Predation risk is an ecological constraint for helper dispersal in a cooperatively breeding cichlid

Abstract

Environmental conditions are thought to be responsible for the extent and benefits of cooperative breeding in many animal societies, but experimental tests are scarce. We manipulated predator pressure in the cooperatively breeding cichlid Neolamprologus pulcher in Lake Tanganyika, where predators have been suggested to influence helper and breeder survival, helper dispersal and group reproductive success. We varied the type and intensity of predation by releasing medium, large, or no predators inside large underwater cages enclosing two or three group territories. Helper and breeder survival, helper dispersal and group reproductive success decreased from the control, to the medium-and large-predator treatments. These effects were modified by helper body size and the number of adults protecting the group from predators, supporting the 'group augmentation hypothesis'. Predators forced helpers to stay closer to, and spend more time inside, protective shelters. The results demonstrate the importance of predators for group living in this species, and support the 'ecological constraints hypothesis' of cooperative breeding, in the sense that subordinates stay at home rather than leave and breed independently under the risk of predation.

Kinship reduces alloparental care in cooperative cichlids where helpers pay-to-stay

“…Our study generally confirms that kinship is an important component in cooperative systems, but remarkably relatedness may have effects contrary to predictions from conventional kin-selection theory, if coercion by dominants is involved. It is important to note here that group augmentation is likely to generate fitness benefits of helping in this species as well 24,48 , but due to our experimental design this mechanism cannot explain the differences found between the experimental treatments in this study. Rather, dominants and unrelated subordinates seem to trade different commodities reciprocally against each other, thereby generating fitness benefits to both.…”

“…Therefore, the cooperative behaviour experimentally elicited in this study is of crucial importance for a test of the pay-to-stay hypothesis, as alloparental egg-care does not provide immediate fitness benefits to unrelated helpers, whereas it involves clear costs 36,37 . As this helping effort is hence altruistic, it can be selected for only if helpers receive other fitness benefits in return, which result from the tolerance in a safe territory that provides them with access to vital resources such as shelter and protection 19,29,48 , and opportunities to share in reproduction 49,50 .…”

“…NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2344 ARTICLE dispersal 19,48 , and individuals are long-lived, reaching 3 years of age or more 34 . For a comprehensive review of cooperative breeding in N. pulcher see ref.…”

The relationship between social status, behaviour, growth and steroids in male helpers and breeders of a cooperatively breeding cichlid

“…Thus, in N. pulcher, there is a potential for conflict between helpers and breeders about the possible participation of helpers in reproduction. Breeder males threaten helpers with aggression and the risk of expulsion (Dierkes et al, 1999;Skubic et al, 2004), while helpers attempt to appease the breeders and reduce the risk of expulsion from the territory by helping and displaying submissive behaviour, depending on environmental constraints (Taborsky, 1985;Balshine-Earn et al, 1998;Heg et al, 2004a;. Buchner et al (2004) found higher cortisol (F) plasma levels in dominant individuals than in subordinates in N. pulcher, confirming a general rule found in many mammal and bird societies, where paternity is shared by dominants and subordinates and the social situation is therefore stressful for the dominants (Schoech et al, 2004).…”

Predation risk drives social complexity in cooperative breeders

“…Individual groups consist of a dominant breeding pair and up to 30 subordinates (25,26,30). Groups are frequently attacked by predatory fish (26), which significantly affects the survival probability of group members, especially small subordinates and fish devoid of protection through large conspecifics (31). Hence, membership in a group is a precondition for survival.…”