Rapid divergent coevolution of Sinopotamon freshwater crab genitalia facilitates a burst of species diversification.

One of the most striking radiations in brachyuran evolution is the considerable morphological diversification of the external reproductive structures of primary freshwater crabs: the male first gonopod (G1) and the female vulva (FV). However, the lack of quantitative studies, especially the lack of data on female genitalia, has seriously limited our understanding of genital evolution in these lineages. Here we examined 69 species of the large Chinese potamid freshwater crab genus Sinopotamon Bott, 1967 (more than 80% of the described species). We used a landmark-based geometric morphometric approach to analyze variation in the shape of the G1 and FV, and to compare the relative degree of variability of the genitalia with non-reproductive structures (the third maxillipeds). We found rapid divergent evolution of the genitalia among species of Sinopotamon when compared to non-reproductive traits. In addition, the reconstruction of ancestral groundplans, together with plotting analyses, indicated that the FV show the most rapid divergence, and that changes in FV traits correlate with changes in G1 traits. Here we provide new evidence for coevolution between the male and female external genitalia of Sinopotamon that has likely contributed to rapid divergent evolution and an associated burst of speciation in this lineage.

Cite this article as:

Yao F, Shi B, Wang X et al. (2020). Rapid divergent coevolution of freshwater crab genitalia facilitates a burst of species diversification. Integrative Zoology 15, 174–86.

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Table S1 Localities and number of specimens of the 69 species of Sinopotamon used in this study.

Table S2 Shapes difference in the genital traits between Sinopotamon and P. spinescens crabs (P‐values are on the right; distances are on the left).

Table S3 Shape difference in the general traits between Sinopotamon and P. spinescens crabs.

Figure S1 Shape variation of the reproductive traits (FV, female vulva; G1, first gonopod) and non‐reproductive traits (TMI, left third maxilliped ischium; TMM, third maxilliped merus and ischium) described by the first 2 principal components.

Figure S2 Reconstruction of ancestral forms of the non‐reproductive traits of the third maxillipeds in Sinopotamon and the outgroup taxa.

Supporting Information

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