Polyandrous female butterflies forage for matings

Butterfly mating systems exhibit great variation and range from strict monandry to strong polyandry. During mating males transfer ejaculates containing both sperm and accessory substances to females. In the polyandrous green-veined white butterfly, Pieris napi (Lepidoptera, Pieridae) these ejaculates average 15% of male body mass, but can represent up to 23% of body mass for individual males. Hence, mating is costly to males, and recently mated males increase copula duration but decrease ejaculate mass transferred to females. Substances transferred to females during mating are later incorporated into female soma and reproductive tissues, and multiply mated female butterflies have higher lifetime fecundity, lay proportionately larger eggs, and live longer compared to once mated females. Here we report that females of P. napi allowed to mate at liberty with recently mated males only (i.e. males that delivered a small ejaculate) increased their lifetime number of matings compared to females allowed to mate with virgin males only (i.e. males that delivered large ejaculates), the former group mating on average 5.1 times (range 2–10) and the latter group mating on average 2.8 times (range 1–4). The lifetime fecundity of the two groups of females did not differ significantly. Because nutrient donation from males is essential for females to realize their potential fecundity, we conclude that females of the polyandrous green-veined white actively forage for matings.     

Low paternity in the hornet Vespa crabro indicates that multiple mating by queens is derived in vespine wasps

Queen mating frequency was studied in the European hornet, Vespa crabro, by analyzing four DNA microsatellite loci in 20 workers from each of 14 nests. Queens were found to be predominantly singly mated (9/14), although double (4/14) and triple mating (1/14) also occurred. For most multiply mated queens, paternity was significantly biased with the majority male fathering on average 80% of the female offspring. The population-wide effective mating frequency was therefore low (1.11), and sister-sister relatedness high (0.701 ± 0.023 SE). Low effective mating frequency in Vespa, in combination with data from other vespines, suggests that high paternity frequency is derived in the group. Some problems with the non-detection of fathers, where the queen was not sampled or shared alleles with males, are analyzed. Received: 16 November 1998 / Received in revised form: 29 March 1999 / Accepted: 12 April 1999     

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     

Role of Familiarity and Preference in Reproductive Success in Ex Situ Breeding Programs

Abstract: Success of captive‐breeding programs centers on consistent reproduction among captive animals. However, many individuals do not reproduce even when they are apparently healthy and presented with mates. Mate choice can affect multiple parameters of reproductive success, including mating success, offspring production, offspring survival, and offspring fecundity. We investigated the role of familiarity and preference on reproductive success of female Columbia Basin pygmy rabbits (Brachylagus idahoensis) as measured by litter production, litter size, average number of young that emerged from the burrow, and average number of young that survived to 1 year. We conducted these studies on pygmy rabbits at the Oregon Zoo (Portland, Oregon, U.S.A.) and Washington State University (Pullman, Washington, U.S.A.) from February to June 2006, 2007, and 2008. Before mating, we housed each female adjacent to 2 males (neighbors). Female preference for each potential mate was determined on the basis of behavioral interactions observed and measured between the rabbits. We compared reproductive success between females mated with neighbor and non‐neighbor males and between females mated with preferred and nonpreferred males. Our findings suggest that mating with a neighbor compared with a non‐neighbor and mating with a preferred neighbor compared with a nonpreferred neighbor increased reproductive success in female pygmy rabbits. Litter production, average number of young that emerged, and average number of young that survived to 1 year were higher in rabbits that were neighbors before mating than in animals who were not neighbors. Pairing rabbits with a preferred partner increased the probability of producing a litter and was significantly associated with increased litter size. In captive breeding programs, mates are traditionally selected on the basis of genetic parameters to minimize loss of genetic diversity and inbreeding coefficients. Our results suggest that integrating genetic information with social dynamics and behavioral measures of preference may increase the reproductive output of the pygmy rabbit captive‐breeding program. Our findings are consistent with the idea that allowing mate choice and familiarity increase the reproductive success of captive‐breeding programs for endangered species.     

