Sperm Precedence Research Articles

The spider Harpactea sadistica : co-evolution of traumatic insemination and complex female genital morphology in spiders

The males of invertebrates from a few phyla, including arthropods, have been reported to practise traumatic insemination (TI; i.e. injecting sperm by using the copulatory organ to penetrate the female's body wall). As all previously reported arthropod examples have been insects, there is considerable interest in whether TI might have evolved independently in other arthropods. The research reported here demonstrates the first case of TI in the arthropod subphylum Chelicerata, in particular how the genital morphology and mating behaviour of Harpactea sadistica (Rezác 2008), a spider from Israel, has become adapted specifically for reproduction based on TI. Males have needle-like intromittent organs and females have atrophied spermathecae. In other spiders, eggs are fertilized simultaneously with oviposition, but the eggs of H. sadistica are fertilized in the ovaries (internal fertilization) and develop as embryos before being laid. Sperm-storage organs of phylogenetically basal groups to H. sadistica provide males with last male sperm priority and allow removal of sperm by males that mate later, suggesting that TI might have evolved as an adaptive strategy to circumvent an unfavourable structure of the sperm-storage organs, allowing the first male to mate with paternity advantage. Understanding the functional significance of TI gives us insight into factors underlying the evolution of the genital and sperm-storage morphology in spiders.

Male infertility, female fertility and extrapair copulations

Females that are socially bonded to a single male, either in a social monogamy or in a social polygyny, are often sexually polyandrous. Extrapair copulations (EPC) have often been suggested or rejected, on both empirical and theoretical grounds, as an important mechanism that enables females to avoid fertility risks in case their socially bonded male is infertile. Here, we explore this possibility in two steps. First, we present a mathematical model that assumes that females have no precopulatory information about male fertility, and shows that a female EPC strategy increases female reproductive success only if certain specific conditions are upheld in the nature of male infertility. In particular, these conditions require both (i) that fertile sperm precedence (FSP) is absent or incomplete within ejaculates of the same male (i.e. that an infertile male is, at least partly, truly infertile), and (ii) the existence of FSP among ejaculates of different males (such that infertile spermatozoa of the infertile male are at a disadvantage when competing against spermatozoa of a fertile male). Second, to evaluate their potential role in the evolution of female EPC, we review the abundance and FSP patterns of the different male infertility types. The conclusion is drawn that some common infertility types, such as poor sperm count or motility, contribute to the evolution of female EPC, whereas other common infertility types, such as sperm depletion or allocation in a social monogamy (but not in a social polygyny), and in particular male driven polyspermy, do not. Also, a deeper look at the arms race between sperm fertilization efficiency and female barriers to sperm may answer the non-trivial question: "why are some types of infertility so common?"

The Interaction of Female Condition and Mating Status on Male‐Male Aggression in a Wolf Spider

AbstractFighting behavior has been studied extensively with strong emphases on factors that independently determine winners and losers as well as how much effort an individual should invest in a given contest for a resource. Much less attention has been paid to how interacting qualities of disputed resources modulate aggression. In a laboratory study, we examined the interactive effects of female condition and mating status on dyadic male aggression in the wolf spider Pardosa milvina. We discovered that males exhibited significantly more aggressive behaviors when in the presence of virgin females in good condition and displayed lower and statistically similar levels of aggression when placed with virgin, poor condition females; mated, good condition females; mated, poor condition females; and no females. Because previous studies have suggested that virgin females alone should be highly prized because of putative first‐mate sperm priority patterns, this study contributes to this body of literature by suggesting that diet history and body condition mitigate the reproductive advantages of mating with virgin females as indicated by levels of male‐male aggression, but further investigation is needed.

