Endurance Rivalry Research Articles

Superior performance of a trailing edge low-latitude population of an intertidal marine invertebrate

The objective of this study is to compare ecologically relevant measures of performance over a broad range of latitude of a species subjected to climate change. Do populations change in relative function over a wide range of latitude? Are populations at the low latitude trailing edge in danger of extinction in the onset of thermal stress? Coastal marine species with planktonic larvae can range over an enormous span of latitude and thermal environments. The fiddler crab Leptuca pugilator extends from high-latitude (41.75°N) winter-frozen Massachusetts tidal flats in the north to subtropical low latitude flats in Florida (24.55°N), where they may be active at the surface over most of the year. We characterized the air environment for males at three sites (New York – latitude 40.0°N, Beaufort, North Carolina – latitude 34.7°N, Panacea Florida, latitude 30.0°N) over the geographic-thermal range, and found major differences in temperature, wind speed, humidity, and vapor pressure deficit. Florida L. pugilator males preferred warmer sand than North Carolina and New York crabs. Local adaptation to latitude-dependent thermal conditions might suggest tradeoffs in performance as a function of temperature. We examined measures of predator escape performance (running speed and righting speed) and overall condition reflecting endurance rivalry success (endurance on a treadmill and major claw closing force) over a wide range of test temperatures. Predator escape rates increase steadily with increasing temperature, but endurance rivalry measures show an intermediate temperature peak of performance. We tested the hypothesis of tradeoffs, with expected local superiority of performance according to regional thermal differences. But instead, the trailing edge Florida males were superior to the higher latitude populations, over a broad range of temperature, but especially at higher temperatures, for all four types of performance measures. The trailing edge population of L. pugilator, in thermal terms, is therefore likely not vulnerable to near future further effects of warming in terms of performance measures related to male reproductive and feeding activities and escape from predators. Fiddler crabs appear to display niche conservatism for stronger performance at tropical temperatures. Such a natural tropical superiority in performance might have to be accommodated in future conceptions of response of marine species to climate change with broad latitudinal distributions in the tropics.

Reduced injury risk links sociality to survival in a group-living primate

Sociality has been linked to a longer lifespan in many mammals, including humans. Yet, how sociality results in survival benefits remains unclear. Using 10 years of data and over 1,000 recorded injuries in rhesus macaques (Macaca mulatta), we tested two injury-related mechanisms by which social status and affiliative partners might influence survival. Injuries increased individual risk of death by 3-fold in this dataset. We found that sociality can affect individuals' survival by reducing their risk of injury but had no effect on the probability of injured individuals dying. Both males and females of high social status (measured as female matrilineal rank and male group tenure) and females with more affiliative partners (estimated using the number of female relatives) experienced fewer injuries and thus were less likely to die. Collectively, our results offer rare insights into one mechanism that can mediate the well-known benefits of sociality on an individual's fitness.

Endurance rivalry among male spotted hyenas: what does it mean to “endure”?

Endurance rivalry among male spotted hyenas: what does it mean to “endure”?

Multi‐night territorial behavior, chorus attendance, and mating success in red‐eyed treefrogs

AbstractFor many frog species that aggregate around ponds or streams, chorus attendance, the percentage of time or nights a given male is present and actively calling at an aggregation, is the strongest documented predictor of inter‐male variation in reproductive success in the wild. Males are, thus, thought to compete via endurance rivalry, where available energetic reserves and individual physiology interact to determine chorus tenure. Frogs often exhibit territorial behavior within these aggregations, and territorial status is likely to influence a male's rate of energy expenditure. While males of several anuran species have been shown to hold territories across nights, it is not well understood whether such calling site fidelity is correlated with chorus attendance or mating success. Using subdermal RFID (PIT) tags to minimize disturbance to chorus structure, we quantified site fidelity, chorus attendance, and mating success for all male red‐eyed treefrogs (Agalychnis callidryas) within a breeding aggregation in Panama across 50 consecutive nights. We found that nearly half of these males held territories across nights, that this cross‐night territorial behavior was highly correlated with chorus attendance, and that chorus attendance was, in turn, the strongest predictor of male mating success. Males were most faithful to calling sites containing vegetation contiguous with adjacent sites and were more likely to remain at a site if they were successful in acquiring a mate there on the previous night. To our knowledge, this is the first study linking male site fidelity to chorus attendance and mating success in anurans. While female mate choice is an established driver of lineage diversification and the evolution of sexual signals, agonistic interactions between males at breeding aggregations are well‐documented from a wide range of anuran taxa. The relationship between male–male interactions and mating success deserves broader research attention among anuran species.

