| department of population ecology | ::: | institute | ::: | university | ::: |  |
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dr hab. Mariusz Cichoń
cichon@eko.uj.edu.pl |
Dep. of Population Ecology Inst. of Environmental Sciences Jagiellonian University Gronostajowa 7, 30-387 Kraków Poland tel. + 48 12 664 52 01 fax + 48 12 664 69 12 |
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Rutkowska J., Cichoń M.
ANIM BEHAV
2002; 64: 817-822
Abstract:
In order to study whether offspring sex is related to the amount of resources invested in eggs we performed an experiment on zebra finches. By manipulation of food supply, two groups of females were forced to either increase or decrease investment in subsequent eggs. Since zebra finches are sexually dimorphic and the reproductive value of the sexes may vary with maternal nutritional status, we expected females to adjust sex of their offspring to the egg quality. Females fed poor quality food for seven weeks prior to egg laying, and supplemented with proteins after laying the first egg, significantly increased mass of subsequent eggs. An increase of egg mass with laying sequence was less pronounced in females fed high quality food prior to laying and experiencing food deterioration after onset of laying. Proportion of sons in subsequent eggs tended to increase in the latter group but was not related to laying sequence in the other group: these patterns differed significantly between the groups. We were not able to show that offspring sex was related to egg mass, but newly hatched male chicks were heavier than female chicks. Moreover we found that the hatching success of male eggs was lower than female eggs. We suggest that differential hatchability of the sexes and sex differences in mass at hatching may constitute an important factor shaping brood sex ratios.
d e s i g n e d b y P a w e ł K a p u s t a