Alternative mating strategies in a desert grasshopper: a transitional analysis

We describe between- and within-individual variation in signalling behaviour for a population of male Ligurotettix coquilletti in a North American desert. For each observation date individual males were categorized as actively-signalling or inactive by the amount and regularity of their stridulation and their signalling location. Few males were active or inactive on all dates they were observed. By comparing the behaviour of individuals on consecutive observation dates, we identified the primary ways that individuals changed between active signalling and inactive behaviour. Behavioural transitions were frequently associated with movement between bushes. Inactive males became active upon moving to a vacant bush, and lone active males often became inactive after moving to a bush containing other males. Male-male aggression (primarily chases involving no contact between the participants, or only very brief contact) had a pronounced, short-term effect upon the signalling behaviour of males that received an attack. Approximately 33% of these recipients that had been stridulating became silent immediately following the chase. However, chases did not markedly alter the behaviour of recipients on the following observation date. Recipients were no more likely to change from inactive to active behaviour than vice versa between the observation dates immediately preceding and following the day of the chase. Although the transition analysis failed to detect marked behavioural changes among recipients, analyses based on longer periods of time revealed that males observed to be recipients were more likely to display inactive behaviour and less likely to mate than males observed to be initiators of aggression.     

Socially cued anticipatory adjustment of female signalling effort in a moth

Juvenile population density has profound effects on subsequent adult development, morphology and reproductive investment. Yet, little is known about how the juvenile social environment affects adult investment into chemical sexual signalling. Male gumleaf skeletonizer moths, Uraba lugens, facultatively increase investment into antennae (pheromone receiving structures) when reared at low juvenile population densities, but whether there is comparable adjustment by females into pheromone investment is not known. We investigate how juvenile population density influences the ‘calling'' (pheromone-releasing) behaviour of females and the attractiveness of their pheromones. Female U. lugens adjust their calling behaviour in response to socio-sexual cues: adult females reared in high juvenile population densities called earlier and for longer than those from low juvenile densities. Juvenile density also affected female pheromonal attractiveness: Y-maze olfactometer assays revealed that males prefer pheromones produced by females reared at high juvenile densities. This strategic investment in calling behaviour by females, based on juvenile cues that anticipate the future socio-sexual environment, likely reflects a response to avoid mating failure through competition with neighbouring signallers.     

Influence of male competition on male mating behaviour in the cave molly, Poecilia mexicana

In many species, male mating behaviour is correlated with male body size, with large males often being preferred by females. Small surface-dwelling Poecilia mexicana males compensate for this disadvantage by being more sexually active and using sneaky copulations. In a cave-dwelling population, however, small males do not show this behaviour. Do small males alter their behaviour in the presence of a large rival? Here, we investigated the influence of male competition on male mating behaviour in the cave form. Two males of different sizes were mated with a female either alone or together with the other male. No aggressive interactions were observed between either fish. There was no statistically significant difference in the frequency of sexual behaviours between the two treatments. In both treatments, large males were more sexually active than small males. Thus, small cave molly males do not switch to an alternative mating behaviour in the presence of a larger rival. Possibly, the extreme environmental conditions in the cave (e.g. low oxygen content and high levels of hydrogen sulphide) favour saving energetic costs, resulting in the absence of alternative mating behaviour in small males.     

When are good genes good? Variable outcomes of female choice in wax moths

Female lesser wax moths (Achroia grisella) choose males based on characters of their ultrasonic advertisement signals. Because a female''s opportunity to obtain increased somatic benefits by mating with a particular male is limited, we investigated whether females obtain genetic benefits for their offspring via mate choice. Controlled breeding experiments conducted under favourable food and temperature conditions showed that developmental characters are heritable, that sire attractiveness and offspring survivorship are unrelated, but that females mating with attractive signallers produce offspring who mature faster than the offspring of females mating with non-attractive signallers. However, under some unfavourable food or temperature conditions, it is the offspring of females mating with non-attractive males who mature faster; these offspring are heavier as well. Thus, the relationship between male attractiveness and offspring development is not environmentally robust, and support for a good genes model of mate choice in A. grisella is dependent on conditions. These findings suggest genotype–environment interactions and emphasize the necessity of testing sexual selection models under a range of natural environments.     

