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1.
The large-male advantage in brown antechinuses: female choice, male dominance, and delayed male death 总被引:1,自引:0,他引:1
Male-biased dimorphism in body size is usually attributed tosexual selection acting on males, through either male competitionor female choice. Brown antechinuses (Antechinus stuartii) aresexually dimorphic in size, and heavier males are known to siremore offspring in the wild. We investigated four possible mechanismsthat might explain this large-male reproductive advantage. Wetested if there is a female preference for large males, a femalepreference for dominant males, if larger males compete moreeffectively for mates, and if there is a survival advantagefor large males during the mating season. We established nestinggroups of males in captivity and conducted mate choice trialsin which males from nesting groups either could or could notinteract. We assessed male dominance rank and recorded survivaltimes after mating. Females did not prefer larger males directly.The results suggest that the other three mechanisms of sexualselection tested account for the large-male advantage: largemales competed more successfully for mates, so were sociallydominant; females rejected subordinates (males they saw losingtwice in contests to previous mates); and dominant males survivedfor longer after their first mating. Females judged male rankbased on direct observation of male competitive interactionsat the time of mating and apparently could not distinguish rankfrom male scent. Effects of size and dominance on male reproductivesuccess are not confounded by age because male antechinusesare semelparous. 相似文献
2.
Sexual selection and mating patterns in a mammal with female-biased sexual size dimorphism 总被引:3,自引:0,他引:3
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. 相似文献
3.
Correlates of reproductive success within alternative mating tactics of the common shrew 总被引:2,自引:0,他引:2
Stockley Paula; Searle Jeremy B.; Macdonald David W.; Jones Catherine S. 《Behavioral ecology》1996,7(3):334-340
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: 334340 (1996)] 相似文献
4.
In species with high male mating effort, there is a trade-offbetween mating effort spent in a current mating and resourcesleft for future matings. Consequently, to maximize their reproductivesuccess, males have to invest strategically, saving resourcesin matings with low reproductive gain for future, more valuablematings. However, as males age, the expected future reproductivesuccess constantly declines. Thus, the importance of resource
rationing may drastically change during a lifetime. Males ofthe scorpionfly Panorpa cognata offer females a costly nuptialgift before copulation, which functions as male mating effort.Resources for the production of these salivary masses are severelylimited for males in poor condition. We found that males investedmore in copulations with high-quality females than in copulationswith low-quality females. However, males ceased to discriminateas they became older. Old males, with a relative small numberof expected future matings, did not invest differentially incopulations with high- versus low-quality females. In copulationswith low-quality females, males invested more in late thanin initial matings, whereas in matings with high-quality females,time of mating had no influence on mating effort. These resultsimply that males adaptively change their resource allocationstrategy during the course of the season. Initial matings seemto be characterized by male prudence; in later matings, malesseem to adopt a more opportunistic mating strategy. 相似文献
5.
Sexual selection in sticklebacks in the field: correlates of reproductive, mating, and paternal success 总被引:8,自引:5,他引:3
Male sticklebacks display multiple ornaments, and these ornamentshave been
shown to be preferred by females in laboratory experiments.However, few field
data exist, and it is not known whether thesepreferences are simultaneously
or sequentially operative ina single population. We report correlates of
reproductive successin two stickleback populations that differ in their
ecology,over several periods within their breeding season. In both
populationslarger males had higher reproductive success, but not in all
periodsof the breeding season. Reproductive success increased withredness of
the throat only in the Wohlensee population, andonly in one period that was
characterized by low average success.In the Wohlensee population, the
parasitic worm Pomphorhynchuslaevis is abundant, and reproductive
success decreased withthe presence of the parasite. In the Roche population,
maleswith nests concealed in a plant had higher mating success. Thesenests
were less likely to fail, suggesting that females preferredto spawn in
concealed nests because of higher offspring survivorship.The different sexual
traits appear to reveal different aspectsof male quality (multiple message
hypothesis): females probablyfind large males attractive because of their
higher paternalquality, but it seems more likely that red males are preferred
forbetter genetic qualities. Females also discriminate on territoryquality,
and male traits may be important in competition forthese territories. The
correlates of reproductive success werenot consistent during the season,
probably due to changes inthe availability of ripe females. Such fluctuating
selectionpressures will contribute to the maintenance of genetic variationin
sexual traits. 相似文献
6.
