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1.
The dimorphisms in morphology and behaviour of male fig wasps are among the most extreme in the animal kingdom, and offer excellent opportunities to test the predictions of certain sexual selection models. Winged males resemble their conspecific females closely, but wingless males are so divergent in form that they have repeatedly been classified into different taxa. Wingless males mate within their natal fig fruits, whereas winged males disperse to mate. Individual species may have winged males, wingless males or both morphs. A key hypothesis proposes that sexual selection on male mating opportunities favours winged males in species with small broods and wingless males in species with large broods. Using data from 114 species in 33 genera, we show that both simple and formal comparative analyses support the correlated evolution of large brood size and male winglessness. Theoretical models further predict that, in male dimorphic species, the proportion of winged males should equal (in cases without local mate competition) or exceed (in cases with local mate competition) the proportion of females developing in fig fruits without wingless males. These predictions are met by eight out of nine male dimorphic species studied. Taken together, the patterns across all species, and between different male dimorphic species, strongly support sexual selection on mating opportunities as the major determinant of male morph ratios in fig wasps.  相似文献   

2.
In many species, mating takes place in temporary patches where only a small number of females produce offspring. In this situation Local Mate Competition (LMC) theory predicts that the optimal sex ratio (defined as proportion males) should become increasingly female biased as the number of females contributing offspring to a patch decreases. However, in a large number of these species, some mating is also likely to occur away from the natal patch (termed partial LMC). In this case the degree of LMC is reduced, and theory predicts a relatively less female biased sex ratio. We tested these two predictions with field data from 17 species of New World non-pollinating fig wasps representing three genera. We present a model which suggests that the average number of females ovipositing in a fruit (i.e. patch) is positively correlated with the proportion of fruit of a given tree species in which that species of wasp occurs. Across species, the overall sex ratio was positively correlated with the proportion of fruit in which that species occurs. Furthermore, the males of some species are wingless, and in these species all mating must take place before females disperse from their natal fruit. In contrast, the males of other species are winged, and in these species mating may also take place away from the natal fruit. Species with winged males had less female biased sex ratios than species with wingless males that occurred in a similar proportion of fruit. Finally, the correlation between sex ratio and the proportion of fruit in which a species occurs was also observed within species when comparing between the fruit crops of different trees. This suggests that individual females facultatively adjust the sex ratio of their offspring in response to variable LMC.  相似文献   

3.
对叶榕传粉小蜂性比率的调节和稳定   总被引:5,自引:0,他引:5  
彭艳琼  杨大荣  王秋艳 《生态学报》2005,25(6):1347-1351
传粉榕小蜂呈现偏雌的性比率,单双倍体性别决定系统、局域配偶竞争和近交效应被认为是调节偏雌性比率的3个主要机制。通过研究影响对叶榕传粉小蜂性比率的因素,结果表明传粉榕小蜂的偏雌性比率随局域配偶竞争强度的降低而增加;受母代雌蜂交配次数的影响,随着母代雌蜂交配次数的增加,子代的偏雌性比率逐渐降低,这一结果首次揭示了传粉榕小蜂的交配制次数对性比率的影响,并在个体水平上定量了性比率变异与雌蜂交配频次的关系。传粉小蜂的性比率与共生的非传粉小蜂的关系,非传粉小蜂的介入直接减少了传粉小蜂的数量,甚至对传粉小蜂的种群有显著影响,结果发现非传粉小蜂对传粉小蜂雌雄性的分配比率没有显著影响,传粉榕小蜂仍能正常地进行繁殖。传粉与非传粉者小蜂之间作用关系的确定,可为进一步理解两者的稳定共生的机制提供科学证据。  相似文献   

