Non-breeding Males Research Articles

Extreme Sexual Dimorphism in Green Woodhoopoe (Phoeniculus Purpureus) Bill Length: A Case of Sexual Selection?

Abstract Adult male Green Woodhoopoes (Phoeniculus purpureus) are only 5–8% larger than adult females in most linear measures but have 36% longer bills. Such sexual dimorphism may result from sexual selection, reproductive role division, or ecological separation. Here, we show that there is little evidence that sexual selection is currently acting on bill dimorphism in the Green Woodhoopoe. (1) Breeding males did not have longer bills than nonbreeding males. (2) There was no significant relationship between bill length and reproductive success of breeding males. (3) Although there was greater variation in male than in female bill length, the coefficient of variation (5.3%) fell within the range of those for naturally selected traits. (4) Although male bill length was found to be positively allometric with body mass, female bill length followed a similar relationship and there was no significant difference between the allometric slopes of the two sexes. Maintenance of the bill dimorphism by reproductive role division also seems unlikely when considering the nesting and provisioning characteristics of the species. We therefore conclude that the extreme sexual dimorphism in Green Woodhoopoe bill length is maintained by ecological separation to reduce foraging competition. We cannot, however, rule out the possibility that the sexual dimorphism initially evolved as a consequence of sexual selection.

Body condition and physiological changes in male green turtles during breeding

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 276:281-288 (2004) - doi:10.3354/meps276281 Body condition and physiological changes in male green turtles during breeding Tim S. Jessop1,*, Mark Hamann2, Colin J. Limpus3 1Center for Reproduction of Endangered Species, Zoological Society of San Diego, San Diego, California 92112, USA 2Queensland Parks and Wildlife Service, PO Box 1735, Bundaberg, Queensland 4670, Australia 3Department of Environment, PO Box 155, Brisbane, Queensland 4002, Australia *Email: tjessop@sandiegozoo.org ABSTRACT: Investigations were made into the body condition, energy metabolite and endocrinal changes of male green turtles Chelonia mydas prior to and during their vernal breeding period in the southern Great Barrier Reef. Prior to migration, breeding males exhibited a higher body condition index than non-breeding males. However, during the migratory reproductive period, breeding males lost significant body condition. Concurrent with these physical changes, breeding males showed a reduction in plasma triglycerides and an increased level of total protein towards the mid- to late breeding period. The plasma steroids corticosterone and testosterone increased and decreased, respectively, during the migratory/breeding phase. The pattern of change in body condition and physiology allude to a high-activity fasting period during the migratory/breeding phase of the male green turtle¹s life history. These marked physiological events during breeding suggest a proximate basis for terminating seasonal reproductive events, and a potential basis for phenotypic variation in male reproductive tactics. KEY WORDS: Chelonia mydas · Male green turtle · Reproduction · Energy requirements · Physiological changes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 276. Online publication date: August 02, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Territorial aggression and hormones during the non-breeding season in a tropical bird

The hormonal control of territorial aggression in male and female vertebrates outside the breeding season is still unresolved. Most vertebrates have regressed gonads when not breeding and do not secrete high levels of sex steroids. However, recent studies implicate estrogens in the regulation of non-breeding territoriality in some bird species. One possible source of steroids during the non-breeding season could be the adrenal glands that are known to produce sex steroid precursors such as dehydroepiandrosterone (DHEA). We studied tropical, year-round territorial spotted antbirds ( Hylophylax n. naevioides) and asked (1) whether both males and females are aggressive in the non-breeding season and (2) whether DHEA is detectable in the plasma at that time. We conducted simulated territorial intrusions (STIs) with live decoys to male and female free-living spotted antbirds in central Panama. Non-breeding males and females displayed robust aggressive responses to STIs, and responded more intensely to decoys of their own sex. In both sexes, plasma DHEA concentrations were detectable and higher than levels of testosterone (T) and 17β-estradiol (E 2). In males, plasma DHEA concentrations were positively correlated with STI duration. Next, we conducted STIs in captive non-breeding birds. Captive males and females displayed robust aggressive behavior. Plasma DHEA concentrations were detectable in both sexes, whereas T was non-detectable (E 2 was not measured). Plasma DHEA concentrations of males were positively correlated with aggressive vocalizations and appeared to increase with longer STI durations. We conclude that male and female spotted antbirds can produce DHEA during the non-breeding season and DHEA may serve as a precursor of sex steroids for the regulation of year-round territorial behavior in both sexes.

