Wing pigmentation in territorial male damselflies, Calopteryx haemorrhoidalis: a possible relation to sexual selection

One striking characteristic in adult males of some odonate species is the presence of wing pigmentation. In Calopteryx species, males show a series of pre- and postcopulatory behavioural displays during which they face females while showing their pigmented wings. One hypothesis to explain the precopulatory flying displays and the associated wing pigmentation is that they may serve a sexual selection function. I investigated this in the territorial damselfly Calopteryx haemorrhoidalis. Males of this species defend aquatic substrates that females use for oviposition. Observational evidence indicated that males with a higher proportion of wing pigmentation were more likely to defend a territory, obtained more matings, had fewer gut parasites, survived in the study site and stayed in territories for longer. Experimental evidence suggested that the relationship mating success and wing pigmentation still held when controlling for the size of the substrate defended by territorial males. Similar to other studies in the Calopterygidae, these results suggest that wing pigmentation may be favoured by sexual selection. I discuss, however, whether an alternative function for male copulatory courtship displays and wing pigmentation, as sexual and/or species recognition, may also explain the evolution of these traits. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Reproductive behaviour of female Chorthippus biguttulus grasshoppers

Female grasshoppers of acoustically communicating species assume series of reproductive states that are associated with particular behaviours. Studies on laboratory populations of Chorthippus biguttulus (L.) revealed that females of this species lack the period of ‘passive copulatory readiness’, increase their attractiveness to males by sound production and mate multiple times before their first oviposition. In particular, female Ch. biguttulus display a period of ‘primary rejection’ after their imaginal moult during which they reject male mating attempts followed by a period of ‘active copulatory readiness’ in which they produce acoustic signals and may copulate with courting males. Female stridulation generally stimulated male mating activity and stridulating females attracted more male mating attempts than mute females in the same cage, indicating that males preferentially court females that signal ‘active copulatory readiness’. After receipt of a spermatophore, Ch. biguttulus females displayed periods of ‘secondary rejection’ followed by re-establishment of ‘active copulatory readiness’. Acoustic responses of females to male songs, an indicator of reproductive readiness, were significantly reduced until 2 days after mating and remained slightly reduced in comparison to pre-mating levels. Some females mated multiple times before their first oviposition and cycled between ‘secondary rejection’ and ‘active copulatory readiness’.     

Courtship tactics in garter snakes: how do a male's morphology and behaviour influence his mating success?

The behavioural determinants of male mating success play a pivotal role in sexual selection, but remain poorly known for most kinds of organisms, including most reptiles. In Manitoba, Canada, large numbers of red-sided garter snakes, Thamnophis sirtalis parietalis, court and mate in early spring near communal overwintering dens. To understand how a male's morphology and behaviour might influence his mating success, we videotaped 21 groups of snakes each comprising four males of varying body sizes plus a female. All males engaged in courtship, and mating occurred in all groups. Males with better body condition courted more vigorously and successfully than their smaller rivals did. The males that obtained matings were those that maintained their own cloaca closest to that of the female, aligned most of their body with the female, showed high rates of caudocephalic waving, chin pressing and tail searching, and did not allow other males to insert their body beside the female's. These behavioural differences between ‘winners’ and ‘losers’ were apparent from the beginning of each trial. Thus, male mating success in this ‘scramble’ system is determined not by chaotic, stochastic struggle (as has often been inferred) but instead is strongly linked to male courtship tactics. Energy stores (as evidenced by good body condition) may be critical determinants of mating success in these vigorous courtship episodes.     

Evolutionary significance of courtship conditioning in Drosophila melanogaster

Males of the fly Drosophila melanogaster initially court mated, unreceptive females but later develop an avoidance reaction against them and even become temporally unresponsive to virgin females. This conditioned inhibition has been described as an associative process, the conditioned stimulus being a mixture of pheromones on the female's cuticle. To assess the evolutionary significance of courtship conditioning we recorded and analysed the male's behaviour during the conditioning process. The time traces of individual males were marked by an abrupt behavioural change. The time he spent courting suddenly decreased, and the frequency of ‘turn-away’ events at the same time sharply increased. Thus, the gradual decline of courtship observed as a group average does not reflect a slow change in motivation of the individual male but rather the interindividual differences of an active, experience-guided all-or-none decision to stop courting and to avoid the female. Three recently collected D. melanogaster strains were each maintained under two distinct mating conditions. Males were kept together with females for either ca. 2 weeks or 18 h. After 21 generations males of the two regimes differed markedly in their behaviour towards mated females. With long interaction periods between males and females, selection favoured courtship conditioning, while with short periods no such selection was observed. Slowly recovering receptivity of mated females may be needed for the maintenance of courtship conditioning. Courtship conditioning in D. melanogaster appears to be a fitness-relevant behaviour adapted to high-density populations with females mating a second time.     

