Effects of maternal quality and mating status on female reproductive success in the polygynous spotless starling

Female mating status may affect reproductive success in avian polygynous mating systems through a combination of differences in female parental quality and status-dependent male assistance in parental care. Traditionally the literature has emphasized male assistance, neglecting evidence for consistency in female parental quality independent of mating status or repeatability in status. We studied the effects of male assistance on breeding success and its association with female mating status in a population of the polygynous spotless starling, Sturnus unicolor, during 3 years. Nestling provisioning by males improved the fledging success of late (mostly second) but not early (mostly first) broods. Reproductive success of females was affected mainly by female maternal quality: (1) primary and secondary females did not differ in output for early broods and in seasonal output despite a greater male assistance at primary nests; (2) monogamous females were more successful despite receiving no more help than other females; and (3) primary and secondary females had different clutch sizes before male assistance in parental care could operate. Female mating status was not significantly repeatable within seasons or between years. Females who changed status between years were as successful when rearing broods as secondary females as they were as primary or monogamous females. Breeding success (proportion of eggs resulting in fledglings) and clutch size were significantly repeatable between years for late but not for early clutches. Performance showed no strong association with female age or condition. Female breeding success seems to be weakly affected by male assistance in this sedentary, colonial species, and more dependent on inherent differences between females. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Relative influence of male and female genital morphology on paternity in the dung beetle Onthophagus taurus

Studies of fertilization success have demonstrated that maleeffects are often a strong and important source of variationin P₂ (the proportion of offspring that are fertilized by thesecond male to mate). More recently there has been emphasison female processes that occur during and after copulation thatmight bias the outcome of male-male interactions. Here we usedthe sterile male technique to evaluate whether female genitalmorphology influences the repeatability of P₂ when the samepair of male dung beetles, Onthophagus taurus, copulated witha series of full-sib females or unrelated females that wereall unrelated to the male pair. Repeatability estimates of measuresof female genital morphology showed that full-sib females variedless in their genital morphology than did unrelated females.Therefore, if female genital traits are an important sourceof variation in male fertilization success, P₂ should be morerepeatable across full-sib than unrelated females. Contraryto this prediction, we show that the repeatability of P₂ didnot differ between female groups. Moreover, specific dimensionsof the female genitalia (sclerotized vagina and bursa) did notcontribute significantly to variance in P₂. In contrast, maleeffects had consistent and repeatable influences on paternityacross females. These were partly explained by variation inthe morphology of male genital sclerites.     

Sexual selection for large male size in a polyandrous butterfly: the effect of body size on male versus female reproductive success in Pieris napi

Sexual selection theory predicts that the larger sex shouldbe that for which fitness increases at the faster rate withsize. In butterflies, as in most invertebrates, females areusually the larger sex, but previous comparative analysis hasshown that relative male size increases with female polyandryamong butterflies. In agreement with this pattern, males arelarger than females in the strongly polyandrous green-veinedwhite butterfly, Pieris napi L., and in this article we assessthe size dependence of reproductive success in both sexes. Inan experiment where virgin males and females were released inthe field, we found no strong association between size and malemating success. However, laboratory experiments showed thatthere was a strong correlation between size and the ejaculatethat the male delivered to the female at mating and that largeejaculates delayed female remating for a longer time comparedto small ejaculates. Moreover, female P. napi utilize male-derivednutrients received at mating to increase their fecundity. Hence,large males sire more offspring both by way of donating morenutrients to female egg production and by way of delaying femaleremating (given that the last male to mate with the female willfather most of the offspring). Laboratory experiments showedthat the association between size and fecundity was low, ornonexistent, among P. napi females allowed to mate only once.However, weak size dependence was found for polyandrous females.We hypothesize that size dependence of female fecundity maybe especially weak among polyandrous butterflies because a fundamentalsource of variation in fecundity relates to their ability tofind nutrient giving males, an ability which may be unrelatedto female size. According to this hypothesis there is a causalassociation between weak size dependence of female fecundityand polyandry, and a strong size dependence of male reproductivesuccess that may underlie the comparative pattern of positivecorrelation between relative male size and polyandry.     