Repeatability and heritability of sperm competition outcomes in males and females of Tribolium castaneum

Differences among males in their success in achieving fertilisations when females mate with more than one partner are now recognised as an important target of sexual selection. However, very few studies have attempted to determine whether particular males are consistently successful in sperm competition and whether success in sperm competition is a heritable trait. Additionally, the potential heritability of female traits that influence the outcome of sperm competition has received only limited attention. Using the polyandrous beetle Tribolium castaneum, we examined repeatability of male success in sperm competition by mating pairs of males carrying different visible genetic markers to a string of different females. Males showed consistency in their ability to successfully transfer sperm to females, but not in their success in sperm competition. Furthermore, when we independently compared success in sperm competition of fathers with their sons, we found no evidence for heritability of this trait. Similarly, females that exhibited high or low first male sperm precedence did not tend to have daughters that showed the same pattern. Our results suggest that we should be wary of assuming that success in sperm competition is heritable through either sex.

Sperm precedence in monarch butterflies (Danaus plexippus)

We characterized sperm precedence in monarch butterflies (Danaus plexippus), using a series of experiments in which we manipulated male mating histories to vary spermatophore size and the number of sperm transferred. Several factors affected the outcome of sperm competition. There was a pattern of second-male sperm precedence, but second-male precedence was rarely complete, and several other factors had significant effects on paternity patterns. Larger males outcompeted smaller males when they were not matched for size. Phosphoglucose isomerase (PGI) genotype affected the outcome of sperm competition under very hot conditions. When sperm from the same pair of males competed in different females, males fared better when they transferred more sperm. These results demonstrate that sperm precedence within a species can be affected by many factors, including the circumstances under which it is measured. Key words: monarch butterflies, PGI genotype, sperm competition, sperm transfer. [Behav Ecol]

Cryptic female choice by female control of oviposition timing in a soldier fly

There is substantial evidence that cryptic female choice (CFC) is present in numerous taxa. Several mechanisms have been proposed for CFC; however, we only have experimental evidence for a few of them. Female control of oviposition timing is a potentially widespread mechanism of CFC, but it has never been experimentally demonstrated. The aims of this study are to test 2 critical predictions of the hypothesis that CFC through control of oviposition timing occurs in the soldier fly Merosargus cingulatus: 1) to determine if M. cingulatus females are less likely to oviposit immediately after mating when the male does not perform copulatory courtship than when he does and 2) to determine if failure to immediately oviposit by the female results in lower reproductive success for the male she just mated with. To answer the first question, I compared the oviposition behavior of females that mated with control males versus females that mated with manipulated males that could not perform copulatory courtship. I showed that M. cingulatus females fail to oviposit immediately after copulation when males do not perform copulatory courtship. To answer the second question, I showed that there is last male sperm precedence in M. cingulatus. Because the last male to mate fertilizes most of the female’s eggs, a male will benefit when females oviposit immediately after mating with him and before remating with another male. Key words: copulatory courtship, cryptic female choice, oviposition timing, postcopulatory sexual selection, soldier fly, Stratiomyidae. [Behav Ecol]

Paternity Allocation in a Mutant Heliothis virescens1Colony

Tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), females can copulate multiple times creating the possibility for sperm competition. We used a colony lacking wild pigmentation on the wings (albino-type) for an experiment in which females double mated. Females copulated 2 days apart with two, 2-day-old males, one albino-type and one wild-type, or in the opposite sequence. A third of the females produced offspring from the first mate, and this group was significantly biased toward producing albino-type compared to wild-type progeny. A fourth of the females produced offspring from the second male exclusively and within this group was a significant bias toward wild-type compared to albino-type progeny. Almost half of the females produced offspring sired in equal proportions by both males simultaneously or in alternated paternities throughout all the reproductive life. These results suggest that regardless of the order in which moths mated, wild-type sperm had potential superior competitiveness. Therefore, sperm precedence is not the main driving force behind the paternity allocation mechanism in this strain of tobacco budworm.

First male sperm precedence in multiply-mated females of the cooperative spider Anelosimus studiosus (Araneae, Theridiidae)

Patterns of sperm usage in multiply-mated females have profound fitness consequences for males, and create strong selective pressure on male behavior. In the cooperative theridiid spider Anelosimus studiosus Hentz 1850 adult males are tolerated in females' webs, and females have been observed to mate multiply with different males. In this experiment, virgin females were mated with two different males on consecutive days under controlled conditions to determine paternity patterns and behavioral responses of males to non-virgin females. The paternity of broods was analyzed using randomly amplified polymorphic DNA (RAPDs). Fifteen broods were analyzed and complete first male sperm precedence was found. Mating behavior differed between first and second males with the first males attempting fewer intromissions, but having a longer total time of intromission. This suggests that the second males are either prevented from normal copulation, or are reacting to the different condition of the females. The sperm precedence pattern is discussed with respect to its ramifications for male behavior, juvenile inclusive fitness, and the evolution of cooperative behavior.

