Impact of mating design on selection response in Brassica rapa L.

The impact of four mating designs on selection response for leaf area was assessed at four different population sizes, using fast-cycling Brassica rapa L. Mating designs were either balanced (partial diallel or pair mating) or unbalanced (factorial mating designs with either one or two testers). When balanced, the mating designs required different numbers of crossings for the same number of parents: the partial diallel design, in the configuration retained here, required three times as many crossings as pair mating. Population sizes were 4, 8, 16, and 32. The percentage of selected individuals was kept constant at 25%. Despite an average estimated heritability around 0.4, the overall response to selection after five generations was fairly weak in all three replicates. For a given population size, selection response was larger under balanced mating designs than under unbalanced ones. There was no difference among balanced mating designs. Both results indicate that effective population size is more important than population size or the number of crossings in maintaining genetic gain.     

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. II. Variance in male mating success and effective population size

Variance in reproductive success is a primary determinant of genetically effective population size (Ne), and thus has important implications for the role of genetic drift in the evolutionary dynamics of animal taxa characterized by polygynous mating systems. Here we report the results of a study designed to test the hypothesis that polygynous mating results in significantly reduced Ne in an age-structured population. This hypothesis was tested in a natural population of a harem-forming fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The influence of the mating system on the ratio of variance Ne to adult census number (N) was assessed using a mathematical model designed for age-structured populations that incorporated demographic and genetic data. Male mating success was assessed by means of direct and indirect paternity analysis using 10-locus microsatellite genotypes of adults and progeny from two consecutive breeding periods (n = 431 individually marked bats). Combined results from both analyses were used to infer the effective number of male parents in each breeding period. The relative proportion of successfully reproducing males and the size distribution of paternal sibships comprising each offspring cohort revealed an extremely high within-season variance in male mating success (up to 9.2 times higher than Poisson expectation). The resultant estimate of Ne/N for the C. sphinx study population was 0.42. As a result of polygynous mating, the predicted rate of drift (1/2Ne per generation) was 17.6% higher than expected from a Poisson distribution of male mating success. However, the estimated Ne/N was well within the 0.25-0.75 range expected for age-structured populations under normal demographic conditions. The life-history schedule of C. sphinx is characterized by a disproportionately short sexual maturation period scaled to adult life span. Consequently, the influence of polygynous mating on Ne/N is mitigated by the extensive overlap of generations. In C. sphinx, turnover of breeding males between seasons ensures a broader sampling of the adult male gamete pool than expected from the variance in mating success within a single breeding period.     

Effects of multiple mating on the fecundity of an invasive pest (Octodonta nipae): the existence of an intermediate optimal female mating rate

Multiple mating is found in many insect taxa where both of the sexes can mate more than once. For males, this leads to the advantage of increasing their paternity by fertilizing more females. However, there is a trade‐off of resource allocation between reproduction and other life‐history characters. In the present study, the impact of increased mating rate on reproductive fitness of the invasive nipa palm hispid beetle Octodonta nipae Maulik (Coleoptera: Chrysomelidae) is investigated. A series of mating frequencies (i.e. 1, 5, 10, 15, 20 times) is selected from video frame playback, ranking from the minimum to maximum mating rate observed under laboratory conditions over a given time period. Fecundity parameters such as lifetime egg production, egg‐hatching rate, effective oviposition period and longevity are investigated for the evaluation of reproductive efficiency. For female O. nipae, increased fecundity is correlated with the mating frequency. Females mating 15 times lay the largest number of eggs (138.82 ± 6.87) and have a hatching rate of 47.43 ± 4.08%. After mating 20 times, females suffer significant declines in oviposition (90.31 ± 8.38 eggs) and egg‐hatching rate (34.16 ± 4.93%). Moreover, the population growth rate reaches a maximum in the females that mate 15 times. The results show that multiple matings in O. nipae have an intermediate optimal range within which female reproductive success is enhanced, providing empirical evidence for the existence of a trade‐off between costs and benefits during copulation based on resource allocation.     

Inbreeding, pedigree size, and the most recent common ancestor of humanity

How many generations ago did the common ancestor of all present-day individuals live, and how does inbreeding affect this estimate? The number of ancestors within family trees determines the timing of the most recent common ancestor of humanity. However, mating is often non-random and inbreeding is ubiquitous in natural populations. Rates of pedigree growth are found for multiple types of inbreeding. This data is then combined with models of global population structure to estimate biparental coalescence times. When pedigrees for regular systems of mating are constructed, the growth rates of inbred populations contain Fibonacci n-step constants. The timing of the most recent common ancestor depends on global population structure, the mean rate of pedigree growth, mean fitness, and current population size. Inbreeding reduces the number of ancestors in a pedigree, pushing back global common ancestry times. These results are consistent with the remarkable findings of previous studies: all humanity shares common ancestry in the recent past.     

