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 17beta-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.     

Oestrogen receptor beta is not present in the pilosebaceous unit of red deer skin during the non-breeding season

Androgens and oestrogens both have roles in skin physiology. Recently a second oestrogen receptor (ERbeta) has been identified in androgen-dependent tissues. The red deer grows a breeding season, androgen-dependent mane when plasma testosterone rises; this is replaced with small neck hairs during the non-breeding season. In non-breeding season deer skin, ERbeta was localised to the blood vessels and arrector pili muscle, but in contrast to human skin, not in the pilosebaceous unit or epidermis. The androgen receptor was not expressed. Further studies with breeding season skin may help to elucidate whether serum androgens or androgen receptor expression can modulate the expression of ERbeta in skin.     

Combined effects of DHEA and fadrozole on aggression and neural VIP immunoreactivity in the non-breeding male song sparrow

The male Song Sparrow, Melospiza melodia morphna, shows high levels of aggression in its non-breeding season, concomitant with basal levels of circulating testosterone (T) and estradiol (E(2)). However, administration of fadrozole, an aromatase inhibitor, decreases non-breeding aggression in the field. Circulating levels of dehydroepiandrosterone (DHEA), an androgen/estrogen precursor, correspond to the seasonal expression of aggression in this species, with high levels in the breeding and non-breeding seasons when aggression is also high, and lower levels during the molt when aggression is low. We test the hypothesis that circulating DHEA up-regulates non-breeding aggression via an aromatase-mediated mechanism. We also hypothesize that this up-regulation of aggression is partially mediated by changes in vasoactive intestinal polypeptide (VIP) in the lateral extent of the bed nucleus of the stria terminalis (BSTl) and lateral septum (LS). Birds were administered either DHEA, fadrozole, or both for 2 weeks and tested for aggression in a lab-based paradigm. As predicted, birds given DHEA were significantly more aggressive. However, fadrozole did not block this effect, and, when administered without DHEA, also led to increased aggression over controls. These results may be explained by the fact that the behaviors measured in field tests, which include more direct attack behaviors, may be under different hormonal regulation than the behaviors measured in the lab paradigm, which represent warning, or threat, behaviors. VIP immunoreactivity (VIP-ir) changed across multiple brain regions with this treatment regimen, most notably in the LSO/VFI subdivision of the lateral septum.     

Territorial aggression does not feed back on testosterone in a multiple-brooded songbird species with breeding and non-breeding season territoriality,the European stonechat

Testosterone mediates reproductive behaviours in male vertebrates. For example, breeding season territoriality depends on testosterone in many species of birds and in some, territorial interactions feed back on testosterone concentrations. However, the degree to which territorial behaviour and testosterone are associated differs even between species with seemingly similar life histories, especially between species that also defend territories outside the breeding season. Here, we investigate the link between territorial behaviour and testosterone in European stonechats. Previous studies found that territorial aggression in stonechats depends on testosterone in a breeding, but not in a non-breeding context. We investigated whether stonechats show a rise in testosterone during simulated territorial intrusions (STI) during the breeding season. Post-capture testosterone concentrations of males caught after an STI were not higher than those of males caught in a control situation regardless of breeding stage. However, most of the males would have been able to mount a testosterone response because the same individuals that did not increase testosterone during the STI showed a substantial increase in testosterone after injections of gonadotropin-releasing hormone (GnRH). GnRH-induced and post-capture testosterone concentrations were positively correlated and both decreased with successive breeding stages. Further, territory owners with a short latency to attack the decoy expressed higher post-capture testosterone concentrations than males with a longer latency to attack the decoy. Thus, there is no evidence for behavioural feedback on testosterone concentrations during male-male interactions in stonechats. In combination with previous studies our data suggest that testosterone functions as an on/off switch of high intensity territorial aggression during the breeding season in stonechats. The among-species variation in the androgen control of territorial behaviour may be only partly a result of environmental differences. Instead, potential differences in how territoriality evolved in different species may have influenced whether and how a reproductive hormone such as testosterone was co-opted into the mechanistic control of territorial behaviour.     

