Size differences within a dominance hierarchy influence conflict and help in a cooperatively breeding cichlid

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 aggression, increased submissive behaviour, increased help by subordinates or avoidance of dominants by subordinates. We created standardised groups each with a breeder male and female and a large and small helper (both males). The size of all group members was kept constant, with the exception of the breeder males, which were either only slightly larger than the largest helper or much larger. This created either large or small size differences between breeder males and the large helper (the 2nd ranked male in the group). We found that large helpers showed more submissive behaviours, reduced affiliative behaviour and kept further from breeding sites when male breeders were small. We did not find a consistent influence of breeder size on aggression. Together, these results support the prediction that conflict between breeder and helper is increased when breeders are small, but that this conflict is expressed through changes in submissive and affiliative behaviours and in space use rather than aggression. In contrast to our predictions, large helpers increased helping (territorial defence) when the male breeder was large; the reasons for this are unclear.

Effect of Protein Realimentation on Lactational Performance in Rats:

Previous research in our laboratory has shown that lactating rats given low protein diets will readily mobilise approximately 20% of body protein to sustain lactational performance. However in such females lactational performance falls markedly around day 6 of lactation and remains at this low level for the remainder of lactation. The objective of this study was therefore to investigate whether this decline in lactational performance coincided with the exhaustion of labile protein reserves, and secondly whether such protein depleted females could reestablish effective lactation in mid lactation when given an increased supply of dietary protein.Sixty six multiparous Sprague-Dawley rats were mated individually with a proven male breeder, mating being confirmed through the presence of vaginal plugs, then transferred to solid bottomed plastic cages for the remainder of the experiment.