海藻有性繁殖生态学研究进展

由于研究技术与方法的不断改进 ,人们对海藻 (seaweeds)早期生活史方面的研究兴趣日益增大。评述了近年来海藻有性繁殖过程中配子释放和受精生态学问题。到达一定生理状态的海藻 ,通过对环境暗示应答而诱导配子形成。海藻生殖器官感受另一些特定的环境条件 ,通过有关信号传递机制 ,触发配子释放。海藻配子释放的时间及其所需的环境条件 ,依不同的种类而变化。配子同步释放以及各种适当的环境条件提高了受精频率和受精成功率 ,有利于受精的各种生物的和非生物的因素组合 ,形成了“机会窗 (the window of opportunity)”的概念。近年来的研究表明 ,海藻 (特别是红藻 )的自然受精成功率比以前所认为的要高得多。受精后合子 (胚 )的散布、集落与附着显著地影响其生存以及种群动态。对今后值得进一步研究的方面作了展望     

Evolution of the alternation of haploid and diploid phases in life cycles. II. Maintenance of the haplo-diplontic cycle

The relative duration of the haploid and the diploid phases during the reproductive cycle varies greatly between organisms. This paper addresses the question of the evolution of haploid, diploid, and haplo-diplontic life cycles. When the life span of haploid and diploid individuals is constant whatever their cycle, we show that the haplo-diplontic cycle has an advantage, which depends on the sex-ratio in anisogamous species and on the probability of fertilization in isogamous species. This is because meiosis and fertilization occur half as often in the haplo-diplontic cycle as in haploid or diploid cycles, for the same number of generations of individuals. This argument is demonstrated using a model which considers a genetic determination of the cycle, and fixed haploid and diploid fitnesses. The relevance of measures of fitness of haploid and diploid individuals in predicting the evolution of life cycles is discussed. Measures obtained in algae are compared with theoretical predictions.     

Sex-limited mutations and the evolution of sexual dimorphism

Abstract.— Although the developmental and genetic mechanisms underlying sex differences are being elucidated in great detail in a number of species, there remains a breach between proximate and evolutionary studies of sexual dimorphism. More precisely, the evolution of sex-limited gene expression at autosomal loci has not been well reasoned using either theoretical or empirical methods. Here, I show that a Mendelian genetic model including elementary details of sexual differentiation provides novel insight into the evolution of sex differences via sex limitation. This model indicates that the nature of allelic effects and the pattern of selection must be known in both sexes to predict the evolution of sex differences. That is, selection interacts with genetic variation for sexual dimorphism to produce unanticipated patterns of trait divergence or convergence between the sexes. Ultimately, this model may explain why previous models for the evolution of sexual dimorphism do not predict the erratic behavior of the sex difference during artificial selection experiments.     

Sex allocation in haplodiploids is mediated by egg size: evidence in the spider mite Tetranychus urticae Koch

Haplodiploid species display extraordinary sex ratios. However, a differential investment in male and female offspring might also be achieved by a differential provisioning of eggs, as observed in birds and lizards. We investigated this hypothesis in the haplodiploid spider mite Tetranychus urticae, which displays highly female-biased sex ratios. We show that egg size significantly determines not only larval size, juvenile survival and adult size, but also fertilization probability, as in marine invertebrates with external fertilization, so that female (fertilized) eggs are significantly larger than male (unfertilized) eggs. Moreover, females with on average larger eggs before fertilization produce a more female-biased sex ratio afterwards. Egg size thus mediates sex-specific egg provisioning, sex and offspring sex ratio. Finally, sex-specific egg provisioning has another major consequence: male eggs produced by mated mothers are smaller than male eggs produced by virgins, and this size difference persists in adults. Virgin females might thus have a (male) fitness advantage over mated females.     

