The effect of environmental change on plastic sex-ratio strategies

Mirjam Borger , Jan Komdeur, David S Richardson, Magdalena Kozielska

Offspring sex ratio manipulation has been widely studied, with numerous adaptive explanations proposed for biased sex ratios. While sex-ratio trends have been observed in many species, such patterns often disappear over time within populations or differ across populations. Environmental change is frequently proposed as underlying these inconsistencies, particularly for strategies relying on environmental cues. A textbook example comes from the Seychelles warbler (Acrocephalus seychellensis) study, where an initially reported environment-dependent sex-ratio trend could not be found in later years, possibly due to environmental change. Using an individual-based simulation inspired by the Seychelles warbler system, we tested how environmental change affects environmentally determined sex-ratio strategies. Our results indicate that such strategies are unlikely to disappear but instead shift to fit new environmental conditions. When strategies rely on multiple cues, strategies may remain constant, yet the relative importance of the cues may change. Moreover, in some cases, environmental improvement can, paradoxically, lead to population extinction, if the population sex ratio becomes extremely biased. More generally, plastic strategies have evolved to be adaptive within the environmental range they have been exposed to and are therefore not always adaptive in new environments outside this range, which, in extreme cases, can lead to population extinction.