Interaction between sexes and between different circadian phenotypes affects lifespan in the fruit fly Drosophila melanogaster

Circadian clocks regulate the daily temporal structure of physiological and behavioural functions. In the fruit fly Drosophila melanogaster Meigen, disruption of daily rhythms is suggested to reduce the fly's lifespan. In the present study, because pairs of mixed‐sex flies are known to show an activity pattern different from that of individual flies, this hypothesis is tested by measuring the lifespan of flies housed same‐sexually or mixed‐sexually under an LD 12 : 12 h photocycle at a constant temperature of 25 °C. The effect of housing wild‐type (Canton‐S) flies with period (per) circadian clock mutant flies is also examined because the mutant flies have different daily activity patterns. When males and females of wild‐type flies are housed together, their lifespan is substantially lengthened (males) or shortened (females) compared with same‐sex housed flies. The shortening of the lifespan in females is significantly enhanced when mated with per mutant males. The shortening effects are significantly reduced when the mixed‐sex interaction is limited for the first 5 days after emergence. A slight elongation in lifespan, rather than a reduction, occurs when wild‐type females are housed same‐sexually with per⁰ or per^L mutant flies. In male flies, the elongation of lifespan occurs not only when wild‐type males are housed with wild‐type, per⁰ or per^L females, but also when housed with per⁰ or per^S mutant males. Mixed‐sex couples always show altered daily locomotor rhythms with an enhanced night‐time activity, whereas same‐sex couples show daily behavioural profiles slightly altered but essentially similar to a sum of the respective two flies. No significant correlation is found between the lifespan and reproductive capacity. These results suggest that the alteration of daily activity rhythms and sexual interaction may have significant impact on the fly's lifespan.     

Circadian locomotor rhythm masked by the female reproduction cycle in cockroaches

Blattella bisignata (Brunner) and B. germanica (L.) are oviparous cockroaches with cyclic reproductive behaviour, but in B. germanica only males show circadian rhythmicity of locomotion at 28°C and DD (constant darkness). In B. bisignata, males and virgin females cockroaches entrained by light–dark cycles show free‐running rhythmicity in DD, and most activities occur during the subjective night. Daily locomotor activities of virgin females show cyclic changes that coincided with ovarian development. Virgin females also exhibit calling behaviour during the subjective night, and this shows a free‐running rhythm. Male mate‐finding locomotion and female calling behaviour are under circadian control, so the timing for both behaviours is synchronized. However, most mated females do not show a locomotor free‐running rhythm under DD conditions. Our results indicate that only mated females could not express a circadian locomotor rhythm. Pregnancy reduces a female’s locomotory intensity and masks the expression of a circadian locomotor rhythm. We attribute the differences in circadian locomotory rhythms between these two species to their living environments and mate‐finding strategies.     

Paternity analyses in wild‐caught and laboratory‐reared Caribbean cricket females reveal the influence of mating environment on post‐copulatory sexual selection

Polyandry is ubiquitous in insects and provides the conditions necessary for male‐ and female‐driven forms of post‐copulatory sexual selection to arise. Populations of Amphiacusta sanctaecrucis exhibit significant divergence in portions of the male genitalia that are inserted directly into the female reproductive tract, suggesting that males may exercise some post‐copulatory control over fertilization success. We examine the potential for male–male and male–female post‐copulatory interactions to influence paternity in wild‐caught females of A. sanctaecrucis and contrast our findings with those obtained from females reared in a high‐density laboratory environment. We find that female A. sanctaecrucis exercise control by mating multiple times (females mount males), but that male–male post‐copulatory interactions may influence paternity success. Moreover, post‐copulatory interactions that affect reproductive success of males are not independent of mating environment: clutches of wild‐caught females exhibit higher sire diversity and lower paternity skew than clutches of laboratory‐reared females. There was no strong evidence for last male precedence in either case. Most attempts at disentangling the contributions of male–male and male–female interactions towards post‐copulatory sexual selection have been undertaken in a laboratory setting and may not capture the full context in which they take place – such as the relationship between premating and post‐mating interactions. Our results reinforce the importance of designing studies that can capture the multifaceted nature of sexual selection for elucidating the role of post‐copulatory sexual selection in driving the evolution of male and female reproductive traits, especially when different components (e.g. precopulatory and post‐copulatory interactions) do not exert independent effects on reproductive outcomes.     