Genetic analysis of the mating system and opportunity for sexual selection in northern water snakes (Nerodia sipedon) 总被引:2,自引:0,他引:2
Prosser Melanie R.; Weatherhead Patrick J.; Gibbs H. Lisle; Brown Gregory P. 《Behavioral ecology》2002,13(6):800-807
We used data collected over 3 years at two study sites to quantifythe rates and consequences of multiple paternity and to determinethe opportunity for selection on male and female northern watersnakes (Nerodia sipedon). We sampled litters from 45 femalesthat gave birth to 811 offspring. Using eight microsatelliteDNA loci (probability of exclusion of nonparental males >0.99), we assigned paternity to 93% of neonates from one studypopulation and 69% of neonates from the other population. Observationsof participation in mating aggregations predicted individual
reproductive success poorly for two reasons. First, males regularlycourted nonreproductive females. Second, more than half ofall sexually mature males obtained no reproductive successeach year, despite the fact that many of them participatedin mating aggregations. The number of sires per litter ranged
from one to five, with 58% of all litters sired by more thanone male. Multiple paternity increased with female size, apparentlyboth because bigger females mated with more males and becausethe larger litters of big females provide paternity opportunitiesto more males. Multiple paternity was also more prevalent inyears with shorter mating seasons. We detected no advantage
to multiple paternity in reducing either the number of unfertilizedovules or stillborn young. Despite the majority of males siringno young each year, some males fathered young with as manyas three different females in one year. Male reproductive successincreased by more than 10 offspring for each additional mate,whereas female success increased by fewer than 2 offspring foreach additional mate. The opportunity for sexual selectionwas more than five times higher in males than females. 相似文献
7.
Genetic similarity, extrapair paternity, and offspring quality in Savannah sparrows (Passerculus sandwichensis) 总被引:1,自引:0,他引:1
Freeman-Gallant Corey R.; Wheelwright Nathaniel T.; Meiklejohn Katherine E.; Sollecito Suzanne V. 《Behavioral ecology》2006,17(6):952-958
The occurrence of extrapair paternity (EPP) in birds is oftenattributed to the action of good-genes sexual selection wherebyfemales "trade up" on male genetic quality by allocating fertilizationsto males with better genes than those possessed by their socialmate. To date, most studies of EPP in birds focus on absolutemeasures of male quality as a criterion for female choice, althoughmultiple mating by females in other taxa is more commonly ascribedto benefits associated with the individual optimization of offspringgenotypes. Here, we examine whether the genetic similarity ofsocial mates predicts female mating patterns in a populationof Savannah sparrows (Passerculus sandwichensis) where as manyas 70% of adults produce extrapair young (EPY). We considerthe influence of genetic similarity across all stages of a female'sdecision-making process, from pair formation through the decisionto produce EPY, to the allocation of fertilizations to specificextrapair sires. In a 4-year study of 175 males, 206 females,and 506 offspring, females were more likely to produce EPY whenpaired to genetically similar males, but they did not appearto be influenced by the size, age, mass, individual heterozygosity,and genetic diversity of their social mates. In paired comparisons,females were almost twice as likely to decrease their geneticsimilarity to males when producing EPY as they were to increaseit. Nonetheless, females did not select especially dissimilarmales when mating outside the pair-bond nor did they pair disassortativelywith respect to genetic similarity. Relative measures of malequality may influence mating patterns in birds, but only atsome points in a female's decision-making process. 相似文献
8.
Parasites physically block host copulation: a potent mechanism of parasite-mediated sexual selection
Research on the role of parasites in sexual selection has focusedmainly on host mate choice favoring relatively unparasitizedmales. But parasites can also generate variance in host reproductivesuccess by influencing the ability of individual hosts to directlycompete among themselves for mates or fertilizations, a subjectarea that has received far less attention. We demonstrate experimentallythat parasitism by mites can drive sexual selection by way ofa novel mechanism involving male competition: physical inhibitionof host copulation. Mite resistance in natural populations isheritable, emphasizing the evolutionary potential of parasite-mediatedsexual selection in this system and indicating that femalesshould be receiving indirect fitness benefits as a result ofthis process. We show that parasitism by mites, Macrochelessubbadius, reduces mating success of male Drosophila nigrospiracula.Smaller males were more strongly compromised, identifying hostbody size as a tolerance trait. As parasite load increased,the rate at which males attempted to copulate but failed becauseof obstruction by mites increased. When mites were removed frominfested males, host mating success was restored. Thus, thephysical presence of the mites per se generates differentialmating success, in this case by interrupting the normal flowof mating behaviors. This study elucidates a potent mechanismof parasite-mediated sexual selection in a system wherein parasiteresistance is demonstrably heritable, and as such expands ourunderstanding of the evolutionary potential of sexual selection. 相似文献
9.
