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1.
Kin selection operates through the fitness of an organism's relatives. In the polyandry context, kin selection may be observable on the one hand in competition between rival males and, on the other hand, in competition between litter mates. Sperm competition theory predicts that males should invest less into mating when competing for fertilizations against a close relative as compared to an unrelated male. We tested this hypothesis with bank voles (Myodes glareolus) by mating each focal male to two females: one of which had previously mated with a full sibling of the focal male and the other one with a male unrelated to the focal male. However, we found no effect of rival male relatedness on mating behavior or proportion of offspring sired by the 2nd male to mate. Possibly, the probability of successive mating of related males with the same female is too low in natural bank vole populations for selection to have fine‐tuned mating behavior in relation to rival male relatedness. Further, polyandry often results in litters sired by multiple males. Litter mates of such litters have a reduced relatedness and are thus expected to be less cooperative during gestation and lactation, which may impair growth. Following double matings with either two full‐sibling males or two unrelated males, we compared offspring growth at birth and during lactation. Against our prediction, there was no difference in growth between litters sired either by two full‐sibling males or by two unrelated males. Either the conflict was not severe enough to be visible with our sample size (N = 16) or it may have been resolved by maternal control of offspring provisioning.  相似文献   

2.
We describe the patterns of paternity success from laboratory mating experiments conducted in Antechinus agilis, a small size dimorphic carnivorous marsupial (males are larger than females). A previous study found last‐male sperm precedence in this species, but they were unable to sample complete litters, and did not take male size and relatedness into account. We tested whether last‐male sperm precedence regardless of male size still holds for complete litters. We explored the relationship between male mating order, male size, timing of mating and relatedness on paternity success. Females were mated with two males of different size with either the large or the small male first, with 1 day rest between the matings. Matings continued for 6 h. In these controlled conditions male size did not have a strong effect on paternity success, but mating order did. Males mating second sired 69.5% of the offspring. Within first mated males, males that mated closer to ovulation sired more offspring. To a lesser degree, variation appeared also to be caused by differences in genetic compatibility of the female and the male, where high levels of allele‐sharing resulted in lower paternity success.  相似文献   

3.
Effects of male‐biased dispersal on inbreeding avoidance were investigated in a semi‐natural population of Myodes (formerly Clethrionomys) rufocanus using a large outdoor enclosure (3 ha). Parentage of 918 voles weaned from 215 litters and relatedness of mates were analysed using microsatellite loci, and dispersal distances were obtained from mark–recapture live‐trapping data. Natal and breeding male‐biased dispersal was observed. There remained, however, chances that incestuous mating could occur, because not all males dispersed from their natal site, and 51 matings occurred between relatives (relatedness r > 0). The number of weaned juveniles from inbred litters was significantly smaller than that from non‐inbred litters. Fourteen incestuous matings occurred between close relatives (r ≥ 0.25), most of which were those between non‐littermate maternal half siblings (four cases) and those between paternal half siblings (seven cases). When comparing the observed frequencies to the expected ones generated by combining every oestrous female with a male randomly chosen from her surroundings, the observed values for inbreeding of r ≥ 0.25 were significantly smaller than the expectations, while no difference was observed for inbreeding of 0 < r < 0.25. These results suggest that male‐biased dispersal is partly effective to avoid incestuous mating, but it does not provide complete separation of male and female close relatives. Additional mechanisms such as kin discrimination based on familiarity may work in inbreeding avoidance of the vole.  相似文献   

4.
We performed a controlled mating experiment to determine whether genetic variation in larval traits in Hyla crucifer was predictable on the basis of mating status or body size of male parent. Larval growth rate was predictably related to body size of the sire. Males from the upper half of the body-size distribution sired offspring with 6% higher growth rates than those of offspring sired by males from the lower half of the body-size distribution. Offspring sired by males that obtained mates in nature had 3% higher growth rates than their half-siblings sired by males that did not mate in nature. Genetic variation for larval-period duration and size at metamorphosis was detected; however, neither mating status nor body size of sire could be used to predict values of these traits in the progeny. Although all three larval traits can affect fitness, there was no evidence that the offspring of some sires would always outperform the offspring of others in all three traits. The predictable association between adult male size and larval growth rate means that the H. crucifer mating system would have a directional effect on larval growth rate if male body size influences the outcome of male-male competition or female choice.  相似文献   

