A test of male infanticide as a reproductive tactic in a cichlid fish

Abstract

Infanticide and offspring cannibalism are taxonomically widespread phenomena. In some group-living species, a new dominant individual taking over a group can benefit from infanticide if doing so induces potential mates to become reproductively available sooner. Despite widespread observations of infanticide (i.e. egg cannibalism) among fishes, no study has investigated whether egg cannibalism occurs in fishes as a result of group takeovers, or how this type of cannibalism might be adaptive. Using the cooperatively breeding cichlid, Neolamprologus pulcher, we tested whether new unrelated males entering the dominant position in a social group were more likely to cannibalize eggs, and whether such cannibalism would shorten the interval until the female's next spawning. Females spawned again sooner if their broods were removed than if they were cared for. Egg cannibalism occurred frequently after a group takeover event, and was rarer if the original male remained with the group. While dominant breeder females were initially highly aggressive towards newcomer males that took over the group, the degree of resistance depended on relative body size differences between the new pair and, ultimately, female aggression did not prevent egg cannibalism. Egg cannibalism, however, did not shorten the duration until subsequent spawning, or increase fecundity during subsequent breeding in our laboratory setting. Our results show that infanticide as mediated through group takeovers is a taxonomically widespread behaviour.

Experimental evidence that chronic outgroup conflict reduces reproductive success in a cooperatively breeding fish

“…Experiment II was a complement to Experiment I, aiming to assess how chronic outgroup conflict impacts reproductive investment in terms of egg size and nutritional content ( Figure 1B ); these are measures that can only be obtained by removing clutches. We therefore collected the first clutch produced by each group following 13 days of treatment, which represents approximately half of a reproductive cycle ( Jindal et al, 2017 ); the experiment ended for a focal group once that clutch was collected. For all response measures analysed, we provide in the main text the effect of treatment (Intruded and Control) and, where significant or near-significant, the interaction between treatment and treatment duration, as the factors of core interest.…”

“…Single intrusion events are known to cause short-term changes in within-group behavioural interactions ( Braga Goncalves and Radford, 2019 ; Bruintjes et al, 2016 ; Taborsky, 1985 ). Crucially, N. pulcher is a highly tractable experimental system—they are easily maintained in captive conditions, where groups display natural behaviour and breed regularly ( Heg and Hamilton, 2008 ; Jindal et al, 2017 ; Wong and Balshine, 2011 )—allowing controlled manipulations and detailed monitoring over extended periods.…”

Filial Cannibalism by Male Fish as an Infanticide to Restart Courtship by Self-Regulating Androgen Levels

“…A typical example of infanticide in animals is that committed by incoming males to induce female estrous behavior [26]. Recently, also in fishes, infanticide following group takeover was observed in a cooperative breeding species, though its endocrinological status was not examined [27]. Similar infanticide to the case of R. nitidus males is the Bruce effect observed in some rodents [28,29] and mammals [30,31], in which parents kill their offsprings to regulate their own endocrine system.…”

Experimental evidence that chronic outgroup conflict reduces reproductive success in a cooperatively breeding fish

“…Experiment I spanned 13 weeks to allow for multiple spawning bouts; we destroyed clutches produced before groups had experienced at least three intrusions (Control=1 clutch, Intruded=2 clutches) as groups would likely not have been significantly affected by treatments within such a short timeframe. In Experiment II, following eight intrusions during the first days, the first clutch produced by each group marked the end of treatment for that group; two weeks represents about half the time of a regular breeding cycle (30,67). Twelve clutches were destroyed during the initial 13 days of treatment (Control=8 clutches, Intruded=4 clutches).…”

“…Single intrusions are known to cause short-term changes in within-group behavioural interactions (2,28,29). Crucially, N. pulcher is a highly tractable experimental system-they are easily maintained in captive conditions, where groups display natural behaviour and breed regularly (20,30,31)-allowing controlled manipulations and detailed monitoring over extended periods.…”