Female mate preferences on high‐dimensional shape variation for male species recognition traits

Females in many animal species must discriminate between conspecific and heterospecific males when choosing mates. Such mating preferences that discriminate against heterospecifics may inadvertently also affect the mating success of conspecific males, particularly those with more extreme phenotypes. From this expectation, we hypothesized that female mate choice should cause Enallagma females (Odonata: Coenagrionidae) to discriminate against conspecific males with more extreme phenotypes of the claspers males use to grasp females while mating – the main feature of species mate recognition in these species. To test this, we compared cerci sizes and shapes between males that were captured while mating with females to males that were captured at the same time but not mating in three Enallagma species. In contrast to our hypothesis, we found only one of forty comparisons of shape variation that was consistent with females discriminating against males with more extreme cerci shapes. Instead, differences in cerci shape between mating and single males suggested that females displayed directional preferences on 1–4 aspects of cerci shape in two of the species in our samples. These results suggest that whereas some directional biases in mating based on cerci shape occur, the intraspecific phenotypic variation in male cerci size and shape is likely not large enough for females to express any significant incidental discrimination among conspecifics with more extreme shapes.     

Constraints on Size-assortative Mating in the Blister Beetle Tegrodera aloga (Coleoptera: Meloidae)

The mating system of Tegrodera aloga is similar to other blister beetles that have evolved sizeassortative mating in that males pass a cantharidin-rich spermatophore to their mates and females vary in size and fecundity. Despite this, previous studies found no assortative mating in this beetle. Results of this study suggest that nonassortative mating is not due to absolute constraints on mate choice. Males courted large females more frequently than small females, suggesting that males prefer big mates. Similarly, female choice is suggested by a large-male mating advantage in the absence of size-related male-male competition. In contrast to previous work, my results suggest that assortative mating may occur under certain conditions and may be due to large-phenotype mating advantages. The question remains, why does assortative mating occur only some of the time? One hypothesis is that assortative mating breaks down when sex ratios become male biased and males no longer discriminate between mates. However, although sex ratios can vary from day to day, assortative mating is not associated with periods when females outnumber males. Rather, the pattern appears to be associated with times of low overall population density. Hypotheses for density-dependent assortative mating are presented.     

Mate Choice by Chemical Cues in Western Redback (Plethodon vehiculum) and Dunn's (P. dunni) Salamanders

Western redback and Dunn's salamanders (Plethodon vehiculum and Plethodon dunni, respectively) can distinguish between potential mates by using chemical cues. In laboratory choice tests, adult males of both species showed significant discrimination between chemical cues of gravid females over non-gravid females of equal body size. Furthermore, males of both species differentiated the odour of paired gravid females that differed by ? 5 mm snout-vent length (SVL). Given that clutch size is related to female body size in these species, adult males may be able to distinguish between females via cues that signal potentially high female reproductive success. In choice tests, P. vehiculum females did not discriminate between two relatively large males that differed by ? 5 mm SVL. However, females of P. vehiculum did discriminate between two relatively small males that differed by the same amount. Apparently, P. vehiculum females ranked males by both absolute and relative body size using chemical cues. This pattern could reflect a female preference for large males or that females avoid mating with the smallest males.     

Male and Female Mate-Choice Decisions by Evarcha culicivora, An East African Jumping Spider

There has been a considerable recent interest in the criteria by which animals choose mates and in the extent to which mating systems tend to be based on mutual mate choice. In this study, we consider Evarcha culicivora, a salticid spider from East Africa. This species has some unusual characteristics, including active display by females as well as males, males that kill females more frequently than females kill males and wide intrasexual variation in body size. For females, larger males are especially dangerous. Here, we demonstrate, using two experimental designs (live‐mate choice and mount choice), that virgin males, virgin females and previously mated males prefer larger opposite‐sex individuals as potential mates, but mated females prefer smaller, safer males as potential mates.     

Mate discrimination in Littorina littorea (L.) and L. saxatilis (Olivi) (Mollusca:Prosobranchia)

The ability of males of Littorina littorea and L. saxatilis to discriminate between mates of different sex, species and size was examined. In partner choice experiments males of L. littorea had the possibility to initiate a copulation with either a female or a male. The males did not show a preference for either sex. There was therefore no evidence that they could determine the sex of a conspecific prior to copulation. The duration of intrasexual copulation was considerably shorter than for intersexual copulation, both in the field and in laboratory experiments. For the two species, intersexual copulations were far more frequent than intrasexual ones. This can partly be explained by the difference in copulation time.Few interspecific copulating pairs were found on the shore. This may reflect a low interspecific encounter rate rather than a mechanism of species recognition. On all of these occasions, however, the active male was of L. saxatilis. It is argued that selection against precopulatory species and sex recognition is a more likely explanation than an hypothesis that states that the required mutations for precopulatory mate identification has not yet occurred. L. littorea males copulated longer with large than with small females. Copulation time was short with parasitized females, which are sterile or of low fecundity. The allocation of mating effort by males is discussed.     