Processes of pair formation leading to assortative mating in biological populations: dynamic interaction model

A model of pair formation that treats mating between two individuals as a dynamic process rather than an instant event is suggested. A number of cases corresponding to polygamous and monogamous matings of individuals are considered. The individual mating preferences are represented in the model by a set of "compatibility probabilities." It is shown that the mating pattern (the distribution of characters among mating pairs) established in a population as a result of the process of pair formation does not uniquely reflect the pattern of mating preferences. Quite different mating patterns may occur in populations with very similar mating preferences, as well as similar mating patterns may occur in populations with different individual mating preferences. The model demonstrates that not only mating preferences of individuals but also specific mechanisms of pair formation play an important role in determining the mating pattern of a population.     

Life history changes in Trogoderma variabile and T. inclusum due to mating delay with implications for mating disruption as a management tactic

Controlling postharvest pest species is a costly process with insecticide resistance and species‐specific control requiring multiple tactics. Mating disruption (MD) can be used to both decrease a female's access to males and delay timing of mating and decreases overall mating success in a population and population growth rate. Development of new commercially available MD products requires an understanding of life history parameters associated with mating delay. These can provide information for targeting proportions of reproducing individuals using MD. After delaying mating for females of two closely related beetle species, Trogoderma variabile and T. inclusum, we surveyed survivorship, number of eggs laid, and number of progeny emerged. With increases in mating age, total number of eggs laid and total number of progeny emerged significantly declined over time. T. inclusum typically had greater numbers of eggs laid and progeny emerged compared to T. variabile as female age at mating increased, suggesting that T. inclusum may be more resistant to long‐term delays in mating. Life span showed an increase as mating age increased but life span significantly decreased almost immediately following mating. Simulations depicting multiple distributions of mating within a population suggest that in a closed population, high levels of mating delay significantly reduced reproductive growth rates. Although reproductive growth rates were decreased with increased mating age, they are still large enough to maintain populations. This study highlights the differences in life history between two closely related species, suggesting that T. inclusum outperforms T. variabile over the course of a life span, but T. variabile has better reproductive capabilities early in life. MD may also be a viable component of a pest management system for these two species as it significantly decreased overall reproductive output and population growth.     

Mating Behavior and Reproductive Potential in the Turnip Moth Agrotis segetum (Lepidoptera: Noctuidae)

We investigated the lifetime mating potential and the reproductive behavior of male and female turnip moths Agrotis segetum (Schiff.) under field and laboratory conditions. The sex ratio was 1 : 1 in a lab-reared population as well as in two wild populations. Males were capable of mating repetitively a relatively large number of times (mean of 6.7 ± 2.7 matings) when given access to new virgin females throughout their lifetimes. Females seldom mated more than once (mean ± 1.3 ± 0.6 matings), indicating a male-biased operational sex ratio. The mean potential lifetime mating was five times higher in males, while the coefficient of variance was lower in males. There was no differences in longevity between animals that were allowed to mate and animals not allowed to mate, indicating no direct costs or benefits of mating in physiological terms. In males, the number of matings was positively correlated with longevity, but this was not the case in females. Nor was there a correlation between the number of female matings and the number of fertilized eggs. There was a negative correlation between the number of eggs fertilized and the number of times males had previously mated, indicating that male ejaculates were limited. Male spermatophore size also decreased with number of achieved matings. Laboratory-reared females attracted males in the field throughout their lifetimes, with a peak at 3–7 days of age. Wild males, allowed to choose between pairs of caged females in the field, were attracted in equal numbers to females of different ages. Females did not show any mate-rejection behavior in the field. They mated with the first male that courted them. No incidence of mate replacement by males arriving later to already courted females were recorded.     

