IEGEBA   24053
INSTITUTO DE ECOLOGIA, GENETICA Y EVOLUCION DE BUENOS AIRES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
A novel egg-rejection method in a host of the screaming cowbird: antiparasitic defence, nest sanitation behaviour or both?
Autor/es:
URSINO, CYNTHIA; DE MÁRSICO, MARÍA CECILIA; GLOAG, ROS; REBOREDA, JUAN CARLOS
Lugar:
Lund
Reunión:
Congreso; 14th International Behavioral Ecology Congress; 2012
Resumen:
A novel egg-rejection method in a host of the
screaming cowbird: antiparasitic defence, nest sanitation behaviour or both?
Cynthia A. Ursino1, María C. De Mársico1,
Ros Gloag2 and Juan C. Reboreda1
1
Departamento de Ecología, Genética y
Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos
Aires, Argentina.
2 Department
of Zoology, University of Oxford, South Parks Road, OX1 3PS, United Kingdom
Rejection
of foreign eggs by hosts of avian brood parasites is a textbook example of an
adaptation evolved in response to the costs of parasitism. Previous studies have
shown that rejector hosts either puncture or grasp eggs to remove them from the
nest, but we found that baywings (Agelaioides badius), a host of the screaming cowbird (Molothrus rufoaxillaris) instead
reject eggs by rolling them out of the nest with their feet. We proposethat this novel egg-rejection method is co-opted
from nest sanitation behaviours
widespread among birds, and has subsequently come under selection pressure as
an anti-parasite defence.
Exploitation of
parental care by obligate avian brood parasites is costly to hosts and should select
for defences. A well-known antiparasitic defence is the rejection of parasite
eggs. Hosts larger than the parasite usually remove parasite eggs by grasping
them with their bills, while smaller hosts puncture the parasite egg before
removing it. We studied host behaviours towards parasite eggs in the baywing (Agelaioides badius), the primary host of
the screaming cowbird (Molothrus rufoaxillaris).
Most baywing nests are multiply parasitized (90-100%), and 30% of all parasitic
eggs are typically laid in advance of hosts? egg-laying. Baywings show intriguing
egg rejection habits; they eject all parasitic eggs laid before they start
their own laying, but accept all those laid subsequently, except when multiple
parasitism results in clutch sizes double or more the usual complement of eggs (i.e.
6-8 vs. 3-4 eggs). In the latter cases,
they reject the entire clutch, including their own eggs, and begin again. Using
microcameras placed within baywing nests, we recorded for the first time egg-laying
by screaming cowbirds and baywings? behaviour towards cowbird eggs. We found baywings
consistently ejected eggs by rolling them out of the nest using their feet, a behaviour
which to our knowledge has not previously been reported in any host of a brood
parasite. We propose that this singular rejection method is likely an
exaptation, derived from nest sanitation behaviours widespread among birds.
While baywings benefit from egg rejection, their technique presumably does not
allow them to selectively reject parasitic eggs, and explains their
all-or-nothing egg rejection strategy.
Keywords: Birds, Cowbirds, Brood parasites