Patterns Of Sperm Use Research Articles

Patterns of sperm use by twice-mated female Queensland fruit flies.

Multiple mating by females, polyandry, is common in insects, including in tephritid fruit flies. Female insects that remate commonly store sperm of multiple males. How the sperm of different males contribute to paternity is an important element of sexual selection. Sexual behavior and reproduction of the Queensland fruit fly (Qfly), Bactrocera tryoni, has been extensively investigated both in relation to understanding this economically important species' reproductive biology and in relation to implications for Sterile Insect Technique (SIT), whereby sterile flies are released to constrain reproduction of pest populations. Despite numerous studies of pre- and postcopulatory sexual selection in Qfly, there have been no direct studies of paternity patterns in polyandrous female Qflies. We used two morphologically distinguishable lines to investigate patterns of sperm use in Qfly. The two lines showed comparable mating performance evidenced by similar mating and remating frequency, copula duration, and proportion of second mate paternity (P2) between reciprocal crosses. The mechanism of sperm usage, with P2 close to 0.5 immediately after the second mating followed by gradual decrease of P2 as females aged, is most consistent with stratification or repositioning of sperm. Patterns observed in the present study are compared with the available information from other tephritid fruit flies, and are discussed in relation to this species' reproductive biology, known patterns of sperm storage, and SIT.

Testing potential mechanisms of conspecific sperm precedence in Drosophila pseudoobscura.

Drosophila pseudoobscura females that co-occur with sister species D. persimilis show elevated fertilization by conspecific sperm when they mate with both a heterospecific and a conspecific male. This phenomenon, known as conspecific sperm precedence (CSP), has evolved as a mechanism to avoid maladaptive hybridization with D. persimilis. In this study, we assessed pericopulatory (during mating) and postcopulatory (after mating) traits in crosses with sympatric or allopatric D. pseudoobscura females and conspecific or heterospecific males to evaluate potential mechanisms of CSP in this system. We observed shorter copulation duration in crosses with sympatric females, but found no difference in quantity of sperm transferred or female reproductive tract toxicity between sympatry and allopatry. Our data show some support for the hypothesis that parasperm, a short, sterile sperm morph, can protect fertile eusperm from the D. pseudoobscura female reproductive tract, though it is unclear how this might affect patterns of sperm use in sympatry vs. allopatry. Overall, these results suggest that copulation duration could potentially contribute to the elevated CSP observed in sympatry.

Female remating rate and pattern of sperm use suggest intense sperm competition in Drosophila antonietae (Diptera: Drosophilidae)

Sperm competition is conceived as a powerful selective force which acts on genes related to reproduction, promoting the evolution of reproductive adaptations and inter-population divergence that may ultimately lead to speciation. Such selective pressure is believed to be particularly strong in species from the Drosophila repleta group since females of most of these species are highly promiscuous. However, sperm competition is determined by many other factors far less explored than female remating rate; consequently, its actual intensity as a selective pressure continues to remain unknown across most taxa. In this paper, we aim to estimate the intensity of sperm competition in Drosophila antonietae, a South American species from the D. repleta group, by means of behavioural and genetic analyses. In sum, our results, while failing to reveal sperm precedence in twice-mated females, show that sperm competition is likely to occur and may strongly reduce males’ reproductive output. In addition, using highly polymorphic microsatellite loci, we confirmed a high incidence of multiple paternity in wild-inseminated females. We discuss the results within an evolutionary context comparing the mating system between D. antonietae and closely related species.

Female remating decisions and a shorter inter-mating interval diminish last-male sperm precedence