Interference between male‐targeted and female‐targeted lures of the Mediterranean fruit fly Ceratitis capitata (Dipt., Tephritidae) in Italy

The efficacy of male‐targeted and female‐targeted baits was compared when lures were presented together or singly in traps for capturing the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). For male‐targeted baits, either trimedlure or ceralure presented singly attracted large numbers of flies, supporting data from many previous reports. The present results are the first published data on the attractiveness of ceralure to a European population of C. capitata. The quaternary female bait consisting of ammonium carbonate, putrescine, trimethylamine and acetic acid was a potent attractant for female flies (and also showed some activity for males). Replacing acetic acid with ammonium acetate in the quaternary female bait did not influence activity. Traps with female‐targeted and male‐targeted baits together always showed a tendency of catching fewer flies than traps with only one type of bait. The decrease was significant in females, regardless of whether ceralure or trimedlure was the male‐targeted bait. In males, the tendency was the same for traps with trimedlure or ceralure alone, catching higher numbers than those with both male and female baits. Our present results suggest that both types of baits mutually decrease the numbers of the non‐target sex in the trap. In conclusion, it is advisable to use both male‐ and female‐targeted baits in separate and distant traps and not jointly in the same trap, lest the efficacy of detection or monitoring trials be compromised.     

Male aggression,limited female choice and the ontogeny of mating behaviour in the flesh fly Sarcophaga crassipalpis

Previous work has shown that male flesh flies (Sarcophaga crassipalpis Macquart) exhibit an ontogeny of behaviour from eclosion through sexual maturity that includes extensive changes in the expression of aggressive, non‐aggressive interactive and non‐interactive behaviours. To determine how the presence of a female flesh fly influences the manifestation of these behaviours, male flesh flies of different ages post‐eclosion are paired with same‐age females and their behaviours are monitored in a simple arena during a 50‐min observation period. All flies are socially isolated until pairing. Although the levels of expression of aggressive and non‐aggressive interactive behaviours are depressed relative to previous findings in male‐opponent pairs, the ontogeny of aggression still occurs as indicated by a significant increase, with age, in the agonistic behaviour ‘hold’. Similar to male‐opponent pairs and individual males, the performance by males of the non‐interactive behaviours ‘walking’ and ‘standing’ diminishes, whereas ‘upside‐down’ increases with age. By contrast, ‘grooming’ shows a significant age‐related decline. No courtship behaviours are observed in the males, although the aggressive behaviour ‘hold’ is a significant transition to mating. Females show no obvious courtship or rejection behaviours, although the significant increase in ‘upside‐down’ with age could possibly be a behavioural gateway to mating. The results of this study indicate that extensive age‐related changes encompassing the entire behavioural repertoire are intrinsic to male flesh flies and persist under a variety of different social contexts.     

Pre-release feeding on yeast hydrolysate enhances sexual competitiveness of sterile male Queensland fruit flies in field cages

Recent laboratory studies of mass‐reared flies in small cages have found that periods of just 24‐ or 48‐h access to yeast hydrolysate can substantially enhance mating performance of mass‐reared male Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q‐flies’). Using field cage tests that provide a better approximation of nature, we here investigated whether access to yeast hydrolysate for 48 h after adult emergence improves the ability of male and female mass‐reared, sterile Q‐flies to compete sexually with wild‐type flies that had been provided continuous access to yeast hydrolysate. Mating probability of sterile males was significantly increased by 48‐h access to yeast hydrolysate; sterile males provided 48‐h access to yeast hydrolysate had mating probability similar to that of wild males provided continuous access to yeast hydrolysate, whereas sterile males deprived of access to yeast hydrolysate had much lower mating probability. Unlike males, access to yeast hydrolysate for 48 h did not increase mating probability of sterile female Q‐flies. We instead found that wild females provided continuous access to yeast hydrolysate had higher mating probability than sterile females that did or did not have 48‐h access to yeast hydrolysate. This result raises the possibility that a bisexual Q‐fly strain might operate essentially as a male‐only release when the flies are given access to yeast hydrolysate during a 48‐h pre‐release holding period. Sterile males given access to yeast hydrolysate for 48 h mated significantly earlier in the evening than wild males and, as in other recent studies, this tendency was associated with an increased tendency to mate on the trees rather than the cage walls. There was no evidence of sexual isolation in this study, as wild and sterile mass‐reared flies showed no evidence of preferential mating with their own kind. Further studies are now needed to assess the potential for pre‐release access to yeast hydrolysate to improve sexual performance and longevity of sterile, mass‐reared, Q‐flies in the field.     

