Resident Males Research Articles

Intrasexual competition enhances reproductive isolation between locally adapted populations.

During adaptation to different habitat types, both morphological and behavioral traits can undergo divergent selection. Males often fight for status in dominance hierarchies and rank positions predict reproductive success. Ecotypes with reduced fighting abilities should have low reproductive success when migrating into habitats that harbor ecotypes with superior fighting abilities. Livebearing fishes in the Poecilia mexicana-species complex inhabit not only regular freshwater environments, but also independently colonized sulfidic (H2S-containing) habitats in three river drainages. In the current study, we found fighting intensities in staged contests to be considerably lower in some but not all sulfidic surface ecotypes and the sulfidic cave ecotype compared with populations from non-sulfidic surface sites. This is perhaps due to selection imposed by H2S, which hampers oxygen uptake and transport, as well as cellular respiration. Furthermore, migrants from sulfidic habitats may lose fights even if they do not show overall reduced aggressiveness, as physiological performance is likely to be challenged in the non-sulfidic environment to which they are not adapted. To test this hypothesis, we simulated migration of H2S-adapted males into H2S-free waters, as well as H2S-adapted cave-dwelling males into sulfidic surface waters. We found that intruders established dominance less often than resident males, independent of whether or not they showed reduced aggressiveness overall. Our study shows that divergent evolution of male aggressive behavior may also contribute to the maintenance of genetic differentiation in this system and we call for more careful evaluation of male fighting abilities in studies on ecological speciation.

"Stink flirting" in ring-tailed lemurs (Lemur catta): Male olfactory displays to females as honest, costly signals.

Sexual selection for honest behavioral displays of quality has driven the development of remarkably complex courtship behavior in many animal species. Olfactory displays are often overlooked as an area of inquiry compared to auditory and visual displays. Ring-tailed lemur (Lemur catta) scent marking of substrates has been studied extensively, although the male olfactory displays of anointing and wafting tails to females has received relatively little attention. We studied the role of male olfactory displays to females, evaluating whether such signals function as honest, costly signals of male dominance status in two groups of wild L. catta at Berenty Reserve, Madagascar. Our results suggest that male tail anointing and tail wafting displays to pre-estrous and estrous females are correlated with male dominance rank, and moreover appear to operate as costly signals, as such displays increase aggression received from males and females while other types of scent marking do not. Furthermore, females showed greater mating preference (as measured by sexual presents) for resident males who performed the "anoint tail" and "waft tail" displays towards them. When males perform the "anoint tail" and "waft tail" displays to females, they receive higher levels of aggression than if they were to perform other types of scent marking. Interestingly, immigrating (peripheral) males performed the "anoint tail" and "waft tail" displays at higher rates than resident males, which could honestly indicate their quality or may simply be associated with the alternative mating strategy of transferring between groups to gain mating opportunities. Our finding that tail anointing and tail wafting displays function as honest signals of dominance for resident males-and that these costly displays appear to positively affect female mate choice-is the first evidence of this function for this particular olfactory signal in L. catta.

Seasonal Changes in Nestmate Discrimination in the Paper Wasp,Polistes metricusSay (Hymenoptera: Vespidae)

Nestmate discrimination in the paper wasp, Polistes metricus Say (Hymenoptera: Vespidae) was examined during each stage (nesting and non-nesting phases) of the colony cycle. Resident wasps of each caste were paired with nestmates or non-nestmates of the same caste in a clear plastic box near the nest in the field and all aggressive and non-aggressive behavioral interactions initiated by the resident wasps were noted. Each wasp caste, particularly the resident foundress, workers, and males exhibited a significantly high proportion of aggressive behaviors towards non-nestmates than towards nestmates, thus demonstrating nestmate discrimination. However, the response of resident fall gynes towards nestmates and non-nestmates was not significantly different. During winter, gynes of P. metricus and P. fuscatus Fabricius were found to overwinter together in the same clusters. The overwintering gynes of P. metricus showed complete tolerance towards conspecifics (non-nestmates) and allospecifics (P. fuscatus). These findings suggest that the acceptance threshold of P. metricus shifts from being restrictive towards the beginning of the nesting phase to being permissive towards the end, which differs from previous studies on P. fuscatus, whose acceptance threshold was more restrictive during the reproductive phase than during the worker phase. However, during the non-nesting (overwintering) phase of the colony cycle, the acceptance threshold likely becomes even more permissive to an “accept-all” level in both species. These shifts in acceptance threshold follow the predictions of Reeve's (1989) conspecific acceptance threshold model, and most likely reflect the cost-benefit ratio assessment of wasps to minimize negative inclusive fitness consequences at each stage of the colony cycle.

