Paternity Success Research Articles

Seminal fluid and accessory male investment in sperm competition.

Sperm production and allocation strategies have been a central concern of sperm competition research for the past 50 years. But during the 'sexual cascade' there may be strong selection for alternative routes to maximizing male fitness. Especially with the evolution of internal fertilization, a common and by now well-studied example is the accessory ejaculate investment represented by seminal fluid, the complex mixture of proteins, peptides and other components transferred to females together with sperm. How seminal fluid investment should covary with sperm investment probably depends on the mechanism of seminal fluid action. If seminal fluid components boost male paternity success by directly enhancing sperm function or use, we might often expect a positive correlation between the two forms of male investment, whereas trade-offs seem more likely if seminal fluid acts independently of sperm. This is largely borne out by a broad taxonomic survey to establish the prevailing patterns of seminal fluid production and allocation during animal evolution, in light of which I discuss the gaps that remain in our understanding of this key ejaculate component and its relationship to sperm investment, before outlining promising approaches for examining seminal fluid-mediated sperm competitiveness in the post-genomic era. This article is part of the theme issue 'Fifty years of sperm competition'.

How female × male and male × male interactions influence competitive fertilization in Drosophila melanogaster.

How males and females contribute to joint reproductive success has been a long‐standing question in sexual selection. Under postcopulatory sexual selection, paternity success is predicted to derive from complex interactions among females engaging in cryptic female choice and males engaging in sperm competition. Such interactions have been identified as potential sources of genetic variation in sexually selected traits but are also expected to inhibit trait diversification. To date, studies of interactions between females and competing males have focused almost exclusively on genotypes and not phenotypic variation in sexually selected traits. Here, we characterize within‐ and between‐sex interactions in Drosophila melanogaster using isogenic lines with heritable variation in both male and female traits known to influence competitive fertilization. We confirmed, and expanded on, previously reported genotypic interactions within and between the sexes, and showed that several reproductive events, including sperm transfer, female sperm ejection, and sperm storage, were explained by two‐ and three‐way interactions among sex‐specific phenotypes. We also documented complex interactions between the lengths of competing males’ sperm and the female seminal receptacle, which are known to have experienced rapid female‐male co‐diversification. Our results highlight the nonindependence of sperm competition and cryptic female choice and demonstrate that complex interactions between the sexes do not limit the ability of multivariate systems to respond to directional sexual selection.

Sperm Morphology and Male Age in Black-Throated Blue Warblers, an Ecological Model System.

Simple SummarySperm cell characteristics can impact the number of offspring a male sires, particularly when females copulate with more than one male in a reproductive cycle. Females copulate with multiple males in many songbird species, but for many of these species, little is known about sperm characteristics. In this paper, we examine the shape of sperm cells in black-throated blue warblers, a species where multiple copulations are common but where sperm morphology was previously unknown. Sperm shape did not correlate with plumage characteristics that may make males more successful at gaining copulation partners. However, older males tended to have longer sperm cells. Previous work shows that older males sire more offspring, and work in other species indicates that longer sperm cells are more effective at fertilizing eggs. Thus, sperm shape may help explain the higher success of older males in this species. Extra-pair paternity may drive selection on spermatozoa and ejaculate characteristics through sperm competition and cryptic female choice. Here, we examine sperm morphology in the black-throated blue warbler (Setophaga caerulescens), an ecological model species where extra-pair paternity is frequent and is linked with male age. We test whether sperm morphology relates to several aspects of male phenotype known or suspected to affect extra-pair paternity success. Sperm morphology did not correlate with the size of the white wing spot, a social status signal, nor with the volume of the cloacal protuberance. However, older males tended to have longer sperm cells. Although the sample size was limited, this pattern is intriguing, as longer cells may be advantageous in post-copulatory sexual selection and older males have larger testes and higher extra-pair paternity success in this species. Changes in sperm morphology with age are not observed in other birds, though they have been observed in insects and fishes. More research on sperm morphology is needed to clarify its role in extra-pair fertilizations in this well-studied species.