Juvenile hormone favors sexually-selected traits but impairs fat reserves and abdomen mass in males and females

The physiological mechanism underlying resource allocation in sexual selection studies has been little studied. One candidate is hormones as these favor resource allocation to reproductive traits but impair survival due to a resource over-expenditure directed to the former traits. We have investigated whether a juvenile hormone analog (JHa, methoprene) administrated topically is involved in the resource allocation to wing pigmentation (an ornamental trait), fat reserves and flight muscle mass in both sexes of Calopteryx haemorrhoidalis and C. virgo. We also investigated the possible negative effect of such implementation on abdomen mass (an indirect measure of egg production) and field-based survival in adult males of C. haemorrhoidalis and C. splendens. We found that males and females treated with JHa, against a control group, developed higher wing pigmentation and showed reduced fat reserves but had no change in muscle mass. In females, JHa decreased abdominal weight (an indicator of fecundity) and in males, survival was impaired only in C. splendens. These results support the idea that JH induces resource allocation to wing pigmentation, a sexually selected trait in both sexes. Thus, this study suggests that the action of JH could be a mechanistic link between ornaments and physiological condition in both males and females.     

Plasmodium male development gene-1 (mdv-1) is important for female sexual development and identifies a polarised plasma membrane during zygote development

Successful development of Plasmodium sexual stages is essential for parasite survival, but the genes involved are poorly understood. We ‘knocked out’ the male development gene-1 (mdv-1) locus in Plasmodium berghei and found it to be important in female gametocyte activation. Indirect immunofluoresence assays show MDV-1 has a punctate cytoplasmic distribution in gametocytes. After activation of both females and males, MDV-1 is more peripherally located but in males exclusively it becomes concentrated in a few large foci. In vitro ookinete conversion assays that test the ability of activated female gametocytes to develop into retort stage ookinetes, suggests a complicit role for MDV-1, with the knock-out parasite producing 86% reduction in ookinetes. The retort stage ookinete develops from the zygote by increasing growth of an apical protrusion and MDV-1 locates at the ‘leading’ extracellular apical pole of this protrusion. In the fully developed ookinete MDV-1 is localised to the posterior pole. In vivo, the knock-out parasites demonstrate a phenotype in which there is a 90% reduction of parasite transmission to oocysts in mosquitoes.     

Hold on: Females modulate sperm depletion from storage sites in the fly Drosophila melanogaster

Among many species of insects, females gain fitness benefits by producing numerous offspring. Yet actions related to producing numerous offspring such as mating with multiple males, producing oocytes and placing offspring in sub-optimal environments incur costs. Females can decrease the magnitude of these costs by retaining gametes when suitable oviposition sites are absent. We used the pomace fly, Drosophila melanogaster, to explore how the availability of fresh feeding/oviposition medium influenced female fitness via changes in offspring survivorship and the modulation of gamete release. Availability of fresh medium affected the absolute number and temporal production of offspring. This outcome was attributable to both decreased larval survival under crowded conditions and to female modulation of gamete release. Direct examination of the number of sperm retained among the different female storage organs revealed that females ‘hold on’ to sperm, retaining more sperm in storage, disproportionately within the spermathecae, when exposed infrequently to fresh medium. Despite this retention, females with lower rates of storage depletion exhibited decreased sperm use efficiency shortly after mating. This study provides direct evidence that females influence the rate of sperm depletion from specific storage sites in a way that can affect both female and male fitness. The possible adaptive significance of selective gamete utilization by female Drosophila includes lowering costs associated with frequent remating and larval overcrowding when oviposition sites are limiting, as well as potentially influencing paternity when females store sperm from multiple males.     

Why Do Males of the Spider Pisaura mirabilis Wrap Their Nuptial Gifts in Silk: Female Preference or Male Control?