Endurance rivalry and female choice jointly influence male mating success in the emerald treefrog (Zhangixalus prasinatus), a lek-chorusing anuran

BackgroundEndurance rivalry and female choice are two important mechanisms of sexual selection in lek-breeding species. Endurance rivalry is when males compete for opportunities to mate by spending more time in leks than others (interaction-independent male-male competition). Because high-quality males can afford to have high lek attendance, females have a higher chance of mating with good-quality males even when they mate randomly. The good gene hypothesis proposes that females can pass good genes on to their offspring by choosing males that display elaborate morphological and/or behavioral traits that reflect the males’ genetic quality. The relative importance of lek attendance and female choice to males’ mating success in anurans is rarely evaluated. In this study, we investigated how these two mechanisms might jointly shape males’ morphological traits in the lek-chorusing emerald treefrog Zhangixalus prasinatus.ResultsOur results show that (1) male lek attendance is positively correlated with body size and condition, and males with higher lek attendance have higher mating success, (2) the dominant frequency of males’ advertisement calls are negatively correlated with body size and males producing lower frequency calls have higher mating success, (3) male body size, but not body condition, has a non-significant positive relationship with mating success and (4) females show preference for calls with lower dominant frequencies in two-choice playback.ConclusionsOverall, both endurance rivalry and female choice play an important role in the mating success of male emerald treefrogs in the field and both are influenced by male body size/condition. By mating with males that have higher lek attendance and produce lower frequency calls, selection may indirectly favor larger males.

The definition of sexual selection.

Sexual selection is a key component of evolutionary biology. However, from the very formulation of sexual selection by Darwin, the nature and extent of sexual selection have been controversial. Recently, such controversy has led back to the fundamental question of just what sexual selection is. This has included how we incorporate female-female reproductive competition into sexual or natural selection. In this review, we do four things. First, we examine what we want a definition to do. Second, we define sexual selection: sexual selection is any selection that arises from fitness differences associated with nonrandom success in the competition for access to gametes for fertilization. An important outcome of this is that as mates often also offer access to resources, when those resources are the targets of the competition, rather than their gametes, the process should be considered natural rather than sexual selection. We believe this definition encapsulates both much of Darwin’s original thinking about sexual selection, and much of how contemporary biologists use the concept of sexual selection. Third, we address alternative definitions, focusing in some detail on the role of female reproductive competition. Fourth, we challenge our definition with a number of scenarios, for instance where natural and sexual selection may align (as in some forms of endurance rivalry), or where differential allocation means teasing apart how fecundity and access to gametes influence fitness. In conclusion, we emphasize that whilst the ecological realities of sexual selection are likely to be complex, the definition of sexual selection is rather simple.

Balancing risk and reward: mating opportunity influences thermal refuge use in fiddler crabs

Behavioural thermoregulation can ameliorate thermal stress but is costly. For species that court in a thermally stressful microhabitat, sexual selection via endurance rivalry favours individuals that are able and willing to endure harsh conditions in the courtship habitat, as retreats to a thermal refuge will reduce mating opportunities. The relative costs and benefits of refuge use versus continued courtship in the face of thermal risk, which vary across abiotic and biotic contexts, determine the optimal behavioural strategy. We examined the social and abiotic factors driving behavioural decisions related to thermoregulatory retreat in the fiddler crab Austruca mjoebergi. Male fiddler crabs perform a courtship display on the thermally stressful intertidal sediment surface. Time on the surface, and thus time available for display, was limited by high temperatures; as temperature increased, surface time decreased. Yet when presented with a stimulus female, males were more likely to perform the courtship display, displayed at a higher rate and increased time spent on the surface. These results demonstrate that behavioural decisions related to thermal retreat depend both on the abiotic conditions that influence the degree of thermal stress and on the social conditions that influence the reproductive prospects of the individual.

