Dimorfismo sexual e polimorfismo no gênero Ptychoderes Schoenherr, 1823 (Coleoptera Anthribidae, Anthribinae, Ptychoderini)

Abstract

The sexual dimorphism exhibited by polyphenic males in some species of the Ptychoderes involves variation in rostrum, antennae and ventrites. The existence of polyphenism should be an important component in the evolutionary process via morphological and behavior novelties. The goal of this study was to determine the variation of monomorphic traits, polyphenism in males, variation of structures with known sexual dimorphism, possible allometric patterns and to test these predictions for Ptychoderes by mapping both male and sexual dimorphism in a phylogenetic reconstruction of the genus Ptychoderes using Mesquite 2.04. Twenty-three morphometric variables were measured in 510 specimens with the following analyses performed: Cluster analysis; Principal Component Analysis (PCA); Canonical Variance Analysis (CVA), analysis of regression of Reduced Major Axis (RMA). Each type of dimorphism was mapped on the previous phylogeny as a separate two-state using parsimony. For all species the sexual dimorphism provided significant differences between the sexes for antennal segments (II-X). The length of rostrum and ventrite V were confirmed as indication of sexual dimorphism (except P. jordani). The unique species without polyphenics males was P. depressus. The others species major and minor males differed significantly for many variables with similarities and differences. In the PCA, the first component (PC1) had a high percentage of the variance in the data for all species; present loadings of the same signal suggesting differences related to the size of the species P. jordani, P. depressus, P. virgatus, P. mixtus and P. callosus and for the species P. viridanus, P. antiquus, P. elongates and P. nebulosus the PC1 presented positive and negative loadings suggesting differences related to the shape (allometry). The PC2 showed both positive and negative loadings for all species, a probable allometric component. The CVA confirmed the groups: major males, minor males and female, when they occurred. We found different allometric patterns for all species, with similarities and differences between species. All these results confirm the hypothesis the polyphenism in males and sexual dimorphism for Ptychoderes. The analyses of allometric patterns for sexual dimorphism results positive allometry for rostral length (RL1) in males and females, with ventrites only for males. The positive allometric patterns related with polyphenism in the antennae were confirmed for larges and small males in almost all species, except in P. nebulosus. The ancestor of the clades in the Ptychoderes phylogeny was predicted to have polyphenic males (except P. depressus) with variables in the rostrum, antennae and ventrites indicative of the sexual dimorphism with positive allometry. These patterns should be linkage to the protection behavior of the female performed by large males during oviposition.