Reproductive parasitism of broodcare helpers in a cooperatively breeding fish

Large male helpers in the cooperatively breeding cichlid Neolamprologus pul cher gain reproductive success by parasitizing the reproductive effort of m ale territory owners. Under controlled, experimental conditions we examined the genetic relatedness between the members of brood pairs (n = 14), their male helpers (n = 8), and offspring (n = 292) in seven families. We used m ultilocus DNA fingerprinting to check for potential reproductive parasitism by male helpers and to assess their fertilization success. Of offspring pr oduced in these families, 10.3% were sired by helpers. In parasitized brood s, helper fertilization success varied between 12.5% and 35.8%. Male helper s parasitized parental reproduction when their body size exceeded 4.5 cm st andard length (SL), even though sexual maturity may be reached much earlier (3.5 cm SL). Two of three parasitic helpers were punished by severe aggres sive attacks when parasitizing the reproduction of breeders, which led to t heir expulsion from the territory This study demonstrates a potential fitne ss benefit to broodcare helpers that is often neglected. It also points to the delicate balance that may exist between cooperative and competitive beh avior in cooperatively breeding species.