Seminal fluid enhances sperm viability in the leafcutter ant Atta colombica

The seminal fluid that accompanies sperm in ejaculates has been shown or suggested to affect sperm competition and paternity success of insects by preventing female remating, inducing oviposition, and forming mating plugs. In Atta leafcutter ants, queens have multiple mates but never remate later in life, although they may live and produce fertilized eggs for several decades. The mating biology and life history of these ants therefore suggests that the major function of seminal fluid is to maximize sperm viability during copulation, sperm transfer, and initial sperm storage. We tested this hypothesis by comparing the viability of testis sperm and ejaculated sperm (mixed with seminal fluid) and found a significant positive effect of seminal fluid on sperm viability. We further quantified this positive effect by adding accessory gland secretion (a major component of seminal fluid) in a dilution series, to show that minute quantities of accessory gland secretion achieve significant increases in sperm viability. Sperm stored by queens for 1 year benefited in a similar way from being exposed to accessory gland compounds after dissection in control saline solution. Our results provide the first empirical evidence that seminal fluid is important for the production of viable ejaculates and that the accessory glands of Atta males—despite their small size—are functional and produce a very potent secretion.     

The evolution of female copulation calls in primates: a review and a new model

Female copulation calls are mating-associated vocalizations that occur in some species of Old World monkeys and apes. We argue that copulation calls have two immediate functions: to encourage mating attempts by other males and to increase mate guarding by the consort male. We hypothesize that female copulation calls have evolved under the selective pressures of risk of infanticide and sperm competition. When male mate guarding is effective, copulation calls allow females to concentrate paternity in dominant males and benefit from their protection against the risk of infanticide. When mate guarding is ineffective, copulation calls may bring genetic benefits to females through facilitation of sperm competition. We present a quantitative model in which interspecific variation in females' promiscuity predicts their tendency to use copulation calls in conjunction with mating. The model predicts that in species with little female promiscuity, copulation calls should be rare and exhibited only in association with mating with dominant males. In species in which females are highly promiscuous, copulation calls should be frequent and unrelated to male dominance rank. The limited data available to test the model support its main predictions as well as the predicted relation between copulation calls and male dominance rank.

Effects of ovarian fluid on sperm velocity in Arctic charr (Salvelinus alpinus)

Numbers of studies in externally fertilizing fish species provide evidence for an effect of ovarian fluid on sperm motility characteristics such as duration of forward mobility, velocity or percent motile sperm cells. Yet, because of variations among females in the quality of their ovarian fluid, such effects might differ between individuals. Additionally, ovarian fluid from different females could also be expected to affect each ejaculate differently, resulting in cryptic female choice. In this study on Artic charr (Salvelnius alpinus), sperm velocity from several males was measured in the diluted ovarian fluid of several females according to a fully balanced crossing design. This design allowed us to estimate variations among females in the effect of their ovarian fluid on the velocity of sperm from different males, and to detect variations among males in the ability of their sperm to swim in ovarian fluid. Sperm velocity was estimated by computer-assisted sperm analysis. Average velocity was found to vary among females, with some females having constantly higher velocity measurements in their ovarian fluid, and among males, indicating that some males had overall faster sperm in ovarian fluid than others. Moreover, variation in sperm velocity was shown to depend on individual female-male interactions. Our results document that females vary in the effect of their ovarian fluid on sperm velocity and that their ovarian fluid may stimulate sperm velocity according to individual characteristics of males. This latter result suggests a potential mechanism for cryptic female choice.

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.     

