Intraspecific variation and the origin and maintenance of the disjunct distribution in the blossomcrown Anthocephala floriceps (Aves: trochilidae)

Texto completo

(1)Intraspecific variation and the Origin and Maintenance of the Disjunct Distribution in the Blossomcrown Anthocephala floriceps (Aves: Trochilidae) Maria Lozano-Jaramillo1*, Alejandro Rico-Guevara2, Carlos Daniel Cadena1 1. Laboratorio de Biología Evolutiva de Vertebrados, Departamento de Ciencias Biológicas,. Universidad de Los Andes 2. Department of Ecology & Evolutionary Biology, University of Connecticut. *Corresponding author, e-mail: [email protected] Abstract Studies about the origin and maintenance of disjunct distributions are of special interest in biogeography. One hypothesis that may account for the origin of disjunct distributions is the extinction of intermediate populations, and once the disjunctions arise they can be maintained by ecological specialization. In this study we tested hypotheses about how did the currently disjunct distribution of a hummingbird endemic to Colombia (Anthocephala floriceps) arose and how it is currently maintained. With the combination of molecular phylogenetic data and models of potential historical distribution analyses we evaluated: (1) the timing of disjunction between the two populations of the species, (2) if the disjunction could have arisen as a result of fragmentation of a formerly widespread range, owing to climate changes during the Pleistocene, and (3) if the disjunct distribution might be currently maintained by specialization of each isolated population to different ecological conditions. Molecular data suggested that the divergence between populations occurred approximately 2.2 million years ago, and predictive distribution models based on climate data indicated that the disjunction might date prior to 130,000 years before present (i.e, it.

(2) was not caused by climatic fluctuations during the Pleistocene). In addition, climate data analyzed using distribution models and a multivariate approach, suggest that each population occurs under distinct ecological conditions; if this reflects adaptations, then it might limit dispersal and explain the maintenance of the disjunction. Our results showing that the distribution of A. floriceps has been disjunct for a long period of time, and that populations have different climatic niches, have taxonomic and conservation implications because each subspecies can be considered as full species under different species concepts, therefore from a conservation standpoint an independent management is worthy of attention. Key Words: Disjunct distribution, Anthocephla floriceps, models of potential distribution Introduction The limits of species’ geographic distributions reflect the interplay of a variety ecological and evolutionary forces such as migration, extinction and speciation (Sexton et al., 2009), and understanding how such forces underlie the origin and maintenance of disjunction distributions, in which closely related taxa occur in widely separate areas, is of central interest in biogeography (Brown and Lomolino, 1998). One hypothesis that may account for the disjunct distributions of species or close relatives is the extinction of intermediate populations, possibly as a result of significant geographic or climatic events. For example, camels and tapirs, which are currently disjunct in South America once occurred in North America, suggesting a continuous distribution became fragmented owing to climatic changes during the Pleistocene (Brown and Lomolino, 1998; Carranza and Arnold, 2003; Renner, 2005). After disjunct distributions arise, the question becomes how are they.

(3) maintained. Possible explanations for the maintenance of disjunctions are dispersal limitation set by geographic or ecological barriers (Schluter, 2001; Sexton et al., 2009; Wiens, 2004), and ecological adaptation in geographically separate areas followed by niche conservatism (Schluter, 2001; Sexton et al., 2009; Wiens, 2004). In cases where historical distributions cannot be studied directly (i.e. using the fossil record), understanding the origin of disjunct distributions can be facilitated by molecular phylogenetic estimates of divergence times between populations, which can then be correlated to historical events (Brown and Lomolino, 2000; Carranza and Arnold, 2003; Seutin et al., 1994). This approach has revealed, for example, that current disjunct distributions in scleroglossan lizards that occur in America and Africa likely arose as a result of recent human introduction because their recent divergence times can only be accounted for people crossing the ocean in the last thousand years (Carranza and Arnold, 2003), whereas the origin of disjunct distributions in plant species of the Crypteroniaceae family was concordant with the splitting of Gondwana (Conti et al., 2002; Renner, 2005). In addition, inferences about historical ranges, and of whether disjunct distributions might be the result of extinction of intervening populations can be made using niche modeling tools (Guisan and Thuiller, 2005; Peterson, 2001) to generate estimates of species’ potential distributions in the past based on climate data (Carstens et al., 2009; Phillips et al., 2006; Richards et al., 2007). For example, such models have suggested that plant species with currently disjunct distributions may have been widely distributed in the past (Carstens et al., 2009; Powell et al., 2005). If currently disjunct populations are relicts of more widespread populations, and one can construct models of the potential distributions at different times in the past, one would expect to find a reduction in the connectivity between.

