Situaciones a las que se aplica el procedimiento de recuperación de consumos

K.-G. Heller

CONTENTS

Introduction ... 137 Material and Methods ... 139 Results ... 139

Comparing Change of Song and Morphology of Male Genitalia in Isolated,

Allopatric Populations of Closely Related Forms ... 139 The Subgenus Parnassiana (Tettigoniidae: Platycleidini: Platycleis) ... 140 Allopatric Forms Differing in Genitalic Morphology, but not in Song ... 142 Allopatric Forms Differing in Song, but not in Genitalic Morphology ... 143 Unusually Variable Species ... 144 Tracking Song Evolution by the Use of Phylogenetic Trees ... 144 Genus Parapholidoptera (Tettigoniidae) ... 145 Poecilimon propinquus Group (Phaneropteridae, Barbitistinae, Poecilimon) ... 146 Other Published Phylogenetic Data ... 147 Conclusions ... 148 Acknowledgements ... 150 Appendix ... 150

INTRODUCTION

Bushcrickets comprise one of the most obvious groups of acoustically active insects. Together with cicadas, they are the loudest singers. In temperate regions tettigoniid species are active day and night and compete acoustically, mainly during daylight, with cicadas. In tropical rain forests they, together with true crickets (Gryllidae), are acoustically dominant at night. The range of the carrier frequencies of their songs is much wider than that of their singing competitors, ranging from 0.6 kHz to more than 100 kHz. Males sing and females respond by approaching the singing male phonotactically or by producing special acoustic response signals. Typically every species has a species-specific song pattern. The first nonverbal description of these species-specific differences was given 150 years ago by Yersin (1854) in Europe, followed by Scudder (1868) in North America, both using musical notation. In the last century, many detailed studies of the song patterns followed, mainly on the tettigoniid fauna of North America and Europe (Alexander, 1956; Heller, 1988; Ragge and Reynolds, 1998; Walker and Moore, 2004). From his studies, Alexander (1957a) established the rule that songs are always different in species occurring simultaneously at one locality. Complementing this observation, behavioural studies showed that females recognise the song of conspecific males (acridids: Perdeck, 1957; gryllids: Walker, 1957; tettigoniids: Bailey and Robinson, 1971). Perdeck (1957) also formulated a hypothesis about the origin of song differences between species. Working with acridids of the genus Chorthippus,

he demonstrated that in these morphologically similar species, the species-specific song pattern represents the main isolating barrier. Other premating and postmating barriers seem to be very weak.

From similar results, Walker (1964) argued that there might be a high percentage of cryptic species not recognised by morphological methods. After having detected differences in song, usually differences in morphology are also found, but some species may differ in song only. For example, no morphological differences have been found between some of the species mentioned by Walker in 1964 (Alexander, 1960) and described later (Walker et al., 2003). From these results it could be concluded that in acoustic Orthoptera, speciation usually starts with differences in song as one of the first steps in the mating process. Perdeck (1957) assumed that the origin of song differences occurred as an adaptation to different acoustic environments in isolated populations, and that the differences possibly enlarged by character displacement or reinforcement. However, even today, identification of unknown specimens and description of new species is done quite often without knowledge of the song. The most important characters used for these purposes are found in morphology. Like many other insects, bushcricket species differ morphologically mainly in male genitalia (Harz, 1969). Obviously, not only the song becomes different during speciation, but also the genitalia. Both are part of a species’ mate recognition system and are used for an exchange of information of different kinds and purposes between the mating partners, for example about identity and quality. Both character complexes are assumed to evolve under sexual selection (Eberhard 1985, 1996; Searcy and Andersson, 1986; Gray and Cade, 2000; Gerhardt and Huber, 2002; Sirot, 2003) and often play a primary role in speciation.