Mating Behavior and Dual‐Purpose Armaments in a Camel Cricket

Sexual selection has often been dichotomized into intersexual and intrasexual components of selection, favoring ornaments and weapons, respectively. Here, we show that a weapon used in male–male combat is sometimes also used in a functionally similar manner for grasping females during mating. The hind legs of adult males of some species of Pristoceuthophilus camel crickets have strongly bent tibia and stout femora with two large conspicuous spines. Here, we show that (1) leg armature is positively allometric, (2) males use these leg modifications when fighting other males, (3) males sometimes use the same leg modifications in the same functional manner for grabbing and holding females for mating, (4) virgin females show more interest in males than do non‐virgin females, and (5) males are more likely to use their leg modifications to grab and hold females when paired with non‐virgin females than when paired with virgin females. We interpret these results as suggesting that males employ an alternative coercive mating strategy when paired with unreceptive females; alternative explanations are also discussed.     

Mating with sperm-depleted males does not increase female mating frequency in the parasitoid Lariophagus distinguendus

Sexual conflicts due to divergent male and female interests in reproduction are common in parasitic Hymenoptera. The majority of parasitoid females are monandrous, whereas males are able to mate repeatedly. Thus, accepting only a single mate might be costly when females mate with a sperm‐depleted male, which may not transfer a sufficient amount of sperm. In the present study, we investigated the reproductive performance in the parasitoid Lariophagus distinguendus Först. (Hymenoptera: Pteromalidae) and studied whether mating with experimentally sperm‐depleted males increases the tendency of females to remate. Males were able to mate with up to 17 females offered in rapid succession within a 10‐h test period. The resulting female offspring, as an indirect measure of sperm transfer, remained constant during the first six matings and then decreased successively with increasing number of copulations by the males. Experimentally sperm‐depleted males continued to mate even if they transferred only small amounts or no sperm at all. Unlike males, the majority of females mated only once during a 192‐h test period. A second copulation was observed only in a few cases (maximum 16%). The frequency of remating was not influenced by the mating status of the first male the females had copulated with, suggesting that these events are not controlled by sperm deficiency of the females. Furthermore, we investigated male courtship behaviour towards mated females. Male courtship intensity towards mated females decreased with increasing time. However, females that had mated with an experimentally sperm‐depleted male did not elicit stronger or longer‐lasting behavioural responses in courting males than those that had mated with a virgin male. As the observed behaviours in L. distinguendus are known to be elicited by a courtship pheromone, these results suggest that females no longer invest in pheromone biosynthesis after mating (as indicated by ceasing behavioural responses of courting males), irrespective of whether they have received a sufficient amount of sperm or not. We discuss the results with respect to a possible mating strategy of sperm‐depleted males.     

Longevity costs of same‐sex interactions: first evidence from a parasitic wasp

Costs of sexual interactions play a key role in life‐history evolution. Although the costs of reproduction have been investigated in both sexes of many insects, the costs of same‐sex interactions have been examined in few species. In parasitic wasps, very little has been reported about the longevity costs of heterosexual interactions, and nothing is known about longevity costs of same‐sex interactions. In this study, the effects of heterosexual and homosexual activities on longevity were evaluated in Psyttalia concolor (Hymenoptera: Braconidae), a synovigenic koinobiont larval‐pupal endoparasitoid of tephritid flies. When compared with individually housed virgin wasps, male longevity was strongly reduced both in males kept with females, and in males kept with other males. When females were kept with males, their longevity was reduced compared with the virgin females and females kept with other females. Overall, the costs of male–female interactions were considerable in both sexes of P. concolor, while same‐sex activities were found to be costly only among males, suggesting that they may have implications for the evolution of the P. concolor mating system.     

Sequential Analysis Reveals Behavioral Differences Underlying Female‐Biased Predation Risk in Stalk‐Eyed Flies

Stalk‐eyed flies are classic models of how sexual selection can drive morphological and behavioral elaboration. Exaggerated ornaments born by stalk‐eyed flies could impose locomotor costs and increase susceptibility to predation; however, a previous study determined that behavior, not eye span, was the major influence on predation risk. Despite the importance of behavior, relatively little is known about how these flies avoid and deter predators. We created an ethogram of behaviors and used it to score individual interactions of male and female Teleopsis dalmanni paired with an actively foraging, generalist arachnid predator (Phidippus audax). Sequential analysis was employed to identify temporal patterns in behavior and determine how males and females differ in their approaches to avoiding predation. Our results indicate that males and females significantly differ when specific behaviors were employed. Patterns in the behavioral transitions suggest that males are more aggressive than females and are more likely to approach a predator to jab, abdomen bob, or display. Males elicited more retreat responses from the predator, whereas females elicited more attacks. Although the behavioral repertoires of male and female stalk‐eyed flies are indistinguishable, their uses of the behaviors differ, particularly the sequential order of presentation, suggesting a strong sex difference in anti‐predatory behavior.     