(4) populations through time, associated with temporal concordance with the divergence dates estimated using molecular phylogenetic data. In addition, climatic data and models of potential distributions can be used to test the hypothesis that disjunct distributions are maintained at present time owing to ecological differentiation between populations found in disjunct areas. Specifically, this hypothesis predicts that one should observe the disjunct populations occur under different ecological environments. The Blossomcrown Anthocephala floriceps (Gould, 1854), the single representative of a monotypic genus of hummingbird (Trochilidae) endemic to Colombia, is a good model to study the origin of disjunct distributions owing to its current distribution, with two subspecies living in regions widely separated by more than 900 km. Anthocephala floriceps floriceps inhabits the highlands of the Sierra Nevada de Santa Marta in northern Colombia, whereas A.f.berlepschi is found in the Andes in Tolima, Huila and Quindío departments (Bangs 1899; Strewe and Navarro 2003; Ridgely and Gaulin, 1980; Umaña and CalderónFranco 2005). In this study we use molecular phylogenetic analyses and niche modeling tools to (1) determine the timing of disjunction between the two populations of A.floriceps, (2) assess whether the disjunct distribution of the species could have arisen as a result of fragmentation of a formerly widespread range owing to climate change over the Pleistocene, and (3) evaluate whether the disjunct distribution might be maintained by specialization of the isolated populations to different ecological conditions. In so doing, we provide information about the degree of genetic and ecological differentiation between the two isolated populations as potentially distinct evolutionary units (Moritz, 1995).. Materials and methods.

(5) DNA was extracted from muscle tissue samples of three specimens of A.f.floriceps and two of A.f.berlepschi (Table 1), using the phenol/chlorophorm protocol (Sambrook 2001). Two mitochondrial (ND2 and ND4) and two nuclear genes (Bfib7 and ODC introns 6 and 7) were amplified and sequenced for all individuals using published primers and protocols described by (McGuire et al., 2007; Parra et al., 2009). Products were purified with ExosapIT (USB) and then sequenced. We combined our data with three sequences of A. f. berlepschi provided by Juan Parra for all genes used except BFib5 (Table 1). As outgroups, we used four of the closest living relatives of our taxa in study reported (McGuire et al., 2009). Outgroup sequences for the ND2 and ND4 genes of the outgroups used were obtained from GenBank; Campylopterus hemileucurus (EU042534.1, EU042214.1), Klais guimeti (AY830495.1, EU042317.1), Orthorhyncus cristatus (AY830508.1, EU042328.1) and Stephanoxis lalandi (GU167250.1, GU166919.1). To estimate the divergence time between the two subspecies of A.floriceps, a chronogram was obtained using a relaxed molecular clock approach in BEAST 1.5.2 (Drummond and Rambaut, 2007) based on a concatenated matrix including sequences of both mitochondrial genes for the two populations and outgroups, and assuming the mitochondrial avian substitution rate of 2% divergence per million years (Weir and Schulter, 2008). This Bayesian inference analysis was conducted using the HKY+G DNA substitution model, which was selected as the best-fit to the data according to the Akaike Information Criterion (AIC) in ModelTest 3.7 (Posada and Crandall, 1998). As an additional way to examine relationships among mtDNA (and also nuclearDNA) haplotypes, we constructed haplotype networks using a median-joining algorithm in the software Network v4.5.1.6 (Bandelt et al., 1999).

