The Mating System of <Emphasis Type="Italic">Amegilla</Emphasis> (<Emphasis Type="Italic">Asarapoda</Emphasis>) <Emphasis Type="Italic">paracalva</Emphasis> Brooks (Hymenoptera: Apidae)

Males of the solitary bee Amegilla (Asarapoda) paracalva employ two mate-locating tactics: aggressive defense of sites from which virgin females are emerging and patrolling flower patches that are visited by conspecific females. At one study site, a single male was able to control an entire emergence area for one or more days. Multiple males patrolled one flower patch, interacting aggressively on occasion but no one individual was able to monopolize this resource. Territorial males at the emergence site secured mates by waiting by tunnels for receptive virgin females to emerge after metamorphosis. Males patrolling the flower patch pounced upon flower visiting conspecifics and mated with receptive females there. Territorial males at the emergence site were larger than average individuals, probably because of the advantage larger males have when grappling with opponents. Flower patrolling males were smaller than territorial males at the emergence sites, perhaps because of the advantages gained by these males from rapid, agile flight.     

Competition from large males and the alternative mating tactics of small males of dawson’s burrowing bee (Amegilla dawsoni) (apidae, apinae, anthophorini)

Males of Dawson’s burrowing bees (Amegilla dawsoni) search for virgin females at three locations: (1) open clay patches where females are emerging from underground brood cells, (2) the vegetated peripheral zone adjacent to emergence areas (through which females pass after emerging), and (3) clusters of flowering plants, which are often some distance from emergence areas. Males of Dawson’s burrowing bees exhibit a size dimorphism with large major and small minors. Major males patrol only the open emergence sites, whereas minor males may be found in all three locations. Although most females are mounted and presumably mated immediately upon emergence, some are not, and these females make up a pool of potential mates for the small males patrolling the peripheral zone and flower patches. The density of males at emergence sites and the probability of male-male aggression change over the course of a day and over the entire flight season. When the level of competition is low, some minor males hunt for mates at emergence areas, where potential mates are relatively numerous. But when the presence of many large rivals makes it unlikely that a small male can avoid being displaced from emerging females, minors make the best of a bad job by shifting to areas where majors are absent.     

Impact of the Timing of Male Emergence on Mating Capacity of Males in Trichogramma evanescens Westwood

In species with highly structured population, such as Trichogramma spp., mating occurs mostly at emergence on the patch and early emerging males have an advantage, as they are present when the first females emerge. However, early emergence of male could also enable males to mature sexually before the emergence of females or enhance their capacity to induce higher receptivity in females. We measured time of emergence of male and female Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) from hosts that were parasitized within a 30 min period. We also measured the effect of male age on their capacity to mate, and the ability of inseminated females to produce daughters. To verify if early emerging males induced higher receptivity in females, we observed the females mate choice between males of different ages. Our results indicated that the mean time of emergence between males and females was 29 min for individuals that develop in 9 days and 10 min for individuals that develop in 10 days. The protandry observed in this species could be the result of either a faster development of males or a male first strategy by the ovipositing female. In T. evanescens, protandry does not permit males to mature sexually nor to induce higher receptivity in females. The main advantage of protandry for males thus appears to be early access to females as they emerge.     

Brothers smell similar: variation in the sex pheromone of male European Beewolves Philanthus triangulum F. (Hymenoptera: Crabronidae) and its implications for inbreeding avoidance

Female choice is thought to increase the fitness returns of females. The complementary choice model states that the best mate depends on the particular genotype of a female. Aculeate Hymenoptera represent a special case of complementary female choice because males should be chosen on the basis of their allele at the sex determination locus. The prevalent sex determination mechanism in bees and wasps (single-locus complementary sex determination) requires that, to produce a daughter, diploid offspring are heterozygous at the sex determination locus. Otherwise, infertile diploid males result. Inevitably, the proportion of diploid males increases with the rate of inbreeding. In the European Beewolf, males scent mark territories to attract mates and the composition of the pheromone might provide a basis for female choice. One crucial prerequisite for females to be able to discriminate against brothers and avoid inbreeding is that the male sex pheromone varies with familial affiliation. This hypothesis was tested by analysing the pheromone of male progeny of eight mothers using gas chromatography and mass spectrometry. A significantly higher similarity was found among brothers than among unrelated individuals. Such a genetic component of a male sex pheromone has not yet been described from aculeate Hymenoptera.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 433–442.     