But what kinds of characters are likely to evolve first and establish a starting point for speciation? Is it typically the acoustic component or do other elements of premating behaviour change first, which may be connected with morphological changes? Are there any rules for this sequence, and are there similarities or differences between bushcrickets and other groups of singing Orthoptera or singing insects in this respect?

Here we should like to present new data and combine these with published examples of species with differing acoustic and morphological characters. These examples may help to understand what can happen during speciation and which characters may change first. The results may give the taxonomist indications what to look for and for which taxonomic level.

Walker (1974) tried to find species in the last step of speciation 30 years ago. He looked for species with acoustical character displacement. If song is important for species recognition in areas where two closely related species with similar songs occur together, larger differences in song might be expected than where only one of the species occurs. Surprisingly to him, Walker (1974) did not find many examples for this phenomenon among acoustic insects and not a single one in bushcrickets. He gave a long list of reasons why it is found so rarely; one of them was insufficient data. In the meantime, some obvious examples of acoustic character displacement were found among the crickets of Hawaii (Otte, 1989), but for bushcrickets still no such examples have been published.

However, the theoretical background has changed. For characters under sexual selection large differences between species would not be surprising even without contact with other species (Panhuis et al., 2001). For theoretical reasons, reproductive character displacement or reinforcement may be restricted only to relatively special conditions (Turelli et al., 2001; Marshall et al., 2002). Therefore, other methods may be more promising for the analysis of character change during speciation:

Comparison of closely related but allopatric forms (populations or subspecies or species): Comparing characters in allopatric forms, which are important for recognition in sympatric species, may indicate which traits differentiate first and may form the starting point for species-specific differences. In one of the few studies of this type, Den Hollander and Barrientos (1994) have shown that in the tettigoniid, Pterophylla beltrani, morphological characters (mainly male genitalia)

Insect Sounds and Communication: Physiology, Behaviour, Ecology and Evolution 138

evolved more rapidly than acoustic signals. They concluded to have found a species in the process of splitting into different species. We will present some more examples from tettigoniids by bringing together separately published data from acoustics and morphology.

Tracking change of song and genitalia in groups where a phylogenetic tree is available: This powerful method depends on the availability and reliability of a phylogenetic tree. At the moment, there are still very few examples, but data will probably increase rapidly mainly due to molecular genetic methods. We shall try to review all data of this type, but it is often difficult (see below).

MATERIAL AND METHODS

Specimens recorded and examined for this work are deposited in the collection of K.-G. Heller (CH, followed by the specimen code). At http://www.dorsa.de the localities of specimens (except those from Turkey) can be seen on a web-based Geographical Information System (GIS) map. Digitised sound recordings are available at the taxonomic database Systax (http://www.biologie.uni-ulm.de/ systax). Details of recorded specimens are given in the appendix (accompanying compact disc [CD]). Authors and years of description of other species mentioned in the text are in Otte et al. (2004).

For sound recording in the field a Uher tape recorder 4200 IC and a Sony WM3 tape cassette recorder were used with Uher M 645 and M 517 microphones (frequency response flat up to 20 kHz and 15 kHz, respectively). For sound recording in the laboratory a Racal store 4 D tape recorder with Bru¨el and Kjaer 4133 and 4135 microphones (frequency response flat up to 40 resp. 70 kHz) were used. After digitising calls, oscillograms (after filtering) and sound analysis were made using the programs Turbolab, Amadeus (Apple) and CoolEdit. Wing movements were registered by an opto-electronic device (Helversen and Elsner, 1977; modified as in Heller, 1988).

Song terminology:

† Calling song: Song produced by an isolated male.

† Syllable: The sound produced by one complete up (opening) and down (closing) stroke

of the forewings.

† Hemisyllable: The sound produced by one unidirectional movement (opening or

closing) of the forewings.

† Duty cycle: Ratio of the durations of sound emission and silent interval.