Suppression of female melon fly,Zeugodacus cucurbitae,with cue‐lure and fipronil bait stations through horizontal insecticide transfer

Melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), is an important quarantine tephritid fruit fly with resident populations established in Hawai'i, USA. In the male‐annihilation approach, male flies are targeted using dispensers with cue‐lure (C‐L) and insecticides, typically organophosphates. The efficacy of the male annihilation approach is thought to be limited to individual male flies, contacting the lure and the pesticide, after which they die. Alternative classes of insecticides, such as fipronil, have been investigated for use in male‐annihilation. We hypothesized that ingestion of fipronil by male flies could lead to horizontal transfer and mortality in female flies. Horizontal insecticide transfer extends pesticide control beyond the individual contacting the toxicant through indirect contact via food sharing or other mechanisms. We tested the possibility for horizontal transfer of fipronil from male to female Z. cucurbitae through field and laboratory studies. Two repeated field trials were conducted to compare the numbers of female flies collected in fields treated with Amulet C‐L (0.34% fipronil active ingredient) bait stations, sanitation, and spot treatments of GF‐120 Fruit Fly Bait to numbers collected in fields where sanitation and spot‐treatments were used without Amulet C‐L. In fields with Amulet C‐L bait stations in conjunction with sanitation and weekly protein bait spot treatments of GF‐120 Fruit Fly Bait, female captures were significantly lower than those in field plots treated with weekly protein bait spot treatments and sanitation. In subsequent laboratory studies, all females died within 6 h after direct exposure to male flies that had access to Amulet C‐L for 1–4 min. The possibility that male regurgitant could be a mechanism for horizontal transfer and subsequent female mortality was determined by collecting regurgitated droplets from fipronil‐fed male flies and feeding them to males and females. Both male and female flies exposed to regurgitant from fipronil‐fed male flies or droplets containing fipronil had higher mortality than the male and female flies that were exposed to regurgitant or droplets with only the C‐L compound or sugar solution. Thus, female flies do experience mortality from exposure to regurgitant from males that have fed on fipronil laced solutions. This provides evidence of at least one mechanism of horizontal transfer of insecticide in tephritid fruit flies. These findings are discussed in the context of Z. cucurbitae integrated pest management programs in Hawai'i.     

Temporal Shifts in Conspicuousness: Mate Attraction Displays of the Texas Field Cricket, Gryllus texensis

Conspicuous mate attraction displays can simultaneously draw the attention of potential mates and predators, placing the signaller in peril of becoming prey. The balance between these countervailing forms of selection has the potential to shape mate attraction displays. Male Texas field crickets (Gryllus texensis; Orthoptera) signal acoustically to attract mates. Mating signals also attract acoustically orienting parasitoid flies (Ormia ochracea; Tachinidae). Both the abundance of female crickets and parasitoid flies fluctuates throughout the night. We show mate attraction displays exhibit diel shifts that correlate positively with expected female cricket presence and negatively with expected parasitoid fly activity. During early evening, when parasitoids are most common and mating is scarce, crickets signal less often and with reduced conspicuousness. During the second half of the evening, when sexually receptive females are abundant and parasitoids are scarce, crickets signal more often and with enhanced conspicuousness. These diel shifts in mate attraction displays do not appear to result from male crickets detecting parasitoid flies or female crickets and altering their behaviour accordingly. Males in close proximity to parasitoid flies or female crickets do not signal differently than lone males. Instead, diel pattern shifts in mate attraction displays appear to be a selective response to trade‐offs between natural selection via parasitism and sexual selection via mate choice.     

Challenging the Aggressive Spillover Hypothesis: Is Pre‐Copulatory Sexual Cannibalism a Part of a Behavioural Syndrome?