Highly variable within and across species, patterns of sperm use not only are often driven by post-copulatory sexual selection but can also be impacted by experimental design. In investigations of paternity bias using competitive double matings, the inter-mating interval is a temporal factor that can affect sperm use patterns if the first male’s sperm is used or lost at an appreciable rate between matings or if its viability or relative competitiveness is influenced by the time since ejaculation. Rapid loss of first-male sperm within the female after mating has been established in the seed beetle (Callosobruchus maculatus), a model system in sperm competition studies. However, our understanding of sperm precedence in this species, which disproportionately favors the last (second) male to mate, is based on long inter-mating intervals. Here, I determine the effect of a shortened inter-mating interval on second-male paternity (P 2) and, importantly, the extent to which females in this species are willing to remate immediately. I find that P 2 is significantly reduced when females remate immediately than when they remate 24 or 48 h after the first mating and that immediate remating is common, indicating that there is a substantial potential for female remating decisions to influence the intensity of sperm competition within species. To understand the variation in inter-mating intervals from a female perspective, I further identify key differences between females that did and did not remate at three inter-mating intervals (0, 24, and 48 h after the initial mating) and discuss potential mechanisms for the observed variation in female refractoriness. Females often mate with multiple males, and in insects it is common for the last male to mate to obtain the greatest share of paternity. One possible explanation for this bias towards last-male sperm use is the passive loss of sperm from the first male with time since mating. Here, I examine the effect of different intervals between matings in a seed beetle species to determine if first-male paternity is increased when females remate sooner. My results show that first males do achieve higher paternity when females remate sooner, which is more common than expected in this species. I also show the differences between females that do and do not remate, which can help explain potential causes for variation in female remating behavior. Together, these results show the significant impact that female remating decisions can have on male competition and, ultimately, their reproductive success.

Paternity analysis of wild-caught females shows that sperm package size and placement influence fertilization success in the bushcricket Pholidoptera griseoaptera.

In species where females store sperm, males may try to influence paternity by the strategic placement of sperm within the female's sperm storage organ. Sperm may be mixed or layered in storage organs, and this can influence sperm use beyond a 'fair raffle'. In some insects, sperm from different matings is packaged into discrete packets (spermatodoses), which retain their integrity in the female's sperm storage organ (spermatheca), but little is known about how these may influence patterns of sperm use under natural mating conditions in wild populations. We examined the effect of the size and position of spermatodoses within the spermatheca and number of competing ejaculates on sperm use in female dark bushcrickets (Pholidoptera griseoaptera) that had mated under unmanipulated field conditions. Females were collected near the end of the mating season, and seven hypervariable microsatellite loci were used to assign paternity of eggs laid in the laboratory. Females contained a median of three spermatodoses (range 1-6), and only six of the 36 females contained more than one spermatodose of the same genotype. Both the size and relative placement of the spermatodoses within the spermatheca had a significant effect on paternity, with a bias against smaller spermatodoses and those further from the single entrance/exit of the spermatheca. A higher number of competing males reduced the chances of siring offspring for each male. Hence, both spermatodose size and relative placement in the spermatheca influence paternity success.

Multiple paternity but no evidence of biased sperm use in female dumpling squid Euprymna tasmanica

Assessing the natural level of multiple paternity and sperm-use patterns provides important information regarding sperm competition and the potential for cryptic female mate choice. We developed 5 novel polymorphic microsatellites for the dumpling squid Euprymna tasmanica and used them to measure multiple paternity from both field- and laboratory-laid clutches. All clutches had multiple paternity, with a minimum of 2 to 4 sires per clutch, consistent with benefits to females of polyandry in this species, and indicating strong potential for sperm competition. We found a higher level of multiple paternity within field-laid eggs than in the first and second clutches from females that laid in the laboratory. The level of multiple paternity did not change over successive clutches from individual laboratory females and sperm from different males did not consistently dominate separate clutches, although individual females differed in patterns of sperm use. This suggests that spermatangia may be somewhat mixed within the female spermatheca at the time of fertilisation. Sperm competition is enhanced by high sperm longevity, and we found that viable sperm could be stored for up to 145 d in the laboratory. Overall, our results suggest strong potential for post-copulatory sexual selection in this species, due to the presence of sperm from multiple males in the female sperm storage organ competing for fertilisation of the female's eggs.

Patterns of sperm use in two populations of Red-sided Garter Snake (Thamnophis sirtalis parietalis) with long-term female sperm storage

Long-term sperm storage may contribute to postcopulatory sexual selection because it enhances the commingling of sperm from different males within the female reproductive tract, which is the prerequisite for sperm competition. Long-term sperm storage and multiple paternity has been documented in snakes, but the identity of the last potential father is usually unknown in studies demonstrating multiple paternity. Here we present the first study in Red-sided Garter Snakes (Thamnophis sirtalis parietalis (Say in James, 1832)) to use experimental population crosses to assess stored sperm usage, mate-order effects, and the potential for interpopulational gametic isolation. We found a high rate of multiple paternity indicative of ubiquitous long-term sperm storage in this system, and observed last-male sperm precedence in all families (n = 66). Postzygotic isolation was absent, and we observed only a weak asymmetry in pattern of sperm precedence in our population crosses.

