Maternal, social and abiotic environmental effects on growth vary across life stages in a cooperative mammal

Abstract

Resource availability plays a key role in driving variation in somatic growth and body condition, and the factors determining access to resources vary considerably across life stages. Parents and carers may exert important influences in early life, when individuals are nutritionally dependent, with abiotic environmental effects having stronger influences later in development as individuals forage independently.Most studies have measured specific factors influencing growth across development or have compared relative influences of different factors within specific life stages. Such studies may not capture whether early-life factors continue to have delayed effects at later stages, or whether social factors change when individuals become nutritionally independent and adults become competitors for, rather than providers of, food.Here, we examined variation in the influence of the abiotic, social and maternal environment on growth across life stages in a wild population of cooperatively breeding meerkats. Cooperatively breeding vertebrates are ideal for investigating environmental influences on growth. In addition to experiencing highly variable abiotic conditions, cooperative breeders are typified by heterogeneity both among breeders, with mothers varying in age and social status, and in the number of carers present.Recent rainfall had a consistently marked effect on growth across life stages, yet other seasonal terms only influenced growth during stages when individuals were growing fastest. Group size and maternal dominance status had positive effects on growth during the period of nutritional dependence on carers, but did not influence mass at emergence (at 1 month) or growth at independent stages (>4 months). Pups born to older mothers were lighter at 1 month of age and subsequently grew faster as subadults. Males grew faster than females during the juvenile and subadult stage only.Our findings demonstrate the complex ways in which the external environment influences development in a cooperative mammal. Individuals are most sensitive to social and maternal factors during the period of nutritional dependence on carers, whereas direct environmental effects are relatively more important later in development. Understanding the way in which environmental sensitivity varies across life stages is likely to be an important consideration in predicting trait responses to environmental change.

Variation in growth of Damaraland mole-rats is explained by competition rather than by functional specialization for different tasks

“…This suggests that competition among subordinates in large groups may be the major social factor reducing growth, while direct resource availability (our study population receives ad libitum food) and interactions with the dominant breeders are unlikely to generate the observed growth patterns. This contrasts with the situation in some cooperative vertebrates where interactions with breeders or more dominant individuals inhibit growth [20] and group size positively influences growth rates [2]. Like the males of many other polygynous and polygynandrous mammals, male Damaraland mole-rats grew faster, achieved higher maximum body masses and needed more time to reach maximum body mass than females.…”

The influence of stress hormones and aggression on cooperative behaviour in subordinate meerkats

“…Meerkats were weighed (to the nearest gram) in the morning immediately after emergence from their sleeping burrow, but before foraging had commenced, after 1-4 hours of foraging, and again in the evening after foraging was completed but before they entered their sleeping burrow (45,46). Birth dates of meerkats were known so we calculated age-corrected body mass as a measure of body condition.…”

A call for full annual cycle research in animal ecology

“…Collectively, several studies illustrate how full annual cycle research is necessary to understand fundamental biology across multiple species groups (e.g. amphibians [8], reptiles [9], birds [10], mammals [11]). …”