The benefits of multiple mating to female seaweed flies, Coelopa frigida (Diptera: Coelpidae)

Female seaweed flies, Coelopa frigida, have the potential to benefit from mating more than once. Single matings result in low fertility so females may benefit directly from multiple copulations by sperm replenishment. A chromosomal inversion associated with larval fitness, with heterokaryotypic larvae having higher viability than homokaryotypes, means that polyandrous homokaryotypic females have a higher probability of producing genetically fit offspring than monandrous homokaryotypic females. We allowed females to mate only once, repeatedly four times to the same male, or polyandrously four times to four different males. Multiply mated and polyandrous females laid more eggs and produced more offspring than singly mated and monandrous females, respectively. Polyandrous females laid more eggs, had higher egg-to-adult survival rates and produced more offspring than repeatedly mated females. Fertility rates did not differ between treatments. The observed fitness patterns therefore resulted from increased oviposition through multiple mating per se, and a further increase in oviposition coupled with higher egg-to-adult offspring survival benefits to polyandry. Daily monitoring of individual females over their entire life spans showed that multiple copulations induced early oviposition, with polyandrous females ovipositing earlier than repeatedly mated females. Singly mated and polyandrous females incurred a longevity cost independent of egg production, whereas repeatedly mated females did not. This suggests that repeatedly mating with the same male may counteract a general cost of mating. Longevity, however, was not correlated with overall female fitness. Our data are discussed in the overall context of the seaweed fly mating system.Communicated by G. Wilkinson     

Influence of alternate reproductive tactics and pre- and postcopulatory sexual selection on paternity and offspring performance in a lizard

Sexual selection theory predicts different optima for multiple mating in males and females. We used mating experiments and genetic paternity testing to disentangle pre- and postcopulatory mechanisms of sexual selection and alternate reproductive tactics in the highly promiscuous lizard Eulamprus heatwolei. Both sexes mated multiply: 30–60 % of clutches were sired by two to four fathers, depending on the experiment. Larger males sired more offspring when we allowed male contest competition: 52 % of large males but only 14 % of small males sired at least one offspring. In the absence of male contest competition, females mated promiscuously and there was no large male advantage: 80 % of large males and 90 % of small males sired at least one offspring, and there was no evidence for last-male precedence. Multiple mating did not yield obvious direct or indirect benefits to females. E. heatwolei represents a complex system in which males attempt to improve their fertility success by limiting rivals from access to females and through adopting alternate reproductive tactics. Conversely, females exhibit no obvious precopulatory mate choice but may influence fitness through postcopulatory means by either promoting sperm competition or through cryptic female choice. Our results support the hypothesis that female multiple mating in nonavian reptiles is best explained by the combined effect of mate encounter frequency and high benefits to males but low costs to females.     

Multiple mating affects offspring size in the opisthobranch Chelidonura sandrana

Offspring size can have pervasive effects throughout the life history stages of many marine invertebrates. Although maternal offspring investment is largely determined by the environmental conditions experienced by the mother, egg size might additionally vary in response to the number and quality of previous mating partners. Positive effects of mating multiply with several different males (polyandry) have been confirmed for a variety of species, whereas such investigations are lacking for marine invertebrates. Here we differentiated between the effects of ejaculate amount (repeatedly mated) and ejaculate diversity (polyandry) on maternal offspring investment in the simultaneously hermaphroditic sea slug Chelidonura sandrana. We found that focal “females” mated with four different “males” produced significantly larger egg capsules and larger veligers, while focal “females” mated four times with the same “male” suffered from reduced mid-term fecundity. We found no effect of veliger size on veliger survival. Our results show that female mating patterns are an important addition to understanding the variation in offspring size in internally fertilizing marine invertebrates.     

Indirect genetic benefits of polyandry in a spider with direct costs of mating

The search for the evolutionary explanation of polyandry is increasingly focused on direct and indirect selection on female resistance. In a polyandrous spider Stegodyphus lineatus, males do not provide material benefits and females are resistant to remating. Nevertheless, polyandrous females may obtain indirect genetic benefits that offset the costs associated with multiple mating. We manipulated the opportunity for females to select between different partners and examined the effect of female mating history (mated once, mated twice, or rejected the second male) on offspring body mass, size, condition, and survival under high- and low-food rearing regimens. We found that multiple mating, not female choice, results in increased female offspring body mass and condition. However, these effects were present only in low-food regimen. We did not find any effects of female mating history on male offspring variables. Thus, the benefits of polyandry depend not only on sex, but also on offspring environment. Furthermore, the observed patterns suggest that indirect genetic benefits cannot explain the evolution of female resistance in this system.     