Female mediation of sperm competition in the millipede Alloporus uncinatus (Diplopoda: Spirostreptidae)

The tropical spirostreptid millipede Alloporus uncinatus has a polygynandrous mating pattern that is apparently shaped by sperm competition (Telford and Dangerfield 1990, 1993a). In the present study radioisotopic labelling of ejaculates was used to quantify the temporal effects of double mating sequences on sperm precedence patterns. Ejaculates of successive males mix completely within the sperm storage organs and are concentrated close to the site of fertilisation, the spermathecal-oviduct junction. When matings follow each other immediately (experiment 1), equal volumes of the ejaculates of each male are stored within the spermathecae, and both males have equal probability of paternity. Where matings are separated by a 24-h delay (experiment 2), the volumetric contribution of the first male is reduced by 54.8 % and last male precedence operates. Although the distal ends of the gonopods play a primary role in the redistribution of ejaculates (Barnett and Telford 1994), by using a single mating sequence we show that they are not responsible for the reduction in ejaculate volume. The most likely explanation is absorption and/or ejection of the first male's ejaculate by the female. Genital functional morphology is used to reconstruct the mechanism of ejaculate distribution.     

Non-aggressive mate guarding by the blue-footed booby: a balance of female and male control

Thirteen pairs of blue-footed boobies (Sula nebouxii) were observed on their colony. Pairs courted frequently and, on average, copulated 24 times during the 30 days before laying, with 38% of those copulations occurring in the last 5 days (presumed fertile period). Males and females increased attendance at the nest site as laying approached. Seven females performed an average seven extra-pair copulations, with 1–2 paired male neighbors, but these were less concentrated in the presumed fertile period than within-pair copulations, and the last two copulations of all 7 females were with their social mates. Rates of female extra-pair copulations were six times lower when their social mate was present, and during the presumed fertile period, no female performed an extra-pair copulation in the presence of her mate. Males did not respond to infidelity of social mates with aggression, prompt copulation, retaliatory copulation, or increase in copulation. Seven of 13 males performed an average of five extra-pair copulations, with 1–3 paired female neighbors, before their own mates began egg-laying. The males' extra-pair copulations represented only 4% of their total copulations during their own mates' presumed fertile periods. Females, the larger sex, apparently control sexual access and copulate with extra males to achieve extra-pair fertilization. Males pursue a mixed strategy: they copulate with extra females, mostly outside their own mate's presumed fertile period, and they copulate increasingly with their social mate as laying approaches, probably assuring some paternity by mate guarding, involving attendance and courtship. Behavior of males and females is also consistent with other hypotheses for extensive joint nest site attendance: pairbonding, copulation access, and territory acquisition. Received: 14 November 1997 / Accepted after revision: 16 May 1998     

Copulatory plugs do not assure high first male fertilisation success: sperm displacement in a lizard

Sperm competition selects for opposing male defensive and offensive reproductive traits, and its outcome may be determined by the effectiveness to which one trait has evolved to out-compete the other. We tested the effectiveness of a first male plug physical interference with a second male insemination (defence) vs the effectiveness of plug and associated sperm displacement by a second male (offence) on the outcome of sperm competition in Iberian rock lizards. We conducted a double mating experiment where we compared the proportion of eggs per clutch fertilised by the same second males (against the same first males) when they copulated with females 30 min (first male plug adhered firmly inside the female cloaca) and 4 h (first male plug loosely adhered or shed from the female cloaca) after first males. We found that second males fertilised the majority of the eggs per clutch in the 30-min treatment, whereas fertilisations were equally shared between the two males in the 4-h treatment. These results show that plugs have little defensive effectiveness, and thus, do not assure high first male fertilisation success. Instead, sperm displacement appears to be associated with plug displacement. That is, because sperm embedded in first male plugs, and displaced from competition for fertilisations by second males, is expected to increase in number with decreasing time allowed for female sperm transport, second males thus enjoy higher fertilisation success. This study shows that offensive plug displacement out-competes plug defensive role in Iberian rock lizards. Moreover, it reveals sperm displacement as a novel sperm competition mechanism in reptiles.     

Mate guarding and copulation behaviour in monogamous and polygynous blue tits: do males follow a best-of-a-bad-job strategy?