Courtship and copula duration influence paternity success in a spider

Courtship can have multiple, nonexclusive, functions, and it often plays a central role in mate choice. In the polyandrous, cannibalistic spider Argiope keyserlingi , males perform vibratory courtship that suppresses female aggression. Although females appear to have a preference (i.e. they shorten their latency to mate) for males performing courtship displays with specific characteristics (i.e. many shudders with consistent shudder duration), they are not more likely to mate with them. Here, we asked whether in this species courtship quality plays a role in postcopulatory sexual selection, by affecting male fertilization success via cryptic female choice. We quantified male courtship performance in a standardized thread assay with no male–female interactions, which simulates male approach to the female on the web. We allowed each unmated adult female to mate with two males. Prior to mating, one male from each pair was sterilized using an irradiation treatment and offspring paternity was assigned using the sterile male technique. Unexpectedly, we found that irradiated males had a fertilization advantage over nonirradiated males. When we controlled for that bias, males performing courtship with a large number of shudders and long copula durations gained the largest paternity shares. Together with evidence from previous studies, our results suggest that courtship quality mediates cryptic female choice, but further investigations are needed to parse out the influence of female control and sperm competition on paternity. • Argiope keyserlingi males perform vibratory courtship to suppress female aggression. • Females perceive variation in courtship quality but mating success is not affected. • Males performing many shudders and long copulations sire more offspring. • Females may cryptically bias paternity based on male courtship performance. • The sterilizing treatment by irradiation conferred a paternity advantage.

Shifts in Male Reproductive Tactics over the Life Course in a Polygynandrous Mammal.

In polygynous and polygynandrous species, there is often intense male-male competition over access to females, high male reproductive skew, and more male investment in mating effort than parenting effort [1]. However, the benefits derived from mating effort and parenting effort may change over the course of males' lives. In many mammalian species, there is a ∩-shaped relationship between age, condition, and resource holding power as middle-aged males that are in prime physical condition outcompete older males [2-8] and sire more infants [9-12]. Thus, males might derive more benefits from parenting effort than mating effort as they age and their competitive abilities decline [13]. Alternatively, older males may invest more effort in making themselves attractive to females as mates [14]. One way that older males might do so isby developing relationships with females and providing care for their offspring [14, 15]. Savannah baboons provide an excellent opportunity to test these hypotheses. They form stable multi-male, multi-female groups, and males compete for high ranking positions. In yellow and chacma baboons (Papio cynocephalus and P.ursinus), there is a ∩-shaped relationship between male age and dominance rank [12], and high rank enhances paternity success [12,16]. Lactating female baboons form close ties ("primary associations" hereafter) with particular males [15-20], who support them and their infants in conflicts [15, 19] and buffer their infants from rough handling [20]. Females' primary associates are often, but not always, the sires of their current infants [16,20-22].

Genotype‐by‐environment interactions for seminal fluid expression and sperm competitive ability

Sperm competition commonly occurs whenever females mate multiply, leading to variation in male paternity success. This can be due to variation in the various traits that might affect sperm competitive ability, which itself depends on both genetic and environmental factors, as well as on genotype-by-environment interactions (GEI). Seminal fluid is a major component of the male ejaculate that is often expected to mediate sperm competition, where different genotypes can differ in their seminal fluid expression as a response to different levels of sperm competition (i.e. exhibit GEI). We therefore here focussed on testing for GEI in expression of two recently identified seminal fluid transcripts, suckless-1 and suckless-2, which potentially modulate sperm competitive ability in the simultaneously hermaphroditic flatworm Macrostomum lignano via their effects on manipulating post-mating partner behaviour and ultimately the fate of transferred ejaculates. In addition, we sought to test for GEI in sperm competitive ability in a standardized sperm competition (P1 and P2 ) assay, to investigate the relationship between natural variation in the expression of these seminal fluid transcripts generated through GEI and relative paternity success. We found GEI for the expression level of suckless-1 and suckless-2, as well as for sperm competitive ability. Moreover, we found a positive relation between the expression of suckless-1 and relative paternity success (P1 ). This suggests that natural variation in the expression of this seminal fluid transcript indeed can influence sperm competition outcomes in M.lignano.