The evolution of sexual size dimorphism in the house finch. III. Developmental basis

Sexual size dimorphism of adults proximately results from a combination of sexually dimorphic growth patterns and selection on growing individuals. Yet, most studies of the evolution of dimorphism have focused on correlates of only adult morphologies. Here we examined the ontogeny of sexual size dimorphism in an isolated population of the house finch (Carpodacus mexicanus). Sexes differed in growth rates and growth duration; in most traits, females grew faster than males, but males grew for a longer period. Sexual dimorphism in bill traits (bill length, width, depth) and in body traits (wing, tarsus, and tail length; mass) developed during different periods of ontogeny. Growth of bill traits was most different between sexes during the juvenile period (after leaving the nest), whereas growth of body traits was most sexually dimorphic during the first few days after hatching. Postgrowth selection on juveniles strongly influenced sexual dimorphism in all traits; in some traits, this selection canceled or reversed dimorphism patterns produced by growth differences between sexes. The net result was that adult sexual dimorphism, to a large degree, was an outcome of selection for survival during juvenile stages. We suggest that previously documented fast and extensive divergence of house finch populations in sexual size dimorphism may be partially produced by distinct environmental conditions during growth in these populations.     

Anisogamy,sexual selection,and the evolution and maintenance of sex

Summary In the present paper we distinguish between two aspects of sexual reproduction. Genetic recombination is a universal features of the sexual process. It is a primitive condition found in simple, single-celled organisms, as well as in higher plants and animals. Its function is primarily to repair genetic damage and eliminate deleterious mutations. Recombination also produces new variation, however, and this can provide the basis for adaptive evolutionary change in spatially and temporally variable environments.The other feature usually associated with sexual reproduction, differentiated male and female roles, is a derived condition, largely restricted to complex, diploid, multicellular organisms. The evolution of anisogamous gametes (small, mobile male gametes containing only genetic material, and large, relatively immobile female gametes containing both genetic material and resources for the developing offspring) not only established the fundamental basis for maleness and femaleness, it also led to an asymmetry between the sexes in the allocation of resources to mating and offspring. Whereas females allocate their resources primarily to offspring, the existence of many male gametes for each female one results in sexual selection on males to allocate their resources to traits that enhance success in competition for fertilizations. A consequence of this reproductive competition, higher variance in male than female reproductive success, results in more intense selection on males.The greater response of males to both stabilizing and directional selection constitutes an evolutionary advantage of males that partially compensates for the cost of producing them. The increased fitness contributed by sexual selection on males will complement the advantages of genetic recombination for DNA repair and elimination of deleterious mutations in any outcrossing breeding system in which males contribute only genetic material to their offspring. Higher plants and animals tend to maintain sexual reproduction in part because of the enhanced fitness of offspring resulting from sexual selection at the level of individual organisms, and in part because of the superiority of sexual populations in competition with asexual clones.     

A comparative study on the evolution of reversed size dimorphism in monogamous waders

Sexual dimorphism in size is common in birds. Males are usually larger than females, although in some taxa reversed size dimorphism (RSD) predominates. Whilst direct dimorphism is attributed to sexual selection in males giving greater reproductive access to females, the evolutionary causes of RSD are still unclear. Four different hypotheses could explain the evolution of RSD in monogamous birds: (1) The ‘energy storing’ hypothesis suggests that larger females could accumulate more reserves at wintering or refuelling areas to enable an earlier start to egg laying. (2) According to the ‘incubation ability’ hypothesis, RSD has evolved because large females can incubate more efficiently than small ones. (3) The ‘parental role division’ hypothesis suggests that RSD in monogamous waders has evolved in species with parental role division and uniparental male care of the chicks. It is based on the assumption that small male size facilitates food acquisition in terrestrial habitats where chick rearing takes place and that larger females can accumulate more reserves for egg laying in coastal sites. (3) The ‘display agility’ hypothesis suggests that small males perform better in acrobatic displays presumably involved in mate choice and so RSD may have evolved due to female preference for agile males. I tested these hypotheses in monogamous waders using several comparative methods. Given the current knowledge of the phylogeny of this group, the evolutionary history of waders seems only compatible with the hypothesis that RSD has evolved as an adaptation for increasing display performance in males. In addition, the analysis of wing shape showed that males of species with acrobatic flight displays had wings with higher aspect ratio (wing span/²wing area) than non-acrobatic species, which probably increases flight manoeuvrability during acrobatic displays. In species with acrobatic displays males also had a higher aspect ratio than females although no sexual difference was found in non-acrobatic species. These results suggest that acrobatic flight displays could have produced changes in the morphology of some species and suggest the existence of selection favouring higher manoeuvrability in species with acrobatic flight displays. This supports the validity of the mechanisms proposed by the ‘display agility’ hypothesis to explain the evolution of RSD in waders.     