4.
Fig‐pollinating wasps (Agaonidae) only reproduce within fig tree inflorescences (figs). Agaonid offspring sex ratios are usually female‐biased and often concur with local mate competition theory (LMC). LMC predicts less female‐bias when several foundresses reproduce in a fig due to reduced relatedness among intra‐sexually competing male offspring. Clutch size, the offspring produced by each foundress, is a strong predictor of agaonid sex ratios and correlates negatively with foundress number. However, clutch size variation can result from several processes including egg load (eggs within a foundress), competition among foundresses and oviposition site limitation, each of which can be used as a sex allocation cue. We introduced into individual Ficus racemosa figs single Ceratosolen fusciceps foundresses and allowed each to oviposit from zero to five hours thus variably reducing their eggs‐loads and then introduced each wasp individually into a second fig. Offspring sex ratio (proportion males) in second figs correlated negatively with clutch size, with males produced even in very small clutches. Ceratosolen fusciceps lay mainly male eggs first and then female eggs. Our results demonstrate that foundresses do not generally lay or attempt to lay a ‘fixed’ number of males, but do ‘reset to zero’ their sex allocation strategy on entering a second fig. With decreasing clutch size, gall failure increased, probably due to reduced pollen. We conclude that C. fusciceps foundresses can use their own egg loads as a cue to facultatively adjust their offspring sex ratios and that foundresses may also produce more ‘insurance’ males when they can predict increasing rates of offspring mortality.  相似文献   

5.
Hamilton's concept of local mate competition (LMC) is the standard model to explain female-biased sex ratios in solitary Hymenoptera. In social Hymenoptera, however, LMC has remained controversial, mainly because manipulation of sex allocation by workers in response to relatedness asymmetries is an additional powerful mechanism of female bias. Furthermore, the predominant mating systems in the social insects are thought to make LMC unlikely. Nevertheless, several species exist in which dispersal of males is limited and mating occurs in the nest. Some of these species, such as the ant Cardiocondyla obscurior, have evolved dimorphic males, with one morph being specialized for dispersal and the other for fighting with nest-mate males over access to females. Such life history, combining sociality and alternative reproductive tactics in males, provides a unique opportunity to test the power of LMC as a selective force leading to female-biased sex ratios in social Hymenoptera. We show that, in concordance with LMC predictions, an experimental increase in queen number leads to a shift in sex allocation in favour of non-dispersing males, but does not influence the proportion of disperser males. Furthermore, we can assign this change in sex allocation at the colony level to the queens and rule out worker manipulation.  相似文献   

6.
1. Parasitic wasps with structured populations are generally assumed to follow the local mate competition (LMC) model: females lay only the minimal number of sons necessary to inseminate all daughters in the emergence patch, and increase this number when faced with additional broods from unrelated females. After emergence, daughters mate with local males before dispersing for host location and oviposition. The main predictions from the model have been verified for many species. 2. Conflicting evidence exists on the status of the egg parasitoids Trichogramma regarding their on‐patch versus off‐patch mating. Although the life‐history traits of several species indicate that mating must occur on the emergence patch, recent data suggest that mating could occur outside the natal patch. 3. In this study, we measured the level of off‐patch mating in the egg parasitoid Trichogramma euproctidis using two isofemale lines in a greenhouse experiment. The impact of the sex ratio on the level of off‐patch mating was also tested. 4. The overall off‐patch mating proportion was 40.5% with a range between 0 and 85.7%, and was influenced by the sex ratio on the emergence patch: the more males available at emergence, the less off‐patch mating occurring. 5. The mating structure of this species can be described as partial LMC.  相似文献   

7.
Females and males of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Erirhinidae), have two elytral color morphs in Texas: the central pattern of their elytra is black (dark morph) or gray (light morph). In southeast Texas, the dark and light females exhibited similar proportions (28.6 and 32.0%, respectively) in populations collected during the spring. In this study, females of the two morphs were collected near rice fields in southeast Texas during April and May 2005. In the laboratory, light females were more active than dark ones. They mated equally successfully with males, irrespective of morph. For females supplied with males for 2 d or kept solitary, and then reared on rice seedlings for 48 d, no significant differences were found between the two morphs in oviposition period, number of eggs deposited, and survival rate. In both morphs, a proportion of mated females did not oviposit throughout the rearing period, implying that a mating experience might be necessary before reproductive development can be initiated. However, oviposition occurred in a proportion of females in which no mating experience could be detected, and their eggs produced larvae, which suggests the probability of existing parthenogenetic females in southeast Texas.  相似文献   

