Maternal investment. Sex differences in avian yolk hormone levels.
It has been suggested that female birds put more resources into eggs fathered by attractive males by laying larger eggs or by adding more testosterone, but this inference could be undermined if eggs of different sex are provisioned differently, as these studies did not control for sex differences. Here we compare hormone concentrations in the yolks of male and female eggs and find that these are significantly different. Our results indicate that it is premature to conclude that female birds invest more in eggs sired by a preferred male, and raise the possibility that yolk sex steroids may be part of the sex-determining process in birds.
Petrie
M
M
Evolution and Behaviour Research Group, Department of Psychology, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK. marion.petrie@ncl.ac.uk
Schwabl
H
H
Brande-Lavridsen
N
N
Burke
T
T
D000818:Animals; D001717:Birds / Q000196:embryology* / Q000378:metabolism; D004530:Egg Yolk / Q000378:metabolism*; D005260:Female; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D008297:Male; D012727:Sex Characteristics; D013256:Steroids / Q000378:metabolism
D012739:Gonadal Steroid Hormones; D013256:Steroids