INTRASPECIFIC BROOD PARASITISM IN THE MOORHEN - PARENTAGE AND PARASITE-HOST RELATIONSHIPS DETERMINED BY DNA-FINGERPRINTING

Parasitic female moorhens (Gallinula chloropus) lay from one to six eg gs in the nests of conspecific neighbours. DNA fingerprinting was used to show that parasitic eggs could be correctly identified when they a ppeared in addition to or outside the host's laying sequence. Moorhen hosts accept all parasitic eggs laid after the 2nd day of their laying period. To understand why moorhen hosts tolerate parasitic eggs, we t ested two hypotheses. (1) The quasi-parasitism hypothesis: females lay their eggs in the evening when the host males are normally in attenda nce at the nest, so host males may allow parasitic females to lay in t heir nests in exchange for fertilizing their eggs. However, DNA finger printing showed that all the parasitic eggs were sired by the parasite s' mates. Parasitic moorhens frequently continue laying a clutch in th eir own nest, without a break in the laying sequence after a parasitic laying bout. The eggs laid by brood parasites in their own nests were also sired by their own mates. Therefore this hypothesis was rejected . (2) The kin selection hypothesis. if one or both members of the host pair are close relatives of the parasite, the costs of rearing parasi tic chicks will be to some degree offset by inclusive fitness benefits . We examined the genetic relationships between parasites and their ho sts using DNA fingerprinting and genealogical data. Natal philopatry b y both sexes was relatively common in this population, and the probabi lity that a neighbour of either sex was a first-order relative (parent -offspring) was calculated as 0.18. Although first-order relatives wer e not preferentially chosen as hosts over individuals that were not fi rst-order relatives, even through random host selection there is almos t a one-in-five chance that brood parasites in this population are clo sely related to their hosts. This may facilitate host tolerance of par asitic eggs. Other hypotheses are also discussed.