Residency Time as an Indicator of Reproductive Restraint in Male Burying Beetles

Abstract

The cost of reproduction theory posits that there are trade-offs between current and future reproduction because resources that are allocated to current offspring cannot be used for future reproductive opportunities. Two adaptive reproductive strategies have been hypothesized to offset the costs of reproduction and maximize lifetime fitness. The terminal investment hypothesis predicts that as individuals age they will allocate more resources to current reproduction as a response to decreasing residual reproductive value. The reproductive restraint hypotheses predicts that as individuals age they will allocate fewer resources to current reproduction to increase the chance of surviving for an additional reproductive opportunity. In this study, we test for adaptive responses to advancing age in male burying beetles, Nicrophorus orbicollis. Burying beetles use facultative biparental care, but the male typically abandons the brood before the female. Previous work in male burying beetles has suggested several factors to explain variation in male residency time, but no study has observed male behavior throughout their entire reproductive lifetimes to determine whether males change residency time in an adaptive way with age. We compared residency time of males that reproduced biparentally, uniparentally, and on different-sized carcasses to determine if they used an adaptive reproductive strategy. Males did not increase residency time as they aged when reproducing biparentally, but decreased residency time with age when reproducing uniparentally. A decrease in parental care with age is consistent with a reproductive restraint strategy. When female age increased over time, males did not increase their residency time to compensate for deteriorating female condition. To our knowledge, this is the first test of adaptive reproductive allocation strategies in male burying beetles.

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

“…Firstly, males may prolong their involvement in care when caring for highly asynchronous broods in response to the female deserting earlier. In support of this suggestion, we found that males remained with the brood for longer when their partner deserted earlier, and similar results showing that males adjust their contribution to the absence of the female have been found in previous studies on the amount of care (Fetherston et al ., ; Smiseth & Moore, ; Rauter & Moore, ; Smiseth et al ., ; Suzuki & Nagano, ; Smith et al ., ). We found that males responded more strongly to female desertion in highly asynchronous broods, but that the total duration of parental care was similar across all hatching patterns.…”

“…We used the amount of time that each parent spent with the brood from the arrival of the first larvae as a proxy for the amount of care they provided (Boncoraglio & Kilner, 2012;Smith et al, 2014). We checked each box twice a day (at 09:00 and 17:15 h) to determine whether the parent was present or absent from the brood chamber.…”

“…We checked each box twice a day (at 09:00 and 17:15 h) to determine whether the parent was present or absent from the brood chamber. If a parent was absent in two consecutive observations, we regarded it as having deserted the brood (Smith et al, 2014). Once the deserting parent had been removed from the box, we weighed it to record its post-breeding body mass.…”

Why does it take two to tango? Lifetime fitness consequences of parental care in a burying beetle

“…The burying beetle, Nicrophorus orbicollis , is an ideal system for studying evolution of parental care because we can directly address each of the difficulties outlined above. First, although they are typically biparental, each parent is capable of rearing offspring alone [ 5 – 8 ]. The facultative nature of biparental care in this species of burying beetle provides opportunity to experimentally assess fitness of parental care strategies within the normal range of behaviors for the species.…”

“…Typically, both parents bury and preserve the carcass and feed and protect larvae until they disperse, and both parents regulate brood size through filial cannibalism [ 9 ]. Although males generally abandon the brood before the female, they usually remain with the female and the larvae until the larvae reach the third instar stage of development [ 6 , 8 , 10 – 11 ]. Second, the costs and benefits of biparental and uniparental reproductive strategies can be quantified relative to a known resource amount.…”