Size, operational sex ratio, and mate-guarding success of the carrion beetle, Necrophila americana

When male insects guard females until oviposition, the benefitsfrom last-male sperm precedence must outweigh the costs of relinquishingadditional fertilizations. The profitability of guarding isincreased when males guard large, fecund females and when femalesare scarce because fewer fertilizations are sacrificed. However,the male reproductive success is not only determined by theprofitability of guarding but also by his ability to maintainguarding. In this study, we used male carrion beetles (Necrophilaamericana) to examine the effects of sex ratio, male relativesize, and female quality on the ability to guard. First, wepresent a model of mate guarding that explores factors, suchas sperm precedence, sex ratio, male size, and female quality,that influence the profitability of postcopulatory riding. Ourmodel predicts that large N. americana males should preferentiallyguard the largest female only when the sex ratio is male biasedand sperm precedence is above 80%. In contrast, small malesgain little from guarding because they are not likely to maintainit and be the last male to mate. Then, we tested these predictionsby manipulating sex ratio, relative male size, and female quality.All males in equal sex ratio and large males in male-biasedsex ratio guarded females significantly longer than did malesin female-biased sex ratio. In male-biased sex ratio, largemales guarded significantly longer and achieved more takeoversthan small males. Large females were guarded longer. The successof guarding males in this beetle depends on their size relativeto other males and the operational sex ratio.     

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.     

Female choice, male interference, and sperm precedence in the red-spotted newt

Darwin first identified female choice and male—male competitionas forms of sexual selection resulting in the evolution of conspicuoussexual dimorphism, but it has proven challenging to separatetheir effects. Their effects on sexual selection become evenmore complicated when sperm competition occurs because spermprecedence may be either a form of cryptic female choice ora form of male—male competition. We examined the effectsof tail height on male—male competition and female choiceusing the sexually dimorphic red-spotted newt (Notophthalmusviridescens viridescens). Experiment 1 examined whether maletail height influenced male mating success. Males with deeptails were more successful at mating with females than thosewith shallow tails. Successful, deep-tailed males also were bigger(snout-vent length; SVL) than unsuccessful, shallow-tailed males,but they did not vary in tail length or body condition. Of these,only tail height and tail length are sexually dimorphic traits.Experiment 2 tested the hypothesis that the differential successof males with deeper tails was due to female choice by examiningboth simultaneous female preference for association and sequentialfemale choice. We found no evidence of female choice. When maleswere not competing to mate with females, tail height did notinfluence male mating success. Successful males did not havedifferent SVL and tail lengths than unsuccessful males. Thus,tail height in male red-spotted newts appears to be an intrasexuallyselected secondary sexual characteristic. Experiment 3 usedpaternity exclusion analyses based on molecular genetic markersto examine the effect of sperm precedence on sperm competitionin doubly-mated females. Sperm precedence likely does not havea pervasive and consistent effect on fertilization success becausewe found evidence of first, last, and mixed sperm usage.     

Male brood care without paternity increases mating success

We investigate under which conditions we can expect the evolutionof costly male care for unrelated offspring, when the benefitof such care is in the form of increased mating success. Thisapplies to male helping behavior that cannot be explained aspaternal care because the male's own offspring does not benefitfrom his behavior. Our model shows that caring for others' offspringcan be a stable strategy for males, if a male that does not"help" loses mating opportunities, for example if females discriminateagainst non-helping males as mating partners. This is possiblewhen females are polyandrous. Increasing population densitydecreases the parameter region where male care is stable. Malecare is also more likely to be stable when male mortality rateis higher than that of females. We discuss the results withspecial reference to the golden egg bug Phyllomorpha laciniata,where females lay eggs on conspecifics, often on males beforemating. Males therefore carry mostly unrelated eggs. We investigatehow oviposition rate and female mating rate influences whenegg carrying is an evolutionary stable strategy. We concludethat in the golden egg bug, male egg carrying could be explainedas a form of mating investment.     