Oestrogen receptor-alpha regulates non-canonical Hedgehog-signalling in the mammary gland

Mesenchymal dysplasia (mes) mice harbour a truncation in the C-terminal region of the Hh-ligand receptor, Patched-1 (mPtch1). While the mes variant of mPtch1 binds to Hh-ligands with an affinity similar to that of wild type mPtch1 and appears to normally regulate canonical Hh-signalling via smoothened, the mes mutation causes, among other non-lethal defects, a block to mammary ductal elongation at puberty. We demonstrated previously Hh-signalling induces the activation of Erk1/2 and c-src independently of its control of smo activity. Furthermore, mammary epithelial cell-directed expression of an activated allele of c-src rescued the block to ductal elongation in mes mice, albeit with delayed kinetics. Given that this rescue was accompanied by an induction in estrogen receptor-alpha (ERα) expression and that complex regulatory interactions between ERα and c-src are required for normal mammary gland development, it was hypothesized that expression of ERα would also overcome the block to mammary ductal elongation at puberty in the mes mouse. We demonstrate here that conditional expression of ERα in luminal mammary epithelial cells on the mes background facilitates ductal morphogenesis with kinetics similar to that of the MMTV-c-src^Act mice. We demonstrate further that Erk1/2 is activated in primary mammary epithelial cells by Shh-ligand and that this activation is blocked by the inhibitor of c-src, PP2, is partially blocked by the ERα inhibitor, ICI 182780 but is not blocked by the smo-inhibitor, SANT-1. These data reveal an apparent Hh-signalling cascade operating through c-src and ERα that is required for mammary gland morphogenesis at puberty.     

Mating season aggression and fecal testosterone levels in male ring-tailed lemurs (Lemur catta)

The challenge hypothesis (J. C. Wingfield, R. E. Hegner, B. G. Ball, and A. M. Duffy, 1990, Am. Nat. 136, 829-846) proposes that in birds, reptiles, and fish, "the frequency or intensity of reproductive aggression as an effect of T[estosterone] is strongest in situations of social instability, such as during the formation of dominance relationships, the establishment of territorial boundaries, or challenges by a conspecific male for a territory or access to mates" (p. 833). To determine the extension of this hypothesis to mammalian species, we tested predictions of the hypothesis in a nonpaternal, seasonal breeding, prosimian primate (ring-tailed lemurs, Lemur catta). Semi-free-ranging males were studied during periods of social stability (premating period) and instability (mating period). The annual mating season consists of several days during which males fight for access to promiscuous group females as each individually becomes sexually receptive for 1 day. Male rates of aggression were compared to fecal testosterone levels within premating and mating periods. In the premating period male rate of aggression was not significantly correlated with testosterone level. By contrast, during the mating season testosterone and aggression levels were positively and significantly correlated. However, on days just preceding estrus, male rate of aggression was not significantly correlated with testosterone, but on days of estrus, when aggressive challenges peaked sharply, testosterone and aggression were highly positively correlated. These results suggest that the challenge hypothesis applies to mammals as well as to birds, reptiles, and fish. In addition, elevations in testosterone were tightly circumscribed around days of estrus, suggesting a compromise between costs and benefits of elevated testosterone levels.     

Habitat use of Tibetan Eared Pheasant Crossoptilon harmani flocks in the non-breeding season

Habitat use by Tibetan Eared Pheasant Crossoptilon harmani flocks in shrub vegetation was investigated in the Lhasa area of Tibet during the non-breeding season of 19951996. Home range composition varied considerably among flocks, but stream belts were consistently used as foraging grounds. Slope direction, altitude and vegetation had little effect on habitat selection. In the absence of supplemental food, core range size was positively correlated with flock size, suggesting that food supplementation could support larger flocks. Flocks regularly roosted on the ground at midday at two or three relatively fixed sites within core ranges. At night they used patches of relatively tall, dense vegetation at the year-round sites in areas near cliffs or in hollows. The size of the night-roost site was related to flock size. Our results strongly suggested that both foraging and night-roosting habitats in the shrub environment are crucial to the birds.     

New estrus synchronization and artificial insemination protocol for goats based on male exposure, progesterone and cloprostenol during the non-breeding season

