Abstract
Cyrtograpsus genus was traditionally considered to be composed of three species: C. angulatus, C. altimanus and C. affinis . However, recent studies have found solid evidence suggesting that C. affinis and C. altimanus belong to a single species and hypothesize that the morphological differences which caused this misclassification could be related to different ecophenotypes or life stages. Here we report a geometric morphometrics study on the carapace shape of Cyrtograpsus specimens from the Rio de la Plata estuary (36°S) and the Nuevo Gulf (42.75°S), testing for shape differences between different sizes (allometry) in the two environments. We found that previous morphological descriptions of the two species were associated with different sizes of a continuous, statistically significant allometric shape variation, concluding that C. affinis is a junior synonym of C. altimanus . We also found significant differences in the carapace shape between estuarine and marine environments, suggesting an effect of the environmental variables on carapace shape and a potential adaptive value of this trait.
Highlights
Morphology has played a central role in species definition, and different forms have usually been defined as species in the absence of intermediate linking forms (Mallet 2005)
The aim of this paper is to test the suggestions of Spivak and Schubart (2003) on the basis of the allometric and geographic differences in carapace shape in specimens from the Río de la Plata estuary and the Nuevo Gulf
The multivariate regression of shape on carapace size was highly significant after 10000 permutations (P
Summary
Morphology has played a central role in species definition, and different forms have usually been defined as species in the absence of intermediate linking forms (Mallet 2005). Some geographic variations acting upon morphology, reproductive patterns, growth rates and mortality are not always consistent with genetic variation. In some situations this variation is related to phenotypic plasticity as a result of different environmental conditions (Orensanz et al 1991, Cadrin 2000). Planktonic dispersal is considered to play a key role in homogenizing gene frequencies, and lack of larval exchange is thought to promote differentiation and increase the genetic structure and morphological differences between distant populations (Levin 2006)
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