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Why mainly males compete and females take a larger share in parental care remains an exciting question in evolutionary biology. Role-reversed species are of particular interest, because such 'exceptions' help to test the rule. Using mating systems theory as a framework, we compared the reproductive ecology of the two most contrasting coucals with regard to sexual dimorphism and parental care: the black coucal with male-only care and the biparental white-browed coucal. Both species occur in the same lush habitat and face similar ecological conditions, but drastically differ in mating system and sexual dimorphism. Black coucals were migratory and occurred at high breeding densities. With females being obligatory polyandrous and almost twice as heavy as males, black coucals belong to the most extreme vertebrates with reversed sexual dimorphism. Higher variance in reproductive success in fiercely competing females suggests that sexual selection is stronger in females than in males. In contrast, resident white-browed coucals bred at low densities and invariably in pairs. They were almost monomorphic and the variance in reproductive success was similar between the sexes. Black coucals were more likely to lose nests than white-browed coucals, probably facilitating female emancipation of parental care in black coucals. We propose that a combination of high food abundance, high population density, high degree of nest loss and male bias in the adult sex ratio represent ecological conditions that facilitate role reversal and polyandry in coucals and terrestrial vertebrates in general.

Polar environments are characterized by discrete periods of continuous light or darkness during the summer and winter months, respectively. Because the light/dark cycle serves as the primary Zeitgeber to synchronize rhythms of most organisms, its seasonal absence in polar regions poses challenges to the circadian organization of organisms that reside in these environments. Although some species become arrhythmic, others, such as migratory songbirds, are able to maintain an intact diurnal rhythm during polar summer. This suggests that birds may switch to alternative environmental cues, such as daily changes in light intensity and ambient temperature, which may have the potential to reset the biological clock. However, identifying the low-amplitude Zeitgeber that synchronizes rhythms in free-living polar-dwelling animals has been difficult to demonstrate. In this study, we measured behavioral and melatonin profiles of free-living Lapland longspurs (Calcarius lapponicus) near Barrow, Alaska (71°N) during the continuous daylight of summer in the Arctic. Diel cycles in activity and male singing were apparent throughout the polar day with a quiescence period of 4-5 hr starting around 24:00 Alaska Daylight Time. This inactivity corresponded with elevated melatonin profiles. In contrast, territorial aggression of males in response to a conspecific intruder was not dependent upon time-of-day. Diel changes in light intensity and ambient temperature were negatively associated with daily melatonin profiles after taking into account time-of-day effects. These results suggest that photic and thermal cues may act either as alternative Zeitgeber cues, or possibly masking agents. Distinguishing between these two possibilities will require further study.

Variation in demographic and physiological attributes of life history is thought to fall on one single axis, a phenomenon termed the Pace-of-Life. A slow Pace-of-Life is characterized by low annual reproduction, long life span and low metabolic rate, a fast Pace-of-Life by the opposite characteristics. The existence of a single axis has been attributed to constraints among physiological mechanisms that are thought to restrict evolutionary potential. In that case, physiological traits should covary in the same fashion at the levels of individual organisms and species. We examined covariation at the levels of individual and subspecies in three physiological systems (metabolic, endocrine and immune) using four stonechat subspecies with distinct life-history strategies in a common-garden set-up. We measured basal metabolic rate, corticosterone as endocrine measure and six measures of constitutive immunity. Metabolic rate covaried with two indices of immunity at the individual level, and with corticosterone concentrations and one index of immunity at the subspecies level, but not with other measures. The different patterns of covariation among individuals and among subspecies demonstrate that links among physiological traits are loose and suggest that these traits can evolve independent of each other.