Mate-sharing costs in polygynous Northern Lapwings Vanellus vanellus

In this study bigamous female Northern Lapwings Vanellus vanellus received significantly less incubation relief from their males than monogamous females. On average, monogamous males spent 34.3% of their time incubating and bigamous males 29.9%. Bigamous males divided their effort between their nests, incubating on average 9.4% on primary nests and 20.5% on secondary nests. Bigamous females compensated for the lack of male relief. Primary females incubated for 71.8% of their time, secondary females for 64.2%, while monogamous females spent 52.7% of their time incubating. As a result, there was no significant difference in total nest attentiveness among nests of different status. Primary and secondary females received equivalent incubation relief from the male. Bigamous males increased their contribution to incubation significantly as the season progressed. A bigamous male's distribution of incubation relief between his females was unrelated to female body mass, or to the degree of asynchrony between primary and secondary females in arrival and laying. Incubation time was significantly, negatively, correlated with total nest attentiveness. Monogamous females spent most time, secondary females spent an intermediate time, and primary females spent the least time on maintenance behaviour (foraging, comfort behaviour, inactivity). No significant differences were found in hatching success among females of different mating status. However, the ratio of unhatched to hatched eggs (i.e. the eggs that remained in the nest at the time of hatching) differed significantly: secondary females hatched a smaller proportion of their eggs than monogamous and primary females.     

The importance of sperm competition risk and nest appearance for male behavior and female choice in the sand goby, Pomatoschistus minutus

To test if an increased sperm competition risk affects malebehavior and mating decisions of both sexes, we performed twoexperiments using the sand goby, Pomatoschistus minutus, a nest-buildingfish with exclusive paternal care. In our first experiment,a nest-holding male, with a confined female, was sequentiallyexposed to a vial with a sneaker male or an empty vial. Whilemale courtship, nest building, displacement fanning, and timeoutside the nest were unaffected, individual males showed ahigher mucus preparation effort inside the nest in the presenceof a sneaker male than when alone. We found such mucus to containsperm, thus clearly suggesting an importance in sperm competition.In our second experiment, a female was free to spawn with twodifferent males, one of which was exposed to a confined sneakermale. Male mating success was not affected by the presence ofa sneaker male. However, the volume of sand the male had puton his nest was positively associated with female spawning decision,while nest-opening width was not. In a partial correlation offive traits thought to attract females (nest-opening width,sand volume, male courtship display, displacement fanning, andmale size), males that fanned well were found to also buildlarge nests or display intensely, but not both. This indicatesthat rather than being jacks-of-all-trades, individual malesfocus on a subset of traits for attracting females.     

Male competition and female choice interact to determine mating success in the bluefin killifish

Whether male competition and female choice act in concert, independently,or in opposition is a critical issue for understanding sexualselection. In complex social systems, the outcomes of pairwiseinteractions may not be accurate indicators of how sexual selectionemerges. We investigated how female choice and male competitioninteract in the bluefin killifish, Lucania goodei, in a 3-stagedexperiment where 1) females could choose between 2 males, 2)those males could interact in the presence of that female, and3) females and males could freely interact and spawn. In thepairwise stages (1 and 2), females displayed pronounced preferencesbetween males and male competition produced a distinctly dominantindividual. None of the morphological traits, including color,measured in males were associated with either female preferenceor male dominance. When all 3 fish interacted (stage 3), maleactivity level was the sole predictor of spawning success. Maleswith elevated activity levels were more aggressive toward malesand females, exhibited intensified courtship, and obtained morespawns. Female preference did not predict the number of spawnswith a male, but it did predict her latency to spawn; femalesspawned more quickly with preferred males. Thus, male competitionand female choice interact to determine reproductive success,but there is evidence for conflict and a cost to females ofassociating with dominant males. Reproductive success in thisspecies is not easily predicted from simple measures of morphologyor female preference and is influenced by complex social interactions,both between males, and between males and females.     