The effects of competition on fitness depend on the sex of both competitors

In intraspecific competition, the sex of competing individuals is likely to be important in determining the outcome of competitive interactions and the way exposure to conspecifics during development influences adult fitness traits. Previous studies have explored differences between males and females in their response to intraspecific competition. However, few have tested how the sex of the competitors, or any interactions between focal and competitor sex, influences the nature and intensity of competition. We set up larval seed beetles Callosobruchus maculatus to develop either alone or in the presence of a male or female competitor and measured a suite of traits: development time, emergence weight; male ejaculate mass, copulation duration, and lifespan; and female lifetime fecundity, offspring egg–adult survival, and lifespan. We found effects of competition and competitor sex on the development time and emergence weight of both males and females, and also of an interaction between focal and competitor sex: Females emerged lighter when competing with another female, while males did not. There was little effect of larval competition on male and female adult fitness traits, with the exception of the effect of a female competitor on a focal female's offspring survival rate. Our results highlight the importance of directly measuring the effects of competition on fitness traits, rather than distant proxies for fitness, and suggest that competition with the sex with the greater resource requirements (here females) might play a role in driving trait evolution. We also found that male–male competition during development resulted in shorter copulation times than male–female competition, a result that remained when controlling for the weight of competitors. Although it is difficult to definitively tease apart the effects of social environment and access to resources, this result suggests that something about the sex of competitors other than their size is driving this pattern.     

Hostplant-habitat structure and the evolution of butterfly mate-locating behaviour

A hostplant-habitat model is described which explains fundamental differences in mate-locating behaviour between butterfly species, based on a sequence of spatially distinctive activities (habitual patrolling, localized perching, territoriality, lek assembly). It gives equal weight to phylogeny and ecology and is consistent with models for the evolution of territoriality and population structure. Perching repeatedly at characteristic sites, territoriality and lek assembly evolve when resources become associated with distinctive hostplant-habitat structures in which topographic features provide predictable vantage points for acquiring mates. Habitual patrolling is an ancestral behaviour which is suited to widespread and unpredictable resource distributions and to species whose individual apparency detracts from the use of topographic vantage points. Hostplants (emergence sites), nectar and thermoregulation sites typically provide resources and act as precursors to localized perching, territoriality and lek assemblages. But these behaviours fail to evolve in species whose habitats do not include obvious topographic landmarks which provide clear vantage points for males awaiting females and focal points for females searching for males. Where these landmarks occur they result in an increase in receptive female density at those locations compared to the remainder of the habitat.     

The Resource-Based Mating System of the Mediterranean Pollen Wasp Ceramius fonscolombei Latreille 1810 (Hymenoptera, Vespidae, Masarinae)

Males of C. fonscolombei patrol and perch at water collection sites or at plants of Reseda, both of which are important resources for female brood care. The mating system can be classified as resource defense polygyny modified by the existence of alternative male mating tactics. Occupying temporary territories at watercollection sites constitutes the primary tactic which is more profitable for larger males. The secondary tactic of patrolling at flowers provides a nonaggressive alternative through which smaller males gain at least some mating success. Males at water collection sites occupy considerably smaller ranges but spend a higher proportion of time patrolling than males at flowers. They frequently grapple with other males, an activity that is absent at flowers. Males at water collection sites copulate about 2.5 times more frequently than males at flowers. The copulation frequency of the males at water collection sites is positively correlated with their body size, while copulation frequency is negatively correlated with body size at flowers. Males patrolling at water collection sites and males patrolling at flowers do not differ in body size, indicating that the decision between alternative mating tactics is not made relative to body size but is influenced by other factors.     

The Mating System of <Emphasis Type="Italic">Habropoda pallida</Emphasis> Timberlake (Anthophorinae: Apidae)

Males of Habropoda pallida searched for recently emerged females at a location in central Arizona where many females had nested in the preceding year. Patrolling males exhibited a variety of mate locating tactics ranging from inspecting existing emergence holes to patrolling flights around flowering creosote bush. These tactics appear to be under the control of a conditional strategy, given that male behavior shifted during the day. Moreover, some marked males mounted dead females placed on the ground in the emergence area as well as mounting dead females pinned to flowers in the emergence area and at a creosote bush some distance away. At least some males exhibited site fidelity in that numerous males marked within the nest site emergence area were recaptured there; others marked at a creosote bush were also seen again at that plant. The mating system of the bee involves scramble competition with individual males attempting to locate receptive emerging and flower-visiting females before rival males. In keeping with the scramble competition hypothesis, males are considerably smaller on average than females and are only aggressive when trying to push their way past rival males already mounted on a potential mate.     

