Helper Response to Experimentally Manipulated Predation Risk in the Cooperatively Breeding Cichlid Neolamprologus pulcher

Abstract

BackgroundWe manipulated predation risk in a field experiment with the cooperatively breeding cichlid Neolamprologus pulcher by releasing no predator, a medium- or a large-sized fish predator inside underwater cages enclosing two to three natural groups. We assessed whether helpers changed their helping behaviour, and whether within-group conflict changed, depending on these treatments, testing three hypotheses: ‘pay-to-stay’ PS, ‘risk avoidance’ RA, or (future) reproductive benefits RB. We also assessed whether helper food intake was reduced under risk, because this might reduce investments in other behaviours to save energy.Methodology/Principal FindingsMedium and large helpers fed less under predation risk. Despite this effect helpers invested more in territory defence, but not territory maintenance, under the risk of predation (supporting PS). Experimentally covering only the breeding shelter with sand induced more helper digging under predation risk compared to the control treatment (supporting PS). Aggression towards the introduced predator did not differ between the two predator treatments and increased with group member size and group size (supporting PS and RA). Large helpers increased their help ratio (helping effort/breeder aggression received, ‘punishment’ by the dominant pair in the group) in the predation treatments compared to the control treatment, suggesting they were more willing to PS. Medium helpers did not show such effects. Large helpers also showed a higher submission ratio (submission/ breeder aggression received) in all treatments, compared to the medium helpers (supporting PS).Conclusions/SignificanceWe conclude that predation risk reduces helper food intake, but despite this effect, helpers were more willing to support the breeders, supporting PS. Effects of breeder punishment suggests that PS might be more important for large compared to the medium helpers. Evidence for RA was also detected. Finally, the results were inconsistent with RB.

Group-size-dependent punishment of idle subordinates in a cooperative breeder where helpers pay to stay

“…With the notable exception of N. pulcher [15,[17][18][19]21,[23][24][25], among cooperative breeders there seems to be little conclusive evidence showing that dominants use aggression to elevate the work rates of helpers [70]. This raises the question of how social and ecological conditions in N. pulcher differ from other known cooperative systems and which ecological factors enable dominant breeders to enforce help from subordinates.…”

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

“…Large helpers reduced cooperative territory maintenance (digging) in their home territories when experimentally provided with alternative breeding options elsewhere 46 . When the risk was experimentally increased by exposing natural groups to a piscivore predator, all helpers increased cooperative territory defence and maintenance, and large helpers in particular increased their defence effort per aggression received from dominants 38 . Finally, subordinates increased defence when experimentally exposed to egg predators that do not pose a physical threat to the helpers themselves 47 .…”

“…Other helping behaviours such as predator defence and territory maintenance might also serve immediate direct fitness benefits to subordinates (that is, being 'selfish' 38,39 ), which is not the case with alloparental care. Alternatively or in addition to the operation of a pay-to-stay mechanism, alloparental care could yield direct fitness benefits to helpers by group augmentation.…”

First- and second-order sociality determine survival and reproduction in cooperative cichlids

“…Group sizes were determined by including all N. pulcher tolerated in the respective territory. As juvenile fish below 1.5 cm standard length (SL) [39] typically do not participate in territory defence or maintenance [40], we calculated group size as the number of all fish larger than 1.5 cm (i.e. both dominant breeders and all subordinates above 1.5 cm SL).…”