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.     

A female preference for experienced males in the almond moth, Cadra cautella

Male mating status can affect female reproductive output if male ejaculate investment declines over consecutive matings. Accordingly, females are predicted to mate preferentially with virgin males. In mildly polyandrous lepidopterans, female fitness is less affected by reduced male investment than in more polyandrous species, and so the predictions for female mating preferences are less clear. We examined female mating preferences in the mildly polyandrous almond moth, Cadra cautella, in which ejaculate size does not affect female reproductive output. First, we allowed females to mate with virgin or once-mated males, in which the males were presented individually or simultaneously. We recorded the latency to mating and, in the case of the simultaneously presented trials, the identity of the successful, copulating male. We found that females mated more frequently with mated males (when simultaneously presented with both males), yet females did not differ in the time taken to initiate copulation with any male. We further examined if this mated male advantage was due to differential mate detection or locomotory behaviour of the male treatments. We tested the ability of virgin and mated males to locate a receptive female within a wind tunnel using long-distance pheromone cues and recorded their activity budget. We found no difference in the ability of mated or virgin males to locate or approach a receptive female, or in their activity levels. These data suggest a female preference for mated males in this species, a preference that may minimise other potential costs of mating.     

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.     

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     

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.     

Space use in territorial amberwing dragonflies: are residents female maximizers or neighbor minimizers?

Residents of mating territories interact with different categories of conspecifics: females, nonneighbor males, and neighbor males. Interaction with these different types of conspecifics is likely to have different costs and benefits; for example, interactions with females will be beneficial, while interactions with neighbors are more likely to be costly. In this study, we investigated patterns of intrusions and space use in territorial male amberwing dragonflies (Perithemis tenera) to test the idea that residents will adjust their use of space to maximize their beneficial interactions with conspecifics while minimizing their costly interactions with conspecifics. Because territories were arranged linearly around the edge of a pond, each resident had two neighbors, one of which was often closer to the focal resident than the other. Residents experienced more intrusions by neighbors and fewer intrusions by females on the side of their closer neighbor. Residents generally perched on the side of their territory that experienced the fewest intrusions by neighbors and the most intrusions by females, but the pattern was more strongly related to neighbor intrusions than female intrusions. Subsequent to pursuits of neighbors and females, residents tended to shift their perches away from where they pursued neighbors but toward where they pursued females. Nonneighbor intrusions were not affected by neighbor proximity, nor did residents adjust their space use in response to nonneighbor intrusions. Our results suggest that residents do adjust their space use in response to intrusions by conspecifics, that their adjustment depends on the type of conspecific that intruded, and that residents may be using a simple decision rule such as "move away from male intrusions, move closer to female intrusions" to adjust their within-territory space use.Communicated by D. Gwynne     

Experience counts: females favor multiply mated males over chemically endowed virgins in a moth (<Emphasis Type="Italic">Utetheisa ornatrix</Emphasis>)

Determining the factors that affect male mating success is essential to understanding how sexual selection operates, including explanations of the adaptive value of female preferences and how variation in male traits is maintained in a population. Although females may appear to choose males based on a single parameter, female mate choice is often a complex series of assessments of male quality that can only be revealed through manipulation of multiple male traits. In the moth Utetheisa ornatrix (Lepidoptera: Arctiidae), females have been shown to judge males primarily on their production of a courtship pheromone, hydroxydanaidal, derived from defensive chemicals acquired as larvae. Recent work, however, suggested that other factors, including prior mating experience by males, may also influence the outcome of precopulatory interactions with females. I ran mating trials with one female and two males to determine whether there were any differences in male mating success based on their prior exposure to females, mating experience, and time between matings. Previously mated males were favored over virgins when both males lacked the pheromone, but courting experience and mating interval did not explain these differences in male mating success. Furthermore, multiply mated males lacking the pheromone were favored over virgin males that produced the pheromone, thus reversing the commonly observed trend of female precopulatory bias towards males with higher levels of the pheromone. These results demonstrate that males with mating experience can secure copulations despite deficiencies in the pheromone, and I provide possible mechanisms and discuss their implications regarding sexual selection.     

