Sperm Competition

A re-examination is made of the old interpretation that the male reproductive system of the short-beaked echidna (Tachyglossus aculateus), and monotremes in general, is ?primitive?. There is an emerging concept of the significance of the male reproductive system in relation to the role of males in conception. Even though some aspects of the male reproductive system of T. aculateus may be considered primitive and impose limitations on their life style, they nevertheless display significant specializations present in the male tract of other mammals: an epididymis with the unique initial segment and a role in post-testicular sperm maturation and storage, and homologues of the prostate gland and penis. The absence of a descended testis and scrotum has not restricted the survival of T. aculateus in virtually all habitats in Australia. However, it may restrict their capacity to breed throughout the year. It is suggested that T. aculateus is also specialised for sperm competition. An estim...

The development of cod aquaculture has raised concerns about its effect on wild stocks. One risk is hybridisation between escapees and wild cod, causing genetic introgression, and, potentially, fitness depressions in wild populations. The potential for hybridisation depends on escapee success in mating competition with wild fish. Cod have a complex mating system, with males likely to adopt either dominant or sub-dominant roles, the latter typically achieving reproductive success through sperm competition. Studies on salmonids indicate that domesticated males predominantly adopt sub-dominant roles. We therefore analysed sperm characteristics of wild and farmed cod Gadus morhua L. around the onset and end of the natural spawning season. Wild and farmed males were also paired in in vitro crosses to assess reproductive success in sperm competition. In the early spawning season, wild males had higher sperm velocity, percentages of motile and progressive cells, and spermatocrit. Sperm velocity was the main determinant of fertilisation success in in vitro sperm competition and, accordingly, wild males had higher reproductive success. At the end of spawning, the percentages of motile or progressive cells and spermatocrit were similar between wild and farmed males, but wild males maintained higher sperm velocity. Our results indicate that farmed males have limited reproductive success in sperm competition with wild male cod. This presumably reduces the risk of genetic introgression from escapees. We hypothesise that impaired sperm quality and lower reproductive fitness of farmed cod are due to inhibition of the full behavioural repertoire, lack of social structure under culture conditions, and/or nutritional deficiencies.

Introduction: Routine semen viability assessment is not sufficient to predict the reproductive performance of bulls. Molecular testing is needed to provide more reliable tools for predicting semen quality, in particular by detecting sperm DNA integrity. It is important to check the quality of frozen semen, as fertilization can only be achieved if sperm from frozen semen are viable and motile, and have good morphology and DNA integrity. The aim of the work is to establish the DNA fragmentation index of spermatozoa of native and frozen bull semen, which is used for artificial insemination of cows and heifers. Materials and methods: The biological material was native and frozen semen of Holstein and Jersey bulls. Native semen was obtained using an artificial vagina by double-sacralization on a surrogate bull and evaluated according to the requirements of the State Standard of Ukraine (DSTU 35.35-97). Frozen sperm was evaluated according to the requirements of the State Standard of Ukraine (DSTU 87 78: 2018). The "Halosperm G2" test was used to determine the sperm DNA fragmentation index. Results: The sperm DNA fragmentation index in native semen ranged from 1.2 to 6.2%. During the study of sperm survival every hour for 5 hours, an increase in the frequency of degraded spermatozoa (range 0.6-3.2%) and spermatozoa with DNA fragmentation (range 1.1-4.8%) was observed over time, individually for each bull. The value of the Pearson correlation coefficient, (r = 0.1218, r = 0.2355, r =-0.0125, r = 0.1566) indicated that there is a very weak linear relationship between sperm viability, motility and genome integrity. The interval of the sperm DNA fragmentation index in depreserved sperm (0 hours) was 1.8-5.6%, in sperm incubated for 1-5 hours from 2.4 to 7.0%, and the dynamics of these indicators depended on the individual characteristics of the bulls. Conclusions: An increase in sperm DNA fragmentation in depreserved sperm by 1.1-1.8 times compared to native sperm and by 1.5-3.7 times in cultured sperm within five hours, caused by the cryopreservation process, was confirmed. The percentage of degraded sperm did not exceed the proportion of sperm with DNA fragmentation in different sperm conditions, indicating the absence of long-term exposure to chronic infections or inflammatory processes and properly selected sperm solvents The correlation between spermatozoa with DNA fragmentation and degradation and their motility and viability after 5 hours of incubation was very weak.