(6) To assess if the distribution of the species could have been more widespread in the past, we used 51 localities obtained from museum specimens (Global Biodiversity Information Facility (http://www.gbif.org), field observations (N. Gutierrez, pers.comm.) and published data (Renjifo et al., 2002) to estimate potential distributions based on a niche model. With these data we used a maximum entropy algorithm (Phillips et al., 2006) using 19 climate variables at a c. 1 km resolution obtained from WorldClim (Hijmans et al., 2005a) using all of Colombia as the spatial extent to generate a model of the potential distribution at present. Following model validation using the receiver operating characteristic (ROC) curve and a binomial test of omission (Phillips et al., 2006), the model was projected onto climate layers for Colombia for 6,000 years before present (ybp), for the Last Glacial Maximum (LGM; aprox. 21,000 ybp) and 130,000 ybp. The extent of potential distributions at these different time periods was compared by eye. To evaluate whether the current disjunct distrtibution of A.floriceps is maintained by specialization of each population to different ecological conditions, we modeled the current distribution of each subspecies using 19 climate variables obtained from WorldClim (Hijmans et al., 2005b) focusing on a spatial extent including the known distribution of each subspecies, and projected it onto geographic space to assess whether it would classify the localities where the other subspecies has been recorded as ecologically suitable. As an additional way to determine whether there are ecological differences between the environments where the different subspecies occur, a principal component analysis (PCA) was performed on the climatic variables.using R v 2.11.1 and separations of localities in multivariate space was examined visually.. Results.

(7) Relationships among haplotypes show the same pattern for all genes: subspecies form monophyletic groups with different haplotypes identified for each subspecies (Fig. 2), suggesting they have been isolated for a sufficient long time to achieve reciprocal monophyly. Indeed, the chronogram based on mtDNA sequences shows subspecies as two reciprocally monophyletic groups that are c. 4.4% divergent, which indicated their divergence dates to c. 2.2 million years before present (mybp) (Fig. 3), although the credibility interval of this estimate was broad (0.5-6.2mypb; Fig. 3). The divergence between A. floriceps and its closest relatives (O.cristatus and S.lalandi) dates to c. 3mybp, with a confidence interval that overlaps with the timing of intraspecific divergence. For the current distribution model, the area under the ROC curve was close to one (0.983); additionally, based on a binomial test of omission, the model produced significant threshold values (p 0.001), suggesting that it adequately predicted species distributions based on climate, which validates the use of this model to examine potential historical distributions. The predicted potential distribution model for 6,000 ybp (Fig. 1b) was similar to current predictions (Fig. 1a), whereas the potential distributions for 21,000 ybp and 130,000 ybp appeared to be considerably larger. However, none of the modeled historical distributions were sufficiently broad to suggest the species was continuously distributed, suggesting that the disjunction may date to periods prior to 130,000 ybp. Potential distribution models for the two subspecies had area under the ROC curves was close to one (A.f.floriceps: 0.981, A.f.berlepschi: 0.944) indicating they adequately predict known distributions of their respective subspecies. However, the distribution model constructed for each subspecies did not predict the current distribution of the other.

(8) subspecies (Fig. 5), implying that each population inhabits environments with different ecological conditions. With the climatic variables, based on factor loadings, the first principal component (PC1) was mainly explained by annual precipitation and the second (PC2) by precipitation of the coldest quarter (Fig. 4). A plot of the first two principal components showed that, each subspecies lives under distinct climatic conditions (Fig. 4), with the Andean subspecies tending to live in more humid areas.. Discussion Our inference of the historical distribution of A.floriceps based on climate data, which we conducted to examine whether its range disjunction may have resulted from fragmentation of a formerly widespread range due to climatic change, showed that over the last 130,000 ybp, climatic conditions have not been suitable for the species to have had a continuous distribution. Therefore, if the species was once formerly widespread, the origin of its range disjunction likely dates to an earlier moment in history, a scenario that is consistent with our molecular data suggesting that the divergence between populations dates to c 2.2 million years before present (mybp) and was likely not associated with Pleistocene climatic changes. However, a Pleistocene origin for the disjunction cannot be fully rejected owing to the wide credibility interval on the divergence time estimate and to the fact that the observed divergence might reflect the timing of gene divergence as opposed to a more recent timing of population divergence (Edwards and Beerli, 2000). Our study also suggests that the currently disjunct distribution of A. floriceps may persist due to specialization of each isolated population to different ecological conditions. Niche.