Darwin first identified female choice and malemale 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 malemale competition. We examined the
effectsof tail height on malemale 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. 相似文献
10.
Susan M. Bertram Sarah J. Harrison Genevieve L. Ferguson Ian R. Thomson Michelle J. Loranger Mykell L. Reifer Deborah H. Corlett Patricia Adair Gowaty 《Ethology : formerly Zeitschrift fur Tierpsychologie》2017,123(11):793-799
Male mating preferences are often a neglected aspect of studies on sexual selection. Male mating preferences may evolve if they provide males with direct‐fitness benefits such as increased opportunity to fertilize more eggs or indirect‐fitness benefits such as enhanced offspring survival. We tested these ideas using Jamaican field crickets, Gryllus assimilis, previously shown to exhibit male mating preferences. We randomly mated males to either their preferred or non‐preferred potential mates and then asked whether mating treatment influenced egg oviposition or offspring viability. Preferred females were not significantly more fecund and did not produce more viable eggs or offspring than non‐preferred females. Male mate preferences were therefore inconsistent with both the direct‐ and indirect‐fitness benefits hypotheses under the conditions of our experiment. Our null results leave us with an open question about what is driving the evolution of mating preferences in male crickets. Future research should explore the whether the offspring of preferred females are more attractive, have stronger immune systems, and/or experience higher adult longevity. 相似文献
11.
Female remating propensity contingent on sexual cannibalism in sagebrush crickets, Cyphoderris strepitans: a mechanism of cryptic female choice 总被引:1,自引:0,他引:1
Male sagebrush crickets (Cyphoderris strepitans) permit femalesto
engage in an unusual form of sexual cannibalism during copulation:females
feed on males' fleshy hind wings and ingest hemolymphoozing from the wounds
they inflict. These wounds are not fatal,and normally only a portion of the
hind wings are eaten at anyone mating, so that mated males are not precluded
from matingagain. As a result, nonvirgin males have fewer material resources
tooffer females than do virgin males, such that females shouldbe selected to
preferentially mate with high-investment virginmales. We tested the
hypothesis that female mating preferencesfavor males capable of supplying
females with the highest materialinvestment. Our results indicate that both
female diet and opportunitiesfor sexual cannibalism influence female mating
behavior. Femalesmaintained on a low-nutrient diet mounted males
significantlysooner than females maintained on a high-nutrient diet,
indicatingthat a female's overall nutrient intake may determine her
propensityto mate. In addition, females were significantly more reluctantto
mount and mate with males whose hind wings had been surgicallyremoved and
thus were incapable of providing females with awing meal. Finally, females
initially mated to dewinged malesremated with winged males significantly
sooner than femalesallowed to feed freely during their initial mating,
resultingin cryptic female choice of investing males. 相似文献
12.
Anders Pape Mller 《Evolution; international journal of organic evolution》1993,47(2):417-431
Male secondary sexual characters are often expressed in females, and the maintenance of the character in females can be due to either direct selection on females favoring the maintenance of the trait, or a correlated response to selection in males. Here I report on determinants of and phenotypic selection on tail length of female barn swallows Hirundo rustica. The homologous trait in males is under strong directional sexual selection. Female tail length was positively associated with several reproductive parameters including total seasonal reproductive success, even when controlling for year and age effects. A change in female tail length from one year to another was often associated with a change in the reproductive parameters correlated with absolute tail length. There was little evidence for an association between female tail length and the duration of the incubation period (only females incubate) and absolute and relative female provisioning rates of offspring, and subsequent size of offspring. Tail length of female barn swallows was positively correlated with that of their mates. Female tail length was a heritable trait as determined from regression of the tail trait of offspring on that of their mother and their father, and there was a positive genetic correlation between the tail trait in males and females. In conclusion, female tail length reliably reflects female reproductive potential, and the trait appears to be under directional selection, which may result in an evolutionary response to selection because of the heritability of the tail trait. 相似文献
13.
