Asynchronous hatching provides females with a means for increasing male care but incurs a cost by reducing offspring fitness

Abstract

In species with biparental care, sexual conflict occurs because the benefit of care depends on the total amount of care provided by the two parents while the cost of care depends on each parent's own contribution. Asynchronous hatching may play a role in mediating the resolution of this conflict over parental care. The sexual conflict hypothesis for the evolution of asynchronous hatching suggests that females adjust hatching patterns in order to increase male parental effort relative to female effort. We tested this hypothesis in the burying beetle Nicrophorus vespilloides by setting up experimental broods with three different hatching patterns: synchronous, asynchronous and highly asynchronous broods. As predicted, we found that males provided care for longer in asynchronous broods whereas the opposite was true of females. However, we did not find any benefit to females of reducing their duration of care in terms of increased lifespan or reduced mass loss during breeding. We found substantial negative effects of hatching asynchrony on offspring fitness as larval mass was lower and fewer larvae survived to dispersal in highly asynchronous broods compared to synchronous or asynchronous broods. Our results suggest that, even though females can increase male parental effort by hatching their broods more asynchronously, females pay a substantial cost from doing so in terms of reducing offspring growth and survival. Thus, females should be under selection to produce a hatching pattern that provides the best possible trade-off between the benefits of increased male parental effort and the costs due to reduced offspring fitness.

Asynchronous hatching in a nonavian species: a test of the hurry-up hypothesis

“…We supplied each pair with a previously frozen mouse carcass (supplied from Livefoods Direct Ltd, Sheffield, UK). Eggs are visible at the bottom of the breeding box8 and can be seen on images obtained by placing the boxes on flat-bed scanners (Canon Canoscan 9000F Mark II, Canon Inc., Tokyo, Japan) (Ford and Smiseth, 2016).…”

“…These hypotheses do not apply to N. vespilloides because it does 455 not incubate its eggs. Previous work on N. vespilloides has found no evidence for the peak load reduction (Smiseth and Morgan 2009) and sexual conflict hypotheses (Ford and Smiseth 2016). Thus, the only remaining hypotheses are the brood reduction (Lack 1947;1954) and insurance hypotheses (Stinson 1979).…”

“…In the models for the time until dispersal, we included laying spread because larvae in synchronous broods disperse sooner after arriving at the carcass than those in asynchronous broods (Ford and Smiseth 2016), and clutch size because larger clutches may use up the resource more quickly and therefore disperse sooner. The 235 models for the absolute number of larvae dispersing and the proportion of eggs producing larvae that survived to dispersal included laying spread and the delay until the first egg was laid to test for a cost of asynchronous laying or starting to lay sooner after encountering the carcass.…”

“…If this is the case, starting to lay soon after encountering the carcass may be associated with a greater laying spread and a greater level of hatching asynchrony if there is a trade-off between accelerating the maturation of some oocytes and maturing all oocytes synchronously. This may be undesirable due to increased mortality of the last hatched offspring in asynchronous broods 95 Takata et al 2014;Ford and Smiseth 2016).…”

“…We found some evidence of a cost of asynchronous laying in that fewer offspring survived from the egg stage until dispersal 405 in more asynchronous broods in the carcass decomposition experiment. Previous work suggests that larvae hatching from the last-laid eggs in asynchronous clutches suffer increased mortality Takata et al 2014;Ford and Smiseth 2016).…”