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.     

Temporal patterns in reproduction may explain variationin mating frequencies in the green-veined white butterfly Pieris napi

There is genetic variation in the female mating rate in the green-veined white butterfly (Pieris napi), and females benefit from male ejaculates that contain both sperm and accessory gland substances. Although polyandry corresponds to higher lifetime fecundity than monandry, some females abstain from remating irrespective of the number of available mates. Explaining genetic variation in mating rates requires that monandrous females perform better than polyandrous ones under some conditions. We experimentally explored the reproductive performance of females either with a low or high intrinsic mating rate by allowing them to mate, feed, and lay eggs freely in a laboratory. Individual females followed different life histories: during the early days of reproduction, females with a low mating rate produced more eggs than females with a high mating rate. Hence, refraining from the benefits of multiple mating may be beneficial, if the time for reproduction is limited, or other female traits associated with polyandry are traded off against longevity. Given the day length of 10 h, a model shows that even if polyandrous females enjoy higher lifetime reproductive success, changeable and unpredictable weather will favor monandry if each period of suitable weather lasts, on average, less than 5 days. Thus, a combination of life history cost and unpredictability of fitness may explain the maintenance of monandry in the wild. Our results are also consistent with the observation that frequency of monandry increases with latitude.     

Female encounter rate and the calling behavior and mating propensity of male Requena verticalis (Orthoptera: Tettigoniidae)

Mating effort, the energy exerted in finding and persuading a member of the opposite sex to mate, may be influenced by how frequently potential mates are encountered. Specifically, males that frequently encounter females may reduce calling effort and be less eager to mate than males that infrequently encounter females. An experiment was set up to test this hypothesis, using the tettigoniid Requena verticalis. We examined the song structure, calling activity and mating propensity of individual males exposed to one of five different encounter rates with virgin females. Song structure and calling effort were significantly altered by an encounter with a female. After an encounter, males significantly increased chirp rate and decreased variability in interchirp interval. Encounters also stimulated a male to call and to continue to call for up to two hours. The elapsed time since mating affected mating propensity but not calling activity. Mating propensity asymptotically increased to reach a maximum by day 17 since last mating. However, neither the frequency of encounters, nor the number of previous encounters experienced by a male, influenced calling activity or the propensity of a male to mate. The significance of changes in song structure and calling activity following an encounter, and of increasing male mating propensity over time, are discussed. Correspondence to: G.R. Allen     

Food or sex—males and females in a sex role reversed pipefish have different interests

In a sex role reversed pipefish, Syngnathus typhle, we found that basic life history allocations were directly influenced by sexual selection. We investigated time allocation to foraging and mating, respectively, in a choice experiment, giving males and females, of small or large body size, a choice between food and a potential partner. We found that males were more interested in foraging than mating, i.e., were more frequently observed in front of the food than in front of the partner, whereas females were more interested in the potential partner. This reflects sexual selection operating differently on the two sexes, as males and females are relatively similar in other life history traits, such as growth, mortality, age of maturity, dispersal, and parental expenditure. Moreover, large individuals allocated more time to mating activities, small to feeding. Individuals more interested in mating compared to food were subsequently more critical when given a choice between a large (high-quality) and a small (low-quality) partner, whereas individuals more interested in food were not selective. These findings are consistent with our predictions: sex-role reversed males can be relatively sure of achieving one or more matings, and should allocate more time to feeding and, hence, to parental investment, growth and/or future reproduction. Females, on the other hand, have more uncertain mating prospects and should allocate time to imminent reproductive activities, thereby foregoing other life history traits such as growth and future egg production. By this, they also sacrifice future fecundity and attractiveness.     