Variation in Lek Attendance and Copulation Success of Independent and Satellite Male Ruffs Calidris pugnax

In lekking male Ruffs, three genetically distinct morphs compete for copulations with the visiting females. Faeder males are female mimics, whereas Independents and Satellites show marked sexual dimorphism, including an elaborate ornamental plumage. Independent males holding a territory on a lek (Residents) have higher mating success than Independents that do not (Marginals), whereas heterogeneity among Satellites is less well understood. Therefore, we compare variation in lek attendance and copulation success between Independent and Satellite males on five leks in northern Norway, over one mating season. Among Independents, Residents were more likely to return to the same lek between years, had longer tenure, higher visitation rate, longer visit duration, fewer arrivals and departures from the lek together with females, and higher daily and seasonal lek attendance than Marginals. We observed qualitatively similar between-individual variation in behaviour among Satellites. Thus, we define two types of individuals: Central Satellites with high lek attachment and Peripheral Satellites with low lek attachment. A notable difference between the morphs was that some Central Satellites (but no Resident Independents) were highly attached to more than one lek on the same day. Lek attendance correlated with copulation success, both on a daily basis and considering the entire season, and this relationship did not differ significantly between the morphs. Given that the mere presence of a male on the lek when a female visited to copulate predicted his copulation success, the unequal distribution of copulations on a lek can be largely explained by unequal lek attendance. After correction for variation in presence, one male on each lek obtained more than his expected share of copulations. Our observations suggest that endurance rivalry, whereby energetic limitations determine the lek attendance of competing males, could be an important determinant of copulation success on Ruff leks.

Sexually selected traits are larger and more variable in male than female beach-spawning capelin, Mallotus villosus.

We evaluated whether morphological traits in capelin, Mallotus villosus, that appear to be sexually selected (pectoral fin, pelvic fin, anal fin, lateral ridge) were larger and more variable in males than females compared with naturally selected morphological traits (eyes, dorsal fin). Photographs were obtained of 136 capelin captured at two spawning sites and standardised measurements were taken of six morphological traits. Males had larger traits than females for a given body size and this was most pronounced in the traits thought to be sexually selected. Body size explained much of the variation in female traits but less variation in male traits, suggesting alternative selection pressures are involved. We suggest that larger male body size aids in endurance rivalry and sexually dimorphic traits help males to remain in physical contact with females while spawning on the beach.

Size, Endurance, or Parental Care Performance? Male–Male Competition, Female Choice, and Non-Random Mating Pattern in the Glassfrog Centrolene savagei

Previous work has shown that Centrolene savagei is unique among the more than 150 species in the family Centrolenidae in demonstrating large-male mating advantage. However, it is still unknown whether non-random mating in this species is mediated by intrasexual and/or intersexual selection. To disentangle the effect of these selective pressures on mating pattern in this species, we monitored the breeding behavior of individuals in a population located in the department of Quindío, Central Andes of Colombia. We conducted diurnal and nocturnal surveys each weekend between February and July of 2016 in which we documented morphological (i.e., body size) and behavioral (i.e., chorus tenure, parental-care behavior) characteristics of males to determine their relationship with mating success. We corroborated that in this population of C. savagei, larger males obtain a higher number of mates than do smaller males; male body size co-varies positively with chorus tenure and drives this mating pattern. Male body size was not related to higher fertilization efficiency of eggs laid by females, or a higher survival of embryos in clutches cared for by them. In sum, the higher mating success of larger males in the glassfrog C. savagei seems most strongly related to a mechanism of endurance rivalry competition (intrasexual selection) than female choice (intersexual selection) based on egg fertilization efficiency or parental care quality.