Effect of multiple mating on the reproductive performance of the rice leaffolder moth,Cnaphalocrocis medinalis (Lepidoptera: Crambidae)

To clarify whether multiple mating of females and males affects the reproductive performance of the rice leaffolder moth, Cnaphalocrocis medinalis (Guenée), we examined the effect of the number of matings (once, twice, or three times) for females (female treatment) and males (male treatment) on the incidence of moth mating, number of eggs laid, egg hatchability, and adult longevity. We also compared the effect of multiple mating imposed on males or females separately with the effect of that imposed on both sexes simultaneously (both sexes treatment). The incidence of mating of females and males that mated three times (3-mated females and males) was significantly lower than for females and males that mated twice or once (2-mated or 1-mated females and males). The incidence of mating of 1-mated moths (both sexes) was significantly higher than for 2-mated or 3-mated moths (both sexes). Two-mated or 3-mated females laid significantly more eggs with significantly higher hatchability than 1-mated females. Females that mated with 1-mated males (second male mating) or 2-mated males (third male mating) laid significantly fewer eggs than those that mated with virgin males (first male mating). Females laid significantly more eggs after the second and third matings for moths of both sexes than after the first mating for moths of both sexes. The mechanisms of improvement and decline of female reproductive performance when multiple mating was imposed on males or females are also discussed in relation to the reproductive biology of C. medinalis.     

Microhabitat selection and audible sexual signalling in the wolf spider Hygrolycosa rubrofasciata (Araneae, Lycosidae)

We studied the microhabitat selection and male sexual signalling behaviour in the wolf spider Hygrolycosa rubrofasciata (Ohlert). Males strike dry leaves with their abdomen, producing an audible sexual drumming signal, and females use this signal to choose mating partners. In the field we followed male drumming rate and microhabitat selection using both the mark–recapture method and direct observations. In the laboratory we conducted an experiment on male microhabitat and drumming substrate selection. We found that in the field males were not distributed randomly among the habitat; fewer males were found in areas that had high sedge cover, low elevation, and low dry leaf cover. In the laboratory experiment, males spent more time on dry leaf substrate. Drumming rate in the field was positively correlated with dry leaf cover and in the laboratory males clearly preferred dry leaves as drumming substrate. Temperature was positively correlated with male drumming rate, and with male and female mobility. We conclude that in H. rubrofasciata male distribution and sexual signalling rate, and thus mating success, are greatly affected by environmental factors. Therefore, males may be sexually selected to make effective use of their signalling habitat by active microhabitat choice. Received: 27 December 1999 / Received in revised form: 14 February 2000 / Accepted: 14 February 2000     

Queuing and queue-jumping: long-term patterns of reproductive skew in male savannah baboons, Papio cynocephalus

In many animals, variance in male mating success is strongly correlated with male dominance rank or some other measure of fighting ability. Studies in primates, however, have varied greatly in whether they detect a relationship between male dominance rank and mating success. This variability has led to debate about the nature of the relation between rank and mating success in male primates. We contribute to the resolution of this debate by presenting an analysis of the relationship between dominance rank and male mating success over 32 group-years in a population of wild savannah baboons. When data were pooled over the entire period, higher-ranking males had greater access to fertile females. However, when we examined successive 6-month blocks, we found variance in the extent to which rank predicted mating success. In some periods, the dominance hierarchy functioned as a queue in which males waited for mating opportunities, so that rank predicted mating success. In other periods, the queuing system broke down, and rank failed to predict mating success when many adult males were in the group, when males in the group differed greatly in age, and when the highest-ranking male maintained his rank for only short periods. The variance within this single population is similar to the variance observed between populations of baboons and between species of primates. Our long-term results provide strong support for the proposition that this variance is not an artefact of methodological differences between short-term studies, but is due to true variance in the extent to which high-ranking males are able to monopolize access to females. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.     

