Male mating strategies and the mating system of great-tailed grackles

Great-tailed grackles (Quiscalus mexicanus) are sexually dimorphic,dichromatic, colonially nesting blackbirds. In this study, males pursued three basic types of conditional mating strategies,each of which employed a different set of mating tactics. Territorialmales defended one or more trees in which several females nested.They achieved reproductive success by siring the offspringof their social mates and through extrapair fertilization.Resident males lived in the colony but did not defend territoriesor have social mates. Transient males passed through the colony, staying no more than a few days, and probably visited more thanone colony. Residents appeared to queue for access to territories,but transients did not. Residents and transients gained allpaternity through extrapair fertilizations and provided noparental care. Territorial males sired the majority of offspring,but residents and transients also sired small numbers of nestlings. Territorial males were larger and had longer tails than nonterritorialmales. The number of social mates was related to body size,and males that sired nestlings were heavier and had longertails than males with no genetic reproductive success. Malesthat gained paternity through extrapair fertilization wereheavier and had longer tails than males that did not. The matingsystem of great-tailed grackles can best be categorized as "non-faithful-female frank polygyny."     

Reproductive correlates of mating system variation in Eichhornia paniculata (Spreng.) Solms (Pontederiaceae)

Comparative studies of related plant species indicate that evolutionary shifts in mating systems are accompanied by changes in reproductive attributes such as flower size, floral morphology, and pollen/ovule ratio. Recent theoretical work suggests that patterns of investment in reproduction should also change with the mating system. In a glasshouse study, we investigated the extent to which mating system differences among populations of Eichhornia paniculata (Pontederiaceae) were correlated with changes in allocation to male and female function, floral display, and the regulation of investment in reproduction through fruit and ovule abortion. Significant differences in the amount of biomass allocated to reproductive structures were evident among six populations of E. paniculata. As predicted by sex allocation theory, the proportion of dry weight allocated to male function decreased with the outcrossing rate of populations. Six of the eight attributes used to characterize floral display also differed significantly among populations. However, with the exception of two attributes describing the number of flowers produced by inflorescences, these were not correlated with outcrossing rate. Levels of fruit and ovule abortion were determined in two populations with contrasting mating systems under different nutrient and pollination treatments. Virtually all fruits initiated by plants from a self-fertilizing population were matured, while the amount of fruit abortion in an outcrossing population increased with flower production. Ovule abortion was low in both populations. Our results demonstrate that the evolution of self-fertilization in E. paniculata is associated with changes in investment to reproduction that normally distinguish selfing and outcrossing species.     

The energetic cost of mating in a promiscuous cephalopod

Costs that individuals incur through mating can play an important role in understanding the evolution of life histories and senescence, particularly in promiscuous species. Copulation costs, ranging from energy expenditure to reduced longevity, are widely studied in insects but have received substantially less attention in other taxa. One cost of mating, the energetic cost, is poorly studied across all taxa despite its potential importance for the many species where copulation is physically demanding and/or frequent. Here, we investigated the energetic cost of mating in both male and female dumpling squid (Euprymna tasmanica). In this species, copulation can last up to 3 h and requires that the male physically restrains the female. We report that the act of copulation halves the swimming endurance of both sexes, and that they take up to 30 min to recover. Such a reduction in post-copulatory performance may have important implications for predator avoidance, foraging ability and energy allocation. Therefore, quantifying this cost is essential to understand the evolution of reproductive strategies and behaviours such as female receptivity and male and female mating frequency.     

Functional pleiotropy and mating system evolution in plants: frequency-independent mating

Mutations that alter the morphology of floral displays (e.g., flower size) or plant development can change multiple functions simultaneously, such as pollen export and selfing rate. Given the effect of these various traits on fitness, pleiotropy may alter the evolution of both mating systems and floral displays, two characters with high diversity among angiosperms. The influence of viability selection on mating system evolution has not been studied theoretically. We model plant mating system evolution when a single locus simultaneously affects the selfing rate, pollen export, and viability. We assume frequency-independent mating, so our model characterizes prior selfing. Pleiotropy between increased viability and selfing rate reduces opportunities for the evolution of pure outcrossing, can favor complete selfing despite high inbreeding depression, and notably, can cause the evolution of mixed mating despite very high inbreeding depression. These results highlight the importance of pleiotropy for mating system evolution and suggest that selection by nonpollinating agents may help explain mixed mating, particularly in species with very high inbreeding depression.     