Caste determination and differential diapause within the first brood of Halictus rubicundus in New York (Hymenoptera: Halictidae)

Summary The partially bivoltine, primitively eusocial sweat bee Halictus rubicundus produces two female castes, gynes and non-gynes, in its first brood in New York. Castes in this brood differentiate within the first few days of adult life, with gynes leaving the population to overwinter as early as mid-June (non-gynes further differentiate into replacement queen and worker subcastes, with older females typically dominant). Analysis of possible mechanisms of caste determination reveals that although gynes average significantly larger than non-gynes within the first brood, this appears largely due to a late mean emergence data coupled with an increase in the size of emerging females over the course of brood emergence, rather than a causal relationship. A strong correspondence between male abundance (relative to newly-emerged females) and the pattern of gyne production, along with data from dissections, suggests that females that mate when young become diapausing gynes, while those that do not mate promptly become non-gynes and do not diapause even though many mate later. Although alternatives to this simple mechanism cannot be ruled out entirely, it nevertheless offers profound implications for theoretical and empirical understanding of the evolutionary origins of the worker caste.     

Audience effect alters male but not female mating preferences

Males often face strong mating competition by neighboring males in their social environment. A recent study by Plath et al. (Anim Behav 75:21–29, 2008a) has demonstrated that the visual presence of a male competitor (i.e., an audience male) affects the expression of male mating preferences in a poeciliid fish (Poecilia mexicana) with a weaker expression of mating preferences when an audience male observed the focal male. This may be a tactic to reduce sperm competition, since surrounding males likely share intrinsic preferences for female traits or copy mate choice decisions. Here, we examined the hypothesis that a same-sex audience would affect female mate preferences less than male mating preferences. Our hypothesis was based on the assumptions that (1) competition for mates in a fashion that would be comparable in strength to sperm competition or overt male–male aggression is absent among Poecilia females, and (2) P. mexicana females typically form female-biased shoals, such that almost any female mate choice in nature occurs in front of a female audience. Poecilia females (P. mexicana, surface and cave form, and the closely related gynogenetic Poecilia formosa) were given a choice between a large and a small male, and the tests were repeated while a conspecific, a heterospecific, or no audience female (control) was presented. Females spent more time in the neutral zone and, thus, less time near the males during the second part of a trial when an audience was presented, but—consistent with predictions—females showed only slightly weaker expression of mate preferences during the second part of the tests. This decline was not specific to the treatment involving an audience and was significantly weaker than the effect seen in the male sex.     

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.     

Female sex pheromone in immature insect males—a case of pre-emergence chemical mimicry?

Sexual selection by competition for mates is a formidable force that has led to extraordinary adaptations in males. Here we present results suggesting a novel case of pheromone mimicry in males of Lariophagus distinguendus, a parasitic wasp of beetle larvae that develop in stored grain. Females of L. distinguendus produce a pheromone even before they emerge from a grain. Males are attracted to the parasitised grain and wait for females to emerge. Males emerging later than others are under enormous selection pressure since females mate only once. We show evidence that developing males fool their earlier emerging competitors by mimicking the female pheromone. Males exposed to pupae of either sex exhibit typical courtship behaviour. Searching males are not only arrested by grains containing developing females but spend as much time on grains containing developing males. Hence, by distracting their competitors away from receptive females late males may increase their own chance to mate with these females. After emergence, males decompose the active compounds within 32 h probably to decrease molestation during their own search for mates. Chemical analyses of active pheromone extracts and bioassays using fractions demonstrate that the active compounds are among the cuticular hydrocarbons.     

Repeatable female preferences, mating order and mating success in the poeciliid fish, Heterandria formosa

Sexual selection via female choice can afford preferred males comparably higher mating success than those males that lack preferred traits. In addition, many models of sexual selection assume that both male traits and female preferences are heritable. In this study we test whether females of the poeciliid fish, Heterandria formosa, have repeatable pre-copulatory preferences for larger males. We also test whether female pre-copulatory preferences are always reliable indicators of male mating success. When given a choice between a large and a small male, females prefer larger males, and the repeatability of this preference is high. Although there are no overall differences in male mating success between large and small males, large males have a higher mating success when they are the first to mate than when they are the second to mate. Likewise, preferred males also have higher mating success when they are the first to mate than when they mate second. Therefore, the repeatable female preferences observed in this study only predict male mating success when the preferred male mates first. These results illustrate that even significantly repeatable female preferences do not translate into male mating success, which is an assumption of many examinations of the importance of female choice in sexual selection.     