Androgens and the Immunocompetence Handicap Hypothesis: Unraveling Direct and Indirect Pathways of Immunosuppression in Song Sparrows

The immunocompetence handicap hypothesis proposes that testosterone (T)‐dependent sexual signals are honest indicators of male health or genetic quality because only high‐quality males are able to withstand the obligate effects of T‐induced immunosuppression. In birds, the basic assumption that T suppresses immune function is equivocal, and the physiological mechanisms underlying T‐induced immunosuppression remain to be investigated. We explored the proximate pathways of T‐induced immunosuppression in song sparrows (Melospiza melodia) by treating captive nonbreeding males with different androgens and measuring several components of acquired immune function. Males implanted with T suppressed cell‐mediated and humoral immune responses compared to males implanted with 5∝‐dihydrotestosterone (DHT), dehydroepiandrosterone, or control (empty) implants. Furthermore, T treatment increased plasma levels of corticosterone and decreased body mass and fat stores in relation to other treatments. The failure of DHT to depress immune function suggests that T‐induced immunosuppression does not occur through a direct pathway because both T and DHT bind to androgen receptors on target cells. Instead, we outline indirect pathways that are likely responsible for suppression of the avian immune system that include stress‐induced immunosuppression, aromatization to estrogen, and alterations in energy allocation that constrain expenditures toward immune system activation.

Indirect consequences of parental care: sex differences in ectoparasite burden and cleaner-seeking activity in longfin damselfish

Many direct costs of parental care have been described for teleost fishes, including reduced body weight, body fat and immune condition. However, few studies have focussed on the indirect consequences of reproduction. In this study, we investigated such consequences in the longfin damselfish Stegastes diencaeus (Jordan & Rutter), a territorial reef fish in which the males provide parental care of eggs. More specifically, we examined patterns of spatial distribution of males and females in relation to substratum suitability for the establishment of nest sites and the consequences of spatial distribution for ectoparasite burden and cleaner-seeking activity. The territories of males and females differed significantly in a number of habitat features. Breeding males, with a nest site present in their territory, were found mainly at the periphery of reef patches, near sand, where vertical substratum suitable for nest sites is present, whereas females and non-breeding males were found in the centre of patches. Cleaning stations occupied by the cleaning gobies Elacatinus evelynae and E. prochilos were also located in peripheral areas, thus, in general, breeding males were closer to cleaning stations than females. Damselfish that were closer to cleaning stations visited them more frequently. During nest-guarding periods, males visited cleaning stations less frequently than during non-guarding periods, but this was not concomitant with an increase in ectoparasite loads during nest-guarding periods. Damselfish in peripheral territories had significantly lower ectoparasite numbers than those situated in the centre of reef patches. These results are consistent with a lower exposure of peripheral damselfish to ectoparasites. These intersexual differences in territory position, proximity to and use of cleaning stations, and ectoparasite loads are indirect consequences of sex differences in reproductive-resource requirements. Such interactions between breeding systems, distributional ecology and other aspects of non-reproductive behaviour are undoubtedly widespread, and their consideration could enhance our general understanding of reef-fish ecology.