This study investigates the importance of mate guarding for males and females in the facultatively polygynous blue tit Parus caeruleus. We present observational data in combination with a paternity analysis using DNA fingerprinting to show that (1) male blue tits guard their mate, since they stay closer to their mate, initiate fewer flights and follow their mate more often during the female's presumed fertile period; (2) polygynous males do not suffer more from lost paternity despite lower mate guarding; (3) in monogamous pairs there is either no relation or a positive relation (depending upon the variable measured) between measures of mate guarding intensity and the proportion of extra-pair young in the nest; and (4) monogamous males that are more often followed by their fertile female suffered less from lost paternity. We conclude that, despite mate guarding, paternity seems to be largely under female control and unattractive males guarding their mate are making the best of a bad situation. Experimental evidence is provided showing that when males were temporarily removed from their territory, their mate suffered from increased harassment from neighbouring males that intruded in the territory and tried to copulate with the female. Almost all of these copulation attempts were unsuccessful because females refused to copulate. We conclude that mate guarding may be beneficial for females because harassment by neigbouring males is prevented.     

Sperm competition and the level of polyandry in a bushcricket with large nuptial gifts

Variation in paternity due to sperm competition or post-copulatory female choice has a major influence on animal mating system evolution and on the levels of genetic variability in natural populations. However, there are relatively few studies comparing the outcome of sperm-competition experiments in the laboratory with natural variation in polyandry among families from the field. In the bushcricket Ephippiger ephippiger, females mate multiply, and the males provide them with a large, nutritious, and probably expensive, donation at mating. We examined paternity in a series of laboratory matings, where females mated with two males, and amongst a series of families collected from a natural population. In the laboratory, paternity was highly bimodally distributed: 24% of families had offspring fathered by the first male to mate, 68% by the second male (in only 8% was paternity shared). In the field, paternity was more mixed: only 27% of families had a single father, 14% had more than two fathers, whilst 59% had two fathers. While unsuccessful matings may contribute to the highly biased paternity in the laboratory, they cannot fully explain the high incidence of complete P2 families. Nonrandom sperm utilisation is therefore likely. Greater sperm mixing in the field probably results from females mating with more males, but the distribution of paternity also reflects an active process of nonrandom sperm utilisation. Confidence of paternity due to last male advantage may be relatively high in this species, and therefore may have facilitated the evolution of the large spermatophore in E. ephippiger.Communicated by D. Gwynne     

Differences in reproductive success between laboratory and wild-derived golden hamsters (Mesocricetus auratus) as a consequence of inbreeding

All laboratory golden hamsters (Mesocricetus auratus) originated from a sibling pairing back in 1930. Due to this extreme founder event, domestic golden hamsters are presumed to be one of the most bottlenecked animal populations. Nevertheless, domestic hamsters show no obvious signs of inbreeding depression in commonly used breeding stocks. To explore the existence of potentially masked inbreeding effects, we compared the reproductive success of laboratory (lab) and wild-derived (wild) golden hamsters. We allowed oestrus females to mate consecutively with lab and wild males. The resulting offspring was genotyped using microsatellites to assess paternity. Finally, we compared male reproductive success to genetic variability, sexual behaviour and different sperm characteristics. Both hamster strains exhibited the expected large difference in genetic diversity (H _wild =0.712±0.062 vs H _lab =0.007±0.007. The reproductive success of wild males dramatically exceeded that of lab males (87% of pups were sired by wild males). Sexual behaviour of wild and lab males only varied in the number of long intromissions (intromissions without ejaculation at the end of the mating). No significant differences were observed in relation to mounting, ejaculation and intromission. There were also no apparent differences in sperm motility, velocity and density or testis histology between wild and lab hamsters. We conclude that the reduced reproductive success of lab males represents a hidden inbreeding effect, although its precise physiological cause remains unclear. These results provide first evidence for a major fitness disadvantage in captive golden hamsters.     

