Social status in randomly constituted groups of male CFLP mice was predictable from early suckling behaviour and rate of weight gain in natal litters. High–ranking males were those that had suckled on more anterior teats and gained weight more quickly. Rank was not predicted by any measures of sibling interaction or hormone (testosterone, corticosterone) concentration. Aggressiveness in eventual high–rankers was associated negatively with the proportion of males in the litter at birth and the amount of maternal attention received. Aggressive social relationships within natal litters did not predict polarized rank relationships in randomized groups. Nevertheless, while still in their natal litters, and in the absence of aggressive rank relationships, eventual rank categories showed the same difference in modulation of testosterone concentration in relation to current immunocompetence (low–rankers modulating, high–rankers not), as has repeatedly been found in randomized groups by earlier studies. The role of maternal condition in determining rank–related life–history development in male mice is discussed.

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