Female Size Influences Mate Preferences of Male Guppies

Guppies (Poecilia reticulata) have a promiscuous mating system in which female choice for brightly coloured males plays an important role. Consequently, much research on guppies has examined how mate choice by females has lead to the evolution of male colour patterns. Much less attention has been devoted to mate choice by males in this species. In this study, we show that male guppies are choosy when selecting a female to associate with, significantly preferring the larger female when presented with two females that differed by ≥2 mm in standard length (SL). The strength of their preference for each female increased with absolute female size. The relative sizes of the females, however, also influenced male mating preferences: males showed stronger preferences for the larger female as the difference in SL between the two females increased. Such a preference for larger females is not unexpected as fecundity generally increases with body size in female fish. Thus, males choosing to mate with the larger female should have higher reproductive success. An apparent, but non‐significant anomaly, whereby males appear to prefer the smaller of the two females when the difference between female SL was <4 mm, deserves further investigation.     

Chemical sex recognition in the harvestman <Emphasis Type="Italic">Discocyrtus prospicuus</Emphasis> (Arachnida: Opiliones)

Several arachnid species use chemicals to detect sexual partners. In harvestmen, there are evidences that chemicals may play a role in intraspecific communication. Using the behavior of Discocyrtus prospicuus (Holmberg 1876), whose males expose the penis to females before they engage in mating posture, we tested if males detect females by contact chemoreception (chemicals left on the substrate) and if males detect females by olfaction. First, we exposed males to three experimental groups, where males had to choose between two substrates: female chemicals/blank control; male chemicals/blank control; female/male chemicals. Then, we gave males access to volatiles of males, females, and control simultaneously. We predicted that males would expose the penis when approaching volatiles and chemicals deposited on the substrate by females. We also tested if males spent more time close to the source of female volatiles and on the substrate with female chemicals and if males tapped the substrate with female chemicals for more time than the others. Finally, we put males and females together to observe if males would expose the penis upon touching the female’s cuticle. Most of our predictions were not supported, though males did tap for more time when exposed to female cues instead of male cues and exposed the penis in 70% of the observations when interacting with the female but only after touching her. Our data does not support olfaction as a way to detect females and corroborate the idea that contact chemicals, either on the substrate or on female’s cuticle, play an important role in the detection and recognition of the opposite sex. This is the first evidence in harvestmen that males may react differently to female/male chemicals.     

Sexual Competition,Coercive Mating and Mate Assessment in the One‐Sided Livebearer,Jenynsia multidentata: Are They Predictive of Sexual Dimorphism?

We investigated the mechanisms of sexual selection operating on body size in the one‐sided livebearer (Jenynsia multidentata), a small fish characterized by male dwarfism. Mating in the one‐sided livebearer is coercive: males approach females from behind and try to thrust their copulatory organ at the female genital pore. Females counter males' mating attempts by either swimming away or attacking them. We tested the hypothesis that the components of sexual selection favouring small size in males (sexual coercion) were more effective than those favouring a large size (male competition and mate choice). When alone, small males had a significantly higher success in their mating attempts than large males. The proportion of successful attempts was also positively correlated with female size. When two males competed for the same female, the large male had a significant mating advantage over the small one. With a 1 : 1 sex ratio, the large‐male mating advantage vanished because each male tended to follow a different female. Large males, however, preferentially defended large females, thus compelling small males to engage with smaller, less fecund females. Males did not discriminate between gravid and non‐gravid females, but preferred mating with larger females. This preference disappeared when males were much smaller than the female, probably in relation to the risk for the male of being eaten or injured by the female. In a choice chamber, male‐deprived females that had their sperm storage depleted remained close to males and showed a preference for large individuals, a behaviour not observed in non‐deprived females. Nonetheless, when placed with males in the same aquarium, all females showed avoidance and aggression. Struggling may represent a way by which the female assesses the skill and endurance of males.     

Natural selection and genetic variation for female resistance to harm from males

The sexual conflict hypothesis predicts that males evolve traits that exploit the higher parental investment of females, which generates selection for females to counter-evolve resistance. In Drosophila melanogaster it is now established that males harm females and that there is genetic variation among males for the degree of this harm. Genetic variation among females for resistance to harm from males, and the corresponding strength of selection on this variation, however, have not been quantified previously. Here we carryout a genome-wide screen for female resistance to harm from males. We estimate that the cost of interactions with males depresses lifetime fecundity of females by 15% (95% CI: 8.2-22.0), that genetic variation for female resistance constitutes 17% of total genetic variation for female adult fitness, and that propensity to remate in response to persistent male courtship is a major factor contributing to genetic variation for female resistance.     

