Lighter Males Research Articles

Lifetime trajectories of male mating effort under reproductive conflict in a cooperatively breeding mammal.

The costs of reproductive conflict can shape the evolution of life-histories in animal societies. These costs may change as individuals age and grow, and with within-group competition. Social costs of reproductive conflict have been invoked to explain why females might gain from delaying maturity or ceasing reproduction midway through life, but not in males. Here, we analyse more than 20 years of data to understand how individual male banded mongooses adjust their reproductive activity in response to the costs of reproductive conflict. In banded mongoose groups, multiple female breeders enter oestrus synchronously that are each guarded by a single male that aggressively wards-off rivals. The heaviest males in the group gained the greatest share of paternity. Those lighter males that are reproductively active paid disproportionate survival costs, and by engaging in reproductive activity early had lower lifetime reproductive success. Our results suggest that reproductive inactivity early in life is adaptive, as males recoup any lost fitness by first growing before engaging in less costly and more profitable reproductive activity later in life. These results suggest that resource holding potential of males and the intensity of reproductive conflict interact to shape lifetime schedules of reproductive behaviour.

The Feast and the Famine: Spring Body Mass Variations and Life History Traits in a Pulse Resource Ecosystem.

AbstractPhenotypic plasticity is the most immediate mechanism of adaptative response to environmental change. Studying plastic changes in response to fluctuating environments provides insights into how such adjustments may impact life history traits. Here, we used a 14-year data set of repeated body mass measurements in male eastern chipmunks (Tamias striatus) to assess the extent of plastic changes for this trait in a resource pulse ecosystem. We first determined the magnitude of variation in body mass at the population level in response to the drastic change in food resource availability from American beech tree seeds (Fagus grandifolia). Males that emerged in the spring from winter torpor following a nonmast year had a lower body mass than males emerging after a mast year, but they tended to recover this loss by mid-June. We found significant among-individual variation in spring body mass plasticity (i.e., individual-by-environment interaction). We then investigated the relationships between individual spring body mass plasticity, longevity, and lifetime reproductive success. Interestingly, heavier males lived longer than lighter males, but more plastic males had a lower longevity and lower lifetime reproductive success than less plastic males. The report of such plastic response in a stochastic resource system provides valuable insights into the interplay between the costs and benefits of phenotypic plasticity as an adaptation to environmental fluctuations.

Factors affecting antler growth period and casting date in red deer

AbstractAntlers are unique structures because they grow rapidly and are cast annually, representing an important energetic and mineral cost for deer. Variables related to the timing of antler growth, such as date of antler casting and length of growth period, therefore, should be affected by somatic resources and availability of food. We examined the effects of body and antler weight, age, and climatic variables, on antler casting date and the period of time antlers were grown as well as possible random effects of individual, year, cohort, and pedigree, based on 244 antlers in a population of 109 males of Iberian red deer (Cervus elaphus) over a 17-year study from 1999 to 2016. Body weight affected casting date, with heavier males casting antlers earlier than lighter males. Antlers also grew faster and were cast earlier among older males than young males. Antler weight influenced casting date and the duration of the growth period: males with heavier antlers cast them earlier and grow them faster than males with light antlers. Nevertheless, age and antler weight interacted; as such, older males grew their antlers slower and delay casting date because they produce heavier antlers, in contrast to younger males, where those with the heaviest antlers grow them faster and cast first. The date of the end of antler growth also influenced casting date, so that antlers that took the longest to develop were cast later than those that finished growing early. We conclude that older and heavier males cast their antlers earlier and grow them faster than younger and lighter males, likely to correlate the subsequent antler growth with the spring peak in plant nutrients, but that this early development is limited physiologically by the size of the antlers.

