Abstract
Modular evolution promotes evolutionary change, allowing independent variation across morphological units. Recent studies have shown that under contrasting ecological pressures, patterns of modularity could be related to divergent evolution. The main goal of the present study was to evaluate the presence of modular evolution in two sister lacustrine species, Astyanax aeneus and A. caballeroi, which are differentiated by their trophic habits. Two different datasets were analyzed: (1) skull X-rays from 73 specimens (35 A. aeneus and 38 A. caballeroi) to characterize skull variation patterns, considering both species and sex effects. For this dataset, three different modularity hypotheses were tested, previously supported in other lacustrine divergent species; (2) a complete body shape dataset was also tested for four modularity hypotheses, which included a total of 196 individuals (110 Astyanax aeneus and 86 A. caballeroi). Skull shape showed significant differences among species and sex (P < 0.001), where Astyanax caballeroi species showed an upwardly projected mandible and larger preorbital region. For the skull dataset, the modularity hypothesis ranked first included three partitioning modules. While for the complete body dataset the best ranked hypothesis included two modules (head vs the rest of the body), being significant only for A. caballeroi.
Highlights
IntroductionExploring morphological diversity raises questions of how morphological variation is organized in the organism, if morphological traits vary independently of each other, or if they are integrated, reflecting a coordination in their development, function and rate of change
The study of morphological change is crucial to understanding biological diversity occurring in nature; evolutionary studies commonly deal with the consequences of the variability in populations, while less commonly dealing with its origins (Wagner & Altenberg, 1996).Exploring morphological diversity raises questions of how morphological variation is organized in the organism, if morphological traits vary independently of each other, or if they are integrated, reflecting a coordination in their development, function and rate of change
We analyzed a total of 73 skulls, 35 A. aeneus and 38 A. caballeroi, from eleven populations within Lake Catemaco, Mexico
Summary
Exploring morphological diversity raises questions of how morphological variation is organized in the organism, if morphological traits vary independently of each other, or if they are integrated, reflecting a coordination in their development, function and rate of change. In this respect, even though entire organisms must be functionally integrated, selection for functional performance could promote evolutionary changes. A module refers to the occurrence of a set of phenotypic traits that are strongly integrated and that are relatively independent from other modules (Wagner & Altenberg, 1996; Klingenberg, 2008). Integration refers to the concentration of all variation in traits on a single dimension (Klingenberg, 2008)
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