The evolution of obligate sex: the roles of sexual selection and recombination

The evolution of sex is one of the greatest mysteries in evolutionary biology. An even greater mystery is the evolution of obligate sex, particularly when competing with facultative sex and not with complete asexuality. Here, we develop a stochastic simulation of an obligate allele invading a facultative population, where males are subject to sexual selection. We identify a range of parameters where sexual selection can contribute to the evolution of obligate sex: Especially when the cost of sex is low, mutation rate is high, and the facultative individuals do not reproduce sexually very often. The advantage of obligate sex becomes larger in the absence of recombination. Surprisingly, obligate sex can take over even when the population has a lower mean fitness as a result. We show that this is due to the high success of obligate males that can compensate the cost of sex.     

Sexual selection and the evolution of secondary sexual traits: sex comb evolution in Drosophila

Sexual selection can drive rapid evolutionary change in reproductive behaviour, morphology and physiology. This often leads to the evolution of sexual dimorphism, and continued exaggerated expression of dimorphic sexual characteristics, although a variety of other alternative selection scenarios exist. Here, we examined the evolutionary significance of a rapidly evolving, sexually dimorphic trait, sex comb tooth number, in two Drosophila species. The presence of the sex comb in both D. melanogaster and D. pseudoobscura is known to be positively related to mating success, although little is yet known about the sexually selected benefits of sex comb structure. In this study, we used experimental evolution to test the idea that enhancing or eliminating sexual selection would lead to variation in sex comb tooth number. However, the results showed no effect of either enforced monogamy or elevated promiscuity on this trait. We discuss several hypotheses to explain the lack of divergence, focussing on sexually antagonistic coevolution, stabilizing selection via species recognition and nonlinear selection. We discuss how these are important, but relatively ignored, alternatives in understanding the evolution of rapidly evolving sexually dimorphic traits.     

Female postmating immune responses,immune system evolution and immunogenic males

Females in many taxa experience postmating activation of their immune system, independently of any genital trauma or pathogenic attack arising from male‐female genital contact. This response has always been interpreted as a product of natural selection as it either prepares the female immune system for antigens arising from an implanted embryo (in the case of placental mammals), or is a “pre‐emptive strike” against infection or injury acquired during mating. While the first hypothesis has empirical support, the second is not entirely satisfactory. Recently, studies that have experimentally dissected the postmating responses of Drosophila melanogaster females point to a different explanation: male reproductive peptides/proteins that have evolved in response to postmating male‐male competition are directly responsible for activating particular elements of the female immune system. Thus, in a broad sense, males may be said to be immunogenic to females. Here, we discuss a possible direct role of sexual selection/sexual conflict in immune system evolution, in contrast to indirect trade‐offs with other life‐history traits, presenting the available evidence from a range of taxa and proposing ways in which the competing hypotheses could be tested. The major implication of this review is that immune system evolution is not only a product of natural selection but also that sexual selection and potentially sexual conflict enforces a direct selective pressure. This is a significant shift, and will compel researchers studying immune system evolution and ecological immunity to look beyond the forces generated by parasites and pathogens to those generated by the male ejaculate.     

Competition between relatives and the evolution of dispersal in a parasitoid wasp

Evolutionary theory predicts that levels of dispersal vary in response to the extent of local competition for resources and the relatedness between potential competitors. Here, we test these predictions by making use of a female dispersal dimorphism in the parasitoid wasp Melittobia australica. We show that there are two distinct female morphs, which differ in morphology, pattern of egg production, and dispersal behaviour. As predicted by theory, we found that greater competition for resources resulted in increased production of dispersing females. In contrast, we did not find support for the prediction that high relatedness between competitors increases the production of dispersing females in Melittobia. Finally, we exploit the close links between the evolutionary processes leading to selection for dispersal and for biased sex ratios to examine whether the pattern of dispersal can help distinguish between competing hypotheses for the lack of sex ratio adjustment in Melittobia.     