The effect of perceived female parasite load on post-copulatory male choice in a sex-role-reversed pipefish

The last several decades of research in behavioral ecology have resulted in a deeper appreciation of post-mating processes and sexual conflict in sexual selection. One of the most controversial aspects of sexual selection is cryptic mate choice. Here, we take advantage of male pregnancy in a sex-role-reversed pipefish (Syngnathus typhle) to quantify cryptic choice based on perceived parasite load and other sources of variance in female fitness. Studies have shown that S. typhle males preferentially mate with females with lower parasite loads and that a male’s perception of female parasite load can be altered by tattooing females. We manipulated the apparent parasite load of females in controlled mating experiments to test the hypothesis that post-copulatory sexual selection is dependent on a male’s perception of female parasite load in pipefish. Our results provided no evidence for cryptic male choice based on perceived female parasite load. However, we found evidence that eggs from larger females were more likely to result in viable offspring than eggs from smaller females and that the first female to mate with a male transferred more eggs per copulation on average. Overall, our results show that potential for post-copulatory sexual selection does exist in pipefish, but the male’s perception of female parasite load does not play a major role in this process.     

Genetic analysis of parentage within experimental populations of a male dimorphic beetle,<Emphasis Type="Italic"> Onthophagus taurus</Emphasis>, using amplified fragment length polymorphism

We used the multilocus DNA fingerprinting technique, amplified fragment length polymorphism, to examine parentage of 902 offspring from eight experimental populations of the dung beetle, Onthophagus taurus. The males of this species exhibit a suit of morphological and behavioural traits that characterise alternative mating tactics. Hornless minor males sneak copulations with females that are guarded by horned major males. Our aims were to provide a prospective assessment of the potential role of frequency dependence in the maintenance of alternative mating tactics, to assess the levels of polyandry, and to determine the patterns of sperm usage by multiply mated females. The average proportion of offspring sired by major and minor males did not co-vary with the relative frequency of each morph present in experimental populations. However, there was some indication that the effective mating frequency (number of females producing offspring sired by a given male) of major and minor males may exhibit frequency dependence. Mating success of both male types declined with increasing numbers of major males. Paternity was positively associated with effective mating frequency. Females produced offspring sired from between one and eight males and, on average, paternity was distributed equally amongst a females mates, regardless of the number of males mated. Differences in fertilisation success among males were not associated with alternative male phenotypes. Neither did a males fertilisation success depend on his genetic dissimilarity with the female. These results are discussed in the context of the evolution of alternative mating strategies, and mechanisms of postcopulatory sexual selection.Communicated by N. Wedell     

Maintenance of variance in sperm transfer rates in a scorpionfly: food availability,genetic basis,and heritability

Variation in traits closely related to fitness is expected to be low. This is because these traits are under directional selection and the best genotype should prevail. However, there have been a number of studies demonstrating the existence of considerable variance in sexually selected traits, which is generally known as the lek paradox. Accordingly, earlier studies found substantial variation in sperm transfer rates in Panorpa vulgaris. Aiming at finding the mechanism that maintains this variation, we analyzed the condition dependence and the narrow sense heritability of sperm transfer rates. Food deprivation in the larval/adult phase caused a decrease in the males’ capability of saliva secretion resulting in shorter copulations and a reduced number of transferred sperm. There was a positive correlation between mean sperm transfer rates and mean body mass. Additionally, intermale variation in sperm transfer rates decreased with increasing food availability. Hence, we suggest that sperm transfer rates in P. vulgaris are influenced by adult feeding history. Heritability analyses of sperm transfer rates did not provide significant results, which is consistent with the general hypothesis that additive genetic variance in traits closely related to fitness is small. Since a trait’s potential to respond to selection is proportional to the amount of contained additive genetic variance, the ascertained small heritability provides a satisfying explanation for the maintenance of substantial variation in sperm transfer rates.     