Egg Incubation Mechanics of Giant Birds

Simple SummaryExtinct giant birds have been a source of imagination, and knowledge of their incubation mechanics is crucial to our understanding of the evolution of avian reproduction. Despite the extensive studies on avian eggs, our understanding of the eggshell mechanics of giant birds, particularly the extinct ones, remains incomplete—most of these prior works were based on empirical or allometric relationships with limited quantitative analysis. In the present study, with the help of advanced three-dimensional computer simulation using data from published fossil records, we obtain more comprehensive quantitative analysis to answer important questions related to contact incubation of giant birds. Specifically, how much safety margin does the reversed sexual size dimorphism (RSSD) of moas provide? What is the theoretical upper limit of body mass for contact incubation? Is the Williams’ egg, or the putative Genyornis oological material (PGOM), really the egg of the extinct giant bird Genyornis newtoni, as commonly accepted since its discovery in 1981?Finite element analysis (FEA) was used to conduct mechanical analyses on eggshells of giant birds, and relate this to the evolution and reproductive behavior of avian species. We aim to (1) investigate mechanical characteristics of eggshell structures of various ratite species, enabling comparisons between species with or without reversed sexual size dimorphism (RSSD); (2) quantify the safety margin provided by RSSD; (3) determine whether the Williams’ egg can have been incubated by an extinct giant bird Genyornis newtoni; (4) determine the theoretical maximum body mass for contact incubation. We use a dimensionless number C to quantify relative shell stiffness with respect to the egg size, allowing for comparison across wide body masses. We find that RSSD in moas significantly increases the safety margin of contact incubation by the lighter males. However, their safety margins are still smaller than those of the moa species without RSSD. Two different strategies were adopted by giant birds—one is RSSD and thinner shells, represented by some moa species; the other is no RSSD and regular shells, represented by the giant elephant bird. Finally, we predicted that the upper limit of body mass for contact incubation was 2000 kg.

PSXI-1 Agent-based simulation model to evaluate the technical performance of reproductive programs in beef cattle

Abstract A stochastic, agent-based simulation model was created to compare the technical performance of reproductive strategies in beef cattle. The model was parameterized using field data and peer-reviewed scientific literature using AnyLogic software. Ten scenarios were evaluated: natural mating (NM) only (ONM); one timed artificial insemination (TAI) plus NM (1TAI+NM); two TAI plus NM, with 24, 32, and 40 days of interval between TAI (2TAI/24+NM, 2TAI/32+NM, and 2TAI/40+NM, respectively); three TAI without NM, with 24, 32, and 40 days of interval between TAI (3TAI/24, 3TAI/32, and 3TAI/40, respectively), and three TAI plus NM, with an interval between TAIs of 24 (3TAI/24+NM) and 32 days (3TAI/32+NM). The size of the female herd was up to 400 individuals. The bull population was 0, 7, or 15 bulls depending on the scenario used. The outcomes were assessed on 320 farms, using a 5,000-day time horizon at one-day time intervals and an animal-by-animal basis. The 3TAI/24+NM resulted in a higher number of births (293 births) and weaned calves (287 calves), while the ONM had the lowest number of births (207 births) as well as weaned calves (203 calves). The heaviest and lightest males at weaning belong to the 3TAI/24 (190.58 ± 0.77 kg) and ONM (166.59 ± 0.93 kg), respectively. The total pregnancy rate was highest in 3TAI/24+NM (0.90 ± 0.00) and lowest for ONM (0.61 ± 0.01). The ONM reach 50% of pregnancy 52.5 days longer when compared to the scenarios that included TAI. Our model accurately represents the main interactions of a real beef cattle herd, with all the advantages of a physical experiment without incurring significant money expenses or alterations to the system. This study suggests that scenarios with three TAI accompanied by early pregnancy diagnosis presented better technical performance and produced more and heavier calves.

An agent-based simulation model to compare different reproductive strategies in cow-calf operations: Technical performance

