In the coevolutionary dynamic of avian brood parasites and their hosts, maternal (or transgenerational) effects have rarely been investigated. We examined the potential role of elevated yolk testosterone in eggs of the principal brood parasite in North America, the brown-headed cowbird, and three of its frequent host species. Elevated maternal androgens in eggs are a common maternal effect observed in many avian species when breeding conditions are unfavorable. These steroids accelerate embryo development, shorten incubation period, increase nestling growth rate, and enhance begging vigor, all traits that can increase the survival of offspring. We hypothesized that elevated maternal androgens in host eggs are a defense against brood parasitism. Our second hypothesis was that elevated maternal androgens in cowbird eggs are a defense against intra-specific competition. For host species, we found that elevated yolk testosterone was correlated with parasitized nests of small species, those whose nest success is most reduced by cowbird parasitism. For cowbirds, we found that elevated yolk testosterone was correlated with eggs in multiply-parasitized nests, which indicate intra-specific competition for nests due to high cowbird density. We propose experimental work to further examine the use of maternal effects by cowbirds and their hosts.
An experiment was conducted to investigate the potential effects of pleasant fragrances on task performance. Participants performed a word formation (anagrams) task under moderate or low stress and in the presence or absence of two different fragrances previously rated as pleasant by a large group of judges. In addition, some participants received a small gift at the start of the experimental session. Results indicated that both exposure to pleasant fragrances and receipt of a small gift significantly increased performance on the anagrams task; moreover, this was true under conditions of moderate as well as low stress. In addition, both exposure to pleasant fragrances and receipt of a small gift increased participants' willingness to help the experimenter by serving as uncompensated volunteers. These results are consistent with an interpretation suggesting that pleasant fragrances can enhance task performance by serving as a source of environmentally generated positive affect.
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