Male-biased reproductive effort in a long-lived seabird.

Background: In dimorphic seabirds, the larger sex tends to provision more than the smaller sex. In contrast, monogamy and biparental care are often associated with equal effort between the sexes. However, the few studies that have tested sex-specific effort in monomorphic seabirds have primarily examined the details of foraging at sea. Hypotheses: Parental effort is also sex-biased in a monomorphic seabird mating system for one of two reasons: (1) If females enter the period of parental care less able to invest in care due to the cost of egg production, male-biased effort may be necessary to avoid reproductive failure. (2) Alternatively, female-biased effort may occur due to the initial disparity in gamete size, particularly in species with internal fertilization. Organism: Leach’s storm-petrel (Oceanodroma leucorhoa), a monomorphic seabird with true monogamy and obligate biparental care. Site: A breeding colony of Oceanodroma leucorhoa at the Bowdoin Scientific Station on Kent Island, Bay of Fundy, New Brunswick, Canada. Methods: Across multiple breeding seasons, we assessed incubation behaviour and chickrearing behaviour through one manipulative and multiple observational studies. We assessed energetic investment by inducing feather replacement and measuring the resulting rate of feather growth during both the incubation and chick-rearing phases of parental care. Conclusions: We observed male-biased effort. Males incubated the egg for a greater proportion of time than did females and, when faced with an egg that would not hatch, males continued to incubate past the point when females abandoned it. Males made a higher percentage of total food deliveries to chicks than did females, resulting in greater mean daily food provisioning by males than by females. During chick rearing, males grew replacement feathers more slowly than did females, indicating that males were more likely to reduce their own nutritional condition while raising chicks than were females. These results support the hypothesis that females enter the period of parental care at a nutritional deficit and males must compensate to avoid reproductive failure.

Effects of apomorphine on mating behavior, flank marking and aggression in male hamsters

In male rats, the dopamine agonist apomorphine (APO) generally facilitates copulatory behavior. However, disruptive effects of high APO doses have been reported. These have been interpreted in diverse ways, as products of a dopaminergic system that inhibits sexual behavior or as consequences of APO's stimulation of competing responses. To test the generality of these effects, we observed APO's impact on copulatory behavior in male hamsters. Several effects were observed, all attributable to a relatively high dose and involving the disruption of male behavior. More unexpectedly, APO treatment caused males to attack estrous stimulus females in the course of these tests. To clarify these effects, we observed the effects of APO on flank marking, a type of scent marking closely allied to aggression and dominance in hamsters. Treatment reliably decreased the latency of marking. It also increased the rate of marking when appropriate measures were taken to prevent this effect from being obscured by drug-induced cheek pouching. Together, these results confirm and extend APO's well-known ability to increase aggression. Further, they suggest that APO-induced aggression can intrude into other contexts so as to disrupt, or possibly facilitate, other forms of social behavior.