RESULTS

Species occurring syntopically at one locality show distinct differences in calling songs in frequency composition and amplitude modulation. Frequency composition depends mainly on the size of body and tegmina of the sound-producing animal and is quite often typical for a genus or a group of species of similar size. Hearing sensitivity typically matches the spectrum of the conspecific song, but the spectral information cannot be used to discriminate between closely related forms. Related species of one genus differ typically in amplitude modulation (Samways, 1976a, 1976b; Heller, 1988; Ragge and Reynolds, 1998; Walker and Moore, 2004). For example, several species of Metrioptera are found together in large parts of Europe without any obvious intraspecific variation in song (Figure 9.1). Although the species have slightly different habitat requirements, at many localities they occur together within acoustic range.

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ONG AND

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ORPHOLOGY OF

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ALE

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ENITALIA

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OPULATIONS OF

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Differences in song or morphology between isolated, allopatric populations of members of one clade are typically smaller than the differences between widespread sympatric species. These are,

however, important in models of allopatric speciation and there is a large literature on this (Otte and Endler, 1989). Here, we shall concentrate on the comparison between differences in song and male genitalia. In the four parts of this section we shall:

† Describe the situation in the subgenus Parnassiana (genus Platycleis) in detail.

† List examples where only one trait (song or morphology) shows differences and the

other seems to be more or less stable.

† Mention rare examples where allopatric populations of one species differ in song and

morphology.

The Subgenus Parnassiana (Tettigoniidae: Platycleidini: Platycleis)

Parnassiana occurs with about 15 taxa (12 monotypic species and one species with three subspecies) on high mountains in Greece. A further species (P. vicheti), endemic to Southern France, probably belongs in another (sub)genus. All described forms occur allopatrically at high altitudes on different mountains (Figure 9.2). The species may be differentiated mainly by their genitalia (Figure 9.3), although a few differences in coloration and pronotum shape are also important (mainly for subspecies recognition; see Willemse, 1985). Calling songs are known for

Metrioptera roeselii Metrioptera oblongicollis Metrioptera bicolor Metrioptera brachyptera Metrioptera saussuriana 200 ms >25°C >21°C >26°C >24°C >25.5°C

FIGURE 9.1 Oscillograms of stridulatory movements and song (synchronous registration of left tegmen movement [here and in Figure 9.2, Figure 9.4 and Figure 9.5 upward deflection represents opening, downward closing] and sound) of some species of the genus Metrioptera (localities of recorded specimen on CD).

Insect Sounds and Communication: Physiology, Behaviour, Ecology and Evolution 140

10 species (Figure 9.3; Heller, 1988; Heller and Willemse, 1989). In all species the song contains two groups of elements: sequences of very short syllables (microsyllables) which can be positioned at the beginning (Figure 9.2: P. parnassica) or end (Figure 9.2: P. tymphrestos) of a syllable group, and sequences where short and long syllables (macrosyllables) alternate. This pattern is unknown in any other European tettigoniid. Series of microsyllables are produced by many other species related to Platycleis (examples in Heller, 1988; see also Figure 9.1: Metrioptera saussuriana) and they are possibly directed towards other males (Samways, 1976). From a comparison with related species it can be assumed that the alternate sequence with macrosyllables carries species-specific information. However, in all Parnassiana this sequence is quite similar. All syllable types are repeated at about the same rate in all species, so there is no evidence for distinct song differences, although the amount of song variation is still insufficiently known for all species. It is known for example that the duration of the alternate syllable series and the frequency of microsyllable series can be very variable within one species (Heller, 1988), indicating that these parameters are not useful for species recognition, but they seem to differ reliably between other species. The differences in male genitalia, however, are so pronounced that the forms have been described as different species. These data suggest that in this group song does not form the starting point for speciation. Some observations on Mt. Tsoumerka may even provide evidence that two species (P. tenuis and an unidentified one) with quite similar songs but different genitalia, occur on the same location (Heller and Willemse, 1989). The same situation as

tymphiensis Song unknown: panaetolikon chelmos tenuis >25°C >25°C >23°C >22°C >29°C >24°C >28°C >25°C 26°C 22.5°C nigromarginata tymphrestos dirphys gionica parnassica menalon fusca _{500 ms} parnon

