Courtship Disruptions and Male Mating Strategies: Examples from Female-Defense Mating Systems

Males frequently interrupt the copulation attempts of other males, and these courtship disruptions may limit the extent to which a few males are able to monopolize mating access to females. Males actively defend sexually receptive females in many species in which females form dense aggregations during the breeding season. Across and within such species there is considerable variation in the mating tactics adopted by males, with males in some cases defending groups of females and in other cases sequentially consorting with individual females. Colonial blackbirds have been central to studying this mating system, and we develop a conceptual model for how courtship disruption may account for variation in male mating tactics in this group. Our model assumes that the frequency of disruptions increases with greater colony size. As a consequence, successful copulations are less likely to occur at large colonies than at small colonies, and males are expected to switch from defending multiple females at the colony to consorting individual females away from it. Results from two species of blackbird support the basic assumptions of this model. In one species, the Montezuma oropendola, disruptions occur rarely and males defend groups of females, whereas in the other species, the yellow-rumped cacique, disruptions are frequent and males defend single females. Moreover, consistent with a key prediction, within each species, males associated with small colonies remain at the colony and defend groups of females, whereas males spend little time defending groups of females at large colonies and rarely attempt copulations there. This model has the potential to explain variation in male mating strategies and female monopolization for other taxa in which females form breeding aggregations.     

动物的婚配制度

婚配制度是动物种群个体为获得配偶普遍采取的一种行为策略。一般分为单配制、一雄多雌制、一雌多雄制和混交制。作为动物的一种进化稳定对策,婚配制度又具有一定的可塑性,有时可以逆转,有时又是兼性的。配偶外交配主要存在于单配制物种中特别是单配制鸟类中。其发现表明通过观察个体间联系来确定的“社会性婚配制度”和通过个体实际上的交配对象来描述的“遗传性婚配制度”有可能存在差异。婚配制度影响有害动物的不育控制,在存在繁殖性竞争的情况下,对单配制和一雄多雌制而言,不育效果最佳。     

啮齿动物的婚配制度及其机制

婚配制度是动物行为生态学的重要研究内容之一。概述了啮齿动物婚配制度的定义、类型和婚配制度的可变性,婚配制度形成的内在调节机制,对有关啮齿动物婚配制度研究作了评述。     

Alternative Mating Tactics and Evolutionarily Stable Strategies

Difficulties with applying Evolutionarily. Stable Strategy (ESS)methodology and terminology to alternative mating behaviors(in which some males in local populations adopt strikingly different,often non-competitive, behavioral patterns) are reviewed. Definitionsfor "tactic" (behavioral phenotype) and "strategy" (evolvedset of rules for expressing tactics) are given. Inconsistentand incorrect applications of "mixed," "pure," and "conditional"ESSs are discussed. Cases of condition-dependent alternative mating tactics arereviewed. Because most alternative behaviors are condition dependent,neither their population-wide nor individual fitness contributionsare expected to equal the fitness contributions of "primary"tactics. Individuals should, however, switch tactics at "equalfitness points." A particular conditional tactic will persistwhen its maintenance cost (genetic or physiological) is lessthan its fitness contribution. In only exceptional cases arethe fitness contributions of tactics expected to be equal: 1)genetic polymorphisms, 2) stochastic "mixed" ESSs, 3) frequency-dependentchoice and, 4) arbitrary assessment. Although alternative tacticsmay occur in cases of genetic polymorphism or genetic equipotence,most mating tactics probably occur when continuous heritablevariation in underlying conditional strategy exists. Selectionfor genetically influenced "roles" (genetic background) mayalso uncover apparent heritability.     

物种繁殖策略和交配对策的变异性

物种繁殖策略和交配对策的变异性是演化生物学研究的新必领域.然而,在实际研究中,由于术语使用混乱和概念错误,常常导致许多结果模糊不清.通过该文,区分了繁殖策略和交配对策的概念,总结了繁殖策略变异性诸假设,阐述并比较了迄今为止繁殖策略和交配对策变异性研究的重要理论和模型,解释了不同交配对策的演化基础和激素调节机理,并在此基础上提出当前物种繁殖策略和交配对策变异性研究的热点问题.     

Mating Systems and Distribution in some Tropical Ferns

Applying mating system genetics as the tool, three tropicalferns, namely, Ceratopteris thalictroides, Pseudodrynaria coronansand Pityrogramma calomelanos were examined for their distributionalpatterns. Absence of recessive lethals in the sporophytes ofP. colomelanos allows its spores to function as a single propagulein the colonization of open habitats through intra-gametophyticselfing and it is widely distributed. The phenomenon of leakylethality and ultimately recessive sporophytic lethality inP. coronans is associated with a restricted distribution ofthe species in the forest. Ecological specialization in thecase of C. thalictroides also renders it a poor colonizer thoughits mating system is directed towards intergemetophytic selfingwith capacity in time for intra-gametophytic selfing.     