Attendance, but not performance, predicts good genes in a lek-breeding treefrog

According to the good-genes hypothesis, females prefer males with costly displays because the costs are reliable indicators of genetic quality. In leks, mating costs result from a multiplicative interaction between the number of display performances (lek attendance) and the energetic expenditure associated with each display performance. If males differ in their allocation strategies between the 2 components of mating effort, the reliability of display performance as an indicator of genetic quality may be disrupted. Here, we investigate the association between male genetic quality and both lek attendance and display performance in the Italian treefrog, Hyla intermedia. We recorded lek attendance and display performance (nightly calling effort) during 2 breeding seasons, and we set up a breeding experiment to evaluate sire effects on 3 larval fitness-related traits (growth rate, age, and size at metamorphosis). Attendance and calling effort were positively correlated with each other and both with male mating success, providing no evidence for a performance-attendance trade-off at the population level. In the breeding experiment, we found some evidence for an effect of sire identity and attendance on growth rate and age at metamorphosis, but no evidence for an effect of sire calling effort. We conclude that female preference, by imposing high-quality standards for calling males, strengthens the role of endurance rivalry in male mating competition, indirectly favoring males of higher-than-average mating effort. Under this scenario, although male displays are unreliable indicators of mating quality, females nevertheless gain benefits because of the reduced risk of coming on low-quality males.

Correlates of Male Consortship Rate in Free-Ranging Rhesus Macaques (Macaca mulatta)

Male–male competition for access to receptive females can take the form of nonrecurring fights and/or a sustained contest over mating opportunities. Male physical condition has been linked to dominance rank and reproductive success in species characterized by intrasexual fights for dominance and access to females. In group-living species characterized by endurance rivalry, however, factors contributing to male reproductive success are less well understood. In such species, particularly seasonally breeding ones with low sexual dimorphism and seniority-based rank, age and social factors other than rank may prove important. In the absence of genetic data, male mate guarding or consortship can serve as an indicator of male reproductive success. To evaluate the contribution of age and intragroup sociality to male consortship rate, I collected behavioral data during one nonmating and one mating season in two social groups of free-ranging rhesus macaques that experience no predation or food scarcity. Higher-ranking males, younger males, or males that exhibited lower rate of intrasexual aggression had higher consortship rates. Male–female dyads that groomed outside consortship did not form consortships as often as dyads that did not engage in nonconsort grooming. This is the first study to identify the significance of male–male aggression and male–female affiliation to male consortship rate in a species characterized by endurance rivalry, high male rank stability, and strong female mate choice. Social behaviors and male age may be particularly important in determining male reproductive success in populations experiencing high food availability and a lack of predation, which are typical of an increasing number of vertebrates in areas densely populated by humans.

Sex-specific thermal constraints on fiddler crab behavior

Sexual selection via endurance rivalry favors increased tenure at the breeding site but can be costly. Here, we investigated thermal constraints on endurance rivalry in fiddler crabs, a group well suited for studies of interactions between sexual and natural selection due to ritualized mating behaviors and extreme sexual dimorphism. Fiddler crab males display in thermally stressful high-intertidal breeding areas. Retreating into burrows, an effective thermoregulatory mechanism, requires a cessation of courtship behaviors. We predicted that males should spend more time on the surface than females and that their ability to do so should decrease with increasing body temperature. In contrast, the amount of time females spend on the surface should be little affected by body temperature. We tested these predictions in the fiddler crab Uca panacea by manipulating body temperatures and monitoring surface activity and habitat choice in large outdoor tanks during the breeding season. Males showed consistently higher surface activity than females. Effects of body temperature on surface activity were sex-specific, occurring in males but not in females, indicating sex-specific thermal constraints on surface behavior and supporting our hypothesized thermal constraints on endurance rivalry.