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.     

Comparative life histories of three species of planktonic calanoid copepods in Dabob Bay,Washington

The life history patterns of Calanus marshallae Frost, C. pacificus Brodsky, and Metridia lucens Boeck were determined in Dabob Bay, Washington, USA, during 1973 and October 1981–September 1982. C. marshallae emerged from diapause and moulted to adults in January–February. One major generation was observed, having been produced mainly during early to mid-March. Most surviving individuals spawned in March, arrested development at the C5 stage, and were in diapause by late May. However, some individuals developed to adults by late April and produced a very minor second generation. C. pacificus emerged from diapause and moulted to adults in February–March. The first generation produced during the spring lagged slightly behind the C. marshallae generation. C. pacificus produced two additional generations, one in late spring and one in the fall. The production of the three generations coincided with or closely followed phytoplankton blooms. Some C. pacificus arrested development at the C5 stage and entered diapause during the summer, but the majority of the population did not do so until fall. M. lucens did not appear to enter a diapause state. The fall and winter population was chiefly adult females which mostly remained at depth and were reproductively immature. Nevertheless, naupliar M. lucens were found on all sampling dates, indicating that reproduction never ceased as it did for the two Calanus species. M. lucens produced generations in late winter/early spring, late spring, and late summer/early fall. Interspecific comparisons between the life histories observed in Dabob Bay and intraspecific comparisons between the life histories in Dabob Bay and other locations are made. The advantages or disadvantages conferred to the copepods by their differing life histories are also discussed.     

Variation of life history traits and mating patterns in female langur monkeys (Semnopithecus entellus)

To determine nutritional and social influences on life history traits and mating behavior in female langur monkeys, new long-term data for a feral population living in multi-male groups under poor nutritional conditions are presented and compared with published long-term data for the same species living in one-male groups under excellent nutritional conditions. Under poor nutritional conditions, conceptions were confined to 5 months per year, coinciding with the period of the highest mating activity. Age at first parturition, gestation periods, lactation periods, and interbirth intervals were all significantly increased resulting in a more than 50% reduced reproductive rate under poor conditions. The pattern of sexual behavior during gestation was influenced by neither nutritional nor social conditions but the frequency was higher in multi-male groups. Furthermore, estrus length was significantly increased in multi-male groups where females tended to mate with as many resident males as available. Both phenomena, together with a high percentage of sexual behavior occurring outside the mid-cycle estrus, are interpreted in the light of paternity confusion in multi-male groups in a species where infanticide by males is regularly observed. The extreme variation in life history traits and mating patterns disclosed here in one species suggests that future cross-species comparisons should strictly select datasets based on local ecological and social conditions.     

Mate with the young, kill the old: reversed sexual cannibalism and male mate choice in the spider Micaria sociabilis (Araneae: Gnaphosidae)

Female mate choice is regarded as a strong selective force that significantly affects male mating success. In extreme cases, mate rejection can result in sexual cannibalism. However, males may choose between their partners as well. The killing of potential female mates, i.e. reversed form of sexual cannibalism, may be related to male mate choice. We examined male mate choice in the spider Micaria sociabilis, focusing on the roles of female mating status (virgin/mated), size and age. Reversed cannibalism reached its highest frequency in the period of generation overlap, i.e. when young males from the summer generation met old(er) females from the spring generation. These results suggest discrimination against old(er) females. The frequency of cannibalism was not affected by female mating status or female size. However, larger males from the summer generation were more cannibalistic than smaller males from the spring generation. We conclude that reversed sexual cannibalism might be an adaptive mate choice mechanism and can be explained in the context of the aggressive spillover hypothesis.     

