Young But Not Old Adult African Striped Mice Reduce Their Activity in the Dry Season When Food Availability is Low

Abstract

An individual′s survival and fitness depend on its ability to effectively allocate its time between competing behaviors. Sex, social tactic, season and food availability are important factors influencing activity budgets. However, few field studies have tested their influences. The African striped mouse (Rhabdomys pumilio) lives in highly seasonal habitats in southern Africa, and individuals can adopt different social tactics. We investigated seasonal changes in activity budgets of different tactics and predicted that individuals will reduce their activity in the non‐breeding season to save energy when food availability is low and that young non‐breeding adults (‘philopatrics’) invest mainly in activities related to gaining body mass to increase survival probability. We predicted old adults (‘breeders’), which bred during the previous breeding season, to invest mainly in maintenance of their social status. We conducted 90 focal observations during the non‐breeding season and 73 during the breeding season. Activity budgets of striped mice were season and tactic specific, with philopatrics, but not breeders, reducing activity when food availability was low, possibly to decrease energy expenditure. Philopatrics of both sexes foraged and basked more in the breeding season than during the non‐breeding season. Male philopatrics gained body mass and female philopatrics maintained their body mass in both seasons. Sex‐specific differences occurred during the breeding season, when female breeders foraged more than male breeders, while male breeders chased other individuals more than female breeders. These findings indicate that individuals adopting different social tactics display distinct behaviors to fulfill tactic‐specific energetic needs.

Both thyroid hormone levels and resting metabolic rate decrease in African striped mice when food availability decreases

“…Glucose is the end product of carbohydrate metabolism and is the primary energy source for the body. In concurrence, glucose levels were higher in the moist season, when food availability was high and striped mice spent large portions of the day foraging (Rimbach et al, 2016;Schradin, 2006). A similar result was reported in a long-term study on striped mice at our field site, where blood glucose levels increased with increasing food availability (Schradin et al, 2015).…”

Do alternative reproductive tactics predict problem-solving performance in African striped mice?

“…It is difficult to disentangle the influence of intrinsic variables since philopatrics are younger, smaller and less competitive than breeding males which are older, the largest and most competitive males (Schradin et al 2009a). For this reason, we expected that the different ARTs (linked to other intrinsic characteristics) in striped mice would predict problem-solving ability, related to, for example, differences in energy availability (Rimbach et al 2016). For instance, the 'Bad competitor' hypothesis suggests that juveniles/subadults should show more foraging novel problem-solving because they have higher metabolic costs (metabolic demands leading to stronger response to food deprivation) and thus need to incur extra risks in order to survive ).…”

“…Behavioural differences between ARTs (Rimbach et al 2016) can also influence problem-solving. For example, time budgets could differ between roamers and breeders, and since roamers have larger home ranges, they might be more likely to encounter novel problems to solve compared to breeders (e.g., in Cape ground squirrels, Xerus inauris, Scantlebury et al 2008).…”