Sperm morphology and count vary with fine-scale changes in local density in a wild lizard population

Given that sperm production can be costly, theory predicts that males should optimally adjust the quantity and/or quality of their sperm in response to their social environment to maximize their paternity success. Although experiments demonstrate that males can alter their ejaculates in response to manipulations of the social environment and studies show that ejaculate traits covary with social environment across populations, it is unknown whether individual variation in sperm traits corresponds to natural variation found within wild populations. Using an island population of brown anole lizards (Anolis sagrei), we tested the prediction that sperm traits (sperm count, sperm morphology, sperm velocity) respond to natural variation in the risk of sperm competition, as inferred from the local density and operational sex ratio (OSR) of conspecifics. We found that males living in high-density areas of the island produced relatively larger sperm midpieces, smaller sperm heads, and lower sperm counts. Sperm traits were unrelated to OSR after accounting for the covariance between OSR and density. Our findings broaden the implications of sperm competition theory to intrapopulation social environment variation by showing that sperm count and sperm morphology vary with fine-scale differences in density within a single wild population.

Influence of artificial selection for duration of death feigning on pre- and post-copulatory traits in male Tribolium castaneum

In many animals, investment in anti-predator traits can affect reproductive success. Conversely, males that invest more resources in mating success may have relatively fewer resources to devote to anti-predator traits, leading to increased predation risk. Although previous studies have reported a trade-off in investment between anti-predator traits and reproductive traits in male animals, few studies have specifically investigated the effects of anti-predator behavior on male reproductive traits. Many animals engage in death-feigning as an anti-predator behavior. Herein, we investigated the relationship between the death-feigning behavior and pre- and post-copulatory reproductive traits of male red flour beetles, Tribolium castaneum. In a previous study, we used artificial selection to establish T. castaneum strains with a genetically longer (L-strain) or shorter (S-strain) duration of death-feigning behavior. In the present study, we compared the attractiveness (a pre-copulatory trait) and paternity success (a post-copulatory trait) between L- and S-strain males. The results showed no significant difference in attractiveness or paternity success between the two strains. The results suggest that death-feigning behavior is not correlated with pre- or post-copulatory reproductive traits in male T. castaneum.

Male–female relationships in olive baboons (Papio anubis): Parenting or mating effort?

Long-term male–female bonds and bi-parental investment in offspring are hallmarks of human society. A key question is how these traits evolved from the polygynandrously mating multimale multifemale society that likely characterized the Pan-Homo ancestor. In all three species of savanna baboons, lactating females form strong ties (sometimes called “friendships”) with one or more adult males. For yellow baboons (Papio cynocephalus) and chacma baboons (Papio ursinus), several lines of evidence suggest that these relationships are a form of male parenting effort. In olive baboons (Papio anubis), females are thought to preferentially mate with their “friends”, and male-female bonds may thus function as a form of mating effort. Here, we draw on behavioral and genetic data to evaluate the factors that shape male-female relationships in a well-studied population of olive baboons. We find support for the parenting effort hypothesis in that sires have stronger bonds with their infants' mothers than do other males. These bonds sometimes persist past weaning age and, in many cases, the sire of the previous infant is still a close partner of the female when she nurses her subsequent offspring. We find that males who have the strongest bonds with females that have resumed cycling, but are not currently sexually receptive, are more likely to sire the female's next offspring but the estimate is associated with large statistical uncertainty. We also find that in over one third of the cases, a female's successive infants were sired by the same male. Thus, in olive baboons, the development of stable breeding bonds and paternal investment seem to be grounded in the formation of close ties between males and anestrous females. However, other factors such as male dominance rank also influence paternity success and may preclude stability of these bonds to the extent found in human societies.