Female choice of large males in the treefrog Hyla chrysoscelis: the importance of identifying the scale of choice

Summary In this study, I detected the presence of female choice for larger males in the treefrog Hyla chrysoscelis. Mated males were larger than unmated males at the scales females could have assessed males: local groups (males found within 2 meters of a mated pair) and the nightly chorus. In addition, females were observed to initiate amplexus with the larger males in local groups. Mated males were larger than unmated males for two of the four seasons studied. Seasonal mating success was also analyzed with a multiple regression model that included size and chorus attendance (nights spent at the breeding site). The partial selection coefficients, which represent the relative magnitude of directional selection, were significant for size in only one season and for chorus attendance in all four seasons. Therefore, there are two possible advantages to being a large male: increased likelihood of obtaining a mate due to female preference, and increased likelihood of mating even if no female preference because of a greater number of opportunities to obtain a mating if matings occurred at random.     

Positive association between social and extra-pair mating in a polygynous songbird, the dickcissel (Spiza americana)

In polygynous species, males appear to gain additional offspring by pairing with multiple females simultaneously. However, this may not be true if some females copulate outside of the social pair bond. Polygynous males could experience lower paternity because of trade-offs among gaining multiple social mates, guarding fertility with these mates, and pursuing extra-pair matings. Alternatively, polygynous males could simultaneously gain extra social mates and have high paternity, either because of female preferences or because of male competitive attributes. We tested four predictions stemming from these hypotheses in a facultatively polygynous songbird, the dickcissel (Spiza americana). Unlike most previous studies, we found that males with higher social mating success (harem size) also tended to have higher within-pair paternity and that the number of extra-pair young a male sired increased significantly with his social mating success. Females that paired with mated males were not more likely to produce extra-pair young. In contrast, extra-pair paternity was significantly lower in the nests of females whose nesting activity overlapped that of another female on the same territory. This pattern of mating was robust to differences in breeding density. Indeed, breeding density had no effect on either extra-pair mating or on the association between polygyny and paternity. Finally, nest survival increased with harem size. This result, combined with the positive association between polygyny and paternity, contributed to significantly higher realized reproductive success by polygynous male dickcissels.     

How reliable are behavioral cues for assessment of male mating status in polyterritorial wood warblers,Phylloscopus sibilatrix?

It has been suggested that polyterritoriality in birds, i.e. mated males defending two spatially separated territories, deceives females into accepting polygyny against their best interest. Mated males singing on secondary territories should make it difficult for new arriving females to assess the mating status of unmated and mated males advertising to females. However, there have been objections to the deception hypothesis, suggesting that differences in territorial behavior between males of different mating status may make correct assessment possible. Polyterritorial males frequently leave their secondary territory to visit the female in the primary territory, thereby revealing their mating status to females in search of mates. The aim of this study is to investigate how reliable behavioral cues are in assessing the mating status of males in polyterritorial wood warblers. Our study shows that singing activity of mated males on secondary territories and unmated males was similar in the morning, while there was a significant difference in the afternoon. Unmated males spent, on average, more time on their territories than mated males spent on their secondary territories. However, there was considerable variation in both unmated and mated males in the frequency in which they left their territories. For instance, unmated males left their territories quite frequently early in the season compared to later. Hence, females must be able to interpret singing behavior and a male leaving his territory differently depending on time of the season and time of the day in order to correctly assess the mating status of advertising males. Estimating the increase in probability of finding an unmated male by using behavioral cues showed that females could increase the probability of finding an unmated male compared to random choice with respect to mating status. The uncertainty was, however, still considerable. The most important factor affecting the probability of finding an unmated male was the proportion of mated males on secondary territories compared to unmated males. Our study suggests that presence on a territory is not a reliable cue for the assessment of male mating status in polyterritorial wood warblers.     

The effects of mating system on male mate choice in a coral reef fish

Summary We show how mate limitation appears to be critical in determining whether or not males exercise mate choice among available females. Thalassoma bifasciatum is a Caribbean reef fish with two distinct mating patterns: group-spawning and pair-spawning. In both mating systems, female fecundity is variable and size dependent, and female availability is high. However, sperm competition among group-spawning males apparently limits the number of effective matings in which a male may engage, whereas territorial pair-spawning males have little or no such limitation. Group-spawning males should be discriminating in their choice of mates and our data confirm this: there is strong evidence for assortative mating in group-spawns, with more large males joining in mating groups around large females. In contrast, pair-spawning males show no indication of mate preferences, and spawn with all females who arrive at their territories.     

