Reproductive success in male Japanese minnows,Pseudorasbora parva: observations under experimental conditions

To evaluate the spawning success of male Japanese minnows,Pseudorasbora parva, and female mate choice, spawning behaviour was observed under both artificial and experimental conditions. Larger males had larger territories and greater reproductive success. The body weight of territorial males decreased during the maintenance of territories, while that of non-territorial males increased significantly. When the weight of non-territorial males exceeded that of territorial males, the former began to establish new territories on the substrate, suggesting a conditional strategy by non-territorial males to trade off immediate reproductive success with growth and hence improve future reproductive success. Females chose males with larger body size, probably based on dominance rank rather than the quality (or size) of territory. It was concluded that females choose males of higher dominance rank and that males compete for large territories, both of which play an important part in male reproductive success.     

Larval nutritional environment determines adult size in Japanese horned beetles <Emphasis Type="Italic">Allomyrina dichotoma</Emphasis>

The effects of larval nutrition and parental size on offspring horn (male) and body size (male and female) were examined in the Japanese horned beetle Allomyrina dichotoma L. (Coleoptera: Scarabaeidae). Offspring-parent regressions for both horn size and body size of males show no heritable effect, and the magnitudes of these traits were primarily determined by the larval nutritional condition. Male Allomyrina dichotoma also displayed dimorphic horn size-body size allometry, that is, larger males had longer horns relative to their body size and vice versa. Because it has been suggested that males of different body sizes adopt different reproductive tactics, the dimorphic horn size–body size allometry and male reproductive tactics are also a result of the larval environment. Similarly, female body size was determined by larval nutrition, and, thus, larval condition might influence future female fecundity. Females under low nutrition treatment spent longer duration of the third larval instar than females under high nutrition. Females under poor nutrition treatment probably attempted to be as large as possible by the extent of larval duration. Since horn and/or body sizes of males and females affect their fitness, this suggests the evolution of female choice for better oviposition site.     

Female canaries produce eggs with greater amounts of testosterone when exposed to preferred male song

Male birdsong has a great influence in the stimulation of female reproduction. However, female physiological responsiveness to song may depend on the degree of complexity of male song. This is expected because females of iteroparous organisms may increase their fitness by matching their reproductive investment to the predicted value of each reproductive attempt. To the extent that the expression of male ornaments is a signal of male quality, we expect females to increase their investment when paired to highly ornamented males. However, female investment may be cryptic and difficult to detect, such as androgen content in the eggs. In this study, we exposed female canaries (Serinus canaria) to attractive and unattractive song repertoires using a crossover design. As predicted, females invested greater concentrations of testosterone in their eggs when exposed to attractive repertoires than when exposed to unattractive repertoires. This implies that song repertoires convey important information about the reproductive value of a given male and suggests that testosterone deposition in egg yolk may be costly.     

Genetic benefits of mate choice separated from differential maternal investment in red junglefowl (Gallus gallus)

Abstract Females may choose more attractive mates to obtain better viability or attractiveness genes for their offspring. A number of studies have demonstrated a positive relationship between paternal attractiveness and offspring quality. However, this pattern could be due to inheritance of paternal genes and/or it could be due to increased maternal investment in the offspring of more attractive males. To isolate female responses to male appearance from paternal genetic effects, I housed female red junglefowl ( Gallus gallus ) with vasectomized (sterile) males and artificially inseminated them. Male junglefowl with larger combs are more attractive to females. Females laid more eggs when housed with a large-combed, as opposed to a small-combed, vasectomized mate. Neither egg volume nor offspring body condition was associated with comb size of the mother's vasectomized mate. Paternal genetics appeared important. Body condition and comb size were greater for the sons of large-combed sperm donor males. This is consistent with the hypothesis that genetic benefits to offspring maintain female preference for the most ornate males. It is possible that greater body condition and comb size in sons of large-combed sires was not caused by genetic differences, but instead was due to compounds in the ejaculate of large-combed sperm donors inducing greater reproductive investment from females. However, females artificially inseminated by large-combed males did not produce more or larger eggs than females artificially inseminated by small-combed males, and thus there is no other evidence consistent with ejaculate-induced differential investment. Furthermore, only in older chicks was body condition significantly related to sire comb size, suggesting genetic rather than differential investment mechanisms.     