Stay-at-home strategy brings fitness benefits to migrants.

In Focus: Lok, T., Veldhoen, L., Overdijk, O., Tinbergen, J. M., & Piersma, T. (2017). An age-dependent fitness cost of migration? Old trans-Saharan migrating spoonbills breed later than those staying in Europe, and late breeders have lower recruitment. Journal of Animal Ecology, 86, 998-1009. In Focus: Grist, H., Daunt, F., Wanless, S., Burthe, S. J., Newell, M. A., Harris, M. P., & Reid, J. M. (2017). Reproductive performance of resident and migrant males, females and pairs in a partially migratory bird. Journal of Animal Ecology, 86, 1010-1021. In this issue, two studies examine the extent to which variation in migratory behaviour influences individual fitness across a population. Lok, Veldhoen, Overdijk, Tinbergen, and Piersma () examine reproductive success and post-fledging survival in a population of Eurasian spoonbills (Platalea leucorodia), comparing individuals that winter in south-west Europe against those migrating to sub-Saharan Africa, while Grist etal. () measure reproductive success in a population of European shags (Phalacrocorax aristotelis) breeding in Scotland that either remain resident or migrate to surrounding waters. Both studies find that individuals migrating longer distances tend to show later initiation of breeding attempts. In turn, longer migration correlates with lower reproductive success in both populations. In spoonbills, this effect is most pronounced in older male birds, while young individuals show little difference in breeding success with respect to migration distance. In shags, fitness benefits of residence were most pronounced when both individuals of a pair were resident, although there was no evidence of assortative mating. Both studies provide fascinating new insights into the role migratory variability can play in shaping population dynamics.

Experience-Dependent Plasticity in Accessory Olfactory Bulb Interneurons following Male-Male Social Interaction.

Chemosensory information processing in the mouse accessory olfactory system guides the expression of social behavior. After salient chemosensory encounters, the accessory olfactory bulb (AOB) experiences changes in the balance of excitation and inhibition at reciprocal synapses between mitral cells (MCs) and local interneurons. The mechanisms underlying these changes remain controversial. Moreover, it remains unclear whether MC-interneuron plasticity is unique to specific behaviors, such as mating, or whether it is a more general feature of the AOB circuit. Here, we describe targeted electrophysiological studies of AOB inhibitory internal granule cells (IGCs), many of which upregulate the immediate-early gene Arc after male-male social experience. Following the resident-intruder paradigm, Arc-expressing IGCs in acute AOB slices from resident males displayed stronger excitation than nonexpressing neighbors when sensory inputs were stimulated. The increased excitability of Arc-expressing IGCs was not correlated with changes in the strength or number of excitatory synapses with MCs but was instead associated with increased intrinsic excitability and decreased HCN channel-mediated IH currents. Consistent with increased inhibition by IGCs, MCs responded to sensory input stimulation with decreased depolarization and spiking following resident-intruder encounters. These results reveal that nonmating behaviors drive AOB inhibitory plasticity and indicate that increased MC inhibition involves intrinsic excitability changes in Arc-expressing interneurons.SIGNIFICANCE STATEMENT The accessory olfactory bulb (AOB) is a site of experience-dependent plasticity between excitatory mitral cells (MCs) and inhibitory internal granule cells (IGCs), but the physiological mechanisms and behavioral conditions driving this plasticity remain unclear. Here, we report studies of AOB neuronal plasticity following male-male social chemosensory encounters. We show that the plasticity-associated immediate-early gene Arc is selectively expressed in IGCs from resident males following the resident-intruder assay. After behavior, Arc-expressing IGCs are more strongly excited by sensory input stimulation and MC activation is suppressed. Arc-expressing IGCs do not show increased excitatory synaptic drive but instead show increased intrinsic excitability. These data indicate that MC-IGC plasticity is induced after male-male social chemosensory encounters, resulting in enhanced MC suppression by Arc-expressing IGCs.

