Geometric morphometric analysis of the freshwater prawn Macrobrachium borellii (Decapoda: Palaemonidae) at a microgeographical scale in a floodplain system

Abstract

Morphometric studies are useful for delineating the shapes of various populations and species over geographical ranges and as evidence of regional differences in crustaceans. Hydrological fluctuations in a floodplain system modulate the dispersal and presence of decapods among habitats and constitute an important macrofactor that regulate other environmental variables and which could explain the richness, distribution and abundance of organisms that live in these systems. Morphological variations among populations of the freshwater prawn Macrobrachium borellii in a floodplain system at a microgeographical scale were studied using geometric morphometrics. Carapace structure was represented using 16 digitised landmarks. Allometry and sexual dimorphism was tested. Variation in shape was explored via Principal Component Analysis. Canonical Variate Analyses was applied to compare the differences in shape between species? populations. The correlations and covariations among shapes and hydrometric level, current velocity, geographical location and hydrologic distances were analysed. The average carapace shape was different between sexes in all sites. Populations that were near each other in terms of hydrological distance had similar shapes, but all of the populations differed in shape from the farthest population. The environmental variables were not good predictors of the carapace shape. Instead, the shape was strongly related to the hydrologic distance and geographical location. The swimming characteristics of these prawns and their passive movements, together with the dynamics of a floodplain system, explain the low morphological variation between populations in this study. The dynamic characteristics of the system influence the dispersal of the prawns and allow populations to remain connected.