The costs and benefits of multiple mating in a mostly monandrous wasp

The taxonomically widespread nature of polyandry remains a puzzle. Much of the empirical work regarding the costs and benefits of multiple mating to females has, for obvious reasons, relied on species that are already highly polyandrous. However, this makes it difficult to separate the processes that maintain the current level of polyandry from the processes that facilitate its expression and initiated its evolution. Here we consider the costs and benefits of polyandry in Nasonia vitripennis, a species of parasitoid wasp that is “mostly monandrous” in the wild, but which evolves polyandry under laboratory culture conditions. In a series of six experiments, we show that females gain a direct fecundity and longevity benefit from mating multiply with virgin males. Conversely, mating multiply with previously mated males actually results in a fecundity cost. Sexual harassment may also represent a significant cost of reproduction. Harassment was, however, only costly during oviposition, resulting in reduced fecundity, longevity, and disrupted sex allocation. Our results show that ecological changes, in our case associated with differences in the local mating structure in the laboratory can alter the costs and benefits of mating and harassment and potentially lead to shifts in mating patterns.     

Determinants of mating and sperm‐transfer success in a simultaneous hermaphrodite

The number of mating partners an individual has within a population is a crucial parameter in sex allocation theory for simultaneous hermaphrodites because it is predicted to be one of the main parameters influencing sex allocation. However, little is known about the factors that determine the number of mates in simultaneous hermaphrodites. Furthermore, in order to understand the benefits obtained by resource allocation into the male function it is important to identify the factors that predict sperm‐transfer success, i.e. the number of sperm a donor manages to store in a mate. In this study we experimentally tested how social group size (i.e. the number of all potential mates within a population) and density affect the number of mates and sperm‐transfer success in the outcrossing hermaphroditic flatworm Macrostomum lignano. In addition, we assessed whether these parameters covary with morphological traits, such as body size, testis size and genital morphology. For this we used a method, which allows tracking sperm of a labelled donor in an unlabelled mate. We found considerable variation in the number of mates and sperm‐transfer success between individuals. The number of mates increased with social group size, and was higher in worms with larger testes, but there was no effect of density. Similarly, sperm‐transfer success was affected by social group size and testis size, but in addition this parameter was influenced by genital morphology. Our study demonstrates for the first time that the social context and the morphology of sperm donors are important predictors of the number of mates and sperm‐transfer success in a simultaneous hermaphrodite. Based on these findings, we hypothesize that sex allocation influences the mating behaviour and outcome of sperm competition.     

The precultural human mating system

What was the precultural human mating system? This paper uses primate cross-species comparisons to arrive at a plausible answer which challenges many current theories. The results of this investigation suggest that (1) our precultural ancestors resided in multimale, multifemale communities; (2) the male-female consortships of our ancestors were genetically programmed to last for a short period, i.e., a few months or less; and, most importantly, (3) the precultural human mating system was a form of «selective promiscuity.» Also, it is suggested that our precultural mating system is a continuing fundamental tendency within us that is being suppressed and modified by culture.     