Scale-independent criteria and scale-dependent agents determining the structure of a ground cricket mosaic hybrid zone (Allonemobius socius - Allonemobius fasciatus)

The structure of the hybrid zone between the ground crickets, Allonemobius socius and Allonemobius fasciatus, approximates an environmental mosaic based on temperature/moisture at regional spatial scales. In the present study, we show that the micro-geographic spatial structure (i.e. single fields) of this hybrid zone is governed by the same criteria. Thus, the criteria that structure this hybrid zone are scale independent, even though the agents that implement these criteria may differ at various scales (climate, latitude, and elevation at regional scales; grass height, slope aspect, and field use at micro-geographic scales). Additionally, the study demonstrates a previously unknown barrier to genetic exchange in this system that acts before conspecific sperm precedence. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 777–796.

Use of sperm precedence to infer the overwintering cost of insecticide resistance in the Colorado potato beetle

1 Resistance to insecticides is a model system for studying adaptation. Although selection for resistance is always strong in areas and seasons where populations are exposed to insecticides, costs of resistance, which may only be expressed in the absence of insecticide use, will shape how quickly resistance will evolve. 2 We used sperm precedence to measure the shifts in resistance to imidacloprid in a natural population during winter diapause in the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Because adult beetles overwinter with viable autumn sperm, but sperm from spring matings take precedence over stored sperm, we used the difference in resistance of springmated and autumn-mated overwintered females to estimate the shift in resistance during the winter. Offspring of autumn-mated females were 2.7- or 2.5-fold more resistant compared with offspring from spring-mated females in two replicate trials. 3 We also measured the resistance of late summer and spring emergent adults in fields treated and untreated with imidacloprid in the first year. Adults from the treated field were 13.7-fold more resistant and adults from the untreated field were 2.6-fold more resistant compared with the next spring’s emergers. 4 These large costs of resistance observed in the field and inferred from resistance declines during diapause help to explain the observation that imidacloprid resistance has increased only slowly over the decade of widespread use against this species, and how insecticide resistance in general can cycle annually.

Effects of body size of both sexes and female mating history on male mating behaviour and paternity success in a spider

In a study of the spider Pholcus phalangioides, we double-mated large or small females with large and small males in all possible combinations to investigate the effects of body size and female mating history on male copulatory behaviour and paternity success. In addition we recorded data on female struggle behaviour. Our aim was to get insights into evolutionary forces that promote and constrain adaptive plasticity in male copulatory behaviour in this species with last-male sperm priority. When mating with virgin females, small males made more movements with both inserted pedipalps (sperm transfer organs) than large males, and males of both size classes showed many more pedipalp movements (PPMs) in large, fecund females. With mated females, in contrast, matings were either very short (5 min, 82% of matings), during which PPMs were little affected by male and female size, or as long as matings with virgin females (78 min, 18%) with comparably strong size effects on PPMs. Genetic paternity analysis showed that the second male fertilized on average 88% of the eggs, independent of his size and behaviour. Variation in relative fertilization success was solely predicted by the first male's behaviour. We suggest that this difference in fertilization returns between first and second males may to a large extent explain the contrasting behavioural patterns in virgin versus mated females. The fact that female struggle behaviour contributed to variation in male copulatory behaviour further highlights that females are not merely passive during mating.

