Hormonal changes in males of a naturally biparental and a uniparental mammal

Blood samples from male hamsters (Phodopus) during their mate's gestation a nd early lactation show that key hormones important in maternal behavior ar e also changing in males and differ for two closely related species with di fferent levels of paternal care. Results of study 1 were consistent with a relationship between higher prolactin, lower testosterone and paternal beha vior during early lactation in P. campbelli and provided no evidence for si milar hormonal changes in P. sungorus. Study 2 sampled males before or afte r the birth. Prolactin did not increase until at least one day after the bi rth in P. campbelli but was high at the end of the pregnancy in P. sungorus . Increasing testosterone concentrations in P. campbelli as the birth appro ached were consistent with mate guarding, high testosterone concentrations on L5 were consistent with paternal aggression in defense of the litter, an d the drop in testosterone after the birth was consistent with reduced aggr ession toward the new pups. Results confirmed that cortisol concentrations were reduced following the establishment of a pair-bond and found that P. c ampbelli males had elevated cortisol before the birth. Results support the hypothesis that mammalian paternal behavior has a hormonal basis which is a nalogous to maternal behavior. (C) 1999 Academic Press.