Duetting correlates with territory quality and reproductive success in a suboscine bird with low extra-pair paternity

AbstractDuetting has been intensively studied, but we still have little consensus about its fitness consequences. Some studies suggest that duetting functions in acoustic mate guarding to prevent cuckoldry (acoustic paternity guarding hypothesis), whereas other studies argue that duetting is a cooperative behavior to defend common resources (territory defense hypothesis). We tested these 2 hypotheses by investigating the relationships among song traits, extra-pair paternity, territory quality and reproductive success in the Rufous Hornero (Furnarius rufus), a Neotropical, socially monogamous bird. We found a low rate of extra-pair paternity (3.33% of 120 offspring and 6.52% of 46 broods), which suggests that acoustic paternity guarding is probably not a primary function of duetting behavior in this species. Female song output was positively correlated with territory quality, measured as the availability of territory foraging patches. The number of young that survived post-fledging was positively correlated with duet duration, but not with territory features. Our results support the territory defense hypothesis, suggesting that female song in duets might be used in the defense of food resources within territories. Our study provides the first evidence that song traits correlate with both territory features and reproductive success in a duetting species.

Female control over multiple matings increases the opportunity for postcopulatory sexual selection.

It is widely acknowledged that in most species sexual selection continues after mating. Although it is generally accepted that females play an important role in generating paternity biases (i.e. cryptic female choice, CFC), we lack a quantitative understanding of the relative importance of female-controlled processes in influencing variance in male reproductive fitness. Here, we address this question experimentally using the guppy Poecilia reticulata, a polyandrous fish in which pre- and postcopulatory sexual selection jointly determine male reproductive fitness. We used a paired design to quantify patterns of paternity for pairs of rival males across two mating contexts, one in which the female retained full control over double (natural) matings and one where sperm from the same two males were artificially inseminated into the female. We then compared the relative paternity share for a given pair of males across both contexts, enabling us to test the key prediction that patterns of paternity will depend on the extent to which females retain behavioural control over matings. As predicted, we found stronger paternity biases when females retained full control over mating compared with when artificial insemination (AI) was used. Concomitantly, we show that the opportunity for postcopulatory sexual selection (standardized variance in male reproductive success) was greater when females retained control over double matings compared with when AI was used. Finally, we show that the paternity success of individual males exhibited higher repeatability across successive brood cycles when females retained behavioural control of matings compared with when AI was used. Collectively, these findings underscore the critical role that females play in determining the outcome of sexual selection and to our knowledge provide the first experimental evidence that behaviourally moderated components of CFC increase the opportunity for sexual selection.

Assessment of Male Reproductive Skew via Highly Polymorphic STR Markers in Wild Vervet Monkeys, Chlorocebus pygerythrus

Male reproductive strategies have been well studied in primate species where the ability of males to monopolize reproductive access is high. Less is known about species where males cannot monopolize mating access. Vervet monkeys (Chlorocebus pygerythrus) are interesting in this regard as female codominance reduces the potential for male monopolization. Under this condition, we assessed whether male dominance rank still influences male mating and reproductive success, by assigning paternities to infants in a population of wild vervets in the Eastern Cape, South Africa. To determine paternity, we established microsatellite markers from noninvasive fecal samples via cross-species amplification. In addition, we evaluated male mating and reproductive success for 3 groups over 4 mating seasons. We identified 21 highly polymorphic microsatellites (number of alleles = 7.5 ± 3.1 [mean ± SD], observed heterozygosity = 0.691 ± 0.138 [mean ± SD]) and assigned paternity to 94 of 97 sampled infants (96.9%) with high confidence. Matings pooled over 4 seasons were significantly skewed across 3 groups, although skew indices were low (B index = 0.023-0.030) and mating success did not correlate with male dominance. Paternities pooled over 4 seasons were not consistently significantly skewed (B index = 0.005-0.062), with high-ranking males siring more offspring than subordinates only in some seasons. We detected 6 cases of extra-group paternity (6.4%) and 4 cases of natal breeding (4.3%). Our results suggest that alternative reproductive strategies besides priority of access for dominant males are likely to affect paternity success, warranting further investigation into the determinants of paternity among species with limited male monopolization potential.