Male mate choice in the Andrew’s toad <Emphasis Type="Italic">Bufo andrewsi</Emphasis>: a preference for larger females

In amphibians, theory predicts that male mate choice with respect to female body size can be expected to occur when female fecundity is related to body size and when the time and energy invested into one mating are relatively large. Based on experimental observations, we tested whether male mate choice occurs in a population of the Andrew’s toad (Bufo andrewsi), a species in which both assumptions are likely to be met. When a male B. andrewsi was placed with a gravid female and a non-gravid similar-sized female, the male did not discriminate between them. When two gravid females with distinct size differences were provided to a male, the male preferred the larger one. In an experiment in which two different-sized gravid females were put in two separate transparent cylinders to exclude potential chemical cues, males spent more time in proximity to the larger gravid females and jumped more frequently towards the larger gravid females than the smaller ones. These findings suggest that male B. andrewsi recognizes female body size, exhibits mate choice, and prefers to mate with larger females that provide greater reproductive potential.     

Experience Affects Female Responses to Male Song in the Variable Field Cricket Gryllus lineaticeps (Orthoptera, Gryllidae)

Search theory predicts that females will use information on search costs and the characteristics of potential mates to adjust their search behavior and mate choices. We examined the effect of previous acoustic experience on female mating responses in the variable field cricket Gryllus lineaticeps . Females of this species prefer calling songs with higher chirp rates to those with lower chirp rates. In this study we examined how female responses to male calling songs change with experience by measuring the responses of females to male calls over a sequence of three trials. Females in one group (group I) were exposed to a sequence of three identical low chirp rate songs and females in a second group (group II) were exposed to two identical low chirp rate songs interspersed by a high chirp rate song. Females in group I did not show a significant difference in their responses to the initial and final low chirp rate presentations, whereas females in group II showed a significantly reduced response to the final low chirp rate song. In addition, the degree to which female responses to the initial and final low chirp rate song changed differed significantly between the treatment groups. Thus acoustic experience appears to affect female mating preferences in this species; exposure to either more attractive songs or more variable songs makes normally unattractive songs even less attractive. These results suggest that females do not use a fixed-threshold search rule in which they mate with any male with a phenotype that exceeds a given threshold. Instead, G. lineaticeps females appear to use a more complex search rule in which they adjust their searching behavior based on the local distribution of male phenotypes.     

Male-male Competition and Female Mate Choice through Courtship Display in the Territorial Damselfish Stegastes nigricans

Both sexes of the herbivorous damselfish Stegastes nigricans maintain individual feeding territories. These territories are distributed contiguously, forming distinct colonies. Females visit male territories to spawn, and eggs are guarded by males until hatching. Male-male competition and female mate choice were studied in two colonies of different size compositions. Only larger individuals bred in both colonies. Some males in the large colony, that were larger than the breeding males in the small colony, did not succeed in reproducing probably because of severe attacks by the larger males while courting. However, females did not choose large size among breeding males. The most important male characteristic in female choice was the frequency of courtship displays in both colonies. Females in the large colony chose males mainly on the basis of the frequency of displays conducted in the females' territories, whereas females in the small colony chose males on the basis of the frequency of displays conducted in the males' territories. This difference may be a result of the difference in colony size. The distances between females' and males' territories were much greater in the large colony, and, because females cannot see courtship displays conducted in distant male territories, males in the large colony may have had to visit female territories frequently in order to conduct courtship near the females.     

Reproductive Decisions in Female European Ground Squirrels: Factors Affecting Reproductive Output and Maternal Investment

Physiological and behavioural parameters associated with reproductive effort and success were investigated in female European ground squirrels Spermophilus citellus . The proportion of reproductive (lactating) females in the study population was over 90% and was not related to age. Timing of oestrus and ovulation was found to be affected by the female's emergence date and condition. Females with low emergence mass showed delayed oestrus. Differences in ovulation dates were shown to affect reproductive output in terms of litter size and sex ratio. Early litters were larger and male biased. X-ray techniques were used to determine intrauterine litter size in individual females. The results indicated that litter size and sex ratio were fixed prenatally. Lactation costs were reflected in the intensity of mass loss and duration of lactation. Mass loss varied with litter size, in that females with large litters showed a more rapid loss than others. The second parental investment parameter, lactation duration, varied among individual females and was dependent on the timing of reproduction and litter size (except yearlings). Early born litters, which were, in most cases, larger than later ones, were nursed longer. Prolonged lactation periods affected female condition in that they started prehibernation fattening later and entered hibernation with a lower mass than individuals that had shorter lactation periods. Yearling females probably could not afford the energetic costs of long lactation, independent of their offspring number. These results indicated that females with higher reproductive output and higher investment were unable to compensate these costs before hibernation. Consequences for these individuals could therefore be lower over-winter survival or a delayed oestrus in the following season.     

