Orthoptera: Gryllidae): Speciation Through Vicariant and Glaciation Events
Total Page：16
File Type：pdf, Size：1020Kb
FORUM Genetic Differentiation of Loxoblemmus Appendicularis Complex (Orthoptera: Gryllidae): Speciation Through Vicariant and Glaciation Events 1 2 1 1 2, 3 WEN-BIN YEH, YU-LIN CHANG, CHUN-HSIEN LIN, FU-SHENG WU, AND JENG-TZE YANG Ann. Entomol. Soc. Am. 97(4): 613Ð623 (2004) ABSTRACT Taxonomic determinationbasedon morphology alone has failedto describethe evo- lutionary history of Loxoblemmus appendicularis Shiraki complex in Taiwan. Phylogenetic analysis using the 16S rDNA sequence reveals that three evolutionary lineages of L. appendicularis have been found to coincide with their area of geographical distribution: the Southern, Eastern, and Northern populations. Sequence distancewas equal between the Northern andSouthern andNorthern and Eastern populations (0.032), whereas between the Southern andEastern populations, the sequence distance was 0.026. Cross-breeding among these three populations has produced abnormal hybrids, suggesting that a possible postzygotic isolating mechanism exists. Biogeographical history suggests the speciation event in L. appendicularis began in the early Pleistocene (1.8 million yr ago [Mya]). Vicariant event createdby the rise of the Central Mountain Range Ͼ1 Mya ledto two separate Eastern andSouthern lineages. The following glacial event andformation of a landbridgebetween Taiwan andthe Chinese continent at the endof Pleistocene reintroduced L. appendicularis, currently known as the Northern population, to western andnorthern Taiwan. Results of sequence divergence, phylogenetic inferences, geographical distribution, and cross-breeding strongly show a current tax- onomic recognition of a single species with three parapatric cryptic species. KEY WORDS Loxoblemmus, Gryllidae, speciation, vicariant, glaciations PHYLOGEOGRAPHIC STUDIES HAVE GREATLY contributedto tral Mountain Range Ϸ2.5Ð1 Mya (Lin 1966, Huang et our understanding of evolutionary history (Avise al. 1997) in the formation of Ͼ100 peaks now above 2000). A clear success of phylogeographical study has 3,000 m in elevation, andthe ongoing tectonic collision been the improved descriptions of geographical dis- along the north-south axis of Taiwan has createddi- tribution, phylogenetic relationships, andgenetic dis- verse habitats for terrestrial organisms. In addition, it tance among evolutionary lineages (Bermingham and is believedthat Taiwan andthe Chinese continent Moritz 1998), especially with regards to the effect of have periodicallybeen connectedandseparatedbe- glaciations (Riddle and Honeycutt 1990) and moun- cause of sea level changes causedby glaciations during tain building (Trewick et al. 2000, Shaw and Lugo the Pleistocene Period. The periodic formation of a 2001). Taiwan is separatedfrom the Chinese continent landbridgeacross the Taiwan Strait has playedan by the shallow Taiwan Strait, which has interrupted important evolutionary role in TaiwanÕs biota. normal gene ßow in a species distributed on both sides The biota of Taiwan is rich in diversity, as has long of the Taiwan Strait. However, geographical history been notedby biologists, because of the extremely (Huang et al. 1997) andmammalian andreptilian fossil variable abiotic environments, such as mountain to- records (Shikama et al. 1975, Otsuka and Shikama pology, climate changes, and the multiple land-bridge 1978, Otsuka 1984) indicate that Taiwan was con- formations during the Pleistocene Ice Ages (Lue and nectedto the Chinese continent before the Pleisto- Chen 1997). The effects of the well-documented geo- cene Period. The present day conformation of Taiwan logical glaciations on the diverse biota of the island began Ϸ5 million yr ago (Mya) during the late Mio- have recently been the subject of an increasing num- cene (Teng 1987, 1990), causedby exhumation from ber of phylogeographic studies that focused on ge- the collision of the Eurasian andPhilippine plates netic patterns andprocesses of colonization andspe- (Teng 1990, Huang et al. 1997). The arc-continent ciation (Wang et al. 1999, 2000, Creer et al. 2001, collision resultedin a drasticexhumation of the Cen- Huang et al. 2001, Huang et al. 2002, Hwang et al. 2003). The diversiÞedspeciesandsubspecies of ter- 1 Department of Biology, Kaohsiung Medical University, Kaohsiung restrial animals in Taiwan might have been formedby 807, Taiwan. 2 Department of Entomology, National Chung-Hsiung University, peripatric speciation when geographic isolation oc- Taichung 402, Taiwan. curredbecause of the absence of a landbridgebe- 3 Corresponding author, e-mail: [email protected]. tween the islandof Taiwan andthe Chinese continent. 