Interaction between the introduced eastern mosquitofish and two autochthonous Spanish toothcarps

In aquaria, adults and young‐of‐the‐year (YOY) of both Spanish toothcarp Aphanius iberus and Valencia toothcarp Valencia hispanica received more aggression in the presence of eastern mosquitofish Gambusia holbrooki. YOY of both species also showed decreased feeding rates, as did V. hispanica adults. Adult V. hispanica also were more aggressive themselves and had their reproductive behaviour disrupted. Cases of eastern mosquitofish predation on small A. iberus were also observed. The occurrence and intensity of these potentially harmful effects, however, seemed to be modulated by water temperature, reproductive condition, relative size of the interacting fishes and species‐specific habitat preferences. Thus, aggression almost disappeared at low water temperatures. Valencia hispanica and eastern mosquitofish used similar vertical positions in the water column and this apparently increased the frequency of their interactions. In contrast, A. iberus preferred positions closer to the bottom than the other two species and this vertical segregation appeared to lead to less direct interaction with eastern mosquitofish. In an outdoor mesocosm experiment, under semi‐natural conditions, the presence of eastern mosquitofish resulted in an almost 70% reduction in the number of o.spring produced by A. iberus. The addition of extra, non‐breeding males of A. iberus had no significant effect. YOY A. iberus from cages with eastern mosquitofish or extra males were significantly smaller (c. 1 mm, or 8% shorter) than those from cages without additional fish. Results for V. hispanica were not conclusive, as very few YOY were recovered. In contrast, eastern mosquitofish did not affect the survivorship of breeding adults of both native species.

Carotenoid status signaling in captive and wild red-collared widowbirds: independent effects of badge size and color

Carotenoid-based plumage ornaments are typically considered to be sexually selected traits, functioning as honest condition-dependent signals of phenotypic quality, but few studies have addressed the function of carotenoid color variation in male contest competition. Using two experiments, we investigated the status signaling function of the variable (ranging from yellow to red) carotenoid throat patch (collar) in the polygynous, sexually dimorphic red-collared widowbird (Euplectes ardens). First, we tested if the red collar functions as a dominance signal by painting spectrometrically controlled collar patches onto the brown plumage of nonbreeding males and staging dyadic male contests over food resources. Red-collared males dominated orange males, which in turn dominated the control brown and novel blue collars. Red dominance persisted when the collar manipulations were reversed within dyads and also when tested against testosterone implanted males. In the second experiment the collar size and color of breeding males were manipulated in the field before and after territories were established. All males with enlarged red and most with enlarged orange or reduced red collars obtained territories, whereas most males with reduced orange and all with blackened (removed) collars failed to establish or retain territories. In addition, among the territorial males, those with reduced signals defended smaller territories, received more intrusions, and spent more time in aggressive interactions. Redness and, to a lesser extent, size of the carotenoid ornament both seem to independently indicate male dominance status or fighting ability in male contest competition. Copyright 2002.

Localization of the cytochrome p450 side-chain cleavage enzyme in the inactive testis of the naked mole-rat.

Spermatogenesis was histologically examined in non-breeding male of the naked mole rat (Heterocephalus glaber) using a light microscopy. Spermatogonia, spermatocytes and spermatids were confirmed in the seminiferous tubules. However, the spermatogenesis was disordered, and many spermatocytes and spermatids were sloughing. Sperms could not be seen in the lumen of the tubules. The characteristic accumulation of interstitial cells was the most noteworthy. In the immunohistochemistry for cytochrome p450 side-chain cleavage enzyme, immunoreactions were not entirely distributed in each interstitial cell, although positive reactions were scattered in the interstitial cell-mass. The findings indicate that few interstitial cells act as a testosterone-synthesizing apparatus in the characteristic structure with accumulated cell-mass. From the immunohistochemical data we suggest the possibility that spermatogonia and Sertoli cells may secrete 17 beta-estradiol. We also suggest that 17 beta-estradiol from spermatogonia and Sertoli cells may inhibit the interstitial cells from synthesizing and secreting testosterone and may suppress the later stages of the spermatogenesis to induce apoptosis of germ cells. The TUNEL methods demonstrated that cell death occurred in some spermatocytes in non-breeding males.