The objective of this study was to create a stochastic, agent-based simulation model of a synthetic population of beef cattle, and then use it to compare the technical performance of different reproductive strategies. The model was parameterized using data from a real beef cattle herd and from the peer-reviewed scientific literature to represent a Nelore cattle herd in the state of São Paulo, Brazil. Ten scenarios were evaluated: natural mating (NM) only (ONM); one timed artificial insemination (TAI) plus NM (1TAI + NM); two TAI plus NM, with 24, 32, and 40 days between inseminations (2TAI/24 + NM, 2TAI/32 + NM, and 2TAI/40 + NM, respectively); three TAI without NM, with 24, 32, and 40 days between TAI (3TAI/24, 3TAI/32, and 3TAI/40, respectively); and three TAI plus NM, with 24 and 32 days (3TAI/24 + NM and 3TAI/32 + NM, respectively). NM began 10 days after the last TAI and was performed until the end of the breeding season. The size of the female herd was set to contain up to 400 individuals. The bull population was established at 0, 7, or 15 bulls depending on the used scenario. Simulation was performed for 5000 days. The outcomes for each scenario are means ± S.E. assessed on 32 farms at 1-day time intervals and on an animal-by-animal basis after steady state was reached (1825 days). The 3TAI/24 + NM scenario resulted in a greater number of births (279.85 ± 0.47 births), while the ONM scenario had the least value (202.38 ± 0.43 births). The heaviest males and females at weaning belonged to 3TAI/24, with 190.85 ± 0.17 kg for males and 173.89 ± 0.13 kg for females. The ONM scenario had the lightest males (166.84 ± 0.18 kg) and females (151.75 ± 0.16 kg). The greatest and least total pregnancy rates were found in 3TAI/24 + NM (0.91 ± 0.00) and ONM (0.62 ± 0.00), respectively. The ONM scenario required 52.5 days more than scenarios that included TAI to reach 50% of pregnancy. The greatest ages at culling for cows was 3TAI/24 + NM (3658.88 ± 10.41 days). In contrast, the lowest age at culling was found in ONM (2823.93 ± 8.28 days). We concluded that the proposed model represents the main interactions of a real beef cattle herd. It has all the advantages of a physical experiment, but does not require incurring significant expenses nor altering the real system. This study offers evidence that the scenarios that present the best technical performance are those that used TAI with a 24-day interval between inseminations.

Does Body Size Influence Male Care? Investigating an Alternative Reproductive Tactic in Manogea porracea (Araneae: Araneidae), a Spider with Amphisexual Care

The balance between the investment of time and energy by males in searching for new partners and in protecting and/or feeding offspring can influence reproductive strategies. Strong competitors may enhance their mating effort, while weak competitors may compensate their disadvantage in intrasexual competition by investing in the increase of offspring survival. This balance and its implications to male reproductive strategies have been extensively investigated in vertebrate species but remain poorly understood in invertebrates, because paternal care is rare. Manogea porracea is the only described solitary spider in which extended male care occurs in the absence of females (i.e. amphisexual care). Large males usually win disputes and prefer large, more fecund females. Therefore, they may increase their reproductive success by prioritizing the investment in the search for additional partners, while small males may compensate their competitive disadvantage by increasing their own parental efforts. We tested the prediction that lighter males will invest in the care of the offspring more often than heavier ones. However, our results indicate that males care for offspring regardless of their size. We discuss how the benefits of parental care may override the costs of reducing the number of potential mates for M. porracea males and suggest new directions for further studies.

Contest dynamics for food and reproductive resources are defined by health condition in a dung beetle

AbstractMale dung beetles compete to obtain food and females, and early resource recognition and appropriation increase the probability of mating. The outcome of such encounters is expected to be defined by self‐ and the opponent’s health condition. In this study, we analyzed the effect of body condition and immune defense on the contest dynamics between males that rolled a food ball with a partner female (owner males) and intruder males of dung beetle Canthon cyanellus. Body condition was measured as body size, body dry mass, lipid mass, and muscle mass; immune defense was estimated via phenoloxidase activity. Owner males with higher lipid mass contacted the food ball significantly earlier than owner males with lower lipid mass. Individuals with lower phenoloxidase activity started to roll food balls earlier than individuals with higher phenoloxidase activity. Owner males that had higher body dry mass, compared to female partners, began to roll the food ball significantly earlier than male–female pairs with lower differences in dry mass. Heavier males won significantly more contests than lighter males. Our results suggest that the health condition is a key factor related to the dynamics and outcome of male–male contests for resources and females in C. cyanellus. Consequently, differences in individual condition are main determinants of contest outcomes in dung beetles.

Self-assessment strategy during contest decisions between male Great Himalayan leaf-nosed bats

Agonistic interactions in animals are often settled based on the rules of an assessment strategy. We tested the predictions of evolutionary game theory models (including two models based on self-assessment: (a) the energetic war of attrition model, (b) the cumulative assessment model, and a third model (c) based on mutual assessment model) during contests between males of the Great Himalayan leaf-nosed bat Hipposideros armiger. We also studied the potential proxies of resource holding potential (RHP: body mass and forearm length) and their relationship to contest duration and the level of escalation. Overall, heavier males won more contests than lighter males, and they had an advantage in physical fights. In physical contests, the contest duration was positively correlated with the body mass of the loser but not the body mass of the winner. These results supported the prediction that males make decisions based on their own RHP (self-assessment: the energetic war of attrition model) rather than on RHP of their opponent (mutual assessment). Contest duration was not related to the forearm length of the winner or the loser. No relationship between body size (i.e., body mass and forearm length) and contest duration was observed for non-physical contests. This did not support any of the predictions applying to the energetic war of attrition model, the cumulative assessment model, and the mutual assessment model, indicating that no assessment occurred during non-physical contests. This study provides the first empirical evidence that bats make decisions based on their own RHP during agonistic interactions. This study provides empirical evidence supporting the hypothesis that during physical contests bats make decisions based on estimates of their own ability (self-assessment) rather than on a process of mutual assessment. This finding will facilitate comparative studies of fighting strategy across bat species.

