as stable distributional constraints on mammal species, with implications for Pleistocene extinctions and climate change projections for biodiversity. Global Ecology and Biogeography 13:305-314.. McCarthy, E. 2006. Handbook of Avian Hybrids of the World. Oxford University Press.. McDonald, D. B., R. P. Clay, R. T. Brumfield, and M. J. Braun. 2001. Sexual selection on plumage and behavior in an avian hybrid zone: experimental tests of male-male interactions. Evolution 55:1443–1451.. 28.
(29) Mayr, E. 1942. Systematics and Origin of Species. Columbia. University Press, New York.. Mettler, R. D. and G. M. Spellman. 2009. A hybrid zone revisited: molecular and morphological analysis of the maintenance, movement, and evolution of a Great Plains avian (Cardinalidae: Pheucticus) hybrid zone. Molecular Ecology 18:3256–3267.. Milá, B., R. K. Wayne, P. Fitze, and T. B. Smith. 2009. Divergence with gene flow and fine-scale phylogeographical structure in the wedge-billed woodcreeper, Glyphorynchus spirurus, a Neotropical rainforest bird. Molecular Ecology 18:2979–2995.. Moore, W. S., and J. T. Price. 1993. Nature of selection in the northern flicker hybrid zone and its implications for speciation theory. Pages 196-225 in Hybrid zones and the evolutionary process (R. G. Harrison, Ed.) Oxford University Press.. Moritz C, C. J. Hoskin, J. B. MacKenzie, B. L. Phillips, M. Tonione, N. Silva, J. VanDerWal, S.E. Williams and C. H. Graham. 2009. Identification and dynamics of a cryptic suture zone in tropical rainforest. Proceedings of The Royal Society Biological Sciences 276:1235-1244.. Motulsky, H., and A. Christopoulos. 2004. Fitting Models to Biological Data Using Linear and Nonlinear Regression. A practical guide to curve fitting. Oxford University Press.. 29.
(30) Olson, S. L., and C. Violani. 1995. Some unusual hybrids of Ramphocelus, with remarks on evolution in the genus (Aves: Thraupinae). Museo Regionale di Scienze Naturali Bollettino (Torino) 13:297-312.. Parra, J.L. 2009. Color evolution in the hummingbird genus Coeligena. Evolution (In press) DOI: 10.1111/j.1558-5646.2009.00827.. Parsons, T. J., S. L. Olson, and M. J. Braun. 1993. Unidirectional spread of secondary sexual plumage traits across an avian hybrid zone. Science 260:1643–1646.. Peterson, T. A., J. Soberon, and V. Sanchez-Cordero. 1999. Conservatism of ecological niches in evolutionary time. Science 285:1265–1267.. Peterson, A. T., E. Martínez-Meyer, and C. González-Salazar. 2004. Reconstructing the Pleistocene geography of the Aphelocoma jays (Corvidae). Diversity and Distributions 10:237-246.. Phillips, S. J., R. P. Anderson, and R. E. Schapire. 2006. Maximum entropy modeling of species geographic distributions. Ecological Modelling 190:231-259.. Plath, K. 1945. Color change in Ramphocelus flammigerus. Auk 62:304. Posada D., and K. A. Crandall. 1998. Modeltest: testing the model of DNA substitution. Bioinformatics 14:817-818.. 30.
(31) Rasner, C. A, P. Yeh, L. S. Eggert, K. E. Hunt, D. S. Woodruff, and T. D. Price. 2004. Genetic and morphological evolution following a founder event in the dark-eyed junco, Junco hyemalis thurberi. Molecular Ecology 13:671-681.. Remsen, J. V., Jr., C. D. Cadena, A. Jaramillo, M. Nores, J. F. Pacheco, M. B. Robbins, T. S. Schulenberg, F. G. Stiles, D. F. Stotz, and K. J. Zimmer. A classification of the bird species of South America. American Ornithologists' Union Version [2009]. [Online.] Available at http://www.museum.lsu.edu/~Remsen/SACCBaseline.html. Richards, C., Carstens, B. and Knowles, L. 2007. Distribution modelling and statistical phylogeography: an integrative framework for generating and testing alternative biogeographical hypotheses. Journal of Biogeography 34: 1833–1845.. Rohwer, S., E. Bermingham, and C. Wood. 2001. Plumage and mitochondrial DNA haplotype variation across a Moving hybrid zone. Evolution 55:405-422.. Rozas J. 2009. DnaSP v5: A software for comprehensive analysis of DNA polymorphism data Bioinformatics 25:1451-1452.. Ruegg, K. C., R. J. Hijmans, and C. Moritz. 2006. Climate change and the origin of migratory pathways in the Swainson’s Thrush (Catharus ustulatus). Journal of Biogeography 33:1172-1182.. 31.