(9) models and PCA analyses show that ecological divergence between populations is significant. If this reflects that each population is adapted to specific climatic conditions and not simply that realized ecological conditions at sites differ but ecological niches do not (Cadena and Loiselle, 2007; McCormack et al.; Warren et al., 2008), then ecological restrictions can possibly limit the expansion of the species’ geographic distribution. The estimated timing of disjunction between both subspecies (2.2mybp) suggest an older dates than those reported divergence for different species of hummingbirds, which often diverged less than 1mybp (Roy et al., 1998). Our analyses further showed that both subspecies do not share haplotypes in four different genes (including nuclear loci, with the higher coalescence times), which suggest substantial divergence of both subspecies because they have been isolated for a long time without the possibility of gene flow (Nielsen and Slatkin, 2000). In conclusion, our analyses suggest that the current distribution of A. floriceps has been disjunct for over a long period of time, even longer than that reported for different species of hummingbirds. Furthermore, each subspecies occurs under distinct ecological conditions, which might reflect evolved differences in their ecological niche. These results could have taxonomic and conservation implications because they suggest each subspecies can be considered as a full species under some species concepts (Baum and Shaw, 1995; Cracraft, 1983; De Queiroz, 2005, 2007), and because they meet the criteria for recognition as evolutionarily significant units worthy of attention from a conservation standpoint and requiring independent management (Moritz, 1994; Moritz, 1995).. Acknowledgments.

(10) We thank the Facultad de Ciencias at Universidad de Los Andes for the funding provided for this study and the Instituto de Genética at Universidad de Los Andes for providing us their facilities in order to complete our genetic analyses. We thank Juan Parra for providing us DNA sequences and Gary Stiles for authorizing the use of tissue samples from the Instituto de Ciencias Naturales at Universidad Nacional de Colombia. We thank members of the Laboratorio de Biología Evolutiva de Vertebrados at Universidad de Los Andes for providing us comments and assistance throughout the study. References Baum, D.A., Shaw, K.L., 1995. Genealogical perspectives of the species problem. Experimental and molecular approaches to plan biosystematics, 289-303. Brown, J.H., Lomolino, Massachusetts.. M.V.,. 1998.. Biogeography.. Sinauer. Associates,. Sunderland,. Brown, J.H., Lomolino, M.V., 2000. Concluding remarks: historical perspective and the future of island biogeography theory. Global Ecology & Biogeography 9, 87-92. Cadena, C.D., Loiselle, B.A., 2007. Limits to elevational distributions in two species of emberizine finches: disentangling the role of interspecific competition, autoecology, and geographic variation in the environment. Ecography 30, 491-504. Carranza, S., Arnold, E.N., 2003. Investigating the origin of transoceanic distributions: mtDNA shows Mabuya lizards (Reptilia, Scincidae) crossed the Atlantic twice. Systematics and Biodiversity 1, 275-282. Carstens, B.C., Richards, C.L., Crandall, K., 2009. Integrating coalescent and ecological niche modeling in comparative phylogeography. Evolution 61, 1439-1454. Conti, E., Eriksson, T., Schˆnenberger, J.r., Sytsma, K.J., Baum, D.A., 2002. Early Tertiary out-ofIndia dispersal of Crypteroniaceae: Evidence from phylogeny and molecular dating. Evolution 56, 1931-1942. Cracraft, J., 1983. Species concepts and speciation analysis. Current Ornithology 1, 159-187. De Queiroz, K., 2005. A Unified Concept of Species and its Consequences for the Future of Taxonomy. Proceedings of the California Academy of Sciences 56, 196-215. De Queiroz, K., 2007. Species Concepts and Species Delimitation. Systematic Biology 56, 879-886..