Influence of male harassment and female competition on female feeding behaviour in a sexual–asexual mating complex of mollies (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, <Emphasis Type="Italic">P. formosa</Emphasis>)

Differential interests between the sexes regarding the number of copulations can result in sexual harassment. Hence, females may have less time available for foraging. Male sexual harassment often leads to fitness reduction in females. We used the mating complex of the bisexual fish Poecilia mexicana and the co-occurring all-female Poecilia formosa to study sexual harassment and its incurred cost on female feeding efficiency. P. formosa is a sperm-dependent parthenogen that requires mating with host males to induce embryogenesis, but the male genes are not used. We therefore predicted P. mexicana males to prefer conspecific females. Hence, costs of male sexual harassment should not occur in unisexuals. While P. formosa are at a disadvantage compared to P. mexicana females due to male mate choice (leading to sperm limitation), this could be traded-off by suffering less from sexual harassment. In our experiment, we found males to direct significantly more pre-copulatory mating behaviour towards conspecific females, whereas actual mating attempts did not differ between species. Contrary to our prediction, both types of females started feeding later and spent less time feeding in the presence of a male partner compared to the time spent feeding with another female, suggesting that females of both species suffer from male harassment. The focal females' feeding time declined with increasing body size of the female competitor, and the same pattern was found when a male was present. We discuss that—besides sexual harassment—other factors such as food competition and female mate choice may affect female feeding efficiency.     

Sex pheromone composition and reproductive isolation in two Busseola species (Lepidoptera: Noctuidae) in Kenya

Closely related species provide an interesting and useful model to understand mate communication diversification. Pre-mating isolation is the result of selection processes and is achieved by utilization of different sex pheromones, but also by different ecological and life traits such as geographic distribution, host-plant specialization and allochrony of sexual behavior. Here, we report sex pheromone identifications and pre-mating isolation of two closely related species of stemborers: Busseola segeta and the yet undescribed Busseola nov. sp., developing on different host-plants and in different geographical locations in Kenya. GC–MS analyses showed that the two species produced the same pheromone components, but in slight different ratios. The respective synthetic pheromone mixtures tested in the field were attractive for males of each species. The low inter-specific variation in the pheromone mixture would allow possible interbreeding in case of accidental introduction of both species in the same environment. Under laboratory conditions, allochrony of the mating period is total and might prevent interbreeding if confirmed in natural conditions. This point would ensure the reproductive isolation between the two species in case of modifications of ecological factors. This study and the chemical structures of the identified pheromone components clearly demonstrate that these Busseola species are closely related although they differ in morphology.     

Multiple signals in the palmate newt: ornaments help when courting

There is increasing evidence that female mate choice is often based on the assessment of multiple male traits, involving both morphology and behavior. We investigated female mate choice for multiple male traits in the palmate newt, Lissotriton helveticus, including male tail filament length, hind foot web size, crest development, body size, ventral coloration, and courtship display activity. Observations of courtship display in the field revealed that females spent more time in front of males with longer tail filaments. Laboratory experiments revealed a more detailed relationship between filament length and courtship display. We found that females took more sperm masses from males with both longer filaments and greater display activity. Experimental shortening of the tail filament length substantially decreased the number of male sperm masses transferred. However, when we experimentally reversed relative filament length between two males in mating trials, male mating success was explained by courtship activity and not by filament length. Our results show that female palmate newts value multiple traits during mate choice, including both morphological ornaments and reproductive behaviors in males. Our results further suggest that, when filament length is below a certain threshold, females may value the information content of courtship activity over that of filament length.     