(32) Ruegg, K. C. 2008. Genetic, morphological, and ecological characterization of a hybrid zone that spans a migratory divide. Evolution 62:452-456.. Sambrook, J., and D. Russell. 2001. Molecular cloning: A laboratory manual. Cold Spring Harbor Laboratory Press, New York.. Schluter, D., and J. N. M. Smith. 1986. Natural selection on beak and body size in the song sparrow. Evolution 40:221-231.. Sibley, C. G. 1958. Hybridization in Some Colombian Tanagers, Avian Genus "Ramphocelus". Proceedings of the American Philosophical Society 102:448-453.. Sorenson, M. D., J. C. Ast, D. E. Dimcheff, T. Yuri and D. P. Mindell. 1999. Primers for a PCR-Based Approach to Mitochondrial Genome Sequencing in Birds and Other Vertebrates. Molecular Phylogenetics and Evolution 12:105-114.. Stamatakis, A., M. Ott, and T. Ludwig. 2005. RAxML-OMP: An Efficient Program for Phylogenetic Inference on SMPs. In Proceedings of 8th International Conference on Parallel Computing Technologies (PaCT2005) 3606:288-302.. Stein, A. C., and J. A. Uy. 2006. Unidirectional introgression of a sexually selected trait across an avian hybrid zone: a role for female choice? Evolution 60:1476-1485.. 32.
(33) Swenson, N. G. 2006. GIS-based niche models reveal unifying climatic mechanisms that maintain the location of avian hybrid zones in a North American suture zone. Journal of Evolutionary Biology 19:717–725.. Swenson, N. G. 2008. The past and future influence of geographic information systems on hybrid zone, phylogeographic and speciation research. Journal of Evolutionary Biology 21:421-434.. Szymura, J. M., and N. H. Barton. 1986. Genetic analysis of a hybrid zone between the Fire-bellied Toads, Bombina bombina and B. variegata, near Cracow in southern Poland. Evolution 40:1141–1159.. Tamura, K., J. Dudley, M. Nei and S. Kumar. 2007. MEGA4: Molecular Evolutionary Genetics Analysis (MEGA) software version 4.0. Molecular Biology and Evolution 24:1596-1599.. Van Der Hammen, T., and E. Gonzalez 1960. Upper Pleistocene and Holocene climate and vegetation of the "Sabana de Bogota" (Colombia, South America). Leidse Geologische Mededelingen 25:261-315.. Van Der Hammen, T. 1961. The Quaternary climatic changes of northern South America. Annals of the New York Academy of Science 95:676-683.. Vines, T. H., S. C. Köhler, M. Thiel, I. Ghira, T. R. Sands, C. J. MacCallum, N. H. Barton and B. Nürnberger. 2003. The Maintenance of Reproductive Isolation in a Mosaic Hybrid. 33.
(34) Zone between the Fire-Bellied Toads Bombina bombina and B. variegata. Evolution 57:1876-88.. 34.
(35) Table 1. Sample sizes per population used for analyses of phenotypic and molecular variation across the hybrid zone between R. f. icteronotus and R. f. flammigerus in western Colombia (see Fig. 1 for the spatial location of sites). Distance Location. (km). Morphology 1911 M. 1956 F. F. M. 4. 4. 0. 3. 2. 22.24. 5. 3. 33.89. 4. 44.51. 5. 54.41. 6. 65.84. 7. 73.93. 8. 84.94. 9. 95.79. 5. 10. 108.91. 4. 11. 129.76 Total. 4. 6. 2. 2. 2009. M. 1. 2. Color. 17. 9. 14. 5. 1911 F. 2. 2. 5. 4. 2. 5. 4. 4. 8. 7. 4. 5. 8. 4. 5. 3. 3. 5. 5. 2. 1. 18. F. 2. 1. 3 21. 1956. 1. 7. 6. M. 8. Cytb 2009. M. F. M. F. 3. 2. 4. 5. 2. 15. 15. 14. 6. 2. 1. 18. 6. 5. 4. 3. 24. 13. 7. 4. 12. 10. 13. 4. 5. 6. 5. 4. 7. 27. 18. 36. 5. 3. 2. 5. 4. 2. 4. 2. 5. 2. 1. 16. 95. 58. 4 60. 40. 27. 19. 25. 35.
(36) Table 2. Cline centers and widths (and their 95% Confidence Intervals, CI, when available) obtained by fitting curves for morphological (PC1) and plumage variables (brightness, chroma and hue) for each time period. All values are given in kilometers, with cline centers measured as the distance along the transect from Ladrilleros-Cali (locality 1-11, Fig. 1). Empty cells indicate that the sigmoidal dose-response model did not converge on parameter estimates.. Males Variable. Females. Center. Hillslope. Width. 74.73. 0.41. 2.45. Brightness. 73.29±CI5.53. 0.082±CI 0.260. 12.20. Chroma. 73.93±CI 0.35. 0.85±CI 2.753e+14. Hue. 73.93±CI 0.7. 1956-1986 PC1 Brightness. 1911. PC1. Center. Hillslope. Width. 1.17. 79.96±CI 12.17. 0.07±CI 0.11. 14.61. 0.90±CI -2.032e+015. 1.11. 80.3±CI 13. 0.06±CI 0.85. 16.91. 75.06. 0.26±CI 2.9. 3.84. 73.89. 1.132. 0.88 ~ 74.37. 0.88. 1.12. 96.24. 0.78. 1.28. 84.78. 0.81. 1.23. Chroma. 2009. Hue. 78.53±CI 3.91. 0.09972±CI 0.058. 10.03. PC1. 84.37. 0.68. 1.45. Brightness Chroma. 84.49. 1.158. 0.86. Hue. 84.53. 0.8205. 1.23. 36.
