Parental care in the Malawian cichlid fish Pseudotropheus zebra 'BB' is extensive and
exclusively maternal; males contribute only genetic material. The costs of searching for
multiple mates (in this case risk of predation on orally incubated eggs) suggested that
females should be monandrous; microsatellite genetypes of seven brooding females and their
young, however, reveal extensive multiple paternity in this species, with a mean of 3.8
paternal individuals per brood. Polygynandry in P. zebra is probably not maintained
by selection for genetically diverse offspring; potential explanations include avoidance
of inbreeding, and bet-hedging on other male characteristics that females are unable to
evaluate when selecting a mate. The observed degree of multiple paternity strongly suggests
that females are free to choose mates as they will, a prerequisite of many theories positing
sexual selection as a key element in Malawi cichlid evolution. It should also result in
elevation of effective population sizes, and thus be antagonistic to runaway evolution of
male secondary sexual characteristics, but not necessarily to other modes of sexual selection.