8.
We constructed a sex allocation model for parasitic wasps to explain the wide variation in their sex ratio, considering the effects of local mate competition, partial dispersal of progeny before mating, and heterogeneity in host quality among patches. We conducted an experiment to compare with the predictions of our model. We considered the following situations. First, the hosts are distributed in discrete patches: a number of female wasps visit and oviposit in each patch. Second, all the progeny do not mate within the natal patch; some of them disperse to take part in population-wide random mating. We calculated ES sex ratios in cases where there are two kinds of patches: good ones and poor ones. We examined the dependency of ES sex ratios on several parameters, i.e., 1) the probability that a daughter mates in her natal patch, 2) the ratio of the female fitness of the good patch to that of the poor patch, 3) the proportion of poor patches, and 4) the number of foundresses in a patch. The result of our experiment showed the same tendency as the calculation in case where the LMC effect is high in each patch. We briefly discuss a possible selection pressure for dispersal of progeny, with special reference to the mating structure of parasitic wasps.  相似文献   

9.
Sex ratio theory allows unparalleled opportunities for testing how well animal behavior can be predicted by evolutionary theory. For example, Hamilton's theory of local mate competition (LMC) is well understood and can explain variation in sex allocation across numerous species. This allows more specific predictions to be developed and tested. Here we extend LMC theory to a situation that will be common in a range of species: asymmetrical LMC. Asymmetrical LMC occurs when females lay eggs on a patch asynchronously and male offspring do not disperse, leading to relatively weaker LMC for males emerging from later broods. Varying levels of LMC then lead to varying optimal sex ratios for females, depending on when and where they oviposit. We confirm the assumptions of our theory using the wasp Nasonia vitripennis and then test our predictions. We show that females adjust their offspring sex ratios in the directions predicted, laying different sex ratios on different hosts within a patch. Specifically, there was a less female-biased sex ratio when ovipositing on an unparasitized host if another host on the patch had previously been parasitized and a less female-biased sex ratio on parasitized hosts if females also oviposited on an unparasitized host.  相似文献   

10.
Summary Species of parasitic Hymenoptera that manifest female-biased sex ratios and whose offspring mate only with the offspring of the natal patch are assumed to have evolved biased sex ratios because of Local Mate Competition (LMC). Off-patch matings, i.e. outcrossing, are inconsistent with the conditions favouring biased sex ratios because they foster a mating structure approaching panmixia. Such a mating structure favours parents who invest equally in daughters and sons, assuming the production of each sex is of equal cost.Pachycrepoideus vindemiae (Rondani) is a solitary pupal parasitoid of patchily distributed frugivorousDrosophila, whose offspring manifest a female-biased sex ratio. Thus this species appears to manifest a population structure and progeny sex ratio consistent with LMC. However, preliminary observations and subsequent greenhouse experiments suggest that the males participate in off-patch matings and that this propensity is unlikely to be an experimental artefact. FemaleP. vindemiae dispersed from patches in which either the males were lacking (12% of the emigrant females), both resident (sibling) and immigrant males were present (23% of the females), only immigrant males were present (14% of the females), or their opportunity to mate could not be determined (14% of the females). Of the 12% that emigrated from a patch lacking males, an estimated 7% mated at an oviposition site and 5% remained unmated, presumably because they arrived at an oviposition site that lacked males before they were dissected to determine whether they were inseminated. Thus the degree of bias in the sex ratios of the progeny (18% males), coupled with the suggested outcrossing potential from the experiments (26–37%), is inconsistent with the assumptions of LMC or variants of it, i.e. asynchronous brood maturation. Thus the explanation for a biased sex ratio in the offspring ofP. vindemiae remains a conundrum. More importantly,P. vindemiae does not appear to be an isolated example.  相似文献   