Concurrent modulation of neuronal and behavioural olfactory responses to sex and host plant cues in a male moth

Mating has profound effects on animal physiology and behaviour, not only in females but also in males, which we show here for olfactory responses. In cotton leafworm moths, Spodoptera littoralis, odour-mediated attraction to sex pheromone and plant volatiles are modulated after mating, producing a behavioural response that matches the physiological condition of the male insect. Unmated males are attracted by upwind flight to sex pheromone released by calling females, as well as to volatiles of lilac flowers and green leaves of the host plant cotton, signalling adult food and mating sites, respectively. Mating temporarily abolishes male attraction to females and host plant odour, but does not diminish attraction to flowers. This behavioural modulation is correlated with a response modulation in the olfactory system, as shown by electro-physiological recordings from antennae and by functional imaging of the antennal lobe, using natural odours and synthetic compounds. An effect of mating on the olfactory responses to pheromone and cotton plant volatiles but not to lilac flowers indicates the presence of functionally independent neural circuits within the olfactory system. Our results indicate that these circuits interconnect and weigh perception of social and habitat odour signals to generate appropriate behavioural responses according to mating state.     

The effect of hunger on mating behaviour and sexual selection for male body size in Gerris buenoi

The set of mating behaviours expressed by an individual may depend upon the state of that individual and local environmental conditions. Understanding how these factors affect mating behaviours may elucidate how a mating system operates, and its consequences for the form and strength of sexual selection. We conducted two experiments on the water striderGerris buenoi to (1) determine the effect of hunger on the mating behaviour of both sexes and (2) examine female choice for large males. In our first experiment, we manipulated hunger (20 h starvation) in both sexes and recorded mating, male harassment, copulation duration and guarding duration. We predicted that hunger would increase female reluctance to mate because mating conflicts with foraging. Female hunger (20 h starvation) decreased mating rate by two-thirds but had no significant effect on male mating behaviour. In a second experiment, we examined the effect of female hunger, and resulting reluctance, on sexual selection for large male size. Hungry females (5 h starvation) were placed with two fed males (one large, one small) and we recorded male premating and mating behaviours. We observed significant large-male mating advantage when females were hungry, but not when satiated. Mating efforts (harassment, premating struggles) were similar for both male phenotypes in both female hunger treatments, suggesting that the mating advantage of large males resulted from increased reluctance of hungry females to mate. Neither male body size nor female hunger explained a significant amount of variation in copulation duration or guarding duration. We discuss our results in light of two competing hypotheses for female choice (active and passive) on male body size and suggest that passive choice for large males acts in this system. Copyright 2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour     

Female preference for multi-modal courtship: multiple signals are important for male mating success in peacock spiders

A long-standing goal for biologists has been to understand how female preferences operate in systems where males have evolved numerous sexually selected traits. Jumping spiders of the Maratus genus are exceptionally sexually dimorphic in appearance and signalling behaviour. Presumably, strong sexual selection by females has played an important role in the evolution of complex signals displayed by males of this group; however, this has not yet been demonstrated. In fact, despite apparent widespread examples of sexual selection in nature, empirical evidence is relatively sparse, especially for species employing multiple modalities for intersexual communication. In order to elucidate whether female preference can explain the evolution of multi-modal signalling traits, we ran a series of mating trials using Maratus volans. We used video recordings and laser vibrometry to characterize, quantify and examine which male courtship traits predict various metrics of mating success. We found evidence for strong sexual selection on males in this system, with success contingent upon a combination of visual and vibratory displays. Additionally, independently produced, yet correlated suites of multi-modal male signals are linked to other aspects of female peacock spider behaviour. Lastly, our data provide some support for both the redundant signal and multiple messages hypotheses for the evolution of multi-modal signalling.     

