Potential impacts of sex-biased dispersal in fragmented desert streams

Authors: Kate S. Boersma, David A. Lytle

Year: 2009 (xli)

Abstract

Sex-biased dispersal, unequal dispersal between the sexes, is common in birds and mammals, but relatively unstudied in the rest of the animal kingdom. Sex-biased dispersal may be fundamentally important in predicting species survival in a meta-population context, where relatively few individuals disperse successfully but account for all of the gene flow between habitat patches. Fragmented desert streams provide an ideal context in which to examine sex-biased dispersal because aquatic inhabitants display a wide range of dispersal capacity, from fish that require perennial water to aquatic insects with a terrestrial adult stage. Giant water bugs, Abedus herberti, are intermediate dispersers between these extremes because they are flightless but breathe air, allowing them a limited capacity to travel over land before desiccating. Field observations suggest that males may be the dispersing sex, but laboratory experiments demonstrate that all reproductive stages are capable of movement away from unfavorable habitats. This lab study indicates that the likelihood of dispersal varies by sex and reproductive condition, with males brooding eggs as the least likely to disperse and non-brooding adults as the most likely. Combining field and laboratory data, we present evidence both for and against the existence of sex-biased dispersal in A. herberti and discuss the potential ecological and evolutionary consequences of uneven dispersal tendency in fragmented systems.