Male remating and female fitness in the wolf spider Pardosa astrigera: the role of male mating history

Although the effects of male mating history on female reproductive output and longevity have been studied in insects, few such studies have been carried out in spiders. In a mating system in which females are monandrous while males are polygynous, females may incur the risk by mating with successful males that have experienced consecutive matings and suffer from the possible depletion of sperm and/or associated ejaculates. Here, we examine the effects of male mating history on male courtship and copulation duration, female reproductive fitness, and female adult longevity of the wolf spider, Pardosa astrigera. Results indicated that male mating frequency had little effect on their subsequent copulation success, and of 35 males tested, about half of the males were able to copulate with five virgin females successively at an interval of 24 h. Male mating history had little effect on their courtship duration. However, male mating history significantly affected male copulation duration, female adult longevity, and reproductive output. Males that mated more frequently copulated longer and more likely failed to cause their mates to produce a clutch, although there was no significant difference in the number of eggs laid and the number of eggs hatched regardless of the first clutch or the second one. Multiple mating of male P. astrigera resulted in significant reduction in female adult longevity. Our results indicate that monandrous females mating with multiple-mated males may incur substantial fitness costs.     

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     

Genetic reconstruction of breeding patterns in gundis (Rodentia: Ctenodactylidae)

Current mating system theory predicts that the number of females breeding in a group will depend on the number of females in the group and the accessibility of unrelated males, whereas the number of males breeding in a group will depend on the ability of males to control access to reproductive females. By combining information on group composition with genetic data, I determined whether breeding patterns in a rock-dwelling rodent, Ctenodactylus gundi, were concordant with these expectations. C. gundi breeding patterns varied from facultative monogamy to uni-male polygyny to multi-male polygyny. The number of reproductive individuals of each sex in a group increased with group size. Whereas communal breeding among related females tended to increase female reproductive success, males breeding in the same group were unrelated to other group members and seemed to compete over access to matings. While some males were assigned offspring from neighboring social groups, most group-living males successfully monopolized the reproduction of females within their group. There was no evidence that females had multiply sired litters, although some bred with alternative males in separate breeding attempts. Although numerous individuals were not assigned as parents or offspring, genetic information enabled me to determine that most unassigned individuals were philopatric group members, whereas only a few were unrelated immigrants into their current social group. Together, these results provide evidence that C. gundi social groups represent fairly distinct reproductive units whose breeding patterns are dependent on group size and composition in accordance with theoretical predictions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mating system shift in a pronghorn population

Summary At the National Bison Range (western Montana, USA), pronghorn (Antilocapra american) maintained a territorial mating system from as early as 1965 through 1978. Preliminary observations in 1981 suggested that the mating system had changed. Data from the ruts, 1982–1984 revealed a progressive decay in territoriality. In this paper, data from the territorial years 1969–1978 are contrasted with data from the decay years 1982–1984, with results as follow: 1. In 1982–84, fewer territories were defended than in 1969–78. This was attributable to a smaller proportion of males defending territories in 1982–84, not to a smaller number of males. 2. In 1982–84, most territory owners either abandoned their territories early in ruts, or lost control of females on them following frequent, persistent intrusions by non-territorial males. Abandonment and loss of control did not occur in 1969–78. 3. In 1982–84, territorial males that maintained control of females on their territories did so by shrinking their zones of defense to small areas around female groups. 4. In 1982–84, following the disruption or severe disturbance of all territories, many females left territories, and mated elsewhere, with non-territorial males. In 1969–78, most females remained on territories throughout rut, and mated with territory owners. —The mating system change followed catastrophic winter mortality, 1978–79, that removed 75% of the males, including all males older than 5 years, and all male fawns, from the population. In 1982–84, the number of males present was not different from the number of males in 1969–1978, but the frequency distribution of male ages was strongly shifted toward younger ages. The small number of older males, 1982–84, likely resulted in smaller proportions of males initially defending territories, and in less effective territory defense. When females then clustered on the few territories where defense was at first successful, they attracted large numbers of non-territorial males. The resulting high rates of raids on these territories, coupled with reduced defense radii by territorial males, allowed females only 12% reclining time (summer percentage was 39%). This increased energy cost, plus an apparently greater risk of injury on weakly defended territories, appeared to prompt many females to seek calmer matings elsewhere. Also, if female pronghorn practiced mate selection based upon horn or body size, they may have reduced their efforts to remain on territories in 1982–84. Males from 1969–78 were larger than males from 1982–84, and showed greater variance in horn size. At least two conditions appear to influence the tendency of males to be territorial. First, males must be at least three years old before they attempt to defend a territory. Second, the declining proportion of males defending territories, 1982–84, that coincided with an increasing number of males three years and older, suggests that males also decide whether or not to attempt territory defense based upon the frequency of territorial defense in the population.     