Characteristics of the Signals of Male <Emphasis Type="Italic">Anoeconeossa bundoorensis</Emphasis> Taylor and Burckhardt (Hemiptera: Aphalaridae) Associated with Female Responsiveness

Sexual selection requires intra-specific variation in the characteristics mediating mate choice. In species reliant on substrate-borne vibrational signalling (SBVS), differences in the attractiveness of individual signallers’ calls can influence relative mating success since they can indicate the quality of the sender. We used laser vibrometry and playback experiments to study duet signalling in a psyllid (Anoeconeossa bundoorensis Taylor and Burckhardt), in particular to identify characteristics linked to female responsiveness. Signals were sex-specific with the syllables (or calls) of the smaller males attaining higher frequencies than the syllables of the larger females. Male syllables build over time with more energy in the second half of the call while those of females have a more uniform energy distribution. Male syllables vary in the timing of the halfway point of energy production. We used playback to examine species recognition and female responsiveness to the first and second halves of male calls. We demonstrated that females responded only to calls of male A. bundoorensis and that they were more likely to respond to the first half of male calls. Based on the results of our second playback experiment, we found that a gradation in energy production is more important for eliciting a female reply than a uniform distribution of energy. Our findings show that the rate of energy production facilitates differentiation between syllables which could be used to indicate the quality of individual males as mates.     

Is there a role for amplifiers in sexual selection?

The amplifier hypothesis states that selection could favour the evolution of traits in signallers that improve the ability of receivers to extract honest information from other signals or cues. We provide a formal definition of amplifiers based on the receiver's mechanisms of signal perception and we present a game-theoretical model in which males advertise their quality and females use sequential-sampling tactics to choose among prospective mates. The main effect of an amplifier on the female mating strategy is to increase her mating threshold, making the female more selective as the effectiveness of the amplifier increases. The effects of the amplifier on male advertising strategy depends both on the context and on the types of the amplifier involved. We consider two different contexts for the evolution of amplifiers (when the effect of amplifiers is on signals and when it is on cues) and two types of amplifiers (the ‘neutral amplifier’, when it improves quality assessment without altering male attractiveness, and the ‘attractive amplifier’, when it improves both quality assessment and male attractiveness). The game-theoretical model provides two main results. First, neutral and attractive amplifiers represent, respectively, a conditional and an unconditional signalling strategy. In fact, at the equilibrium, neutral amplifiers are displayed only by males whose advertising level lays above the female acceptance threshold, whereas attractive amplifiers are displayed by all signalling males, independent of their quality. Second, amplifiers of signals increase the differences in advertising levels between amplifying and not-amplifying males, but they decrease the differences within each group, so that the system converges towards an ‘all-or-nothing’ signalling strategy. By applying concepts from information theory, we show that the increase in information transfer at the perception level due to the amplifier of signals is contrasted by a decrease in information transfer at the emitter level due to the increased stereotypy of male advertising strategy.     

Age-specific reproductive behaviours in male roe deerCapreolus capreolus

The behaviour of active male roe deerCapreolus capreolus Linnaeus, 1758 was studied in a wild population on Storfosna island (Norway), during the pre-territorial and territorial seasons (February–August) of 1994. Observed behaviours were grouped in seven categories (mating, aggression, display, marking, vigilance, moving and maintenance), and the proportion of time spent in each behaviour by three age classes (yearlings, subadults and adults) was compared. Time spent in each behaviour varied significantly between months for all male age classes. From February to August, time spent in maintenance decreased, while time spent in vigilance increased. The time spent in mating increased both in adult and subadults but did not vary significantly for yearlings throughout the months. When comparing age classes within a month, there were no significant differences in time spent in each behaviour. Surprisingly, adult territorial males did not invest significantly more time in mating, with respect to yearlings and subadults. This may be consistent with the oligogynous mating system of roe deer, in which the reproductive success is divided amongst several years and their territoriality, which could be a tactic to reduce the competition for mating.     