Male Body Size Predicts Reproductive Success But Not Within-Clutch Paternity Patterns in Gopher Tortoises (Gopherus polyphemus).

In many vertebrates, body size is an important driver of variation in male reproductive success. Larger, more fit individuals are more likely to dominate mating opportunities, skewing siring success and resulting in lower effective population sizes and genetic diversity. The mating system of the gopher tortoise (Gopherus polyphemus) has been characterized as both female-defense and scramble-competition polygyny. Mating systems are typically not fixed and can be influenced by factors such as population density, demographic structure, and environmental conditions; however, most populations will have a predominant strategy that results from local conditions. We assessed how male body size influences patterns of paternity and reproductive success in a natural population of gopher tortoises in Florida, United States. Using microsatellites, we assigned parentage of 220 hatchlings from 31 nests collected during 2 reproductive seasons. Larger males were significantly more likely to sire offspring and sired more offspring than smaller males; however, the likelihood of a clutch being multiply sired was unrelated to male body size. We also found evidence of mate fidelity across years. Although paternity patterns in this high-density population are more consistent with defense polygyny, female monopoly by males was incomplete, with both large and small males contributing to multiply sired clutches. Additional behavioral data are needed to clarify the role of female mate selection in paternity outcomes. The context-dependence of mating systems underscores the need to compare parentage patterns across populations and to recognize the potential for more than 1 strategy to be employed within a single population.

Is there indirect selection on female extra-pair reproduction through cross-sex genetic correlations with male reproductive fitness?

One key hypothesis explaining the evolution and persistence of polyandry, and resulting female extra‐pair reproduction in socially monogamous systems, is that female propensity for extra‐pair reproduction is positively genetically correlated with male reproductive fitness and consequently experiences positive cross‐sex indirect selection. However, key genetic correlations have rarely been estimated, especially in free‐living populations experiencing natural (co)variation in reproductive strategies and fitness. We used long‐term life‐history and pedigree data from song sparrows (Melospiza melodia) to estimate the cross‐sex genetic correlation between female propensity for extra‐pair reproduction and adult male lifetime reproductive success, and thereby test a key hypothesis regarding mating system evolution. There was substantial additive genetic variance in both traits, providing substantial potential for indirect selection on female reproductive strategy. However, the cross‐sex genetic correlation was estimated to be close to zero. Such small correlations might arise because male reproductive success achieved through extra‐pair paternity was strongly positively genetically correlated with success achieved through within‐pair paternity, implying that the same successful males commonly sire offspring produced by polyandrous and monogamous females. Cross‐sex indirect selection may consequently have limited capacity to drive evolution of female extra‐pair reproduction, or hence underlying polyandry, in systems where multiple routes to paternity success exist.

Paternity success in ladybirds: function of mating interval and order

Multiple matings result in varying paternity share based on mating interval and order. Thus, assessing the effect of mating interval and order on patterns of sperm usage and paternity is crucial. We designed consecutive and delayed double-mating experiments to investigate paternity variation in ladybird, Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae), using two distinct morphs of the species as phenotypic markers of paternity. The time to commence mating, copulation duration and reproductive output were recorded. The morphs of the offspring from the two setups were taken as a measure of paternity accumulated by the males. The time to commence mating decreased for the second mating in the consecutive mating treatment, while the reverse was observed in the delayed mating treatment. Consecutive double matings reduced the mating duration. Fecundity increased when second mating occurred after a few days, though percent egg viability remained unaffected. The second male accrued higher paternity (P2 = 0.61) than the first male (P1 = 0.39) in the consecutive mating treatment, while in the delayed mating treatment, the overall paternity share of the first 0.49 (P1) and last male was equal 0.51 (P2). Thus, our study revealed that both mating order and the time interval between successive matings regulate the male paternity share. This finding is reported for the first time in this ladybird species.