5.
To determine if the nonrandom, non-resource-based mating system of Bufo woodhousei affects tadpole performance, I performed a series of controlled matings and reared the tadpoles to metamorphosis in the laboratory and field. I asked whether differences in paternal identity, mating status, or body size were related to differences in tadpole mass, larval period duration, metamorphic mass, or survival of offspring. Although both laboratory and field rearings indicated that male and female parentage affected most offspring traits, no correspondence existed between either laboratory and field metamorphic mass or laboratory and field survival of offspring sired by the same male. The lack of correspondence between sire breeding values in the laboratory and field for two of three traits raises doubts as to the validity of drawing conclusions concerning how evolution might be expected to work from laboratory studies. Paternal effects were more pronounced in the field than in the laboratory, despite what is usually presumed to be a greater amount of environmental variation in the field. In the laboratory neither sire body size nor mating status affected any trait, but in the field larger males produced offspring that were 10% heavier at transformation than offspring sired by small males. This predictable relationship between sire phenotype (body size) and offspring performance means that nonrandom mating based on male body size could have a directional effect on offspring performance. Because larger males mate disproportionately often in this population (Woodward, 1982a; Mitchell, unpubl.), the mating system may exert a directional effect on metamorphic body size.  相似文献   

6.
Multiple paternity is relatively common across diverse taxa; however, the drivers and implications related to paternal and maternal fitness are not well understood. Several hypotheses have been offered to explain the occurrence and frequency of multiple paternity. One set of hypotheses seeks to explain multiple paternity through direct and indirect benefits including increased genetic diversity or enhanced offspring fitness, whereas another set of hypotheses explains multiple paternity as a by‐product of sexual conflict and population‐specific parameters such as density. Here, we investigate mating system dynamics in a historically studied population of the American alligator (Alligator mississippiensis) in coastal South Carolina. We examine parentage in 151 nests across 6 years and find that 43% of nests were sired by multiple males and that male reproductive success is strongly influenced by male size. Whereas clutch size and hatchling size did not differ between singly sired and multiply sired nests, fertility rates were observed to be lower in multiply sired clutches. Our findings suggest that multiple paternity may exert cost in regard to female fitness, and raise the possibility that sexual conflict might influence the frequency of multiple paternity in wild alligator populations.  相似文献   

7.
Mating system and philopatry influence the genetic structure of a social group in mammals. Brandt's vole (Lasiopodomys brandtii) lives in social groups year-round and has male biased dispersal, which makes the vole a model system for studies of genetic consequences of mating system and philopatry. This study aimed to test the hypotheses that: (1) multiple paternity (MP) would exist in Brandt's voles, enhance offspring genetic diversity and reduce genetic relatedness between littermates; (2) promiscuity would occur in this species in that males and females mate with multiple partners; and (3) plural breeders of a social group would be genetically related because of philopatry of female juveniles in Brandt's voles. Paternity analysis indicated that MP occurred in 11 (46%) of 24 social groups examined and that promiscuity existed in this species. Multiple paternity litters had twice the offspring genetic diversity and half the average within-litter genetic relatedness of single paternity litters. We also found plural breeding females in six social groups. Average pairwise genetic relatedness of plural breeders ranged from 0.41 to 0.72 in four social groups, suggesting first-order kinship. Future studies need to investigate effects of reproductive skew and MP on population genetic structure of Brandt's voles.  相似文献   

8.
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   

9.
Mating system of the meadow vole, Microtus pennsylvanicus   总被引:1,自引:0,他引:1  
Previous studies on parental and spacing behavior of Microtuspennsylvanicus suggest a promiscuous mating system, but attemptsto find multiple paternity in single litters have been unsuccessful.In this paper we present evidence of multiple paternity in singlelitters conceived in the wild early in the breeding season.The proportion of litters sired by multiple males was estimated,by a conservative method, to be 33.1%.We argue that the presenceof promiscuity, rather than polygyny, in M. pennsylvanicus isthe result of two factors. First, overwintered breeding malesare similar in age and size, resulting in small variation incompetitive ability among males. This reduced variation in competitiveability reduces the possibility that some males defend severalfemales and others defend none. Second, the habitat structureof the meadow vole makes it difficult for a male to detect othermales nearby, and this reduces the possibility that one maleexcludes others from mating when a female comes into estrus.  相似文献   