Behaviour before beauty: Signal weighting during mate selection in the butterfly Papilio polytes

Mating displays often contain multiple signals. Different combinations of these signals may be equally successful at attracting a mate, as environment and signal combination may influence relative signal weighting by choosy individuals. This variation in signal weighting among choosy individuals may facilitate the maintenance of polymorphic displays and signalling behaviour. One group of animals known for their polymorphic patterning are Batesian mimetic butterflies, where the interaction of sexual selection and predation pressures is hypothesized to influence the maintenance of polymorphic wing patterning and behaviour. Males in the female‐limited polymorphic Batesian mimetic butterfly Papilio polytes use female wing pattern and female activity levels when determining whom to court. They court stationary females with mimetic wing patterns more often than stationary females with non‐mimetic, male‐like wing patterns and active females more often than inactive females. It is unclear whether females modify their behaviour to increase (or decrease) their likelihood of receiving male courtship, or whether non‐mimetic females spend more time in cryptic environments than mimetic females, to compensate for their lack of mimicry‐driven predation protection (at the cost of decreased visibility to males). In addition, relative signal weighting of female wing pattern and activity to male mate selection is unknown. To address these questions, we conducted a series of observational studies of a polymorphic P. polytes population in a large butterfly enclosure. We found that males exclusively courted active females, irrespective of female wing pattern. However, males did court active non‐mimetic females significantly more often than expected given their relative abundance in the population. Females exhibited similar activity levels, and selected similar resting environments, irrespective of wing pattern. Our results suggest that male preference for non‐mimetic females may play an active role in the maintenance of the non‐mimetic female form in natural populations, where males are likely to be in the presence of active, as well as inactive, mimetic and non‐mimetic females.     

Endocrine manipulations and ontogenesis of male sexual behaviour in Locusta: studies on azadirachtin-induced over-aged nymphs

ABSTRACT. Dose-response relations of the moult-inhibitory and lethal effects of azadirachtin (AZA) injected into fifth and fourth instar hoppers of Locusta migratoria migratorioides are presented. The optimal dose for obtaining maximum number of long-surviving over-aged nymphs is 1.6 and 1.0 μg of AZA per insect for young fifth and fourth instar nymphs, respectively. Over-aged male nymphs are capable of exhibiting sexual behaviour. The mating behaviour of fifth instar over-aged male nymphs, and of chemically allatectomized but otherwise similar over-aged male nymphs (obtained by combined precocene treatment and injection of AZA), with and without injections of exogenous Juvenile Hormone III (JH), is investigated quantitatively; the results are compared with those obtained for normal, chemically allatectomized, and chemically allatectomized plus JH-injected adult males. Over-aged fifth instar male nymphs show a low intensity of mating behaviour and in chemically allatectomized ones this intensity is even lower. Injections of JH intensify the mating behaviour of chemically allatectomized fifth instar over-aged male nymphs in a dose-dependent way, but less markedly so than in chemically allatectomized adult males. We conclude that the intensity of male mating behaviour of the over-aged nymphs is subnormal and their response to the mating behaviour intensifying effect of the JH is weaker than that of adult males. The relations between endocrine factors and ethological ontogenesis of male sexual behaviour in locusts are discussed.     

Extreme Costs of Mating for Male Two-Spot Ladybird Beetles

Male costs of mating are now thought to be widespread. The two-spot ladybird beetle (Adalia bipunctata) has been the focus of many studies of mating and sexual selection, yet the costs of mating for males are unknown. The mating system of A. bipunctata involves a spermatophore nuptial gift ingested by females after copulation. In this study, we investigate the cost to males of mating and of transferring spermatophores in terms of lifespan, ejaculate production and depletion of nutritional reserves. We found that males faced a strong trade-off between mating and survival, with males that were randomly assigned to mate a single time experiencing a 53% reduction in post-mating lifespan compared to non-mating males. This is among the most severe survival costs of a single mating yet reported. However, spermatophore transfer did not impact male survival. Instead, the costs associated with spermatophores appeared as a reduced ability to transfer spermatophores in successive matings. Furthermore, males ingested more food following spermatophore transfer than after matings without spermatophores, suggesting that spermatophore transfer depletes male nutritional reserves. This is to our knowledge the first report of an effect of variation in copulatory behaviour on male foraging behaviour. Overall, our study highlights the advantages of assessing mating costs using multiple currencies, and suggests that male A. bipunctata should exhibit mate choice.     