Polymorphism of a genital organ under sexual selection in Monacha kuznetsovi from the Caucasus (Gastropoda: Hygromiidae)

During mating the dart apparatus of the land snail group Helicoidea transfers an allohormone that increases paternity success. Thus, this organ is under sexual selection. Despite this selective advantage, the dart sac has independently been lost in many lineages in the Helicoidea, presumably because natural selection counteracts sexual selection. However, the selective pressures that result in the loss of the organ have not been examined experimentally because most species show no variation in the presence or absence of the dart sac. Using nuclear multilocus data and mitochondrial sequences, we show that a so far misidentified morph of the genus Monacha without appendicula, a homologue of the dart sac, is conspecific with M. kuznetsovi with appendicula. This is only the second case of polymorphy with regard to the presence or absence of the dart sac or its homologue in the Helicoidea. Monacha kuznetsovi might therefore be a suitable model organism to study how the interplay between sexual selection and natural selection may affect the evolution of the genital organs.

Sperm morphology, sperm motility and paternity success in the bluethroat (Luscinia svecica).

Postcopulatory sexual selection may select for male primary sexual characteristics like sperm morphology and sperm motility, through sperm competition or cryptic female choice. However, how such characteristics influence male fertilization success remains poorly understood. In this study, we investigate possible correlations between sperm characteristics and paternity success in the socially monogamous bluethroat (Luscinia svecica svecica), predicting that sperm length and sperm swimming speed is positively correlated with paternity success. In total, 25% (15/61) of broods contained extra-pair offspring and 10% (33/315) of the offspring were sired by extra-pair males. Paternity success did not correlate significantly with sperm morphology or any aspects of sperm motility. Furthermore, sperm morphology and sperm motility did not correlate significantly with male morphological characters that previously have been shown to be associated with paternity success. Thus, the sperm characteristics investigated here do not appear to be strong predictors of paternity success in bluethroats.

Male dominance relationships in an extremely large chimpanzee community at Ngogo, Kibale National Park, Uganda

Abstract Male dominance hierarchies occur in many group-living primates and some non-primate mammals. Variation in aspects of agonistic relationships such as how many dyads show bidirectionality in aggression leads to variation in dominance hierarchies along a continuum from egalitarian (relatively small agonistic power differences between adjacently-ranked individuals, shallow hierarchies) to despotic (relatively large differences, steep hierarchies). Ranks usually depend mostly or entirely on individual characteristics that influence fighting ability (e.g., body size) and show inverse-U shaped relationships to age. However, coalitionary support sometimes also influences ranks. Chimpanzees (Pan troglodytes) form multi-male, multi-female communities within which males compete for status. Males typically form dominance hierarchies, and data from multiple study show that rank is positively related to paternity success. Males also often form coalitions and some dyads form long-term alliances. Effective coalitionary support can help individuals improve and maintain their ranks, and some evidence supports the hypothesis that coalitionary aggression generally, and the positions that males hold in coalitions networks specifically, influences paternity success. Hierarchy steepness varies among communities and within communities over time; variation in the number of prime-aged males per community is a likely source of this variation. Long-term data from an extremely large chimpanzee community with unusually many males, at Ngogo, Kibale National Park, Uganda, are largely consistent with previous analyses of male chimpanzee dominance hierarchies, but show several notable contrasts. Males at Ngogo formed significantly linear hierarchies and hierarchy steepness was greater than expected if the outcomes of agonistic interactions were random. However, variation in steepness did not show the significant inverse relationship to the number of “prime-aged” males documented for other chimpanzee communities and average steepness was high given the large number of males. Ranks showed an inverse-U shaped relationship to age, although individual rank trajectories varied considerably, but males attained their highest lifetime ranks at later ages and maintained relatively high ranks to later ages than those at other chimpanzee research sites. Two measures of coalition networks, strength and Bonacich power, showed significant positive relationships with male ranks. Strength is the rate at which males joined coalitions. Bonacich power is a measure of network centrality that assesses a male’s relational power, or influence (Bonacich, 1987): a male with high Bonacich power formed coalitions with relatively many other males who were also central in the coalition network, i.e., he was strongly connected to powerful others. On average, males also attained maximum values for these and other network measures relatively late and maintained relatively high values to relatively late ages. High coalition network strength, Bonacich power, and eigenvector centrality early in adulthood were associated with high peak ranks at later ages. However, the direction of causality between participation in coalition networks and ranks is not yet clear, and the effects of body size on dominance ranks and individual rank trajectories remains to be explored. Ngogo is a favourable habitat for chimpanzees and survivorship there is unusually high; this presumably facilitates the ability of males to maintain high competitive ability longer than at other sites and shifts rank trajectories toward older ages and leads to relatively steep hierarchies despite the fact that many male dyads have similar competitive ability. Future work will assess the impact of coalitions on dominance relationships in more detail and the relationship of coalitionary aggression to paternity success.

