Patterns of testosterone in three Nearctic-Neotropical migratory songbirds during spring passage (original) (raw)
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Early elevation of testosterone advances migratory preparation in a songbird
Journal of Experimental Biology, 2011
The timing of events associated with spring migration can be an important determinant of fitness for migratory birds. The need to prepare and maintain physical condition for migration is one demand that must be met for early arrival on breeding areas, and this demand is compounded by the energetic demands of the physiological transition to breeding. Here, we examined whether migratory birds, specifically males, can adequately meet both of these demands by elevating the sex steroid testosterone early during migratory preparation. To test this, we used a captive experiment in which we photostimulated male dark-eyed juncos (Junco hyemalis) and manipulated circulating testosterone. We predicted males with elevated testosterone would prepare to migrate and breed faster than control males or males where the ability of testosterone to bind with receptors, or be converted to estradiol, was inhibited (testosterone inhibited). We measured migratory preparation using mass, food intake, fat deposits and nocturnal activity (Zugunruhe). To estimate breeding preparation, we measured the diameter of the cloacal protuberance (CP). We found that males in the testosterone treatment group began migratory preparation approximately 10days before controls. There was no difference in the magnitude of peak migratory condition between testosterone-implanted birds and controls. Males implanted with testosterone also reached the onset of breeding preparation faster and had larger peak CP diameter compared with controls. Testosterone-inhibited birds showed no signs of migratory preparation and only a weak increase in CP diameter. These results demonstrate that early elevation of testosterone during migratory preparation could incur benefits for males in terms of the ability to depart earlier from non-breeding areas and arrive in a more advanced breeding condition. This experiment demonstrates that there may be important physiological underpinnings to known winter to breeding season carry-over effects in migratory birds.
Testosterone Secretion in a Socially Monogamous but Sexually Promiscuous Migratory Passerine
General and comparative endocrinology, 2016
The steroid hormone testosterone (T) influences a multitude of traits critical to reproduction in vertebrates. In birds, high male T supports territory establishment and mate attraction, but is thought to interfere with parental care. Interspecific comparisons indicate that migratory species with short, synchronous breeding seasons have the highest peak T, and that the seasonal profile of T exhibits a rapid decline with the onset of incubation by females. We describe the T profile of the migratory, socially monogamous, and biparental Eastern Kingbird (Tyrannus tyrannus) from the high desert of eastern Oregon, USA, where breeding occurs within a short 2-3 month period. Eastern Kingbirds are socially monogamous but exhibit high rates of extra-pair paternity as ∼60% of broods contain extra-pair young. We therefore evaluate whether Eastern Kingbirds exhibit the "typical" T profile expected for a synchronously breeding migratory species, or whether T is maintained at a more con...
Testosterone in tropical birds: effects of environmental and social factors
2004
Abstract: Previous investigations suggest that male tropical birds have lower plasma testosterone concentrations than northern latitude species. To test whether this generalization is valid, we analyzed all currently available plasma testosterone data of tropical birds. We focused on peak breeding testosterone levels using phylogenetic and conventional statistics. Explanatory variables considered were social mating system, type of territoriality, breeding season length, and altitude.
Ibis, 2004
The Bluethroat Luscinia svecica is a migratory passerine that exhibits a socially monogamous pair bond and a high level of parental care. Males are territorial both when wintering and breeding whereas females are territorial only in winter. We investigated changes in body condition and testosterone levels during successive life‐history stages and determined their relationships. Sex‐specific patterns were observed in the variation in body condition and testosterone level. Male body condition varied mainly during the winter. It peaked at the onset of the prenuptial moult and then decreased, whereas it remained stable throughout breeding. In contrast, female body condition varied mainly during the breeding season. It increased during the prelaying stage and then abruptly decreased until fledgling provisioning. As in other monogamous and territorial passerines, testosterone levels in Bluethroat males were low during winter, increased in late winter, peaked during the prelaying stage and...
Testosterone, migration distance, and migratory timing in song sparrows Melospiza melodia
Hormones and Behavior, 2016
In seasonally migratory animals, migration distance often varies substantially within populations such that individuals breeding at the same site may overwinter different distances from the breeding grounds. Shorter migration may allow earlier return to the breeding grounds, which may be particularly advantageous to males competing to acquire a breeding territory. However, little is known about potential mechanisms that may mediate migration distance. We investigated naturally-occurring variation in androgen levels at the time of arrival to the breeding site and its relationship to overwintering latitude in male and female song sparrows (Melospiza melodia). We used stable isotope analysis of hydrogen (δ 2 H) in winter-grown claw tissue to infer relative overwintering latitude (migration distance), combined with 14 years of capture records from a long-term study population to infer the arrival timing of males versus females. Relative to females, males had higher circulating androgen levels, migrated shorter distances, and were more likely to be caught early in the breeding season. Males that migrate short distances may benefit from early arrival at the breeding grounds, allowing them to establish a breeding territory. Even after controlling for sex and date, androgen levels were highest in individuals that migrated shorter distances. Our findings indicate that androgens and migration distance are correlated traits within and between sexes that may reflect individual variation within an integrated phenotype in which testosterone has correlated effects on behavioral traits such as migration.