Resource Acquisition and Alternative Mating Strategies in Water Striders

Behavioral polymorphisms occur among male and female water striders,Gems remigis, when competing for food and mates. Individualsof both sexes vie for positions in the fastest flowing portionsof streams. Here prey capture rates are highest, as are thoseof swimming and aggression. Only the largest females, and maleswith the largest first appendages, can regularly maintain positionsin these areas. The remaining females are arranged along theflow gradient according to their size with the smallest holdingpositions in pools of slow moving water. For the remaining malesneither overall size, nor the size of the first appendages,appears to determine which males swim near the edge of streams,or which males swim as satellites behind those occupying thefast flowing productive areas. Preliminary data show that matingsuccess of edge and satellite males are about equal, but significantlyless than that of the centrally positioned males with the largestfirst appendages. Thus although it appears that morphologicalphenotype influences male competitive behavior, when the absolutesize of the critical trait is small males adopt behavior afterassessing the actions of others. For these "subordinate" males,behavioral assessment appears to produce an "ideal free" spatialdistribution.     

Estimating Long-Term Mating Systems Using DNA Sequences

Plant mating systems often involve a mixture of self fertilizations and outcross fertilizations. The degree of selfing has a large impact on the genetic composition of natural populations and on the evolution of the mating system itself in response to such factors as inbreeding depression. This paper describes a means of estimating the long-term rate of self-fertilization from samples of alleles taken from individuals in a population. Use is made of the genealogy of pairs of alleles at a locus within individuals and pairs between individuals. The degree of selfing is closely related to the extent to which the number of nucleotide sites differing within an individual is reduced relative to the number differing between individuals. Importantly, the estimate of long-term selfing is largely independent of population size and is not affected by historical fluctuations in population size; instead it responds directly to the mating system itself. The approach outlined here is most appropriate to evolutionary problems in which the long-term nature of the mating system is of interest, such as to determine the relationship between prior inbreeding and inbreeding depression.     

Emergence of Polymorphic Mating Strategies in Robot Colonies

Polymorphism has fascinated evolutionary biologists since the time of Darwin. Biologists have observed discrete alternative mating strategies in many different species. In this study, we demonstrate that polymorphic mating strategies can emerge in a colony of hermaphrodite robots. We used a survival and reproduction task where the robots maintained their energy levels by capturing energy sources and physically exchanged genotypes for the reproduction of offspring. The reproductive success was dependent on the individuals'' energy levels, which created a natural trade-off between the time invested in maintaining a high energy level and the time invested in attracting mating partners. We performed experiments in environments with different density of energy sources and observed a variety in the mating behavior when a robot could see both an energy source and a potential mating partner. The individuals could be classified into two phenotypes: 1) forager, who always chooses to capture energy sources, and 2) tracker, who keeps track of potential mating partners if its energy level is above a threshold. In four out of the seven highest fitness populations in different environments, we found subpopulations with distinct differences in genotype and in behavioral phenotype. We analyzed the fitnesses of the foragers and the trackers by sampling them from each subpopulation and mixing with different ratios in a population. The fitness curves for the two subpopulations crossed at about 25% of foragers in the population, showing the evolutionary stability of the polymorphism. In one of those polymorphic populations, the trackers were further split into two subpopulations: (strong trackers) and (weak trackers). Our analyses show that the population consisting of three phenotypes also constituted several stable polymorphic evolutionarily stable states. To our knowledge, our study is the first to demonstrate the emergence of polymorphic evolutionarily stable strategies within a robot evolution framework.     

Territory Area as a Determinant of Mating Systems

Territoriality is an integral part of breeding behavior in manyanimals. Because the reproductive success of territorial malesis often limited by access to females, breeding males shouldbehave as "area maximizers" when the basis of female choiceis either the abundance of resources within the territory orterritory area per se. Being reproductively more limited byenergy, territorial females should be "energy maximizers." Aseries of simple analytical models of territory area for suchforagers is developed to explore how changes in local food productionand/or local competitor density affect both the probabilityof a territorial male securing more than one mate (polygyny)and the probability of his and his mates' reproductive successincreasing. Two cases are modeled (only males territorial vs.both sexes territorial), each for various sets of assumptionsregarding interactions between food production, feeding efficiency,and competitor density. Concurrent responses in territory area,territory food reserves, net energy gain, and time budgetingprovide testable sets of predictions for each scenario. Whereonly males are territorial (Case I), changes in food productioncan have different (indeed, opposite) effects upon an individualmale's probability of becoming polygynous, depending upon whetherthe basis of female choice is the abundance of food within theterritory or another factor positively correlated with territoryarea. Increases in competitor density usually decrease the probabilityof polygyny regardless of the basis of female choice. Whereboth sexes are territorial and territories overlap intersexually(Case II), the mating system becomes a function of the numberof female territories within each male's territory, which varieswith the ratio of male to female territory areas. In this case,the probability of polygyny occurring will increase if foodproduction for both sexes increases without concurrent increasesin competitor density, and will decrease if competitor densityfor both sexes increases without concurrent increases in feedingefficiency. Few data are presently available to test eitherthese general predictions or numerous sets of secondary predictionstabulated in the text. Available evidence is largely consistentwith the models, but mostly circumstantial. This is becausethe predictions of these and other models of territory areaare strongly assumption dependent, and few published studieshave investigated these assumptions. These analyses demonstratethat to accurately assess the mechanisms by which environmentalfactors affect territory area, and thus mating systems, testsof the underlying assumptions of models are essential.     