(37) Figure Legends. Fig. 1. Map of localities across the Ramphocelus hybrid zone from the Pacific lowlands to the eastern slope of the Cordillera Occidental of the Colombian Andes. Blue dots indicate localities of historical and Blueberry dots current specimens sampled for phenotypic variation. Black dots indicate populations in which samples were grouped along the transect for cline-fitting analyses. Green lines indicate main roads. Populations and localities: 1: Ladrilleros, La Barra, Bahía Muerte, Bahía Málaga, 2: Bajo Calima, 3: Buenaventura, Río Raposo ., 4: Anchicayá, Zabaletas, 5: San José, 6: El Placer, Bajo Anchicayá, 7: Juntas, Jiménez, Río Blanco, La Elsa, Loboguerrero, Zelandia, 8: El Salado, Queremal, 9: Calima, San Antonio, La Cumbre, 10: Cali, Navarro, 11: Palmira, Florida.. Fig. 2. Potential distributions of R. flammigerus predicted by MaxEnt using climate data for 6,000 years ago (dark gray) and the present (light gray) showing conditions suitable for contact in the current location of the hybrid zone between the two forms (inset, the dotted line indicates the position of our study transect) existed since 6,000 ya. Dots are localities used to construct the model.. Fig. 3. Potential distribution of R. flammigerus predicted by MaxEnt using climate data for 21,000 year ago (dark gray) and the present (light gray) showing a smaller predicted range during the LGM in contrast with predicted current range, suitable conditions for two forms were not continuous along the transect (i.e. the dotted line) suggesting that these two forms were possibly disjunct during the LGM. Dots are localities used to construct the model.. Fig. 4. Phylogenetic tree showing relationships among haplotypes of R. flammigerus inferred by the Maximum Likelihood method. Numbers on each node are ML bootstrap 37.
(38) values. Locality 1: Lad: Ladrilleros, locality 3: V/B: Buenaventura locality 6: BAn: Bajo Anchicaya, LDel: La Delfina, locality 7: Anc: Alto Anchicaya, locality 8: Que: Queremal, Sal: El Salado, locality 9: PeB: Peñas Blancas, LCu: La Cumbre, LEL: La Elvira, Coc: Cocorná Antioquia, Pop: Popayán Cauca.. Fig. 5. Haplotype network showing that genetic variation was not consistent with position along the hybrid zone. Colors were assigned for illustration based on the position of localities in relation to patterns of variation in coloration along the transect, ranging from yellow in the icteronotus extreme (localities 1-6), to orange in the center of the hybrid zone (localities 7-8) to red in the flammigerus extreme (localities 9). The size circles are proportional to the number of individuals sharing a particular haplotypes. Note the lack of clear genetic structure across the transect. Fig. 6. Bayesian skyline plot showing increasing population’s size from the most recent ancestor towards present time for R. flammigerus populations inferred using the program BEAST. The median estimates are shown as solid line, and the Bayesian credibility intervals (i.e., 95% highest posterior densities) are shown by the blue areas. Time zero is the present, with increasing values representing time into the past expressed in units of mutations per site.. Fig. 7. Morphological data for historical and current specimens provides evidence of clinal variation in body size as indicated by PC1 from Ladrilleros (0 km) to Cali (130 km), and apparent movement of the hybrid zone. Data are shown separate for males (A) and females (B).. 38.
(39) Fig. 8. Plumage coloration as measured by brightness, for historical and current specimens provides evidence of clinal variation in bright from Ladrilleros (0 km) to Cali (130 km). Data are shown separate for males (A) and females (B).. Fig. 9. Plumage coloration as measured by chroma, for historical and current specimens provides evidence of clinal variation in rump color from Ladrilleros (0 km) to Cali (130 km), and apparent movement of the hybrid zone. Data are shown separate for males (A) and females (B).. Fig. 9. Plumage coloration as measured by hue, for historical and current specimens provides evidence of clinal variation in rump color from Ladrilleros (0 km) to Cali (130 km), and apparent movement of the hybrid zone. Data are shown separate for males (A) and females (B).. 39.
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(46) Fig. 7. A.. MALES. B. FEMALES. 46.
(47) Fig. 8. A.. MALES. B. FEMALES. 47.
(48) Fig. 9. A.. MALES. B. FEMALES. 48.
(49) Fig. 10. A.. MALES. B. FEMALES. 49.
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