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Sex-related polichromatism has been observed as a determinant factor of insects’ sexual selection, especially in some groups of Odonata. In this group, the female androchromatic condition is frequently assumed to be useful to avoid unnecessary multiple mating events that can be harmful, since the androchromatic female is usually not recognized by the males. Species of Ischnura genus can be classified as monandrous or polyandrous accordingly to their mating system. By assuming that the androchromatism allows an almost monandric behavior, it is suggested that this polymorphism evolution has been favored in polyandric populations. We aimed to test this hypothesis by using phylogenetic, morphological and behavioral information. Morphological data concerning androchromatism was found for 27 species, while behavioral information were found for 17 (from a 65 total). Species for which both kinds of data were available (plus Telebasis salva and Coenagrion resolutum) were used in the phylogenetic reconstruction based on published molecular data. For that purpose, COII gene sequences were aligned by ClustalW2 and analyzed by MrBayes software, resulting in a consensus tree. As information about outgroups’ mate systems were lacking, 16 possibilities of characters evolution were tested in a sensitivity analysis. Since the usage of several statistical tests with the same data could inflate the probability of type I errors, we applied Bonferroni correction, considering p values as statistically significant only when lesser than 0.003. The number of character changes were tallied and compared by a Fisher’s exact test that returned 16 non-significant associations between variables, with p values ranging from 0.04 to 0.59. Recent studies have demonstrated the ancestral state for Ischnuran species as polyandric and polymorphic, the later being an old adaptation that does not influence organism’s fitness nowadays. It was also observed that colour alleles frequencies were highly similar in different populations, suggesting a non-random selection of this character, but morph frequencies must be under selective mechanisms unrelated to local environment. The reproductive isolation must play a role on the evolutionary pattern here exposed, as well as learned mate recognition and female behaviour. However, the lowest p value found here (0.04) reflects a reasonable evolutionary scenario where the plesiomorphic condition is heteromorphic females, and then polyandric system arose, suggesting that the later character evolved idependently, but may have leaded to changes in damselflies’ chromatomorphism. The test results indicate an independent evolution of polichromatism and mating systems in Ischnura. |