The role of doublesex in the evolution of exaggerated horns in the Japanese rhinoceros beetle

Male‐specific exaggerated horns are an evolutionary novelty and have diverged rapidly via intrasexual selection. Here, we investigated the function of the conserved sex‐determination gene doublesex (dsx) in the Japanese rhinoceros beetle (Trypoxylus dichotomus) using RNA interference (RNAi). Our results show that the sex‐specific T. dichotomus dsx isoforms have an antagonistic function for head horn formation and only the male isoform has a role for thoracic horn formation. These results indicate that the novel sex‐specific regulation of dsx during horn morphogenesis might have been the key evolutionary developmental event at the transition from sexually monomorphic to sexually dimorphic horns.     

Sex-limited expression of ornamental feathers in birds

Extravagant secondary sexual characters show sexual size dimorphismin some species but are completely sex limited in others. Sexualornamentation has been hypothesized to benefit mainly malesthrough sexual selection, but the costs of secondary sexualcharacters initially would be experienced by both sexes. Theevolution of sexual size dimorphism of ornaments and, eventually, the complete sex-limited expression of these characters, willdepend on the effects of sexual and natural selection on thetwo sexes. A phylogenetic analysis controlling for similaritiesdue to common ancestry of 60 independent evolutionary originsof feather ornamentation in birds was used to investigate ecologicalfactors correlated with sexual size dimorphism and sex-limited expression of secondary sexual characters. When the size ofan ornament is large relative to body size, the trait willbe particularly costly for females, resulting in selectionfor increased sexual size dimorphism of the ornament. Indeed,sexual size dimorphism of ornaments was positively related to the relative size of male ornaments but was unrelated torelative size of female ornaments. Species with polygynousand lekking mating systems with little or no male parentalcare (in particular nest building and incubation) demonstratedsex-limited expression of ornaments as compared to monogamous species. Species with no food provisioning of offspring by themale showed a trend for increased sexual size dimorphism ofornaments. Therefore, large natural selection costs duringreproduction imposed by the expression of secondary sexualcharacters are related to the evolution of sexual size dimorphismof ornaments and eventually their complete loss from females.     

Male-biased mutation, sex linkage, and the rate of adaptive evolution

An interaction between sex-linked inheritance and sex-biased mutation rates may affect the rate of adaptive evolution. Males have much higher mutation rates than females in several vertebrate and plant taxa. When evolutionary rates are limited by the supply of favorable new mutations, then genes will evolve faster when located on sex chromosomes that spend more time in males. For mutations with additive effects, Y-linked genes evolve fastest, followed by Z-linked genes, autosomal genes, X-linked genes, and finally W-linked and cytoplasmic genes. This ordering can change when mutations show dominance. The predicted differences in substitution rates may be detectable at the molecular level. Male-biased mutation could cause adaptive changes to accumulate more readily on certain kinds of chromosomes and favor animals with Z-W sex determination to have rapidly evolving male sexual displays.     

The phylogeny of diving beetles (Coleoptera: Dytiscidae) and the evolution of sexual conflict

A model of evolution based on conflicts of interest between the sexes over mating decisions is examined in relation to diving beetles (Dytiscidae). The model predicts the following evolutionary sequence: (1) cost to females of mating increases, (2) females evolve behavioural resistance to male mating attempts, (3) males evolve devices to overcome female resistance, and (4) females evolve morphological counter-adaptations to the male devices. This model is tested using species of Dytiscidae, in which (1) some species have a very long mating duration while others mate quickly, (2) females of some species resist male mating attempts by swift and erratic swimming when seized by a male, (3) males of some species possess a grasping device in the form of sucker-shaped setae on the legs used to adhere to the pronota or elytra of females prior to mating, and (4) females of some species have a modified dorsal cuticle with irregular sculpturing which appears to interfere with the male adhesive setae. The predicted order of evolution of some of these features was tested in a cladistic analysis of 52 taxa in Dytiscidae and Hygrobiidae using characters from adult and larval morphology and a portion of the gene wingless . The combined analysis resulted in nine most parsimonious cladograms. The consensus cladogram of these indicates that male sucker setae arose a single time in a clade of Dytiscinae. Nested within this clade are five groups with an independently derived, modified dorsal cuticle in females. This pattern of characters in Dytiscinae is consistent with the prediction implied by the model of sexual selection. The utility of wingless as a marker for phylogenetic analysis of diving beetles is discussed, and the resulting phylogeny is compared with previous analyses and current classification.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 359–388.     

The large-male advantage in brown antechinuses: female choice, male dominance, and delayed male death

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.