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)]     

Behavioral estimates of male mating success tested by DNA fingerprinting in a polygynous mammal

We used DNA fingerprinting to determine paternity of 80 calvesborn into the individually monitored population of red deer(Cervus elaphus) on the Isle of Rum, Scotland. Using the paternityinformation, we investigated the assumptions and predictionsof behavioral estimates of male mating success, on which previousstudies in this population have relied. Over an 11- day intervalin the rut centered on a female's estimated date of conception,the probability that a male fathers a calf is closely relatedto the number of days he holds the female in his harem, increasingfrom 0.12 for 1 day to 1.0 for 6 days or more. We compared threemethods for estimating the reproductive success of individualmales from field observations of harem membership with truesuccess revealed by DNA fingerprinting. All three methods accuratelyidentified the relative success of individual males but werepoor predictors of absolute success: the behavioral methodsunderestimate the true success of successful males and overestimatethe success of many males who, in fact, fail to father any calves.In consequence, variance in male mating success is greater thanprevious behavioral estimates for this population suggested.Both harem membership data and observations of mating and otherestrous behavior can be used to identify males most likely tofather a specific calf.     

Pairing success of male Gammarus lacustris infected by two acanthocephalans: a comparative study

The costs of parasitism to host reproduction can be best assessedusing field studies to determine overall mating success andexperimental studies to examine how parasites may affect matingbehavior. We compared the influence of two parasites, Polymorphusparadoxus and P. marilis (Acanthocephala), on the pairing successof their intermediate host (Gammarus lacustris, Crustacea) inboth the field and laboratory. Parasitism significantly loweredthe pairing success of male gammarids. In the field, P. paradoxus-infectedmales paired significantly less often than P. marilis-infectedor uninfected males. Those infected by P. marilis were alsofound in precopula significandy less often than uninfected ones.In the laboratory, the pairing success of males infected byeither parasite was significantly reduced in both competitiveand noncompetitive situations. As in the field studies, thepairing success of P. paradoxus-infected males was significantlylower than that of P. marilis-infected and uninfected males.Polymorphus marilis-infected males were also outcompeted byuninfected individuals, however, their pairing success improvedwhen alone with a female (noncompetitive experiments). We relatethe differential influence of the two parasites on the pairingsuccess of male gammarids to their effects on the physiologyand behavior of G. lacustris.     

Sexual selection and mating patterns in a mammal with female-biased sexual size dimorphism

In mammals, species with highly male-biased sexual size dimorphismtend to have high variance in male reproductive success. However,little information is available on patterns of sexual selection,variation in male and female reproductive success, and bodysize and mating success in species with female-biased size dimorphism.We used parentage data from microsatellite DNA loci to examinethese issues in the yellow-pine chipmunk (Tamias amoenus), asmall ground squirrel with female-biased sexual size dimorphism.Chipmunks were monitored over 3 years in the Kananaskis Valley,Alberta, Canada. We found evidence of high levels of multiplepaternity within litters. Variation in male and female reproductivesuccess was equal, and the opportunity for sexual selectionwas only marginally higher in males than females. Male and femalereproductive success both depended on mating success. We foundno evidence that the number of genetic mates a male had dependedon body size. Our results are consistent with a promiscuousmating system in which males and female mate with multiple partners.Low variation in male reproductive success may be a generalfeature of mammalian species in which females are larger thanmales.     

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.     

A multivariate analysis of phenotype and paternity in male harbor seals, Phoca vitulina, at Sable Island, Nova Scotia

Understanding the links between phenotype and reproductive successis critical to the study of the evolution of mating systemsand life-history patterns. We examined the relationship betweenphenotype and mating success of male harbor seals (Phoca vitulinaconcolour) at Sable Island, Canada. Cluster analyses of eighttraits including mating success determined by genetic paternityanalysis, haul-out behavior, body mass, and mass change identifiedfour groups of males with distinct characteristics. The most successfulmales were of moderate body size, were rarely sighted alone,were associated with many different groups on shore, and weresighted on the haul-out relatively infrequently. Large malesthat hauled out frequently alone, previously thought to be sociallydominant, were less likely to be successful. Also less successfulwere smaller, younger males. Contrary to our hypotheses, andunlike most terrestrially breeding pinnipeds, body size and reproductiveeffort were not positively associated with mating success, and somesuccessful males appeared to spend considerable time foragingin deep water.     

Postmating sexual selection: the effects of male body size and recovery period on paternity and egg production rate in a water strider

The role of male body size in postmating sexual selection wasexplored in a semiaquatic insect, the water strider Gerris lateralis.To separate effects of male size per se from those due to numericsperm competition, male recovery period (shown here to be proportionalto ejaculate size) was manipulated independently of body sizein a factorial experiment where virgin females were mated firstwith sterile males and then with focal males. Both relativemale fertilization success and female reproductive rate were measured.The number of sperm transferred increased with male recoveryperiod, an effect that was mediated by longer copulation duration,but there were no effects of body size on ejaculate size. Neithermale size nor recovery period had any significant direct effectson male fertilization success. However, copulation durationinfluenced relative fertilization success, suggesting that malesable to transfer more sperm also achieved higher fertilizationsuccess. Females exercised cryptic female choice by modulatingtheir reproductive rate in a manner favoring large males andmales that were successful in terms of achieving high relativefertilization success. Thus, successful males gained a twofoldadvantage in postmating sexual selection. This study has important implicationsfor previous estimates of sexual selection in this group of insectsbecause pre- and postmating sexual selection will be antagonisticdue to limitations in male sperm production: males mating frequently(high mating success) will on average transfer fewer sperm ineach mating and will hence tend to fertilize fewer eggs permating (low fertilization success).     