Seasonal and Sexual Dimorphisms in the Green Anole Forebrain

During the breeding season, male green anole lizards extend a throat fan (dewlap) in courtship. This behavior is facilitated by testosterone (T). Females extend a much smaller dewlap less often, even with the same dose of T. During the nonbreeding season when T is low, dewlap extension is reduced. To determine if parallels exist between structure and function, we investigated neuron soma size and density in the preoptic area (POA) and ventromedial nucleus of the amygdala (AMY), which are involved in the display behavior, in breeding and nonbreeding males and females. Cells from breeding animals were larger than cells from nonbreeding animals, but they were not sexually dimorphic. No significant effects existed in neuron density. This experiment indicates that portions of the anole forebrain important for sexual behavior are plastic and might be influenced by seasonal changes in steroid hormones. To investigate whether T can reverse the seasonal difference in soma size in both sexes, gonadectomized nonbreeding anoles were implanted with an empty or T propionate-filled capsule; animals were also tested for male-typical courtship behavior. Males and females treated with T had higher rates of dewlap extension, but across treatment groups these rates were greater in males. Neuron soma size in the POA and AMY was larger in males than females, but no effects of treatment were detected. Taken together, the results indicate that T can stimulate behavior in the nonbreeding season and suggest that a dissociation exists between the regulation of the courtship display and soma size of relevant brain regions.

Dynamic Endocrine Responses to Stress: Evidence for Energetic Constraints and Status Dependence in Breeding Male Green Turtles

During reproduction, male vertebrates may exhibit a continuum of interactions between sex and adrenal steroids during stressful events, the outcome of which may be important in either reducing or promoting male reproductive success. We studied adult male green turtles (Chelonia mydas) to examine if they altered plasma corticosterone (CORT) and androgen levels in response to a standardized capture/restraint stressor as potential mechanisms to maintain reproductive activity during stressful events. At the population level, we found that migrant breeding males had a significantly smaller CORT response to the capture/restraint stressor compared to nonbreeding males and that this decreased response coincided with the generally poorer body condition of migrant breeders. In contrast, plasma androgen levels decreased significantly in response to the capture/restraint stressor in migrant breeding males, but not in nonbreeding and premigrant breeding males. For individual migrant breeding males, the magnitude of their CORT and androgen responses to the capture/restraint stressor was highly correlated with their body condition and body length, respectively. Our results demonstrate that male green turtles exhibit complex interactions in their endocrine responses to a capture/restraint stressor and that variation in these interactions is associated with differences in males' reproductive, energetic, and physical state. We hypothesize that interplay between physical status and plasma hormone responses to stressors could have important consequences for male green turtle reproduction.

Energy expenditure and testosterone in free-living male yellow-pine chipmunks.

The onset of mating in yellow-pine chipmunks (Tamias amoenus) follows emergence from a prolonged period of energy conservation during hibernation. Energy expenditures are greatly accelerated to meet the demands of the reproductive season. When emerging from hibernation, typical male chipmunks (breeders) have enlarged testes and a high level of plasma testosterone (T). However, certain males that do not participate in reproduction (nonbreeders) maintain small testes and low plasma T levels and emerge several weeks later than the breeders. The timing of the terminal arousal from hibernation and onset of mating are associated with increased plasma T levels. Experimental elevation of T levels in T. amoenus outside the mating season has been associated with a decrease in body mass, further suggesting an effect of T on energy balance. To test this hypothesis, we measured daily energy expenditure (DEE) in free-living, nonbreeding male chipmunks in the presence and absence of a T-implant. We also measured DEE in breeding males when endogenous T levels were high. DEE of the nonbreeders was not affected by our manipulation of plasma T, and the DEE of breeding males did not differ from that of nonbreeders. We conclude that energy expenditure on a daily basis in male yellow-pine chipmunks is not influenced by levels of T. However, on a seasonal basis, the earlier emergence from hibernation by breeding males, which appears to be influenced by T, represents an overall seasonal energy expenditure that exceeds that of nonbreeding males.