Paternity costs from polyandry compensated by increased fecundity in the hide beetle

Polyandry-induced sperm competition is assumed to impose costson males through reduced per capita paternity success. In contrast,studies focusing on the consequences of polyandry for femalesreport increased oviposition rates and fertility. For thesespecies, there is potential for the increased female fecundityassociated with polyandry to offset the costs to males of sharedpaternity. We tested this hypothesis by comparing the proportionand number of offspring sired by males mated with monandrousand polyandrous females in the hide beetle, Dermestes maculates,both for males mating with different females and for males rematingwith the same female. In 4 mating treatments, monandrous femalesmated either once or twice with the same male and polyandrousfemales mated either twice with 2 different males or thricewith 2 males (where 1 male mated twice). Polyandrous and twice-matingmonandrous females displayed greater fecundity and fertilitythan singly mating monandrous females. Moreover, males rematedto the same female had greater paternity regardless of whetherthat female mated with another male. In both polyandrous treatments,male mating order did not affect paternity success. Finally,although the proportion of eggs sired decreased if a male matedwith a polyandrous female, multiply mating females or femalesthat remated with a previous mate laid significantly more eggsand thus the actual number of eggs sired was comparable. Thus,males do not necessarily accrue a net fitness loss when matingwith polyandrous females. This may explain the absence of anyobvious defensive paternity-protection traits in hide beetlesand other species.     

Population differences in female resource abundance, adult sex ratio, and male mating success in Dendrobates pumilio

In this study I examined the relationship among abundance ofreproductive resources, population density, and adult sex ratioin the strawberry dart-poison frog, Dendrobates pumilio, andhow these variables in turn influence the mating system, malereproductive success, and sexual selection. I studied the matingbehavior in two populations of D. pumilio living in a primaryand secondary rainforest on the Caribbean slope of Costa Rica.The abundance of tadpole-rearing sites (reproductive resourcesfor females) was approximately 10-fold higher in the secondary forest. Accordingly, the population density was higher and theadult sex ratio was strongly female biased in the secondaryforest, whereas the adult sex ratio was even in the primaryforest. The female-biased sex ratio was associated with a higherlevel of polygyny and higher male mating and reproductive successin the secondary forest. In contrast, the level of polyandrydid not differ between habitats. As expected, the opportunityfor sexual selection on male mating success was lower in thesecondary forest, the habitat with high female density. Inconclusion, my results suggest that ecological variables suchas resource availability have a great impact on the matingsystem and sexual selection through their effect on population structure. Moreover, the results of this study give furtherevidence that the opportunity for sexual selection is influencedby the adult sex ratio and hence by the operational sex ratioin a population.     

Sequential mate encounters: female but not male body size influences female remating behavior

Whether and how individuals choose sequentially among matesis an important but largely neglected aspect in sexual selectionstudies. Here, we explore female remating behavior in the cellarspider Pholcus phalangioides. We focus on body size as one ofthe most important traits involved in mate choice. Large andsmall females (n = 216) were double mated with large or smallmales in all eight possible combinations. All females copulatedwhen virgin, but only 82% accepted a second male. The chanceof a female remating was not significantly predicted by thebody size of the second or first male or by the size differencebetween the two. In contrast, a previous study demonstrateda male size effect in that larger males monopolized femalesuntil egg laying when two males of different sizes were present.We suggest that sequential encounters are more common undernatural conditions than male monopolization of females becauseestimates of concurrent multiple paternity together with observationsin a natural population do not favor mate guarding as the predominantmating strategy in this species. It follows from our study thatthe intensity of sexual selection on male size may be greatlyoverestimated when using a competitive laboratory setting fora species in which females generally encounter mates in a sequentialfashion. Female remating probability was significantly predictedby female size, with large females remating with higher probabilitythan small females. Thus, when mating with large females, malesmay gain higher fertilization success through increased femalefecundity but also face a higher sperm competition risk.     