Why do female pied flycatchers mate with already mated males: deception or restricted mate sampling?

The polygyny threshold model suggests that females make an optimal choice between mated and unmated males. However; in birds in which males provide parental care, the fitness of secondary females is often lower than expected from this model. This has been explained by the deception hypothesis, which states that males hide their mating status and deceive females into polygyny. Yet there is no direct evidence that secondary females are unaware of male mating status when they settle. Alternatively, females settle with mated males as a result of mate competition and costs of searching. We used videofilming at nestboxes defended by males to study mate sampling of female pied flycatchers Ficedula hypoleuca. The females visited on average only 2.74 males (range 1–8, n = 43). Most (16 of 19) of the polygynous matings occurred because females had only visited mated males, or the unmated males visited became occupied by competitors during the sampling period. Among females that could choose between both mated and unmated males, the majority (13 of 16) settled with unmated males. These results lend little support to the deception hypothesis but are consistent with the view that females are able to detect male mating status but sometimes settle with mated males because of cost of searching. Prospecting females seemed willing and able to suffer the cost of fighting with aggressive primary females in the males' secondary territory if no alternative mating options were available. In addition to male mating status, females took male quality (plumage colour, age) into account in mate choice but the former appeared to be the more important. Correspondence to: T. Slagsvold     

Multiple mating in the ant Acromyrmex versicolor: a case of female control

In eusocial insects, polyandrous mating has the potential to reduce genetic relatedness of individuals within a colony, which may have a profound effect on the stability and social structure of the colony. Here we present evidence that multiple mating is common in both males and females of the desert leaf-cutter ant Acromyrmex versicolor. Females seem to have complete control over the number of matings, and mate on average with three males, even though the sperm transferred in a single copulation is sufficient to fill the spermatheca. To determine whether there is a bias in the representation of sperm from different mates in the spermatheca, females were mated to three or four males in controlled mating experiments and were subsequently allowed to found colonies in the laboratory. Paternity analysis of the offspring by random amplified polymorphic DNA analysis showed that all males that have been mated to a female successfully contributed sperm to the production of her offspring. No significant asymmetry in sperm use was detected, suggesting complete sperm mixing. Different hypotheses to explain polyandrous mating are discussed, and it is argued that the best hypothesis to explain polyandrous mating and complete sperm mixing in A. versicolor is that utilizing genetically diverse sperm confers a selective advantage on females. Received: 14 June 1995/Accepted after revision: 26 November 1995     

Does it matter that male beaugregory damselfish have a mate preference?

Male beaugregory damselfish (Stegastes leucostictus) spent more time courting larger females in both two-choice and single presentations. Female size was significantly correlated with gonad weight. We also verified that female fecundity was extremely variable within a natural population. We found that male reproductive success was highly correlated with both clutch size and clutch number. However, clutch size was not significantly correlated with clutch number, indicating that males that received larger clutches did not receive more egg clutches. Furthermore, there was no difference between the number of offspring produced by males that mated with the largest females and by males that mated with the most females. Thus, although males preferred larger females, males produced similar numbers of offspring by mating with large females or mating with many females. Received: 7 March 1997 / Accepted after revision: 1 November 1997     

Sperm competition as a mechanism of female choice in the field cricket,Gryllus bimaculatus

Summary While traditionally viewed as an extension of intermale competition, mechanisms of sperm competition may be used by multiply mating females for mate choice. In the field cricket G. bimaculatus sperm were shown to mix in the spermatheca. The proportion of offspring sired by the second male increased with spermatophore attachment duration and, therefore, the number of sperm transferred. There was no second male advantage for single matings after an initial double mating. However, the proportion ofoffspring sired by the second male increased in proportion to the number of times he mated such that second males mating three times after an initial double mating had the advantage at fertilization. The data suggested that sperm were utilized in proportion to their numerical representation in the spermatheca. The mechanism of sperm precedence may, therefore, be one of sperm dilution. Female G. bimaculatus may control the degree of sperm competition as a mechanism of mate choice. By accepting large quantities of sperm from chosen males they may determine the paternity of their offspring by diluting out the sperm stored from previous matings.     