(11) Edwards, S.V., Beerli, P., 2000. Perspective: gene divergence, population divergence, and the variance in coalescence time in phylogeographic studies. Evolution 54, 1839-1854. Guisan, A., Thuiller, W., 2005. Predicting species distribution: offering more than simple habitat models. Ecology Letters 8, 993-1009. Hijmans, R.J., Cameron, S.E., Parra, J.L., Jones, P.G., Jarvis, A., 2005a. Very high resolution interpolated climate surfaces for global land areas. International Journal of Climatology 25, 19651978. Hijmans, R.J., Cameron, S.E., Parra, J.L., Jones, P.G., Javis, A., 2005b. Very high resolution interpolated climate surfaces for global land areas. Wiley, Chichester, ROYAUME-UNI. McCormack, J.E., Zellmer, A.J., Knowles, L.L., Does niche divergence accompany allopatric divergence in Aphelocoma jays as predicted under ecological speciation?: insights from tests with niche models. Evolution 64, 1231-1244. McGuire, J.A., Witt, C.C., Altshuler, D.L., Remsen, J.V., 2007. Phylogenetic Systematics and Biogeography of Hummingbirds: Bayesian and Maximum Likelihood Analyses of Partitioned Data and Selection of an Appropriate Partitioning Strategy. Oxford University Press. McGuire, J.A., Witt, C.C., Remsen, J.V., Dudley, R., Altshuler, D.L., 2009. A higher-level taxonomy for hummingbirds. Journal of Ornithology 150, 155-165. Moritz, C., 1994. Defining ‘Evolutionarily Significant Units’ for conservation. TREE 9. Moritz, C., 1995. Uses of molecular phylogenetics for conservation. Philosophical transactionsRoyal Society of London. 349, 6. Nielsen, R., Slatkin, M., 2000. ikelihood analysis of ongoing gene flow and historical association. Evolution 54, 44-50. Parra, J.L., Remsen Jr, J.V., Alvarez-Rebolledo, M., McGuire, J.A., 2009. Molecular phylogenetics of the hummingbird genus Coeligena. Molecular Phylogenetics and Evolution 53, 425-434. Peterson, A.T., 2001. Predicting species geographic distributions based on ecological niche modeling. The Condor 103, 599-605. Phillips, S.J., Anderson, R.P., Schapire, R.E., 2006. Maximum entropy modeling of species geographic distributions. Ecological Modelling 190, 231-259. Powell, M., Accad, A., Shapcott, A., 2005. Geographic information system (GIS) predictions of past, present habitat distribution and areas for re-introduction of the endangered subtropical rainforest shrub Triunia robusta (Proteaceae) from south-east Queensland Australia. Biological Conservation 123, 165-175. Renjifo, L.M., Franco-Maya, A.M., Amaya-Espinel, J.D., Kattan, G., López-Lanús, B., 2002. Libro rojo de aves de Colombia. 257-259. Renner, S.S., 2005. Relaxed molecular clocks for dating historical plant dispersal events. Trends in Plant Science 10, 550-558..