Condition-dependent ways to manage acoustic signals under energetic constraint in a tree frog

Because resources needed to produce sexual displays are limited, courting males are expected to face trade-offs between investing in display properties selected by females and investing in the amount of display. This should be particularly the case in species with energetically expensive displays and high intrasexual competition through endurance rivalry like chorusing anurans. Studies that manipulated the energetic constraint in calling anurans have led to conflicting results, potentially due to nonsimultaneous assessment of call properties selected by females and the calling activity (i.e., the total number of calls emitted by a male), and/or to the use of different strategies to face display trade-offs by males. We investigated display trade-offs in 36 males Hyla arborea (L.) by manipulating their energetic constraint through starvation/feeding experiments while recording their overall call production during 10 consecutive nights. Even when considering simultaneously calling activity and call properties, the energetic constraint does not appear to impact call production. However, when focusing on individual responses, it appears that males cannot maintain both calling activity and within-bout call rate. Big and high-condition males mainly decrease this call property along the experiment, whereas small and low-condition males mainly decrease calling activity. Moreover, males who maintained calling activity the most are those who lost the most condition and, when refed, starved males only increased calling activity. These results suggest that calling activity is costlier to maintain than call properties but may confer a greater advantage in mating success, leading to different allocation strategies among males of different conditions.

Activity Predicts Male Reproductive Success in a Polygynous Lizard

Activity patterns and social interactions play a key role in determining reproductive success, although this is poorly understood for species that lack overt social behaviour. We used genetic paternity analysis to quantify both multiple paternity and the relative roles of activity and social behaviour in determining reproductive success in a nondescript Australian lizard. During the breeding season we intensively followed and recorded the behaviour of a group of seven males and 13 females in a naturalistic outdoor enclosure to examine the relative roles of body size, activity and social interactions in determining male fertilization success. We found multiple paternity in 42% of clutches. No single behaviour was a significant predictor of male fertilization success in isolation, but male-female association, interactions and courtship explained 41% of the variation in male fertilization success. Males with the highest number of offspring sired invested heavily in interacting with females but spent very little time in interactions with males. These same males also sired offspring from more clutches. When taken collectively, an index of overall male activity, including locomotion and all social interactions, significantly explained 81% of the variation in the total number of offspring sired and 90% of the variation in the number of clutches in which males sired offspring. We suggest that the most successful male strategy is a form of endurance rivalry in which active mate searching and interactions with females have the greatest fitness benefits.

Impact of Body Reserves on Energy Expenditure, Water Flux, and Mating Success in Breeding Male Northern Elephant Seals

In capital breeders, individual differences in body size and condition can impact mating effort and success. In addition to the collateral advantages of large body size in competition, large nutrient reserves may offer advantages in endurance rivalry and enable the high rates of energy expenditure associated with mating success. We examined the impacts of body reserves and dominance rank on energy expenditure, water flux, mating success, and breeding tenure in the adult male northern elephant seal, a polygynous, capital breeder. Adult males expended energy at a rate of 159 ± 49 MJ d (-1), which is equivalent to 3.1 times the standard metabolic rate predicted by Kleiber's equation. Despite high rates of energy expenditure and a long fasting duration, males spared lean tissue effectively, deriving a mean of 7% of their metabolism from protein catabolism. Body composition had a strong impact on the ability to spare lean tissue during breeding. When controlling for body size, energy expenditure, depletion of blubber reserves, and water efflux were significantly greater in alpha males than in subordinate males. Large body size was associated with increased reproductive effort, tenure on shore, dominance rank, and reproductive success. Terrestrial locomotion and topography appeared to strongly influence energy expenditure. Comparisons with conspecific females suggest greater total seasonal reproductive effort in male northern elephant seals when controlling for the effects of body mass. In polygynous capital breeding systems, male effort may be strongly influenced by physiological state and exceed that of females.

The reproductive ecology of resident manta rays (Manta alfredi) off Maui, Hawaii, with an emphasis on body size

In resident manta rays (Manta alfredi) off Maui, sexual maturity appears delayed until growth exceeds 90% of maximum size, an indicator that large body size provides a reproductive advantage at the expense of a shorter reproductive time period. In this study, 286 surveys were conducted between 2005 and 2010 using photo-identification and photogrammetry to study the reproductive ecology of a resident population of manta rays off Maui, Hawaii, and investigate the reproductive benefits of large body size in each sex. Although reproductive activities occurred year-round, mating trains and late-term pregnant females were significantly more likely to be observed during the winter months. Some females were pursued by males during both winter and summer of the same year, suggesting multiple ovulations may be possible in a single year. Males likely detect a female’s reproductive state by positioning directly behind her, or passing through her bodily excretions. The mean pregnancy rate was estimated at 0.56 pregnancies/adult female/year with larger females pregnant more often, and more likely in consecutive years. The operational sex ratio was heavily skewed with 2.68 adult males per reproductively available female. Although males appear to compete with one another for females within a mating train, no direct physical competition was ever observed between males. Evidence of highly dynamic mating trains lasting more than one day suggests endurance rivalry may be the primary mating strategy among males, during which larger males may benefit from greater energy reserves. The study area appears to be an important staging area for mating individuals in this population.