Selected polyandry: female choice and inter-sexual conflict in a small nocturnal solitary primate (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Sex-specific interests over the maximization of reproductive success lead to an inter-sexual conflict over the optimal mating system in a species. Traditionally, the outcome of this inter-sexual conflict has been studied from the male perspective but it also depends on female mating strategies, such as manipulating the temporal distribution of sexual activity, advertisement, and mate choice. We used a small nocturnal primate, the gray mouse lemur (Microcebus murinus) to determine the relative importance of female mating strategies on the outcome of this conflict in a species where females are solitary during their activity period. We studied their mating behavior over three consecutive annual mating seasons and determined the genetic relationships among more than 300 study animals to quantify individual reproductive success. We found that most females were receptive asynchronously. Females did not exhibit any obvious direct mate choice, probably due to a highly male-biased operational sex ratio and the corresponding costs of choosiness. However, females exercised indirect choice for multiple matings. They mated with 1–7 males up to 11 times during their single night of receptivity. As a result, mixed paternity was common but heavier males sired more offspring, meaning that indirect female choice for superior males cannot be excluded. Females exhibited a mixed mating strategy, avoiding costly direct mate choice but still counteracting male efforts to monopolize mating, successfully increasing genetic variability among offspring. Thus, females had a major influence on the outcome of the inter-sexual conflict despite male monopolization attempts.Communicated by J. Setchell     

Polyandry, multiple mating, and female fitness in a water strider Aquarius paludum

Contrary to Bateman’s principle, polyandry appears to be a common female mating strategy. Several hypotheses have been proposed to explain the evolution of polyandry. It is assumed that females gain either material or genetic benefits from multiple matings, or that they are coerced into mating by males. In water striders, mating is generally assumed to be costly to females, and they are thought to mate for reasons of convenience, adjusting their resistance to mating according to male harassment. Here, we tested the effect of number of matings (with the same male) and number of partners on female fitness in a water strider Aquarius paludum. In the first experiment, we regulated the time females spent with a male and found that females’ egg production increased with multiple matings up to a point. The result supports the existence of an optimal female mating frequency. In the second experiment, we tested how polyandry affects the number of eggs laid and egg hatching success. We conducted three different trials: females mated four times with either a single male, two different males, or with four different males. Females that mated with four different males laid the lowest number of eggs and had the lowest egg hatching success, suggesting that polyandry reduces females’ egg production and egg hatching success in A. paludum. We conclude that A. paludum females probably gain material benefits from mating but no genetic benefits were found in this study.     

Mate sampling behaviour of female pied flycatchers: evidence for active mate choice

Summary This paper presents major new evidence for active mate choice of female pied flycatchers, Ficedula hypoleuca. Fifteen color-ringed females were released into a study area containing 23 unmated males defending one nestbox each. Through intensive surveillance, the behavior of the females was observed during 2 consecutive days. Twenty-two of the males received a total of 131 female visits. Six of the females settled in the study area, and their premating period lasted 1.3–2.5 days. The females were seen searching for mates for at least 6–32 h and were seen visiting at least 1–9 different males. Hence, some of the females rejected males before mating. Nevertheless, the females settled close to the site of release (range: 16–243 m), suggesting that they mated with one of the first males encountered. Females visited males most frequently in the morning, and the diurnal distribution of visits was significantly correlated with male song activity. Offprint requests to: S. Dale     

Levels of polyandry and intracolonial genetic relationships in Apis florea

DNA was extracted from worker and drone pupae of each of five colonies of the dwarf honey bee Apis florea. Polymerase chain reactions (PCR) were conducted on DNA extracts using five sets of primers known to amplify microsatellite loci in A. mellifera. Based on microsatellite allele distributions, queens of the five colonies mated with at least 5–14 drones. This is up to 3 times previous maximum estimates obtained from sperm counts. The discrepancy between sperm count and microsatellite estimates of the number of matings in A. florea suggests that despite direct injection of semen into the spermatheacal duct, either A. florea drones inject only a small proportion of their semen, or queens are able to rapidly expel excess semen after mating. A model of sexual selection (first proposed by Koeniger and Koeniger) is discussed in which males attempt to gain reproductive dominance by increasing ejaculate volume and direct injection of spermatozoa into the spermatheca, while queens attempt to maintain polyandry by retaining only a small fraction of each male's ejaculate. It is shown, at least in this limited sample, that the effective number of matings is lower in A. florea than in A. mellifera.     