Intrasexual mounting in the beetle Diaprepes abbreviatus (L.).

The weevil Diaprepes abbreviatus shows three kinds of same-sex mountings: males mount other unpaired males, males mount males already engaged in copulation and females mount other females. Four hypotheses were evaluated in order to explain same-sex matings by males: (i) female mimicry by inferior males, (ii) dominance of larger males which affects the behaviour of small males, (iii) sperm transfer in which smaller males gain some reproductive success by 'hitchhiking' their sperm with the sperm of larger males, and (iv) poor sex recognition. Data from mate choice and sperm competition experiments rejected the female mimicry, dominance and sperm transfer hypotheses and supported the poor sex recognition hypothesis. We tested three hypotheses in order to explain female mounting behaviour: (i) females mimic male behaviour in order to reduce sexual harassment by males, (ii) females mount other females in order to appear larger and thereby attract more and larger males for mating, and (iii) female mimicry of males. The results of our mate choice experiments suggested that the female mimicry of males hypothesis best explains the observed female mounting behaviour. This result is also consistent with the poor sex recognition hypothesis which is the most likely explanation for male and female intrasexual mating behaviour in many insect species.     

Female Age Determines Remating Behavior in Wild Mexican Fruit Flies

Male and female age are important factors that can influence mating and remating behavior. Females can discriminate against or prefer older males, but there have been relatively fewer studies on how female and male age influence female remating. Here we showed in wild flies of the Mexican fruit fly Anastrepha ludens (Loew), that when females were given a choice between males of different ages, younger females preferred to mate with younger males over older males, while older females were less selective. Also, when given a choice between males of different ages, older females had longer copulation durations than younger females. On the other hand, older males and females had lower mating success, compared with young and middle-aged flies under no choice conditions. However, middle-aged females mated faster compared to young females and young males mated faster compared to middle-aged males. Male age did not influence female remating, while female age strongly determined female remating, with no females remating when they were old. It is unclear if female receptivity mechanisms are switched off at older ages, or if females are reluctant to remate due to possible costs of mating. We discuss our results in terms of how male and female age can influence mating decisions.     

Sexual cooperation and conflict in butterflies: a male-transferred anti-aphrodisiac reduces harassment of recently mated females

Sexual selection theory predicts that the different selection pressures on males and females result in sexual conflict. However, in some instances males and females share a common interest which could lead to sexual cooperation. In the pierid butterfly Pieris napi the male and the recently mated female share a common interest in reducing female harassment by other males soon after mating. Here we show that P. napi males transfer an anti-aphrodisiac to the female at mating, methyl-salicylate (MeS), which is a volatile substance which mated females emit when courted and which makes males quickly abandon them. A 13C-labelling experiment demonstrated that only males synthesize MeS. The effect of this antiaphrodisiac is so strong that most males will refrain from mating with virgin females to whom MeS has been artificially applied. In P. napi, males also transfer nutrients to females at mating. This increases female fecundity and longevity and so females benefit from remating. Hence, sexual cooperation gradually turns to conflict. Future research is required to reveal which sex controls the gradual decrease in the MeS titre which is necessary for allowing mated females to regain attractiveness and remate.     

Non-random Mating in the Dance Fly Empis borealis: The Importance of Male Choice

In the dance-fly Empis borealis (Diptera, Empididae), females form swarms to which males, carrying a nuptial gift, come for mating. We examined whether males or females were choosy and/or competed for mates. First, measurements of the size relationships between copulating males and females, nuptial gifts and the swarming females from different swarms were assessed. Second, male visiting time in differently sized female swarms was recorded. Larger (wing-length) females participated disproportionately in copulations in each swarm, but not for the population at large. Female mating status (virgin/non-virgin) or proximity to oviposition (egg size) did not influence the likelihood of copulation. No assortative mating pattern was found: male size and size of nuptial gift did not correlate with size of the mating female. The time spent by males in swarms increased with the number of females present and it took longer when males left a swarm without copulation than when doing so. Male visiting time per female was negatively correlated with number of females in swarms. Males more often left smaller than larger swarms without mating. We conclude that E. borealis males discriminate among females but find no evidence for male competition or for female choice. It is still a question to what degree females compete for males.     

