Mating success of male bushy-tailed woodrats: when bigger is not always better

To determine the factors that regulate mating opportunitiesof male bushy-tailed woodrats (Neotoma cinerea), we used stepwisemultiple regression on measurable morphological and behavioraltraits. DNA fingerprinting was used to determine the paternityof juveniles, allowing mating success (the number of femalesmated with), and reproductive success (the number of offspringfathered) to be quantified. Both measures of male success weresignificantly related to the growth rate of males while reproductivelyactive. The most successful males were those that had higher growthrates, indicating that there is relatively little cost (weightloss) associated with successful mating in male woodrats. Ourfindings demonstrate that although this species is highly sexuallydimorphic, large body size does not influence mating success.In addition, it appears that male mating success cannot be predictedfrom morphological measures and may instead be determined bybehavioral or olfactory cues.     

Extreme polygyny among southern elephant seals on Sea Lion Island, Falkland Islands

Elephant seals are known from long-term behavioral studies tobe highly polygynous and to show high variance in reproductivesuccess among males. However, genetic studies have determinedthat the level of polygyny varies between the closely relatednorthern and southern elephant seals. In the present study,we investigate paternal success at the Sea Lion Island southernelephant seal colony in the Falkland Islands by using both behavioralmeasures and genetic markers. We find that the average successof harem holding males at Sea Lion Island is significantly higherthan both the northern species and the nearby southern elephantseal population at Punta Delgada. We compare genetic paternitywith various behavioral indices of male mating success, andwe find that the behavioral measures provide a good estimateof the variance in male reproductive success. Only 28.2% ofmales achieved paternities, and among these, harem holders accountedfor 89.6%. We discuss the implications of our results in thecontext of the demographic and physical environment. Specifically,a comparatively high variance in resource holding potentialamong males, differences in male social behavior, and a smalltidal cycle limiting peripheral male access during female departurefrom the harem at this colony may be important factors leadingto the comparatively high variance in male reproductive successat Sea Lion Island.     

The association between rank,mating effort,and reproductive success in male Barbary macaques (Macaca sylvanus)

The association between social rank, mating effort, and reproductive success of male Barbary macaques (Macaca sylvanus) has been evaluated by longterm behavioral observations and subsequent paternity determination via oligonucleotide DNA fingerprinting in a large semifreeranging group. All offspring born between 1985 and 1988 that survived to at least 1 year of age (n=75) were available for paternity testing. The exclusion of all but one of the potential fathers from paternity was possible in 70 cases (93%). Mating activities were recorded using ad lib. and focal female sampling techniques. The analysis of male mating effort was restricted to the most likely days of conception. Male rank correlated significantly with male mating success in all four breeding seasons and with male reproductive success in three of the four seasons. Mating success and reproductive success also showed a significant correlation, with the exception of one breeding season, in which the proportion of males per fertilizable female was especially high. Poor mating success was almost always associated with poor reproductive success, while good mating success was less predictive for a male's actual reproductive success. This was apparently a consequence of sperm competition, resulting from the promiscuous mating system. Male mating success is not necessarily an unreliable indicator for reproductive success, provided that sufficient sample sizes are available and that conception periods can be determined. Sperm competition and other factors may weaken the association, however.     

How Pronghorn Females Avoid Inbreeding Depression

After a bottleneck in a closed population of pronghorn (Antilocapra americana), some inbred matings occurred, and we detected significant inbreeding depression. But inbred matings occurred less frequently than would be expected by chance. Pronghorn females chose mates after a sampling period and had complete control of the mating decision. Therefore, to discover the behavioral mechanism by which females avoided mating with close kin, we studied female movements and courtship sequences. When females moved from one harem to another in the sampling process, they did not shift to harem males of lower coancestry as they approached estrus. Rather, females progressed more slowly through the later courtship stages when the harem male was related vs. unrelated. Also, the rates of male courtship acts were higher within unrelated vs. related pairs. Some females appeared to use multiple mating as an inbreeding avoidance strategy. Our results suggested that inbreeding avoidance by female pronghorn occurred primarily by reactions to the late stages of male courtship, rather than by spatial avoidance of related males.     