Hermaphrodite sex role preferences: the role of partner body size, mating history and female fitness in the sea slug Chelidonura sandrana

Costs and benefits associated with matings and the effects of mating frequency on fitness commonly differ between the sexes. As a result, outcrossing simultaneous hermaphrodites may prefer to copulate in the more rewarding sex role, generating conflicts over sperm donation and sperm receipt between mates. Because recent sex role preference models remain controversial, we contrast here some of their assumptions and predictions in the sea slug Chelidonura sandrana. For this hermaphrodite with sperm storage and internal fertilisation, risk-averse models assume that fitness pay-offs are constantly higher in the female than in the male function in any single mating. Moreover, excluding mutual partner assessment, these models predict male mating behaviour to be independent of receiver traits. The competing gender ratio hypothesis assumes that relative fitness pay-offs, and thus the preferred mating roles, vary and may reverse between matings and predicts that ejaculation strategies co-vary with receiver quality. We found that field mating rates of C. sandrana substantially exceeded what is required to maintain female fertility and fecundity, indicating large variation in direct female benefits between matings. We further demonstrate that male copulation duration adaptively increased with partner body size (i.e. fecundity) but decreased with recent partner promiscuity. These findings are compatible with the gender ratio hypothesis but contradict risk-averse models.     

Intraspecific variation of testis size and sperm length in the yellow-pine chipmunk (<Emphasis Type="Italic">Tamias amoenus</Emphasis>): implications for sperm competition and reproductive success

Comparative analyses have found that relative testis size is a strong predictor of the prevalence of sperm competition for many taxa, including mammals, yet underlying this pattern is the assumption that intraspecific variation in testis size is related to individual fitness. Because intraspecific variation in ejaculate investment underlies interspecific patterns, it is critical to understand the causes and consequences of intraspecific variation in ejaculate investment. We examined relationships between ejaculate investment (testis size and sperm length) and reproductive success, body size and condition in the yellow-pine chipmunk (Tamias amoenus), a small ground squirrel in which sperm competition occurs. We examined genetic estimates of male reproductive success from a wild population of yellow-pine chipmunks and determined that males with large testes had higher annual reproductive success than males with small testes. This result provides empirical support for the numerous comparative studies that indicate testis size is associated with the intensity of sperm competition. In addition, males in good condition had relatively larger testes than males in poor condition, but there was no evidence of sperm length being dependent on condition. Finally, contrary to many predictions, males that invested more in sperm production (relatively heavy testes) produced shorter sperm, not longer sperm, than males that invested less.Communicated by P.M. Kappeler     

Applying the discrete vortex method in environmental fluid mechanics: A study of the time-averaged near wake behind a circular cylinder

This work illustrates the discrete vortex method (DVM) as a tool for simulating environmental fluid mechanics problems involving transport in the wake of a bluff body. The DVM was used to model both the long-time-averaged and instantaneous features of flow past a circular cylinder. Simulations were performed for Re = 140, 000. Verification testing was accomplished by refining time-step and vortex element circulation. The DVM was validated through comparison with experimental data from Cantwell and Coles. Verification testing demonstrated that, while global convergence is not possible for an unsteady flow simulation, it is possible to have convergence to physical results. This verification entails identifying a range of parameters in which a flow containing coherent structures and matching physical conditions is attainable. Validation tests demonstrated excellent agreement between experimental and simulated results for time-averaged velocity and shear stress profiles, as well as Strouhal number.     

Fertilisation success in the fly Dryomyza anilis (Dryomyzidae): effects of male size and the mating situation

Male fertilisation success in relation to male size and the mating situation (ordinary pair formation with a single, nonvirgin female vs. take overs) was examined in the fly Dryomyza anilis. In ordinary matings, large males achieved higher fertilisation success than small ones when they were the second to mate with the female. Take overs differ from ordinary pair formation in that the second male experiences intensified sperm competition. This is because in take overs the female is not able to discharge any of the sperm inseminated by the first male as she usually does before a new mating. Compared with ordinary matings, take overs reduced the fertilisation success of the second male by 8–10%, whereas that of the first male was 7–14% higher in take overs. Even though the intruder was always larger than the paired male his superior fertilisation success did not compensate for the effect of the sperm already present in the female. In D. anilis, males can increase their fertilisation success by tapping the female's external genitalia with their claspers or having several copulation bouts per mating. Thus, in a take over, the intruder could respond to the intensified sperm competition by performing more tapping sequences per copulation bout or more copulation bouts per mating. In matings observed in the wild, males performed more tapping sequences after a take over than after pair formation with a single female, although the difference was not significant. The results show that there are differences in fertilisation success between males of different size. In addition, different mating situations can result in considerable variation in the fertilisation success of an individual male. Higher fertilisation success for the first male after a take over may be significant, in particular, for the reproductive success of small males, which frequently lose their females to large males.     