Phenotypic flexibility allows animals to adjust their physiology to diverse environmental conditions encountered over the year. Examining how these varying traits covary gives insights into potential constraints or freedoms that may shape evolutionary trajectories. In this study, we examined relationships among haematocrit, baseline corticosterone concentration, constitutive immune function and basal metabolic rate in red knot Calidris canutus islandica individuals subjected to experimentally manipulated temperature treatments over an entire annual cycle. If covariation among traits is constrained, we predict consistent covariation within and among individuals. We further predict consistent correlations between physiological and metabolic traits if constraints underlie species-level patterns found along the slow-fast pace-of-life continuum. We found no consistent correlations among haematocrit, baseline corticosterone concentration, immune function and basal metabolic rate either within or among individuals. This provides no evidence for constraints limiting relationships among these measures of the cardiovascular, endocrine, immune and metabolic systems in individual red knots. Rather, our data suggest that knots are free to adjust individual parts of their physiology independently. This makes good sense if one places the animal within its ecological context where different aspects of the environment might put different pressures on different aspects of physiology.

The immunocompetence handicap hypothesis (ICHH) posits that the hormone testosterone mediates a trade-off between investment in reproduction and immunological condition. In this study, we tested the ICHH in the Red Bishop Euplectes orix, a polygynous weaverbird. Males of this strongly sexually dimorphic species show an elaborate courtship display to attract females and compete aggressively with other males for nesting sites in breeding colonies. We experimentally elevated testosterone levels in breeding male Red Bishops kept in an aviary with a subcutaneous implantation of testosterone-releasing pellets. We then compared behaviour, development of territory size and immunological condition (as assessed through a white blood cell count) of the experimental group with a control group treated with placebos. In addition, we measured the primary and secondary response to phytohaemagglutinin (PHA) to investigate the effect of testosterone on both innate and acquired immunity. Males with elevated levels of testosterone enlarged their territories and conducted more courtship behaviour, while showing a decrease in health, expressed by an increased heterophil/lymphocyte ratio compared with the control group. Males of the control group showed an increase of the secondary response to PHA, as expected under the assumption that repeated exposure to an antigen enhanced the immune response due to acquired immunity. However, males with experimentally increased testosterone levels did not show such an enhanced immune response in the secondary PHA test (although sample size and power of the statistical tests were low), indicating that testosterone treatment might directly or indirectly suppress some component of the acquired immune response.

Florida scrub-jays (Aphelocoma coerulescens) in the suburbs breed earlier than jays in native habitat. Amongst the possible factors that influence this advance (e.g., food availability, microclimate, predator regime, etc.), is exposure to artificial lights at night (LAN). LAN could stimulate the reproductive axis of the suburban jays. Alternatively, LAN could inhibit pineal melatonin (MEL), thus removing its inhibitory influence on the reproductive axis. Because Florida scrub-jays are a threatened species, we used western scrub-jays (Aphelocoma californica )t o investigate the effects of LAN upon reproductive hormones and melatonin. Jays were held under conditions inwhichthedark-phaseofthelight:dark cyclewas withoutillumination andthenunder low levels of LAN. Under both conditions, birds were exposed first to short-days (9.5L:14.5D) that were gradually increased to long-days (14.5L:9.5D). At various times, blood samples were collected during the light part of the cycle to measure reproductive hormones (luteinizing hormone, LH; testosterone, T; and estradiol, E2). Similarly, samples to assess melatonin were collected during the dark. In males, LAN caused a depression in LH levels and levels were � 4� greater under long- than short-days. In females, there was no effect of LAN or photoperiod upon LH. LAN resulted in depressed T levels in females, although there was no effect on T in males. E2 levels in both sexes were lower under LAN than under an unlighted dark-phase. Paradoxically, MEL was higher in jays underLAN,andunderlong-days.MELdidnotdiffer bysex.LANdisrupted theextraordinarily strong correlation between T and E2 that existed under unlighted nocturnal conditions. Overall, our findings fail to support the hypothesis that LAN stimulates the reproductive axis. Rather, the data demonstratethatLANtendstoinhibitreproductivehormonesecretion,althoughnotinaconsistent fashion between the sexes. J. Exp. Zool. 319A:527-538, 2013. © 2013 Wiley Periodicals, Inc. How to cite this article: Schoech SJ, Bowman R, Hahn TP, Goymann W, Schwabl I, Bridge ES. 2013. The effects of low levels of light at night upon the endocrine physiology of western scrub- jays (Aphelocoma californica). J. Exp. Zool. 319A:527-538.