棉铃虫成虫对性信息素的电生理和行为反应研究

通过EAG和风洞实验,研究了棉铃虫雌雄成虫对性信息素组分和诱芯(Z-11-16Ald∶Z-9-16Ald=97∶3)的电生理反应。其中棉铃虫雌、雄蛾对诱芯的平均EAG反应测定值分别为1.06mV和4.32mV,分别高出对照(无性信息素空白诱芯)0.67mV和0.366mV,差异均达到极显著水平(雌蛾：t＝25.020, P≤0.01;雄蛾：t＝44.269,P≤0.01);棉铃虫雌蛾对性信息素组分(Z-11-16-Ald和Z-9.16Ald)的EAG反应值随浓度增加而增加;雄蛾在被剪除触角后与雌蛾不能正常交配,而雌蛾在被剪除触角后仍有40%的交配率,比正常雌雄蛾的交配率(70%)有所下降;在风洞实验中,雄蛾没有顺风远离诱源的飞行行为,趋向诱源的比率为81.8%,与对照有显著差异。研究表明性信息素组分对棉铃虫的交配活动有明显的影响。     

Nest and mate choice in the red bishop (Euplectes orix) : female settlement rules

We investigated female settlement in a colony of red bishops(Euplectes orix), a territorial and highly polygynous weaverbirdwidely distributed over sub-Saharan Africa. An earlier studyshowed that male reproductive success is mainly determinedby the number of nests a male builds in his territory, whichappeared to be a good indicator of male quality. Because malesprovide no parental care or food resources within the territory,females sharing a territory do not compete for material resourcesand might therefore be expected to settle preferentially interritories of males that build many nests to gain the possiblegenetic benefit of high-quality offspring. An analysis of femalesettlement, however, revealed that females did not show a preferencefor territories of males with many nests and that the distribution of female breeding attempts with regard to the number of vacantnests within a territory could be explained best by randomfemale settlement in 3 out of 4 years. Females settled moreoften than expected by chance (in 3 out of 4 years) in territoriesalready containing occupied nests, indicating that residentfemales did not discourage settlement of additional females.However, sharing a territory with other females might imposecosts in terms of an increased predation risk because nestsin territories that contained other nests with young sufferedfrom higher predation than nests in territories that did notcontain other nests with young. Females therefore might tradethe possible benefits of settling in territories of males withmany nests against the costs of sharing a territory with otherfemales. This might result in the mating pattern found withrandom female settlement and male reproductive success beingdirectly proportional to the number of nests built. We discuss possible implications of this mating pattern for sexual selectionon males.     

Sexual conflict among polygynous pied flycatchers feeding young

In the polygynous pied flycatcher, Ficedula hypoleuca, reproductivesuccess of females is constrained by male food provisioningduring the nestling period. Hence, there will be conflictinginterests among the male and each of his mates as to how malefeeding effort should be shared among broods. This paper describesthree experiments designed to examine the parental behaviorof the members of a bigynous trio, i.e., the male and his twomates, in light of these conflicts. In all experiments, primaryand secondary broods were manipulated to hatch on the same dayto reduce the difference in brood-reproductive value due toage. Males divided their effort equally when the two broodswere the same size. However, males did not allocate their investmentin proportion to brood size when brood sizes differed, but investedmore heavily per young in the larger broods. This finding suggeststhat males tried to optimize the joint effort of their two mates.Males and females showed similar responses to experimental reductionin brood demands, which indicates no difference in their willingnessto invest in offspring. When one of the male’s mates wasremoved temporarily, the male increased his total feeding rateand provided proportionately more food to the "motherless" brood.Through flexible allocation of parental investment, males seemable to optimize their reproductive interests in the two broods.The only way a polygynously mated female might successfullyincrease the amount of male assistance at her nest is to makeher own brood more valuable for the male, relative to the otherbroods he might have. We discuss some ways this might be achieved.[Behav Ecol 1991;2:106–115]     

Sexual selection in a moth: effect of symmetry on male mating success in the wild