Behavioral syndromes influence mating systems: floater pairs of a lizard have heavier offspring 总被引:2,自引:0,他引:2
Variation in correlated behaviors or behavioral syndromes couldhave interesting effects on mating systems, especially if thevariation in syndrome exists in both sexes. Both males and femalesof the lizard Eulamprus heatwolei display two behavioral typesof a behavioral syndrome, defined by correlations between territorial,exploratory, and predator avoidance behaviors. We tested howthis variation in behavioral syndrome influences reproductivesuccess, pairing patterns, and offspring weight. We used spatialbehavior and residency in the field to identify territorialand floater individuals. Females were relocated to the laboratoryto give birth, and all offspring, dams, and potential sireswere genotyped to determine offspring paternity. During fieldsurveys, 164 lizards were caught of which 27.5% were territorialand the rest were floaters. Paternity was assigned to 66% ofthe 104 offspring produced by 33 dams. Territorial sires fathereda greater proportion of the offspring of territorial dams thanfloater sires. Larger territorial males were more likely tosire the entire clutch or share paternity with fewer additionalsires than smaller territorial males. Floater sire size, however,did not influence the number of fathers per litter. Floaterfemales produced heavier offspring than their territorial counterparts,and offspring fathered by floaters were heavier than maternalhalf-sibs fathered by territorial males. We speculate that differencesin offspring weight may be the result of differences in yolkprovisioning by females and parent genetic compatibility. 相似文献
14.
Dreiss A.; Richard M.; Moyen F.; White J.; Moller A.P.; Danchin E. 《Behavioral ecology》2006,17(1):13-19
Sex allocation theory proposes that parents should bias thesex ratio of their offspring if the reproductive value of onesex is greater than that of the other. In the monogamous bluetit (Parus caeruleus), males have a greater variance in reproductivesuccess than females, and high-quality males have higher reproductivesuccess than high-quality females due to extrapair paternity.Consequently, females mating with attractive males are expectedto produce broods biased toward sons, as sons benefit more thandaughters from inheriting their father's characteristics. Songand plumage color in birds are secondary sexual characters indicatingmale quality and involved in female choice. We used these malesexual traits in blue tits to investigate adaptive sex ratiomanipulation by females. We did not find any relationship betweenmale color ornamentation and brood sex ratio, contrary to previousstudies. On the other hand, the length of the strophe bout (i.e.,the mean number of strophes per strophe bout) of fathers waspositively related with the proportion of sons in their broods.The length of the strophe bout is supposed to reflect male qualityin terms of neuromuscular performance. We further showed thatsons produced in experimentally enlarged broods had shorterstrophe bouts than sons raised in reduced broods. These resultsare consistent with the hypothesis that females adjust the sexratio of their broods in response to the phenotype of theirmate. 相似文献
15.
No direct or indirect benefits to cryptic female choice in house crickets (Acheta domesticus) 总被引:1,自引:0,他引:1
Cryptic female choice in crickets occurs through the prematureremoval of a male's spermatophore after copulation, which terminatessperm transfer. Although it is known that this behavior candirectly influence the paternity of offspring, its effects onfemale fitness have not been directly assessed. We tested thehypothesis that spermatophore removal by female house crickets(Acheta domesticus) confers fitness benefits on females, byrandomly assigning mates to females but permitting some femalesto freely remove spermatophores after mating (cryptic-choicetreatment) while forcing others to accept complete ejaculates(no-choice treatment). Although there was about a two-fold differencein the volume of ejaculate received by females of the two treatments,there were no significant differences in female longevity, reproductiveoutput, or offspring quality, as measured by offspring massand developmental time. Although differential spermatophoreremoval by females imposes strong sexual selection on males,the absence of a clear treatment effect suggests that femalesobtain no direct or indirect genetic benefits through theirpostcopulatory mating preferences. 相似文献
16.
Male mating success in a North American pitviper: influence of body size,testosterone, and spatial metrics
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Charles F. Smith Gordon W. Schuett Melissa Amarello 《Biological journal of the Linnean Society. Linnean Society of London》2015,115(1):185-194
Males with enhanced traits relative to conspecifics often show increased mating and reproductive success and thus have a fitness advantage. The opportunity or potential for sexual selection is predicted to occur under these conditions. Here, we investigated proximate determinants of mating success in male copperhead snakes (Agkistrodon contortrix), a medium‐sized pitviper of North America. Specifically, we investigated the relationships of body size (snout‐vent length, body mass), body condition index, spatial metrics (total distance moved, home range size), and plasma testosterone concentration on mating success in males. The single mating season lasts from August through September. We compared a set of candidate linear mixed models and selected the best‐fitting one using the adjusted Akaike Information Criterion (AICc). The AICc‐selected model (model 2), with testosterone, body condition index, and home range size as predictor variables, showed that male mating success was positively correlated with testosterone. To our knowledge, this is the first report to show the relationship of testosterone and individual mating success in any snake species. A parallel study conducted on male fitness in A. contortrix of the same population used microsatellite markers to assign parentage of fathers (known mothers). Unlike our study, they found that snout‐vent length was positively correlated with reproductive success and that males were experiencing greater sexual selection. This relationship has been detected under natural conditions in other species of snakes. Although behavioural data are important in any mating system analysis, they should not stand alone to infer parentage, relationships or selection metrics (e.g. Bateman gradients). Long‐term sperm storage by females, female cryptic choice, and other factors contribute to the complexity of mating success of males. Accordingly, we thus conclude that estimates of reproductive success and fitness in cryptic species, such as copperheads and other snakes, require robust molecular methods to draw accurate conclusions regarding proximate and evolutionary responses. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 185–194. 相似文献
17.