0013-8746/04/0613Ð0623$04.00/0 ᭧ 2004 Entomological Society of America 614 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 97, no. 4 Although the ecosystem in Taiwan supports diverse cesses of L. appendicularis by vicariant andglaciation communities of fauna andßora, the phylogeographic events are herein hypothesizedanddiscussed. impact on insect fauna has been poorly studied. Loxoblemmus The cricket genus Saussure (Saussure Materials and Methods 1877) has 46 species worldwide. Of these, 36 species are distributed throughout East Asia. Taxonomic rec- Collecting Materials. Forty-six individuals of L. ap- ognition of this genus has always met with some dif- pendicularis complex from various localities through- Þculties, because the descriptive characters of many out Taiwan (Fig. 1) were analyzedin this study. species overlap. Loxoblemmus appendicularis is small Twenty specimens of other Loxoblemmus species, L. (Ϸ1.5 cm) in body length and is one of the most equestris, and L. sylvestris, andthe three other genera, common local crickets in Taiwan. Fieldobservation Teleogryllus, Brachytrupes, and Velarifictorus, were andlaboratory observation have shown this species to usedas outgroups for comparisons. Collecting infor- have an annual life cycle without hibernatedeggs. The mation andsequence accession numbers (AY239043Ð numerous nymphs usually hatch in July andAugust AY239108) are shown in the Appendix. andmolt six times until adulthoodisreachedaround DNA Extraction, Amplification, and Direct Se- May to July. All stages live in moist or semimoist sites quencing. Live crickets were collected, Þxed, and pre- Ϫ Њ such as grasslands or in leaves under the trees. They servedin 95% ethanol at 20 C. The anterior leg was feedalmost entirely on the tiny roots of grasses or trees selectedfor homogenization by glass homogenizer in andoccasionally on the deadbodiesof other small 500 l digestion buffer containing 100 mM Tris-Cl (pH invertebrates or spiders. The taxonomic characters of 8.0), 10 mM EDTA, 100 mM NaCl, 0.5% SDS, 50 mM dithiothreitol, and 0.5 mg/ml proteinase K. The mix- L. appendicularis Shiraki Shiraki 1930 have been based Њ on a common andhighly conservedheadshape and ture was incubatedat 50 C overnight andextracted antennae forms (Gorochov 1985). Unfortunately, with phenol-chloroform (modiÞed from the process characters such as body size, head shade, front ridge, describedbyYeh et al. 1997). ExtractedcrudeDNA was dissolved in 50 l TE buffer, andan aliquot of 10 antennae form, andveins in the tegmen are variable. Thus, the taxonomic determination of this species l crudeDNA was diluted10-foldandusedasa DNA complex has been ambiguous (Yang 1992). Prelimi- template in the following ampliÞcation reaction. Polymerase chain reaction (PCR) was employedto nary molecular evidence on L. appendicularis complex amplify a partial sequence of the mitochondrial 16S in Taiwan reveals three distinct clusters exist in the rDNA gene. The primers usedto amplify the region mitochondrial DNA sequence (Yeh et al. 1999). Thus, were 5Ј-GCCTGTTTATCAAAAACAT-3Ј (16SR21) these clusters couldbe usedto addressquestions con- and5 Ј-CCGGTCTGAACTCAGATCA-3Ј (16S22), cerning the patterns in L. appendicularis evolutionary which correspond, respectively, to nucleotides 13416Ð process. 13396 and12866Ð12884 of the 16S rDNA gene of Dro- In the past decade, molecular characters have been sophila yakuba (Clary andWolstenholme 1985). Am- usedto identifyinsect species. This has been espe- pliÞcation was carriedout for 35 cycles in a Þnal cially helpful in determining intraspeciÞc diversity volume of 100 l containing 10 mM Tris-Cl (pH 9.0), (Mukha et al. 2000, Palmer et al. 2000) andin solving 50 mM KCl, 1.5 mM MgCl2, 0.01% gelatin, 0.1% Triton- the problem of sibling species (Kelley et al. 2000, Yeh X100,2UofSuperTaq polymerase (HT Biotechnol- et al. 2000, Parsons andShaw 2001), as well as that of ogy, LTD, Taiwan), 0.2 mM of each dNTP, 20 pmol of the species complex (Yeh et al. 1997, Guillet et al. each primer, and2 l of DNA template. The reaction 2000). Molecular evidence is also the means of deter- was carriedout with the following temperature pro- mining whether or not introgression or hybridization Þle: denaturation for 50 s at 95ЊC, annealing for 1 min has occurred(Dowling andSecor 1997). Further- at 50ЊC, andextension for 1 min at 72 ЊC. AmpliÞed more, genetic analyses of natural species assemblages DNA fragment was excisedfrom agarose gel andex- render it increasingly likely that speciation occurs tractedfrom the gel with the Nucleotrap Kit (Mach- under sympatric conditions (Bush and Smith 1998, erey-Nagel, Germany) or puriÞeddirectlyfrom am- Hellberg 1998, Schliewen et al. 2001, Dawson et al. pliÞedproductusing the PCR puriÞcation Kit, 2002). Qiaquick (Qiagen, England). The resulting DNA We are interestedin genetic patterns andthe col- product was sequenced directly using radioisotope onization process of this species.