Effects of female and male size on female mating and remating decisions in a bean beetle

The body sizes of individuals of the choosing and chosen sexes in a mate choice may affect sequential mating of females. We examined the effects of the body sizes of females and their mates on attributes of female first mating, and the effects of body sizes of females and their previous and potential future mates on female remating in the adzuki bean beetle, Callosobruchus chinensis. Large- and small-sized adults were derived from larvae reared under conditions of low and high density in a bean, respectively. The speed of first mating of large females was not affected by the size of courting males, whereas small females initiated mating more rapidly when courted by small males. The remating probability of large females was not affected by first male size, whereas small females that mated first with smaller males were more likely to remate. These data suggest that pre- and post-copulatory female choices for male size depend on the female’s size, and the small females might be more willing to copulate with smaller males but prefer larger males to sire their offspring after copulation. A possible explanation for this preference is that small females may suffer greater harm from copulating with larger males.     

Preference for conspecifics evolves earlier in males than females in a sexually dimorphic radiation of fishes

Speciation by sexual selection is generally modeled as the coevolution of female preferences and elaborate male ornaments leading to behavioral (sexual) reproductive isolation. One prediction of these models is that female preference for conspecific males should evolve earlier than male preference for conspecific females in sexually dimorphic species with male ornaments. We tested that prediction in darters, a diverse group of freshwater fishes with sexually dimorphic ornamentation. Focusing on the earliest stages of divergence, we tested preference for conspecific mates in males and females of seven closely related species pairs. Contrary to expectation, male preference for conspecific females was significantly greater than female preference for conspecific males. Males in four of the 14 species significantly preferred conspecific females; whereas, females in no species significantly preferred conspecific males. Relationships between the strength of preference for conspecifics and genetic distance revealed no difference in slope between males and females, but a significant difference in intercept, also suggesting that male preference evolves earlier than females’. Our results are consistent with other recent studies in darters and suggest that the coevolution of female preferences and male ornaments may not best explain the earliest stages of behavioral isolation in this lineage.     

Reproductive and developmental biology of the oriental cockroach Blatta orientalis (Dictyoptera)

At 27 degrees C and 45% r.h. in the laboratory, the oriental cockroach Blatta orientalis (L.) developed to adulthood in seven to nine instars for males (66% had eight instars) and eight to ten instars for females (67% had nine instars) in mixed groups, with up to twelve instars for isolated females. Nymphal development lasted 185 +/- 2 days for males, 216 +/- 4 days for females, with 89% survival to adulthood. Adult longevity was significantly more for males than females in mixed groups. Virgin females lived for 135 +/- 6 days compared with 87 +/- 9 days for females kept with males. After an initial maturation time of 12.2-13.5 +/- 0.4 days for mated and unmated females, oothecae were produced, on average, every 6-7 (range 2-29) days. Ootheca viability was 68% from females kept with males, 32% from females kept apart from males. Numbers of nymphs emerging were 14.1 +/- 0.26 after 45 days from mated female oothecae 8.2 +/- 0.3 after 49 days from unmated females. With sexual reproduction the sex ratio of progeny reaching adulthood was 1.1 males per female (n = 443), whereas unmated females produced only female progency, which is consistent with parthenogenetic reproduction. Drawings of the ventral aspect of the terminalia are given to show features useful for instar determination and for distinguishing between male and female nymphs and adults of B. orientalis.     

Female defense polygyny in the territorial triggerfish <Emphasis Type="Italic">Sufflamen chrysopterum</Emphasis>

The occurrence of polygyny requires specific environmental conditions such as female aggregation or patchy resource distribution. However, it is difficult to determine the factors responsible for polygyny in species in which the territories of both sexes overlap. To overcome this, we performed female removal experiments in the polygynous triggerfish Sufflamen chrysopterum (Balistidae) in the Okinawa coral reef. Both sexes defended their territories exclusively against consexuals of the same species, and female aggregation was absent. Each male territory included 1–3 female territories, and nonterritorial males were significantly smaller than territorial males. Further, the body size of territorial males was positively correlated with that of the largest female in their territories, and larger males tended to mate with more females. The results of the female removal experiments (n = 10 females) indicated that females competed for better territories rather than larger mates. In contrast, males abandoned the territories once the females emigrated. These results strongly suggest that males defend females rather than sites and compete for larger and a greater numbers of females. Thus, in S. chrysopterum, female defense polygyny occurs in the absence of female aggregation.     