Seasonal Variation in Mate Choice of Photinus ignitus Fireflies

Mate choice by either sex may vary with changes in the associated costs and benefits, determined by factors such as the availability of potential mates and variation in mate quality. We examined seasonal variation in operational sex ratio, courtship behavior, spermatophore mass, egg count, and the relationship between morphological traits and mating success in Photinus ignitus fireflies to determine if mate choice in either sex varied with the availability and relative reproductive investment of fertilizable females and sexually active males. Successfully mating males had larger lanterns than unsuccessful males when the operational sex ratio was male‐biased. In addition, female responsiveness to male signals increased as the number of courting males decreased, and male spermatophore mass decreased with body size across the mating season. Successfully mating females had larger body mass than unsuccessful females. Female body mass predicted egg count and female rejection by males increased as the season progressed and female size decreased. These results suggest that both male and female P. ignitus exhibit mate choice, and that such choice is influenced by seasonal variation in the abundance and quality of potential mates.     

Seeking a Sex‐Specific Coolidge Effect in a Simultaneous Hermaphrodite

In polygamous mating systems, a capability to discriminate against familiar mates may be beneficial to both sexes. Polyandrous females, for instance, may enhance the odds of finding sires with optimal genetic compatibility or high genetic quality by mating with multiple different males; polygynous males, in addition, may more efficiently invest their limited ejaculates across multiple (rather than single) females. The Coolidge effect facilitates this kind of mate discrimination, as sexual motivation declines across consecutive copulations with a familiar partner but resurrects with a novel mate. In simultaneous hermaphrodites, we expect the Coolidge effect to show sex role‐dependent patterns and vary with previous sex‐specific mating activity. Using the promiscuous hermaphroditic sea slug Chelidonura sandrana, we investigated (1) whether sexual motivation indeed declines when repeatedly exposed to familiar partners, (2) whether the Coolidge effect occurs in a sex‐specific manner and (3) whether ejaculation is strategic with respect to partner familiarity. We found neither mating latency, nor penis intromission duration, mating propensity or the frequency of sex role alternations to vary significantly with treatments. Furthermore, slugs did not donate larger ejaculates to novel than to familiar partners. Partner novelty thus elicited no detectable response in sexual motivation or mating effort in C. sandrana. We suggest that the sea slugs' promiscuous mating system in often large mating aggregations makes mate discrimination based on novelty obsolete in comparison with more relevant criteria such as partner body size or mating history.     

Differential mating success of virgin female katydidsRequena verticalis (Orthoptera: Tettigoniidae)

Male katydids (Orthoptera: Tettigoniidae) invest in offspring through nutrients provided in a large spermatophore. Previous research with Requena verticalishad shown that almost all of the investment of males mating with recently mated (4 days previously) females is in eggs fertilized by the female's previous mate. Thus males are predicted to discriminate against such females as mates. In experiments placing males with both a virgin and a female mated 4–5 days previously, virgin females obtained almost all matings. Although male discrimination of mates was noted in the experiments, there was no evidence that such discrimination was against nonvirgins in both this experiment and one in which a single virgin or mated female was placed with a male. Instead, the results suggest that the differential mating was a result of interfemale competition. The mating advantage held by virgin females over nonvirgins appeared to be lost once the latter had oviposited. Finally, there was no evidence from both single- and paired-female experiments that males preferred larger females as mates.     

Male age, mating status and nuptial gift quality in a bushcricket

Female mate choice occurs in many animals, and in some species females prefer older males. Because older males have demonstrated their survival ability, they may be of higher genetic quality, providing genetic benefits to the offspring of their mates. However, in species where females receive direct benefits of matings, younger males may be more likely to provide more fertile or more nutritious ejaculates, so females may discriminate against older males. Males of the bushcricket Ephippiger ephippiger (Orthoptera: Tettigoniidae) produce large spermatophores at mating (>30% of body weight, circa 10% protein content). Female E. ephippiger discriminate against the song of older males. We examined the effects of male age and mating history on male reproductive investment (spermatophore size, sperm number, nitrogen content). Males produced spermatophores with significantly fewer sperm and of lower nitrogen content on their fourth mating, despite free access to food and a 1-week interval between matings, indicating that there is a cost of mating to males. There was no indication that older virgin males produced lower-quality spermatophores. Rather, older males produced bigger spermatophores of higher nutritional value and containing more sperm. Male age and mating history seem likely to be strongly correlated in the field. We conclude that female E. ephippiger probably prefer the songs of younger males, because in the field, this preference correlates with male mating history and therefore resources provided at mating. Thus, female preference for younger males could reflect discrimination against low-quality nuptial gifts.     