Agonistic interactions in the dragonfly Micrathyria ungulata: does male fighting investment come from an innate ability or an indomitable will?

In fights between males for access to mating territories, the winner may be the rival with the highest fighting capacity or that places the highest value on the disputed site. However, it is also possible that both factors simultaneously affect dispute settlement. Therefore, a better understanding of contest resolution rules may be achieved by simultaneously investigating how winning chances depend on individual motivation linked to resource value and on individual traits linked to fighting capacity. In this study, we used males of the dragonfly Micrathyria ungulata to evaluate whether individual fighting ability, individual motivation, or the interaction between both factors determine the individual investment in territorial contests. For this, we simulated the approach of an intruder to trigger a territorial defense response by either resident (marked males present in the territory for at least 1 day before the experiment) or substitute males (marked males that occupied the territories after we removed the residents). Resident males fought longer against the potential intruder than their substitute counterparts. However, traits related to fighting ability had a marginal effect on the time invested in fights. These results indicate that resident males are more willing to invest in fights regardless of their physical or physiological attributes. Distinct motivational levels among individuals should increase the variation in mean contest duration among rival pairs. If this effect is widespread, it may have important implications for studies that investigate contest rules by relating fighting duration and individual traits. In many species, the winner of territorial fights is the individual with higher fighting ability or the one that values more the disputed resource and consequently is more motivated to fight. However, because these two factors may interact to determine the winner, investigations should benefit by simultaneously evaluating the effect of fighting ability and motivation on contest resolution. Here, we induced fights between focal males against artificially introduced rivals to test if male investment in fights is affected by an interaction between traits linked to fighting ability and motivational status. We showed that the prior occupation of a territory was the main determinant of the time spent fighting. We conclude that the previous occupation of a territory may increase individual motivation to fight due to higher valuation of the resource and eventually may surpass the effect of fighting ability to determine the winner.

Reproductive performance of resident and migrant males, females and pairs in a partially migratory bird.

Quantifying among‐individual variation in life‐history strategies, and associated variation in reproductive performance and resulting demographic structure, is key to understanding and predicting population dynamics and life‐history evolution. Partial migration, where populations comprise a mixture of resident and seasonally migrant individuals, constitutes a dimension of life‐history variation that could be associated with substantial variation in reproductive performance. However, such variation has rarely been quantified due to the challenge of measuring reproduction and migration across a sufficient number of seasonally mobile males and females.We used intensive winter (non‐breeding season) resightings of colour‐ringed adult European shags (Phalacrocorax aristotelis) from a known breeding colony to identify resident and migrant individuals. We tested whether two aspects of annual reproductive performance, brood hatch date and breeding success, differed between resident and migrant males, females and breeding pairs observed across three consecutive winters and breeding seasons.The sex ratios of observed resident and migrant shags did not significantly differ from each other or from 1:1, suggesting that both sexes are partially migratory and that migration was not sex‐biased across surveyed areas.Individual resident males and females hatched their broods 6 days earlier and fledged 0.2 more chicks per year than migrant males and females on average. Resident individuals of both sexes therefore had higher breeding success than migrants.Hatch date and breeding success also varied with a pair's joint migratory strategy such that resident–resident pairs hatched their broods 12 days earlier than migrant–migrant pairs, and fledged 0.7 more chicks per year on average. However, there was no evidence of assortative pairing with respect to migratory strategy: observed frequencies of migrant–migrant and resident–resident pairs did not differ from those expected given random pairing.These data demonstrate substantial variation in two key aspects of reproductive performance associated with the migratory strategies of males, females and breeding pairs within a partially migratory population. These patterns could reflect direct and/or indirect mechanisms, but imply that individual variation in migratory strategy and variation in pairing among residents and migrants could influence selection on migration and drive complex population and evolutionary dynamics.