Male Reproductive Behavior of the Social Wasp Polistes fascatus (Hymenoptera: Vespidae)

Populations of male Polistes fuscatus simultaneously exhibit two different mate-locating tactics. Some males defend territories in female nesting and hibernation sites. These males frequently do not occupy the same territory each day, and they drag their gasters over perches, which may function to apply a secretion to the perch. Another segment of the population patrols large overlapping areas in female foraging sites. In contrast to territorial males, patrolling males do not rub their gasters on perches, and males seen on more than one day are tenacious to one area. Males in both sites are aggressive to other males and attempt to copulate with females. A laboratory study indicates that large males have an advantage in male-male competition. The mean size of patrollers is smaller than that of territorial males, indicating that patrollers are competitively inferior males. Yet there is considerable size overlap of males between the two sites, suggesting that there is also overlap in the range of probability of mating success between the two sites.     

Male parasitism and intrasexual competition in a burrowing barnacle

Summary In sexually dimorphic animals, large male body size is often associated with direct interference competition among males for access to females or resources used in reproduction. In constrast, small male body size may be associated with indirect scramble competition among males for temporal or spatial access to females. Minute, “parasitic” males of the acrothoracican barnacleTrypetesa lampas (Hancock) appear to compete with one another for permanent attachment sites on the external body of the female. Several spatial patterns suggest indirect male-male competition: 1) males were consistently aggregated on the anterior surface of the female ovarian disc; 2) the average distance from attached males to the site of insemination correlated positively with local male density; 3) average male body size on a female decreased as a function of male density; 4) the distribution of males on the left and right hand sides of the female ovarian disc was more even than expected, suggesting that males avoided crowded settlement sites. The number of males attached to a female increased with female body size and matched a null model in which males colonized female “targets” of differing areas. These results suggest that competition between males primarily affected settlement sites and male body sizes within, rather than among, females. Male parasitism may have evolved through both sexual selection for efficient access to females (Ghiselin 1974) and natural selection for reduced burrow density in a space-limited habitat (Turner and Yakovlev 1983).     

Maternal investment in a bee species with facultative nest guarding and males heavier than females

1. Maternal investment can be influenced by several factors, especially maternal quality and possibilities for future reproduction. Mass provisioning Hymenoptera are an excellent group for measuring maternal investment because mothers distribute food sources to each brood cell for each offspring separately. Generally in aculeate Hymenoptera, larger females produce larger offspring and invest more in female offspring than in male offspring. 2. This study investigated patterns of maternal investment in Ceratina chalcites, which has an uncommon type of sexual size dimorphism in Hymenoptera: on average, males are heavier than females. It was found that larger females produce a significantly higher proportion of male offspring, as males are the costlier sex in this species. 3. Facultative nest guarding by females was observed. Females can guard offspring until adulthood, as is typical for bees of genus Ceratina (34.43% of nests); however, in the majority of cases (65.56% of nests), females plug and abandon the nest. Significant differences were found in the amount of investment between guarded and unguarded nests. Guarded nests had a greater number of provisioned brood cells and a higher proportion of male offspring. It is suggested that mothers have two facultative strategies – either she makes a large investment in the offspring of one nest or she abandons the first nest and carries out a second nesting elsewhere.     

Intraspecific competition and the maintenance of monogamy in tree swallows

Intraspecific competition for access to breeding resources maylimit male mating success typically monogamous birds. We examinedthe potential for intraspecific competition to limit polygynyin tree swallows at Beaverhill Lake, Alberta, Canada. In thispopulation, polygynous males raisedmore fledglings than monogamousmales, and there was little or no cost to females from nestingpolygynously. Under these conditions one might expect polygynyto be more common than that observed(8% of males). We foundthat females were most aggressive toward conspecific intrudersearly in the breeding season. This aggression was associatedwith (1) females settling farther apart than expected underrandom settlement, (2) later settlement by secondary than bymonogamous females, and (3) no relationship between female settlementdate and male territory size instead of the negative correlationexpected if females settled randomly without competition. Earlyin the season, males also settled farther apart than expectedif they had settled randomly, and among males with two or morenest boxes on their territory, males with widely separated nestboxes were more likely to be polygynous. Monogamy is probablythe most common pairing association in this population becauseintraspecific competition for nest sites prevents most malesfrom gaining a territory with nest sites far enough apart topermit two females to breed without one female excluding theother. Females appeared to be defending an area surroundingtheir nest box to limit nest usurpation or intraspecific broodparasitism, rather than to limit any loss of male parental carefrom polygyny.     

