Natalie Pilakouta, Seonaidh Jamieson, Jacob A. Moorad, and Per T. Smiseth

Significance

When relatives mate, their inbred offspring often suffer a reduction in fitness-related traits known as “inbreeding depression.” Environmental stresses such as starvation and competition can exacerbate these fitness costs of inbreeding. However, caring parents could mitigate the fitness costs of inbreeding by neutralizing the effects of these environmental stresses. We tested the hypothesis that maternal care can buffer against inbreeding depression in the offspring in burying beetles. Indeed, the female's presence led to a higher increase in larval survival in inbred than in outbred broods, and it increased the lifespan of inbred but not outbred adults. Our findings suggest that parental care can moderate the severity of inbreeding depression, possibly affecting how parental care strategies and inbreeding avoidance mechanisms evolve.

Abstract

When relatives mate, their inbred offspring often suffer a reduction in fitness-related traits known as “inbreeding depression.” There is mounting evidence that inbreeding depression can be exacerbated by environmental stresses such as starvation, predation, parasitism, and competition. Parental care may play an important role as a buffer against inbreeding depression in the offspring by alleviating these environmental stresses. Here, we examine the effect of parental care on the fitness costs of inbreeding in the burying beetle Nicrophorus vespilloides, an insect with facultative parental care. We used a 2 × 2 factorial design with the following factors: (i) the presence or absence of a caring female parent during larval development and (ii) inbred or outbred offspring. We examined the joint influence of maternal care and inbreeding status on fitness-related offspring traits to test the hypothesis that maternal care improves the performance of inbred offspring more than that of outbred offspring. Indeed, the female's presence led to a higher increase in larval survival in inbred than in outbred broods. Receiving care at the larval stage also increased the lifespan of inbred but not outbred adults, suggesting that the beneficial buffering effects of maternal care can persist long after the offspring have become independent. Our results show that parental care has the potential to moderate the severity of inbreeding depression, which in turn may favor inbreeding tolerance and influence the evolution of mating systems and other inbreeding-avoidance mechanisms.

See: http://www.pnas.org/content/112/26/8031.abstract.html?etoc

PNAS June 30, 2015 vol. 112 no. 26 8031-8035

Fig. 1.

Inbreeding depression (δ) in offspring when the female parent was present (black bars) or absent (gray bars) during the larval stage. Three of these fitness traits (time to dispersal, survival to dispersal, and mass at dispersal) were measured before independence; the other two traits (survival from dispersal to eclosion and posteclosion lifespan) were measured after offspring became independent. Inbreeding depression was calculated as a proportional change in mean fitness of outbred (w_o) and inbred (w_i) offspring, using the equation δ = (w_o − w_i)/w_o.