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.     

Male Reproductive Tactics in an Explosive Breeding Toad Population

American toad (Bufo amencanus) males use one of two differentreproductive tactics. Some males are stationary and call. Othersare silent and mobile. Based on field studies, I developed acomputer program that simulates the behavior of females andmales to determine the probability of mating success of malesengaging the different tactics and the factors that effect malereproductive success. Field studies indicate that non-calling males can be successful.Non-calling males were more numerous and smaller than callingmales. Population size changed greatly both between and withinnights. Contact rates for non-calling males were greater thanthose for calling males. The results of the preliminary simulations indicate that malemating success is a function of the population size and theoperational sex ratio. In small populations, contact rate hasno effect on male success. The effect of contact rate on malesuccess has not been tested in large populations. In large populations,mating success is also a function of the ratio of calling tonon-calling males. Generally, in small populations (n > 20)calling males are more successful than non-calling males. Inlarge populations (n > 40) the success of noncalling malesis equal to or greater than the success of calling males.     

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.     

Microsatellite determination of male reproductive success in a natural population of the territorial ornate dragon lizard, Ctenophorus ornatus

It is now evident that the genetic mating system can be very different to the observed mating system. However, it is less well known what makes particular individuals more (or less) successful than expected from the observed system. In this study the observed territorial structure of a field population of the agamid lizard, Ctenophorus ornatus, was compared with the mating system as evidenced by microsatellite parentage assignment. This study also investigated whether any male traits predicted reproductive success. Sixty-five per cent of clutches were sired at least partially by a male other than the main territory-holding male and 35% of clutches were sired by a male with no overlap of the female's territory. Multiple paternity was moderately frequent at 25% of clutches. Male chest patch size predicted territory size and the number of females in the territory, but did not predict reproductive success. Instead, male head depth and body size were independently related to the number of offspring sired. As male head depth also predicted the number of females in a territory, these males are likely to be gaining increased reproductive success as a consequence of the higher number of females in their territories. Larger body size males, however, did not have a greater number of females in their territory and instead had more extra-territorial copulations. Whether these extra-territorial copulations are due to female choice or success in male competition is unknown.     

Lifetime mating success of males in a natural population of the papilionid butterfly,Atrophaneura alcinous (Lepidoptera: Papilionidae)

Lifetime mating success of males in a natural population of the papilionid butterfly, Atrophaneura alcinous, was investigated and causes of the variation were examined. The most successful males mated with 5 females, whereas about 73% of the males failed to mate. Body size of males was not correlated with their eclosion date, longevity and lifetime mating success. There was no trade-off between mating success and longevity, and long-lived males had a disproportionately high mating success. Although number of available females per male per day was not variable among males with different longevities, long-lived males had higher mating efficiency. Time interval between matings by non-virgin males was shorter than that from eclosion to the first mating. High lifetime mating success of long-lived males was strongly related to their mating experience, not to their age per se.     

Age-related decrease in male reproductive success and song quality in Drosophila montana

In the present paper, we have studied the effects of aging onmale reproductive success and song quality in Drosophila montana.We analyzed the reproductive success of wild-caught males attheir normal breeding age during the mating season and aftermaintaining the males in laboratory from 1 to 5 months. In linewith the mutation accumulation theory of aging, none of thefactors affecting the reproductive success of wild-caught malesduring the mating season were related to male longevity. However,mating activity and progeny production of the males decreasedwith male age. Interestingly, there was no significant variationin progeny production between males at their normal breedingage, whereas at older age, the variation between males becomessignificant. The quality of sexually selected song traits deterioratedwith male age in concert with the decrease in male reproductivesuccess. The size of the males did not have an effect on malereproductive success at the normal breeding age, but at olderage, larger males were able to maintain the sexually selectedcarrier frequency of the song at higher level than the smallermales. We conclude that by experimentally extending the reproductiveage of the males beyond that which they normally experiencein nature, it is possible to expose relationships between reproductivesuccess, sexually selected characters, and body size that arenot apparent when analyzed for the males at their normal breedingage.     