Sexually mature and immature yearling male European ground squirrels: A comparison of behavioral and physiological parameters

Early puberty may increase lifetime reproductive success, but may also entail diverse costs. In male European ground squirrels (Spermophilus citellus), age at sexual maturity varies among individuals. We compared sexually active and inactive yearling males under standardized conditions in outdoor enclosures. Non-reproductive yearling males hibernated significantly longer than mature males and emerged when the mating period had already started. Testosterone concentrations peaked in the precocious males during premating and mating, and were depressed in the non-reproductive individuals throughout the study period. Emergence body mass was similar in both groups, although sexually immature males were significantly heavier at the end of the active season. Additionally, non-reproductive yearlings grew faster than precocious individuals. Male–male aggression peaked during mating and the following 4 weeks. Intense aggressive interactions like chases and fights were mostly initiated by reproductive males and were directed towards mature competitors. Aggressive behavior in immature males was mainly expressed as spatial displacements. Non-agonistic interactions with females were only observed in sexually active males. Concentrations of fecal cortisol metabolites did not differ between the two male groups and were elevated in the second half of the active season. Leucocyte numbers were reduced during mating in mature males, whereas in immature animals, cell numbers did not change significantly. Our results indicate that early puberty in European ground squirrels involves lower growth rates, high intrasexual aggression, lower prehibernatory body mass, and probably worse immunological condition during mating.     

The social organization of feral peafowl

Peafowl are usually reported to have a mating system based on harem defence by adult males. In a small feral population near Oxford, males defended small (<1 ha) territories while females remained in one flock that ignored male territory boundaries. After mating, females become solitary. At no time did a female associate selectively with one male or remain within his territory, nor did males attempt to follow or guard female groups. Two out of four males were seen to mate. These differed from the other two in being neither very old nor very young; they held territories smaller than that of the young male and were no larger or longer-tailed. However, they spent more time displaying. We suggest that peafowl have a mating system similar to a lek: males defending small, clumped territories visited by females for mating.     

Evolution of outcrossing in experimental populations of Caenorhabditis elegans

Caenorhabditis elegans can reproduce exclusively by self-fertilization. Yet, males can be maintained in laboratory populations, a phenomenon that continues to puzzle biologists. In this study we evaluated the role of males in facilitating adaptation to novel environments. For this, we contrasted the evolution of a fitness component exclusive to outcrossing in experimental populations of different mating systems. We introgressed a modifier of outcrossing into a hybrid population derived from several wild isolates to transform the wild-type androdioecious mating system into a dioecious mating system. By genotyping 375 single-nucleotide polymorphisms we show that the two populations had similar standing genetic diversity available for adaptation, despite the occurrence of selection during their derivation. We then performed replicated experimental evolution under the two mating systems from starting conditions of either high or low levels of diversity, under defined environmental conditions of discrete non-overlapping generations, constant density at high population sizes (N = 10⁴), no obvious spatial structure and abundant food resources. During 100 generations measurements of sex ratios and male competitive performance showed: 1) adaptation to the novel environment; 2) directional selection on male frequency under androdioecy; 3) optimal outcrossing rates of 0.5 under androdioecy; 4) the existence of initial inbreeding depression; and finally 5) that the strength of directional selection on male competitive performance does not depend on male frequencies. Taken together, these results suggest that androdioecious males are maintained at intermediate frequencies because outcrossing is adaptive.     

Male Drosophila melanogaster show adaptive mating bias in response to female infection status

Given the non-trivial cost of reproduction for males and substantial variation in female quality, males have been predicted to show mating bias as an evolved strategy. Using a large outbred population of Drosophila melanogaster, we test this prediction and show that males may adaptively bias their mating effort in response to the infection status of females. Given a simultaneous choice between females infected with pathogenic bacteria and sham infected females, males preferentially mated with the latter, who had a higher reproductive output compared to infected females. This may provide evidence for pre-copulatory male mate choice. Assessment of the reproductive behaviour ensured that the observed pattern of mating bias was not due to differences in receptivity between females infected with pathogenic bacteria and sham infected females. Further, there was no evidence for post-copulatory male mate choice measured in terms of copulation duration.