Microgeographic variation in body size and development time in the waterstrider, Limnoporus notabilis

Abstract

Body size and development time were compared among four population of Limnoporus notabilis (Heteroptera: Gerridae), in the southwestern corner of mainland British Columbia, Canada. Comparisons based on both field-caught and lab-reared animals indicated significant, heritable variability in body size among these four populations. Although body size and development time tended to be positively correlated, the variability in development time among populations was significant only for females. Comparisons of food availability at two of the study sites indicated that the observed patterns of variability in body size and development time could not be the result of genetic or phenotypic adaptations to food supply. These patterns also do not appear to reflect direct adaptation to season length. Both body size and development time were, however, positively associated with environmental heterogeneity, as indicated by habitat stability and continuity. In seasonal habitats, this positive association is complicated by selection for rapid development, leading to populations of large L. notabilis with relatively short development times. The hypothesis is thus advanced that microgeographic variability in body size and development time in L. notabilis reflects the interplay between selective adaptation to environmental heterogeneity, as proposed by Roff (1977, 1978) and dingle et al. (1980), and selection for rapid development in seasonal habitats.