This study assesses the effectiveness of a method designed to induce and synchronize ovulation in goats during the non-breeding season, allowing for systematic timed artificial insemination (AI), without the need for prior estrus detection. This method (IMA.PRO2) induces ovulation through the "male effect" and a single 25 mg dose of progesterone given at the time of buck exposure, and early lysis of the induced corpus luteum by the administration of 75 microg of cloprostenol 9 days later. The method was tested in three separate experiments. In experiment 1, estrus was detected in 87.5% of the treated goats 37.0 +/- 1.4 h after cloprostenol administration, with the preovulatory LH surge occurring 40.5 +/- 1.6 h after the cloprostenol injection. In experiment 2, data from 503 does revealed no significant differences in fertility rates between two groups inseminated 48 h (65.5+/-4.0%) or 52 h (63+/-3.0%) after receiving cloprostenol. In experiment 3, 2184 does, comprising 37 replicate groups on 12 farms, were randomly assigned to two trial subgroups. Does in the first subgroup were treated with the IMA.PRO2 method and goats from the second group were given intravaginal progestagens for 11 days, plus 350 IU of eCG and 75 microg of cloprostenol on Day 9 of this treatment. Goats from both subgroups were cervically inseminated at the same time, 50 h after cloprostenol administration in the first group and 46 h after sponge removal in the second. The pregnancy rate achieved with the new method was 64.6%, significantly higher than the yield observed for the use of progestagens plus eCG (46.8%, P<0.01). The simple method proposed as an alternative to the use of progestagen-eCG treatment provides good pregnancy rates to AI undertaken at a fixed time point, and reduces the amount of hormone needed to synchronize estrus in the animals.     

Sex promotes spatial and dietary segregation in a migratory shorebird during the non-breeding season

Several expressions of sexual segregation have been described in animals, especially in those exhibiting conspicuous dimorphism. Outside the breeding season, segregation has been mostly attributed to size or age-mediated dominance or to trophic niche divergence. Regardless of the recognized implications for population dynamics, the ecological causes and consequences of sexual segregation are still poorly understood. We investigate the foraging habits of a shorebird showing reversed sexual dimorphism, the black-tailed godwit Limosa limosa, during the winter season, and found extensive segregation between sexes in spatial distribution, microhabitat use and dietary composition. Males and females exhibited high site-fidelity but differed in their distributions at estuary-scale. Male godwits (shorter-billed) foraged more frequently in exposed mudflats than in patches with higher water levels, and consumed more bivalves and gastropods and fewer polychaetes than females. Females tended to be more frequently involved and to win more aggressive interactions than males. However, the number of aggressions recorded was low, suggesting that sexual dominance plays a lesser role in segregation, although its importance cannot be ruled out. Dimorphism in the feeding apparatus has been used to explain sex differences in foraging ecology and behaviour of many avian species, but few studies confirmed that morphologic characteristics drive individual differences within each sex. We found a relationship between resource use and bill size when pooling data from males and females. However, this relationship did not hold for either sex separately, suggesting that differences in foraging habits of godwits are primarily a function of sex, rather than bill size. Hence, the exact mechanisms through which this segregation operates are still unknown. The recorded differences in spatial distribution and resource use might expose male and female to distinct threats, thus affecting population dynamics through differential mortality. Therefore, population models and effective conservation strategies should increasingly take sex-specific requirements into consideration.     

Coal Tit fat-storing patterns during the non-breeding season: the role of residence status

According to the optimal body mass hypothesis, resident individuals, having priority of resource access and better knowledge of food availability in an area, should carry smaller fat reserves than transients whose resource predictability is lower. We tested this prediction in a free-living population of Coal Tits Parus ater in sub-alpine coniferous forest during three winters. We examined the role of residence status in determining the daily patterns of fat accumulation of individuals using time of day, temperature, season, year and body size as covariates. Only time of day, residence status and temperature significantly affected daily variation of fat score in Coal Tits. Fat scores were higher in transients than residents, although within residents, juveniles did not carry significantly more fat than adults. Our results show that fattening strategies are associated with residence status in the Coal Tit, in support of the hypothesis that transient individuals facing lower food predictability carry larger body fat reserves. The finding that within residents, patterns of fat accumulation did not differ between adults and juveniles, suggests that residence per se , involving higher food predictability, rather than age-related dominance or hoarding behaviour, determines fattening strategies in wild Coal Tits.     

Time budgets of Tibetan eared pheasants during the non-breeding season in an alpine scrub habitat

Time allocations of the group-living Tibetan eared pheasants Crossoptilon harmani with and without supplementary food were investigated by full-day sampling from winter through spring in an alpine scrub zone,south Tibet.At a flock scale,both the different food-supply flocks displayed similar daily patterns of activity,foraging in the morning and evening,and resting around midday.In terms of individual activity,either foraging or resting was highly synchronous with the flock's.Non-provisioned birds spent mor...     