Marker‐Based Paternity Test in Polycross Breeding of Timothy

ABSTRACTAlthough the polycross is a useful and cost effective mating design, a lack of paternal pedigree information is a major limitation for polycross breeding in forage grasses such as timothy (Phleum pratense L.). This study describes a paternity test for use in timothy breeding using polymorphic data on 27 genomic simple sequence repeat markers. The paternity test is a simple exclusion statistical test with a combination of maternal information. It successfully determined paternity (success rate = 97%) for 112 progeny plants derived from three polycross groups (A, B, and D). Indirectly selected paternal parents in polycrosses were inferior to maternal parents directly selected by polycross progeny tests mainly for forage yield. Chi‐squared values (χ2) in goodness‐of‐fit tests of the frequency distribution of paternal parents compared with the expected probabilities revealed unbalanced selection in Polycrosses B and D (χ2 = 141.4∗** and 82.7∗**, respectively). Significant differences among the maternal and paternal parents in breeding values for competitiveness toward legumes and low‐digestibility fiber content indicate that unbalanced paternal selection would result from individual phenotypic selection for these traits. These results demonstrate that implementation of a marker‐based paternity test in timothy polycross breeding could significantly improve the selection of superior paternal parents and redress problems of parental imbalance.

Seminal fluid enhances competitiveness of territorial males' sperm in a fish with alternative male reproductive tactics.

The most common adaptation to sperm competition in males is represented by an increase in the sperm number and/or quality released at mating, to raise their probability of egg fertilization. However, rapidly mounting evidence highlights that seminal fluid may directly influence the competitive fertilization success of a male by affecting either own and/or rival sperm performance. In the black goby, Gobius niger, an external fertilizer with guard-sneaker mating tactics and high sperm competition level, sneaker ejaculates contain less seminal fluid and more sperm, that are also of better quality, than those of territorial males. However, territorial males gain a higher paternity success inside natural nests. Here, we ask whether the seminal fluid can contribute to the reproductive success of territorial males by enhancing their sperm performance and/or by decreasing that of sneaker males. Using sperm and seminal fluid manipulation and in vitro fertilization tests, we found that own seminal fluid influences the velocity and fertilization ability of sperm only in territorial males, making them as fast as those of sneakers and with a similar fertilization rate. Moreover, both sneaker and territorial sperm remain unaffected by the seminal fluid of rival males. Thus, black goby males respond to the different level of sperm competition faced by differential allocation of sperm and non-sperm components of the ejaculate, with sneakers primarily investing in sperm of intrinsic high quality and territorial males relying on the effect of seminal fluid to increase the lower intrinsic quality of their sperm.