Female Gryllus vocalis Field Crickets Gain Diminishing Returns from Increasing Numbers of Matings

Although female insects generally gain reproductive benefits from mating frequently, females do not mate unlimited numbers of times. This study asks whether the limit on female mating rate is imposed by trade‐offs between reproduction and survival. Female Gryllus vocalis were given the opportunity to mate 5, 10, or 15 times with novel males, and the effects on daily fecundity (egg production), fertility (proportion of eggs that were fertilized), and female post‐experimental longevity were measured. Females that mated 10 times laid more eggs and had a higher proportion of fertile eggs than females that mated 5 times. However, females that mated 15 times did not lay significantly more eggs or have a higher proportion of fertile eggs than females that mated 10 times. Although number of matings did not affect the date that females laid their last egg, mating more times was associated with a prolonged period of laying fertile eggs. Number of matings did not affect female post‐experimental longevity. Thus, there was no trade‐off between female reproductive effort and survival, even when females mated very large numbers of times. When females were allowed to mate ad libitum, the average number of times that females mated was greater than the number of times that confers maximal fitness. The lack of cost to mating explains why females might be willing to mate beyond the point of diminishing reproductive returns.     

INFERENCE OF SPERM COMPETITION FROM BROODS OF FIELD-CAUGHT DROSOPHILA

In field studies of multiple mating and sperm competition there typically is no experimental control over the number of times that a female mates, the interval between matings, or the genetic identity of multiple fathers contributing to a brood. Irrespective of this complexity, high-resolution molecular markers can be used to assign paternity with considerable confidence. This study employed two highly heterozygous microsatellite loci to assess multiple paternity and sperm displacement in a sample of broods taken from a natural population of Drosophila melanogaster. The large number of alleles present at each of the loci makes it difficult to derive explicit maximum-likelihood estimates for multiple paternity and sperm displacement from brood samples. Monte Carlo simulations were used to estimate maximum-likelihood parameters for the distribution of female remating frequency and the proportion of offspring sired by the second or subsequent mating males. Estimates were made based on genotypes scored at two distinct marker loci because they were found to give statistically homogeneous results. Fitting a Poisson distribution of number of matings, the mean number of males mated by a female was 1.82. The sperm displacement parameter estimated from doubly mated females were 0.79 and 0.86 for the two loci (0.83 for the joint estimate). The overall probability that a multiply mated female will be misclassified as singly mated was only 0.006, which indicates that microsatellites can provide excellent resolution for identifying multiple mating. In addition, microsatellites can be used to generate relatively precise estimates of sperm precedence in brood-structured samples from a natural population.     

Mating structure and the cost of deleterious mutation: I. Postponing inbreeding

Mating structure governs the distribution of alleles in populations and thus the extent to which the phenotypes associated with the alleles are manifested. A mating system which initially achieves more genetic identity within individuals than between individuals enhances the probability that a finite population without reproductive excess will become extinct from a recessive lethal or semidominant lethal mutation; however, such a mating system decreases the number of deaths that will ensue if the population size is maintained by replacement of inviable progeny with individuals engendered from the entire mating pool. This is illustrated with Markov chain models for half-sib and double-first-cousin mating in populations of four individuals and by various techniques for analogous large populations. An appropriate choice of mating strategy can mitigate the effect of deleterious mutations, but the determination of which strategy is appropriate depends on how much reproductive excess is available and on the relative costs assigned to individual deaths and the extinction of a population.     

Rhythmicity of mating and oviposition inCallosobruchus subinnotatus (Pic) (Coleoptera: Bruchidae)

Mating and oviposition behaviors were studied inCallosobruchus subinnotatus. Copulation was most frequent during the late scotophase, 2–3 h before onset of photophase. The females were less willing to mate during photophase, which increased the time to initiate mating while decreasing the duration of mating. Females exhibited increased movement prior to mating, resting immediately after mating, and remained stationary for 6 h when oviposition commenced. Multiple mating by both males and females affected the number of eggs laid, duration of mating, and uncoupling time at the end of mating. Females that mated two or three times laid more eggs than females that mated once or more than three times. Females that remainedin copula for less than 18 min showed greater readiness to remate than those that remainedin copula longer. There was a gradual decrease in the number of eggs females could lay with an increase in the number of previous matings by males.     

二化螟的多次交配及其对雌蛾产卵量的影响

【目的】利用性诱防控和监测水稻二化螟Chilo suppressalis的有效性在田间已经得到认可。但雄蛾具有多次交配能力,致使性诱防治二化螟的应用策略一直存在争论。本研究的目的是探索二化螟雄蛾的多次交配及其对雌蛾繁殖力的影响,认识性诱防控害虫的机理。【方法】利用行为学方法调查了雌雄蛾以不同比例配对(1∶1, 4∶1和10∶10)时雄蛾的交配次数和交配持续时间,并结合解剖学方法,观察分析了二化螟雄蛾的交配次数对精巢、交配囊和精包大小以及雌蛾产卵量的影响。【结果】二化螟雌雄蛾按1∶1配对时,交配雄蛾和多次交配雄蛾的比例分别为74.0%和36.0%,平均交配1.7次,首次交配主要发生在0-1日龄,绝大部分具有多次交配能力的雄蛾的首次交配发生在0-1日龄。雌雄蛾按4∶1配对时,交配雄蛾和多次交配雄蛾的比例分别为69.4%和51.3%,平均交配2.1次,显著高于按1∶1配对。雌雄蛾按10∶10配对时,交配雄蛾和多次交配雄蛾的比例分别为65.5%和37.8%,平均交配1.9次。雄蛾第3次交配的持续时间显著长于第1和2次交配,但是交配1-3次雄蛾的精巢体积无显著差异。与不同交配次数雄蛾进行交配的雌...     

