Reproductive competition and the evolution of extreme birth synchrony in a cooperative mammal
Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK.Biology letters (Impact Factor: 3.25). 02/2011; 7(1):54-6. DOI: 10.1098/rsbl.2010.0555
Reproductive events in animal societies often show a high degree of temporal clustering, but the evolutionary causes of this synchronization are poorly understood. Here, we suggest that selection to avoid the negative effects of competition with other females has given rise to a remarkable degree of birth synchrony in the communal-breeding banded mongoose (Mungos mungo). Within banded mongoose groups, births are highly synchronous, with 64 per cent of females giving birth on exactly the same night. Our results indicate that this extreme synchrony arises because offspring suffer an increased risk of infanticide if their mother gives birth before other females, but suffer in competition with older littermates if their mother gives birth after them. These findings highlight the important influence that reproductive competition can have for the evolution of reproductive synchrony.
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- "Firstly, if all females within a social group or within an area of habitat come into oestrus at around the same time, they may be able to attract more males, thereby gaining better choice of potential mates. Secondly, there may be benefits of birth synchrony to offspring care and survival, as females within a group giving birth at same time may allow opportunities for allomothering (Schulte, 2000), and reduce individual risk of infanticide (Hodge et al., 2011;Poikonen et al., 2008) or predation (Gregg et al., 2001;Sinclair et al., 2000). This phenomenon of oestrous synchrony has long been suspected in elephants (Bechert et al., 1999;Dublin, 1983;Poole, 1989;Rasmussen and Schulte, 1998;Slade et al., 2003), and has recently been demonstrated in captive African elephants (Weissenböck et al., 2009). "
ABSTRACT: Routine faecal steroid monitoring has been used to aid the management of five captive Asian elephant (Elephas maximus) females at Chester Zoo, UK, since 2007. Progestagen analysis initially revealed synchronized oestrous cycles among all females. However, a 14- to 20-week period of temporary acyclicity subsequently occurred in three females, following several management changes (increased training, foot-care and intermittent matriarch removal for health reasons) and the initiation of pregnancy in another female. The aim of this study was to retrospectively investigate whether these management changes were related to increased adrenal activity and disruption of ovarian activity, or whether social factors may have been involved in the temporary cessation of cyclicity. Faecal samples collected every other day were analysed to investigate whether glucocorticoid metabolites were related to reproductive status (pregnant, cycling, acyclic) or management (training, foot-care, matriarch presence). Routine training and foot-care were not associated with adrenal activity; however, intensive foot-care to treat an abscess in one female was associated with increased glucocorticoid concentration. Matriarch presence influenced adrenal activity in three females, being lower when the matriarch was separated from the group at night compared to being always present. However, in the females that exhibited temporary acyclicity, there was no consistent relationship between glucocorticoids and cyclicity state. Although the results of this study do not fully explain this occurrence, the highly synchronized nature of oestrous cycles within this group, and the concurrent acyclicity in three females, raises the question of whether social factors could have been involved in the temporary disruption of ovarian activity.
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- "Male mate choice is also predicted to occur where there is variation in female quality and where receptive females are encountered simultaneously (Edward & Chapman 2011). Indeed, high levels of promiscuity within banded mongoose societies mean that males have access to females which vary in genetic compatibility, and the high degree of female reproductive synchrony seen within banded mongoose groups (Hodge et al. 2011) means that males do encounter receptive females simultaneously. The extent to which females synchronize breeding within groups could in fact promote male choice even in the absence of high male reproductive investment as male mating opportunities are limited by the fact that they can only guard one female at a time. "
ABSTRACT: Inbreeding and inbreeding avoidance are key factors in the evolution of animal societies, influencing dispersal and reproductive strategies which can affect relatedness structure and helping behaviours. In cooperative breeding systems, individuals typically avoid inbreeding through reproductive restraint and/or dispersing to breed outside their natal group. However, where groups contain multiple potential mates of varying relatedness, strategies of kin recognition and mate choice may be favoured. Here, we investigate male mate choice and female control of paternity in the banded mongoose (Mungos mungo), a cooperatively breeding mammal where both sexes are often philopatric and mating between relatives is known to occur. We find evidence suggestive of inbreeding depression in banded mongooses, indicating a benefit to avoiding breeding with relatives. Successfully breeding pairs were less related than expected under random mating, which appeared to be driven by both male choice and female control of paternity. Male banded mongooses actively guard females to gain access to mating opportunities, and this guarding behaviour is preferentially directed towards less closely related females. Guard-female relatedness did not affect the guard's probability of gaining reproductive success. However, where mate-guards are unsuccessful, they lose paternity to males that are less related to the females than themselves. Together, our results suggest that both sexes of banded mongoose use kin discrimination to avoid inbreeding. Although this strategy appears to be rare among cooperative breeders, it may be more prominent in species where relatedness to potential mates is variable, and/or where opportunities for dispersal and mating outside of the group are limited. © 2015 John Wiley & Sons Ltd.
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- "In many species where socially subordinate individuals attempt to gain some parentage, they reproduce just after dominant individuals to avoid detection (and subsequent punishment) or infanticide (e.g. Poikonen et al., 2008; Hodge et al., 2011). Indeed, a study in captive N. pulcher social groups showed that when subordinate females reproduce, they also do so shortly after the dominant female in their group has laid (Heg et al., 2009). "
ABSTRACT: While a large number of studies have described animal social networks, we have a poor understanding of how these networks vary with ecological and social conditions. For example, reproductive periods are an important life-history stage that may involve changes in dominance relationships among individuals, yet no study to date has compared social networks of dominance interactions (i.e. dominance networks) across reproductive contexts. We first analyzed a long-term dataset on captive social groups of the cooperatively breeding cichlid Neolamprologus pulcher, and found that eviction events were significantly more common around reproduction than expected by chance. Next, we compared the structure of dominance networks during early parental care and non-reproductive periods, using one of the first applications of exponential random graph models in behavioral biology. Contrary to our predictions, we found that dominance networks showed few changes between early parental care and non-reproductive periods. We found no evidence that dominance interactions became more skewed towards larger individuals, became more frequent between similar-sized individuals, or became more biased towards a particular sex during parental care. However, we did find that there were relatively more dominance interactions between opposite-sex dyads in the early parental care period, which may be a by-product of increased sexual interactions during this time. This is the first study in behavioral ecology to compare social networks using exponential random graph modeling, and demonstrates a powerful analytical framework for future studies in the field