Octopamine in male aggression of Drosophila

BACKGROUND: In mammals and humans, noradrenaline is a key modulator of aggression. Octopamine, a closely related biogenic amine, has been proposed to have a similar function in arthropods. However, the effect of octopamine on aggressive behavior is little understood. RESULTS: An automated video analysis of aggression in male Drosophila has been developed, rendering aggression accessible to high-throughput studies. The software detects the lunge, a conspicuous behavioral act unique to aggression. In lunging, the aggressor rears up on his hind legs and snaps down on his opponent. By using the software to eliminate confounding effects, we now show that aggression is almost abolished in mutant males lacking octopamine. This suppression is independent of whether tyramine, the precursor of octopamine, is increased or also depleted. Restoring octopamine synthesis in the brain either throughout life or in adulthood leads to a partial rescue of aggression. Finally, neuronal silencing of octopaminergic and tyraminergic neurons almost completely abolishes lunges. CONCLUSIONS: Octopamine modulates Drosophila aggression. Genetically depleting the animal of octopamine downregulates lunge frequency without a sizable effect on the lunge motor program. This study provides access to the neuronal circuitry mediating this modulation.     

Interspecific aggression in captive male lemmings

Two experiments were conducted with lemmings to determine which of two species, Lemmus trimucronatus and Dicrostonyx groenlandicus, was capable of exercising aggressive social dominance over the other in staged, dyadic encounters, and which was able to outcompete the other for a single shelter. Agonistic behaviour occurred in all dyadic encounters, but dominance was not established by either species. A sequential analysis of encounters revealed that each species had a distinct fighting strategy. In shelter competition, prior residence was a crucial factor in the outcome. However, one species did not completely exclude the other. Further evidence to support species differences in fighting strategies was derived from the shelter experiments. These results are discussed in relation to ecological considerations.     

Infestations of Ornithonyssus bursa,a haemotophagous mite,on starlings over the non-breeding season

Abstract

Ornithonyssus bursa (Berlese) (Dermanyssidae) is found in nests and neotboxes and on nestlings of the starling (Sturnus vulgaris L.), sometimes in large numbers, during the breeding season. During the non-breeding season the nestboxes and nest material are devoid of live mites. O. bursa overwinters ectoparasitically on starlings, and is present on approximately 25% of the population at the beginning of the breeding season. These nucleus populations build up rapidly in nest boxes during the breeding season.     

House Finch Carpodacus mexicanus roosting behaviour during the non-breeding season and possible effects of mycoplasmal conjunctivitis

We studied House Finch Carpodacus mexicanus roosting behaviour during the non-breeding season using radiotracking and direct observations in Ithaca, NY, USA. In contrast to what has been reported in the literature and in contrast to what should be expected from Newton's European studies of cardueline finches, House Finches roost in small groups (mean 3.5; maximum 11) and do not display at roost sites. Seventy-seven per cent of the birds re-used the same tree on successive observations. In winter, birds re-used the same roost tree more often than in the autumn, and birds with mycoplasmal conjunctivitis tended to move more between roost trees than did birds without conjunctivitis. A small number of radiotagged birds that roosted in the same tree were observed together in the daytime more often than by chance, suggesting the existence of social bonds between birds (some same sex) during the non-breeding season. In the autumn the birds often roosted in leafed deciduous trees and closer to their daytime feeding locations than they did in winter. In winter all birds roosted in evergreen trees. It is possible that the reliable and predictable food sources at feeding sites offered by the public might have changed House Finch roosting behaviour.     

Morphological and functional changes of stallion spermatozoa after cryopreservation during breeding and non-breeding season

The study compared quality and freezability of stallion semen during breeding and non-breeding seasons. Ejaculates were collected twice per week from four stallions during May (n = 24) and December (n = 24). The semen was mixed with skim milk extender, centrifuged and resuspended in fresh extender. Aliquots of this sperm suspension were separated from extender and diluted in TALP medium for sperm evaluation or with cryoextender (type "Gent" or a combination of Triladyl and skim milk). Samples of 0.5ml were cryopreserved in straws using a programmed freezer. Parameters of sperm quality were evaluated before and after freezing/thawing. These included percentages of motile spermatozoa and of morphological intact sperm. Typical injuries were demonstrated by scanning electron microscopy (S.E.M.). The acrosomal status was visualised using FITC-conjugated peanut agglutinin, and the acrosome reaction was induced by calcium ionophore A 23187. The chromatin stability was estimated by acridine orange test.In winter, the average percentages of motile and morphologically normal sperm (67 and 74.3%, respectively) were higher than during the breeding season in May (59 and 65.9%; P < 0.05). After freezing/thawing the proportions of vital and intact sperm decreased significantly. The number of motile sperm declined to 15 and 18% in May and December (range 5-40%), and of morphologically intact sperm to 51% in both seasons. Results of S.E.M. showed typical membrane ruptures in the acrosomal region and some sperm with abnormal necks. The proportion of frozen sperm with spontaneous acrosome reaction was higher during winter (86.5 versus 77.0%), suggesting a higher degree of membrane reactivity. Percentages of spermatozoa with denaturated chromatin were minimal and showed minimal differences between fresh and frozen state, stallions or seasons. An additional decondensation treatment with papain and DTE revealed a slightly enhanced number of spermatozoa with denaturable DNA after cryopreservation, especially in December (5.4 +/- 1.3%). The influence of cryoextenders was not significant for most sperm parameters, but there was a high variability between the stallions. Altogether, the influence of factors on the quality of spermatozoa has the following rank order: cryopreservation > stallion > season. Different cellular structures seem to have different susceptibilities to physicochemical stress. The cryopreservation of sperm during December results in survival rates similar to those measured during the breeding season, even more important for successful preservation is the selection of suitable semen donors.     