Most theories on sexual behaviours are based on adaptive explanations. However, masturbation, a common but scarcely discussed sexual behaviour, appears a Darwinian puzzle. Why would individuals waste valuable resources such as time, energy and, for males, sperm? We combined targeted surveys with information from published accounts to test hypotheses about why masturbation occurs, using a phylogenetically broad dataset on the presence or absence of masturbation across 120 bird species. We find masturbation is widespread in birds, but strongly phylogenetically conserved, typically being fixed (as present or absent) or nearly so within broad clades. Masturbation is more common in males, though the widespread evidence for masturbation in females suggests that maintaining fresh sperm in testes cannot be the single explanation. We find no difference in masturbation occurrence between juveniles and adults, further suggesting that it does not solely represent practice copulations before maturity. Species with indiscriminate matings are more likely to masturbate than socially monogamous species or species with long-term pair bonds. Importantly, as masturbation is more commonly reported in wild than captive birds, we find it is therefore not a negative or maladaptive response to captivity. Instead, it is part of a wider repertoire of sexual behaviours exhibited in birds. Overall, our data are consistent with masturbation serving as an outlet for increased sexual arousal, a means of increasing reproductive success through postcopulatory selection, or both.

The occurrence of polyandry in Planococcus citri, presumed by earlier observations of mating behavior, was confirmed using microsatellite genotyping of pools of over 400 eggs resulting from controlled crosses of one female with two males. The genetic contribution of both mated males was confirmed in 13 out of 43 crosses. In three crosses it was possible to determine that only the first male fertilized the eggs, which may be due to sperm competition or unviable sperm supply. The microsatellite analysis also allowed the confirmation of aspects of the chromosomal inheritance detected previously in cytogenetic studies in Planococcus citri, namely that only one of the alleles is transmitted by the male, indicating that the males are functionally haploid, supporting the observation of Paternal Genome Elimination (PGE) in these insects.

Sperm competition game theory predicts that males should respond to increasing sperm competition risk by increasing ejaculate expenditure. There is considerable support for this prediction from a diverse range of taxa. However, the cues males use to assess risk and the fitness returns for strategic ejaculation are less well understood. We explored the role of acoustic cues in the assessment of sperm competition risk by manipulating male experience of acoustically signaling conspecifics in the field cricket Teleogryllus oceanicus. Compared with males reared in acoustic isolation, males reared in song-dense environments mimicking a high sperm competition risk produced ejaculates with a greater percentage of viable sperm. However, acoustic experience had only a weak and nonsignificant effect on competitive fertilization success. We argue that female influences on paternity are likely to have a strong moderating effect on male fitness returns from prudent allocation and call for more studies that address the consequences of strategic ejaculation for male fitness.

Invasive slugs cause damage to biodiversity as well as to horticultural and agricultural crops. To develop methods to mitigate problems with recently emerging invasive species, basic ecological knowledge about them in their new environment is crucial. We investigated the egg-laying substrate preference of Krynickillus melanocephalus in a laboratory experiment in which the slugs could choose between four different substrates. Slugs were mainly observed in contact with birch leaf compost, and less so with gravel, potting soil and sphagnum moss. Almost 90% of the eggs were found buried in birch leaves, although eggs were found also in the other substrates. In addition, we tested the winter survival of the eggs by examining their susceptibility to low temperatures. Eggs subjected to freezing temperatures did not survive, and at 8 °C, 60-70% of the eggs hatched after three months (640 degree days). In areas where K. melanocephalus is present, transporting any soil, gravel or compost material could potentially contribute to spreading the species. Particularly, leaf composts may warrant attention in this areas.

In many species, each female pairs with a single male for the purpose of rearing offspring, but may also engage in extra-pair copulations. Despite the prevalence of such promiscuity, whether and how multiple mating benefits females remains an open question. Multiple mating is typically thought to be favoured primarily through indirect benefits (i.e. heritable effects on the fitness of offspring). This prediction has been repeatedly tested in a variety of species, but the evidence has been equivocal, perhaps because such studies have focused on pre-reproductive survival rather than lifetime fitness of offspring. Here, we show that in a songbird, the dark-eyed junco ( Junco hyemalis), both male and female offspring produced by extra-pair fertilizations have higher lifetime reproductive success than do offspring sired within the social pair. Furthermore, adult male offspring sired via extra-pair matings are more likely to sire extrapair offspring (EPO) themselves, suggesting that fitness benefits to males accrue primarily through enhanced mating success. By contrast, female EPO benefited primarily through enhanced fecundity. Our results provide strong support for the hypothesis that the evolution of extra-pair mating by females is favoured by indirect benefits and shows that such benefits accrue much later in the offspring's life than previously documented.

