Genetic variation of stag beetles (Coleoptera, Lucanidae) in Taiwan: subspecific differentiation events of endemic montane stag beetles and phylogeography of Neolucanus swinhoei complex
| Autor: | Cheng-Lung Tsai, 蔡正隆 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Evolutionary history of Taiwanese biota has significantly affected by the climatic oscillation in Pleistocene and vicariance events of the Central Mountain Range (CMR). With the influence of glaciation events and the mountain hindrances, issues upon genetic differentiation, speciation, and taxonomic recognition of nine endemic stag beetles have been appealing in Taiwan. Several taxonomic debates have been carrying on for decades over Taiwanese stag beetles, which consist of a high proportion of endemic species and subspecies, i.e. about 87%, featuring morphological variations associated with local adaptation. Phylogeographic studies involving population structure, genetic differentiation, molecular dating, and dispersal routes of Taiwanese organisms could be applied to resolve the evolutionary processes of extant taxa. The study herein is to survey genetic variations of Taiwanese stag beetles and to unravel the evolutionary history of several montane stag beetles. Phylogenetic inferences based on COI+16S rDNA+28S rDNA of 48 Taiwanese lucanid species have confirmed most species are monophyletic groups; and the intraspecific (2%) genetic distances of the two mitochondrial genes could be applied concordantly for taxonomic identification. COI and 16S rDNA have also confirmed the two subspecific status each for Lucanus ogakii, L. kanoi, and Prismognathus davidis which are congruent with their geographic distribution in this island and their subspecific split events might have occurred 0.7-1 million years ago (Mya). Moreover, genetic differentiation including introgression/hybridization events might have occurred among L. ogakii, L. kanoi, and L. maculifemoratus. About the more complicated evolutionary story in a 90-year controversy of Neolucanus swinhoei complex, a group of stag beetles with overlapping morphological characteristics, limited/weak flight capability, and two-week adult lifespan, nine morphological characteristics and four molecular amplicons, i.e. COI, 16S rDNA, 28S rDNA, and wingless, are exploited to address their taxonomic status and genetic differentiation. Phylogenetic inferences based on COI+16S rDNA+wingless showed one eastern and three western lineages, with the latter consisting of one low-hill Widespread and two montane lineages. The differentiation events of western and eastern lineages might have occurred ca. 1 Mya and the differentiation in western ones happened approximately 0.50-0.75 Mya. In consideration of these stag beetles have shared phylogeographical history, overlapping morphological characteristics, and intermingled DNA sequences from different populations within each lineage, all of these stag beetles should be regarded as Neolucanus swinhoei Bates, 1866. To further elucidate the evolutionary history of N. swonhoei complex, more individuals were collected from different altitudinal populations of the northwestern (NW) areas and across Taiwan Island. Results showed the coexistence of both NW-CMR and Widespread Lineage in many altitudinal populations, and Widespread Lineage existed all over Taiwan Island. Calibration dating showed that these two lineages might have originated prior to 0.64 Mya and differentiated during 0.45-0.64 Mya. In NW-CMR Lineage, four major clades are corresponding to their geographic distribution and their diversification events could be dated back to 0.25-0.48 Mya in Riss/Mindel glaciations. Similar genetic compositions are found among montane populations in the same muntain area and the demographic analysis showed a dispersal trend from hill to montane areas which would facilitate the genetic exchanges among different montane populations. Finally, to understand the origination of eastern populations of the Widespread Lineage would be helpful to elucidate the effect of the CMR hindrance. Phylogenetic inference, on the basis of COI and 16S rDNA, showed a tendency of north-south genetic differentiation and high variance components within populations. Meanwhile, molecular dating shown major diversifications were associated with Riss glaciations, while the subsequent forming lineages were in correlation to the Last Glacial Maximum. Both genes revealed that major haplotypes across all populations might be resulted by ancestral polymorphisms and the possible expansion events during glacial cycles. Although the CMR did play a vital effect on their dispersal, the eastern populations might have originated via lower mountain areas of northern and southern CMR. Thus, geological effects of mountain hindrance accompanied by periodical glaciations could have been vital impact leading to the genetic differentiation of these limited/weak flight capability, two-week adult lifespan, and montane-adaptive stag beetles. |
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