Genetic mating system and the significance of harem associations in the bat Saccopteryx bilineata

We analysed the polygynous mating system of the bat Saccopteryx bilineata using behaviour observations and genetic data on 11 microsatellite DNA loci. Basic social units in S. bilineata are harem groups that consist of single males and up to eight females. Colonies comprise several harem groups, and the composition of colonies and harems is often stable over several reproductive seasons. The combination of parentage exclusion and likelihood-based parentage assignment in this study produced detailed parentage information for a large colony of S. bilineata. Reproduction occurred mostly within the colony (17% extra-colony paternity), but social associations in harems within the colony did not represent reproductive units (70% extra-harem paternity). The latter finding was consistent over three reproductive seasons. Spatial association of the roosting sites of males and females could not explain parentage patterns in the colony. Even though intra-harem paternity was less frequent than expected, it contributed significantly to reproduction of harem males. On average, the number of offspring sired by a male with females in his harem territory increased significantly with harem size, which corresponds to the higher energetic investment that is related to the maintenance of large harems. However, extra-harem paternity was not correlated with a male's harem size or intra-harem reproductive success. This suggests that individual preferences of females rather than male traits associated with the ability to defend large harems are most likely to cause the detected differences between social association and genetic mating system.     

Environmental and demographic drivers of male mating success vary across sequential reproductive episodes in a polygynous breeder

Ecological and social factors underpinning the inequality of male mating success in animal societies can be related to sex ratio, sexual conflict between breeders, effects of nonbreeders, resource dispersion, climatic conditions, and the various sequential stages of mating competition that constitute the sexual selection process. Here, we conducted an individual‐based study to investigate how local resource availability and demography interact with annual climate conditions to determine the degree of male mating inequality, and thus opportunity for sexual selection across two sequential reproductive episodes (harem and subsequent mate acquisition) in a naturally regulated (feral) horse population in Sable Island National Park Preserve, Canada. Using a 5‐year, spatially explicit, mark‐resight dataset and hierarchical mixed‐effects linear modeling, we evaluated the influence of adult sex ratio (ASR) on mating success and then tested for effects of freshwater availability, density, unpaired male abundance, and precipitation during each breeding season. Unpaired male abundance, freshwater availability, and ASR differed in their effects on male mating success according to year and selection episode. Opportunity for sexual selection in males associated with harem acquisition increased with ASR, and unpaired male abundance further explained weather‐related interannual variation after accounting for ASR. In contrast, once a harem was secured, ASR had little effect on male mating inequality in regard to acquiring additional females, while interannual variation in mating inequality increased with decreasing freshwater availability. Our findings show that local demography, resource availability, and weather effect opportunity for sexual selection in males differently depending on selection episode, and can attenuate or accentuate effects of ASR.     

Correlates of reproductive success within alternative mating tactics of the common shrew

Male common shrews (Sorex araneus) adopt two discrete matingtactics. The most successful males, in terms of number of offspringfathered, are those that establish large overlapping home rangesin areas of high female density early in the breeding season.An alternative, less successful mating tactic is to travel longdistances in search of mating opportunities. This study is aninvestigation of correlates of reproductive success for malesadopting these different mating tactics. Reproductive successunder natural conditions was assessed using DNA fingerprinting,and survival of offspring was monitored in the field. The numberof offspring fathered by males with overlapping home rangeswas positively correlated with the number of female ranges overlappedduring the breeding season and with testes mass. The numberof offspring fathered by males that made long-distance movementswas positively correlated with their epididymal sperm counts.It is argued that competitively superior (overlapping) malesachieve high reproductive success by competing to maximize thenumber of females inseminated, whereas those adopting an alternativemating tactic instead compete largely via sperm competition,aiming to maximize insemination success with any particularfemale. There was no significant difference in the fluctuatingasymmetry (FA) of males adopting different mating tactics (FAwas measured as the difference in length of the paired lateralscent glands). Fluctuating asymmetry was not related to thenumber of offspring fathered by males adopting either matingtactic, but was significantly correlated with the proportionof male offspring fathered that survived to sexual maturity.Although apparently not correlated with mating success in thisspecies, FA may reflect some aspect of genetic quality thataffects offspring survival. [Behav Ecol 7: 334–340 (1996)]     

