Shape variations between populations of Aegla uruguayana (Crustacea, Decapoda, Anomura). A phenotypic plasticity case?

GIRI F.; COLLINS P.

New York

Congreso; Congreso Evolution 2006; 2006

Society for the Study of Evolution (SSE), the Society of Systematic Biologists (SSB), and the American Society of Naturalists (ASN)

 The Anomura is a crustacean marine group with the only freshwater family that inhabit the aquatic southamerican environments, the aeglids crabs. Their register in continental area correspond since to cretacic era?? and their displacement is very poor. This makes suppose a narrow relationship among environmental factors, isolation time and phenotype differences among the populations. The more widely spread within the Aeglidae family is Aegla uruguayana from southern region of South America. This crab inhabits rivers, streams, shallowlakes and lagoons of the center of Argentina, Uruguay and the South-west of Brazil. The objective of the present study is to determine the existence of phenotypic plasticity in the cephalothorax shape of A. uruguayana by geometric morphometric method. A total of 438 individuals from 20 populations from 5 sub-basins between 54º and 65º latitude (“Atlantic”, Uruguay, La Plata, Paraná and “Mountain”) were photographed covering the species’ distribution. Using a symmetrization process 17 landmarks (out of 32) was obtained to analyze the crab shape. The landmarks were digitized by the tpsDig. The configurations were superimposed through the GPA. PCA, Discriminant, and Dissimilarity analysis (cluster UPGMA) were performed to compare the data. Also, sexual dimorphism was explored, and then each group was analyzed. With PCA (1 and/or 1, 2, 3 and 4) data from the consensus configuration of each sub-basin, a reaction norm model was constructed evidencing differences among the environments (these results was supported by a MANOVA analysis running from the weight matrix; Wilkis’ λ= 0.035, F= 17.837, p< 0.0001 o ANOVA RW1 p< 0.0001). We could observe that La Plata specimens present a shape close to the “consensus configuration”, which is correlated with the geographical center of the species’ distribution. Also, we can see latitudinal shape differences among populations the “Atlantic” and “Mountain” population and the La Plata population. Other longitudinal shape differences were observed among the La Plata, Paraná and Uruguay populations. The differences in shape were observed mainly as stylized cephalothorax in the “Atlantic” population, and a more shortened and wider cephalothorax in the “Mountain” crabs. The Uruguay, Paraná and La Plata populations (that form the macrosystem La Plata Basin) don’t present significant differences in the cephalothorax shape (see differences in the axis 1, 2, 3 and 4). These could be due to diverse causes as a result of the relationships among the basins. Thus, the “Atlantic” and “Mountain” population differs of the other populations (Paraná, La Plata and Uruguay) in geologic characteristic. Also, these populations (“Atlantic” and “Mountain”) present larger isolation, distance, temperature regimen, geologic origin and time than the other ones, determining possibly the biggest differences in the shapes.