Sexual selection is generally caused by female choice and male–malecompetition. In female choice process, female preference isfavored indirectly and/or directly by sexual selection. In indirectselection, females expressing the preference might gain indirectgenetic benefits. In direct selection, females expressing thepreference might gain direct benefits or avoid male-imposedcosts. The white-tailed zygaenid moth Elcysma westwoodii ismonandrous, and males often gather around a female to mate withher, suggesting a high opportunity for sexual selection on maletraits. We quantified phenotypic selection on male morphologyin this species in the field. The morphological characters analyzedincluded body weight, antenna length, forewing length, hindwing length, hind wing tail length, genital clasper length,and the fluctuating asymmetry (FA) of these bilateral traits.In E. westwoodii, selection favored males with more symmetricgenital claspers, as well as longer and more symmetrical hindwings and antennae. Negative correlations between FA and sizewere also detected in the clasper and the antenna. Our resultssuggest that FAs of male traits, in particular the genital clasper,may have indirect and direct influences on mating success. Duringa copulatory attempt, an E. westwoodii male will try to graspthe female's abdominal tip with his claspers but often failto do so because of the female's reluctance to mate. The femaleabdominal tips are smooth and strongly sclerotized and couldthus be difficult for males to grasp. We hypothesize that moresymmetrical male claspers are more efficient in overcoming femalereluctance.     

Male courtship signals and female signal assessment in Photinus greeni fireflies

The evolutionary dynamic of courtship signaling systems is drivenby the interaction between male trait distributions and femalepreferences. This interaction is complex because females maychoose mates based on multiple components of male signals, andfemale preference functions may vary depending on mate availability,female reproductive state, and environmental conditions. InPhotinus fireflies (Coleoptera: Lampyridae), flying males emitbioluminescent flash signals to locate sedentary females, whichreply selectively to attractive male flash signals with theirown response flash. In this study, we first examined temporalvariation in the paired-pulse flash patterns produced by Photinusgreeni males in the field and found significant among-male variation(70% of total variation) in interpulse intervals (IPIs). Therewas no significant relationship between male IPI and spermatophoresize, suggesting that P. greeni male courtship signals do notprovide females with reliable indicators of male material resources.In laboratory playback experiments, we presented P. greeni femaleswith simulated flash signals to assess how IPI and pulse durationindependently affected the likelihood of female flash response.We also examined the effects of female body mass and time duringthe mating season on female preference functions, hypothesizingthat females would be less discriminating when they were heavier(more fecund) and when mate availability declined. We foundthat P. greeni females discriminated among signals within theirspecies' range based primarily on flash pattern IPI. Neitherthe time during the mating season nor female weight alteredfemale preference functions for IPI, although season did influencefemale response to pulse duration. These results reveal thatP. greeni females discriminate among conspecific males basedprimarily on male IPIs, the same signal character previouslyshown to be important for firefly species recognition. Fieldplayback experiments indicated that female responsiveness peakednear the average IPI given by males at different ambient temperatures,suggesting that fireflies exhibit temperature coupling similarto that seen in many acoustically signaling animals.     

Interacting effects of predation risk and male and female density on male/female conflicts and mating dynamics of stream water striders

We used a factorial experiment to examine interacting effectsof male density, female density, and sunfish (predation risk)on mating dynamics of the stream water strider (Aquarius remigis).Many of our results corroborated earlier studies on the isolatedeffects of each factor on mating behavior. The effect of eachfactor, however, depended on the other factors. For example,in low density pools, predation risk decreased male generalactivity, male/female harassment rates, mating activity, andmating duration and increased the large male mating advantage.At higher densities, however, water striders apparently enjoyed"safety in numbers" and did not alter their mating dynamicsin response to the presence of predators. Female activity showeda particularly complex response to male density and fish. Whenmales were scarce, fish caused females to reduce their activity.However, when males were abundant, fish increased female activity,probably because fish decreased male activity thus releasingfemales from harassment by males. The three treatment factorsalso had interacting effects on male mating success. In theabsence of fish, when females were scarce, increased male densityresulted in a decrease in mean male mating success; however,when females were abundant, increased male density enhancedmean male mating success. In contrast, in the presence of fish,male density had little effect on male mating success. Manyof the observed mating patterns can be explained by the effectsof ecological and social factors on male/female conflicts; thatis, on male harassment of females and female reluctance to mate.     

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.