FEMALE CHOICE FOR AN INDICATOR OF MALE SIZE IN THE SONG OF THE BLACK-HORNED TREE CRICKET,OECANTHUS NIGRICORNIS (ORTHOPTERA: GRYLLIDAE: OECANTHINAE)

The calling song of male crickets, including Oecanthus nigricornis (Walker), attracts females for mating and provides a model system of sexual communication. We give the first conclusive identification of a feature of cricket song that is both attractive to females and indicates a phenotypic feature (body size) that determines male mating success and female reproductive benefits. We do this by first testing for correlations between song characteristics and aspects of male phenotype that are hypothesized to indicate male quality. We show that song is a reliable indicator of male size and male age, and that large male size is associated with increased female fecundity. We then use playbacks of synthetic songs that mimic natural variation in song parameters to study song preferences and we compare preferences under different presentation regimes to determine whether choices are based on relative song quality or some fixed criterion. Females show a preference for the lower frequency songs produced by large males, but only during simultaneous playbacks. Thus female choice is based on the relative quality of calls that can be sampled simultaneously. These results provide strong support for the hypothesis that females use variation in calling song to assess male mate quality.     

Female freshwater crayfish adjust egg and clutch size in relation to multiple male traits

Females may invest more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred partners may be fitter than offspring sired by non-preferred ones. In this study, we tested the differential maternal allocation hypothesis in the freshwater crayfish, Austropotamobius italicus, by means of a pairing experiment aimed at evaluating the effects of specific male traits (body size, chelae size and chelae asymmetry) on female primary reproductive effort. Our results showed that females laid larger but fewer eggs for relatively small-sized, large-clawed males, and smaller but more numerous eggs for relatively large-sized, small-clawed males. Chelae asymmetry had no effects on female reproductive investment. While the ultimate consequences of this pattern of female allocation remain unclear, females were nevertheless able to adjust their primary reproductive effort in relation to mate characteristics in a species where inter-male competition and sexual coercion may mask or obscure their sexual preferences. In addition, our results suggest that female allocation may differentially affect male characters, thus promoting a trade-off between the expression of different male traits.     

The Influence of Physical and Acoustic Experience on Sequential Mate Preference in the Cricket Gryllus bimaculatus. Is Song Important?

Female Gryllus bimaculatus alter their mate choice based on size depending on previous experience with males. Male crickets sing to attract mates and several studies have identified call parameters important in female choice. We tested the hypotheses that exposure to acoustic stimuli before and/or after mating, from males of different sizes, in isolation and together with physical exposure influences female choice (willingness to mate and spermatophore retention time [SRT]). Females exposed to ad lib. song of multiple males post-mating had a shorter SRT than females in acoustic isolation. Exposure to ad lib. song of multiple males prior to mating had no effect on SRT. Females did not alter SRT depending on exposure to acoustic stimuli from males of different sizes either post or ante mating. Females exposed to acoustic and physical stimuli (though gauze) from large males had a shorter SRT than those exposed to small males but only when the exposure was post-mating. We were unable to identify any correlation between call parameters and body size in G. bimaculatus. Females use male song to locate potential mates but physical exposure to males is needed to allow females to judge male size and this exposure only influences SRT if it takes place post-mating.     

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.     