The mate-guarding behaviour of male kokanee oncorhynchus nerka

AbstractThe patterns of mate-guarding in kokanee (non-anadromous Oncorhynchus nerka) are analysed and discussed in relation to existing theory of precopulatory mate-guarding. Male salmon typically guard females prior to spawning events and aggressively exclude other males from their vicinity. Mate-guarding is thought to increase the likelihood of releasing gametes before other males (during a spawning event) and fertilising the greatest proportion of the clutch. The optimal duration of mate-guarding can be considered in a game context because the mate-guarding behaviour of other males influences the probability of finding an unguarded female if a male leaves a female in search of other opportunities. At the Meadow Creek spawning channel, males guarded females, searched for unguarded females, or joined groups of non-breeding males and females. In accordance with mate-guarding theory, males continued to guard the same females after presumed spawning events (but during her egg deposition period) more often than expected on the basis of random pairing. This prevented some males from ever pairing with females. Gaining familiarity with habitat features may confer a competitive advantage to mate-guarding males and may favour prolonged mate-guarding. Because of the importance of finding nesting females quickly, before other males, unpaired males may wait for pairing opportunities rather than occupy distant satellite positions to breeding pairs.

Dehydroepiandrosterone in Songbird Plasma: Seasonal Regulation and Relationship to Territorial Aggression

Many male animals are territorial in the breeding season, when plasma testosterone (T) levels are high, and nonterritorial in the nonbreeding season, when plasma T levels are basal. In contrast to this common pattern, male song sparrows (Melospiza melodia morphna) are territorial year-round, except briefly during molt. Song sparrows are highly aggressive in the nonbreeding season (autumn and winter), even though plasma T, 5α-dihydrotestosterone, androstenedione (AE), and 17β-estradiol levels are undetectable (≤0.1 ng/ml). Castration has no effect on nonbreeding territoriality. However, aromatase inhibitors decrease aggression in the nonbreeding season, indicating a role for estrogens in winter. The androgenic substrate for brain aromatase in winter is unclear, because plasma T and AE levels are basal. Here, we measured plasma levels of dehydroepiandrosterone (DHEA). DHEA is a precursor to AE and T, and the avian brain can convert DHEA into sex steroids. In nonbreeding male song sparrows, plasma levels of DHEA were detectable and several times higher than plasma AE and T levels. Plasma DHEA levels were similar in the breeding and nonbreeding seasons, but significantly lower during molt, which parallels seasonal changes in male aggression. Adrenal glands and testes from nonbreeding males had high concentrations of DHEA, suggesting that both tissues may secrete DHEA. However, stress and gonadotropin-releasing hormone (GnRH) did not increase plasma DHEA in nonbreeding birds. We hypothesize that in the nonbreeding season, circulating DHEA, possibly of adrenal origin, is converted into active sex steroids by steroidogenic enzymes in the brain. This mechanism would create high local levels of sex steroids in the brain to support winter aggression.

Male Colour Type and Lifetime Breeding Success in the Pied FlycatcherFicedula hypoleuca

Abstract. The lifetime breeding success of male Pied Flycatchers was evaluated over a period of nine years (1991–99). The breeding success of males recorded in at least two breeding seasons, and nesting at least once in the study area, was analysed. The lifespan number of offspring was positively and significantly correlated with longevity. The reproductive investment in the first year of life did not correspond with longevity, and hence nonbreeding males in the first year did not compensate for the losses in fecundity. There were no differences in longevity between dark, intermediate and female-like coloured males. Darker males were less successful in their breeding attempts in the first year than paler birds. Breeding in the first year of life positively influenced the future number of fledglings, and the greater investment in reproduction in this year positively affected future brood size in dark males. Among males successfully breeding in the study area from their first season, dark males reared signi...