Mating behavior of the marine copepodOithona davisae

Oithona davisae Ferrari and Orsi were collected from the innermost region of Tokyo Bay, Japan, in 1980 and 1981. The mating behavior of this marine cyclopoid copepod consists of several steps, starting with the paddling of the male in random search of a mate. This behavior is followed by a spiraling movement in pursuance of a mate. Next is the copulatory grasp during which the male grasps the fourth swimming legs of the female partner by means of his first antennae. Whilst in this position, the male's urosome vibrates to allow the spermatophores to extrude from his genital openings. The mating behavior then culminates in the spermatophore transfer. Males do not grasp the uro-some or caudal setae of the mating partner before proper copulatory grasp. The specialized setae of the female's fourth legs may help the male to grasp her legs firmly. Spiraling occurs when the male approaches or traverses the trail of a female that is ready to copulate and that presumably emits a sex-attractant pheromone. The turning radius reduces gradually from more than 1 mm to ca. 0.25 mm as the male approaches the mate female. Females may register spiraling as a mate (male)-approaching signal. Spiraling may lead the male to locate a pheromone source more accurately, and to promote diffusion of the pheromone to prevent other males from pursuing the source. This swimming strategy can increase the copulatory chance of mature virgin females.     

The evolutionary consequences of mate copying on male traits

In some species, a female's mating preference can be influenced by the matings she observes. Mate copying occurs when a female alters her mating preference in favor of the type of males she has observed mating with other females. Here I present a model that explores the consequences of mate copying on the evolution of male traits. In contrast to previous work, I show that mate copying can have diverse evolutionary consequences. Mate copying can cause (positive or negative) directional selection on male traits or (positive or negative) frequency-dependent selection on male traits. The type of selection generated by mate copying depends on the details of how females are influenced by the matings that they observe. I discuss my results in relation to previous theoretical work that posits that mate copying can only hamper the spread of novel male traits.     

Mate attraction by females in a sexually cannibalistic praying mantis

We studied mate attraction by females of the praying mantid, Tenodera aridifolia sinensis, testing honest signaling of mate availability versus deceptive signaling to attract males for sexual cannibalism. We experimentally varied female diet and mating history and measured the rate of attraction of a wild population of males to caged females. Honest signaling theory predicts that virgin females will attract males at the greatest rate whereas deceptive signaling predicts that hungry females (which are more likely to cannibalize males) will attract more males, particularly among non-virgin females. Our results show that hungry females did not attract more males than well-fed females. Indeed, the opposite was true: hungry females attracted significantly fewer males. Moreover, hungry females were no more likely than well-fed females to attract males subsequent to mating, and mated females attracted males at a lower rate than did virgin females. We also observed female T. aridifolia sinensis and male Mantis religiosa arriving at the caged females and we discuss the significance of these observations. The results refute the hypothesis of deceptive signaling and show that mate attraction signals of female T. aridifolia sinensis are honest indicators of female mate availability and a lower risk of sexual cannibalism.     

Age-related female mating decisions are condition dependent in wolf spiders

Female mating behaviors are known to be sensitive to a variety of individual factors both external and internal to a female; however, mating decisions are likely due to a suite of interacting factors. By independently manipulating female and male diet in the wolf spider Rabidosa rabida and testing females across age groups, we demonstrate that, in addition to its independent effect, female nutritional condition interacts with female age to influence female mating behavior. Overall, high-quantity diet (HD) females were more likely to mate than low-quantity diet (LD) females. Within the LD females, older individuals were more likely to mate than younger individuals, while within HD females, mating probabilities were equal across females of different age classes. With respect to mate choice, only female age influenced the likelihood of mating based on male diet. Young females were choosier as they were more likely to mate with HD males than LD males; in contrast, older females were equally likely to copulate with males of each diet treatment. In addition, the likelihood of pre-sexual cannibalism was dependent on both female and male diet. High-quantity diet females were more likely to cannibalize than LD females, and attacks were directed towards LD males most often. We discuss our results in terms of costs versus benefits of female mate choice.