What advantages do male cichlids get when they act as nannies in helping other parents in raising their fry? According to research published in a recent issue of the online journal PLoS ONE, they get to father some of their own offspring.
Rick Bruintjes and colleagues discovered this while studying the Daffodil cichlid (Neolamprologus pulcher). The Daffodil cichlid is a cooperative-breeding cichlid in which unrelated or distantly-related subordinate cichlids help a dominant pair in looking after and raising their offspring.
Subordinates stay within the territory of the dominant pair only because of the protection conferred against predators. They risk expulsion if they try to get in on the act of breeding, which usually means a death sentence, as the mortality risk outside of the territories is high.
Although experiments in the laboratory have shown that subordinates get to sire some of their own offspring, it has been difficult to extrapolate the results as natural behaviour in the wild, since the gonads of the subordinate individuals have been shown to be much smaller than those of the dominant individuals.
The authors combine parentage analysis and detailed behavioural observations to investigate if subordinates participate in reproduction in the field and if so, whether and how this affects subordinate helping behaviour.
The authors caged two randomly-selected adjacent breeding groups of Daffodil cichlids in Lake Tanganyika at Kasakalawe Point, Zambia (39 such cages were erected, enclosing 78 breeding groups).
Piscivores were removed from the cages, and one to four subordinate individuals were sexed, measured and marked to facilitate individual identification.
The groups were left in the cages for two weeks, during which behavioural observations were made on one large and one small subordinate per group in random order three times for 10 minutes each. At the end of the two weeks, the authors sampled all the eggs, fry and fish found inside the cages for DNA.
The authors also subjected every breeding group to two standardised experimental manipulations in order to measure the propensity of the subordinates to help.
In the first treatment, the breeding shelter was carefully half–covered with sand to induce digging behaviour, and digging frequencies of all group members were recorded for 10 minutes.
In the second treatment, an egg predator (Telmatochromis vittatus) was placed in a transparent cylindrical tube for 10 minutes 5cm/2" outside the breeding shelter. All aggression against the predator by the group members was recorded.
The authors found that while dominant females were the mothers of almost all (99.7%) of the offspring, the dominant males only sired 88.8% of them. Subordinate females did not participate in reproduction, but male subordinates were the fathers in 27.8% of all clutches.
Although the subordinate males made no extra effort in digging out the breeding shelter when it was partially buried by sand whether or not they sired part of the brood, they were motivated enough to expend additional effort in protecting the brood from egg predators when they were fathers of some of the fry.
The experiment suggests that male subordinate Daffodil cichlids do reproduce within the breeding group and, if successful, they apparently raise their brood care effort accordingly.
For more information, see the paper: Bruintjes R, D Bonfils, D Heg and M Taborsky (2011) Paternity of subordinates raises cooperative effort in cichlids. PLoS ONE 6, e25673.
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