The energetics of male–male endurance rivalry in free-ranging rhesus macaques, Macaca mulatta

In many animal species, males engage in endurance rivalry, competing for mating opportunites over extended durations. In the rhesus macaque, a seasonally breeding primate species, energetically costly mating behaviours such as consortship lead to greater reproductive success, and the ability of males to improve their body condition before the mating season may be crucial in determining their ability to use such strategies. Here, we explore relationships between male dominance rank, behaviour, body mass index (BMI) and energetics (assessed through urinary C-peptide of insulin levels, UCPs) in free-ranging rhesus macaques during a 6-month birth season and subsequent 6-month mating season. We analysed measures of general activity, mating behaviours and restlessness, here defined as the rate of change between behaviours. During the birth season, high-ranking males spent more time feeding on high-energy food, were less restless and spent less time travelling than low-ranking males. Restlessness and travelling time were both negatively correlated with male BMI and UCPs. Males in good condition during the birth season were in good condition at the onset of the mating season. During the mating season, high-ranking males participated in more consortships, which were positively correlated with copulatory activity. Copulation was negatively correlated with UCP levels, demonstrating the cost of such mating activities. As a consequence, by the end of the mating season, high-ranking males were in the worst condition. Our results suggest that male rhesus macaques engage in competitive endurance rivalry, and that male condition built during the previous birth season is an integral part of mating success.

Body size and sexual selection in the koala

Sexual selection is often characterized by polygynous breeding systems, size dimorphism, and skewed operational sex ratios. Koalas are sexually dimorphic in multiple domains, yet are absent from the literature on sexual selection and the structure of their mating system is unclear. We provide the first documentation of the strength of sexual selection in koalas by using microsatellite markers to identify sires. We combine the genetic data with morphological data in order to assess the role of body size in regulating reproductive output. During our 4-year study, 37% of males were identified as possible sires. Males were significantly larger than females, with sires heavier than non-sires. Male body mass correlated with annual reproductive output, with Crow’s Index of Opportunity for Selection revealing that variation in male reproductive success was threefold higher than that of females. Since it appears that male koalas rarely engage in physical confrontations over access to females, size dimorphism could be based upon non-agonistic competition and/or female mate choice. We propose that size dimorphism in koalas evolved as a consequence of endurance rivalry promoting vocal sexual advertisements that attract females. We suggest that female choice is a key mediator of male reproductive output.

Unreliable preferences, reliable choice and sexual selection in leks

In leks, male mating effort depends on the multiplicative interaction between signal costs (performance) and time spent advertising (lek attendance). Most models of strategic signalling, by considering the costs and neglecting the time, make the assumption that signal costs alone can be informative of a male's mating effort and, thus, of his quality and condition. However, if males of different qualities use different rules to trade performance against attendance then the amount of honest information conveyed by signals may sensibly decrease. I used a two-person, zero-sum game to investigate the effect of female choice on advertising and lek attendance. The model predicts that under strong female choice, low-quality males invest proportionally more on performance and less on attendance than high-quality males, making mating signals unreliable cues of signaller quality. In contrast, under weak female choice, both low- and high-quality males are expected to invest in attendance to the detriment of performance and mating signals are expected to convey reliable information. These results show that female choice and endurance rivalry are not alternative mechanisms of sexual selection, because the latter depends on the former, and that an honest communication system (in which females increase the probability of mating with a higher-than-average-quality male by expressing their mate preferences) can be maintained even under unreliable advertising signals, as long as the risk of preferring the low-quality (but most attractive) male is more than compensated for by the low probability of coming upon him (because of his low attendance).