Clinal pattern in Aegla uruguayana (Anomura, Aeglidae) by studying the cephalothorax shape change.

GIRI F.; COLLINS P.

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2014 vol. 113 p. 914 - 930

0024-4066

South America has been influenced by different geoclimatic events ever since its separation from Africa. The inland water fauna has evolved in response to the changing landscape. Currently, there are indications of variations in populations, occurring to different degrees that would indicate a clinal pattern in morphology. Among South America?s fauna, the freshwater anomuran, Aegla, is an enigmatic group due to its endemicity and be composed by only one genus. Of all the species in this family, Aegla uruguayana, has the broadest distribution. Its native habitats have been influenced by several marine transgressions during the Miocene - Quaternary Periods; thus their current distribution has most likely been a more recent development. Its habitat spreads across a number of isolated basins and sub-basins that display distinct degrees of isolation/connection, making possible clinal variation patterns in the morphology of this species. The aim of this study is to evaluate the pattern of carapace shape variation in A. uruguayana and how it relates to the isolation and/or connection of populations from different basins and sub-basins in order to determine any extant clinal patterns. The specimens studied belong to 25 separate populations, representing all areas in which the species currently exists. A total of 523 crabs were analysed. We identified 13 landmarks and four semi-landmarks in the carapace. The aeglids were divided into seven size intervals to avoid an allometry effect. In each size category, shape relationships analysed by PCA suggest a geographic pattern corresponding to the distribution of the populations studied. An evaluation of covariation between body shape and geographic coordinates reveals a strong pattern and shows that population distribution had a significant effect on species morphology. Additionally, according to covariance analysis, the variation in shape was not associated with other environmental variables studied. We observed a clinal pattern throughout the species distribution, which could be attributed to genetic drift. It is possible that this process is being amplified by the geographic isolation of the basins, differences in environmental characteristics, and low dispersal ability.