When it is costly to have a caring mother: food limitation erases the benefits of parental care in earwigs

Abstract

The aggregation of parents with offspring is generally associated with different forms of care that improve offspring survival at potential costs to parents. Under poor environments, the limited amount of resources available can increase the level of competition among family members and consequently lead to adaptive changes in parental investment. However, it remains unclear as to what extent such changes modify offspring fitness, particularly when offspring can survive without parents such as in the European earwig, Forficula auricularia. Here, we show that under food restriction, earwig maternal presence decreased offspring survival until adulthood by 43 per cent. This effect was independent of sibling competition and was expressed after separation from the female, indicating lasting detrimental effects. The reduced benefits of maternal presence on offspring survival were not associated with higher investment in future reproduction, suggesting a condition-dependent effect of food restriction on mothers and local mother -offspring competition for food. Overall, these findings demonstrate for the first time a long-term negative effect of maternal presence on offspring survival in a species with maternal care, and highlight the importance of food availability in the early evolution of family life.

Short-term benefits, but transgenerational costs of maternal loss in an insect with facultative maternal care

“…[4,28]). Previous studies already revealed that the maternal presence reduces nymph survival when families had restricted food access [21], but increased nymph survival when families had access to low quality food [15]. Here, the effects of maternal presence under ad libitum, high quality food could reveal an increased expression of sibling rivalry when juveniles have access to maternal resources, as proposed in a recent model [29].…”

“…Under our experimental conditions, these effects did not translate into the production of high quality nymphs by maternally-deprived females, as we found no parent-of-origin effect of maternal loss on the mean weight and survival rate of these nymphs. However, the accelerated developmental time of the offspring of maternally-deprived females could be indicative of parent-of-origin effects that increase the level of sibling rivalry among these offspring [15,21]. On a proximate level, the transgenerational effects of maternal loss on nymph defence could be mediated by a parent-of-origin effect on the offspring's chemical signatures.…”

“…Note that two families did not produce enough adults and could thus not be used in experiment 2. Mating pairs were maintained under standard laboratory conditions for two months, after which females were isolated to allow egg laying [21]. The resulting eggs were cross-fostered on average 5.7 + 0.7 (+s.e.)…”

“…Although the early foraging capability of nymphs allows them to survive in the absence of a tending mother, maternal loss has been shown to entail short-term costs under suboptimal food quality, as it reduces the survival rate of nymphs until their fourth and last developmental instar [15]. Conversely, a second study showed that maternal loss enhances nymph survival rate when food quantity is limited, a result possibly due to a mother-offspring conflict over restricted food access [21].…”

“…To this end, we reared nymphs with or without their mother under ad libitum food conditions and then monitored their development and survival rates until adulthood, as well as measured body size and forceps length in adults (two known fitness-related traits [22,23]). If maternal care was a key component of offspring development and survival, we would expect that maternally-deprived adults emerge earlier due to developmental stress [21], survive less well and exhibit smaller body and forceps sizes compared with maternally-tended adults. In our second experiment, we used the adults produced in the first experiment to determine whether maternal loss had long-term and transgenerational effects on the expression of maternal care.…”