Department of Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Hinterkappelen, Switzerland.
PLoS One. 2010 May 26;5(5):e10784. doi: 10.1371/journal.pone.0010784.
We 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 FINDINGS: Medium 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/SIGNIFICANCE: We 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.
我们通过在野外实验中操纵合作繁殖的慈鲷 Neolamprologus pulcher 的捕食风险，在水下笼子里释放无捕食者、中等或大型鱼类捕食者，来包围两到三个自然群体。我们评估了助手是否会根据这些处理方式改变他们的帮助行为，以及群体内部冲突是否会改变，测试了三个假设：“支付以停留”（PS）、“风险回避”（RA）或（未来）生殖利益（RB）。我们还评估了助手在有风险的情况下是否减少了食物摄入，因为这可能会减少其他行为的投资以节省能量。
方法/主要发现：中等和大型助手在捕食风险下的进食量减少。尽管如此，在捕食风险下，助手们在领地防御方面投入更多，但在领地维护方面投入较少（支持 PS）。与对照处理相比，在实验中仅用沙子覆盖繁殖庇护所会导致更多的助手在捕食风险下挖掘（支持 PS）。引入的捕食者对两种捕食者处理方式的攻击没有差异，并且随着群体成员大小和群体大小的增加而增加（支持 PS 和 RA）。与对照处理相比，大型助手在捕食处理中增加了其帮助比率（帮助努力/受到的繁殖者攻击，群体中占主导地位的一对的“惩罚”），这表明它们更愿意 PS。中型助手没有表现出这种效应。与中型助手相比，大型助手在所有处理中也表现出更高的屈服比率（屈服/受到的繁殖者攻击），支持 PS。
结论/意义：我们得出的结论是，捕食风险会降低助手的食物摄入量，但尽管如此，助手们还是更愿意支持繁殖者，支持 PS。繁殖者惩罚的影响表明，PS 可能对大型助手比中型助手更重要。还检测到了 RA 的证据。最后，结果与 RB 不一致。