Among avian species with biparental care, male alternative reproductive opportunities can occur in the form of either extrapair fertilizations or additional social mates. We manipulated testosterone (T) levels in male house sparrows to assess whether participation in parental care detracts from male success in securing alternative matings; we also compared the annual reproductive success of males that engaged in normal levels of care with the success of males that displayed increased mating effort at the expense of parental care. Our results showed that the incidence of polygyny among high-T/low-parenting males was elevated relative to control males, but that success in obtaining extrapair mates was independent of hormonal treatment. Thus, male parental care seems to carry an opportunity cost in terms of reduced acquisition of additional social mates. Despite this cost, between-treatment comparisons of the estimated number of fledglings sired annually suggest that, in this species, the value of male contributions to care is sufficiently high to favor the reductions in T that facilitate normal male parenting.

Since tools of molecular genetics became readily available, our understanding of bird mating systems has undergone a revolution. The majority of passerine species investigated are socially monogamous, but have been shown to be genetically polygamous. Data sets from natural populations of juncos suggest that multiple mating by females results in a sexual selection gradient as steep for females as for males (a result that does not support Bateman's predictions). However, in males, fitness is enhanced directly through fertilization success with multiple matings; in females fitness benefits may be enhanced immediately through direct access to food, protection against predators, or other resources received from males, or they may be delayed through improvement in offspring quality (e.g., through good genes, or greater genetic compatibility between the female and the extra-pair male). But a steep sexual selection gradient for females can be difficult to interpret. If all females copulate with multiple partners that are equally likely to fertilize eggs, then females that produce larger clutch sizes, for any reason, will appear to have copulated with more males. That is, multiple sires have a higher probability of detection in larger clutches than in smaller ones, giving the impression that females that mate with multiple males increase their reproductive success. Yet, in most studies in which there is a correlation between number of offspring produced by females and number of extra-pair males, causation has not been clearly established and other factors may explain the results. Additional complications in understanding male and female reproductive strategies are: (1) Molecular studies cannot detect extra-pair copulations that did not result in fertilizations; yet if a female acquires food or other resources from extra-pair males, such extra-pair matings may have significant effects on female fitness. Thus, molecular studies provide only a conservative estimate of the number of extra-pair copulations or ''mates'' that a female has. (2) Clutch size affects the probability that any given male will be successful in fertilizing a female's eggs. Specifically, at any given point, a male's chances of fertilizing at least one egg in the female's clutch will be greater as clutch size increases. We predict that in avian species with small clutch sizes, males may be selected to be choosy and avoid extra-pair copulations, while females should be selected to be less discriminating. Moreover, if extra-pair males provide resources that increase female fitness, the females should seek extra-pair copulations, whether or not the males are likely to fertilize any of her eggs. Laboratory studies with insects have yielded clearer evidence of the causal relationship between multiple mating and increased female fitness. We review studies on a tenebrionid beetle in which female fecundity increases directly with number of mates. In these experiments, the nutritive value of the spermatophores does not fully explain the increase in female reproductive success.

