Abstract
A study on relative growth, sexual dimorphism and ontogenetic trajectory was carried out in a population of the aeglidAegla marginata coming from Barrinha River, Iguape River Basin, Tunas do Paraná, Paraná State, Brazil. The size the of morphological sexual maturity was estimated for males and females. The analysis of sexual dimorphism and ontogenetic trajectory were performed using geometric morphometric technique. Males reach maturity with 10.58 mm of carapace length (CL) and females with 10.38 mm CL. Sexual size dimorphism was only visible among adults, with males reaching larger sizes. This is probably related to the reproductive strategy of males. However, sexual shape dimorphism was found for both juveniles and adults: the posterior region of the carapace was wider in females. As the contrast of this feature was stronger in adults, it can be considered that large abdomen is advantageous for egg incubation. The allometric trajectories of juveniles presented similar directions, becoming divergent during the adult phase. The shape variation inA. marginataoccurred gradually throughout its development, with no abrupt transformation upon reaching sexual maturity. The reproductive adaptation is the main reason for the morphological variation within populations ofA. marginata.
Highlights
Allometry can be characterized as the shape variation of body structures influenced by the variation of their size or the total size of the organism
The percentage of correct classification from the Discriminant Analysis for juveniles was 74.22% for males and 65.07% for females, and for adults, it was 89.55%
The value obtained for the morphological sexual maturity in females from Barrinha River population (10.38 mm carapace length (CL)) was higher than the size of functional maturity (9.2 mm CL) obtained from the Mirante das Antas River, which belongs to the same hydrographic basin (Silva et al 2016)
Summary
Allometry can be characterized as the shape variation of body structures influenced by the variation of their size or the total size of the organism (see revision in Mitteroecker et al 2013). One of the causes for allometric variation in the body plan of organisms is sexual dimorphism, a common and widely studied feature in the animal kingdom (Shine 1989, Fairbairn 1997). It may arise as a result from pressure exerted by natural or sexual selection (Fairbairn 1997). Male chelipeds show positive allometric growth (see Oliveira and Santos 2011 for review), which can be considered a characteristic to favor males with larger chelipeds
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