11.
Sex allocation theory has long generated insights into the nature of natural selection. Classical models have elucidated causal phenomena such as local mate competition and inbreeding on the degree of female bias exhibited by various invertebrates. Typically, these models assume mothers facultatively adjust sex allocation using predictive cues of future offspring mating conditions. Here we relax this assumption by developing a sex allocation model for haplodiploid mothers experiencing local mate competition that lay a fixed number of male eggs first. Female egg number is determined by remaining oviposition sites or remaining eggs of the mother, depending on which is exhausted first. Our model includes parameters for variation in foundress number, patch size, fecundity and offspring mortality that allow us to generate secondary sex ratio predictions based on specific parameterizations for natural populations. Simulations show that: 1) in line with classical models, factors that increase sib‐mating result in mothers laying relatively more female eggs; 2) high offspring mortality leads to relatively more males as fertilization insurance; 3) unlike classical model predictions, sub‐optimal predictions, such as more males than females are possible. In addition, our model provides the first quantitative predictions for the expected number of males and females in a patch where typically only one mother utilizes a given patch. We parameterized the model with data obtained from seven species of southern African fig wasps to predict expected means and variances for numbers of male and female offspring for typical numbers of mothers utilizing a patch. These predictions were compared to secondary sex ratio data from single foundress patches, the most commonly encountered situation for these species. Our predictions matched both the observed number and variance of male and female offspring with a high degree of accuracy suggesting that facultative adjustment is not required to produce evolutionary stable sex ratios.  相似文献   

12.
Fig wasps have been known as one of the best-documented examples of female-biased sex ratio predicted from the local mate competition (LMC) theory. However, observed sex ratios appear more female-biased than predicted. Before a close match between theory and observation can be claimed, the number and sex ratio of offspring left by each foundress in a multi-foundress syconium need to be determined. We examined the clutch size and sex ratio of individual females of the pollinator fig wasp Blastophaga nipponica (Agaonidae) in experiments using a pair of fertile and sterile females in which sequence and time interval of entering syconia were manipulated. To determine the number and sex ratio of offspring left by each foundress in a multi-foundress syconium, we prepared sterilized females that could oviposit ordinarily but whose offspring could not develop at all, by irradiating the females with 60Co gamma rays. Female fig wasps contributed different numbers and sex ratios of offspring to the total brood within a syconium, due to different entry times among them. The variation in clutch sizes with different entry times appeared to be caused by competition for oviposition sites, and sex ratios to be adjusted according to the clutch size.  相似文献   

13.
Female-limited color polymorphisms occur in a variety of animal taxa where excessive male sexual harassment may explain the coexistence of multiple female color morphs. In the color polymorphic damselfly Ischnura elegans, mature and immature female color morphs coexist at the mating site where males are in search for suitable mating partners. Here, we study male preference and female mating propensity for the two immature female morphs. As would be expected, compared to mature morphs, both immature female morphs mate much less. Within immature females, one morph consistently mates more frequently compared to the other morph, a pattern that is similar for the ontogenetically corresponding mature female morphs. Preference experiments with the two differently colored immature female morphs, however, did not indicate male mate preference for either morph. Low mating frequencies of immature females at natural sites in combination with relatively high attractiveness of immature models in terms of male preference indicate that female behavior influences female mating success.  相似文献   

14.
Non-pollinating wasps distort the sex ratio of pollinating fig wasps   总被引:2,自引:0,他引:2  
In fig wasps, mating occurs among the offspring of one or a few foundress mothers within the fig, from which the mated females disperse to found new broods. Under these conditions, males will compete with each other for mating, and such local mate competition can result in female-biased sex ratios. In addition to pollinating wasps, non-pollinating wasp species are also associated with figs and develop in flower ovaries or parasitize the larvae of primary galling wasps. While studying the fig wasp Pegoscapus tonduzi , which pollinates Ficus citrifolia in Brazil, we examined the influence of non-pollinating fig wasps on the sex ratio of species that pollinate F. citrifolia to determine whether the presence of non-pollinating wasps resulted in a distorted sex ratio. There was a positive relationship between the sex ratio of P. tonduzi and the number of non-pollinating wasps that was independent of the number of foundresses and brood size. In addition, the number of non-pollinating wasps correlated negatively with the number of pollinating females, but was not significantly related to the number of pollinating males. This finding suggested that non-pollinating wasps had a direct effect in distorting the sex ratio of P. tonduzi broods. Our results indicate that the secondary sex ratio may not precisely reflect the primary sex ratio when there is a high infestation of non-pollinating fig wasps.  相似文献   