No paternal genetic integration in desert tortoises (Gopherus agassizii) following translocation into an existing population

Translocations are a tool widely used by wildlife managers, yet their impact is often insufficiently evaluated. Most translocation studies only assess the initial establishment phase, and the majority of long-term persistence studies to date have only tracked female fecundity. Male genetic integration for mitigative translocations have as of yet not been assessed and could greatly undermine the validity of translocation evaluations. To test for successful male integration, we determined genetic paternity of 92 desert tortoise hatchlings (Gopherus agassizii), from both resident and translocated females, four years after the initial translocation event and found that all 35 hatchlings with a paternal match in our genotype database were sired by residents. Given that translocated males constitute 46% of the genotyped males found in the home ranges of the females, they produce significantly fewer offspring than resident males in the same area (G-test, p value <0.0001). This is the first study assessing paternal genetic integration following a translocation of a wild sourced population into a native resident population. We hypothesize that male condition following the translocation, female mate preference for prior residents and competitive exclusion by resident males may contribute to the lower reproductive output of translocated males. We advocate the use of genetic paternity testing in other species to determine the generality of male translocation success across taxa given this unexpected and alarming result.

Intraspecific Competition and Inbreeding Depression: Increased Competitive Effort by Inbred Males Is Costly to Outbred Opponents.

A recent theoretical model suggests that intraspecific competition is an important determinant of the severity of inbreeding depression. The reason for this is that intraspecific competition is density dependent, leading to a stronger negative effect on inbred individuals if they are weaker competitors than outbred ones. In support of this prediction, previous empirical work shows that inbred individuals are weaker competitors than outbred ones and that intraspecific competition often exacerbates inbreeding depression. Here, we report an experiment on the burying beetle Nicrophorus vespilloides, in which we recorded the outcome of competition over a small vertebrate carcass between an inbred or outbred male resident caring for a brood and a size-matched inbred or outbred male intruder. We found that inbred males were more successful as intruders in taking over a carcass from a male resident and were injured more frequently as either residents or intruders. Furthermore, inbred males gained less mass during the breeding attempt and had a shorter adult life span than outbred males. Finally, successful resident males reared a substantially smaller brood comprised of lighter larvae when the intruder was inbred than when it was outbred. Our results shows that inbred males increased their competitive effort, thus contradicting previous work suggesting that inbred males are weaker competitors. Furthermore, our results shows that inbred intruders impose a greater cost to resident males, suggesting that outbred individuals can suffer fitness costs as a result of competition with inbred ones.

Male Dispersal Pattern in Golden Snub-nosed Monkey (Rhinopithecus roxellana) in Qinling Mountains and its Conservation Implication

Golden snub-nosed monkey (Rhinopithecus roxellana) is one of the most endangered primate species found in China, exhibiting multilevel society consisting of several one-male-females together with their offspring units (OMU), and all-male units (AMU). Female dispersal patterns of the species within herd have been well documented, whereas those of the males within or between herds are still poorly understood. Our results based a long-term observation indicate that more than half of sub-adult males, and half of the deposed males that stayed a short period in OMU disperse between herds, three of them established their own OMU in new herd after the dispersal. Smaller number of the sub-adult and adult males, compared with adult females, stayed in natal herd, implying sub-adult males started dispersing and male-biased dispersal occurred between herds. High frequencies of resident males were wounded as their OUMs were taken over, and resident males co-operation defend bachelor males were found. Mating competition among males within the herd may have contributed to the scenarios of male-biased dispersal. The results also suggest that maintaining connection between isolated herds and establishing the corridors among the fragmented habitats for the species will greatly benefit increasing its gene flow and promoting conservation status.