Males of the spider Pisaura mirabilis present a nuptial prey gift to the female during courtship as a mating effort. The gift is usually round and wrapped in white silk. It was suggested that the wrapped gift functions as a sensory trap by mimicking the female's eggsac implying that males exploit the female maternal care instinct and not her foraging motivation in a sexual context. The shape of the gift (round) and appearance (white) should then increase female acceptance of males. We tested these predictions experimentally and found that neither gift shape (round or oblong) nor silk wrapping (wrapped or unwrapped) facilitated female acceptance, in contrast unwrapped gifts were accepted faster than wrapped ones. Instead, we found that silk wrapping benefited the males because it significantly decreased the risk of females stealing the gift without copulation and consequently directly increased male mating success. Large oblong gifts were difficult for males to handle during copulation, resulting in shorter copulations for oblong vs. round gifts. Thus, round gifts were not preferred by the females but were beneficial to the males. Our results indicate two adaptive benefits to males of wrapping the nuptial gift: to reduce the risk of losing the gift to females without copulation, and make it possible to reshape an oblong prey into a round gift that facilitates the male's access to the female's genitalia. Our results suggest that the male gift wrapping trait may be selected though sexual conflict over remating rate.     

Sexual selection in an anadromous population of threespine sticklebacks — no role for parasites

Summary We examined the hypothesis that trematode parasites played a role in the evolution of the red colour of male threespine sticklebacks (Gasterosteus aculeatus L.) and whether the parasites affected female fitness. Parasites (blackspot disease) played no role either in determining the outcome of male—male competition for breeding territories or in female mate choice. Among males with territories, mating success was highly variable. Some males obtained over 3000 eggs (approximately 10 matings) whereas others received none. In 1 year of the 2 year study, males with the greatest amount of red nuptial coloration had the greatest mating success. Although male colour may sometimes affect female choice in this system, this preference has probably not evolved because of the Hamilton—Zuk mechanism of sexual selection. The parasites had small, but statistically significant effects on female fitness. Females with high parasite loads were in poorer condition and produced fewer eggs than less parasitized fish.     

Immune system activation affects male sexual signal and reproductive potential in crickets

Parasite-mediated sexual selection theory posits that individuals(usually females) choose mates by assessing the expression ofcostly secondary sexual signals, which provide reliable indicationsof parasite resistance. If these signals are indeed reliable,then immune-compromised males are predicted to exhibit changesin the sexual signal that are discernable by the female. Moreover,the mating pair is predicted to exhibit some reduction in reproductivefitness if the male is immune compromised. Here, we addressedthese predictions in the ground cricket, Allonemobius socius,by injecting juvenile males with lipopolysaccarides, which allowedus to activate the immune system without the introduction ofa metabolically active pathogen. As a consequence, we were ableto disentangle the cost of immune system activation from thecost of infection. We found that immune activation had a long-termeffect on male calling song and the males' ability to providepaternal resources, which can constrain male and female reproductivepotential. We also found that song interpulse interval variedsignificantly with the male's immune treatment and may thereforeprovide choosy females with a way to avoid mating with immune-compromisedmales. In short, our data support the parasite-mediated theoryof sexual selection, suggesting that female's gain direct benefitsby mating with males who are immune competent.     

Females lay fewer eggs for males with greater courtship success in a lekking Drosophila

The evolutionary basis for female mate choice in lek mating systems has been a common subject of research in animal behaviour. Because males apparently provide only gametes to females in lekking species, most research has focused on possible indirect (genetic) benefits that females might gain by discriminating among males. Despite the emphasis on indirect benefits, it has been recognized that females in non-resource-based systems such as leks could potentially gain direct benefits via mate choice if males varied in fertilization abilities, for example. Previous evidence has shown that females of a lekking Hawaiian Drosophila, D. grimshawi, vary in fecundity when mated to certain males, and that females possess preferences for vigorously courting males. This study tests the hypothesis that D. grimshawi females gain direct benefits by preferentially mating with more sexually vigorous males. Male courtship vigour (performance of wing and head-under-wing displays) and the consequences of female choice on offspring production were evaluated separately using different females. Unexpectedly, matings involving more vigorously courting males resulted in fewer offspring being produced. Reduced offspring number resulted because females laid fewer eggs when mating with males having greater courtship success. These results are discussed in light of sexual conflict and possible multiple mating by females. Females also demonstrated considerable variation in mating behaviour and behavioural variation was correlated with mating benefits. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Do individuals in better condition survive for longer? Field survival estimates according to male alternative reproductive tactics and sex