Pre‐copulatory cannibalism – females devouring males during courtship – may bring no benefit to either sex. The ‘aggressive spillover hypothesis’ (ASH) posits that pre‐copulatory cannibalism represents a spillover of female aggressiveness from the juvenile foraging context, when aggressiveness is advantageous, to the adult mating context, when aggressiveness may be non‐adaptive or maladaptive. The ASH suggests that individuals exhibit limited plasticity in aggressive behaviours because they are genetically canalised for indiscriminate aggressiveness towards prey and conspecifics, including males. Hence, a tendency to employ pre‐copulatory cannibalism is a part of the female aggression syndrome, an assertion generally accepted in the personality field. We here re‐evaluate the previous findings in the light of personality criteria, which we propose for ASH validation: between‐individual differences, repeatability and heritability in tendency for pre‐copulatory attacks (and pre‐copulatory cannibalism) and voracity towards prey, and their correlation. To re‐evaluate ASH and to allow for additional or alternative explanations, we ask whether pre‐copulatory cannibalism depends on female hunger, mating status, size and/or male quality. Finally, we ask whether cannibalistic females have a reduced reproductive success as predicted by the ASH. While repeatability and heritability in voracity towards prey and its correlation with the tendency to engage in pre‐copulatory cannibalism were found in certain systems, we lack any evidence for repeatability and heritability in pre‐copulatory cannibalistic attempts and for its maladaptiveness. Rather than only resorting to the ASH, foraging and mate choice hypotheses may also explain pre‐copulatory cannibalism. We suggest clarifying the use of the terms sexual cannibalism (effect) and female aggressiveness or tendency to attack and devour males (cause), and argue that male strategies to avoid cannibalism should be considered. We propose testing the ASH as the explanation for pre‐copulatory cannibalism in those cases where female tendency to devour males correlates with actual pre‐copulatory cannibalism and when all the above criteria are fulfilled. Finally, we propose future directions for studying the ASH.     

Individual Variation in Behavioural Reactions to Unfamiliar Conspecific Vocalisation and Hormonal Underpinnings in Male Chimpanzees

It has been established that various species exhibit personality, defined as intra‐individual consistency and inter‐individual variation in behavioural phenotypes. For example, certain individuals may demonstrate consistently greater behavioural reactions and elevated stress responses. We conducted playback experiments and hormonal analyses on male chimpanzees (Pan troglodytes) in captivity to investigate the patterns and proximate mediators of individual variations in behavioural reactions. We found intra‐individual consistency and inter‐individual variation in behavioural reactions (intensive vigilance towards the direction of speakers) to vocalisations by unfamiliar chimpanzees. This behavioural reaction was positively correlated with changes in salivary cortisol concentration, suggesting that stress is a proximate factor mediating the variation in behavioural reactions. The males who were highly responsive to the conspecific vocalisation also exhibited high behavioural reactions towards the neutral broadcast stimulus (the jungle crow’s Corvus macrorhynchos ‘ka’ vocalisation). This observation is consistent with the notion that male chimpanzees vary in intrinsic behavioural tendency to different stimuli.     

Does Female Personality Determine Mate Choice Through Sexual Cannibalism?

Animal personalities (e.g. consistent across‐context behavioural differences between individuals) can lead to differences in mate choice. However, evidence for this link remains limited. Pre‐mating sexual cannibalism can be a behavioural syndrome (i.e. a suboptimal personality) in which adaptive female aggression towards heterospecific prey spills over on non‐adaptive aggression towards courting males, independently of the female mating or feeding status (i.e. the ‘aggressive spillover hypothesis’, ASH). On the other hand, sexual cannibalism can also be a form of mate choice by which females selectively kill or mate with males depending on the male phenotype. We introduce the hypothesis that the most aggressive females in the population will not only attack males more frequently, but will be less likely to impose sexual selection on males through sexual cannibalism. Assuming that in a field common garden experiment in which females were fed ad libitum the rate of weight gain by a female may reflect her voracity or aggressiveness, we show that in the cannibalistic burrowing wolf spider Lycosa hispanica (formerly L. tarantula), voracity towards heterospecific prey predicts a female's tendency towards sexual cannibalism. Unmated females with higher weight gains were more cannibalistic and attacked males regardless of the male phenotype. On the other hand, females that were less voracious tended to be less cannibalistic, and when they did kill a male, they were selective, killing males in poorer condition and mating with those in better condition. Our results demonstrate that females with different phenotypes (growth rates) differently imposed selection on male condition, tentatively supporting the hypothesis that female aggression levels can spill over on sexual selection through sexual cannibalism.     

