Sex ratio in the mother's environment affects offspring population dynamics: maternal effects on population regulation.

Classic population regulation theories usually concern the influence of immediate factors on current populations, but studies investigating the effect of parental environment factors on their offspring populations are scarce. The maternal environments can affect offspring life-history traits across generations, which may affect population dynamics and be a mechanism of population regulation. In cyclical parthenogens, sexual reproduction is typically linked with dormancy, thereby providing a negative feedback to population growth. In this study, we manipulated population sex ratios in the mother's environment to investigate whether this factor affected future population dynamics by regulating offspring sexual reproduction in the rotifer Brachionus calyciflorus. Compared with females in male-biased environments, those in female-biased environments produced fewer mictic (sexual) offspring, and their amictic (asexual) offspring also produced a lower proportion of mictic females at a gradient of population densities. Moreover, populations that were manipulated under male-biased conditions showed significantly smaller population sizes than those under female-biased conditions. Our results indicated that in cyclical parthenogens, mothers could adjust the sexual reproduction of their offspring in response to the current population sex ratio, thus providing fine-scale regulation of population dynamics in addition to population density.