15.
榕树及其传粉榕小蜂繁殖上相互依存,被认为是生物界中协同进化时间最悠久,相互关系最密切的一对生物;在大多数榕树种类的隐头花序内,除了传粉榕小蜂外,还共存着多种非传粉小蜂,它们的繁殖行为直接影响着榕树和传粉榕小蜂的繁殖和互惠稳定。钝叶榕(Ficus curtipes Corner),是一种雌雄同株的绞杀性榕树。研究在西双版纳热带植物园里共收集钝叶榕100个隐头果内的榕小蜂,获得9493号标本;其中,包括1种传粉小蜂和5种非传粉小蜂,钝叶榕传粉小蜂Eupristina sp.占总数的4466%,杨氏榕树金小蜂Diaziella yangi 占46.13%,而其它4种非传粉小蜂(Lipothymus sp., Sycobia sp., Philotrypesis sp.和Sycoscopter sp.)仅占9.20%。前3种榕小蜂雌蜂进到果腔产卵,其余3种在果外产卵。观测23个钝叶榕榕果出蜂情况发现,6种榕小蜂在钝叶榕隐头花序内遵循严格的羽化出蜂顺序,首先是Sycobia sp.,次之是Lipothymus sp.,再次之是杨氏榕树金小蜂,最后是钝叶榕传粉小蜂、Philotrypesis sp.和Sycoscopter sp.。5种非传粉小蜂的交配场所与雄蜂翅型无关,雄蜂有翅型的杨氏榕树金小蜂大部分交配在果内完成,而且它们的雄蜂为争夺交配机会存在激烈的打斗行为;雄蜂无翅型的Lipothymus sp.有部分雄蜂爬出隐头果,在果壁和附近的叶片背面交配;雄蜂有翅型的Sycobia sp.,其所有交配都发生在果外;Philotrypesis sp.和Sycoscopter sp. 雄蜂均无翅,它们的交配全发生在果内。局域配偶竞争使榕小蜂性比偏雌,杨氏榕树金小蜂雄蜂虽然有翅,但大部分交配发生在榕果内,这将影响其最佳的性比率。因此,依赖雄蜂翅型并不能很好地预测榕小蜂的交配场所和性比率。  相似文献   

16.
Sex ratio manipulation by ovipositing females was surveyed in 3 solitary ectoparastic wasp species,Dinarmus basalis (Pteromalidae),Anisopteromalus calanrae (Pteromalidae), andHeterospilus prosopidis (Braconidae), that parasitize azuki bean weevil (Callosobruchus chinensis (L) (Coleoptera: Buruchidae)) larvae within azuki beans (Vigna angularis). Variables were local mate competition (LMC) and host quality (HQ). We used host age as a measure of host quality (from 9-to 16-day-old hosts), changed the number of ovipositing females to control the level of local mate competition (1 female and 10 females), and examined oviposition patterns of the wasps. The offspring sex ratios (proportion of females) of the 3 wasp species respond qualitatively same to HQ and LMC. The common qualitative tendency among the 3 species is an increase of sex ratios increase with host age. In the process of changing the sex ratio (9–13-day-old) 3 wasp species respond only to HQ. In the hosts that end development in size (14–16-day-old) wasps respond to LMC. The response of sex ratio change to LMC in the old host ageclasses are different among the 3 species. In the situation that there exists LMC (10 females) sex ratios are the same among the 3 wasps. However, the sex ratios in no LMC (single female) are heterogeneous among the 3 wasps.  相似文献   

