NTaiwan+S Ryukyus Geothelphusa

Pleistocene speciation of freshwater crabs (Crustacea: Potamidae: Geothelphusa) from northern Taiwan and southern Ryukyus, as revealed by phylogenetic relationships

H.-T. Shih, P. K. L. Ng, T. Naruse, S. Shokita & M.-Y. Liu

The phylogenetic relationship among freshwater crab species of Geothelphusa from northern Taiwan and the Yaeyama Group of islands (including Iriomote and Ishigaki) in the southern Ryukyus was studied using the mitochondrial genes 16S rRNA and COI. Our results support the hypothesis that speciation of Geothelphusa among these islands was the result of cyclic glaciations and interglaciations during the Pleistocene. Two main clades, one the Taiwan Group (containing several clades, including most Taiwanese Geothelphusa species except Geothelphusa miyazakii but including Geothelphusa minei from Yaeyama), was estimated to be separated from its sister group, the southern Ryukyus-northern Taiwan (SRN) clade (including G. miyazakii, Geothelphusa shokitai, Geothelphusa fulva and G. marginata from northern Taiwan, the Pinnacle Islands [=Diaoyutai Islands or Senkaku Islands] and Yaeyama) at about 5.3 million years ago (mya). G. shokitai was separated from others within the SRN clade at 2.4 mya, but was probably derived from G. miyazakii in northern Taiwan. The ancestor of G. miyazakii is hypothesised to have dispersed from ancestors in Yaeyama and then isolated at 2.0 mya during the Pleistocene interglaciations. This is similar to the speciation of G. minei in Yaeyama at 1.5 mya, except that its ancestors originated from north-eastern Taiwan. Four clades of freshwater crabs are present in the Fushan Botanical Garden, located in the mountainous area of north-eastern Taiwan, which might be due to the historical rearrangements of the drainage and proximity of the various river origins.

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Keywords: 16S rRNA; Biogeography; COI; Freshwater crabs; Geothelphusa; Glaciations; Phylogeny

Fig. 1. Collection sites (circles) for the genus Geothelphusa from northern Taiwan, the Pinnacle Islands [=Diaoyutai Islands or Senkaku Islands] and the Yaeyama Group in the southern Ryukyus (numbers beside circles correspond to Table 1). The different lines indicate the possible biogeographical boundaries for five clades, NW (north-western Taiwan), NESR (north-eastern Taiwan-southern Ryukyus), W (western Taiwan), E (eastern Taiwan), M (montane Taiwan) and SRN (southern Ryukyus-northern Taiwan), based on current results.

Fig. 2. Bayesian inference (BI) tree of the genus Geothelphusa from northern Taiwan and Yaeyama in the southern Ryukyus, and outgroups, based on the combined 16S rRNA and COI genes. Support values (≥50%) for BI, maximum likelihood (ML) and maximum parsimony (MP) are represented at the nodes. Locality names and the corresponding numbers in Fig. 1 are parenthesised behind haplotypes. The divergence times estimated are shown in reverse colour at the main nodes. For calibration points, see main text. Green highlights represent haplotypes sampled from the Fushan Botanical Garden (no. 29 in Fig. 1). For abbreviations and haplotypes, see Table 1.

Fig. 3. Genealogical network for the combined 16S rRNA and COI haplotypes observed from the SRN clade (including Geothelphusa miyazakii, G. shokitai, G. fulva and G. marginata; thick lines and thick circles) and the NESR clade (including G. tali and G. minei; thin lines and thin circles) from northern and north-eastern Taiwan, the Pinnacle Islands, Iriomote and Ishigaki (Fig. 1). The arrows indicate the colonization direction (see Section 4). Unlabelled nodes indicate inferred haplotypes not found in the sampled populations. Green highlights represent the haplotypes sampled from the Fushan Botanical Garden (no. 29 in Fig. 1). Numbers beside haplotypes correspond to the collection sites in Table 1 and Fig. 1.

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