SICB Posters, Part 2: Birds

Following (below the fold) are a few of the bird posters that I saw yesterday at SICB.

• Class. Substantial data exists on the behavioral endocrinology of temperate-zone birds, yet ornithologists are just beginning to examine and compare tropical birds to temperate zone birds. In a recent comparative study, tropical birds had lower mean peak testosterone levels on average than temperate birds. However, several tropical species in the study had comparable or higher peak testosterone levels than temperate species. In contrast, in a study of peak testosterone levels in three species of the genus Zonotrichia, distributed from the arctic to the equator, the tropical Zonotrichia had the highest peak testosterone levels of all. Despite phylogenetic control within the Zonotrichia genus, the tropical population studied was at a high elevation, while the temperate and arctic populations were at low elevations. To investigate the effect of elevation on testosterone of tropical Zonotrichia, Class and Moore compared the peak testosterone levels of the rufous-collared sparrow, Zonotrichia capensis, found at two elevations at the same latitude in the Andes of central Ecuador. They found that higher elevation populations of Z. capensis had higher mean peak testosterone levels. They concluded that high elevation tropical environments are ecologically equivalent to high latitude environments, making it possible to compare birds living in similar habitats in different locations.
• Jawor. In female mammals, progesterone (P) can influence sexual receptivity, and maternal and intrasexual aggression. But less is known about the role of P in female birds. Previous studies in dark-eyed juncos, Junco hyemalis, found that when females establish dominance they do not elevate testosterone (T), raising the question of whether P might play a role in female aggression. In this study Jawor and Ketterson asked whether resident females altered either their P or P/T ratios in response to an intrusion by a female conspecific, and whether P co-varied with the type of aggression displayed. Thirty-five females were allowed to associate with a male for 2 days prior to the introduction of either a conspecific intruder or a heterospecific control intruder. Plasma samples were collected from resident females prior to their introduction to a male and following 30 minutes of interaction with the intruders. During intrusions, resident females were scored according to the type and number of aggressive acts displayed. They found that females increased P following an intrusion, but the magnitude of increase was not affected by intruder type. In the case of T, there was a nearly significant interaction between the magnitude of change in T and intruder type but there were no significant effects of intrusion or intruder on P/T ratios. Finally, levels of these hormones were not related to the aggression shown. Jawor and Ketterson concluded that P but not T increased regardless of intruder type and the increase may be a response to associating with a male. The findings do not support a role for P in female intrasexual aggression in juncos. However, further studies are needed to determine whether P functions in conjunction with other hormones to influence aggression.
• Okekpe. Sex ratio theory assumes that parents will maximize their parental investment and production costs by adjusting offspring sex ratio when fitness returns of sons and daughters are differentially influenced by ecological and social circumstances. Recently, a number of studies on birds have indicated that females, being the heterogametic sex, are capable of using pre-ovulatory mechanisms to skew offspring sex ratios; however, no one has conclusively identified the mechanism responsible for this phenomenon. An experimental study in chickens found that exogenous progesterone (P) administered during meiosis I results in male-biased offspring ratios as did a low quality, food restricted diet in zebra finches, Taeniopygia guttata. Okekpe and colleagues investigated whether diet manipulation in zebra finches resulted in significant changes in both circulating P and corticosterone (B) levels at the time of ovulation. Their preliminary analyses indicated that a low quality diet or food restrictions were successful in skewing the offspring ratio toward males.

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