The dynamics of male harem dominance in southern elephant seals (Mirounga leonina) at the South Shetland Islands

Breeding chronology, harem structure and changes in male harem dominance were studied at Stranger Point, Isla 25 de Mayo/King George Island, principally by extensive field census work during the 2003 breeding season. Males were individually identified and their size estimated by using a photogrammetric method. Peak female haul out for the population occurred on 31 October, when a total of 276 females were observed along 7 km of coastline, distributed in ten harems with a median size of 16 females. Overall sex ratio and harem sex ratio for the breeding population were 1:6.7 and 1:10.6, respectively. A total of 33 males were identified associated with harems. Male size conferred an advantage in terms of dominance hierarchy, since dominant males (4.91±0.15 m) were significantly longer than subordinate males (4.63±0.19 m). Harems were dominated by an average of 4.5 (range 2–7) different males during the breeding season. Elephant seals at Stranger Point breed in very low density aggregations. The main breeding events in this population occurred later than at other breeding sites, which agrees with previous observations in the area. Male movement among harems suggests that differences in mating success among males could be achieved through their different behaviours.     

Mating system structure and population density in a polygynous lizard, Sauromalus obesus (= ater)

Increases in population density often are associated with achange in mating system structure in numerous taxa. Typically,male interactions are minimal in extremely low density populations.As density increases, males exhibit territoriality but if densitybecomes too high, the energetic cost of defending a territorywill eventually outweigh the reproductive benefits associatedwith territoriality. Consequently, males in high density populationsmay abandon territoriality and adopt dominance polygyny, lekking behavior, or scramble competition. We investigated the relationshipbetween population density and mating system structure in threepopulations of the chuckwalla, Sauromalus obesus (= ater),near Phoenix, Arizona. Densities in the Phoenix Mountains (2.7chuckwallas/ha) were lower than any population previously studied.In the Santan Mountains (10.9 chuckwallas/ha), densities weresimilar to populations studied in the Mojave Desert, and inthe South Mountains (65 chuckwallas/ha), densities were the highest yet recorded. Male mating behavior was examined by determininghome range overlap and by making direct behavioral observations.Male home range size decreased with increasing population density.There was little overlap in home ranges among males in allthree populations, whereas home ranges of males and femalesconsistently overlapped, indicating that males were strictly territorial. This conclusion was supported by behavioral observationsof interactions among individuals in a natural setting. Thenumber of females wihin male territories was correlated withfood resources (plants) in all three populations. Female homerange size appeard to be related to food resources whereasmale home ranges appeared to be related to female distribution,population density, and geology. The retention of territoriality in spite of high population densities raises new questions aboutthe relationship between density and resource defense.     

High opportunity for postcopulatory sexual selection under field conditions

In polygamous systems, male fitness is determined not only by mating success but also by fertilization success. Despite the growing interest over the past several decades in postcopulatory sexual selection, its relative importance compared to precopulatory sexual selection remains a subject of debate. Here, we use extensive behavioral observations of a seminatural population of Hawaiian swordtail crickets, Laupala cerasina, and molecular paternity assignment to measure the opportunities for pre‐ and postcopulatory selection. Because postcopulatory selection has the potential to operate at multiple stages, we also separately attribute its effects to factors specific to mating events versus factors specific to males. We find that variance in postcopulatory success is over four times as great as variance in precopulatory success, with most of it unexplained by male mating order or the number of nuptial gifts given. Surprisingly, we also find that male singing effort is under postcopulatory selection, suggesting that males who sing more frequently also have more competitive ejaculates. Our results are consistent with the hypothesis that high polyandry levels promote greater relative postcopulatory selection. They also highlight the need for detailed behavioral observations under conditions as natural as possible when measuring mating and reproductive success.     