Multiple mating by both sexes in an invasive insect species,Aethina tumida (Coleoptera: Nitidulidae)

Multiple mating by both sexes is common among sexually reproducing animals. Small hive beetles (SHB), Aethina tumida, are parasites of bee nests endemic to sub-Saharan Africa and have become a widespread invasive species. Despite the considerable economic damages they can cause, their basic biology remains poorly understood. Here we show that male and female small hive beetles can mate multiple times, suggesting that costs for mating are low in this species. In an invasive A. tumida population in the United States, a combination of laboratory experiments for males and paternity analysis with eight polymorphic DNA microsatellite markers for field-caught females were used to estimate the number of mating by both sexes. The data show that females and males can mate multiple times—females mated with up to eight males, whereas males mated with at least seven females. The results also showed that A. tumida displayed a skewed paternity, although this was not consistent among the tested females. Thus, first or last male advantage seem to be unlikely in A. tumida. Our observations that individuals of both sexes of A. tumida can mate multiple times opens new research avenues for examining drivers of multiple mating and determining the role it may play in promoting biological invasions.     

Evolution of mating types in finite populations: The precarious advantage of being rare

Sexually reproducing populations with self‐incompatibility bear the cost of limiting potential mates to individuals of a different type. Rare mating types escape this cost since they are unlikely to encounter incompatible partners, leading to the deterministic prediction of continuous invasion by new mutants and an ever‐increasing number of types. However, rare types are also at an increased risk of being lost by random drift. Calculating the number of mating types that a population can maintain requires consideration of both the deterministic advantages and the stochastic risks. By comparing the relative importance of selection and drift, we show that a population of size N can maintain a maximum of approximately N^1/3 mating types for intermediate population sizes, whereas for large N, we derive a formal estimate. Although the number of mating types in a population is quite stable, the rare‐type advantage promotes turnover of types. We derive explicit formulas for both the invasion and turnover probabilities in finite populations.     

马铃薯块茎蛾的交配行为

在温度为(24±2)℃、光周期为L∶D=14∶10、相对湿度为50%～70%环境条件下观察了马铃薯块茎蛾Phthorimaea operculella(Zeller)交配行为。结果表明,1～2日龄、3～4日龄成虫交配高峰期分别发生在进入暗期后的8.0～10.0h、6.5～8.0h内。两性交配率随日龄的增加显著下降。马铃薯块茎蛾雄成虫具有多次交配能力,在连续发生2次以上行为交配时会导致雄蛾有效交配率下降。雄蛾平均有效交配次数可达3.8次/头,最高达6次。增加雄性比例不会显著提高单雌产卵量,但将性比(♀:♂)由1∶1升至2∶1时即可显著降低单雌产卵量。     

Flexible mating patterns in an obligate brood parasite

Polygamous mating is expected to occur in obligate avian brood parasites because the lack of parental care reduces the need for a stable reproductive bond. Unlike nesting species, an absence of the constraints resulting from raising offspring might also favour a flexible mating system that adjusts to changing ecological conditions. Information on brood parasites' mating systems and their spatio‐temporal variation is, however, still scant. Here we analysed the genetic mating patterns of Great Spotted Cuckoos Clamator glandarius in two populations in northern and southern Spain and compared the results with those of previous studies. Parentage analyses showed high levels of polygamy in both populations that contrast with a prevalence of monogamy previously reported in the southern population. We suggest that the differences arise from an increase in population density, which in turn increases the probability of intraspecific encounters and therefore opportunities for mating. We also found that a greater number of mates increased the number of offspring produced, both in males and in females. The increase in offspring production in females might be the result of enhanced fertilization success during the lengthy laying period. Our data, combined with previous reports, demonstrate plasticity in the genetic mating patterns of the Great Spotted Cuckoo that may be associated with large fluctuations in population density.     