10.
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   

11.
Understanding the mating system and reproductive strategies of an endangered species is critical to the success of captive breeding. The big‐headed turtle (Platysternon megacephalum) is one of the most threatened turtle species in the world. Captive breeding and reintroduction are necessary to re‐establish wild populations of P. megacephalum in some of its historical ranges in China, where the original populations have been extirpated. However, the captive breeding of P. megacephalum is very difficult and this may be due to its mysterious reproductive strategies and special behavior (e.g., aggressive temperament and territoriality). In this study, we achieved successful captive breeding of P. megacephalum by creating a habitat that mimics natural conditions and then investigated its mating system using microsatellite makers. A total of 16 clutches containing 79 eggs of P. megacephalum were collected, and 52 were hatched successfully over two breeding seasons. Of the 15 effective clutches, 6 clutches (40%) exhibited multiple paternity. There was no significant correlation between clutch size and multiple paternity, and no significant difference in hatching success between multiple‐sired and single‐sired clutches. However, there was significant correlation between male body size and the number of offspring, with higher‐ranked males contributing to more clutches. Our results provide the first evidence of multiple paternity and male hierarchy in P. megacephalum. These findings suggest that multiple paternity and male hierarchy should be considered in captive breeding programs for P. megacephalum, and creating a habitat that mimics natural conditions is an effctive way to achieve successful captive breeding and investigate the mating systems of this species.  相似文献   

12.
We report experimental results consistent with the hypothesis that constraints on the expression of male mating preferences affect breeder fitness, offspring viability and performance. If constraints on the expression of mating preferences are common, tests of fitness variation associated with mate preferences must eliminate as many constraints on mate preferences as possible. We tested whether male mate preferences influenced breeder fitness, offspring performance and viability in typically polygynous house mice, Mus domesticus, from a feral source population. Our ‘free mate choice’ trials not only eliminated female preferences, male-male and female-female competition, but also our best guesses of the traits mediating choosers' preferences. Males mated with their preferred (P) females sired more litters than males mated with their nonpreferred (NP) females. Offspring viability was significantly lower when males' reproduced with females they did not prefer compared with females they did prefer. Adult sons of males that mated with their P females were socially dominant to sons of males that mated with their NP females. Adult offspring from P pairings built better nests than offspring from NP pairings. The slope of the survivorship curve for P offspring was significantly higher than for NP offspring. These results showed (1) males' mate preferences affected their fitness, (2) males that mated with females they preferred produced more litters than males that mated with females they did not prefer, and (3) their offspring were significantly more viable and performed significantly better on standardized performance tests. This is the first demonstration of fitness benefits of male choice behaviour in a mammal species with typical paternal investment. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.   相似文献   

13.
1.  Optimal parental sex allocation depends on the balance between the costs of investing into sons vs. daughters and the benefits calculated as fitness returns. The outcome of this equation varies with the life history of the species, as well as the state of the individual and the quality of the environment.
2.  We studied maternal allocation and subsequent fecundity costs of bank voles, Myodes glareolus , by manipulating both the postnatal sex ratio (all-male/all-female litters) and the quality of rearing environment (through manipulation of litter size by −2/+2 pups) of their offspring in a laboratory setting.
3.  We found that mothers clearly biased their allocation to female rather than male offspring regardless of their own body condition. Male pups had a significantly lower growth rate than female pups, so that at weaning, males from enlarged litters were the smallest. Mothers produced more milk for female litters and also defended them more intensively than male offspring.
4.  The results agree with the predictions based on the bank vole life history: there will be selection for greater investment in daughters rather than sons, as a larger size seems to be more influencial for female reproductive success in this species. Our finding could be a general rule in highly polygynous, but weakly dimorphic small mammals where females are territorial.
5.  The results disagree with the narrow sense Trivers & Willard hypothesis, which states that in polygynous mammals that show higher variation in male than in female reproductive success, high-quality mothers are expected to invest more in sons than in daughters.  相似文献   

