Geometrical Morphological Analysis Of The Male First Ventral Limb, Female Genital Pore And Third Maxillopod Of Crab

The genus Sinopotamon Bott,1967 is one of the most species-rich freshwater crab group endemic to China.The morphological characters of the male first gonopod(G1)are used as an useful tool for taxonomic classification of Sinopotamon according to Dai in Fauna Sinica(Decapoda,Potamidae).The evaluation of G1 and vulvae are mostly based on a subjective non-quantitative visual description.However,whether the co-evolution exists or not between the vulva and G1 cannot be explained.The third maxilliped has important roles in screening and cleaning.The proportion of the third maxilliped merus and ischium was mainly described,however,its change are hardly used in trational classification.In this study,the geometric morphometrics was employed to quantify the morphological features for the first time.We obtained a total of 2,648 photographs of the vulvae.G1,and third maxilliped from 948 individuals of 69 Sinopotamon species(81.2%of total).Based on the deformation from the analysis of the vulvae,G1 and nonsexual character of third maxilliped in Sinopotamon,we discussed the geometric shape change of G1,vulvae.the third maxilliped merus and ischium,and uncovered coevolution between the vulvae and G1.We analyzed the morphological features of vulvae,G1,third maxilliped merus and third maxilliped ischium by geometric morphometrics,and subsequently discussed the role of these traits in Sinopotamon classification.The main results and conclusions of this paper are as follows:(1)The upper and lower margins of vulvae tend to expand,and the inner and outer margins trend to adduction.The vulvae have the tendency to become taller and rounder in the overall deformation.Shape variations of the dorsal view and ventral view of the G1 in Sinopotamon have been outward and upward bending and widened in the overall deformation.The deformation of G1 was in conformity with the vulvae deformation.That may be due to the coevolution of the lock and key relationship between the two structures.(2)The deformation of the vulvae,G1,third maxilliped merus and ischium in Sinopotamon was analyzed by geometric morphometrics.The morphological variance in the vulvae was observed(total variance=0.01409181),the variance in G1 was observed(total variance=0.00770768).The vulvae and G1 are the reproductive structure,the higher variation occurred in vulvae than G1.And the shape variation of third maxilliped merus and ischium is less than that the G1 and vulvae.That suggests that the higher variation of vulvae and G1 coordinated deformation may be more beneficial to the speciation in Sinopotamon.(3)Geometric variation of the structures mainly occured in the outer edges and the whole shape of vulvae,stocky degree of G1 and bending degree in the tip of G1,length of the third maxilliped merus,width of the third maxilliped ischium.These provide basis for the consideration morphological changes between species in Sinopotamon.(4)The mahalanobis distance and procrustes distance analysis showed that the G1 is the highest resolution between species in Sinopotamon,82.35%and 66.11%of the samples were significant difference of G1;secondly is third maxilliped merus(74.93%and 64.75%),the lowest is vulvae(59.42%and 30.31%).It suggests the whole shape of G1 is the best classification characters,support the whole shape of G1 as the genus as a kind of important basis.The third maxilliped merus has higher resolution,is expected to as important basis in species identification in Sinopotamon.