Reproductive trade-offs from mating with a successful male: the case of the tephritid fly Anastrepha obliqua

In lekking species, females may become sperm-limited when mating with sexually successful males, and this may be exacerbated by a poor male diet. Polygynous males may also be limited by the amount of accessory gland products (AGPs) they can transmit to females, which in turn may influence the females’ refractory period and longevity. Here, we tested the effect of male mating history, larval and adult diet on copula duration, mating intervals, female fecundity, fertilisation success, life span and likelihood to remate using sexually successful males of the lekking tephritid fly Anastrepha obliqua. Flies originated from either a native or exotic host fruit and were protein-fed or deprived. Male diet and larval host influenced copula duration, while the time elapsed between matings was affected by the interaction of mating order and male adult diet. Female fecundity was not influenced by female position in mating order or protein inclusion into the male diet. However, mating order and male larval diet influenced female fertilisation success. Importantly, as males mated successively they were less able to induce a refractory period on females, as the last females to mate with a male were more likely to remate and had slightly longer life spans than the first females to mate with males. These results might be attributed to a decrease in male AGPs with increasing male mating frequency. We discuss the role of conditional expression of male mating frequency with respect to A. obliqua’s life history, the trade-off that females face when mating with a successful male, the effect of larval diet on adult sexual performance and the possibility for sexual conflict to occur due to high male mating rates and fitness costs to females.     

Sex ratio,local mate competition and mating behaviour in the aphid Pemphigus spyrothecae

Summary The primary sex ratio and the selective factors associated with it were investigated in the aphid Pemphigus spyrothecae. The sexuparae gave birth to an average of 1.99 ± 0.01 (1–2) males and 5.06 ± 0.09 (2–6) females [± SE (range), n = 147]. The average weight of individual males was 16.2±0.86 (13–18) g (n = 5) and of females 40.7 ± 0.71 (38–46) g (n = 15). The overall investment ratio by the mother sexuparae was therefore 1:6.4, equivalent to a proportionate investment in sons of 0.135 (interquartiel range: 0.117–0.165). There was a highly significant correlation between the size of the sexupara and the number of her daughters: the number of sons was independent of sexupara size. Field observations and laboratory experiments showed that the sexuparae aggregate on poplar bark before giving birth to the sexuals: they appear to behave in such a way that there is always at least one other sexupara in the crevice with them. The average number of sexuparae forming a foundress group, within which offspring could potentially mate with each other, was 2.48±0.19 (1–9) (n = 80). The life-time activity patterns of the sexuals (which moult four times but do not feed) was described. Both sexes are active shortly after birth; they are then immobile for a long period but become very active again after emerging as adults (after about 42 h in males, 51 h in females). Each male can mate with up to 14 females. The females are receptive to a second male for only a relatively short period (ca. 15–20 min) after their first mating. There is considerable competition between males during mating (just as intense between clonal sibs as non-sibs) and evidence for post-copulatory mate-guarding by the males. There is no evidence that females prefer to mate with non-sibs rather than sibs. The observed sex ratios and the mating behaviour of the aphids are discussed in relation to models of local mate competition assuming variable female fecundity, as developed by Frank (1987a, b) and Yamaguchi (1985) (the constant male hypothesis) and by Stubblefield and Seger (1990).     