Sex in the dark: determinants and consequences of mixed male mating tactics in<Emphasis Type="Italic"> Microcebus murinus</Emphasis>, a small solitary nocturnal primate

In mammals with solitary females, the potential for males to monopolize matings is relatively low, and scramble competition polygyny is presumed to be the predominant mating system. However, combinations of male traits and mating tactics within this type of polygyny have been described. The main aim of our study was to identify the relative importance of, and interactions among, potential determinants of contrasting male reproductive tactics, and to determine their consequences for male reproductive success in a small solitary nocturnal Malagasy primate, the gray mouse lemur (Microcebus murinus). We studied their mating behavior over three consecutive annual mating seasons. In addition, we determined the genetic relationships among more than 300 study animals to quantify the reproductive success of individual males. We found that, with a given relatively low overall monopolization potential, successful male mouse lemurs roamed extensively in search of mates, had superior finding ability and mated as early as possible. However, contest competition was important too, as temporary monopolization was also possible. Males exhibited different mating tactics, and heavier males had a higher reproductive success, although most litters had mixed paternities. Switching between tactics depended on short-term local variation in monopolization potential determined by a pronounced dynamic in fertilization probability, number of alternative mating opportunities, and the operational sex ratio. This study also revealed that the dynamics of these determinants, as well as the mutual interactions between them, necessitate a detailed knowledge of the mating behavior of a species to infer the impact of determinants of alternative mating tactics.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by S. AlbertsThis revised version was published online in August 2004 with corrections to Figure 2.     

非稳态条件下藻类种间非生物资源竞争理论及研究进展

从理论及实验研究的角度论述了藻类非稳态种间资源竞争研究进展。实验室内稳态条件下的竞争理论得到了大量实验验证,由于自然水体处于非稳状态,非稳态条件下藻类种间资源竞争日益成为藻类水华形成机制研究的重点。主要理论包括Tilman的R*法则和资源比假说,Grover的拾遗者-机会主义者交替竞争假说(VIS),中度干扰假说(IDH)及关键光强(CLIH)假说。这些假说的提出丰富了藻类资源竞争的理论体系,为研究自然状态下藻类增殖和竞争行为奠定理论基础。今后的藻类种间资源竞争的研究重点为非稳态下物理条件变化以及物理、化学和生物资源共同变化下藻类种间关系及生物多样性的研究。     

Sperm competition and evidence of sperm fertilization patterns in the carrion ball-roller beetle Canthon cyanellus cyanellus LeConte (Scarabaeidae: Scarabaeinae)

Field observation and laboratory experiments were conducted to investigate sperm competition and patterns of sperm fertilization under different experimental conditions in the carrion ball-roller beetle Canthon cyanellus cyanellus. Males in nature can mate with females whose spermathecae contains fertile sperm from other males. Sperm precedence was investigated using a visible genetic marker. The progeny of red (homozygous recessive) virgin females mated once with a red male and afterward, once with a green beetle (homozygous dominant) and vice versa, revealed that regardless of its color, the last male to mate fertilized c.a. 50% of the eggs, suggesting strong sperm competition. Males were able to achieve higher levels of paternity (more than 80%) when mated ad libitum with previously mated females, although large amount of variance in paternity does not exclude the possibility of first male sperm precedence or female cryptic choice. These results suggest that repeated mating and sperm replacement are the mechanisms by which last males achieve sperm precedence.