Since tools of molecular genetics became readily available, our understanding of bird mating systems has undergone a revolution. The majority of passerine species investigated are socially monogamous, but have been shown to be genetically polygamous. Data sets from natural populations of juncos suggest that multiple mating by females results in a sexual selection gradient as steep for females as for males (a result that does not support Bateman's predictions). However, in males, fitness is enhanced directly through fertilization success with multiple matings; in females fitness benefits may be enhanced immediately through direct access to food, protection against predators, or other resources received from males, or they may be delayed through improvement in offspring quality (e.g., through good genes, or greater genetic compatibility between the female and the extra-pair male). But a steep sexual selection gradient for females can be difficult to interpret. If all females copulate with multiple partners that are equally likely to fertilize eggs, then females that produce larger clutch sizes, for any reason, will appear to have copulated with more males. That is, multiple sires have a higher probability of detection in larger clutches than in smaller ones, giving the impression that females that mate with multiple males increase their reproductive success. Yet, in most studies in which there is a correlation between number of offspring produced by females and number of extra-pair males, causation has not been clearly established and other factors may explain the results. Additional complications in understanding male and female reproductive strategies are: (1) Molecular studies cannot detect extra-pair copulations that did not result in fertilizations; yet if a female acquires food or other resources from extra-pair males, such extra-pair matings may have significant effects on female fitness. Thus, molecular studies provide only a conservative estimate of the number of extra-pair copulations or ''mates'' that a female has. (2) Clutch size affects the probability that any given male will be successful in fertilizing a female's eggs. Specifically, at any given point, a male's chances of fertilizing at least one egg in the female's clutch will be greater as clutch size increases. We predict that in avian species with small clutch sizes, males may be selected to be choosy and avoid extra-pair copulations, while females should be selected to be less discriminating. Moreover, if extra-pair males provide resources that increase female fitness, the females should seek extra-pair copulations, whether or not the males are likely to fertilize any of her eggs. Laboratory studies with insects have yielded clearer evidence of the causal relationship between multiple mating and increased female fitness. We review studies on a tenebrionid beetle in which female fecundity increases directly with number of mates. In these experiments, the nutritive value of the spermatophores does not fully explain the increase in female reproductive success.

The epaulets of male Red-winged Blackbirds (Agelaius phoeniceus) are frequently cited as a sexually selected plumage ornament, but a number of laboratory and field studies provide little evidence that they are currently experiencing sexual selection. We used hair dye to dull epaulets of free-living territorial males prior to pair formation to determine if manipulated males experienced disadvantages in comparison with control males. We found no differences between control males and males with dulled epaulets in territorial behavior (territory size, song rate, trespass rate, and loss of territory), paternal care (time spent on territory and in antipredator sentinel behavior, and response to a model crow to simulate the threat of predation), pairing success (number of social mates), apparent reproductive success (numbers of nesting attempts, eggs/nest, nestlings/egg, and fledglings/nestling), or realized reproductive success (numbers of within-pair, extra-pair, and total fledglings as determined by DNA fingerprinting). We then used a meta-analysis of 11 published studies of Red-winged Blackbirds to determine if there is an overall effect of epaulet color or size on male-male competition, female choice, or reproductive success. Our results show that epaulet size has a small positive effect on male reproductive success, but epaulet color has no effect on male-male competition, female choice, and male reproductive success. One explanation for the seeming contradiction between studies that show that epaulets are necessary for territory defense and those that conclude that epaulets are not currently under selection is that epaulets serve as one of several cues of species recognition, especially among males at close range. An alternative explanation proposes counter-balancing intersexual advantages and intrasexual disadvantages of epaulet expression. Additional studies are needed to test these alternatives.

Resumen. La mancha alar en los machos de Agelaius phoeniceus funciona tanto en el contexto intra-sexual como inter-sexual, pero existe poca evidencia de que ésta covaríe con el éxito reproductivo en esta especie, que ha sido bastante estudiada. Utilizamos un análisis de pasos usando caracteres territoriales de los machos, éxito de apareamiento y éxito reproductivo de los machos no manipulados para estimar la selección direccional actual. El tamaño de los territorios tuvo un efecto positivo sobre el número de compañeros de una pareja. El número de compañeros adquiridos fuera de la pareja tuvo un efecto positivo sobre el número de polluelos extra-pareja, y el número de polluelos volantones intra-y extra-pareja tuvo un efecto positivo sobre el número total de volantones. También intensificamos el rojo de la mancha alar de machos territoriales silvestres para determinar si los machos manipulados y control diferían en su comportamiento territorial, éxito de apareamiento o éxito reproductivo. En comparación con los machos control, los machos manipulados incurrieron en tasas más altas de traspaso de límites y de disputas territoriales, perdieron sus territorios más frecuentemente y no fueron capaces de producir crías extra-pareja. Sin embargo, a pesar de estas diferencias, el éxito reproductivo alcanzado por los machos control y manipulados no difirió significativamente, probablemente debido a que los machos con las manchas rojas intensificadas asignaron más tiempo a comportamientos de vigilancia anti-depredatorios y fueron más agresivos ante un depredador simulado que los machos control. Una falta aparente de selección sexual actual sobre el color de la mancha alar puede ser una forma de contrarrestar la selección sexual en la que la agresividad hacia machos con manchas más rojas se opone a la preferencia por parte de las hembras de manchas más rojas, o puede ser el resultados de que los machos compensan la pérdida de cópulas extra-pareja al aumentar su cuidado parental.