Journal of Avian Biology, 2011
In migratory birds, the timing of departure from wintering grounds is often dependant on the quality of habitat on an individual's territory and may influence individual fitness, resulting in an interaction of life history stages across large geographical distances. American redstart Setophaga ruticilla males who overwinter in high quality habitats arrive early to breed and subsequently produce more offspring than late arrivers. Since many migratory species overlap vernal migration with the physiological transition to breeding, we examined if breeding preparation plays a role in this seasonal interaction. We tested the hypothesis that early arriving male redstarts from high quality winter habitats are in superior breeding condition by simultaneously measuring winter habitat quality (stable-carbon isotopes) and breeding preparation (circulating androgen, cloacal protuberance (CP) diameter) upon arrival at breeding grounds. Compared with late arrivers, early arriving males were from higher quality winter habitats and had higher androgen, but smaller CPs. Males arriving with higher androgen were in more advanced physiological migratory condition, as measured by haematocrit. Early arrivers were more likely to successfully breed, but there was no significant relationship between androgen upon arrival and breeding success. One possible explanation for these relationships is that androgen measured during arrival is most relevant in a migratory context, such that birds with high androgen may benefit from effects on migratory condition, positively influencing fitness through earlier arrival.
Correlated evolution of male and female testosterone profiles in birds and its consequences
Behavioral Ecology and Sociobiology, 2005
Circulating levels of testosterone in adults have mainly evolved as a consequence of selection on males for increased levels, while levels of circulating testosterone in females may be an indirect consequence of selection on males. A review of the literature revealed that intense directional selection for high levels of circulating testosterone in birds is likely to be mainly due to direct selection on males. A comparative study of testosterone levels in birds revealed a strong positive relationship between peak testosterone levels in adult females and peak levels in males. The slope of this relationship was significantly less than unity, implying that the testosterone levels in females have been reduced in species with high levels in males. An analysis of the order of evolutionary events suggested that peak concentration of testosterone in females changed after peak concentrations of testosterone in males. Females in colonial species of birds had significantly higher circulating peak testosterone levels compared to females of solitary species, and relative levels after controlling for the effects of peak levels in males were also larger, suggesting that any costs of high testosterone levels in females are particularly likely in colonial birds. Direct selection on male circulating testosterone levels may increase the costs that females incur from high testosterone titers. For example, high female levels may negatively affect ovulation and laying and may also affect the levels of testosterone that females deposit in their eggs and hence the exposure of pre- and post-hatching offspring to testosterone. This in turn may affect not only offspring behavior, but also offspring development and the trade-offs between growth, development of immune function, and behavior in offspring.
General and …, 2010
Comparative hormone studies can reveal how physiology underlies life history variation. Here, we examined seasonal variation in plasma testosterone concentration between populations of male orangecrowned warblers (Vermivora celata) breeding in Fairbanks, Alaska (V. c. celata) and on Santa Catalina Island, California (V. c. sordida). These populations face different ecological constraints and exhibit different life histories. Alaska birds have a short breeding season, low annual adult survival, and high reproductive rates. In contrast, Catalina Island birds exhibit high adult survival and low reproductive rates despite having a long breeding season. We examined seasonal variation in male testosterone concentrations as a potential mechanism underlying differences in male reproductive strategies between populations. From 2006 to 2008, we sampled males during the pre-incubation, incubation, and nestling stages. Alaska males exhibited a seasonal testosterone pattern typical of northern passerines: testosterone levels were high during pre-incubation and declined during incubation to low levels during nestling provisioning. Testosterone concentrations in Catalina Island males, however, did not vary consistently with breeding stage, remained elevated throughout the breeding season, and were higher than in Alaska males during the nestling stage. We hypothesize that in Alaska, where short seasons and high adult mortality limit breeding opportunities, the seasonal testosterone pattern facilitates high mating effort prior to incubation, but high parental investment during the nestling stage. On Catalina Island, elevated testosterone levels may reflect the extended mating opportunities and high population density facing males in this population. Our results suggest that population variation in seasonal testosterone patterns in orange-crowned warblers may be a function of differences in life history strategy and the social environment.