Prudent sperm use by leaf-cutter ant queens

In many species, females store sperm between copulation and egg fertilization, but the consequences of sperm storage and patterns of sperm use for female life history and reproductive success have not been investigated in great detail. In hymenopteran insect societies (ants, bees, wasps), reproduction is usually monopolized by one or relatively few queens, who mate only during a brief period early in life and store sperm for later use. The queens of some ants are particularly long-lived and have the potential to produce millions of offspring during their life. To do so, queens store many sperm cells, and this sperm must remain viable throughout the years of storage. Queens should also be under strong selection to use stored sperm prudently when fertilizing eggs. We used the leaf-cutter ant Atta colombica to investigate the dynamics of sperm use during egg fertilization. We show that queens are able to fertilize close to 100 per cent of the eggs and that the average sperm use per egg is very low, but increases with queen age. The robustness of stored sperm was found to decrease with years of storage, signifying that senescence affects sperm either directly or indirectly via the declining glandular secretions or deteriorating sperm-storage organs. We evaluate our findings with a heuristic model, which suggests that the average queen has sperm for almost 9 years of normal colony development. We discuss the extent to which leaf-cutter ant queens have been able to optimize their sperm expenditure and infer that our observed averages of sperm number, sperm robustness and sperm use are consistent with sperm depletion being a significant cause of mortality of mature colonies of Atta leaf-cutter ants.

Female multiple mating in wild and laboratory populations of the two‐spot ladybird, Adalia bipunctata

Female mating rate is an important variable for understanding the role of females in the evolution of mating systems. Polyandry influences patterns of sexual selection and has implications for sexual conflict over mating, as well as for wider issues such as patterns of gene flow and levels of genetic diversity. Despite this, remarkably few studies of insects have provided detailed estimates of polyandry in the wild. Here we combine behavioural and molecular genetic data to assess female mating frequency in wild populations of the two-spot ladybird, Adalia bipunctata (Coleoptera: Coccinellidae). We also explore patterns of sperm use in a controlled laboratory environment to examine how sperm from multiple males is used over time by females, to link mating with fertilization. We confirm that females are highly polyandrous in the wild, both in terms of population mating rates (approximately 20% of the population found in copula at any given time) and the number of males siring offspring in a single clutch (three to four males, on average). These patterns are consistent across two study populations. Patterns of sperm use in the laboratory show that the number of mates does not exceed the number of fathers, suggesting that females have little postcopulatory influence on paternity. Instead, longer copulations result in higher paternity for males, probably due to the transfer of larger numbers of sperm in multiple spermatophores. Our results emphasize the importance of combining field and laboratory data to explore mating rates in the wild.

High variation in sperm precedence and last male advantage in the scorpionfly Panorpa germanica L. (Mecoptera, Panorpidae): Possible causes and consequences

In the last decades, many insect species have been studied in terms of sperm competition. Patterns of sperm use are often inferred from the mean species value of P 2, defined as the mean proportion of offspring sired by the second male in double-mating trials. In Panorpa germanica (Mecoptera, Panorpidae), P 2 largely depends on relative copulation durations of both males, but with the second male on average having some advantage over the first male. Estimating the presence of fertile sperm inside the female's reproductive tract in relation to time after copulation we conclude this partial last male sperm precedence not to be caused by natural death, loss, or depletion of first male sperm. Estimating sperm transfer rates of both mates of a female we, furthermore, found that the high intraspecific variance in P 2 that can be observed cannot solely be explained by variances in sperm transfer rates among P. germanica males. Other factors possibly causing the observed patterns of paternity success are discussed.

Genetic Studies Using the Orange Body Color Type of <I>Nezara viridula</I> (Hemiptera: Pentatomidae): Inheritance, Sperm Precedence, and Disassortative Mating

Abstract Nezara viridula (L.) (Hemiptera: Pentatomidae), the southern green stink bug, has body color polymorphisms. N. viridula f. smaragdula is the common green morph, whereas the rare morph N. viridula f. aurantiaca is uniformly orange. Crossing studies were conducted to determine the inheritance of the orange body color trait. Mendelian genetic analysis suggested that orange body color is a simple, sex-linked recessive trait. In sperm precedence studies using orange females crossed with green and then orange males, or vice versa, the proportion of offspring attributable to the second male, P2, averaged 73.3% (extremes 23.5–100%). The average P2 in the first egg mass deposited after the new pairing was 71.8%. The pattern of sperm use provided evidence for incomplete sperm mixing, sperm stratification, and sperm displacement. Green females preferred mating with orange males (88%) compared with green males (12%), suggesting that disassortative mating may operate.