Polygyny and male parental care in Savannah sparrows: effects on female fitness

Summary To determine the effects of male mating status on female fitness, we compared the reproductive success, survival, and future fecundity of female Savannah sparrows (Passerculus sandwichensis) mated to monogamous vs. polygynous males in a 5-year study on Kent Island, New Brunswick, Canada. The proportion of males with more than one mate varied from 15 to 43% between years and sites. Polygynous and monogamous males fledged young of equal size in every year of the study. Females who shared paternal care with other females laid as many eggs per clutch and clutches per season as monogamously mated females. In most years polygynously mated females showed no delay in laying a second clutch, and they suffered no reduction in fecundity the following year. Recruitment of a female's offspring into the breeding population was generally independent of her mating status. Fitness costs of being mated to a polygynous male were only apparent in one year of the study, during which females mated to polygynous males had higher over-winter mortality than those mated to monogamous males. That same year, young raised by polygynous males were only one-third as likely to survive to reproductive maturity (as inferred by returns) as those raised by monogamous males. A male's mating status had no effect on his own survivorship. A male's mating status did not necessarily reflect his contributions to raising nestlings, which may partially explain why monogamously and polygynously mated females had equal fitness. At 35 nests the proportion of food deliveries brought by individual males varied from 0 to 75%; on average, males brought fewer than 30% of all food deliveries. Yet parental care by polygynous males was no less than that of monogamous males, at least at the nests of their primary females. Secondary females tended to receive less male assistance during the nestling stage, but their reproductive success was indistinguishable from that of primary females. Females feeding young without male assistance made as many food deliveries/h as did pairs in which males brought at least 30% of all food deliveries. Unassisted females did not suffer diminished fledging success or produce smaller fledglings. The benefits of polygyny for male Savannah sparrows are clear: polygynous males recruit more surviving offspring into the breeding population than monogamous males. The fitness of females, on the other hand, appears to be unaffected by whether their mate was monogamous or polygynous except in occasional years. Polygyny may be maintained in this population by the constraints of a female-biased sex ratio, the inability of females to predict a male's paternal care based on his morphology or behavior, the poor correlation between a male's mating status and his assistance at the nest, and inconsistent natural selection against mating with a polygynous male. Correspondence to: N.T. Wheelwright     

Female-enhanced male competition determines the first mate and principal sire in the spider Linyphia litigiosa (Linyphiidae)

Summary Two to five days before sexual maturation, female sierra dome spiders (Linyphia litigiosa: Linyphiidae) undergo a transformation in their behavior toward males that visit their webs. During this latter part of their penultimate instar, females change from consistently positioning themselves far away from males to actively maintaining close proximity, reactions I call avoidant and associative behavior, respectively. Consistent associative behavior ceases after the female's first mating and thus is limited to soon-to-mature penultimate females. When a mate-seeking male fords an associative female, he attempts to guard her until she matures; this is often a multi-day affair. In contrast, males guard immature avoidant and mature mated females for only a single day. This dichotomy in male guarding times can be understood by the fact that associative behavior signals that the female will soon develop peak reproductive value. Upon completion of their final molt, 98% of females immediately mate with the current guarding male. Secondary suitors are not as likely to achieve mating. Moreover, first mates father 1.8 times more offspring, on average, than secondary mates. Whenever they meet on any female's web, males fight until one of the contestants withdraws. Fights typically are intensive, occasionally deadly, and often result in usurpation of the web by the newly arriving male. Larger males win more fights, but other qualities (e.g., vigor and persistence) appear to be important when contestants differ by less than 10–20% in body weight. Prolonged (i.e., multi-day) guarding of associative females enhances the intrasexual selection process by ensuring that every male that arrives at the web finds it already guarded. Therefore every male that finds the web becomes a participant in a series of male-male conflicts and web usurpations which span the period between the resident female's commencement of associative behavior and her sexual maturation. Since unforced male departures from the webs of associative females are rare, victors are retained on the web until they themselves lose a fight. This facilitates a steady increase in the fighting ability of sequential guards throughout the associative period, up until female maturation and mating. On my study site, first mates represented the final winners in a combative sorting process based on a minimum average of 2 fights; they were heavier and larger than secondary mates and randomly sampled males. The combination of (1) associative behavior by nearly mature females, (2) high mating propensity of newly mature females, and (3) first male sperm priority, constitutes a system whereby females enhance male-male competition and boost the expected fighting prowess of the principal sire of their progeny. Since males appear to make no material contribution toward progeny, the female's behavior probably functions to improve the genetic constitution of the offspring. In addition, the timing of associative behavior may limit prolonged guarding by food-stealing males to a period (1) encompassing the female's pre-molt fast and (2) before the heavy yolking of eggs, thereby ameliorating the nutritional costs of intrasexual selection.