Sex differences in compensatory and catch-up growth in the mosquitofish Gambusia holbrooki

In many taxa, temporary nutritional shortage early in development can favour compensatory strategies that include elevated growth (‘compensatory growth’) and/or extension of the usual period of development (‘catch-up growth’) once conditions improve. The net gains from each strategy depend on the extent to which larger body size increases fitness relative to associated costs (e.g. long-term effects on adult performance, or a greater risk of juvenile mortality). These costs and benefits are likely to differ between the sexes due to sex-specific selection. We documented the responses of male and female mosquitofish (Gambusia holbrooki) to 3 weeks of low food availability (7–28 days old) that restricted subsequent growth and morphology compared to control fish continuously reared on a high food diet (N = 635 fish total). Neither sex elevated their growth rate immediately after being returned to a normal diet compared to control fish. When measured over the entire period until maturation, however, females showed compensatory growth. Males did not. Both sexes also exhibited catch-up growth but the delay until maturation was significantly longer for males. Despite early growth restriction, both sexes eventually matured at almost the same size as control fish, although males had a significantly smaller gonopodium (a sexually selected trait) than that of control males. Reasons for these sex differences are discussed.