Sexual dimorphism in house sparrow eggs.

Cordero, P. J.; Griffith, S. C.; Aparicio, J. M.; Parkin, D. T.

Recent evidence has revealed an apparently high degree of control by female birds over the physiological aspects of their reproduction and offspring sex allocation, consistent with adaptive hypotheses of sex allocation and differential investment in their offspring. In the house sparrow, we investigated possible mechanisms that may be used by females to enhance the fitness returns from a reproductive effort. Using molecular techniques, we demonstrate that house sparrow eggs containing male embryos are significantly larger than those containing female embryos. We also found that male embryos were laid randomly with respect to laying order. We speculate that this sexual dimorphism of eggs is adaptive, because male house sparrows show greater variance in condition-dependent reproductive success than females. More important, the result provides further evidence of the ability of females to detect or control ovulation of either male or female ova and to differentially invest in one sex over the other.

SEXUAL dimorphism in animals; ENGLISH sparrow; SEX allocation; ANIMAL offspring sex ratio; EGG incubation; BIRD eggs; ANIMAL behavior

Behavioral Ecology & Sociobiology, 2000, Vol 48, Issue 5, p353

0340-5443

Academic Journal

10.1007/s002650000252