17.
Philotrypesis, a major component of the fig wasp community (Hymenoptera: Pteromalidae), is a model taxon for studying male fighting and mating behaviour. Its extreme sexual dimorphism and male polymorphism render species identification uncertain and in-depth research on its ecology, behaviour and other evolutionary topics challenging. The fig wasps' enclosed habitat within the syconia makes their mating behaviour inaccessible, to the extent of matching conspecific females and males. In this study, we combine morphological and molecular analyses to identify species of Philotrypesis sampled from south China and to associate their extraordinarily dimorphic genders and labile male morphologies. Morphological evaluations of females identify 22 species and 28 male morphs. The mitochondrial cytochrome c oxidase I and nuclear internal transcribed spacer 2 data detect 21 species using females, and 15 species among the males. Most of the males match the species as delimited by females. Both markers reveal cryptic species in P. quadrisetosa on Ficus vasculosa. Most species of wasps live on one species of fig but three species co-occur in two hosts (F. microcarpa and F. benjamina), which indicates host switching.  相似文献   

18.
Abstract. 1. Pollinating fig wasps (Hymenoptera, Agaonidae) display sex ratio adjustment, producing less female‐biased combined sex ratios as the number of ovipositing females (foundresses) inside a fig increases. Because males have low mobility, the oviposition sites (galled ovules) chosen by each foundress are likely to have consequences for the mating structure of wasp populations within the figs. 2. In this study, the spatial location of male and female progeny of the pollinating fig wasp Liporrhopalum tentacularis developing within figs of its host plant Ficus montana was examined to investigate two questions: (i) are male and/or female wasp offspring clustered together or interspersed? and (ii) is their distribution affected by whether one or two foundresses are present? Microsatellite markers were used to identify the progeny of different foundresses in dual‐foundress figs. 3. More offspring developed in the central part of the figs, compared with the ostiolar and basal parts, irrespective of foundress number. Neither male nor female wasp offspring were clustered within a fig. 4. The sons of the second foundress to enter a fig were positioned at similar minimum distances to both sibling and non‐sibling females, whereas the sons of the first foundress were closer to their sibling females than to non‐sibling females. If male wasps mate predominantly with females in adjacent galls, then the positioning of sons by the second foundresses is beneficial for them both in terms of reduced sibling mating and because they are provided with ready access to the female progeny of the first foundress.  相似文献   

19.
Recent investigations of mate choice indicate that the genetic effect of sires on offspring fitness may depend on the interaction between maternal and paternal genotypes and the environmental conditions experienced by the offspring. Alternative colour morphs of the pygmy grasshopper, Tetrix subulata , represent ecological strategies that differ in body size, life history, thermoregulatory behaviour, and habitat selection. The hypothesis that selection promotes behaviours maintaining coadapted gene complexes predicts individuals to mate assortatively with respect to colour morph. On the other hand, the bet-hedging hypothesis predicts that the temporal variability of the environment inhabited by these animals may select for disassortative mating behaviour resulting in heterogeneous offspring. To distinguish between these competing hypotheses, we investigated mating behaviours using dual-choice experiments. Our results were not in agreement with the prediction of assortative mating but suggest instead that matings were random with regard to colour morph. Polyandry was common, and females mated with the second male regardless of whether the first mating was assortative or disassortative. Polyandry also was equally frequent among females in triads in which the two males belonged to different colour morphs as in triads where both males belonged to the same colour morph. A field experiment confirmed that polyandry occurred also among free-ranging individuals, and uncovered variation in mating success among male colour morphs, probably due to indirect effects of coloration on activity or habitat use. The consequences of this random and polyandrous mating strategy for the evolutionary dynamics of the colour polymorphism remain to be explored.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 491–499.  相似文献   

20.
A model for sex allocation is presented where mothers have differing abilities to assess their arrival order at a patch in low-density populations. Mothers either oviposit with no knowledge, some knowledge, or they know their arrival order exactly. Furthermore they deposit single eggs in patches hence all matings within a patch are between unrelated individuals. The male offspring however, are also able to mate with females from male-less patches through dispersal. Whereas the first model predicted sex ratios of equality, the models incorporating knowledge both predicted female biased sex ratios. This is shown to be due to an asymmetry in mating opportunities that we have termed random asymmetrical mate competition (RAMC) that only knowledgeable females are able to use to their advantage. Data from the out-breeding non-pollinating fig wasp Otitesella pseudoserrata, suggests that these mothers do have knowledge of their arrival orders and supports the concept and predictions of RAMC.  相似文献   

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