Population density and the evolution of male aggression

In some cases male animals engage in aggressive contests for access to females, in others they adopt more passive strategies and invest in traits that assist them in detecting females or in competing with rivals in other ways, such as sperm competition. One possible factor determining the fitness of these different strategies is population density. Theoretically, aggressive tactics should be found at intermediate population densities. At low densities males that invest in traits related to searching for mates could be favoured, whereas at the highest densities males that fight over females might pay excessive costs for this behaviour because of the number of rival males that they will encounter. Current empirical evidence is mostly consistent with this scheme: in some cases it seems that traits that are associated with locating mates are favoured at low densities, with aggression related traits favoured at higher densities, and in other cases aggression is selected but as density increases less aggressive strategies become more common. There remain substantial differences between species, however, and I discuss how variation in mating system, in the costs of aggression and in the nature of sperm competition, plus ecological differences between species, can change the relationship between population density and the fitness consequences of aggressive and passive behavioural strategies.     

The induction of oestrus in ewes during the non-breeding season using pre-used CIDRs and oestradiol-17β treatment

The fertility obtained in sheep after the use of intravaginal progesterone devices is related to the content of progesterone of the device. The hypothesis of this study was that the reproductive response of anoestrous ewes to the ram-effect could be improved by the administration of oestradiol-17β in conjunction with CIDRs treatment—using previously used CIDRs in a 5-day progestagen priming. Therefore, the objective was to determine if oestradiol-17β treatment increases fertility of anoestrous ewes primed with used CIDRs and stimulated by the ram-effect. The hypothesis was tested with CIDRs that had been previously used for 12 or 18 days. The trial was performed during the non-breeding season using 158 Corriedale ewes. Ewes had been isolated from rams since Day −35 (Day 0 = introduction of the rams). A CIDR (0.3 g progesterone, InterAg, Hamilton, New Zealand) was inserted on Day −5 in all ewes with CIDR that had been previously used for 12 days (n = 62) or 18 days (n = 96). Also on Day −5, 29 and 53 ewes that had received CIDRs of 12 or 18 days, respectively, received an intra-muscular treatment of 50 μg of oestradiol-17β (E groups). The ewes that did not receive the oestradiol-17β treatment remained as the control group (C group). Overall the treatment groups were thus: C12 (n = 33), C18 (n = 43), E12 (n = 29), and E18 (n = 53). On Day 0 all CIDRs were withdrawn, and ewes were placed with 18 rams and 20 ewes hormonally induced to exhibit oestrus. Sexual receptivity of ewes treated with CIDRs was estimated from marks on the rumps of the ewes daily from Day 0 to Day 5, and the pregnancy status diagnosed with transrectal ultrasonography on Day 40. The percentage of ewes exhibiting oestrus and pregnancy rates were lower in ewes synchronized with previously used CIDRs for 18 days, compared to those used for 12 days. The responses of ewes in oestrus were 39.4, 14.0, 65.5, and 32.1% for the C12, C18, E12, and E18 groups respectively, with pregnancy rates of 30.3, 14.0, 34.5, and 17.0%. Administration of oestradiol-17β increased the frequency of oestrous response in ewes that were treated with CIDRs previously used for 12 days (P < 0.05), but not in those treated with CIDRs used for 18 days. It could be concluded that the administration of oestradiol-17β only improved the percentage of ewes responding to oestrus when CIDRs previously used for 12 days were used for 5 days before the introduction of rams. No positive effect on fertility was observed irrespective of the period during which CIDR had been previously used.