XAVIER GLAUDAS JAVIER A. RODRÍGUEZ‐ROBLES 《Biological journal of the Linnean Society. Linnean Society of London》2011,103(3):681-695
We used radiotelemetric data and behavioural observations to characterize seasonal (mating versus post‐mating seasons) and sexual variation in movement patterns, as well as to examine some of the ecological factors contributing to the evolution of the mating system in a venomous predator from the Mojave Desert of North America, the speckled rattlesnake, Crotalus mitchellii. Mating occurs in spring from late April to early June, shortly after emergence from hibernation, when snakes are predictably aggregated around the dens. Males and females travelled further per unit time in the mating season compared to the post‐mating season. Males also travelled longer distances per unit time than females in the mating and post‐mating seasons, and males with larger home ranges during the mating season had more potential mating partners. The results obtained suggest that males actively locate females during the mating season, and that the drastic increase in distance travelled by males during the mating season may be caused by strong male–male competition for access to females, probably because of the limited availability of sexually receptive females. Furthermore, males fight for access to females, and males of larger size are more likely to acquire females. Therefore, sexual selection apparently acts on two different male phenotypic traits: investment in mate‐searching activities and male body size. The present study demonstrates that combining quantitative spatial analyses and behavioural observations in an explicit temporal context can significantly advance our understanding of the ecology and evolution of organismal mating systems. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 681–695. 相似文献
18.
Some models of sexual selection predict that individuals vary in their genetic quality and reveal some of this variation in
their secondary sexual characteristics. Alpine whitefish (Coregonus sp.) develop breeding tubercles shortly before their spawning season. These tubercles are epidermal structures that are distributed
regularly along the body sides of both males and females. There is still much unexplained variation in the size of breeding
tubercles within both sexes and with much overlap between the sexes. It has been suggested that breeding tubercles function
to maintain body contact between the mating partners during spawning, act as weapons for defence of spawning territories,
or are sexual signals that reveal aspects of genetic quality. We took two samples of whitefish from their spawning place,
one at the beginning and one around the peak of spawning season. We found that females have on average smaller breeding tubercles
than males, and that tubercle size partly reveals the stage of gonad maturation. Two independent full-factorial breeding experiments
revealed that embryo mortality was significantly influenced by male and female effects. This finding demonstrates that the
males differed in their genetic quality (because offspring get nothing but genes from their fathers). Tubercle size was negatively
linked to some aspects of embryo mortality in the first breeding experiment but not significantly so in the second. This lack
of consistency adds to inconsistent results that were reported before and suggests that (i) some aspects of genetic quality
are not revealed in breeding tubercles while others are, or (ii) individuals vary in their signaling strategies and the information
content of breeding tubercles is not always reliable. Moreover, the fact that female whitefish have breeding tubercles of
significant size while males seem to have few reasons to be choosy suggests that the tubercles might also serve some functions
that are not linked to sexual signaling. 相似文献
19.
Antechinus agilis is a small sexually size dimorphic marsupial with a brief annual mating period of 2-3 weeks. All males die after this period, and females give birth to up to 10 young. Mating is thought to be promiscuous, however, there is no field data to confirm this. Using microsatellites, we investigated paternity patterns over two seasons in a wild population. Male weight was significantly positively related to the number of females fertilized and with the number of offspring sired, in both years. Furthermore, selection gradients indicated selection for larger males. Both results suggest that size dimorphism in A. agilis can be explained by sexual selection for larger males. The proportion of offspring sired within litters, did not relate to male size. Therefore, larger males are more successful through higher mating access, not through their sperm outcompeting that of smaller males. As expected from their known ranging behaviour, the number of offspring within litters left unassigned to a father did not depend on the grid location of the mother. Female size did not differ between successful reproducing and unsuccessful females. However, females that weaned offspring had larger heads than females that did not wean offspring. Males did not 'prefer' mating with larger females, nor did assortative mating occur. From our results, the mating system of A. agilis is clearly promiscuous. Selection for larger males occurred in both years, even though in one year the operational sex ratio was highly female biased, suggesting that the potential reproductive rate is a better predictor of the direction of sexual selection in A. agilis. 相似文献
20.
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. 相似文献