Senescence and costs of reproduction in the life history of a small precocial species

Abstract

Species following a fast life history are expected to express fitness costs mainly as increased mortality, while slow‐lived species should suffer fertility costs. Because observational studies have limited power to disentangle intrinsic and extrinsic factors influencing senescence, we manipulated reproductive effort experimentally in the cavy (Cavia aperea) which produces extremely precocial young. We created two experimental groups: One was allowed continuous reproduction (CR) and the other intermittent reproduction (IR) by removing males at regular intervals. We predicted that the CR females should senesce (and die) earlier and produce either fewer and/or smaller, slower growing offspring per litter than those of the IR group. CR females had 16% more litters during three years than IR females. CR females increased mass and body condition more steeply and both remained higher until the experiment ended. Female survival showed no group difference. Reproductive senescence in litter size, litter mass, and reproductive effort (litter mass/maternal mass) began after about 600 days and was slightly stronger in CR than IR females. Litter size, litter mass, and offspring survival declined with maternal age and were influenced by seasonality. IR females decreased reproductive effort less during cold seasons and only at higher age than CR females. Nevertheless, offspring winter mortality was higher in IR females. Our results show small costs of reproduction despite high reproductive effort, suggesting that under ad libitum food conditions costs depend largely on internal regulation of allocation decisions.

Photoperiod influences the development and the expression of personality traits and social behaviour in wild cavies (Cavia aperea)

“…Litter size, litter mass and pup birth mass as well as maternal mass vary seasonally with the lowest values in winter (Rübensam et al, 2015;Trillmich et al, 2019). Similar effects were found under field conditions (Rood & Weir, 1970) and also for the closely related dark-backed cavy (Cavia magna; Kraus et al, 2005).…”

“…All of these experiments were run using the same manipulation of photoperiod under the same feeding conditions as used in our present experiment. This suggests that growth rate of pups until weaning is a variable trait that depends substantially on factors other than photoperiod, like maternal size and condition (Kasparian et al, 2005; Trillmich et al, 2019).…”

“…Our observations may indicate the adult's tendency to get herself into optimal condition for the winter leading to a slightly lower motivation of mothers to care for autumn offspring. It may also relate to the finding that in outdoor conditions litters of autumn pups tend to be smaller but individual pups heavier than those born in spring (Rübensam et al, 2015; Trillmich et al, 2019). We found a similar pattern here, even though in our sample it was not statistically significant.…”

“…From laboratory experiments, we know that exposing pregnant females to increasing photoperiods indicating spring accelerates maturation of males and females while a deceasing photoperiod indicating autumn leads to slower growth and delayed maturation (Guenther, Palme, et al, 2014; Trillmich et al, 2009). Litter size, litter mass and pup birth mass as well as maternal mass vary seasonally with the lowest values in winter (Rübensam et al, 2015; Trillmich et al, 2019). Similar effects were found under field conditions (Rood & Weir, 1970) and also for the closely related dark‐backed cavy ( Cavia magna ; Kraus et al, 2005).…”

Reproduction affects immune defenses in the guinea pig even under ad libitum food

“…These observations suggest that the allocation of resources to the immune response during pregnancy as well as during lactation led to reduced allocation to offspring even under ad libitum food conditions. In other words, the adaptive immune response induces a trade-off between maintenance of maternal condition at the expense of offspring development as similarly observed in ageing female wild cavies (Cavia aperea) [63] and other animals [64,65].…”