14.
Captive breeding is an integral part of many species recovery plans. Knowledge of the genetic mating system is essential for effective management of captive stocks and release groups, and can help to predict patterns of genetic diversity in reintroduced populations. Here we investigate the poorly understood mating system of a threatened, ancient reptile (tuatara) on Little Barrier Island, New Zealand and discuss its impact on the genetic diversity. This biologically significant population was thought to be extinct, due to introduced predators, until 8 adults (4 males, 4 females) were rediscovered in 1991/92. We genotyped these adults and their 121 captively-bred offspring, hatched between 1994 to 2005, at five microsatellite loci. Multiple paternity was found in 18.8% of clutches. Male variance in reproductive success was high with one male dominating mating (77.5% of offspring sired) and one male completely restricted from mating. Little Barrier Island tuatara, although clearly having undergone a demographic bottleneck, are retaining relatively high levels of remnant genetic diversity which may be complemented by the presence of multiple paternity. High variance in reproductive success has decreased the effective size of this population to approximately 4 individuals. Manipulation to equalize founder representation was not successful, and the mating system has thus had a large impact on the genetic diversity of this recovering population. Although population growth has been successful, in the absence of migrants this population is likely at risk of future inbreeding and genetic bottleneck.  相似文献   

15.
The ring-tailed coati (Nasua nasua) is the only coati species in which social groups contain an adult male year round, although most males live solitarily. We compared reproductive success of group living and solitary adult male coatis to determine the degree to which sociality affects reproductive success. Coati mating is highly seasonal and groups of female coatis come into oestrus during the same 1-2 week period. During the mating season, solitary adult males followed groups and fought with the group living male. This aggression was presumably to gain access to receptive females. We expected that high reproductive synchrony would make it difficult or impossible for the one group living male to monopolize and defend the group of oestrous females. However, we found that group living males sired between 67-91% of the offspring in their groups. This reproductive monopolization is much higher than other species of mammals with comparably short mating seasons. Clearly, living in a group greatly enhanced a male's reproductive success. At the same time, at least 50% of coati litters contained offspring sired by extra-group males (usually only one offspring per litter); thus, resident males could not prevent extra-group matings. The resident male's reproductive advantage may reflect female preference for a resident male strong enough to fend off competing males.  相似文献   

16.
Mate selection for inbreeding avoidance is documented in several taxa. In mammals, most conclusive evidence comes from captive experiments that control for the availability of mates and for the level of genetic relatedness between mating partners. However, the importance of mate selection for inbreeding avoidance as a determinant of siring success in the wild has rarely been addressed. We followed the reproduction of a wild population of eastern chipmunks (Tamias striatus) during five breeding seasons between 2006 and 2009. Using molecular tools and parentage assignment methods, we found that multiple paternity (among polytocous litters) varied from 25% in an early-spring breeding season when less than a quarter of females in the population were reproductively active to 100% across three summer breeding seasons and one spring breeding season when more than 85% of females were reproductively active. Genetically related parents were common in this population and produced less heterozygous offspring. Furthermore, litters with multiple sires showed a higher average relatedness among partners than litters with only a single sire. In multiply sired litters, however, males that were more closely related to their partners sired fewer offspring. Our results corroborate findings from captive experiments and suggest that selection for inbreeding avoidance can be an important determinant of reproductive success in wild mammals.  相似文献   

17.
Morphological structures used as weapons in male–male competition are not only costly to develop but are also probably costly to maintain during adulthood. Therefore, having weapons could reduce the energy available for other fitness‐enhancing actions, such as post‐copulatory investment. We tested the hypothesis that armed males make lower post‐copulatory investments than unarmed males, and that this difference will be most pronounced under food‐limited conditions. We performed two experiments using the male‐dimorphic bulb mite Rhizoglyphus robini, in which males are either armed “fighters” or unarmed “scramblers.” Firstly, we tested whether fighters and scramblers differed in their reproductive output after being starved or fed for 1 or 2 weeks. Secondly, we measured the reproductive output of scramblers and fighters (starved or fed) after one, two or three consecutive matings. Scramblers sired more offspring than fighters after 1 week, but scramblers and fighters only sired a few offspring after 2 weeks. Scramblers also sired more offspring than fighters at the first mating, and males rarely sired offspring after consecutive matings. Contrary to our hypothesis, the fecundity of starved and fed males did not differ. The higher reproductive output of scramblers suggests that, regardless of nutritional state, scramblers make larger post‐copulatory investments than fighters. Alternatively, (cryptic) female choice generally favours scramblers. Why the morphs differed in their reproductive output is unclear. Neither morph performed well relatively late in life or after multiple matings. It remains to be investigated to what extent the apparent scrambler advantage contributes to the maintenance and evolution of male morph expression.  相似文献   