Patterns of sperm use in the scorpionfly Panorpa germanica L. (Mecoptera: Panorpidae)

Sperm competition can be a powerful selective force in the evolution of reproductive strategies and mating systems. In studies on sperm competition, patterns of sperm use are typically reported as the mean species value of P 2, determined as the proportion of offspring sired by the second male to copulate with a doubly mated female. However, the within-species variance in P 2 has mostly been ignored, although taking this variance into account may be crucial for understanding the underlying mechanisms of sperm competition. Paternity analysis among the offspring of doubly mated females of Panorpa germanica (Mecoptera, Panorpidae) revealed a relationship between relative copulation durations of both males and the proportion of offspring each male will sire. This correlation between proportional copulation durations and paternity suggests mixing of sperm from different males inside the female’s spermatheca. Yet, sperm mixing appears to be incomplete, as paternity was overall slightly shifted towards the second male on average fathering a higher proportion of the offspring than its relative copulation duration would predict in case of complete sperm mixing. For individual males, however, the outcome of sperm competition is rather unpredictable as the intraspecific variance in P 2 was found to be very high, irrespective of copulation durations. Possible causes of the observed variance in P 2 and the partial last male sperm precedence are discussed.

Sperm death and dumping in Drosophila.

Mating with more than one male is the norm for females of many species. In addition to generating competition between the ejaculates of different males, multiple mating may allow females to bias sperm use. In Drosophila melanogaster, the last male to inseminate a female sires approximately 80% of subsequent progeny. Both sperm displacement, where resident sperm are removed from storage by the incoming ejaculate of the copulating male, and sperm incapacitation, where incoming seminal fluids supposedly interfere with resident sperm, have been implicated in this pattern of sperm use. But the idea of incapacitation is problematic because there are no known mechanisms by which an individual could damage rival sperm and not their own. Females also influence the process of sperm use, but exactly how is unclear. Here we show that seminal fluids do not kill rival sperm and that any 'incapacitation' is probably due to sperm ageing during sperm storage. We also show that females release stored sperm from the reproductive tract (sperm dumping) after copulation with a second male and that this requires neither incoming sperm nor seminal fluids. Instead, males may cause stored sperm to be dumped or females may differentially eject sperm from the previous mating.

Influence of female reproductive anatomy on the outcome of sperm competition in Drosophila melanogaster.

Females as well as males can influence the outcome of sperm competition, and may do so through the anatomy of their reproductive tracts. Female Drosophila melanogaster store sperm in two morphologically distinct organs: a single seminal receptacle and, normally, two spermathecae. These organs have different temporal roles in sperm storage. To examine the association between sperm storage organ morphology and sperm competition, we used a mutant type of female with three spermathecae. Although the common measure of sperm competition, P(2), did not differ between females with two and three spermathecae, the pattern of sperm use over time indicated that female morphology did affect male reproductive success. The rate of offspring production by females with three spermathecae rose and fell more rapidly than by females with two spermathecae. If females remate or die before using up second male sperm, then second male reproductive success will be higher when they mate with females with three spermathecae. The results indicate that temporal patterns of sperm use as well as P(2) should be taken into account when measuring the outcome of sperm competition.

Copulation and sperm release in Gasteracantha cancriformis (Araneae: Araneidae): differential male behaviour based on female mating history

Female spiders have two separate reproductive tracts, one on each side of the body, which receive and store sperm. Thus, females may be virgin or nonvirgin on both sides, or virgin on one side and nonvirgin on the other side. To examine whether male orb-weaving spiders, G.cancriformis, respond differentially to females based on mating history, we presented males to (1) virgin females, (2) females that had previously mated with one of their two tracts and (3) females that had mated previously with both reproductive tracts. Prior to copulation, males showed no differential responses in terms of latency to courtship, number of courtship bouts, number of insertion attempts, or latency to copulation. Female mating history influenced copulatory frequency and sperm release by the male, but not duration of copulation. Nearly all males copulated twice with virgin females, once with each reproductive tract. They released nearly all sperm contained in their palps. Males that encountered nonvirgin reproductive tracts were more likely to depart after a single copulation without attempting a second. Such males rarely released sperm, but the few that did released as many as males mating with virgin tracts. Thus, sperm were released in an all-or-none fashion. Female mating history did not influence the frequency of intersexual cannibalism. This suggests that differential response by males is more likely related to female patterns of sperm use than to high levels of intersexual killing.

