ASPECTOS DA BIOLOGIA REPRODUTIVA DE ESPÉCIES DE Drosophila (DIPTERA: DROSOPHILIDAE) PERTENCENTES A GRUPOS IRMÃOS

Abstract

The theory that the origin of the sexes is the result of disruptive selection for small and mobile and large and nutritious gametes would have as consequence the evolution of sex-specific reproductive strategies, under a model of antagonistic coevolution between sexes. Different adjustments of this coevolution could lead to interpopulation differentiation and, over time, in speciation. In this way, the analysis of reproductive traits that are under sexual and nonsexual selection is fundamental for the understanding of the origin of biodiversity. Among insects, specimens of the Drosophila genus are models for several theories of speciation. However, there is a very large gap in data about species occurring on forest in Brazil. The objective of this work was to initiate the analysis of reproductive characteristics of two phylogenetic closely related Drosophila species that occur in forest areas of the Neotropical region, D. maculifrons of the guaramunu group, and D. mediostriata of the tripunctata group, which were not studied hitherto about the reproductive characters analyzed here. In this work, precopula characters, such as testicle size, and postcopula, such as copulation duration, risk of sperm competition, number of spermatozoa stored in the spermathecae, and the progeny produced by the females per copulation, were analyzed. With the exception of the latter character (progeny/copulation), the other characteristics were analyzed in two populations of D. maculifrons and D. mediostriata collected in Mixed Ombrophilous Forest areas, in the city of Guarapuava-PR: PMA and SSF. The male testes of both species were removed, photographed and measured. The observation of copulation occurred in replicates of mass crossings during three hours. The risk of sperm competition was determined by the occurrence of polyandry, investigated through F1 paternity analysis of females inseminated in the wild, using microsatellite loci. Spermathecas of females mated with a single male were removed, and, by means of the crushing technique, slides were stained with DAPI and observed under a fluorescence microscope to estimate the number of spermatozoa stored. After copulation, females were placed in oviposition chambers and the number of eggs were counted daily. The larvae were transferred to culture medium, and the number of adult offspring produced was determined. The testes of males and the number of spermatozoa stored in the female spermathecae of D. maculifrons were significantly larger than those of D. mediostriata. There was also a significant interpopulation difference in the number of spermatozoa stored, being higher in the SSF population for both species. The populations with longer copulation duration (SSF for D. maculifrons, PMA for D. mediostriata) obtained lower rates of parent males per offspring, a higher contribution to the progeny of the last mating male with the female, and a lower proportion in the population of females inseminated by more than one male. There was no significant interspecific difference in the progeny per copulation, and in the egg-adult viability, which was very low for both species (around 20%). The results indicate a relationship between larger testes of D. maculifrons with higher number of stored spermatozoa than D. mediostriata; and longer copulation duration and lower risk of sperm competition between the population of both species. However, the superiority of testes size and in the stored spermatozoa in D. maculifrons was not reflected in a higher number of progeny/copula than in D. mediostriata, suggesting that sexual selection on duration of copulation is effective in decreasing sperm competition risk for the male, but does not increase female fitness.