Male tree weta are attracted to cuticular scent cues but do not discriminate according to sex or among two closely related species

Recognition of conspecifics is an essential precursor of successful mating. Where related species coexist, species discrimination might be important, but because related species are similar, species signal recognition may actually be low. Chemical cues such as cuticular hydrocarbons (CHCs) are frequently used by insects to identify suitable sexual partners. We predicted that New Zealand tree weta (Hemideina spp.), a genus of nocturnal ensiferan Orthoptera that live both allopatrically and sympatrically, use chemical signals from either frass or CHCs to find mates. In a series of six laboratory trials using both H. thoracica and H. crassidens, we found that male tree weta, but not female tree weta, occupied cavities primed with female cuticular cues more often than cavities without. However, males did not discriminate between chemical cues of male and female conspecifics, or between conspecifics and heterospecifics. In field trials, tree weta did not occupy artificial cavities primed with either female frass or female cuticular cues more often than unscented cavities. However, in both trials weta preferentially returned to cavities that had already been occupied earlier in the trials. A final field trial confirmed the presence of mixed species harems during the mating season in one region of sympatry. Our results suggest that selection on sex and species specific chemical cues that could be used to find conspecific mates is weak. Mixed species aggregations suggest that identification of conspecific mating cues has not evolved to be species specific. We infer that for male tree weta, the cost of mating with heterospecifics is likely less than not mating at all.     

Effect of the mating plug on female chemical attractiveness and mating acceptance in a scorpion

After mating, females may experience a decline in sexual receptivity and attractiveness that may be associated with changes in the production and emission of sex pheromones. In some cases, these changes are produced by chemical substances or structures (e.g., mating plugs) produced by males as a strategy to avoid or reduce sperm competition. In scorpions, sex pheromones may be involved in finding potential mates and starting courtship. Here, we tested the hypothesis that the males of Urophonius brachycentrus, a species that produces a mating plug, use chemical communication (sex pheromones) to detect, localize, and discriminate females according to their mating status (virgin or inseminated), aided by chemical signaling. We also explored the effect of extracting of the mating plug on chemical communication and mating acceptance. We used Y‐maze olfactometers with different stimuli to analyze male choice and exploration time. To evaluate mating acceptance, we measured the attractiveness and receptivity of females of different mating status. We found that chemical communication occurs through volatile pheromones, but not contact pheromones. Males equally preferred sites with virgin or inseminated females with removed mating plug. In turn, females with these mating statuses were more attractive and receptive for males than inseminated females. This study suggests that the mating plug significantly affects female chemical attractiveness with an effect on volatile pheromones and decreasing sexual mating acceptance of females. The decline in the female's sexual receptivity is a complex process that may respond to several non‐exclusive mechanisms imposed by males and strategically modulated by females.     

The evolution of sex differences in mate searching when females benefit: new theory and a comparative test

Sexual selection is thought to have led to searching as a profitable, but risky way of males obtaining mates. While there is great variation in which sex searches, previous theory has not considered search evolution when both males and females benefit from multiple mating. We present new theory and link it with data to bridge this gap. Two different search protocols exist between species in the bush-cricket genus Poecilimon (Orthoptera): females search for calling males, or males search for calling females. Poecilimon males also transfer a costly nuptial food gift to their mates during mating. We relate variations in searching protocols to variation in nuptial gift size among 32 Poecilimon taxa. As predicted, taxa where females search produce significantly larger nuptial gifts than those where males search. Our model and results show that search roles can reverse when multiple mating brings about sufficiently strong material benefits to females.     

Effect of the primary host for production of both sexes on the mating interaction in an autoparasitoid species