Scramble competition polygyny in the milkweed leaf beetle: combat, mobility, and the importance of being there

I examined the scramble competition mating system of the milkweedleaf beetle, Labidomera clivicollis(Coleoptera: Chrysomelidae),using data on lifetime mating success of two breeding cohortsin Austin, Texas, USA (30° N, 97° W) and one in Bridgeport,New York, USA (43° N, 76° W). Data from six daily censuseswere combined with focal animal samples to examine the importanceof combat between males and to evaluate the extent to whichthe characters elytron length, vagility, and emergence datewere correlated with male mating success. In both populations,emergence date was the only consistent determinant of the numberof mates a male obtained during his lifetime. Males emergingearlier in the season had higher mating success because theywere active for more of the breeding season. Male body size(elytron length) was not correlated with mating efficiency orlifetime mating success in either population. Males formed prolongedmating associations with females that lasted for up to 2.5 daysand paired males in the New York population had a strong advantageover interlopers attempting to mate with the female. Only 10%of takeover attempts were successful. Selection favored vagilemales in New York, where the sex ratio was male biased, butnot in Texas, where it was female biased. Males that were morevagile had higher mating efficiencies in New York but did nothave higher lifetime mating success because of a trade-off betweenmating efficiency and survival. Behavioral data demonstratedthat lone males spent more time walking and less time feedingthan lone females; mating males were unable to feed at all.The survival disadvantage that comes with increased vagilitymay be due to loss of time spent feeding. The characters examinedsuggest that the most important thing a male L. clivicolliscan do to increase his lifetime mating success is to be presentfor as much of the breeding season as possible.     

Queuing for harem access in colonies of the greater sac-winged bat

Colonies of the greater sac-winged bat, Saccopteryx bilineata, consist of nonterritorial males and males that defend harem territories in which females roost. The traits of nonterritorial males that define their success in harem take-overs are so far unknown. We predicted that the time nonterritorial males spent in the colony and their proximity to harems would be important factors. We temporarily removed harem holders from a colony of 60 greater sac-winged bats on consecutive days and observed which of the nonterritorial males took over the harem. To test for consistency of results, we repeated the experiments in some of the territories. In a second set of experiments, we removed both the harem holder and the corresponding usurper from the first experiment. On average, usurping males preferred territories with a large harem over territories with a small harem and they belonged to groups of males who spent the daytime near the corresponding harems. Usurpers in the second experiment were present in the colony for a shorter time than usurpers in the first experiment. Overall, the results support the hypothesis that nonterritorial males form overlapping peripheral groups for harems and that they live in a hierarchy according to their tenure in the group. Group membership and hierarchy seemed to be the factors that determined whether a male occupied a vacant harem. Hence, instead of floating, the pattern of harem succession in greater sac-winged bats is best described by queuing of nonterritorial males for access to a harem. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Experimental tests of copying and mate choice in fallow deer (Dama dama)

In fallow deer (Dama dama), as well as in other lek-breedingungulates, receptive females arriving at leks commonly joinmales that are defending large harems. This tendency enhancesdifferences in harem size and mating success between males.It could occur because females independendy move to the samemales, because females are attracted to males with females,or because females are attracted to each other. Using controlledexperiments with estrous female fallow deer, we show that, althoughfemales are more attracted to males with harems than to thosewithout, they are as frequently attracted to groups of femaleswithout a male as to female groups with males. We conclude thatfemale fallow deer joining leks are attracted to each otherand copy each other's movements. As yet, there is no firm evidencein fallow deer or in other lek-breeding ungulates that femalescopy each other's choice of mating partners. Key words: Damadama, fallow deer, lek breeding, mate choice, copying behavior.[Behav Ecol 4: 191–193 (1993)]     

Females decide whether size matters: plastic mate preferences tuned to the intensity of male-male competition

Recent studies have indicated that mating success of large malesmay improve under increasing levels of mating competition. Thisoutcome is explained 1) if male mating competition is overridingfemale preferences for male traits that are unrelated to, ornegatively correlated with, male size and dominance and, inso doing, dictates the distribution of matings or 2) if femalesalter their preferences with respect to large males when male–malecompetition is intense. Under both hypotheses, one could expectlarge, dominant males to be more successful under intense competitionthan under weak competition. However, only the first explanationpredicts that male mating success under intense competitionshould be determined by dominance; traits that are unrelatedto male dominance should be uncorrelated to mating success.In contrast, if females change their preferences (explanation2), males with traits beneficial to females independent of thecompetitive environment can maintain a high mating success underall levels of male–male competition. We tested these alternativesusing a small marine fish, the sand goby, Pomatoschistus minutus.The mating success of large males increased under conditionsallowing intense male competition, whereas females showed apreference for good nest building independent of the level ofcompetition. These findings suggest that females are in controlof their choice by altering their preference for male size inresponse to the intensity of male–male competition ratherthan female preference being overshadowed by male dominance.This plasticity of preferences implies that the strength ofsexual selection is not constant at the population level.     

