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Constraints and flexibility in mammalian social behaviour: introduction and synthesis
No full textThis paper introduces a Theme Issue presenting the latest developments in research on the interplay between flexibility and constraint in social behaviour, using comparative datasets, long-term field studies and experimental data from both field and laboratory studies of mammals. We first explain our focus on mammals and outline the main components of their social systems, focusing on variation within- and among-species in numerous aspects of social organization, mating system and social structure. We then review the current state of primarily ultimate explanations of this diversity in social behaviour. We approach the question of how and why the balance between behavioural flexibility and continuity is achieved by discussing the genetic, developmental, ecological and social constraints on hypothetically unlimited behavioural flexibility. We introduce the other contributions to this Theme Issue against this background and conclude that constraints are often crucial to the evolution and expression of behavioural flexibility. In exploring these issues, the enduring relevance of Tinbergen's seminal paper ‘On aims and methods in ethology’, with its advocacy of an integrative, four-pronged approach to studying behaviour becomes apparent: an exceptionally fitting tribute on the 50th anniversary of its publication
The influence of stress hormones and aggression on cooperative behaviour in subordinate meerkats
Full text linkIn cooperative breeders, aggression from dominant breeders directed at subordinates may raise subordinate stress hormone (glucocorticoid) concentrations. This may benefit dominants by suppressing subordinate reproduction but it is uncertain whether aggression from dominants can elevate subordinate cooperative behaviour, or how resulting changes in subordinate glucocorticoid concentrations affect their cooperative behaviour. We show here that the effects of manipulating glucocorticoid concentrations in wild meerkats (Suricata suricatta) varied between cooperative activities as well as between the sexes. Subordinates of both sexes that were treated with a glucocorticoid receptor antagonist (mifepristone) exhibited significantly more pup protection behaviour (‘babysitting’) compared to those treated with glucocorticoids (cortisol) or controls. Females treated with mifepristone had a higher probability of exhibiting pup food provisioning (‘pupfeeding’) compared to those treated with cortisol. In males, there were no treatment effects on the probability of pupfeeding, but those treated with cortisol fed a higher proportion of the food they found to pups than those treated with mifepristone. We also used 19 years of behavioural data to show that dominant females did not increase the frequency with which they directed aggression at subordinates at times when their need for assistance was highest. Our results suggest that it is unlikely that dominant females manipulate the cooperative behavior of subordinates through the effects of aggression on their glucocorticoid levels and that the function of aggression directed at subordinates is probably to reduce the probability they will breed
Data from: The development of individual differences in cooperative behaviour: maternal glucocorticoid hormones alter helping behaviour of offspring in wild meerkats
Full text linkThe phenotype of parents can have long-lasting effects on the development of offspring as well as on their behaviour, physiology and morphology as adults. In some cases, these changes may increase offspring fitness but, in others, they can elevate parental fitness at a cost to the fitness of their offspring. We show that in Kalahari meerkats (Suricata suricatta), the circulating glucocorticoid (GC) hormones of pregnant females affect the growth and cooperative behaviour of their offspring. We performed a 3-year experiment in wild meerkats to test the hypothesis that GC-mediated maternal effects reduce the potential for offspring to reproduce directly and therefore cause them to exhibit more cooperative behaviour. Daughters (but not sons) born to mothers treated with cortisol during pregnancy grew more slowly early in life and exhibited significantly more of two types of cooperative behaviour (pup rearing and feeding) once they were adults compared to offspring from control mothers. They also had lower measures of GCs as they aged, which could explain the observed increases in cooperative behaviour. Because early life growth is a crucial determinant of fitness in female meerkats, our results indicate that GC-mediated maternal effects may reduce the fitness of offspring, but may elevate parental fitness as a consequence of increasing the cooperative behaviour of their daughters
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Male immigration triggers increased growth in subordinate female meerkats.
Full text linkThere is increasing evidence that some vertebrates can adjust their growth rate in relation to changes in the social context that affect their probability of breeding. Here, we show that, in meerkats (Suricata suricatta), which are singular cooperative breeders, subordinate females increase in body mass after their father is replaced as the dominant male in their natal group by an immigrant male, giving them regular access to an unfamiliar and unrelated mating partner, while their brothers showed no similar increase nor did subordinate females living in other stable groups (where male immigration did not occur did) in this time period. Moreover, subordinate females showed a greater increase in growth rate when their father was succeeded by an unfamiliar immigrant male than when he was replaced by a familiar male who was already resident. These results suggest that female meerkats can adjust their rate of growth to changes in the kinship composition of their groups that provide them with increased access to unrelated breeding partners, which may occur in other mammals as well when breeding opportunities change
Increased food availability raises eviction rate in a cooperative breeding mammal
Full text linkIn group-living mammals, the eviction of subordinate females from breeding
groups by dominants may serve to reduce feeding competition or to reduce
breeding competition. Here, we combined both correlational and experimental
approaches to investigate whether increases in food intake by dominant
females reduces their tendency to evict subordinate females in wild meerkats
(Suricata suricatta). We used 20 years of long-term data to examine the association
between foraging success and eviction rate, and provisioned dominant
females during the second half of their pregnancy, when they most commonly
evict subordinates. We show that rather than reducing the tendency for dominants
to evict subordinates, foraging success of dominant females is positively
associated with the probability that pregnant dominant females will evict subordinate
females and that experimental feeding increased their rates of
eviction. Our results suggest that it is unlikely that the eviction of subordinate
females serves to reduce feeding competition and that its principal function
may be to reduce reproductive competition. The increase in eviction rates following
experimental feeding also suggests that rather than feeding
competition, energetic constraints may normally constrain eviction rates.The KMP is supported by the Universities of Cambridge,
Zurich and Pretoria. Components of this research were supported
by the Natural Environment Research Council (grant no. NE/
G006822/1) and the European Research Council (grant no. 294494).http://rsbl.royalsocietypublishingam2017Mammal Research InstituteZoology and Entomolog
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