Migrating silver-haired bats fine-tune torpor to save energy

Ultra-distance marathon runners are almost a race apart. Covering thousands of miles over weeks and even months, these extreme human athletes require mental stamina and physical endurance. Yet, many migratory species take these distances in their stride. ‘Some studies suggest that silver-haired bats spend their winters in southern USA and their summers in the Canadian boreal forest’, says Dylan Baloun, currently a graduate student at the University of Saskatchewan, Canada. But the bats that undertake these odysseys are at a natural disadvantage. ‘They are nocturnal, so daytime stopovers are mandatory’, says Baloun, who explains that stopovers can be extremely costly for some species – totalling ∼70% of the entire migration cost for some birds. But, the mini mammals have a nifty energy-saving trick up their sleeves. ‘Bats use torpor’, says Baloun, explaining that they drop their body temperature while they rest to conserve energy. However, no one had directly measured how much energy the torpid mammals conserve while hanging out during the day and how the roost temperature affects their energy saving. So, Baloun and PI Chris Guglielmo from the University of Western Ontario, Canada, packed up their lab and headed out to the Long Point Bird Observatory to catch bats in the act.‘It is difficult to bring and maintain state-of-the-art physiological equipment into the field, even with a mobile laboratory trailer to maintain a stable climate’, says Baloun, who ventured out into the near-by woods at night to retrieve silver-haired bats during their spring and autumn migrations. Back in the temporary lab, the duo weighed and scanned the animals using magnetic resonance to measure how much fat and muscle the animals were carrying. Then, after attaching a thermometer to each bat to track its body temperature, they snuggled the individual animals inside soft cloth bags where they could slip into torpor and slumber away at roost temperatures of 10, 17.0 or 25°C. Finally, when the bats were preparing to depart again during the following dusk, the duo repeated the body measurements before allowing the animals to continue on their way.Calculating how much fat and muscle the bats lost during their daytime stopover and converting the loss into the amount of energy consumed during their slumber, the duo could see that the animals used essentially the same amount of energy over the course of the day, regardless of the temperature in their roost. The team then calculated the total amount of torpor experienced by each animal and it was clear that the bats were fine tuning how cold they became and for how long, with the result that they all consumed similar amounts of energy during their stopover regardless of the air temperature. And when the duo calculated how much energy the bats consumed during their break, they were impressed to see that it was as low as 15–20% of the total migration energy cost. ‘By entering a state of torpor, bats save energy for future migratory and potentially reproductive costs’, says Baloun.However, the team also realised that some of the bats were conserving energy and using torpor in slightly different ways, with bats that carried more weight using less torpor at the warmer temperatures, while the heavier females consumed more energy during spring stopovers than the lighter males. ‘Body mass was a major determinant in how bats used torpor’, says Baloun.So, migrating bats have the ability to dramatically reduce their energy costs during enforced daytime stopovers and the study adds another piece to the puzzle of how these tiny mammals pull off extreme feats of endurance, at which most of us can only marvel.