Maintenance of androdioecy in the freshwater shrimp Eulimnadia texana: sexual encounter rates and outcrossing success

The clam shrimp Eulimnadia texana has a rare mating system known as androdioecy, in which males and hermaphrodites cooccur butthere are no pure females. In this species, reproduction takesplace by outcrossing between males and hermaphrodites, or byselfing within a hermaphrodite; this system provides a uniqueopportunity to examine the adaptive significance of out-crossingand selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understandthe propensity of these shrimp to mate and to estimate a parameterof a model developed by Otto et al. (American Naturalist 141:329-337),which predicts the conditions for stability of the mixed matingsystem in E. texana. Here we present evidence that mating frequencyis environmentally sensitive, with greater numbers of encountersand matings per male when males are rare and in younger males.However, the effects of shrimp density, relative male frequency,and shrimp age interact in a complex way to determine malemating success. Overall, mating frequency was determined bya combination of encounter rates between the sexes and theproportion of encounters resulting in mating. The mating rateswere then used to estimate one of four parameters of the Ottoet al. model, and these estimates were combined with previousestimates of the other three parameters to examine the fitof the predicted to the observed sex ratios in the two populations.     

Trade-off between pre and post-copulatory traits depends on locomotor activity in male Tribolium castaneum beetles

Locomotor performance is an indicator of dynamic exercise; thus, it is a central trait in many animal behaviours. Although higher locomotor endurance may increase male reproductive success (e.g., in mate searching and male–male contests), investment in other male reproductive traits (e.g., male attractiveness and sperm competition) may be decreased through energy consumption due to higher activity levels. Here, I investigated male attractiveness, mating success, and paternity success using males of the red flour beetle Tribolium castaneum selected for higher (H) and lower (L) locomotor endurance. Although there was no difference in male attractiveness between the selection regimes, H males had significantly higher mating success than L males. Conversely, L males had significantly higher paternity success than H males. Therefore, there was a trade-off between mating success and paternity success among the selection regimes, suggesting that locomotor endurance affects male reproduction in T. castaneum, and individual variation of locomotor endurance may be maintained within a population.     

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.     

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.     

Estimating a Key Parameter of Mammalian Mating Systems: The Chance of Siring Success for a Mated Male

Studies of multiple paternity in mammals and other animal species generally report proportion of multiple paternity among litters, mean litter sizes, and mean number of sires per litter. It is shown how these variables can be used to produce an estimate of the probability of reproductive success for a male that has mated with a female. This estimate of male success is more informative about the mating system that alternative measures, like the proportion of litters with multiple paternity or the mean number of sires per litter. The probability of success for a mated male can be measured both theoretically and empirically, and gives an estimate of the intensity of sperm competition and of a male's “confidence of paternity” upon mating. The probability of success for mated males for ten “exemplar” species of mammals is estimated and they are compared for insights into the functioning of their mating systems.     

Emergence and mating behavior of the oriental fruit moth Cydia molesta (Lepidoptera: Tortricidae) and its potential for reproduction

The Oriental fruit moth, Cydia molesta (Busck, 1916) (Lepidoptera: Tortricidae), is a key pest of fruit and is widely distributed around the world. There are important connections between its behavior and biology and its management in agriculture, but few studies have investigated the associations between adult behaviors and oviposition. In this study, adult emergence, mating, and reproduction were investigated under laboratory and field conditions. The ratio of females to males at eclosion was approximately 1:1. When one virgin female had access to one virgin male, 66% and 34% of the couples copulated just once and twice, respectively; and the infertility rate of eggs (21.39 ± 1.25%) did not vary daily. Males, given access to one new female daily, could copulate multiple times, whereas females seldom mated more than once, indicating a male-biased operational sex ratio, but mating status of the male parent had no effect on progeny egg reproduction. Also, the number of eggs that hatched by all female partners of a male was inversely proportional to copulation duration for the female laying the eggs for total female reproductive success; and the number of eggs laid by all female partners of a male was proportional to their number of matings for total male reproductive success. However, the total number of eggs that hatched did not significantly differ for eggs laid by a female given new virgin males daily for mating (17.75 ± 4.28) versus eggs laid by virgin females (19.17 ± 7.51) presented daily with a male that re-mated daily with the series of females. Therefore, our results showed that females engaged in mate choice and males engaged in mate competition, affecting egg production, a factor that may be used to enhance mating disruption technology against Cydia molesta.     

Uncertainty in territory quality affects the benefits of usurpation in a Mediterranean wrasse

Individuals should defend sites when the expected benefits ofthe territory exceed the cost of defense. However, if territoryqulaity is unpredictable or difficult to assess, the expectedpattern of territorial behavior is less clear. In a Mediterraneanwrasse, Symphodus ocellatus, mating success is skewed with 2%of nesting males getting more than 20% of the spawning success.Yet, variation in mating success is not explained by any knownphysical characteristic of males or their territories. Instead,females prefer nests with a recent history of mating successbecause males are less likely to desert the offspring she leavesbehind. Thus, territory quality is transient and determinedby interactions between the sexes. I measured the frequencyof territorial takeovers and the uncertainty in mating successamong days at a nest. Observations indicated that S. ocellatusmales usurped their neighbor's successful nests when males wereunsuccessful and larger than their successful neighbor. Sitesthat achieved mating success had a significantly higher probability(0.84) of remaining sucessful between consecutive days thanunsuccessful territories had of becoming successful (0.30).Unsuccessful males obtained higher and more certain fitnessreturns if they usurped a successful neighbor's territory. Interactionswithin and between the sexes drive uncertainty in success, whichinfluences territorial behavior in this species.