Evolution of mating systems in coral reef gobies and constraints on mating system plasticity

Social and mating systems can be influenced by the distribution, abundance, and economic defendability of breeding partners and essential resources. Polygyny is predicted where males can economically defend multiple females or essential resources used by females. In contrast, monogamy is predicted where neither sex can monopolise multiple partners, either directly or through resource control, but where one mate is economically defendable. The mating system and reproductive behaviour of five species of coral reef goby were investigated and contrasted with population density and individual mobility. The two most abundant species (Asterropteryx semipunctatus and Istigobius goldmanni) were polygynous. In contrast, the less populous and more widely dispersed epibenthic species (Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis) were pair forming and monogamous. All five species had low mobility, mostly remaining within metres (3 epibenthic species) or centimetres (2 cryptobenthic species) of a permanent shelter site. Interspecific differences in the mating system may have been shaped by differences in population density and the ability of reproductive individuals to economically defend breeding partners/sites. However, in a test of mating system plasticity, males of the three monogamous species did not mate polygynously when given the opportunity to do so in experimental manipulations of density and sex ratio. Mate guarding and complex spawning characteristics, which have likely co-evolved with the monogamous mating system, could contribute to mating system inflexibility by making polygynous mating unprofitable for individuals of the pair forming species, even when presented with current-day ecological conditions that usually favour polygyny.     

The mating behavior and reproduction performance in a multi-sire mating system for pigs

An important aim of organic animal production is to allow natural animal behaviour. Regarding reproduction techniques, artificial insemination is permitted but natural mating is preferred. The outdoor multi-sire system, where the sows are placed in large paddocks with a group of boars, is one example of a service system, which complies well with the organic ideals of facilitating natural animal behavior. However, very little knowledge is available about such system. Seven groups of in total of 47 sows and 31 boars were observed to study the mating behavior in an outdoor multi-sire mating system and the subsequent reproduction results. The time of start of courtship, behavior and the cause of disruption if the courtship was terminated, were recorded each time a boar courted a sow. All aggressive interactions between the boars were also recorded to estimate the boar ranking order. The observations revealed numerous poor quality matings, a huge variation in the number of times sows are mated, and overworked boars. Only 35% of all copulations lasted 2 min or more and 63% of all copulations were disrupted, mainly by competitor boars. The higher social status of the boar, the more copulations did it disrupt (p < 0.05). The outcome was an unacceptable variation in reproduction results. Only 71% of all estrus sows conceived, corresponding to a pregnancy rate of 77% of all mated sows. A large inter-group variation in reproduction performance was observed, indicating scope for improvements. In some groups all sows showed estrus and all sows conceived. Recommendations for improvement of the system are proposed.     

Paternal investment and the human mating system

Paternal investment has long been considered responsible for the evolution of predominantly monogamous marriage in humans. However, male-male competition resulting in mate-guarding and male coercion could be equally important. In this review, I use a comparative approach to examine the effect of variation in human paternal investment on our mating system. I conclude paternal investment is important but so too is mate-guarding. I propose a model of our mating system incorporating both factors. Variation in the mating system is explained by variation in male resource control and contribution, resulting in ecologically imposed monogamy or polygyny, as predicted by the polygyny threshold model, as well as variation in male-male competition for status, resulting in socially imposed monogamy or polygyny.     

Inbreeding under a cyclical mating system

Summary General recursion formulae for the coefficient of inbreeding under a cyclical mating system were derived in which one male and one female are selected from each of the n families per generation (population size N = 2 n). Each male is given the family number of his sire in each generation, while his mate comes from another family, varying systematically in different generations. Males of the r-th family in generations 1, 2, 3,..., t = n–1 within each cycle mate with females from families r+1, r+2, r+3,..., r+t to produce generations 2, 3, 4,..., t+1=1, respectively. The change in heterozygosity shows a cyclical pattern of rises and falls, repeating in cycles of n–1 generations. The rate of inbreeding oscillates between <-3% to >6% in different generations within each cycle, irrespective of the population size. The average rate of inbreeding per generation is approximately 1/[4 N-(Log₂N+1)], which is the rate for the maximum avoidance of inbreeding. The average inbreeding effective population size is approximately 2 N–2.     