Biases in sperm use in the mallard: no evidence for selection by females based on sperm genotype

If we are to understand fully the factors influencing fertilization success, it is essential to untangle male and female effects on sperm use. In many species, differences in fertilizing ability have been found between males or male genotypes, but the impact of female effects is less clear and may vary between taxa. Here, we examine sperm use in the mallard ( Anas platyrhynchos ), a species of bird in which forced copulation forms a major component of the mating system, to investigate whether there is any evidence for post–insemination female choice or rejection of particular sperm genotypes. Current models of sperm use in birds suggest observed patterns of paternity are a result of passive sperm loss from the reproductive tract and the relative timing of inseminations. Although this type of model successfully predicted average values of last male precedence observed in this species, there was considerable variation between females in their pattern of sperm use, with a tendency for females to use sperm of a single genotype. However, females did not consistently prefer one genotype over another in repeated inseminations with identical sperm mixtures, suggesting that post–insemination female preference based on sperm genotype did not account for this variation.

Sperm Use Patterns of Individual Fall Armyworm (Lepidoptera: Noctuidae)

The incidence of multiple mating and patterns of sperm use were examined in females of the fall armyworm, Spodoptera frugiperda (J. E. Smith), using electrophoretic markers. Thirty-five of 66 females mated more than once. Of these, 27 mated twice, 7 mated three times, and 1 mated four times. Eight twice-mated females and their progeny fit experimental criteria established for subsequent examination of sperm use patterns. Maximum likelihood methods were employed to assign probabilities of paternity to daily progeny groups subsequent to the second mating. Considerable variation was observed among females. Two females continued to produce progeny fathered by sperm from the first mating, four females switched to sperm predominantly from the second mating, and two females produced progeny that exhibited nearly equal paternity. The time interval between first and second matings did not seem to influence sperm use. Female benefits from multiple mating do not appear to be related to sperm replenishment or enhanced reproductive output but may simply be to compensate for the possibility of infertile initial matings.

Genetic basis for remating in Drosophila melanogaster. III. Correlated responses to selection for female remating speed.

Two natural populations ofDrosophila melanogaster selected for fast and slow female remating (Gromko and Newport,Behav. Genet.18: 621–632, 1988) were analyzed for correlated responses to selection. Several of the correlated responses differed between the lines derived from the two different source populations. In particular, the degree to which female receptivity to remating was dependent on the number of sperm in storage ceptivity to remating was dependent on the number of sperm in storage remained high in one pair of fast and slow selected lines but not in the other. In the line which retained sperm dependence (JEFFERS), fast and slow remating was achieved by changes in the threshold at which remating occurred. In the other line (COMP) changes in the temporal pattern of sperm use were seen. Thus both the level of the receptivity threshold and the existence of a sperm effect appeared to be selectable features of this species. Mated female attractiveness and receptivity were shown to be genetically distinct from virgin female attractiveness and receptivity. Effects of the genotype of the female on copulation duration were found.

Multiple Insemination and Male Sexual Selection in Natural Populations of Drosophila pseudoobscura

Data are presented which indicate a high frequency of concurrent multiple paternity in the progeny of females in a natural population of Drosophila pseudoobscura. A probability model is presented and used to obtain maximum-likelihood estimates of parameters describing the pattern of sperm use and the amount of concurrent multiple paternity in several population samples. The probability that two randomly selected offspring from a single randomly selected female have the same father was found to be .79. Estimates of effective mating frequency of male genotypes suggest that one of the samples came from a population in which there was nonrandom mating. Some evolutionary consequences of multiple matings in Drosophila are discussed.

Multiple Matings and Use of Sperm in the Boll Weevil, Anthonomus grandis12

Virgin female boll weevils, Anthonomus grandis Boheman, from a mutant strain with pearl-colored eyes were mated in various combinations to males of the same pearl strain or to males with brown (wild-type) eyes to study the use of sperm in multiple matings. Sperm from the last mating took precedence over sperm from other matings only when at least 24 hours separated the matings. The advantage of sperm from the last mating ranged from about 10% when 1 day separated matings to 90% when 4 days intervened. This advantage lasted from about 7 days when the interval between matings was short to more than 45 days from the longest interval. It is concluded from other data that most field females will follow the pattern of sperm use shown by closely spaced multiple matings.