An integrative view of sexual selection in Tribolium flour beetles

Sexual selection is a major force driving the evolution of diverse reproductive traits. This evolutionary process is based on individual reproductive advantages that arise either through intrasexual competition or through intersexual choice and conflict. While classical studies of sexual selection focused mainly on differences in male mating success, more recent work has focused on the differences in paternity share that may arise through sperm competition or cryptic female choice whenever females mate with multiple males. Thus, an integrative view of sexual selection needs to encompass processes that occur not only before copulation (pre-mating), but also during copulation (peri-mating), as well as after copulation (post-mating), all of which can generate differences in reproductive success. By encompassing mechanisms of sexual selection across all of these sequential reproductive stages this review takes an integrative approach to sexual selection in Tribolium flour beetles (Coleoptera: Tenebrionidae), a particularly well-studied and economically important model organism. Tribolium flour beetles colonize patchily distributed grain stores, and juvenile and adult stages share the same food resources. Adults are highly promiscuous and female reproduction is distributed across an adult lifespan lasting approximately 1 year. While Tribolium males produce an aggregation pheromone that attracts both sexes, there appears to be little pre-mating discrimination among potential mates by either sex. However, recent work has revealed several peri-mating and post-mating mechanisms that determine how offspring paternity is apportioned among a female's mates. During mating, Tribolium females reject spermatophore transfer and limit sperm numbers transferred by males with low phenotypic quality. Although there is some conflicting evidence, male copulatory leg-rubbing appears to be associated with overcoming female resistance to insemination and does not influence a male's subsequent paternity share. Evidence suggests that Tribolium beetles have several possible post-mating mechanisms that they may use to bias paternity. Male sperm precedence has been extensively studied in Tribolium spp. and the related Tenebrio molitor, and several factors influencing male paternity share among a female's progeny have been identified. These include oviposition time, inter-mating interval, male strain/genotype, the mating regimen of a male's mother, male starvation, and tapeworm infection. Females exert muscular control over sperm storage, although there is no evidence to date that females use this to differentiate among mates. Females could also influence offspring paternity by re-mating with additional males, and T. castaneum females more readily accept spermatophores when they are re-mating with more attractive males. Additional work is needed to examine the possible roles played by both male and female accessory gland products in determining male paternity share. Sexual selection during pre-mating episodes may be reinforced or counteracted by peri- and post-copulatory selection, and antagonistic coevolution between the sexes may be played out across reproductive stages. In Tribolium, males' olfactory attractiveness is positively correlated with both insemination success and paternity share, suggesting consistent selection across different reproductive stages. Similar studies across sequential reproductive stages are needed in other taxa to provide a more integrative view of sexual selection.

Factors Affecting Mating Tactics in the Fiddler Crab, Uca vocans hesperiae

AbstractThe mating strategies of male fiddler crabs are variable and highly flexible within species. In this study I examine three types of mating strategy used by individual male Uca vocans hesperaie. The most common strategy, termed a ‘standard gambit’, where males approached females at their burrow entrance and initiated courtship, accounted for 63% of mating attempts and 75% of successful matings. The rarest strategy (4% of mating attempts) was the ‘dig out’, where males attempted to mate with females whose burrows they had excavated. This strategy accounted for 19% of successful matings. ‘Herding’ behaviour which involved a male attempting to herd a female into a burrow and mate, contributed 33% of mating attempts but were generally unsuccessful, accounting for only 2.6% of successful matings. Males used more than one strategy during the study period. Smaller males used the standard gambit strategy more often than herding or dig outs while larger males used the herding strategy more often. There was no relationship between male size and mating success and males did not preferentially mate with females of a certain size. The predominant strategy adopted by males over the lunar cycle depended on female behaviour. Herding behaviour was induced by female wandering which escalated at full moon. Standard gambits were the commonest strategy adopted at and around new moon. The low success rate of male mating attempts (16%) indicates a reluctance by females to mate multiply. This may lead to conflict between the sexes because in fiddler crabs there is last male sperm precedence.

A Zone of Overlap and Hybridization Between <I>Allonemobius socius</I> and a New <I>Allonemobius</I> sp.

