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.