Host switch in obligate brood parasites: How often does it occur?

DOMINGUEZ, M.; DI GIÁCOMO, A.; REBOREDA, J.C.; MAHLER, B.

Lund

Congreso; 14th International Behavioral Ecology Congress; 2012

Universidad de Lund

Obligate avian brood parasites lay their eggs in nests of other host species, which thereafter provide all parental care. Brood parasites may be host specialists, if they use one or a few host species, or host generalists, if they parasitize many hosts. Parasitic cowbirds differ in their strategies, with the Screaming Cowbird (Molothrus rufoaxillaris) being a specialist and the Shiny Cowbird (Molothrus bonariensis) being a generalist. Although host use differs at population level,  three previous studies showed that both species show host preference at individual level, which translates into genetic differentiation in mtDNA haplotype frequency distribution between hosts. However haplotypes were not unique to one host species, indicating host switches by brood parasitic females. The aim of our study was to analyze the host switching rates that explain the genetic patterns previously found between hosts. Using ɸST values, and estimating 40 laying females in an 600 ha area, we examined the number of female migrants (host switchers) per generation (m) in three different cowbird populations. As expected, in the same location host switching rates for the generalist brood parasite were higher than those for the specialist brood parasite  (one migrant each 3 and 9 generations, respectively). However, host switching rates in the generalist brood parasite vary between populations according to the hosts that are being used.