We know little of the proximate mechanisms underlying the expression of signaling traits in femal... more We know little of the proximate mechanisms underlying the expression of signaling traits in female vertebrates. Across males, the expression of sexual and competitive traits, including ornamentation and aggressive behavior, is often mediated by testosterone. In the white-shouldered fairywren (Malurus alboscapulatus) of New Guinea, females of different subspecies differ in the presence or absence of white shoulder patches and melanic plumage, whereas males are uniformly ornamented. Previous work has shown that ornamented females circulate more testosterone and exhibit more territorial aggression than do unornamented females. We investigated the degree to which testosterone regulates the expression of ornamental plumage and territorial behavior by implanting free-living unornamented females with testosterone. Every testosterone-treated female produced a male-like cloacal protuberance, and 15 of 20 replaced experimentally plucked brown with white shoulder patch feathers but did not typ...
ABSTRACTDevelopmental exposure of embryos to maternal hormones such as testosterone in the avian ... more ABSTRACTDevelopmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus–pituitary–adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific ...
Plasma levels of luteinizing hormone (LH), testosterone, 5α-dihydrotestosterone (5α-DHT), estradi... more Plasma levels of luteinizing hormone (LH), testosterone, 5α-dihydrotestosterone (5α-DHT), estradiol-17β, and corticosterone were measured in free-living and captive European Blackbirds (Turdus merula) during autumn. Free-living birds were designated as sedentary or migratory according to whether they remained in or disappeared from the study area during the winter season. Captive birds that increased body weight, deposited fat, and developed Zugunruhe in autumn were designated as migratory, whereas those that failed to do so were regarded as sedentary. The results do not support the hypothesis that plasma levels of gonadal hormones are elevated in sedentary birds, thus inhibiting autumnal migration. Plasma levels of LH and of testosterone were low in both adult and first-year free-living males, although testosterone levels were higher in migratory than in sedentary free-living first-year males. In captivity, however, testosterone levels were not different between first-year sedentar...
In males it is frequently testosterone (T) that activates the expression of sexually selected mor... more In males it is frequently testosterone (T) that activates the expression of sexually selected morphological and behavioral displays, but the role of T in regulating similar traits in females is less clear. Here, we combine correlational data with results from T and gonadotropin-releasing hormone (GnRH) manipulations in both sexes to assess the role of T in mediating sexually dimorphic coloration and morphology in the red-backed fairy-wren (Malurus melanocephalus). We show that: (1) natural variation in female expression of ornamental traits (darkened bills and red back feathers) is positively associated with age and circulating androgen titres, (2) females have the capacity to express most male-typical traits in response to exogenous T, including carotenoid-pigmented body plumage, shorter feathers, darkened bill and enlarged cloacal protuberance, but (3) appear constrained in production of male-typical melanin-pigmented plumage, and (4) low androgen levels during the pre-nuptial mol...
Embryos of several bird species tolerate acute hypothermia. However, the extent to which it can b... more Embryos of several bird species tolerate acute hypothermia. However, the extent to which it can be tolerated by wild species living under natural conditions is poorly documented. At a single American kestrel (Falco sparverius) nest 15 days into incubation, we observed a 21-h bout of egg neglect by the parents during which nest (egg) temperature averaged 12.7°C. Normal incubation patterns resumed thereafter, and one of three viable eggs hatched 32 days after incubation onset, an incubation period 2.5 days longer than the mean in this study. The nestling appeared to develop and fledge normally. Although embryonic tolerance of extended hypothermia is known to occur in some seabirds, its presence in Falconiformes has not heretofore been recorded. Embryonic hypothermic tolerance may be adaptive in species with extended periods of parental absence during incubation.
We know little of the proximate mechanisms underlying the expression of signaling traits in femal... more We know little of the proximate mechanisms underlying the expression of signaling traits in female vertebrates. Across males, the expression of sexual and competitive traits, including ornamentation and aggressive behavior, is often mediated by testosterone. In the white-shouldered fairywren (Malurus alboscapulatus) of New Guinea, females of different subspecies differ in the presence or absence of white shoulder patches and melanic plumage, whereas males are uniformly ornamented. Previous work has shown that ornamented females circulate more testosterone and exhibit more territorial aggression than do unornamented females. We investigated the degree to which testosterone regulates the expression of ornamental plumage and territorial behavior by implanting free-living unornamented females with testosterone. Every testosterone-treated female produced a male-like cloacal protuberance, and 15 of 20 replaced experimentally plucked brown with white shoulder patch feathers but did not typ...
ABSTRACTDevelopmental exposure of embryos to maternal hormones such as testosterone in the avian ... more ABSTRACTDevelopmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus–pituitary–adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific ...
Plasma levels of luteinizing hormone (LH), testosterone, 5α-dihydrotestosterone (5α-DHT), estradi... more Plasma levels of luteinizing hormone (LH), testosterone, 5α-dihydrotestosterone (5α-DHT), estradiol-17β, and corticosterone were measured in free-living and captive European Blackbirds (Turdus merula) during autumn. Free-living birds were designated as sedentary or migratory according to whether they remained in or disappeared from the study area during the winter season. Captive birds that increased body weight, deposited fat, and developed Zugunruhe in autumn were designated as migratory, whereas those that failed to do so were regarded as sedentary. The results do not support the hypothesis that plasma levels of gonadal hormones are elevated in sedentary birds, thus inhibiting autumnal migration. Plasma levels of LH and of testosterone were low in both adult and first-year free-living males, although testosterone levels were higher in migratory than in sedentary free-living first-year males. In captivity, however, testosterone levels were not different between first-year sedentar...
In males it is frequently testosterone (T) that activates the expression of sexually selected mor... more In males it is frequently testosterone (T) that activates the expression of sexually selected morphological and behavioral displays, but the role of T in regulating similar traits in females is less clear. Here, we combine correlational data with results from T and gonadotropin-releasing hormone (GnRH) manipulations in both sexes to assess the role of T in mediating sexually dimorphic coloration and morphology in the red-backed fairy-wren (Malurus melanocephalus). We show that: (1) natural variation in female expression of ornamental traits (darkened bills and red back feathers) is positively associated with age and circulating androgen titres, (2) females have the capacity to express most male-typical traits in response to exogenous T, including carotenoid-pigmented body plumage, shorter feathers, darkened bill and enlarged cloacal protuberance, but (3) appear constrained in production of male-typical melanin-pigmented plumage, and (4) low androgen levels during the pre-nuptial mol...
Embryos of several bird species tolerate acute hypothermia. However, the extent to which it can b... more Embryos of several bird species tolerate acute hypothermia. However, the extent to which it can be tolerated by wild species living under natural conditions is poorly documented. At a single American kestrel (Falco sparverius) nest 15 days into incubation, we observed a 21-h bout of egg neglect by the parents during which nest (egg) temperature averaged 12.7°C. Normal incubation patterns resumed thereafter, and one of three viable eggs hatched 32 days after incubation onset, an incubation period 2.5 days longer than the mean in this study. The nestling appeared to develop and fledge normally. Although embryonic tolerance of extended hypothermia is known to occur in some seabirds, its presence in Falconiformes has not heretofore been recorded. Embryonic hypothermic tolerance may be adaptive in species with extended periods of parental absence during incubation.
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