Male reproductive success in a promiscuous mammal: behavioural estimates compared with genetic paternity

Molecular techniques have enabled behavioural ecologists to reassess mating systems from a genetic perspective. Studies of paternity frequently reveal that mating behaviour does not always reflect parentage, and may bring to light alternative mating tactics. Here we present a comparison of behavioural and genetic measures of male reproductive success in a mammalian mating system in which both sexes are highly promiscuous. Rather than having a stable harem social structure, Soay rams (Ovis aries) on the island of Hirta, St Kilda, UK usually consort with individual oestrous ewes sequentially. Not all matings occur between consort pairs, however, and ewes have been seen to mate with up to 10 different rams on the same day. Using locus-specific polymorphism at five protein and 10 microsatellite DNA loci, we determined paternity for 236 lambs born into three cohorts, and compared paternity with estimates of mating success derived from more than one census of rutting behaviour. The correlation between the number of ewes with which each ram was witnessed in consort and the number of paternities assigned was positive and statistically significant, and rams that were observed in consort with a ewe were 18 times more likely to have sired her offspring than other candidate rams. However, most lambs (73%) were not sired by a ram seen in consort with the oestrous mother. Many juveniles, yearlings and some adult rams were rarely seen in consort with ewes, yet were assigned a significant number of paternities. These results suggest that mating tactics differ between age groups, and that alternative mating strategies among adults that do not involve forming consorts with many females also confer mating success. For these reasons, census-based observations of consort associations between individuals cannot be used to accurately estimate individual male reproductive success in this population.     

Poisson distribution of male mating success in laboratory populations of Drosophila melanogaster.

Variation among males and females in reproductive success is a major determinant of effective population size. Most studies of male mating success in Drosophila, however, have been done under conditions very different from those in typical cultures. We determined the distribution of male mating success in five laboratory populations of D. melanogaster maintained on a 14 d, discrete generation cycle fairly representative of standard Drosophila cultures. Mating success was measured as the number of matings a male could achieve under conditions closely approximating a regular culture vial of these populations. Preliminary studies determined that most mating in these populations occurred within 14 h of the flies attaining sexual maturity. Consequently, individual virgin males were marked with white paint on their thorax, put into vials with varying numbers of unmarked virgin flies of both sexes, and monitored continuously for matings over a period of up to 14 h. At various times during the assay, virgin males and females were added to these vials in proportions simulating the pattern of eclosion in culture vials. The observed variation in the number of matings per male in the five populations was, by and large, consistent with a Poisson distribution, suggesting that male mating success in short-generation-time, discrete-generation laboratory cultures of D. melanogaster may fulfil a fundamental assumption of the Wright-Fisher model of genetic drift in finite populations.     

Female fertility and mating type distribution in a Philippine population ofFusarium verticillioides

Fusarium verticillioides is a common causal agent of maize ear rot in the Philippines. Eighty isolates were collected from healthy and infected maize cobs from Laguna province. Fifty isolates crossed with one of the mating type A testers. The ratio of MATA-1:MATA-2 is 27:23, which follows a Mendelian ratio of 1:1. The effective population number, Ne, was determined by mating type and male/hermaphrodite polymorphisms. The effective population number for mating type, Ne mt, is 81% of the count (total population), and that for male/hermaphrodite status, Ne f, is 36-42% of the count (total population). Sexual reproduction in Philippine isolates of F. verticillioides does not occur frequently, compared to F. verticillioides in other regions of the world.     

Repeated copulation in the brown planthopper, Nilaparvata lugens Stál (Homoptera; Delphacidae)

Abstract. 1. Mating of the brown planthopper, Nilaparvata lugens , was investigated in relation to oviposition. Females became unreceptive immediately after mating and showed various types of repelling behaviour to courting males. As a result, females usually did not mate repeatedly in quick succession, but after ceasing to lay fertilized eggs they behaved as virgins and mated again before producing more fertilized eggs.
2. Copulation, followed by deposition of fertilized eggs, occurred twice, or in a few cases three times, throughout the adult stage. Copulation lasted about 2 min at the first mating and about 1 min at the second or third mating.
3. When the number of fertilized eggs began to decrease rapidly, oviposition rate also decreased, but it increased again immediately after re-mating. Repeated copulation was also related to the potential rate of population increase. In the present experiments, the estimates of net reproductive rate ( R ₀) in brachypterous females was 287.7 (first mating), 88.3 (second mating) and 7.2 (third mating) and in macropterous females 286.8, 120.6 and 3.6 respectively.
4. In a patchy environment, repeated copulation following an invasion may contribute to the increase of a population.