Effects of season length and uniparental care efficiency on the evolution of parental care

Parental care patterns differ enormously among and even within species. In Chinese penduline tits (Remiz pendulinus), for example, biparental care, female-only care, male-only care, and biparental desertion all occur in the same population; moreover, the distribution of care patterns differs systematically between populations. By means of an individual-based model, we show that such diversity can readily evolve. We report five main findings. First, under a broad range of parameters, different care patterns (e.g. male care and biparental care) coexist at equilibrium. Second, for many parameters, alternative evolutionary outcomes are possible; this can explain differences in care patterns across populations. Third, rapid evolutionary transitions can occur between alternative equilibria; this can explain the often-reported evolutionary lability of parental care patterns. Fourth, season length has a strong but non-monotonic effect on the evolved care patterns. Fifth, when uniparental care efficiency is low, biparental care tends to evolve; however, in many scenarios uniparental care is still common at equilibrium. Our study sheds new light on Triver's hypothesis that the sex with the highest pre-zygotic investment is predestined to invest a lot post-zygotically as well. We also discuss the implications of climate change, which simultaneously affects season length and efficiency of parental care.