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

Shifts in energy allocation and reproduction in response to temperature in a small precocial mammal

BACKGROUND

Species adjust to changes in temperature and the accompanying reduction in resource availability during the annual cycle by shifts in energy allocation. As it gets colder, the priority of energy allocation to maintenance increases and reproduction is reduced or abandoned.

RESULTS

We studied whether and how young female guinea pigs (Cavia porcellus) adjust even under ad libitum food conditions growth, storage of fat reserves and reproduction when kept at 5 °C versus 15 °C, and how offspring born into these conditions compensate during development to independence. Reproducing females grew less in the cold. Their lower weight resulted largely from less fat storage whereas growth in fat free mass was about the same for both groups. The increased need for thermoregulation diminished fat storage most likely due to the development of more brown fat tissue. Reproductive activity did not differ between groups in terms of litter frequency, mass and size. However, females in 5 °C weaned pups later (around day 25) than females in 15 °C (around day 21). Later weaning did not make up for the higher energy expenditure of pups in cold conditions leading to slower growth and less fat storage. Female pups born into the cold matured later than those born in 15 °C. Investment in reproduction continued but allocation to individual pups declined.

CONCLUSIONS

In more thermally demanding conditions female guinea pigs - even under ad libitum food abundance - transfer the higher costs of maintenance and reproduction largely to offspring.

Fitness consequences of seasonally different life histories? A match–mismatch experiment

To survive and reproduce successfully, animals have to find the optimal time of breeding. Species living in nontropical environments often adjust their reproduction plastically according to seasonal changes of the environment. Information about the prevailing season can be transmitted in utero, leading to the adaptation of the offspring to the prevailing season. After birth, animals acquire additional personal information about the environment, which allows them to adjust their reproductive investment. Here, we tested in a full-factorial match–mismatch experiment the influence of reproductive adjustments according to maternal and personal information. We bred wild cavies (Cavia aperea), a precocial rodent, either into increasing (spring) or decreasing (autumn) photoperiod and, subsequently, after weaning, transferred female offspring to the matching or mismatching season. We measured growth, specific metabolic rate (sRMR) and reproductive events across six months. Although sRMR was elevated for females primed for good (spring) conditions when transferred to the mismatching autumn condition, we found no maternal effects on reproduction. Females adjusted their reproductive decisions according to the season they personally experienced, thereby implying a potentially high level of plasticity. Females reproducing in spring started reproduction earlier with a lower reproductive effort than females reproducing in autumn but, ultimately, the two groups did not differ in survival, growth, or reproduction. These data suggest important developmental plasticity, highlight the use of personal information acquired after weaning over early information provided until weaning, and point out the potential value of multiple cues, such as food abundance and quality and temperature besides photoperiod.

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

Reproduction is one of the costliest processes in the life of an animal. Life history theory assumes that when resources are limiting allocation to reproduction will reduce allocation to other essential processes thereby inducing costs of reproduction. The immune system is vital for survival. If reproduction reduces investment in immune function, this could increase the risk of disease, morbidity and mortality. We here test in the guinea pig, if even under ad libitum food conditions, pregnancy and lactation reduce the activity of the adaptive and innate immune system compared to the reaction of non-reproducing animals. In response to a challenge with keyhole limpet haemocyanin the antibody-mediated adaptive immunity during (pregnancy and) lactation was reduced. Pregnant and lactating females showed higher levels of bacterial killing activity, an integrated measure of innate immunity, than non-reproducing females. However, two major effectors of the innate immunity, the natural antibody and the complement of pregnant and lactating females showed lower levels than in non-reproducing females. Pregnant and lactating females did not differ significantly in the expressed levels of innate immunity. Our results indicate that changes in the immune response during reproduction are physiological adjustments to predictable allocation problems, because they happen even under ad libitum food availability.