Sperm transfer is affected by mating history in the simultaneously hermaphroditic snail Lymnaea stagnalis

Abstract. Males are predicted to strategically allocate sperm across mating partners in order to maximize their chances of paternity. This requires that males have the ability to detect aspects of their partner's mating history or the number of potential mates. We investigated whether simultaneous hermaphrodites mating in the male role strategically adjust sperm transfer depending on rearing conditions. The pond snail Lymnaea stagnalis (Basommatophora) is known to donate sperm repeatedly to different partners during a breeding season and store received sperm for >3 months. The rearing conditions of the donor as well as the recipient affect the amount of sperm transferred. Sperm donors raised in isolation transfer more sperm than those raised in groups. Furthermore, isolated sperm donors transfer less sperm to partners that were raised in groups than to those raised in isolation, i.e., virgins. These findings suggest that snails raised in isolation shift their sex allocation toward the male function and indicate that they can somehow assess the mating status of their partner.     

植物交配系统及其在植物保护中的应用

植物交配系统是影响植物居群遗传结构最关键的生物学因素之一。在具体实践中,对遗传育种方法的选择和植物保护策略的制定具有指导意义。本文回顾了植物交配系统的研究历史,分析了相关概念,讨论了植物交配系统的变异与进化,介绍了相关的基本原理和研究方法,对研究中使用的分析工具作了比较。对国内外植物交配系统研究的进展,讨论了在实际研究中的取样及针对不同植物的保护策略问题,强调了植物交配系统信息在植物保护中的重要性,认为在植物保护中应加强植物交配系统的研究。     

Effects of mating system in Japanese quail

Summary A 17-generation selection experiment was conducted to study direct and correlated responses to mass selection under a mating system with alternating generations of full-sib inbreeding and wide outbreeding (population I) as compared with a mass selected, randomly mated population (population II). The selection criterion was an index of total egg mass to 78 days divided by adult female body weight. Estimates of heritabilities and genetic correlations are reported. Estimated heritabilities for the index were 0.38±0.04 and 0.29±0.05 in population I and II, respectively. Realized heritabilites were 0.10±0.05 and 0.12±0.03. For most traits studied the mean phenotypic values in the cyclic mated population decreased for inbred generations. Increased inbreeding levels also caused outbred generation means of population I to decrease through the first six or seven generations. After this period of adaptation to inbreeding selection response was positive for the index and positively correlated traits. Total response to selection under the cyclic inbred-outbred mating system did not exceed selection response made under random mating. However, the rate of response in the cyclically mated population exceeded that in the randomly mated population in later generations when the cyclically mated population had apparently adapted to inbreeding.Published with approval of the Director of the Montana Agricultural Experiment Station, Journal Series No. 1221     

Global analysis of a two-allele mating system

The global analysis of a two-allele mating system is provided. One allele is dominant to the other. Mating is random, but mating between unlike phenotypes has a lower fertility than that between like phenotypes. The generations are discrete and non-overlapping. The population is considered to be infinite, and the model is deterministic. There are three equilibria of the difference equations. Two of the equilibria are the (two) homozygous states, and these are asymptotically stable. The third equilibrium is polymorphic but is unstable. It is proven that almost all populations converge to one of the two homozygous states. The remaining populations converge to the unstable equilibrium, and lie on a curve that separates the basins of attraction for the other two equilibria. This curve is shown to satisfy some simple properties.     

The mating system and gene dynamics of plateau pikas

Evolutionary theory suggests that mating systems should have substantial effects on gene dynamics of local populations. In polygynous species, local 'breeding groups' may produce significant genetic structure, due to genetic differences among groups, and rate of loss of genetic variation from such populations may be considerably slowed. We examined possible influences of the variable mating system and family group structure on genetic properties of a population of plateau pikas (Ochotona curzoniae). Pika gene dynamics were examined via F-statistics and effective population sizes (N(e)), calculated from genetic correlations within and among individuals and families. Genetic correlations were estimated from mating patterns, population demography, and dispersal patterns. Substantial genetic structure within the population was indicated by a strongly positive F(LS). Genetic influence of natal dispersal out of pika families was indicated by a strongly negative inbreeding statistic (F(IL)=-0.34). Effective size of the population was not greatly different from the census population, whereas a traditional estimate of effective size of the population was much lower, indicating that the family structure of the pikas results in a slowed loss of genetic variation over time. Thus, even though mating patterns of plateau pikas were variable, family structure had a strong influence on pika gene dynamics.     

