Desiccation stress acts as cause as well as cost of dispersal in Drosophila melanogaster

Environmental stress is one of the important causes of biological
dispersal. At the same time, the process of dispersal itself can incur
and/or increase susceptibility to stress for the dispersing individuals.
Therefore, in principle, stress can serve as both a cause and a cost of
dispersal. We studied these potentially contrasting roles of a key
environmental stress (desiccation) using Drosophila melanogaster. By
modulating water and rest availability, we asked whether: (a) dispersers
are individuals that are more susceptible to desiccation stress, (b)
dispersers pay a cost in terms of reduced resistance to desiccation
stress, (c) dispersal evolution alters the desiccation cost of dispersal,
and (d) females pay a reproductive cost of dispersal. We found that
desiccation was a clear cause of dispersal in both sexes, as both male and
female dispersal propensity increased with increasing duration of
desiccation. However, the desiccation cost of dispersal was male-biased, a
trend unaffected by dispersal evolution. Instead, females paid a fecundity
cost of dispersal. We discuss the complex relationship between desiccation
and dispersal, which can lead to both positive and negative associations.
Furthermore, the sex differences highlighted here may translate into
differences in movement patterns, thereby giving rise to sex-biased
dispersal patterns.