Recently, it has been shown that group-living subordinate clownfish Amphiprion percula increase their growth rate after acquiring the dominant breeder male position in the group. Evidence was found for strategic growth adjustments of subordinate fishes depending on the threat of eviction, i.e. subordinates adjust their growth rates so they remain smaller than the dominant fish and thereby limit...

In recent years, the commercial broiler breeder industry has reported problems of male aggression towards females [Millman, S.T., 1999. An investigation into extreme aggressiveness of broiler breeder males. Unpublished PhD Thesis, University of Guelph]. Although this aggression is shown by the males and is apparently a defect in their behaviour [Millman, S.T., Duncan, I.J.H., 2000. Strain diffe...

We tested whether subordinate helper males of the Lake Tanganyika cooperatively breeding cichlid Neolamprologus pulcher show elevated excretion levels of the stress hormone cortisol and reduced levels of 11-ketotestosterone and testosterone when living in groups with a small breeder male, compared to similar helper males living in groups with a large breeder male, in a full-factorial repeated m...

In size-structured groups, conflict over rank, resources or access to breeding opportunities is expected to be greatest among individuals that are similar in size. We tested this general prediction using the cooperatively breeding African cichlid, Neolamprologus pulcher. We predicted that, when size differences between group members were small, we would observe some or all of: increased aggress...

In social groups, subordinates may gain dominant breeding status either by inheriting the top position in their current group or by dispersing to join a new group. The pathway to breeder status is likely to vary between males and females as a result of sex differences in the costs of dispersal and inbreeding. We report results from a field study conducted to explore sex differences in the rates...

corticosterone in male and female virgin and breeder rats. Acta Endocrinol 62: 411-424, 1969 14. lams SG, Wexler BC: Aldosterone, deoxycorticosterone and corticosterone differences between arteriosclerotic breeder vs nonarteriosclerotic virgin rats. Atherosclerosis 24: 63-73, 1976 15. Wexler BC, True CW: Carotid and cerebral arteriosclerosis. Circ Res 12: 659-666, 1963 16. Wexler BC: Spontaneou...

We examined the proximate causes of delayed breeding and alloparental behavior in the cooperatively breeding red-cockaded woodpecker by measuring plasma concentrations of testosterone (T) and prolactin (PRL) in female breeders, male breeders, and male helpers during different stages of the reproductive cycle. Male breeders and helpers have low T during the prebreeding period, highest T during c...

corticosterone in male and female virgin and breeder rats. Acta Endocrinol 62: 411-424, 1969 14. lams SG, Wexler BC: Aldosterone, deoxycorticosterone and corticosterone differences between arteriosclerotic breeder vs nonarteriosclerotic virgin rats. Atherosclerosis 24: 63-73, 1976 15. Wexler BC, True CW: Carotid and cerebral arteriosclerosis. Circ Res 12: 659-666, 1963 16. Wexler BC: Spontaneou...

Breeder turnover can influence population growth in social carnivores through changes to group size, composition and recruitment. Studies that possess detailed group composition data that can provide insights about the effects of breeder turnover on groups have generally been conducted on species that are not subject to recurrent annual human harvest. We wanted to know how breeder turnover affe...

This experiment was one part of a larger study investigating problems of aggression towards females by male broiler breeder fowl. To investigate causal mechanisms, we were interested in determining (1) if feed-restriction during rearing affects behaviour towards females at sexual maturity and (2) if aggressiveness towards females is correlated with general levels of aggressiveness. We compared ...