Plumage colour predicts dispersal propensity in male pied flycatchers

Melanin-based colouration of tegument structures may be related to variability in the expression of certain strategies or behaviours within a species, including the propensity to disperse. This is because melanin synthesis may be physiologically linked to certain behaviours and personality traits, as proposed by the hypothesis of the pleiotropy in the melanocortin system (HPMS). During a 28-year period (1988–2015), we studied the melanin-based dorsal colouration of male pied flycatchers (Ficedula hypoleuca) in relation to natal dispersal movements between contrasting (pine and oak) habitats. In addition, the relationship between tonic immobility (TI), a measure of individual fearfulness towards predators, and plumage colour was examined using a shorter time series. Consistent with HPMS, males’ dispersal propensity was related to their plumage colour, with the blackest individuals being more likely to disperse into a new habitat to breed. Blacker males remained for longer in TI than lighter ones. The positive relationship between plumage melanisation and TI might result from the pleiotropic effect of the melanocortin system on glucocorticoid-mediated stress and fearfulness responses as well as on eumelanin synthesis. This study provides solid empirical support for the HPMS in relation to natal dispersal behaviour. Individual behaviour can be integrated with other phenotypic traits via the pleiotropic effects of some biochemical pathways. Recent research has shown connections between melanin-based colouration, personality and certain life history traits. However, the relationship between colouration and natal dispersal—a critical phase of life—has received comparatively little attention. We studied this link in the pied flycatcher, a small bird in which males exhibit considerable variation in dorsal plumage colour, ranging from brown to black. By following individuals from fledging to settlement, we show that males with a higher percentage of black feathers are more likely to disperse into novel environments than lighter males. Furthermore, we found an association between plumage melanisation and individual fearfulness to predators, possibly due to the shared pathways of melanin synthesis and stress responses. Our results highlight the potential of the interplay between melanin production and individual behaviour to explain the maintenance of colour variability in natural populations.

Sex-dependent effects of larval food stress on adult performance under semi-natural conditions: only a matter of size?

Organisms with complex life-cycles acquire essential nutrients as juveniles, and hence even a short-term food stress during development can impose serious fitness costs apparent in adults. We used the Glanville fritillary butterfly to investigate the effects of larval food stress on adult performance under semi-natural conditions in a population enclosure. We were specifically interested in whether the negative effects observed were due to body mass reduction only or whether additional effects unrelated to pupal mass were evident. The two sexes responded differently to the larval food stress. In females, larval food stress reduced pupal mass and reproductive performance. The reduced reproductive performance was partially mediated by pupal mass reduction. Food stressed females also had reduced within-patch mobility, and this effect was not dependent on pupal mass. Conversely, food stress had no effect on male pupal mass, suggesting a full compensation via prolonged development time. Nonetheless, food stressed males were less likely to sire any eggs, potentially due to changes in their territorial behavior, as indicated by food stress also increasing male within-patch mobility (i.e., patrolling behavior). When males did sire eggs, the offspring number and viability were unaffected by male food stress treatment. Viability was in general higher for offspring sired by lighter males. Our study highlights how compensatory mechanisms after larval food stress can act in a sex-specific manner and that the alteration in body mass is only partially responsible for the reduced adult performance observed.

First Evidence of Inclusive Sexual Selection in the Ant Cataglyphis cursor: Worker Aggressions Differentially Affect Male Access to Virgin Queens

AbstractSexual selection typically shapes the traits of individuals capable of reproduction. However, in social species, it may also affect the behaviour of non‐reproductive individuals if this increases their inclusive fitness. We examined the potential role of workers during mating in the polyandrous ant Cataglyphis cursor. In this species, mating takes place on the ground near the nest entrance, and workers chase away foreign males trying to mate with young queens (gynes). We investigated the effects of worker aggression on male mating attempts by placing three or four males in the presence of one foreign gyne and 20 of her nestmate workers and contrasted this with a second group of 3–4 males in the presence of another gyne without nestmate workers (n = 8 paired replicates). Workers strongly attacked males (more than 20 aggressions per minute), although this did not affect the total number of mating attempts by the 3–4 males or the skew in the number of mating attempts among these males. However, there was an interaction between worker aggression and relative male weight, as relatively heavy males attempted to mate more often than lighter males in the absence of worker whereas the reverse occurred in the presence of workers. Our study is the first to experimentally test the potential role of non‐reproductive individuals in sexual selection. It shows that workers could potentially change male mating success by disfavouring heavier males.

Mating success is predicted by the interplay between multiple male and female traits in the small hairy maggot blowfly

