Source of egg-size variation in Chubut Steamer Ducks (Tachyeres leucocephalus)

SVAGELJ WALTER S; AGÜERO MARÍA LAURA; GARCÍA BORBOROGLU PABLO

EMU

CSIRO PUBLISHING

Año: 2012 vol. 112 p. 167 - 172

0158-4197

Intraspecific egg-size variation is of biological interest as egg size may influence offspring quality and its survival. Although several studies have analysed spatial or temporal variation in egg size in waterfowl, no study analysed variation along the breeding distribution range of a particular species. Chubut Steamer Ducks (Tachyeres leucocephalus) are flightless marine waterfowl endemic to a small section of coastline in Patagonia, Argentina. Here, we partitioned and analysed sources of variation in egg size in 989 eggs from 175 Chubut Steamer Duck clutches registered during 1998 and 2004-2008 seasons at 31 islands along the breeding distribution range of the species. In relation to other Anseriformes, we find a low level of egg-size variation (CV = 6.4%) at the species level. Most egg-size variation was due to differences within clutches (59.0%) and among clutches (34.5%); variation among islands within geographical areas accounted just for 6.5% of variation, while there was no variation among geographical areas. Egg-size variation was not related to year, apparent clutch size or latitude. The low variation at the species level and the lack of egg-size variation among geographical areas could be consequence of the low genetic diversity and the restricted distribution range of the species.