18.
Canid social groups are typically thought to consist of extendedfamilies, that is, a dominant breeding pair and related nonbreedingsubordinates, that principally obtain indirect fitness benefitsfrom helping to raise the offspring of the dominant pair. Consequently,the monogamous pair has been viewed as the basic fundamentalunit of canid social organization. However, there have beenfew genetic studies that have tested this assumption. We analyzedthe parentage of red foxes (Vulpes vulpes) in a high-density(19.6–27.7 adult foxes/km2) population in Bristol, UK,to determine (1) whether groups typically produced a singlelitter of cubs annually and (2) whether male and female foxesexhibited monogamous mating strategies. Social monogamy (theproduction of one litter in a social group) was observed orassumed in 54% of breeding attempts (N = 13 group-years). However,polyandrous and polygynous patterns of mating were common. Multiplepaternity was confirmed in 38% of litters (N = 16) containingoffspring with resolved maternity and paternity (N = 30 cubs);when including cubs with unresolved paternity (N = 20), multiple-paternitymay have occurred in 69% of litters. Litters were sired by anaverage of 1.6 identified males (range = 1–4); when includingcubs with unresolved paternity, litters may have been siredby up to seven males. Only 20% (6/30) of cubs with resolvedmaternity and paternity were sired by males within the socialgroup. Within groups, dominant females did not breed with subordinatemales; dominant males did breed with subordinate females. Dominantand subordinate females both produced cubs with dominant andsubordinate males from other social groups. Mean adult relatednessin groups typically ranged from 0.15–0.35, indicativeof second-order rather than first-order relatives.  相似文献   

19.
In group‐living species with male dominance hierarchies where receptive periods of females do not overlap, high male reproductive skew would be predicted. However, the existence of female multiple mating and alternative male mating strategies can call into question single‐male monopolization of paternity in groups. Ring‐tailed lemurs (Lemur catta) are seasonally breeding primates that live in multi‐male, multi‐female groups. Although established groups show male dominance hierarchies, male dominance relationships can break down during mating periods. In addition, females are the dominant sex and mate with multiple males during estrus, including group residents, and extra‐group males—posing the question of whether there is high or low male paternity skew in groups. In this study, we analyzed paternity in a population of wild L. catta from the Bezà Mahafaly Special Reserve in southwestern Madagascar. Paternity was determined with 80–95% confidence for 39 offspring born to nine different groups. We calculated male reproductive skew indices for six groups, and our results showed a range of values corresponding to both high and low reproductive skew. Between 21% and 33% of offspring (3 of 14 or three of nine, counting paternity assignments at the 80% or 95% confidence levels, respectively) were sired by extra‐troop males. Males siring offspring within the same group during the same year appear to be unrelated. Our study provides evidence of varying male reproductive skew in different L. catta groups. A single male may monopolize paternity across one or more years, while in other groups, >1 male can sire offspring within the same group, even within a single year. Extra‐group mating is a viable strategy that can result in extra‐group paternity for L. catta males.  相似文献   

20.
Multiple male mating (MMM) causes sperm competition, which may play an important role in the evolution of reproductive traits. The frequency of multiple paternity (MP), where multiple males sire offspring within a single litter, has been used as an index of MMM frequency. However, MP frequency is necessarily lower than MMM frequency. The magnitude of the difference between MMM and MP frequency depends on litter size (LS) and fertilization probability skew (FPS), and this difference may be meaningfully large in animals with small LSs. In this study, we propose a method to estimate MMM frequency using an individual‐based model with three variables (MP frequency, LS and FPS). We incorporated observed paternity skew data to infer a possible range of FPS that cannot be measured in free‐living populations and tested the validity of our method using a data set from a grey‐sided vole (Myodes rufocanus) population and from hypothetical populations. MP was found in 50 out of 215 litters (23.3%) in the grey‐sided vole population, while MMM frequency was estimated in 67 of 215 litters (31.2%), with a certainty range of 59–88 (27.4%–40.9%). The point estimation of MMM frequency was realized, and the certainty range was limited within the practical range. The use of observed paternity skew was very effective at narrowing the certainty range of the estimate. Our method could contribute to a deeper understanding of the ecology of MMM in free‐living populations.  相似文献   

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