Intersexual selection drives the evolution of reproductive traits, including ornamentation and courtship behaviour. However, most studies attempting to explain the relationships between reproductive traits are oversimplified because traits are evaluated independently, and assessment of mate choice is restricted to one sex. Further research is required to understand the extent to which interactions between traits influence mating decisions in both sexes. The small hairy maggot blowfly, Chrysomya varipes, offers an ideal opportunity to examine how interactions between foreleg ornamentation (males have conspicuous white and black hairs, whereas females have only black hairs) and complex courtship behaviour influence mating success in males and females. This study involved mate choice trials between single females and males that varied in foreleg ornamentation. Courtship investment was quantified for males, and ornamentation and body size were quantified for both sexes. Mating success was predicted by time invested in courtship, but not by either male and female ornamentation or body size alone. However, there was a significant interaction between courtship investment, ornamentation and body size. At any given courtship investment, males with more ornamentation had an increased probability of mating success. Females with more ornamentation also had an increased probability of mating success, because males invested more courtship in more ornamented females. Furthermore, the lightest males had an increased probability of mating success compared to the heaviest males, as lighter males invested more in courtship. Female weight, however, did not significantly affect the probability of mating. The results suggest that male foreleg ornamentation in C. varipes acts as an amplifier of the visual courtship display, adding to a small but growing body of evidence that multiple male and female traits can interact to influence mating decisions.

The individual counts: within sex differences in foraging strategies are as important as sex‐specific differences in masked boobies Sula dactylatra

Understanding how animals allocate their foraging time is a central question in behavioural ecology. Intrinsic factors, such as body mass and size differences between sexes or species, influence animals’ foraging behaviour, but studies investigating the effects of individual differences in body mass and size within the same sex are scarce. We investigated this in chick‐rearing masked boobies Sula dactylatra, a species with reversed sexual dimorphism, through the simultaneous deployment of GPS and depth‐acceleration loggers to obtain information on foraging movements and activity patterns. Heavier females performed shorter trips closer to the colony than lighter females. During these shorter trips, heavier females spent higher proportions of their flight time flapping and less time resting on the water than lighter females did during longer trips. In contrast, body mass did not affect trip duration of males, however heavier males spent less time flapping and more time resting on the water than lighter males. This may occur as a result of higher flight costs associated with body mass and allow conservation of energy during locomotion. Body size (i.e. wing length) had no effect on any of the foraging parameters. Dive depths and dive rates (dives h−1) were not affected by body mass, but females dived significantly deeper than males, suggesting that other factors are important. Other studies demonstrated that females are the parent in charge of provisioning the chick, and maintain a flexible investment under regulation of their own body mass. Variation in trip length therefore seems to be triggered by body condition in females, but not in males. Consequently, shorter trips are presumably used to provision the chick, while longer trips are for self‐maintenance. Our findings underline the importance of accounting for the effects of body mass differences within the same sex, if sex‐specific foraging parameters in dimorphic species are being investigated.

Genetic analysis of body color phenotypes in the fruit flyDrosophila melanogaster: supporting evidence through laboratory-selected dark and light strains

In the fruit fly Drosophila melanogaster Meigen, 1830, abdominal melanisation varies in a quantitative manner, but little attention has been paid to the genetic basis of different phenotypic classes and their ecological significance in the wild populations. Laboratory-selected darker and lighter body color strains were used for determining the genetic basis of body color phenotypes. Based on such genetic characterization, we interpreted body color variation of wild flies collected along a latitudinal gradient. Our results are interesting in several respects. First, laboratory selection produced lighter females and also lighter males, in contradiction of the well-known sexual dimorphism in D. melanogaster. The laboratory-selected darker and lighter strains showed lack of phenotypic plasticity, whereas F1flies from reciprocal crosses showed significant levels of phenotypic plasticity. Second, for both sexes, F2phenotypic classes resulting from reciprocal crosses between selected darker and lighter strains fit a two-locus model with a stronger maternal effect in males than in females. Third, changes in continuously varying abdominal melanisation of wild-caught flies were sorted into phenotypic bins of body color phenotypic classes and such data on geographical populations of D. melanogaster are consistent with climatic selection. Thus, we may suggest that for ecological genetic studies, greater emphasis should be laid on the analysis of bins of phenotypic classes of body melanisation in laboratory and wild populations of D. melanogaster.

Effects of Male age and Size on Mating Success in the Bumblebee Bombus terrestris

In social insects, the reproductive strategies adopted by colonies emerge as a complex property of individual behaviours, but as yet we are often unable to fully explain them in evolutionary terms. In bumblebees, colonies adopt either a short-lived strategy specializing in male production, or a longer-lived strategy in which mainly new queens are produced, but this results in males emerging long before mates are available; this strategy can only easily be explained if older males are at a significant reproductive advantage. Here we examine how age and morphological characters influence mating success of male bumblebees. In two separate experiments in which single virgin males and females were confined together, we found that young males and heavy males mated more swiftly and copulated for less time compared to old males or lighter males, respectively. However, in competitive situations age proved to be unimportant and the only factors to influence mating success were the lengths of the fore and hind tibiae, with strong directional selection for long leg length. Fore and hind legs are both used in courtship, so both traits are associated with plausible mechanisms under selection. It has previously been argued that, in times of food stress, bumblebee colonies should produce males as male size is less likely to be strongly correlated with fitness than female size. Our results suggest that this may not be so, since aspects of male size directly impact on their mating success. Our results leave unexplained the emergence of males many days before new queens. © 2011 Springer Science+Business Media, LLC.

Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa

New Zealand's extinct flightless moa radiated rapidly into a large number of morphologically diverse species, which produced an equally large range of egg morphologies. The exact number of moa species, as well as the characteristics of the eggs they laid, remains contentious. Moreover, like most extinct species, we understand little about their nesting and incubation habits. We used a modified ancient DNA extraction procedure to recover exogenous mitochondrial and nuclear DNA from the inside and outside surfaces of moa eggs. We used sequences from the inside of 69 eggshells to directly assign these remains to seven of the 10 currently recognized moa species. In addition we were able to assign, to the species level, six of the rare reconstructed "whole" eggs. These molecular results enabled us to identify two distinct lineages within the genus Euryapteryx. Members of these lineages differed in eggshell thickness, with one lineage being characterized by a relatively thin eggshell. Unexpectedly, several thin-shelled eggs were also shown to belong to the heaviest moa of the genera Dinornis, Euryapteryx and Emeus, making these, to our knowledge, the most fragile of all avian eggs measured to date. Moreover, sex-specific DNA recovered from the outer surfaces of eggshells belonging to species of Dinornis and Euryapteryx suggest that these very thin eggs were likely to have been incubated by the lighter males. The thin nature of the eggshells of these larger species of moa, even if incubated by the male, suggests that egg breakage in these species would have been common if the typical contact method of avian egg incubation was used.

What limits male range sizes at different population densities? Evidence from three populations of water voles

AbstractIn many mammalian species, females compete with each other for food and space to raise offspring, while males compete with each other for access to females. Few studies have examined the factors which limit male range sizes or the degree of overlap between male ranges. We deduced four possible responses of the range ‐sizes of non‐territorial male small mammals to increasing population density and/or levels of forage abundance. These were: (1) male range sizes might remain the same irrespective of population density; (2) at high population densities males may become territorial, and their ranges small and non‐overlapping; (3) at high forage abundance/population densities, males' ranges may become smaller but remain intra‐sexually overlapping; (4) at high forage abundance, male range sizes may increase. We examined the relationship between population density, range lengths and range overlaps and body weights of both sexes in a comparative study of three populations of water voles Arvicola terrestris. Male range sizes were smaller at higher population densities, but their ranges remained both inter‐ and intra‐sexually overlapping. Heavier males had larger ranges than did lighter males at all sites. These results comply with what would be expected if male range sizes were at least partially restricted by the number of ranges of other individuals with which they overlapped. Although we could not discount the hypothesis that forage abundance may also have had a direct effect on male range sizes, our results implied that male range sizes were at least partially determined by social factors.

Male Dominance and Female Chemosensory Preferences in the Rock-dwelling Snow Vole

The aim of this study was to examine how factors affecting male scent attractiveness to females interact with factors influencing male social dominance in rock-dwelling snow voles, Chionomys nivalis. We analysed the effect of particular phenotypic traits of male fitness, including relative body weight, bilateral asymmetry levels and haematocrit volume, upon relative success at both intra- and intersexual processes (measured as the outcome of social interactions among males and the level of attraction of males' odours to females, respectively). We found that males achieving more dominant status were those of higher relative body weight, which may give them physical advantage in intrasexual contests. Although social status of experimental males was not directly influenced by haematocrit volumes or levels of asymmetry, data from their original population indicate that relative heavier males are indeed more symmetric than lighter males. Regarding the attractiveness of male's odours, results show that relative body weight was unimportant to females, which principally favoured scents of individuals with higher haematocrit volumes. In addition, females tended to be more attracted towards the scents of less asymmetric males. These findings suggest that relative success of male C. nivalis at intra- and intersexual levels might be influenced by different factors. Nevertheless, due to the tight interrelationship between traits of male fitness, attraction to females and achievement of dominant status may not be completely independent. We further hypothesize that intrinsic information contained in male odour cues could be adaptively, and differently, used by conspecifics of both sexes in this species.