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Among avian species with biparental care, male alternative reproductive opportunities can occur in the form of either extrapair fertilizations or additional social mates. We manipulated testosterone (T) levels in male house sparrows to assess whether participation in parental care detracts from male success in securing alternative matings; we also compared the annual reproductive success of males that engaged in normal levels of care with the success of males that displayed increased mating effort at the expense of parental care. Our results showed that the incidence of polygyny among high-T/low-parenting males was elevated relative to control males, but that success in obtaining extrapair mates was independent of hormonal treatment. Thus, male parental care seems to carry an opportunity cost in terms of reduced acquisition of additional social mates. Despite this cost, between-treatment comparisons of the estimated number of fledglings sired annually suggest that, in this species, the value of male contributions to care is sufficiently high to favor the reductions in T that facilitate normal male parenting.

In many species, each female pairs with a single male for the purpose of rearing offspring, but may also engage in extra-pair copulations. Despite the prevalence of such promiscuity, whether and how multiple mating benefits females remains an open question. Multiple mating is typically thought to be favoured primarily through indirect benefits (i.e. heritable effects on the fitness of offspring). This prediction has been repeatedly tested in a variety of species, but the evidence has been equivocal, perhaps because such studies have focused on pre-reproductive survival rather than lifetime fitness of offspring. Here, we show that in a songbird, the dark-eyed junco (Junco hyemalis), both male and female offspring produced by extra-pair fertilizations have higher lifetime reproductive success than do offspring sired within the social pair. Furthermore, adult male offspring sired via extra-pair matings are more likely to sire extra-pair offspring (EPO) themselves, suggesting that fitne...

Among avian species with biparental care, male alternative reproductive opportunities can occur in the form of either extrapair fertilizations or additional social mates. We manipulated testosterone (T) levels in male house sparrows to assess whether participation in parental care detracts from male success in securing alternative matings; we also compared the annual reproductive success of males that engaged in normal levels of care with the success of males that displayed increased mating effort at the expense of parental care. Our results showed that the incidence of polygyny among high-T/low-parenting males was elevated relative to control males, but that success in obtaining extrapair mates was independent of hormonal treatment. Thus, male parental care seems to carry an opportunity cost in terms of reduced acquisition of additional social mates. Despite this cost, between-treatment comparisons of the estimated number of fledglings sired annually suggest that, in this species, ...

The epaulets of male Red-winged Blackbirds (Agelaius phoeniceus) are frequently cited as a sexually selected plumage ornament, but a number of laboratory and field studies provide little evidence that they are currently experiencing sexual selection. We used hair dye to dull epaulets of free-living territorial males prior to pair formation to determine if manipulated males experienced disadvantages in comparison with control males. We found no differences between control males and males with dulled epaulets in territorial behavior (territory size, song rate, trespass rate, and loss of territory), paternal care (time spent on territory and in antipredator sentinel behavior, and response to a model crow to simulate the threat of predation), pairing success (number of social mates), apparent reproductive success (numbers of nesting attempts, eggs/nest, nestlings/egg, and fledglings/nestling), or realized reproductive success (numbers of within-pair, extra-pair, and total fledglings as ...

Since tools of molecular genetics became readily available, our understanding of bird mating systems has undergone a revolution. The majority of passerine species investigated are socially monogamous, but have been shown to be genetically polygamous. Data sets from natural populations of juncos suggest that multiple mating by females results in a sexual selection gradient as steep for females as for males (a result that does not support Bateman's predictions). However, in males, fitness is enhanced directly through fertilization success with multiple matings; in females fitness benefits may be enhanced immediately through direct access to food, protection against predators, or other resources received from males, or they may be delayed through improvement in offspring quality (e.g., through good genes, or greater genetic compatibility between the female and the extra-pair male). But a steep sexual selection gradient for females can be difficult to interpret. If all females copul...