Reproductive consequences of bilateral asymmetry for individual male red-winged blackbirds

We used morphological and breeding data from a 2-year fieldstudy of red-winged blackbirds (Agelaius phoeniceus) to testthe hypothesis that males characterized by low levels of bilateralasymmetry (i.e., high developmental competence) realize a reproductiveadvantage. Specifically, we evaluated each of several distinctcomponents of male reproductive success relative to asymmetrymeasures made on five bilaterally paired characters. Resultsof a male removal experiment generally failed to support theprediction that symmetry would be associated with success incompetition for access to breeding territories: establishedterritory owners and nonterritorial replacement males were effectivelyindistinguishable in this regard. Similarly, there was no indicationthat symmetrical males were more likely to establish territoriesin high-quality marsh habitat than in marginal upland fieldhabitat. Finally, monitoring of breeding activity in high-qualityhabitat revealed that male symmetry was generally unrelatedto recruitment of social mates (i.e., harem size), the productivityof those mates (average female reproductive success), withinpairpaternity (assessed using DNA-based analysis of parentage),or extrapair mating success. Collectively these results indicatethat symmetry is not an important determinant of reproductivesuccess among individual male red-winged blackbirds. This observation,in combination with the results of several other recent investigations,suggests that the fitness consequences of subtle departuresfrom perfect symmetry may be less significant and/or less ubiquitousthan initially suggested.     

Ontogenetic colour change signals sexual maturity in a non-territorial damselfly

Conspicuous colouration increases male reproductive success through female preferences and/or male–male competition. Despite the advantages of conspicuous colouration, inconspicuous male morphs can exist simultaneously in a population due to genetic diversity, condition dependence or developmental constraints. We are interested in explaining the male dichromatism in Xanthagrion erythroneurum damselflies. We reared these damselflies in outdoor insectaries under natural conditions and showed that this species undergoes ontogenetic colour changes. The younger males are yellow and change colour to red 6–7 days after their emergence. We took red and yellow male reflectance spectra and found that red males are brighter than yellow males. Next, we aimed to determine whether ontogenetic colour change signals sexual maturity with field observations and laboratory experiments. Our field observational data showed that red males are in higher abundance in the breeding territory, and they have a higher mating frequency than yellow males. We confirmed these field observations by enclosing a red and a yellow male with two females and found that yellow males do not mate in presence of red males. To determine whether colour change signals sexual maturity, we measured mating success of males before and after colour changes by enclosing a single male at different age (day 3-day 7) and colour (yellow, intermediate and red) with a single female in a mating cage. Males did not mate when yellow but the same male mated after it changed colour to red, suggesting the ontogenetic colour change signals sexual maturity in this species. Our study shows that male dichromatism can be age-dependent and ontogenetic colour change can signal age and sexual readiness in non-territorial insects.     

Reproductive success in the mandrill, Mandrillus sphinx: correlations of male dominance and mating success with paternity, as determined by DNA fingerprinting

Considerable controversy exists concerning possible effects of sexually selected phenotypes via intermale competition on reproductive success. The mandrill ( Mandrillus sphinx ) is an extreme example of evolution by sexual selection, and hence we have studied a semi-free-ranging colony of mandrills in Gabon to gather information on male rank, mating success and paternity, as determined by DNA fingerprinting. Two morphological variants or adult male were identified; 'fatted' males, with maximum secondary sexual coloration, which occupied dominant positions in the social group, and 'non-fatted' males, with muted secondary sexual adornments, smaller testes and lower plasma testosterone levels, which lived as peripheral/solitary individuals. DNA fingerprinting analyses on infants born over five successive years showed that only the two most dominant, fatted males in the group had fathered off spring. Throughout the annual mating season these males attempted to mate-guard and copulate with females during periods of maximal sexual skin tumescence. Male rank and mating success were strongly positively related and the alpha male sired 80–100% of the resulting offspring during three consecutive years. Non-fatted adult males and group associated subadult males engaged in infrequent, opportunistic matings and did not guard females. Loss of alpha status resulted in a fall in reproductive success, but the effect was gradual; the deposed alpha male continued to father 67% and 25% of infants born during the next two years. Thus these results of behavioural and genetic studies on mandrills demonstrate unequivocally that clear-cut relationships exist between male secondary sexual development, social dominance, copulatory behaviour and reproductive success in the social group.     