FIGURE 9.2 Distribution map and oscillograms of song of the species of the subgenus Parnassiana (genus Platycleis) and of stridulatory movements (in eight species only; synchronous registration of left tegmen movement and sound). Localities of recorded specimen on CD, distribution data from Willemse, F., Catalogue of the Orthoptera of Greece, Fauna Graeciae, Hellenic Zoological Society, Athens, 1984, p. 1, i–xii, 1–275; Willemse, L. and Willemse, F., Entomol. Ber. Amsterdam, 47, 105–107, 1987; Heller, K.-G. and Willemse, F., Entomol. Ber., 49, 144–156, 1989.

in Parnassiana occurs in some other groups where songs are similar but genitalia are different in allopatric populations.

Allopatric Forms Differing in Genitalic Morphology, but not in Song

Many published examples describe allopatric forms which differ in genitalic morphology, but not in song. Probably the most striking example is found among the Greek species of Eupholidoptera. Among the about 21 completely allo- or parapatric species, the song pattern of all those studied (14) is the same, with the possible exception of the east Aegean E. prasina, which may have a faster syllable rate (Heller, 1988; Willemse and Heller, 2001). In male genitalia, however, very large differences between most species are observed (Willemse, 1985; Willemse and Heller, 2001).

Psorodonotus and the subgenus Tessellana of Platycleis contain distinctly less subspecies or species, respectively, than Eupholidoptera in Europe, but present otherwise the same picture. Within each genus the three subspecies of Psorodonotus and four species of Tessellana have nearly identical songs (Heller, 1988), but differ in morphology of genitalia (Harz, 1969). Other examples are Acrometopa macropoda, Platycleis albopunctata, Zeuneriana, Pholidoptera, Pterolepis spoliata, Callimenus and Uromenus (Heller, 1988).

Ragge and Reynolds (1998) discussed two species complexes within the genus Metrioptera — the M. saussuriana and M. roeselii complexes. The widespread M. saussuriana and the local M. buysonii, which do not differ in song, show small but stable differences in genitalia. They occur close together in the Pyrenees (maps in Voisin, 2003). The Italian M. caprai shows only small differences in genitalia compared with M. saussuriana. The song of some populations of this species is very similar to that of M. saussuriana, but others have a higher syllable number per syllable group. In the M. roeselii complex several local allied forms have been described in

Central Greece Peloponnisos

tymphiensis tenuis tymphrestos dirph nigromarginata chelmos

ys gionica

panaetolik on

parnassica menalon parnon fusca

FIGURE 9.3 Male genitalia of the species of the subgenus Parnassiana (genus Platycleis). First row: left cercus, dorsal view. Second row: titillator, anterior view. Third row: titillator, lateral view. (Figures from Willemse, F., Entomol. Ber. Amsterdam, 40, 103–112, 1980; Willemse, L. and Willemse, F., Entomol. Ber. Amsterdam, 47, 105–107, 1987; Heller, K.-G. and Willemse, F., Entomol. Ber., 49, 144–156, 1989.) Bottom row: distribution.

Insect Sounds and Communication: Physiology, Behaviour, Ecology and Evolution 142

southern Europe. Some show relatively large differences in genitalia, but the song patterns of all of them are the same (Ragge and Reynolds, 1998; Fontana, 2001).

In the ampliatus group of Poecilimon, songs of the two parapatric species, P. ampliatus and P. ebneri, are quite similar, while the male cerci show distinct differences. P. ampliatus differs further from P. ebneri in the possession of a large dorsal gland which the female feeds on during mating (Heller and Lehmann, 2004).