Reproduction at All Costs: The Adaptive Stress Response of Male Arctic Ground Squirrels

We tested the hypothesis that adult male arctic ground squirrels (Spermophilus parryii plesius) exhibit an adaptive stress response during the mating period that may compromise their survival, whereas males at other times (nonreproductive adult males and juvenile males) have a normal functional stress response. We assessed the physiological responsiveness of the stress axis, of energy mobilization, and of the immune response by subjecting adult breeding males, adult nonbreeding males, and juvenile males to a hormonal challenge and an immunocompetence challenge. At the onset of the breeding season in spring, only 25–30% of the population were males, and of those present during the mating period, half disappeared soon thereafter, and 82% were not replaced by immigrants. Adult breeding males had the highest levels of free cortisol, the lowest maximum corticosteroid-binding capacity, slight dexamethasone resistance, the lowest hematocrit, the lowest number of white blood cells, the highest number of eosinophils, and the poorest ability to respond to the foreign antigen challenge in comparison with the other two male classes. All of these characteristics were indicative of chronic stress in breeding males that may directly compromise their survival. Juvenile males in mid-August also showed many, but not all of these characteristics, indicative of a prolonged period of stress, presumably associated with the period of dispersal. Testosterone levels remained high irrespective of age or breeding condition, decreased when dexamethasone was injected, and increased when ACTH was injected. These latter results are unique in mammals. High testosterone levels and their augmentation with stressors may play a key role in maintenance of aggressive behavior. We conclude that breeding male arctic ground squirrels exhibit an adaptive stress response in which they trade off survival for reproduction. We hypothesize that similar stress responses may have evolved in other species with comparable life histories.

REPRODUCTION AT ALL COSTS: THE ADAPTIVE STRESS RESPONSE OF MALE ARCTIC GROUND SQUIRRELS

We tested the hypothesis that adult male arctic ground squirrels ( Spermo- philus parryii plesius) exhibit an adaptive stress response during the mating period that may compromise their survival, whereas males at other times (nonreproductive adult males and juvenile males) have a normal functional stress response. We assessed the physiological responsiveness of the stress axis, of energy mobilization, and of the immune response by subjecting adult breeding males, adult nonbreeding males, and juvenile males to a hormonal challenge and an immunocompetence challenge. At the onset of the breeding season in spring, only 25-30% of the population were males, and of those present during the mating period, half disappeared soon thereafter, and 82% were not replaced by immigrants. Adult breeding males had the highest levels of free cortisol, the lowest maximum corticosteroid- binding capacity, slight dexamethasone resistance, the lowest hematocrit, the lowest number of white blood cells, the highest number of eosinophils, and the poorest ability to respond to the foreign antigen challenge in comparison with the other two male classes. All of these characteristics were indicative of chronic stress in breeding males that may directly com- promise their survival. Juvenile males in mid-August also showed many, but not all of these characteristics, indicative of a prolonged period of stress, presumably associated with the period of dispersal. Testosterone levels remained high irrespective of age or breeding condition, decreased when dexamethasone was injected, and increased when ACTH was injected. These latter results are unique in mammals. High testosterone levels and their augmentation with stressors may play a key role in maintenance of aggressive behavior. We conclude that breeding male arctic ground squirrels exhibit an adaptive stress response in which they trade off survival for reproduction. We hypothesize that similar stress re- sponses may have evolved in other species with comparable life histories.

Primary sex ratio bias in an endangered cooperatively breeding bird, the black-eared miner, and its implications for conservation

The aim of our study was to investigate primary and adult sex ratios in the cooperatively breeding black-eared miner, Manorina melanotis. We used genetic methods to determine the sex of all birds. Observations were made to quantify differences in helping behaviour between the sexes. As in other miners, Manorina spp., non-breeding males provided most of the help in raising young. Male and female nestlings did not differ significantly in weight, suggesting that both sexes are equally costly to produce. Like other miners, the adult sex ratio in black-eared miners is male-biased (64.4%). However, unlike its congeners, the black-eared miner’s primary sex ratio was strongly biased toward females (62.5%). This suggests that females suffer higher juvenile mortality than males. Our study illustrates how understanding sex ratios is both of theoretical interest and relevant to biological conservation.

High levels of extra-pair paternity in an isolated, low-density, island population of tree swallows (Tachycineta bicolor).

