Group composition affects male reproductive partitioning in a cooperatively breeding cichlid

Abstract

Individuals within groups of cooperatively breeding species may partition reproduction, with the dominant pair often taking the largest share. The dominant's ability to reproductively control subordinates may depend on differences in competitive ability, due to, e.g. body size differences, but may also depend on the number of same-sex competitors inside the group. We tested experimentally whether subordinates reproduce more when these subordinates are large or when a second subordinate of the same sex need to be controlled by the dominants, using the cooperatively breeding cichlid Neolamprologus pulcher. Dominant pairs were assisted by a large and a small unrelated subordinate; sexes of these fish were varied in a full-factorial design (giving four treatments). Dominant males lost significantly more parentage to the large subordinate male when a small subordinate male was also present, compared to when a small subordinate female was present. However, subordinate paternity was generally low and did not significantly curb total dominant male reproductive output, which was more affected by the sizes and numbers of reproductive females present inside his group. Dominant female maternity, clutch sizes and total output did not depend on the treatments. Subordinate-subordinate reproduction was virtually absent (one out of 874 offspring). Female subordinates were more likely to provide care for their own broods. In contrast, male subordinates did not adjust their level of care to their parentage. Variability in female subordinate alloparental brood care was particularly high, with females showing more care than males in general. We also detected effects of growth rate and food ration on parentage independent of the treatments, most notably: (i) a trade-off between dominant male growth rate and paternity; (ii) a decrease in dominant male paternity with increasing food ration; (iii) a positive effect of growth rate on paternity in small males. We conclude that dominant males should be sensitive to the number and sizes of subordinate males present in their group, particularly when these subordinates are not helpful or grow fast, and food is plentiful. Dominant females should be less sensitive, because female subordinates do not appear to impose reproductive costs and can be helpful through alloparental brood care.

The building-up of social relationships: behavioural types, social networks and cooperative breeding in a cichlid

“…Keeping such affiliative ties might help to counteract any negative effects of low exploration activity on finding alternative groups (e.g. Bergmü ller et al 2005;Heg et al 2008b), for example, to improve their social position ('queuing', Stiver et al 2006), because peaceful interactions with neighbouring groups might facilitate dispersal to these groups (see also Stiver et al 2004Stiver et al , 2006Stiver et al , 2007Bergmü ller et al 2005;Fitzpatrick et al 2008).…”

Reproductive sharing in relation to group and colony-level attributes in a cooperative breeding fish

“…By contrast, we predicted that extra-pair maternity (EPM) would be low regardless of territory location or density, because females in this species can recognize and destroy competitor eggs [27]. Regarding within-group characteristics, we predicted that parentage loss would increase as group size and the number of same-sex subordinates increased [4,5] and that subordinates closer in size to the dominant would be more likely to reproduce [8]. Finally, we predicted that a larger size difference between the dominant male and female would allow the dominant male to exert more control over group dynamics, facilitating subordinate or neighbouring female reproduction and suppressing subordinate or neighbouring male reproduction [9].…”

“…Individuals within a group may also come into conflict when group members mate with neighbouring individuals, as the offspring of neighbours may parasitize the resources and parental care of current group members [3]. Both within-group factors, such as group size and composition, and between-group factors, such as the density and location of neighbouring groups, influence the ability of individuals to pursue reproduction within their group [4,5] as well as pursue reproductive opportunities with neighbouring individuals [6,7]. Therefore, it is difficult to understand variation in individual behaviour or reproductive success without exploring how both within-group and between-group social structure affect the quality and quantity of reproductive opportunities.…”

Paternity of Subordinates Raises Cooperative Effort in Cichlids

“…This might make attempts to obtain direct fitness benefits via parentage more rewarding. In a few cooperatively breeding birds and mammals, subordinates participating in reproduction also increased their helping effort in the field [22], [29], [64], [65] and a laboratory study of N. pulcher revealed that female subordinates may increase alloparental care in response to their participation in reproduction [30], [38]. These data suggest that more generally, directs fitness benefits might be an important modifier of subordinate helping intensities in cooperative breeders.…”

“…By participating in reproduction, subordinates face a threat of eviction [35], which may be detrimental due to the high mortality risk outside of territories [36]. In the laboratory, male subordinates unrelated to the breeding pair were found to participate in reproduction [31], [35], [37], [38]. However, their reproductive role in nature was questioned because subordinates have smaller gonads than breeders [17].…”