A more complicated situation is found in Ephippiger. There has been a long discussion about the taxonomic status of species related to Ephippiger ephippiger (Kidd and Ritchie, 2000). Obviously local forms do exist, but their status is unclear. They differ mainly in male genitalia (Fontana, Kidd in preparation; Kidd and Ritchie, 2000) and song with high variability concerning syllable numbers per syllable group. In the western part of the range of E. ephippiger three mainly allopatric archetypes (Kidd and Ritchie, 2000) may be found, but they hybridise where they meet. Obviously neither differences in song nor in genitalia are large enough to prevent mixing of the gene pools. Over the whole range of the species, the pattern of song variation and its relationship to morphological variation is not sufficiently known.

Another well-known example from North America is the genus Orchelimum. Two parapatric species, O. nigripes and O. pulchellum, differ slightly in genitalia, but not in song (Walker, 1974). Hybridisation between these forms has been documented in two contact zones (Shapiro, 1998). It should be noted that Orchelimum species are long-winged animals capable of relatively fast dispersal while all other examples mentioned above concern short-winged animals.

Belocephalus contains five species falling into two groups (see Walker and Moore, 2004). Members of both groups may occur sympatrically. The three are morphologically quite similar; allopatric species of the B. sabalis group all have the same song, but one species differs clearly in life-history traits, while the other two are geographically separated. The other two allopatric species of the B. subapterus group are morphologically similar, but differ mainly in song and belong to the species treated in the following subsection. However, within B. subapterus there are two geographically separated forms (with hybrid zone) differing in male genitalia only.

Allopatric Forms Differing in Song, but not in Genitalic Morphology

In a few examples among allopatric forms, only the song seems to have changed. Species will be mentioned here where only the song and the stridulatory organs together have changed, or at least the song much more than genitalia.

The most distinctive examples are found in Decticus verrucivorus. This well-known and widespread species shows some variability in wing length and body size (Samways and Harz, 1982). In the song, which has been recorded at many localities in Europe (Ragge and Reynolds, 1998), no significant differences have been found, except in Spain. Specimens from the Iberian Peninsula produced a quite distinct song, which was used to establish a subspecies, Decticus verrucivorus assiduus (Ingrisch et al., 1992). No differences were found in genitalia. Recently, in another form of this group from south Italy, a song pattern was detected which also differs slightly from that of the nominate subspecies (Fontana et al., 1999).

Two other examples of song change with no, or only minor, divergence in genitalic morphology are found in Poecilimon. Heller (1984) described the subspecies P. obesus artedentatus, now usually considered as a species (Willemse and Heller, 1992), differentiated clearly in song and morphology of the stridulatory file. This is a possible example of reproductive character displacement because P. artedentatus occurs in an area where another species of Poecilimon, P. nobilis, is found with a song very similar to that of P. obesus. The second example concerns Poecilimon paros. This island species was discovered by its song, which differs distinctly from that of its allopatric sister, P. hamatus (Heller and Reinhold, 1992). A small difference in the shape

of the male cerci has now been found, which can be used for morphological separation of both species. A similar discovery was made recently in Turkey, where the new species P. martinae differs from its sister species, P. inflatus, mainly in song, but also in morphology of the male cerci (Heller, 2004).

In east Asia, two species of Hexacentrus, H. japonicus and H. unicolour, are very similar in morphology, but differ in song (Inagaki et al., 1986). They are largely allopatric, but overlap in a small area in Japan where they prefer separate habitats (Inagaki et al., 1986). Morphologically they can be differentiated by small differences in male genitalia (Inagaki and Sugimoto, 1994) and the structure of the stridulatory file (Inagaki et al., 1990). In the laboratory interspecific hybrids can be obtained (F1 and F2) (Inagaki and Sugimoto, 1994).

At this point those rare examples should be mentioned where not only allo- but also sympatric species differ only by song. Among bushcrickets only some species of North American Amblycorypha belong to this category (Walker et al., 2003). Walker (1964) expected that

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