Ski areas affect Pacific marten movement, habitat use, and density

ABSTRACTAlpine ski recreation is one of the most popular outdoor winter sports globally but often involves habitat modification and dense human activity, both of which can harm wildlife. We investigated the effects of ski area development and winter recreation activities on movement, occupancy, and density of Pacific martens (Martes caurina) in the Lake Tahoe region of California and Nevada, USA by comparing 3 ski and 3 control study areas. We systematically surveyed martens using live traps and hair snares during spring–summer and winter seasons from 2009 through 2011 to identify how martens responded to the year‐round effects of habitat fragmentation from ski area development and the seasonal effects of winter recreation activities. Martens selectively moved between remnant forest patches with the shortest crossing distances across open, non‐forested ski runs in both seasons, with the effect more pronounced in females. Overall, habitat connectivity was reduced by 41% in ski areas compared to habitat not fragmented by ski runs. During spring–summer, occupancy rates were not different between habitat within or outside of ski operations areas. During winter, however, occupancy was significantly lower inside (52%) ski area boundaries than outside (88%) them. Reduced detection probability in ski areas indicated martens also reduced the frequency of use of operations areas in winter. Using spatially explicit capture‐recapture models, we found that marten density did not differ between ski areas and controls during spring, but during winter female density declined at ski areas by 63% compared to spring–summer and was &lt;50% of female density compared to controls. This suggests that females seasonally avoid habitat in ski areas by shifting their habitat use to areas outside ski operations boundaries during winter. Although male marten density did not differ, the lack of resident males &gt;3 years old coupled with higher annual turnover rates suggests male densities at ski areas may be reliant on annual male immigration. In winter, martens avoided using habitat in ski operations areas when recreation activity was greatest. Winter ski recreation may not be incompatible with marten use of habitat in ski areas, but habitat fragmentation from ski areas affects marten movement and recreation activities affect seasonal habitat occupancy and female density. Maintaining functional habitat connectivity, via networks of short ski run crossings that link habitat in and out of ski areas, will be important for maintaining or improving marten use of remnant habitat in developed ski areas. © 2017 The Wildlife Society

Spontaneous discrimination of urine odours in wild African lions, Panthera leo

Olfactory communication is the primary mode of communication for many mammals, yet research on this form of signalling is still largely descriptive in most species. Thus, despite the apparent importance of scent marking in the social lives of wild felids, experimental studies directly investigating the function of olfactory communication are lacking. We conducted scent presentation experiments to investigate whether wild African lions can discriminate another lion's social group and sex from a sample of its urine. Our results indicated that lion urine has the potential to signal depositor sex and social group, and that lions can use urine to discriminate males from females and residents from nonresidents. The response of lions to urine was also dependent on both the sex and age of the subject receiving the presentation. Female lions responded less frequently to urine from resident females than to either nonresident females or resident males. Males responded more strongly to urine from resident males than resident females, but did not appear to differentiate urine from nonresident and resident females. Observations of flehmen and further scent-marking responses from lions provide additional evidence that lion urine functions in scent marking. These results establish that urine scent-marks contain sufficient information for receivers to discriminate the sex and social affiliation of the signaller, and demonstrate the functional relevance of scent marking in African lions.

The Influence of Incubation Conditions and Sex on Growth and Dispersal in Hatchling Lizards

AbstractDispersal is a critical process that has profound influence on ecological and evolutionary processes. Many proximate factors influence natal dispersal, but it is currently unclear whether the conditions experienced during incubation play an important role. We manipulated incubation temperature and used mark–recapture of released hatchlings to test this hypothesis. We tested this hypothesis on the prairie lizard (Sceloporus consobrinus) using two experimental islands in a local reservoir. Incubation conditions influenced some aspects of hatchling morphology, but had little influence on the probability of dispersal. As generally predicted for a polygynous species, males were more likely to disperse than females; however, the growth rate of dispersing vs. resident individuals varied depending on sex. Dispersive male lizards did not grow faster than resident males, whereas female dispersers grew significantly slower than resident females. Although our study was not specifically designed to test for differential costs of dispersal for males and females, this pattern is consistent with recent research demonstrating sex‐specific fitness costs of dispersal.

Intragroup Lethal Aggression in West African Chimpanzees (Pan troglodytes verus): Inferred Killing of a Former Alpha Male at Fongoli, Senegal

Lethal coalitionary aggression is of significant interest to primatologists and anthropologists given its pervasiveness in human, but not nonhuman, animal societies. Chimpanzees (Pan troglodytes) provide the largest sample of recorded lethal coalitionary aggression in nonhuman primates, and most long-term chimpanzee study sites have recorded coalitionary killing of conspecifics. We report an inferred lethal attack by resident males on a former alpha male chimpanzee (P. t. verus) at Fongoli in Senegal. We describe the male’s presence in the community, his overthrow, social peripheralization for >5 yr, and his attempt to rejoin the group as well as circumstances surrounding his death. We report attacks by multiple chimpanzees on his dead body, most frequently by a young adult male and an older female. The latter also cannibalized the body. Coalitionary killing is rare among West African chimpanzees compared to the East African chimpanzee (P. t. schweinfurthii). This pattern may relate to differences in population densities, research effort, and subspecies differences in biology and behavior.