Molecular genetic studies have suggested that apparently nonbreeding males ('floaters') may account for a significant proportion of extra-pair paternity (EPP) in avian populations. Attempts to determine the influence of breeding density on EPP are therefore confounded by the presence of a subpopulation of floaters whose numbers are difficult to estimate. To study EPP in a tree swallow (Tachycineta bicolor) population with few floaters, we chose a nestbox grid on an island with an excess of available breeding sites and very few floaters. We obtained DNA samples from 13 complete families and performed DNA profiling on them using four microsatellite loci. For comparison, we also obtained a sample of 58 extra-pair young (EPY) from a mainland population typed at five microsatellite loci. Paternity assignments among resident males in both populations were made using the microsatellite profiles and a likelihood-based statistical method. Of the 67 island nestlings typed, we found 37 (55%) nestlings from 11 (85%) different nests that were EPY. The proportion of nestlings that were EPY and the proportion of broods containing EPY did not differ significantly between island and mainland populations studied previously. There was no significant difference between island and mainland populations in the proportion of extra-pair paternities assigned among neighbouring resident males. Male breeding density does not appear to affect the ability of female tree swallows to obtain extra-pair fertilizations, at least over the range of densities studied so far. The rate of EPP has remained remarkably consistent over many years, studies and populations implying an important role of active female choice in determining EPP.

Androgen Metabolism in the Brain of the Green Anole Lizard (Anolis carolinensis): Effects of Sex and Season

Courtship behavior in male green anoles is partly mediated by the 5α-reductase enzyme, which converts testosterone (T) to 5α-dihydrotestosterone. This study aimed to determine whether the activity of 5α-reductase is enhanced in breeding males compared to females and nonbreeding males who do not normally display masculine behaviors. In some cases, aromatase, which converts T to 17β-estradiol, also was assessed to determine whether the pattern of its activity in anoles is similar to that in other vertebrates. 5α-Reductase is greatest in the brainstem, so its activity was determined separately in homogenates of whole brain and brainstems. The following comparisons were done in different assays: (1) breeding males with breeding females, (2) nonbreeding males with nonbreeding females, and (3) breeding males with nonbreeding males. Aromatase activity was greater in breeding males (mean ± SE, 0.61 ± 0.06 fmol/min/mg protein) than in breeding females (0.41 ± 0.08 fmol/min/mg protein). It was also greater in breeding males (0.84 ± 0.16 fmol/min/mg protein) than in nonbreeding males (0.33 ± 0.07 fmol/min/mg protein). In contrast, sex or seasonal differences did not exist in 5α-reductase activity. The results are consistent with those of other vertebrate species in which male-biased sex dimorphisms and seasonal differences occur in aromatase, but not in 5α-reductase activity. The greater levels of aromatase activity in breeding male anoles suggest that this enzyme might mediate male-specific functions. The equivalently high levels of 5α-reductase activity in both sexes suggests that, in addition to facilitating male courtship behavior, the enzyme has a basic function common to both sexes.

Effects of Habitat Fragmentation on Pairing Success of Ovenbirds: Importance of Male Age and Floater Behavior

AbstractBetween 1996 and 1998, we compared pairing success of territorial male Ovenbirds (Seiurus aurocapillus) in forest fragments created by forestry (n = 3) and agriculture (n = 10) to contiguous forest plots (n = 3) in the southern boreal mixedwood forest of central Saskatchewan. The percentage of Ovenbird males paired per site was lower in fragments created by agriculture (86 ± 3%) and forestry (87 ± 3%) than in contiguous forest (97 ± 3%). At the individual level, second-year males (82%) were less likely to be paired than after-second-year males (94%), whereas males closer to edges were less likely to be paired than those in forest interiors. Although pairing success differed among landscapes, those differences were smaller than reported in studies conducted in eastern North America. The high density of birds in our study area may have resulted in intense intraspecific competition, which could have prevented unpaired individuals from maintaining territories. Removal experiments in 1997 and 1998 demonstrated floaters occurred in contiguous forest, but rarely occurred in fragments created by agriculture. The presence of floaters in contiguous forest suggests the ratio of breeding to nonbreeding males in forest fragments and contiguous forest may be similar, but that the strategy (i.e. floater vs. territorial) used by unpaired birds may differ among landscapes.