Size-dependent mating preference of the male fiddler crab Austruca perplexa

In many animals, females prefer large males to small males, which allow large males to be choosier than small males when selecting a mate. We investigated the courtship intensity of small- and large-sized male fiddler crabs (Austruca perplexa) by examining their claw-waving rates (waves/min) towards small- and large-sized females. We found that large males showed a greater preference for large females by producing more waves/min towards them, whereas small males did not show any apparent preference for either large or small females. Moreover, the waving rate of large males was positively correlated with female size, but there was no correlation between waving rate and female size in small males. These results indicate that large males in a population become choosier and show strong mate choice, which is most likely due to their greater preference among females.     

Evolution of mating system and the genetic covariance between male and female investment in Clarkia (onagraceae): selfing opposes the evolution of trade-offs

Sex allocation theory has assumed that hermaphroditic species exhibit strong genetically based trade-offs between investment in male and female function. The potential effects of mating system on the evolution of this genetic covariance, however, have not been explored. We have challenged the assumption of a ubiquitous trade-off between male and female investment by arguing that in highly self-fertilizing species, stabilizing natural selection should favor highly efficient ratios of male to female gametes. In flowering plants, the result of such selection would be similar pollen:ovule (P:O) ratios across selfing genotypes, precluding a negative genetic correlation (r(g)) between pollen and ovule production per flower. Moreover, if selfing genotypes with similar P:O ratios differ in total gametic investment per flower, a positive r(g) between pollen and ovule production would be observed. In outcrossers, by contrast, male- and female-biased flowers and genotypes may have equal fitness and coexist at evolutionary equilibrium. In the absence of strong stabilizing selection on the P:O ratio, selection on this trait will be relaxed, resulting in independence or resource-based trade-offs between male and female investment. To test this prediction, we conducted artificial selection on pollen and ovule production per flower in two sister species with contrasting mating systems. The predominantly self-fertilizing species (Clarkia exilis) consistently exhibited a significant positive r(g) between pollen and ovule production while the outcrossing species (C. unguiculata) exhibited either a trade-off or independence between these traits. Clarkia exilis also exhibited much more highly canalized gender expression than C. unguiculata. Selection on pollen and ovule production resulted in little correlated change in the P:O ratio in the selfing exilis, while dramatic changes in the P:O ratio were observed in unguiculata. To test the common prediction that floral attractiveness should be positively genetically correlated with investment in male function, we examined the response of petal area to selection on pollen and ovule production and found that petal area was not consistently genetically correlated with gender expression in either species. Our results suggest that the joint evolutionary trajectory of primary sexual traits in hermaphroditic species will be affected by their mating systems; this should be taken into account in future theoretical and comparative empirical investigations.     

The mating system and male mating success of the Virginia opossum (Didelphis virginiana) in Florida

The mating system of the Virginia opossum, a solitary, nocturnal marsupial, was studied over a period of two years in north–central Florida. There were two mating seasons each year, both lasting about four weeks and starting in mid-January and late April, respectively. Radio-tracking males and females revealed that, independent of body size, males doubled their home ranges during these periods to include an average of 5.9 females within their new ranges. Females were visited regularly and, on the night of oestrus, males directly competed for access to the female. Dominance and hence mating success was strongly related to body mass but not age. Dominant males weighed on average 3.18 kg (N = 20) compared to 2.65 kg of unsuccessful males. The largest of the competing males was successful in 20 of 23 cases involving at least two competitors. Individual male mating success varied from zero to three matings during a breeding season, but the range was probably underestimated. Mate searching activities were costly, as most males lost weight during both mating seasons. Weight changes were a function of body mass, with males over 2.2 kg losing up to 23% in weight and smaller males gaining weight. There was also evidence that male breeding activities entailed a survival cost.