In Space and Time: Territorial Animals are Attracted to Conspecific Chemical Cues.

Territorial animals lay scent marks around their territories to broadcast their presence, but these olfactory signals can both attract and repel con-specifics. Attraction or aversion can have a profound impact in terms of space use and thereby influence an individual's access to resources and mates. Here, we test the impact of chemical signals on the long-term space use and activity of receivers, comparing the response of males and females, territory holders, and temporary visitors in Sceloporus undulatus lizards in the field. We placed either male femoral gland secretions (chemical) or blank (control) cues on resident male landmarks, repeatedly over 5 d, while monitoring the activity and location of all lizards in the vicinity. We found that resident males and females, but not non-resident males, were active on more days near landmarks treated with chemical cues than landmarks treated with control cues. Non-resident males remained closer to chemical than control cues. These results suggest that territorial scent marks are attractive to conspecifics and impact space use, but that the specific effects depend on receiver sex and residency status. Such subtle or gradual changes in behavior may frequently be overlooked by short-term choice experiments. Future studies investigating the behavioral significance of a communicative signal should consider these finer details of behavior for a more comprehensive assessment.

Proximal Association of Land Management Preferences: Evidence from Family Forest Owners.

Individual behavior is influenced by factors intrinsic to the decision-maker but also associated with other individuals and their ownerships with such relationship intensified by geographic proximity. The land management literature is scarce in the spatially integrated analysis of biophysical and socio-economic data. Localized land management decisions are likely driven by spatially-explicit but often unobserved resource conditions, influenced by an individual’s own characteristics, proximal lands and fellow owners. This study examined stated choices over the management of family-owned forests as an example of a resource that captures strong pecuniary and non-pecuniary values with identifiable decision makers. An autoregressive model controlled for spatially autocorrelated willingness-to-harvest (WTH) responses using a sample of residential and absentee family forest owners from the U.S. State of Missouri. WTH responses were largely explained by affective, cognitive and experience variables including timber production objectives and past harvest experience. Demographic variables, including income and age, were associated with WTH and helped define socially-proximal groups. The group of closest identity was comprised of resident males over 55 years of age with annual income of at least $50,000. Spatially-explicit models showed that indirect impacts, capturing spillover associations, on average accounted for 14% of total marginal impacts among statistically significant explanatory variables. We argue that not all proximal family forest owners are equal and owners-in-absentia have discernible differences in WTH preferences with important implications for public policy and future research.

Sensitivity of California Thrashers (Toxostoma redivivum) to song syntax

Many birds have songs with variable structure and sequences. In earlier studies, we characterized some features from the song structures of California Thrashers (Toxostoma redivivum). In the Thrashers, there were a large number of phrase types, dozens to hundreds and the songs that were sequences of these many phrases were not random, but show some structure referred to as syntax. For example, a syntactic rule might be that phrase type A can be followed by phrase type B, but not type C. We, along with others, have assumed that syntax is an important feature of songs. This paper describes an experimental attempt to determine that syntax is important to California Thrashers by recording the reaction of territorial thrashers to playbacks of other thrasher songs, some of which obeyed the syntax rules we had discovered while others violated those rules. We also obtained video recordings of their behaviour near the playback speakers. We observed differences in the reactions to the birds that heard these two types of playbacks. Resident males reacted to either playback type, but more strongly when the original order was preserved. We observed difference in their behavioural response to correct or altered syntax. This indicates that the syntax of their songs is perceived in territorial defence by the birds.