Encarsia sophia (Girault and Dodd) is an autoparasitoid in the hymenopteran family Aphelinidae. The females develop as primary parasitoids on whitefly nymphs (primary hosts), whereas the males develop as hyperparasitoids on their own species or on other primary parasitoid species (secondary hosts). The autoparasitoids not only parasitise whiteflies but also kill them with strong host-feeding capacity. In this study, female and male E. sophia were reared on the primary hosts Trialeurodes vaporariorum and Bemisia tabaci ‘Q’, and the host-feeding and parasitism of wasps on both whitefly species were determined for the four possible different mating combinations: (i) E. sophia females reared on B. tabaci (ESF-BT) mated with E. sophia males from B. tabaci (ESM-BT), (ii) E. sophia females reared on T. vaporariorum (ESF-TV) mated with E. sophia males from T. vaporariorum (ESM-TV), (iii) ESF-BT mated with ESM-TV, and (iv) ESF-TV mated with ESM-BT. ESF-TV mated with ESM-TV killed the largest percentage of whitefly nymphs through host feeding. The ESF-TV with larger body size mating with larger ESM-TV killed more whitefly nymphs through host feeding than those mating with smaller ESM-BT. Whether B. tabaci or T. vaporariorum were used as hosts, ESF-TV mated with ESM-TV and ESM-BT and ESF-BT mated with ESM-BT significantly parasitised more whitefly nymphs than ESF-BT mated with ESM-TV. In general, ESF-BT mated with ESM-TV killed significantly fewer whitefly nymphs through parasitism and host feeding than the other three mating combinations on both whitefly species. These results indicated that the performance of autoparasitoids on insect pests was not only dependent on females but was also affected by mating with males from different primary host species.     

Interspecific interactions and learning variability jointly drive geographic differences in mate preferences

Co‐occurrence of closely related species can cause behavioral interference in mating and increase hybridization risk. Theoretically, this could lead to the evolution of more species‐specific mate preferences and sexual signaling traits. Alternatively, females can learn to reject heterospecific males, to avoid male sexual interference from closely related species. Such learned mate discrimination could also affect conspecific mate preferences if females generalize from between species differences to prefer more species‐specific mating signals. Female damselflies of the banded demoiselle (Calopteryx splendens) learn to reject heterospecific males of the beautiful demoiselle (C. virgo) through direct premating interactions. These two species co‐occur in a geographic mosaic of sympatric and microallopatric populations. Whereas C. virgo males have fully melanized wings, male C. splendens wings are partly melanized. We show that C. splendens females in sympatry with C. virgo prefer smaller male wing patches in conspecific males after learning to reject heterospecific males. In contrast, allopatric C. splendens females with experimentally induced experience with C. virgo males did not discriminate against larger male wing patches. Wing patch size might indicate conspecific male quality in allopatry. Co‐occurrence with C. virgo therefore causes females to prefer conspecific male traits that are more species specific, contributing to population divergence and geographic variation in female mate preferences.     

Sex Differences in “Time Out” from Reproductive Activity and Sexual Selection in Male Bushcrickets (Orthoptera: Zaprochilinae: <Emphasis Type="Italic">Kawanaphila mirla</Emphasis>)

Animals of many species prefer some partners over others. Discriminating among potential mates causes strong sexual selection that shapes characters and behaviors. In bushcrickets the sexes shows different latencies to remate due to differences in investment in production of the nuptial gift by males and the induced refractory period in females. We conducted experiments with the Australian bushcricket Kawanaphila mirla to test the variation in male mating success by female choice. Male remating intervals under unlimited access to food and mates were around two days, whereas most females did not remate within 12 days. Males had therefore a much shorter “time-out” from mating than females. The adult sex ratio from field samples was near to 1:1. Consequently, the OSR was male-biased with more males than females ready to mate. This male-biased OSR led to mating competition in males and choosiness in females. In a field enclosure with unlimited supply of receptive females the number of matings varied widely between males, with twenty percent of males neglected by the females. The number of matings within this enclosure was neither related to male size nor to song characters, recorded previously in the lab. However, the number of matings by individual males was positively correlated to the size of their spermatophore producing accessory gland. Females appear to prefer males with a large nutritive donation, thereby receiving a direct fitness benefit.     

Complex Courtship Behavior in the Striped Ground Cricket, Allonemobius socius (Orthoptera: Gryllidae): Does Social Environment Affect Male and Female Behavior?

Complex courtship in the striped ground cricket, Allonemobius socius, involves a series of behaviors alternating between the sexes. We examined if complex courtship allows either or both genders to evaluate their mate and how mating behavior changes in different social environments. While complex courtship may allow discrimination by both sexes, here only females exhibited a preference. Males did not alter their courtship behavior or change spermatophore size for different size females. In contrast, females initiated copulation more quickly with bigger males possessing bigger spermatophores. In a different social environment (additional male, female, or both), males were less likely to omit courtship songs and female discrimination of mates changed. The distinct differences in male and female behavior suggest that subtle changes in social environment can have important consequences in structuring courtship and mating behavior.     

