Gerridae

Abstract: Water striders (Heteroptera: Gerridae) exhibit two different types of mating behavior. The most common mating system (type I) is characterized by strong apparent conflicts of interest between the sexes, and conspicuous pre– and postcopulatory struggles. Some species exhibit a mating system that involves much less apparent conflict (type II) and lack the intense copulatory struggles. I argue that the predominant mating system in water striders is a direct consequence of sexual conflicts over mating decisions. Matings involve high costs to females (increased predation risk and energetic expenditure) but few, if any, balancing direct benefits. Sperm–displacement rates are high, and males thus gain from rematings. Mating frequencies are high; females mate multiply for reasons of convenience. In these species, males are considered to have ‘won’ the evolutionary conflict over the mating decision in the sense that they have made acceptance of superfluous matings ‘the best of a bad job’ for females, by evolving behavioral and morphological traits that make it costly for females to reject males attempting copulations. Females, however, have apparently evolved a variety of counteradaptations to male harassment, to gain control over mating. Further, I suggest that sexual conflict may have played a crucial role in the evolution of type II matings from type I matings.

Abstract: We addressed the general hypothesis that life history differences among eastern populations of the North American water strider, Aquarius remigis (Heteroptera: Gerridae), along a north-south gradient are manifestations of genetic differentiation due to natural selection. We raised offspring of two field-caught populations from each of three latitudes in a common laboratory environment at 20° C and two photoperiods. Nearly all Quebec (PQ) individuals (ca. 46° N) entered diapause to reproduce the following spring (univoltine life cycle), while intermediate proportions of New York (NY; ca. 43° N) and New Jersey (NJ; ca. 41° N) individuals reproduced directly, producing a second generation (bivoltine life cycle). PQ females were smaller, developed faster, and laid smaller eggs than NY and NJ individuals; NY and NJ populations differed little in these variables. NY females had longer life spans than either PQ or NJ females, but lower oviposition rates. Total reproductive output did not differ across latitudes. Photoperiod affected body length, development time, and reproductive pathway, resulting in a latitude by environmental interaction. PQ individuals reproduced directly under 15L : 9D (summer) conditions only, while the NY and NJ populations exhibited more direct reproduction under 13L : 11D (spring or fall) conditions. Some life history characters of the NY and NJ populations displayed the higher variability indicative of phenological transition zones. These results indicate local adaptation of populations to long-term climatic patterns. Water striders appear to adapt to longer seasons by extending development, growing larger, and breeding directly. Larger body size and extended or rapid development are associated with bivoltinism and increase in egg size, but not necessarily with higher fecundity or oviposition rate. The phenological transition zone appears to be unrelated to a transition zone a little further south established by allozyme data and morphology, as all populations studied here could be electrophoretically identified as northern "type".

Abstract: The hemipteran infraorder Gerromorpha, or the semiaquatic bugs, includes approximately 1500 species that occupy the adaptive zone defined by water surfaces. Most species occur on freshwater, but several lineages have colonized marine habitats, and others have become secondarily terrestrial. These bugs are conspicuously adapted for life on the surface film, especially with respect to locomotion, feeding, reproductive behavior, and life history (2). Their two-dimensional habitats make semiaquatic bugs ideal subjects for behavioral studies, and their striking patterns of wing polymorphism have challenged life-history enthusiasts since early in the century. Since Andersen's (2) comprehensive review a decade ago, over 200 papers about gerromorphans have appeared, setting the stage for new approaches in comparative biology. In this review, we cover the literature about gerro­ morphans appearing since 1980, emphasizing work on broader evolutionary themes. We aim to provide a synthesis useful to research workers and to underscore the advantages of using gerromorphans in ecological and behav­ ioral studies. We also illustrate the interactions now possible among sys-

Abstract: 1. Body size is a central element in current theories of life-history evolution. Models for optimal age at maturity are based on the assumptions that there is a trade-off between development time and adult size and that larger size provides a reproductive advantage. 2. The results of large, replicated experiments with the water strider Gerris buenoi (Heteroptera: Gerridae) contradict both these assumptions. Individual rearings under field conditions showed that there is a negative, not a positive, correlation between development time and adult size. The physiological basis of growth, with stretch-induced moulting, may provide a partial explanation for this correlation. 3. This study examined a number of fitness components for their correlations with female size: lifetime fecundity, reproductive life span, average volume per egg, total volume of eggs laid, and the proportion of eggs hatched. None of these traits was correlated with female size. 4. The data on water striders suggest an alternative scenario for life-history evolution, in which size is not an adaptive trait, but evolves as a correlated response to selection on other traits. This expands the range of possible models, and opens life-history theory to the debate about adaptation and optimality.