A role of her own: female cowbirds, Molothrus ater, influence the development and outcome of song learning

Previous work has shown that captive female cowbirds, Molothrus ater, can influence the outcome of male song development by affecting retention or deletion of song elements and by stimulating improvization. Here we looked for evidence of female influence during the process of learning, as males progress from subsong to plastic song to stereotyped song. In a longitudinal study, we measured the rate and timing of vocal development in captive, juvenile male brown-headed cowbirds, M. a. artemisiae. Half the young males were housed with female cowbirds from their own population (South Dakota: SD) and half with female cowbirds from a M. a. ater population (Indiana: IN). Both populations of females prefer local songs and differ in the time of breeding, with SD females breeding 2 weeks later than IN females. The results showed significant effects of female presence on the age at which males advanced through stages of vocal development: the SD males with SD females, as opposed to SD males with IN females, developed stereotyped song earlier, reduced motor practise earlier, and produced more effective playback songs. Longitudinal observations of social interactions showed that the two groups of females reliably differed in social responses to males. Degree of social proximity of females to males in the winter predicted song maturity, rate of rehearsal and song potency. Thus, females can stimulate the progression of song learning, as well as prune song content. Copyright 2000 The Association for the Study of Animal Behaviour.     

Male dwarf chameleons assess risk of courting large, aggressive females

Conflict between the sexes has traditionally been studied in terms of costs of mating to females and female resistance. However, courting can also be costly to males, especially when females are larger and aggressively resist copulation attempts. We examined male display intensity towards females in the Cape dwarf chameleon, Bradypodion pumilum, in which females are larger than males and very aggressive. We assessed whether aggressive female rejection imposes potential costs on males and whether males vary their display behaviour with intensity of female rejection, female size or relative size differences. Males persisted in courtship after initial female rejection in 84% of trials, and were bitten in 28% of trials. Attempted mounts were positively associated with males being bitten. Males reduced courtship with increased intensity of female rejection. Male courtship behaviour also varied with female size: males were more likely to court and approach smaller females, consistent with the hypothesis that larger females can inflict more damage. These results suggest that, in addition to assessing female willingness to mate, male dwarf chameleons may use courtship displays to assess potential costs of persistence, including costs associated with aggressive female rejection, weighed against potential reproductive pay-offs associated with forced copulation.     

Sex differences in scent marking in Propithecus edwardsi of Ranomafana National Park, Madagascar

In this study we compared the scent-marking rates of females with those of males. Specifically, we examined the ability of season, dominance status, and natal status to explain the frequency of scent marking in female sifakas living wild in Ranomafana National Park, Madagascar, and compared the results with those published for males [Pochron et al., American Journal of Primatology, in press]. We also sought to determine whether vulnerability to infanticide affects marking frequency in adults of either sex, and whether female reproductive status affects female marking behavior. We found that males marked at twice the rate of females, and like males, females in single-female groups marked at the highest rates. Dominant females and non-natal females marked at higher rates than did subordinate females and natal females, a pattern also seen in males. This suggests that scent marks may convey important information about status. Neither females nor males varied their marking frequency with the presence of vulnerable infants. Females did not alter marking frequency with reproductive state, and like males, they marked at higher rates in the period prior to the mating season than they did in the mating season itself. This implies that females may use scent marks more for intrasexual aggression or territoriality than for mate attraction.     

Cryptic female choice during spermatophore transfer in Tribolium castaneum (Coleoptera: Tenebrionidae)

Sexual selection in both males and females promotes traits and behaviors that allow control over paternity when female mates with multiple males. Nonetheless, mechanisms of cryptic female choice have been consistently overlooked, due to traditional focus on sperm competition as well as difficulty in distinguishing male vs. female influence over processes occurring during and after mating. The first part of this study describes morphology and transformation of Tribolium castaneum spermatophores inferred from dissecting females immediately after normal or interrupted copulations. T. castaneum males are found to transfer spermatophores as an invaginated tube that everts inside the female bursa and which is filled with sperm during copulation. This sequence of events makes it feasible for females to control the sperm quantity transferred in each spermatophore. Through manipulation of the male phenotypic quality (by starvation) and manipulation of female control over sperm transfer (by killing a subset of females), the second part of this study examines whether females use control over transferred sperm quantity as a cryptic choice mechanism. Fed males transferred significantly more sperm per spermatophore than starved males but only when mating with live females. These results suggest an active differentiation by live females against starved males and provide an evidence for the proposed cryptic female choice mechanism.     