Differential dispersal and female-biased sex allocation in a parasitic wasp

1. Differential dispersal of males and females from a population is predicted to result in biased sex-allocation decisions, even in the absence of sibmating.
2. Mated Bracon hebetor Say (Hymenoptera: Braconidae) females produce distinctly female-biased sex ratios (≈ 30% male), yet sibmating is not a feature of the mating biology of this species. Therefore the dispersal behaviour of male and female B. hebetor from caged subpopulations was examined.
3. A higher proportion of females than males dispersed from the caged subpopulations. Furthermore, females dispersed earlier than males. This suggests that the level of competition for mates experienced by males is higher than the level of competition for hosts experienced by sisters.
4. Roughly half of the dispersing females left after they had mated. Females generally mate once in their lifetimes, suggesting that competition between brothers for mates may be high.     

Site-specific mate-finding strategies and oviposition behavior inCrocothemis erythraea (Brullé) (Odonata: Libellulidae)

Mate-finding strategies and adaptations in pre- and postcopulatory behaviors to avoid male disturbance were studied in Crocothemis erythraea at two different sites. At ponds without perch sites males patrolled with temporal partitioning of the limited oviposition sites and male-male disputes were rare. The arrival rate of females was high. At temporary marshes with dense emergent vegetation the oviposition sites were widely distributed. Males mainly perched and interacted with longer disputes. At both types of habitats with high male densities females showed a similar number of copulations per visit and oviposition durations. Postcopulatory behavior to avoid male disturbance and to decrease remating of the female differed in both sexes. At the ponds with patrolling males the probability of remating in guarded and unguarded ovipositions was similar and higher than at the marshes. At the marshes 78% of rematings occurred when the guarding male was still involved in disputes with the previously disturbing male. At the ponds females hovered before escaping successfully from approaching males and they changed to another oviposition site where they continued oviposition. Females at the marshes remated after surprise attacks by neighboring males.     

Pupation site and emergence time influence the mating success of bagworm females,Oiketicus kirbyi

In commercial oil palm plantations in Costa Rica, we tested the hypotheses that pupation site and emergence time affect the mating success of protogynous female bagworms,Oiketicus kirbyi (Guilding) (Lepidoptera: Psychidae). Greater proportions of female than male pupae on upper leaves of oil palms and greater proportions of mated females in the upper rather than lower crown strata support the hypothesis that selection of pupation site by female larvae influences the mating success of adults. Increasing captures of males with increasing trap height further suggest that enhanced mating success of females in tree tops may be attributed either to most effective dissemination of sex pheromone on higher sites, or to males foraging predominantly in the upper strata of oil palms. As the majority of females pupated in the middle rather than upper crown of oil palms, selection of pupation site by females may be affected by additional as yet unknown factors. Emergence of females significntly preceded emergence of males. Increasing proportions of mated females throughout the emergence seasons probably resulted from an increased ‘availability’ of males. In tropical rainforests with local variations inO. kirbyi developmental time and stage, protogyny may represent an evolutionary strategy that furthers outbreeding.     

Male orientation to trail sex pheromones in parasitoid wasps: does the spatial distribution of virgin females matter?

We studied male locomotory response to trails and patches of sex pheromone (left respectively by free-ranging females and females constrained to stay on a small area) in the two parasitoids Aphelinus asychis (Hymenoptera: Aphelinidae) and Trichogramma brassicae (Hymenoptera: Trichogrammatidae). Under the hypothesis that the spatial distribution of virgin females differs between these species (scattered among host plants in A. asychis, gregarious at emergence sites in T. brassicae), we predicted that male locomotory response to their sex pheromones should also differ: A. asychis males should follow pheromone trails on plants in order to encounter the females along these trails, whereas T. brassicae males should stay on pheromone patches, at emergence sites, and mate the females on these patches. Using an improved video-tracking system, we found that males of both species respond to conspecific sex pheromone trails and patches, but that the response does not differ much between species. Males released on marked substrates walked in a more convoluted pattern (i.e. higher path fractal dimension and higher number of crossings within tracks) than males released on unmarked substrates. On pheromone patches, males turned persistently in the same direction when leaving the patch, which explains a higher number of visits on marked patches than on unmarked patches, and possibly, higher track convolution on pheromone trails. Contrary to our hypothesis, male A. asychis did not follow female trails more accurately than male T. brassicae, and male T. brassicae did not stay longer on pheromone patches than male A. asychis. We argue that these discrepancies between our predictions and the observed responses originates from discrepancies between the assumed spatial distribution of virgin females and their actual distribution in the wild.     