This study investigates the zone of overlap and hybridization between a new species in the Allonemobius species complex and Allonemobius socius (Scudder 1877). The new species, Allonemobius sp. nov. Tex was previously misidentified as Allonemobius fasciatus (De Geer 1773). Our survey of genetic variation at 13 allozyme loci shows that the new species differs from A. fasciatus in at least two allozyme loci. A. sp. nov. Tex is distributed mainly in Texas, and it is sympatric with A. socius in some parts of its distribution where the two species hybridize. In addition to the two fixed allelic differences between the two species, there is also a unique allele at a third locus in A. sp. nov. Tex. The proportion of hybrids in the mixed populations where the two species co-occur is always low, resulting in bimodal hybrid index scores. The bimodal distribution suggests that there is reproductive isolation between the new species and A. socius. This reproductive isolation is maintained, at least in part, through conspecific sperm precedence, which also serves as the major barrier to gene flow between A. socius and A. fasciatus.

Why do male Columbian ground squirrels give a mating call?

Male Columbian ground squirrels, Spermophilus columbianus, give a repetitive vocalization after copulation. This ‘mating call’ sounds similar to certain alarm calls that are given during attacks by terrestrial predators. During 2005–2006, we investigated (1) the acoustic structure and similarity of mating calls and alarm calls; (2) the environmental context when mating calls occur; (3) whether males that are likely to benefit from mate guarding (viz., males that have sperm precedence because they are the first to copulate in a female's series of matings) give mating calls to guard oestrous females; and (4) whether mating calls advertise the caller to females that have not yet mated. Our approach was to observe mating behaviour in the field and quantify reactions of squirrels to mating calls and alarm calls, both in and out of their normal context, with playback experiments. Males that were the first to copulate with an oestrous female called during mate guarding, and guarded females experienced delays before subsequent copulations. Although sound characteristics of mating calls and alarm calls did not differ, squirrels became vigilant and sought protection upon hearing alarm calls, but continued feeding during mating calls. However, when we played recorded mating calls to squirrels after breeding season, they usually reacted as if an alarm call had been given. We conclude that (1) the male mating call is an intrasexual or intersexual signal that announces postcopulatory mate guarding, and (2) contextual information is important for assessing the message of mating calls.

Sperm precedence in Callosobruchus chinensis estimated using the sterile male technique

P2, the proportion of offspring sired by the second male to mate, is an indicator of the outcome of postcopulatory sexual selection, which occurs through sperm competition and/or cryptic female choice. We determined the appropriate dose of gamma radiation for sterilization of adult males and, using the sterile male technique, measured P2 in the adzuki bean beetle, Callosobruchus chinensis. Adult males of C. chinensis were almost completely sterilized when irradiated at 80 Gy. Thus, we obtained sterile males through irradiation at this dose. Neither the probability of female first mating nor the probability of female remating was affected by whether females were paired with normal or sterile males. The P2 calculated from the hatching success of eggs laid by females that mated both with normal and sterile males did not differ between reciprocal mating sequences, indicating that the sterilization has no effect on sperm fertilizing ability. The P2 was estimated at 0.25. This study shows that female remating in C. chinensis means the coexistence of sperm from two males and thus the occurrence of postcopulatory sexual selection within the female reproductive tract, resulting in first-male sperm precedence.

Females reward courtship by competing males in a cannibalistic spider

Despite widespread recognition that intersexual interactions shape reproductive strategies, studies of male competition do not typically include effects imposed by females. In cannibalistic redback spiders, escalated fighting between rival suitors is predicted, as males are unlikely to mate with more than one female, and strong first-male sperm precedence favours mating with virgins. In staged competitions for matings between size mismatched rivals, smaller males adopted an alternative sneaking strategy. However, despite initial agonistic interactions, larger males did not pursue or incapacitate smaller males. When inter-male competition occurred, females struck at males frequently, although strikes were rarely seen when males courted in the absence of a rival. After minimal fighting, larger males engaged in significant courtship (3 h) rather than killing inferior rivals. Prolonged courtship was favoured by female behaviour, as males that attempted rapid copulation (smaller, sneaking males) were cannibalised before mating was completed. This premature cannibalism significantly decreases paternity in redback spiders. Thus, significant features of male competitive behaviour (i.e. prolonged courtship by larger males) may be predicted with consideration of the female’s response to male reproductive strategies. Although the effect of females may be more subtle in systems without the extreme reversed size-dimorphism of redbacks, these results suggest that female interests should be explicitly considered when studying inter-male interactions.