Territoriality and male reproductive success in arctic ground squirrels

Although territorial defense is a common form of reproductivecompetition among male vertebrates, the exact reproductiveconsequences of this behavior are often poorly understood.To explore relationships between territoriality and reproductivesuccess in a nongroup-living mammal, we quantified patterns of space use, mating success, and fertilization success formales in a free-living population of arctic ground squirrels(Spermophilus parryii plesius). Because litters of this speciesare sired almost exclusively by a female's first mate, we predictedthat territory ownership would be associated with first accessto estrous females. During the 2-week period when mating occurred,each male in the study population attempted to defend a distinctportion of the habitat, although the success of this defensevaried among individuals. Twenty-six of 28 females monitoredmated with the male on whose territory they resided. However,the majority of females observed throughout estrus (65%; n= 20) also mated with at least one other male, indicating thatterritory ownership was not associated with exclusive accessto females. In contrast, territory ownership was significantly associated with first access to estrous females; 20 (71.4%)of 28 females mated first with the male on whose territorythey resided. In this regard, the behavior of S. parryii plesiusparallels that of socially monogamous birds in which territorialdefense by males functions to deter extrapair copulations byfemales. Although territorial defense represents an important component of male reproductive success in arctic ground squirrels,other aspects of male behavior (e.g., the ability to dominateagonistic interactions on the day of a female's estrus) arealso critical. We suggest that future studies of vertebratemating systems will benefit by viewing such defense as onlyone of multiple axes along which conspecific males compete foraccess to females.     

Sexual selection and condition dependence of courtship display in three species of horned dung beetles

Sexual selection has traditionally been divided into competitionover mates and mate choice. Currently, models of sexual selectionpredict that sexual traits are expressed in proportion to thecondition of their bearer. In horned beetles, male contestcompetition is well established, but studies on female preferencesare scarce. Here I present data on male mating success and condition dependence of courtship rate in three species of horn-dimorphicdung beetles, Onthophagus taurus, Onthophagus binodis, andOnthophagus australis. I found that in the absence of malecontest competition, mating success of O. taurus and O. australiswas unrelated to their horn length and body size, whereas inO. binodis horn size had a negative effect but body size hada positive effect on male mating success. Overall, in O. binodismajor morph males had greater mating success than minor morphmales. In all three species male mating success was affectedby courtship rate, and the courtship rate was condition dependent such that when males were manipulated to be in poor conditionthey had lower courtship rates than males that were manipulatedto be in good condition. My findings provide new insight intothe mating systems of horned dung beetles and support an importantassumption in indicator models of sexual selection.     

Sex-specific differences in reindeer calf behavior and predation vulnerability

According to reproductive strategy theory, males in polygamousbreeding systems should invest in morphological or behavioralfeatures that increase reproductive success. When the earlydevelopment of such traits conflicts with predator protection,we expect that male calves will exhibit risk-taking behavior,such as high activity level and increasing distance from mother,to a greater extent than female calves. We investigated sexdifferences in mother–calf distance, calf activity levels,and calf mortality in a semi-domesticated reindeer (Rangifertarandus) population. The results show that male calves strayfarther away from their mothers, exhibit a higher level of locomotivebehavior in terms of play and walking, and are more vulnerableto predation than are female calves. Although mother–calfdistance increased over time in 1- to 6-month-old calves, noevidence was apparent for an increase in sex difference in mother–calfdistance over this period. The results suggest a trade-off betweenpredation vulnerability and investments in behavioral traitsthought to be important for future reproductive success andsuggest that these sex-related differences in behavior are apparentas early as 6 months of age.