Influences of sex, size, and symmetry on ejaculate expenditure in a moth

Although sperm fundamentally function to fertilize eggs, forcesarising from both sexes select for optimal ejaculate composition.Sperm competition is one recognized agent in the evolution ofsperm and ejaculate structure. Few studies, however, have examinedhow female factors influence ejaculate structure, despite somebehavioral evidence for male mate choice. Male Plodia interpunctella(Lepidoptera, Pyralidae) accrue all resources for reproductionas larvae. Adults emerge with a limited sperm complement andare therefore under intense selection to optimize gamete allocation.I detected no effect of male body weight on ejaculate size.However, female reproductive potential (ovary masses) was dictatedby body weight In addition, heavier females had greater spermathecalvolumes, but there was no such relationship with bursal size.Finally, heavier females showed a higher mating frequency. Ifound that mating males were sensitive to female size and producedlarger ejaculates when mating with heavier females. Males mayejaculate more sperm into larger females either because it paysthem to "spend" more reproductive resources on matings thatprovide greater reproductive potential, or because heavier (longerlived and more attractive) females mate more frequently andhave larger spermathecal volumes. Alternatively, females maycontrol spermatophore formation and "accept" an appropriateejaculate to maximize fertility. Males may therefore be alsoselected to ejaculate more sperm into larger females to counteractgreater risks of sperm competition associated with heavier females.There was no association between male or female femur asymmetryand ejaculate size. P.interpunctella may be selected to exercisemodulation of ejaculate size because males invest paternally,sperm for the single reproductive episode are limited, and femalefecundity and mating pattern vary between individuals and areassociated with body weight. More obvious variability in malereproductive behavior and choice may therefore be paralleledat the cryptic gametic level by plasticity in ejaculate allocation.     

Female sailfin mollies, Poecilia latipinna, remember males and copy the choice of others after 1 day

Theoretical and experimental evidence indicates that females copy the mate choice of other females under certain conditions. In all mate choice copying experiments with fish to date, females were allowed to copy the choice of a model female immediately after the focal female had observed a model female interacting with a male. It is not known whether females continue to copy the choice of the model female after a longer interval. We investigated whether sailfin molly females also copy the choice of other females when they are prevented from copying immediately after observing a model female next to a previously nonpreferred male. We performed three copying experiments in which females could copy the choice of the model female immediately after, 1 h after or 1 day after observing the model female next to the previously nonpreferred male. In control experiments, we tested whether females chose consistently when they had no opportunity to copy, and whether females showed shoaling behaviour under these conditions. Females copied the choice of the model female immediately after, 1 h after and even 1 day after the observation of the model female interacting with the previously nonpreferred male. Females chose consistently between males when they had no opportunity to copy, and females did not shoal under these conditions. We conclude that females remember individual males with whom a model female had interacted, even after 1 day. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Female Oviposition Decisions and Their Impact on Progeny Life-History Traits

An important factor affecting the life-history of an organism is parental investment in reproduction: reproductive decisions are almost invariably costly. Therefore, reproductive decisions should be beneficial in terms of increased offspring number or fitness. For example, egg laying decisions in many insects can influence resource availability of the offspring through changes in the larval density, and resource availability will have effects on many life-history traits. Here we studied whether female reproductive decisions affect offspring fitness in Callosobruchus maculatus seed beetles. Females laid more eggs on black-eye beans than on mung beans. However, when the difference in the surface area of the beans was accounted for, the number of eggs was not higher in black-eye beans. This together with the poisson distribution of eggs on each of the bean types suggests that females tend to lay their eggs randomly. We found that development time was longer, larval mortality lower and adult survival higher in black-eye beans. We also found interactions between bean type and larval density on size of the offspring such that in mung beans the emergence mass and pronotum width decreased with increasing larval density, but in black-eye beans larval density did not affect the size measures. We conclude that when there is a risk that larval denisty will become high within a bean and there is variable resources available, there exist clear benefits that females might obtain by choosing black-eye beans as a resource for their offspring. However, in contrast to many earlier studies, our results suggest that females may not be making any active oviposition decisions. Therefore, to unequivocally determine whether females do capitalise the potential benefits by active decision making, some further experimentation is required.     