THE ACCUMULATION OF REPRODUCTIVE BARRIERS DURING SPECIATION: POSTMATING BARRIERS IN TWO BEHAVIORALLY ISOLATED SPECIES OF DARTERS (PERCIDAE: ETHEOSTOMA)

Identifying the manner in which reproductive barriers accumulate during lineage divergence is central to establishing general principles of species formation. One outstanding question is which isolating mechanisms form the first complete barrier to gene flow in a given lineage or under a particular set of conditions. To identify these initial reproductive barriers requires examining lineages in very early stages of divergence, before multiple reproductive barriers have evolved to completion. We quantified the strength of three postmating barriers in a pair of darter species and compared these estimates to each other and to the strength of behavioral isolation (BI) reported in a previous study. Results reveal no evidence of gametic incompatibility but intermediate levels of conspecific sperm precedence and hybrid inviability. As BI is nearly complete, our analysis comparing the strength of multiple reproductive barriers implicates the evolution of mate choice as central to both the origin and maintenance of these species. Further examination of ecological isolation and hybrid sterility is necessary to determine the role of these barriers in darter speciation.

Polyandry in the wild: temporal changes in female mating frequency and sperm competition intensity in natural populations of the tettigoniid Requena verticalis

Empirical tests of sexual selection theory generally utilize model systems under laboratory settings, and extend conclusions to evolutionary processes occurring in nature. The biological significance of laboratory findings will depend largely on the mating rates of females and patterns of paternity in natural populations, information on which is generally lacking. Here we use microsatellite markers to provide rare estimates of female mating rates and patterns of parentage in a species of tettigoniid, Requena verticalis, which has been used extensively to test theory on the evolution of male parental investment and its influence on the direction of sexual selection. We found that although the number of males having a genetic representation in the female's sperm stores was higher for females collected late in the breeding season than those collected early in the season, overall the female mating rate was lower than that expected from laboratory observations. Analysis of parentage of offspring produced by females at the end of the breeding season revealed that all males represented in the sperm stores fathered offspring, although paternity was biased away from that expected from random sperm utilization. The data show that the complete first male sperm precedence documented in laboratory studies of this species does not persist in natural populations. Our data provide a solid underpinning for conclusions drawn from laboratory studies of this species.

Sperm dumping in a haplogyne spider

AbstractThe present study shows that females of Silhouettella loricatula (Arachnida: Araneae: Oonopidae) manage to process sperm in an unusual and previously unknown way. The male ejaculate consisting of spermatozoa and globular secretion is enclosed in a secretory sac. This may avoid the mixing of sperm from different males and at least severely limit sperm competition. The process of sperm enclosure occurs within the female's sperm storage site (receptaculum) as the ejaculate is not surrounded by a sac inside the male's sperm‐transferring organs (palpal bulbs). The secretion forming the sac is produced by glands adjoining the receptaculum. The possibility that globular secretions in the male palpal bulbs partly contribute to the sac cannot be ruled out completely. It is suggested that in S. loricatula, the main function of sperm enclosure in a sac is enabling females to dump the ejaculate of a male. The present study represents the first report on sperm dumping in the family Oonopidae. During five first and three second copulations in the laboratory, the dumping of a sac was observed. One dumped sac was sectioned and contained spermatozoa. Two couples were flash‐fixed with liquid nitrogen early during copulation, which revealed the mechanism of the sac dumping. By muscle contractions, the receptaculum is bent backwards and the sac moved into the genital opening. The actual sac dumping occurs most probably in cooperation with the male, which moves his pedipalps rhythmically during the entire copulation. Extensions and furrows on the emboli suggest that they may additionally be used as copulatory courtship devices. The enclosure of sperm from the current male in secretion takes place during or immediately following copulation as all mated females sacrificed after copulation had a new sac containing spermatozoa in the receptaculum. Dumping sperm of a previous male during the next copulation may allow females to bias sperm precedence.