The Starling Mating System as an Outcome of the Sexual Conflict

Many bird species demonstrate a variable mating system, with some males being monogamously mated and other males able to attract more than one mate. This variation in avian mating systems is often explained in terms of potential costs of sharing breeding partners and compensation for such costs. However, whenever there is a difference in the optimal mating system for males and females, a sexual conflict over the number of partners is expected. This paper contains a verbal model of how a conflict between male and female European starlings (Sturnus vulgaris),resulting from the fitness consequences of different mating systems for males and females differing over time, determines the mating system. We demonstrate that males and females have contrasting fitness interests regarding mating system, such that males gain from attracting additional mates whereas already mated females pay a cost in terms of reduced reproductive success if males are successful in attracting more mates. We demonstrate how this can be traced to the rules by which males allocate non-sharable care between different broods. Furthermore, we demonstrate that there exist male and female conflict behaviours with the potential to affect the mating system. For example, aggression from already mated females towards prospecting females can limit male mating success and males can circumvent this by spacing the nest-sites they defend. The realised mating system will emerge as a consequence of both the fitness value of the different mating systems for males and females, and the costs for males and females of intersexual competition. We discuss how this model can be developed and critically evaluated in the future.     

Cuticular hydrocarbons as a basis for chemosensory self‐referencing in crickets: a potentially universal mechanism facilitating polyandry in insects

Females of many species obtain benefits by mating polyandrously, and often prefer novel males over previous mates. However, how do females recognise previous mates, particularly in the face of cognitive constraints? Female crickets appear to have evolved a simple but effective solution: females imbue males with their own cuticular hydrocarbons (CHCs) at mating and utilise chemosensory self‐referencing to recognise recent mates. Female CHC profiles exhibited significant additive genetic variation, demonstrating that genetically unique chemical cues are available to support chemosensory self‐referencing. CHC profiles of males became more similar to those of females after mating, indicating physical transfer of CHCs between individuals during copulation. Experimental perfuming of males with female CHCs resulted in a female aversion to males bearing chemical cues similar to their own. Chemosensory self‐referencing, therefore, could be a widespread mechanism by which females increase the diversity of their mating partners.     

Horizontal transmission of begomoviruses between Bemisia tabaci biotypes

We have previously shown that the monopartite Tomato yellow leaf curl virus (TYLCV), a begomovirus (family Geminiviridae, genus Begomovirus) infecting tomato plants can be transmitted in a gender-dependent manner among its insect vector the whitefly Bemisia tabaci type B (Gennaduis) (Aleyrodidae: Hemiptera) during mating. Viruliferous females were able to transmit the virus to non-viruliferous males and vice versa, in the absence of any other virus source. The recipient insects were able to infect tomato plants. In this communication, we present evidence that two bipartite begomoviruses infecting cucurbits, Squash leaf curl virus (SLCV) and Watermelon chlorotic stunt virus (WmCSV) can be transmitted in a gender-dependent manner among whiteflies. In addition we show that TYLCV can be transmitted during mating among individuals from the same biotype (from B-males to B-females and vice versa; and from Q-males to Q-females and vice versa). However, viruliferous males of the B biotype are unable to transmit the virus to females of the Q biotype (and vice versa); similarly, viruliferous males of the Q biotype are unable to transmit the virus to females of the B biotype (and vice versa). These findings support the hypothesis that a pre-zygotic mating barrier between the Q and B biotypes is the cause for the absence of gene flow between the two biotypes, and that virus transmission can be used as a marker for inter-biotype mating. To be transmitted during mating, the virus needs to be present in the haemolymph of the donor insect. Abutilon mosaic virus (AbMV), a bipartite begomovirus that can be ingested but not transmitted by B. tabaci, is absent in the whitefly haemolymph, and cannot be transmitted during mating. Mating was a precondition for horizontal virus transfer from male to female, or female to male. Virus was not transmitted when viruliferous B. tabaci were caged with the non-vector non-viruliferous whitefly Trialeurodes vaporariorum (Westwood) (Aleyrodidae: Hemiptera) and vice versa.     

Male Lekking duration and Mating Benefits in a Lek-Forming Hawaiian Drosophila

Variation in lekking duration of males of a Hawaiian Drosophila, D. grimshawi, was examined in laboratory enclosures. The relationship between variation in male lekking activity and number of eggs laid by females, proportion of eggs hatching, and total offspring production was investigated. Females mating highly active males laid fewer eggs and thus had lower offspring production than females mating less active males, even though other studies have shown that D. grimshawi females prefer more active males as mates. These results are discussed in terms of conflict between males and females over mating benefits and in trade-offs faced by males between lekking duration and offspring production per mating. Testis mass was not related to lekking activity levels, but males with heavier testes produced more offspring per mating, suggesting that males may vary in other ways that correlate with possible direct fitness gains for females.