On Nonrandom Mating Systems for Attaining Hardy-Weinberg Equilibrium

LI (1988) showed that random mating is a sufficient, not a necessary condition for the Hardy-Weinberg principle. A nonrandom mating population that behaves like a random mating population is thus called a ‘pseudo-random mating population’ by him. The pseudo-random mating system studied by him has been focused on those populations in which the parental generation is in Hardy-Weinberg proportions. In other words, the mating type frequency deviations from random mating for each parental genotype add up to zero. In this article these restrictions are relaxed and new pseudo-random mating systems that immediately yield Hardy-Weinberg offspring are also obtained. This is possible because reciprocal crosses have identical segregation probabilities for an autosomal locus, and the manipulation of the combined frequency of reciprocal crosses does not change the gene frequency of the population. A comparison of these new patterns with that of Li is given in the Discussion.     

Habitat, Niche, and Evolution of Sirenian Mating Systems

Lek polygyny, monogamy and scramble promiscuity have been reported in the two families and five species of Recent sirenians. Evidence for lek mating in the dugong or "sea pig" (Dugong dugon), monogamy in Steller's sea cow (Hydrodamalis gigas), and scramble promiscuity in the three manatees or "river cows" (Trichechus manatus, Trichechus senegalensis, and Trichechus inunguis), as well as in one dugong population, is reviewed. Sirenians are long-lived "K-strategists" with precocious young, few potential young per female lifetime, high female investment in a few young, little apparent opportunity for post-copulatory male investment, and "paenungulate" reproductive physiologies that appear to increase uncertainty as to female receptivity and assurance as to paternity. Common features notwithstanding, diverse habitats, climates, and niches may account for mating system diversity. Scenarios for evolution of diverse mating systems, based on our understanding of mating systems in terrestrial herbivores, are presented. The dugong retains the ancestral low latitude marine, seagrass dependent, bottom-feeding, niche characteristic of diverse, tusked, Oligocene and Miocene sirenian faunas. With a long breeding season and high polygyny potential, retention of tusks by male dugongs in the absence of any foraging function suggests that tusks may have always had social functions and lekking may be of ancient origin. The sea cow lineage, isolated on the shoreline of the northeastern Pacific as seagrasses declined, turned to surface foraging on chemically undefended kelps and lost both tusks and molar teeth. As it followed kelps northwards, adaptation to a cold-temperate climate compressed the breeding season, limited the polygyny potential, and, in conjunction with incentives for paternal investment, favored pair bonding and the monogamous mating system postulated by George Steller (1751). Manatees, evolving in botanically-rich fresh waters of the Amazon basin as an aberrant offshoot of the marine dugongid line, remained in the tropics and retained a high polygyny potential, but became generalist foragers in the upper few meters of the water column. Labyrinthine river systems provided little opportunity for male aggregation and display (or rhizome foraging) and tusks were lost as the uncertainty of female inseminability drove the mating system toward scramble promiscuity and sperm competition. An observation of manatee-like behavior in a dense and sedentary dugong population in eastern Australia suggests plasticity in sirenian mating, and the likelihood that a form of scramble promiscuity may exist where no suitable site for lekking is available, where large group size makes female defence impossible, or where vulnerability of territorial males to hunting has resulted in extirpation of a lekking tradition. Dugong and manatee life history characteristics conform to expectations based on observed differences in mating systems.     

Modelling of Yeast Mating Reveals Robustness Strategies for Cell-Cell Interactions

Mating of budding yeast cells is a model system for studying cell-cell interactions. Haploid yeast cells secrete mating pheromones that are sensed by the partner which responds by growing a mating projection toward the source. The two projections meet and fuse to form the diploid. Successful mating relies on precise coordination of dynamic extracellular signals, signaling pathways, and cell shape changes in a noisy background. It remains elusive how cells mate accurately and efficiently in a natural multi-cell environment. Here we present the first stochastic model of multiple mating cells whose morphologies are driven by pheromone gradients and intracellular signals. Our novel computational framework encompassed a moving boundary method for modeling both a-cells and α-cells and their cell shape changes, the extracellular diffusion of mating pheromones dynamically coupled with cell polarization, and both external and internal noise. Quantification of mating efficiency was developed and tested for different model parameters. Computer simulations revealed important robustness strategies for mating in the presence of noise. These strategies included the polarized secretion of pheromone, the presence of the α-factor protease Bar1, and the regulation of sensing sensitivity; all were consistent with data in the literature. In addition, we investigated mating discrimination, the ability of an a-cell to distinguish between α-cells either making or not making α-factor, and mating competition, in which multiple a-cells compete to mate with one α-cell. Our simulations were consistent with previous experimental results. Moreover, we performed a combination of simulations and experiments to estimate the diffusion rate of the pheromone a-factor. In summary, we constructed a framework for simulating yeast mating with multiple cells in a noisy environment, and used this framework to reproduce mating behaviors and to identify strategies for robust cell-cell interactions.