Mate switching as a function of mate quality in convict cichlids, Cichlasoma nigrofasciatum.

We examined mate switching between mated pairs of monogamous convict cichlids as a function of mate quality (size). A mated pair was established in each half of a 284-litre aquarium, an opaque partition separating the two pairs. When the partition was removed, mis-assorted pairs (large males with small females competing with small males with large females) re-sorted themselves such that the larger male and the larger female paired with each other 46% of the time. In contrast, when we exposed initially assorted pairs to each other, large pairs remained intact most of the time and dominated smaller pairs. The pair containing the large male, whether re-sorted or intact, dominated over the other pair and was the only one seen to spawn. Re-sortment resulted both from a preference of males for larger females and of females for larger males, and from the ability of larger individuals to displace their smaller consexual. Small females, however, when paired with a large male, often dominated large females and prevented the large female from mating with the large male. Re-sortment was also influenced by the compatibility of large individuals in their initial pairing situation. Large individuals that had been more compatible with their initial mates were less likely to switch mates. Our results support both the better-option and the incompatibility hypotheses of mate-switching. The availability of more than one breeding site in the aquarium had no effect on the frequency of re-sortment. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.