There is a gap in terms of the supposed survival differences recorded in the field according to individual condition. This is partly due to our inability to assess survival in the wild. Here we applied modern statistical techniques to field‐gathered data in two damselfly species whose males practice alternative reproductive tactics (ARTs) and whose indicators of condition in both sexes are known. In Paraphlebia zoe, there are two ART: a larger black‐winged (BW) male which defends mating territories and a smaller hyaline‐winged (HW) male that usually acts as a satellite. In this species, condition in both morphs is correlated with body size. In Calopteryx haemorrhoidalis, males follow tactics according to their condition with males in better condition practicing a territorial ART. In addition, in this species, condition correlates positively with wing pigmentation in both sexes. Our prediction for both species was that males practicing the territorial tactic will survive less longer than males using a nonterritorial tactic, and larger or more pigmented animals will survive for longer. In P. zoe, BW males survived less than females but did not differ from HW males, and not necessarily larger individuals survived for longer. In fact, size affected survival but only when group identity was analysed, showing a positive relationship in females and a slightly negative relationship in both male morphs. For C. haemorrhoidalis, survival was larger for more pigmented males and females, but size was not a good survival predictor. Our results partially confirm assumptions based on the maintenance of ARTs. Our results also indicate that female pigmentation, correlates with a fitness component – survival – as proposed by recent sexual selection ideas applied to females.     

Acoustic mimicry and disruptive alternative calling tactics in an Australian bushcricket (Caedicia; Phaneropterinae; Tettigoniidae; Orthoptera): does mating influence male calling tactic?

Abstract.  Male calling and searching tactics are described for a duetting Australian bushcricket, Caedicia sp. 12 (Phaneropterinae; Tettigoniidae; Orthoptera). The repertoire of Caedicia sp. 12 consists of the calling song and, by nonduetting males, a series of calling tactics that include short-click calling, disruptive over-singing and a call mimicking the entire duet. Nonduetting males respond to the production of a duet by another male and a female with short-click calls that mimic the female call at the conclusion of a duet. By manipulating the male's mating history, it is found that this form of calling behaviour is more likely to occur within the male's 6-day postmating refractory period; the low cost tactic allows males to re-mate during spermatophore replenishment. Males also produce disruptive calls in response to a duet, where the male may over-sing the duetting male's signal or produce a call that appears to mimic the entire duet; the male produces a calling song followed by a short signal that has the same latency as the female's reply within a duet. Males also over-sing crucial elements of the duetting-male's song that are normally critical for the female's conspecific recognition. There is no evidence that females search for the duetting male partner, but males unable to enter a duet will search for the call of a responding female. Searching by males is more common when these males are producing disruptive calls. Alternative male calling tactics are discussed as a set of conditional strategies for securing unmated females.     

Do female fruit flies (Drosophila serrata) copy the mate choice of others?

Female mate-choice copying is a social learning phenomenon whereby a female's observation of a successful sexual interaction between a male and another female increases her likelihood of subsequently preferring that male. Although mate-choice copying has been documented in several vertebrate species, to our knowledge it has not yet been investigated in insects. Here, we investigated whether female mate-choice copying occurs in the fruit fly Drosophila serrata, a model system for the study of mate preferences and the sexual selection they generate. We used two complementary experiments in which focal females were given a choice between two males that differed in either their apparent (as determined visually by the focal female) or actual recent mating success. Mate-choice copying was evaluated by testing whether focal females mated more frequently with the ‘preferred’ male as opposed to the other male. In both experiments, however, we found no evidence for mate-choice copying. We discuss possible reasons for the apparent absence of mate-choice copying in this species.     

A test of speciation via sexual selection on female preferences

Sexual selection for divergent female preferences has been proposed to stimulate speciation. We tested this basic model by selecting for divergence in the courtship repertoire of the house fly Musca domestica L. Specifically, we subjected replicate strains to artificial selection for differentiation along the first two principal components of the phenotypic intercorrelation structure of five courtship traits. Highly significant differentiation in courtship repertoire resulted, and the magnitude of the selection response was highest along the first principal component (representing the ‘size’, or general intensity, of courtship). Videotaped matings of the crosses between divergent lines (i.e. males of one strain mating with females from a different line) showed that the selection responses in the intensities of male performances were due to shifts in female preferences. In particular, the males were able to accommodate the demands of ‘foreign’ females (as well as their own) in the no-choice situation (i.e. only one male and one female per mating chamber). In contrast to this plasticity of the males, the females were consistent in their differential resistance responses, regardless of the type of male involved in the courtship. Multiple-choice mate choice tests revealed significant reproductive isolation among some lines, although the effect was asymmetrical. The patterns of nonrandom mating were largely due to females from more genetically healthy lines (i.e. with overall high mating propensity) discriminating against males from populations with more inbreeding depression. We suggest that the inability to achieve true (symmetrical) reproductive isolation could have been due to low evolutionary potential in the ‘shape’ of courtship, as defined by the second principal component. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Sperm competition and the significance of female multiple mating in the predatory mite Parasitus fimetorum