Protandry and mate assessment in the wartbiter Decticus verrucivorus (Orthoptera : Tettigoniidae)

Summary Protandry, or early male emergence, is prevalent in the majority of insects. There are several explanations, both adaptive and incidental for this widespread phenomenon. Here I report the occurrence of protandry in the wartbiter, Decticus verrucivorus, and argue that the explanation for the evolution of protandry in this species is the result of selection acting on males in relation to sperm competition. It has previously been shown that sperm mixing occurs in this species, leading to a reduction in confidence of paternity with number of matings. Emerging early and thereby having a higher probability of mating with virgin females benefits males in two ways: both through a 100% assurance of paternity and because female egglaying rate decreases over time. A singly mated female can lay up to 30% of her lifetime egg production during her first refractory period, during which time the eggs are exclusively fertilized by the first male. Wartbiter males seem also to be able to assess female mating status and transfer larger spermatophores when mating with virgin females than when mating with already mated females. This holds true both for previously mated and virgin males. Thus, it seems that male wartbiters allocate their resources differentially depending on female quality.     

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.     

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     

Sperm precedence and sperm storage in multiply mated red flour beetles

In insects, the last male to mate with a female often gains access to a disproportionate number of subsequent fertilizations. This study examined last-male sperm precedence patterns in doubly and triply mated Tribolium castaneum females. Sperm storage processes were investigated by measuring the quantity of sperm stored within the female spermatheca following single, double, and triple matings. Both doubly mated and triply mated females exhibited high last-male sperm precedence for progeny produced during the first 48 h following the last mating, with females in both groups exhibiting parallel declines in sperm precedence 1 and 2 weeks later. The number of sperm stored by females increased by 33% between singly mated and doubly mated females, indicating that the spermatheca is filled to only two-thirds capacity following insemination by the first male. Based on the proportion of stored sperm from first and second matings, we tested predictions about sperm precedence values based on models of random sperm mixing. High initial last-male sperm precedence strongly supports stratification of last-male sperm. By 1–2 weeks after double matings, sperm precedence declined to levels indistinguishable from values expected under random mixing. These results provide insight into mechanisms of sperm storage and utilization in this species. Received: 20 August 1997 / Accepted after revision: 24 May 1998     

Polyandrous mating in treetops: how male competition and female choice interact to determine an unusual carnivore mating system

The diversity of mammalian mating systems is primarily shaped by sex-specific reproductive strategies. In the present study, we explored determinants and consequences of a unique mating system exhibited by fossas (Cryptoprocta ferox), the largest Malagasy carnivore, where females mate polyandrously on traditional mating trees, and males exhibit intrasexual size dimorphism. Males face both contest and scramble competition, and inter-sexual size dimorphism can be pronounced, but its magnitude depends on the male morph. Using a continuous behavioral observation of six estrous females over 4 years, we investigated correlates of male contest competition and female choice based on 316 copulations. Furthermore, we assessed correlates of male scramble competition based on testes size and movement data obtained from GPS tracking. We found that females dominated males regardless of their smaller size and that females actively solicited copulations. Heavy males had highest mating success during the female’s peak mating activity, but were discriminated against afterwards. Female choice and male–male competition thus converged to generate a mating advantage for heavier males. Our results suggest that females actively seek polyandrous matings, presumably for indirect genetic benefits. Since body mass is the major determinant of male mating success and is at the same time dependent on the degree of sociality and associated hunting mode of the respective male morph, a male’s feeding ecology is likely to influence its reproductive tactic. A combination of benefits from female polyandry and the consequences of different subsistence strategies may thus ultimately explain this unusual mating system.