(12) Richards, C.L., Carstens, B.C., Knowles, L.L., 2007. Distribution modelling and statistical phylogeography: an integrative framework for generating and testing alternative biogeographical hypotheses. Journal of Biogeography 34, 1833-1845. Roy, M.S., Torres-Mura, J.C., Hertel, F., 1998. Evolution and history of hummingbirds (Aves: Trochilidae) from the Juan Fernandez Islands, Chile. Ibis 140, 265-273. Schluter, D., 2001. Ecology and the origin of species. Trends in Ecology & Evolution 16, 372-380. Seutin, G., Klein, N., Ricklefs, R.E., Bermingham, E., 1994. Historical Biogeography of the Bananaquit (Coereba flaveola) in the Caribbean Region: A Mitchondrial DNA Assessment. Evolution 48, 1041-1061. Sexton, J.P., McIntyre, P.J., Angert, A.L., Rice, K.J., 2009. Evolution and Ecology of Species Range Limits. Annual Review of Ecology, Evolution, and Systematics 40, 415-436. Warren, D.L., Glor, R.E., Turelli, M., 2008. Environmental niche equivalency versus conservatism: quantitative approaches to niche evolution. Evolution 62, 2868-2883. Weir, J.T., Schulter, D., 2008. Calibrating the avian molecular clock. Molecular Ecology 17, 23212328. Wiens, J.J., 2004. Speciation and ecology revisited: phylogenetic niche conservatism and the origin of species. Evolution 58, 193-197. Strewe R, and Navarro C. 2003. New distributional records and conservation importance of the San Salvador Valle, Sierra Nevada de Santa Marta, Northern Colombia. Ornitología Colombiana 1: 2941. Umaña AM and Calderón-Franco D. 2005. Caracterización Biológica Corredor PNN PuracéGuácharos - Grupo GEMA, IAvH. 8:135-159..

(13) Table 1. Subspecies A.f.floriceps A.f.floriceps A.f.floriceps A.f.berlepschi A.f.berlepschi A.f.berlepschi A.f.berlepschi A.f.berlepschi. Tissue number ICN 36492 ICN 36491 ICN 36467 ANDES-BT 1311 ANDES-BT 1315 IAvH 1253 IAvH 1269 IAvH 1255. Locality Santa Marta, Cuchilla de San Lorenzo Santa Marta, Cuchilla de San Lorenzo Santa Marta, Cuchilla de San Lorenzo Huila, Algeciras, Vereda Las Brisas, Finca Bélgica Huila, Algeciras, Vereda Las Brisas, Finca Bélgica Huila, Palestina Huila, Palestina Huila, Palestina.

(14) Figure 1. Potential distributions for A. floriceps predicted using climatic data. Models are shown for climatic conditions of (a) current, (b) 6,000 ybp, (c) 21,000 ybp and (d) 130,000 ybp climatic conditions. Dots on the current distribution map indicate localities used to build the models. Areas in red denote areas of habitat suitability according to 10-percentile training presence threshold value (0.328). Figure 2. Haplotype networks showing no alleles are shared between subspecies of A.floriceps in any of the genes analyzed. The blue color indicates haplotypes from A.f.floriceps and red color indictates halplotypes from A.f.berlepschi. Circle size reflect allele frequencies of the total samples used . (a) ND2, (b) ND4, (c) Bfib7 and (d) ODC. Figure 3. Divergence time estimates (mya) among the A.floriceps subspecies and outgroups, based on a Bayesian relaxed molecular clock analysis. Node bars indicate 95% credibility intervals on node ages: scale bar shows time in million years. Values on each clade indicate posterior probabilities when greater than 0.7. Figure 4. Principal component plot showing the two subspecies of A.floriceps occur in climatically different environments. Appriximately 88% of the variance was accounted by PC1 and PC2, with most (76.4%) accounted by PC1. Factor loadings suggest that PC1 is mainly an annual precipitation axis and PC2 a precipitation of the coldest quarter axis. Blue and red dots represent localities of A.f.floriceps and A.f.berlepschi respectively. Figure 5. Current potential distribution models generated using climatic data. (a) Localities of known occurrence of A.f.berlpeschi projected onto ecological niche models built for A.f.floriceps and (b) viceversa. Red and blue dots indicate localities of A.f.berlepschi and A.f.floriceps respectively, used to build the models. Dark areas denote areas of habitat suitability..

(15) Fig. 1 (a). (b). (c). (d).

(16) Fig. 2.

(17) Fig. 3.

(18) Fig. 4.

(19) Fig. 5. (a). (b).

(20)