Hilltopping in the Pipevine Swallowtail Butterfly (Battus philenor)

In central Arizona, receptive females of the pipevine swallowtail, Battus philenor, are widely scattered in time and space, and in this region the butterfly's mating system is one in which males patrol mountain peaks. Hilltopping males engage intruding males in ascending flights that appear to be ritualized aerial combat with individuals defending patrolling sites for relatively short periods on any given day. The day-to-day appearance of marked males is irregular, unlike the site fidelity shown by males of many other hilltopping insects. The distinctive pattern of male territoriality in B. philenor may be partly a response to very low male and female density in the observed population. Males at the hilltop chase, court, and attempt to copulate with virgin females released near them. Males assess the receptivity of females rapidly, and receptive females permit a lengthy copulation to occur after a courtship that lasts less than 30 s. During an initial copulation males pass a spermatophore that weighs about 6% of their body mass, with partners on following days receiving a smaller but still substantial donation.     

Location before emergence of the female bee, Centris pallida, by its male (Hymenoptera: Anthophoridae)

Large numbers of males of the bee Centris pallida Fox have been observed patrolling areas in which females are emerging. Males locate specific sites at which a buried bee is about to emerge and dig down to meet the other individual, male or female. If it is a female, mating is initiated when she scrambles into the excavation pit created by the male. Males fight intensely with one another for possession of digging sites and for unburied virgin females. Experiments indicate that males locate conspecifics beneath the surface on the basis of extremely non-specific olfactory cues; they are capable of locating buried honey bees and other insects. The evolution of digging behaviour is traced to selection favouring males that are first to reach a virgin female which will mate just once in her lifetime. A number of examples are given of other insects that have evolved similar abilities, apparently in response to similar selection pressures.     

Sex, bugs and Haldane's rule: the nematode genus Pristionchus in the United States

The haplodiploid sex determining mechanism in Hymenoptera (males are haploid, females are diploid) has played an important role in the evolution of this insect order. In Hymenoptera sex is usually determined by a single locus, heterozygotes are female and hemizygotes are male. Under inbreeding, homozygous diploid and sterile males occur which form a genetic burden for a population. We review life history and genetical traits that may overcome the disadvantages of single locus complementary sex determination (sl-CSD). Behavioural adaptations to avoid matings between relatives include active dispersal from natal patches and mating preferences for non-relatives. In non-social species, temporal and spatial segregation of male and female offspring reduces the burden of sl-CSD. In social species, diploid males are produced at the expense of workers and female reproductives. In some social species, diploid males and diploid male producing queens are killed by workers. Diploid male production may have played a role in the evolution or maintenance of polygyny (multiple queens) and polyandry (multiple mating). Some forms of thelytoky (parthenogenetic female production) increase homozygosity and are therefore incompatible with sl-CSD. We discuss a number of hypothetical adaptations to sl-CSD which should be considered in future studies of this insect order.     

Territorial behavior of both sexes in the water striderMetrocoris histrio (Hemiptera: Gerridae) during the mating season

Territorial behavior of overwintered individuals of Metrocoris histriowas observed in an upstream area. Adults of both sexes held territories, but male territories were larger than those of females. Severe competition occurred among males for territories which give them access to receptive females. The effects of male body length and midleg length on establishment of territories were not significant. The effect of female midleg length on activity of females entering preferred foraging sites was equally not significant. Instead, territorial behavior increased with male age and males stayed longer at prime sites. Females of intermediate age were likely to occupy prime sites. Females had longer territory residence time than males. The sexes were dimorphic with respect to midleg length, and dimorphism in M. histriomay be related to a difference in life history, in that sexual selection may be relaxed due to asynchronous adult emergence patterns.