Influence of host-plant density and male harassment on the distribution of female Euphydryas anicia (Nymphalidae)

Summary We studied behavioral mechanisms underlying the spatial distribution of Euphydryas anicia (Lepidoptera: Nymphalidae) females searching for larval host plants on a flat plain in Colorado. The rate of female movement, as represented by an empirically estimated diffusion coefficient, is affected by two factors. First, when searching in areas of high host-plant density, females tend to make sharper turns and fly for shorter distances between landings, compared to areas of low plant density. As a result, the rate of female displacement is lowered when they search in areas of high host-plant density, and thus females tend to aggregate in such areas. The second factor affecting female movement is the presence of males. Harassment by males induces females to increase the rate of their movement, and females are often chased out of host patches by males. Our results explain the observed spatial and temporal patterns of female distribution in relation to the distribution of host plants and males. In years when host plants are plentiful, harrassement by males in one host patch induces females to move to another. This pattern of female movement tends to disrupt the relationship between the spatial distributions of host plants and females, as well as females and males. In the year when hosts were concentrated in a single large patch, females could not easily avoid male harassment, and consequently we observed strong corelations of female-host distributions and male-female distributions.     

No Coolidge Effect in Decorated Crickets

Female decorated crickets, Gryllodes sigillatus , obtain genetic benefits by mating with different males and, when given a choice, prefer novel males over previous mates. It is unknown, however, whether males exhibit a similar preference for novel females. Although female crickets control copulation, there are at least two ways in which males can exercise choice: (1) the amount of courtship directed towards prospective mates and (2) the size of the spermatophore transferred to the female at mating. To determine whether males devote more courtship effort to novel females while controlling for female behavioral cues, male courtship effort toward two dead females, one, a previous mate and the other, a novel female, was measured. To determine whether males manufacture larger spermatophores when paired with novel females, males were mated to novel or previous mates, and the different components of the spermatophore weighed. Males did not spend more time courting dead novel females than previous mates. There was no difference in the latency to remating of males confined with novel females and those paired with previous mates, and there was no difference in the mass of spermatophores transferred to novel and familiar females. Contrary to previous studies in other taxa, this study suggests that male crickets do not prefer novel mates and thus, are not subject to the Coolidge effect. Although mating with novel females may be beneficial to males, selection on males to identify and discriminate against previous mates may be relaxed because of a strong female preference for novel males.     

Dynamics of male residence and female oestrus during a breeding season of blue monkeys in the Kakamega Forest, Kenya

Blue monkeys (Cercopithecus mitis stuhlmanni) are seasonal breeders with a dynamic mating system in which typical one‐male social units are regularly disrupted and replaced by multi‐male ones. The number of males in the group is correlated with the number of oestrous females. We used observations of male presence and female oestrus on individual days during a 6‐month period to assess whether the presence of multiple males in a group stimulates female oestrus or whether oestrous females attract multiple males to the group. We confirmed prior observations with our finding that the number of males in a group was significantly correlated (r_s = 0.435, P < 0.0001) with the number of oestrous females across 126 observation days. A transition matrix did not show an obvious relationship between day‐to‐day changes in the numbers of oestrous females and males. However, cross‐correlation analysis provided stronger support for the idea that the number of oestrous females attracts males to a group than for the idea that the influx of strange males stimulates oestrus in female blue monkeys. Autocorrelation analysis showed that while female oestrus appeared to show a high degree of synchrony, as expected in a seasonal breeder, there was no evidence that the number of males accompanying a group of females influenced the likelihood of other males joining or leaving the group. Overall, our results confirm that female oestrous behaviour stimulates changes in male residence patterns. However, other observations suggest that changes in male residence may also stimulate female oestrus in some circumstances.     

The alteration of attractiveness of intact males mice to females chemosignals, subjected of ionizing radiation in sublethal dose

After irradiation in a dose 4 Gy female mice of CBA and C57Bl/6 (female CBA during 18-23 days, female C57Bl/6 - 4-10 days) secretes with urine volatile components (chemosignals) which possess higher, than secretes intact females, attractiveness for intact males the same strains irrespective of a genotype. When estimation relative attractiveness postradiation secretes female mice CBA and C57Bl/6 intact males prefer chemosignals singenic (genetically identical) females during 1-23 day after irradiation. Observed olfactorial reaction male mice more differ from norm. In which males prefer chemosignals of allogenic (with a strange genotype) females. This disturbances identifed as postradiation reversion attractiving males of chemosignals, dependent on the genotype of females. Typical for norm chemosignalisation at females restored for 43 days after the irradiation. The mechanism and biological advisability of this phenomenon are discussed.