Gerris

Abstract: Sexual size ratios (mean female length divided by mean male length) of 12 species of temperate waterstriders in the subfamily Gerrinae (Hemiptera, Gerridae) are analyzed to test both potentially nonadaptive and adaptive hypotheses for the evolution of sexual size dimorphism. Females tend to be larger than males, and regression of female length on male length (both log-transformed) reveals significant hypoallometry for size dimorphism. Both adaptive and nonadaptive explanations for the evolution of this allometry are discussed. Of these, only a nonadaptive model is consistent with the available data. Two closely related genera, Limnoporus and Gerris, are included in the data set, but covariance analysis reveals no significant effect of phylogeny on patterns of variation in size dimorphism. It is suggested, however, that the basic female bias may reflect descent from a common, highly dimorphic ancestor, rather than adaptation within this taxon. Four adaptive hypotheses are considered. Comparisons of the dev...

Abstract: Studies of phenotypic selection in natural populations are often concerned with simply detecting selection. In adopting a more mechanistic approach, this study compares the sexual selection regimes in natural populations of the water strider Gerris odontogaster with a priori predictions of selection, based on a number of previous field and laboratory studies of the behavioral mechanisms of selection. In this species, a general reluctance of females to mate allows for intersexual selection for ability to subdue reluctant females in males. Female reluctance to mate has been shown to decrease with increasing population density, suggesting that sexual selection should be weaker in high density populations. Three different populations with large differences in population density were studied. A number of traits including parasite load, body mass, body size and male abdominal process length were found to experience significant sexual selection. The investigated populations differed considerably with regard to the total strength of selection on the measured traits and the form of selection on single traits. In general, males in the population with the highest density experienced the weakest selection for grasping ability. This pattern is ascribed to density-related alterations of female mating behavior. Selection for male grasping ability, as reflected by selection on male abdominal process length, is reduced in high-density populations where reluctant females are more easily subdued. Further, the studied populations differed significantly in mean phenotype and phenotypic variance for male abdominal process length. It is suggested that interpopulational differences in selective regimes may generate local adaptations with respect to male abdominal process length, and that gene flow may contribute to the maintenance of the high genetic variation in this trait. It is further suggested that more empirical effort should be made in quantifying and understanding spatial and temporal variation in selection in natural populations, since this may provide information on the prevalence of local adaptations in metric traits and on the mechanisms of selection.

Abstract: The Romanian fauna comprises two species of Aquarius Schellenberg, 1800, eight species of Gerris Fabricius, 1794 and one species of Limnoporus Stal, 1868, and we hereby update the distribution and provide insights on the phenology and ecology of all eleven species in this country. We furthermore update the distribution of the two closely related species Gerris gibbifer Schummel, 1832 and G. maculatus Tamanini, 1946 in southeastern Europe. Gerris maculatus is recorded for the first time from Hungary, Montenegro and Slovenia, and the first detailed localities from Romania and Serbia are given. All bibliographic records of G. gibbifer from Romania, Macedonia and Serbia are based on misidentification and this species is thus excluded from the faunal lists of these countries. Both G. gibbifer and G. maculatus occur in Croatia, Hungary, Ukraine, and probably Slovenia.

Abstract: Reproductive traits, diapause, and wing dimorphism of four pond skater species occurring in central Alberta, Canada, are explained as adaptive responses to a complex of habitat features. Species using temporary habitats had greater fecundity, but habitat permanence alone was a poor predictor of reproductive longevity, preoviposition period, or reproductive rate. Fecundity and longevity were significantly lower and more variable in direct than in diapaused breeders. There was no geographical or annual variation in fecundity, suggesting that values observed are good measures of reproductive potential. Overwintered females of species from temporary habitats (Gerris buenoi and Limnoporus dissortis) lived longer than those from more permanent habitats (G. comatus and G. pingreensis), and, concomitantly, are able to spread reproduction over several ponds. Proportion of summer-generation bugs breeding without diapause was inversely related to habitat permanence for the Gerris species, but few nondiapause breeder...