Females of the predatory mite Parasitus fimetorum (Gamasida; Parasitina) inhabiting animal manure indiscriminately copulate with many mates. The sperm competition between the males was estimated by electrophoresis of allozymes and the effects of multiple mating on female reproduction were investigated. When females were forced to mate only once, their fecundity decreased drastically compared to the case of multiple mating (but longevity was unaffected). When one female mated with two males, the outcome of sperm competition depended greatly upon the mating interval. When the second mating occurred immediately after the first, the female fecundity decreased as in the case of single mating and the second male fertilized only a few eggs. However, when there was an interval of 1 day between the two matings, the females achieved normal fecundity and the second male fertilized approximately half the eggs. This suggests that the spermatophore deposited by the first male may act as a short-term copulatory plug in the female's genital opening. When one female mated with several males with 1 day intervals, three or more males shared fertilization of the eggs. This study suggests that the multiple mating of females is a necessary stimulus to continue oogenesis and some physiological factors for this stimulation may exist in spermatophores.     

Mating,insemination, and ovulation in the tsetse fly, Glossina morsitans

Virgin females of the tsetse fly, Glossina morsitans orientalis, retain their first egg within the right ovary whereas mated females ovulate. The component of the mating act which causes ovulation and thereby initiates the ovarian cycles which follow, is not insemination, the construction of a spermatophore in the uterus, or a humoral factor associated with the testes, accessory glands or ejaculatory ducts of donor males, or ‘full’ spermathecae of donor females. The ovulation rate increases with copulation time and females are shown to ‘add up’ their ‘sexual experience’ independently of that of the males. Inter-specific matings between G. morsitans and G. austeni also result in ovulation, but an unidentified factor associated with the completion of the mating act was also apparent. It is suggested that a ‘mechanical’ factor probably with nervous and endocrine components is responsible for the release of the egg from the ovary. Observations on the construction of empty spermatophores by aspermic males of G. morsitans are included.     

Heritable variation in the timing of spermatophore removal, a mechanism of post-copulatory female choice in crickets

Female crickets can exert post-copulatory mating preferences by prematurely removing a male's spermatophore after copulation, which terminates sperm transfer. Although most models of sexual selection assume that female mating preferences are heritable, there has been little work addressing genetic variation underlying post-copulatory mate choice. We used a paternal half-sib design, in which different males were randomly assigned as mates to several females to create half-sib families, to determine the heritability of spermatophore retention time in female house crickets, Acheta domesticus. There was significant additive genetic variance in the timing of spermatophore removal by females [h(2) = 0.50 +/- 0.19 (+/- SE)], suggesting that the timing of spermatophore removal is determined, in part, by the female's own genotype independent of the quality of her mate. The relatively high heritability of spermatophore retention time may be reflective of the absence of strong selection on this trait, consistent with previous work showing no difference in the fitness of females permitted to freely remove the spermatophore of their mates and those forced to accept complete ejaculates.     

Mating Behavior of Cephalonomia tarsalis (Ashmead) (Hymenoptera: Bethylidae) and the Effect of Female Mating Frequency on Offspring Production

The courtship behavior of Cephalonomia tarsalis, a solitary semiectoparasitoid of Oryzaephilus surinamensis, was investigated in the laboratory. Courtship behavior includes a series of stereotypic movements. Males play the most active role, executing the majority of courtship action, and females respond with relatively limited observable behaviors. Males typically keep antennae still during encounters with females prior to mounting, which may be correlated with recognition of the female's sexual status. After mounting, males display a series of movements on females, such as antennae touching female's antennae, antennae or mouth touching female's head or thorax, and walking around on female, which may serve to stimulate females towards increased receptivity. Females signal receptivity by assuming a stereotypical posture of remaining stationary, with head down, and antennae still in front of the body. The male then inserts his aedeagus and the pair copulates. After an average of 40.4 s of copulation, females signal the end of copulation by waving the antennae and moving away from the copulation site. Males continue copulating for a short time after females start moving but dismount soon thereafter. After dismounting, the two wasps move away from each other immediately, and they typically begin grooming. Neither males nor females exhibit mating preference based on mate's mating status in both choice and no-choice tests. The male is polygynous and the mated female can mate multiple times within the first 3 days after starting oviposition. However, female mating frequency does not affect the production of female progeny.