Análise morfométrica intraespecífica de duas espécies de Aegla (Crustacea: Decapoda: Anomura) com ampla distribuição geográfica

Abstract

Crustaceans of the genus Aegla occur in continental waters, in southern South America. The genus is composed by more than 70 species, most of them characterized by having restricted distributions. Unlike this pattern, the species Aegla longirostri and Aegla platensis have wide geographic distributions. Moreover, both species form non-monophyletic groups, which may indicate that these groups are formed by cryptic species. Therefore, the objective of this study was to analyze populations of A. longirostri and A. platensis through a geometric morphometric approach, in order to clarify their intraspecific relationships. For A. longirostri, we analyzed 120 individuals from 6 populations, totalizing 20 animals per population. For A. platensis, we analyzed 110 individuals from 11 populations (four Argentinean and seven Brazilian), totalizing 10 animals per population. For both species, the animals were photographed in dorsal view, and 19 landmarks were defined on the carapace. Both sides of the carapace were symmetrized, and the landmarks coordinates were superimposed. Variations in centroid size were tested with an analysis of variance (ANOVA) and Tukey s test. For A. longirostri, we also used a Procrustes ANOVA. Variations in carapace shape were explored through a principal component analysis (PCA), and afterwards through a linear discriminant analysis (LDA) and a canonical variate analysis (CVA), based on the first 8 principal components. The Mahalanobis distances between the populations were calculated. For statistical test of carapace shape differences, we used multivariate analysis of variance (MANOVA), and for pairwise comparisons among populations we used Bonferroni corrections for adjust of p-value after multiple MANOVAs. For A. longirostri, CV1 and CV2 represented 46.5% and 23.1% of the variation, respectively. The most geographically distant population showed the highest values of Mahalanobis distance. The pairwise comparisons showed that all populations of A. longirostri differ significantly in carapace shape. For A. platensis, CV1 and CV2 represented 28.5% and 22.2% of the variation, respectively. There was a separation between Argentinean and Brazilian populations, with high values of Mahalanobis distances between populations from both countries. The pairwise comparisons showed that all populations of A. platensis differ significantly in carapace shape, with the exception of a pair of Argentinean populations and a pair of Brazilian populations. Some characteristics of the aeglids indicate that these animals may have low dispersal potential, thus the geographic distance may have led to an interruption of the gene flow between populations. Added to the non-monophyletic grouping, the intraspecific difference in carapace shape in A. longirostri and A. platensis could be an evidence that populations of both species are fragmented.