THE INFLUENCE OF POLLINATOR PHYLOGEOGRAPHY AND MATE PREFERENCE ON FLORAL DIVERGENCE IN A SEXUALLY DECEPTIVE DAISY

Divergent mate preferences and subsequent genetic differentiation between populations has been demonstrated, but its effects on interspecific interactions are unknown. Associated species exploiting these mate preferences, for example, may diverge to match local preferences. We explore this idea in the sexually deceptive, fly‐mimicking daisy, Gorteria diffusa, by testing for association between genetic structure in the fly pollinator (a proxy for mate preference divergence) and geographic divergence in floral form. If genetic structure in flies influences interactions with G. diffusa, we expect phylogeographically distinct flies to be associated with different floral forms. Flies associated with forms exploiting only feeding behavior often belonged to several phylogeographic clades, whereas flies associated with forms exploiting male‐mating behavior always belonged to distinct clades, indicating the possibility of pollinator‐mediated floral divergence through phylogeographic variation in mating preferences of male flies. We tested this hypothesis with reciprocal presentations using male flies from distinct clades associated with separate floral forms. Results show that males from all clades exhibit similar preferences, making pollinator driven divergence through geographic variation in mate preference unlikely. Males, however, showed evidence of learned resistance to deceptive traits, suggesting antagonistic interactions between plants and pollinators may drive deceptive floral trait evolution in G. diffusa.     

Female Attraction to Conspecific Chemical Cues in the Palmate Newt Triturus helveticus

Although chemosignals are largely used in sexual communication in urodeles, olfactometer studies in newts provided contrasting results about the sex specificity of female behavioural responses. Because long‐range sexual advertisement is believed to be costly, some species might restrain this activity to close interactions with conspecifics. We tested chemical‐mediated sexual attraction in female palmate newt (Triturus helveticus) by measuring the attraction to male and female odours in a linear water olfactometer. Unexpectedly, females were attracted towards conspecifics regardless of sex. They did not show attraction towards Limnaea stagnalis, a common sympatric aquatic gastropod. These results do not support the use of long‐range male sexual signalling in the palmate newt. Instead, conspecific attraction is likely to promote aggregation of males and females in breeding ponds. Observations in the field and in the laboratory tend to support the aggregative behaviour of this species. We discuss the possible function of conspecific attraction in this context. Heading towards any conspecific would increase the probability of finding potential mates. Chemical cues do not need to be sex‐specific at that stage so that long‐range sexual advertisement might be unnecessary. This work emphasizes the need for studies investigating the evolutionary relationships between sexual signalling systems and population‐distribution patterns.     

SIZE DIFFERENCES,SEX RATIO,AND SPATIAL DISTRIBUTION OF MALE AND FEMALE WATER TUPELO,NYSSA AQUATIC A (NYSSACEAE)

Many dioecious plant species show spatial segregation of the sexes along a gradient of habitat quality. This study explores the spatial distribution and size of male and female Nyssa aquatica (water tupelo) trees along a water depth gradient. Individuals were mapped to determine the spatial distribution of male and female trees and the relationship between distribution of males and females and water depth. Nearest neighbor analysis indicated that males and females were randomly distributed in space. Comparisons among plots, however, indicated that there were more male trees in the shallowest plot. Height and diameter at breast height were measured for each tree. Males were significantly larger in height and basal area than females. Coring of male and female trees indicated that size differences between the sexes cannot be attributed to age differences, suggesting that male water tupelo trees allocate more resources to growth than do female trees.     

Virgin females compete for mates in the male lekking species Ceratitis capitata

Abstract. Aggressive behaviour occurring in intrasexual competition is an important trait for animal fitness. Although female intrasexual aggression is reported in several insect species, little is known about female competition and aggressive interactions in polygynous male lekking species. The interactions of female Mediterranean fruit flies, Ceratitis capitata (a male lekking species), with other females and mating pairs under laboratory conditions are investigated. Mature, unmated (virgin) females are aggressive against each other and against mating pairs, whereas immature females are not. Female aggression against other females decreases dramatically after mating; however, mated females maintain aggression against mating pairs. In addition, higher intrasexual aggression rates are observed for mature, virgin females than for virgin males of the same age. The results show that female aggressiveness is virginity related, suggesting female competition for mates. These findings have important implications for understanding the physiological aspects of a complex social behaviour such as aggression and should stimulate further research on female agonistic behaviour in male lekking mating systems.