Reproductive strategies of rhesus macaques

Reproductive strategies incorporate a multitude of mechanisms that have evolved to promote the reproductive success of individuals. Evolutionary perspectives tend to emphasize the advantages of male-male competition and female choice as mediators of differential reproduction. Male rhesus macaques have not been observed to fight for access to sexually receptive females, although they suffer more wounds during the mating season. An increased likelihood of attacks appears to coincide with male troop entry. Males who spend more time in consort and mate with more females tend to sire more offspring. Genetic analysis of paternity has pinpointed age and endurance rivalry, rather than agonistic competition, as key variables associated with variation in progeny production. Female rhesus macaques often copulate with multiple males during their ovulatory period, and tend to conceive on the first cycle of the mating season. Female reproductive success is more likely to be a function of offspring survivorship than the identity of particular male partners. The role of female choice as a direct mediator of male reproductive success is unresolved, but female mate selection seems to indirectly affect male reproductive success because female preference for mating with novel males seems to foster male dispersal. Evaluating whether mating preferences for particular male phenotypes affectsfemale reproductive success is a task for the future. A common denominator to the reproductive strategies of both female and male rhesus macaques is that feeding patterns affect body condition which influences reproductive output and regulates relative reproductive success.     

First experimental evidence for female mate choice in a nocturnal primate

Female mate choice can be hypothesised in most nocturnal primates, since females show a higher investment in their offspring than males. The aim of this experimental study was to investigate if female grey mouse lemurs perform mate choice and whether age, relatedness (to the male), or male advertisement call activity systematically influence their decisions. A two-way mate choice design was developed in which females could choose between two males. Mate choice was deduced from the time spent in proximity to the males and from mating behaviour. During oestrus 12 of 17 females participated actively in the experiment and all of them showed either a significant spatial (n=11) or behavioural (n=1) preference for one male. In four cases copulations were observed. The influence of age on female mate choice was not statistically significant. In the cases with copulations, however, females mostly preferred the older male. This might indicate a preference for older age as an indicator of experience, fitness, and/or status. The influence of relatedness on female mate choice could not be definitely clarified. However, results imply a mechanism of kin recognition on the basis of familiarity. In the majority of choices, females preferred the male with higher trill call activity. Since trill call activity correlates with the relative dominance status of males, these results suggest an importance of the male dominance status for female mate choice in grey mouse lemurs. Altogether our findings indicate that females use a complex of different cues to choose their mates.     

SEXUAL SELECTION IN A WOLF SPIDER: MALE DRUMMING ACTIVITY,BODY SIZE,AND VIABILITY

Females are often believed to actively choose highly ornamented males (males with extravagant morphological signals or intense sexual display), and ornaments should be honest signals of male viability. However, this belief is relying only on some pieces of empirical evidence from birds. Our study reports active female choice on sexual display that indicates male viability in spiders. We established trials in which we studied female choice in relation to male courtship drumming activity and body size. Females chose the most actively drumming males as mating partners, but the body size of the males did not seem to be selected. Male drumming activity turned out to be a good predictor of male viability, whereas male viability was independent of male body mass. Our results suggest that by actively choosing mates according to male drumming performance, but independently of male body mass, females are preferring viable males as mates. Because Hygrolycosa rubrofasciata males do not provide obvious direct benefits to their offspring, females may gain some indirect benefits; offspring may have higher chance of survival, or the offspring may inherit the attractiveness of their father.     

Female Preferences for Call Traits and Male Mating Success in the Neotropical Frog Physalaemus enesefae

Female preferences for male call traits may affect male mating success and the evolution of exaggerated secondary sexual traits. We used phonotaxis experiments to examine female preferences in the frog Physalaemus enesefae in relation to variation in male call duration, dominant frequency, intercall interval and amplitude (dB SPL). Females preferred long calls, low and average dominant frequency calls, short intercall intervals and more intense calls. We compared the patterns of female preferences with those of acoustic variation among males to test the prediction that properties with low within‐male variation are associated with stabilizing or weakly directional female preferences, whereas properties with high within‐male variation are associated with directional preferences. Females had weakly directional preferences for the dominant frequency of the call and strongly directional preferences for call duration and call rate. We also determined whether the temporal relationship between calls influenced preferences based on the dominant frequency of the call. Preferences for low‐frequency over high‐frequency calls disappeared when calls partially overlapped. Females preferred the leading call regardless of its dominant frequency. We also investigated mating patterns in the field. There was size‐assortative mating, as male and female body sizes snout‐vent length (SVL) were positively correlated. In addition, differences in the frequency distributions of body length (SVL) between mated and unmated males approached significance; lower SVL classes were underrepresented among mated males. These patterns may reflect female preferences for lower dominant frequency calls, as there is a negative correlation between male mass and the dominant frequency of the call.