Divergent cloacal gland photo-responsiveness in male Japanese quail exposed to short days and associated differences in social interactions and reproduction

Quail under short d (SD) reduce their gonadal development, and consequently their cloacal gland (CG) size, aggressiveness, sexual behaviors, and reproductive performance. However, some quail appear nonresponsive to SD inhibition. When male quail were arbitrarily classified according to their CG involution during maximum photoinhibition (5 wk after SD exposure) as either nonresponsive (NR-SD) or responsive (R-SD), NR-SD quail showed intermediate CG volume between R-SD quail and the control quail kept on long d (C-LD). Herein, we evaluate whether NR-SD and R-SD male Japanese quail differ in their social interactions and reproductive performance while under SD; C-LD males were used as fully reproductive control. First, we assessed over 4 consecutive d, brief (5-min) home cage encounters between individually housed C-LD, NR-SD, or R-SD males and an unfamiliar C-LD male visitor. To determine male reproductive capacity, the following wk, males received the visit (10-min) of a mature female over 3 consecutive days. C-LD, NR-SD, and R-SD resident males showed higher aggressiveness than their photostimulated male visitors, respectively, in 100, 64, and 0% of the studied cases and were also able to, respectively, fertilize 100, 100, and 15% of their female visitors. Second, male-female encounters were again repeated 4 wk later to further assess reproductive performance and behavior. Naive C-LD, NR-SD, and R-SD males also were evaluated to assess potential consequences of the previous male-male interactions on the later performance. The number of males performing aggressive pecks towards females showed a C-LD>NR-SD>R-SD pattern. While mounts, CG contacts, and reproductive capacity showed a C-LD = NR-SD>R-SD pattern, copulatory efficiency exhibited an NR-SD>C-LD = R-SD pattern. Sexual behaviors were not modulated by previous male-male brief social interactions. Findings suggest that NR-SD males are able to breed similarly to their C-LD counterparts, which could be considered an indicator of a reduced reproductive dependence on seasonal photoperiod cues. Differences in the expression of aggressions between NR-SD and C-LD males may underlie the observed NR-SD improved copulatory efficiency when interacting with females.

Exceptional endocrine profiles characterise the meerkat: sex, status, and reproductive patterns.

In vertebrates, reproductive endocrine concentrations are strongly differentiated by sex, with androgen biases typifying males and estrogen biases typifying females. These sex differences can be reduced in female-dominant species; however, even the most masculinised of females have less testosterone (T) than do conspecific males. To test if aggressively dominant, female meerkats (Suricata suricatta) may be hormonally masculinised, we measured serum androstenedione (A4), T and estradiol (E2) in both sexes and social classes, during both ‘baseline’ and reproductive events. Relative to resident males, dominant females had greater A4, equivalent T and greater E2 concentrations. Males, whose endocrine values did not vary by social status, experienced increased T during reproductive forays, linking T to sexual behaviour, but not social status. Moreover, substantial E2 concentrations in male meerkats may facilitate their role as helpers. In females, dominance status and pregnancy magnified the unusual concentrations of measured sex steroids. Lastly, faecal androgen metabolites replicated the findings derived from serum, highlighting the female bias in total androgens. Female meerkats are thus strongly hormonally masculinised, possibly via A4’s bioavailability for conversion to T. These raised androgen concentrations may explain female aggressiveness in this species and give dominant breeders a heritable mechanism for their daughters’ competitive edge.

Birdsong learning as a social process

This paper describes a 30-year investigation into the role of social and ecological factors affecting song learning in song sparrows, Melospiza melodia. It addresses the question of why song sparrows learn the songs they do, given that they are exposed to many more songs than they will keep for their final repertoire of 7–11 song types. A young song sparrow moves from his natal area at about 1 month of age, eventually settling in an area where he learns the songs of the resident males and attempts to establish his own territory. Birds that share many songs with their neighbours in their first breeding season (the spring following their hatch summer) survive for more years on territory than birds that do not. Many features of the song-learning process lead to a high level of sharing with first-year neighbours, including preferentially learning the songs of their tutor-neighbours who survive the winter, and learning songs that are shared by several tutors. Social interaction appears to be critical in song learning, but indirect effects (eavesdropping on adults countersinging) seem to be at least as important as direct interaction between the young bird and his tutor-neighbours. Although our evidence suggests that the song-learning strategy of young song sparrows is beneficial to them, a preliminary analysis suggests it may not benefit their tutors.