Female defence polygyny in the bumblebee wolf,Philanthus bicinctus (Hymenoptera: Sphecidae)

Summary In the digger wasp Philanthus bicinctus the first adult males emerge about a week before the first females. The sex ratio of emerging wasps is near unity. Females appear to mate once and do so when they first start to nest, not when they first emerge.Males defend mating territories in a large area of female ground nests. Territoriality begins when females first start to nest and throughout the season coincides with the digging activities of females initiating rests. During the day territoriality occurs only when females are engaged in digging activities.Males compete for certain territory sites within the resting area; the most frequently occupied male territories are in areas where the density of nests is highest. About half of the males are excluded from nesting area territories. Some of these males defend areas among the flowers of snakeweed where females occasionally forage; this appears to be a loser tactic of males unable to obtain nesting area territories.Although there was no significant difference in the sizes of males on nesting area and snakeweed territories, within the nesting area larger males usually occupy territories with the higher nest densities.     

Population density and the intensity of sexual selection on body length in spatially or temporally restricted natural populations of a seed bug

Summary Population density affects the dynamics of mate acquisition and the opportunity for sexual selection in natural populations of the seed bug, Neacoryphus bicrucis Say (Hemiptera : Lygaeidae). The opportunity for sexual selection and the intensity of directional sexual selection on body length increased as the population density declined within a season for a population in a small, disjunct patch of host plant, Senecio anonymus. In a larger, dispersed population, both measures of selection were greater in host plant patches of low rather than high adult density when the population was sampled at peak density. Under conditions of higher density, males were more likely to share plants, larger males were less likely to monopolize patches of host plant to which females were attracted for mating, and smaller males were more likely to mate in the presence of large males. Thus, resource defense polygyny collapsed under high density, obviating the advantage of size in territory control, and resulted in scramble competition among males for mates. The population exhibited significant additive genetic variation for body length. This suggests that natural selection acting on other components of fitness favors smaller size or that the direction of sexual selection on size fluctuates between generations in response to the between-year variation in population density. Thus, strong sexual selection appears to impose a significant genetic load.     

Resource defense polygyny shifts to female defense polygyny over the course of the reproductive season of a Neotropical harvestman

Although studies classify the polygynous mating system of a given species into female defense polygyny (FDP) or resource defense polygyny (RDP), the boundary between these two categories is often slight. Males of some species may even shift between these two types of polygyny in response to temporal variation in social and environmental conditions. Here, we examine the mating system of the Neotropical harvestman Acutisoma proximum and, in order to assess if mate acquisition in males corresponds to FDP or RDP, we tested four contrasting predictions derived from the mating system theory. At the beginning of the reproductive season, males fight with other males for the possession of territories on the vegetation where females will later oviposit, as expected in RDP. Females present a marked preference for specific host plant species, and males establish their territories in areas where these host plants are specially abundant, which is also expected in RDP. Later in the reproductive season, males reduce their patrolling activity and focus on defending individual females that are ovipositing inside their territories, as what occurs in FDP. This is the first described case of an arachnid that exhibits a shift in mating system over the reproductive season, revealing that we should be cautious when defining the mating system of a species based on few observations concentrated in a brief period. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The cost of sexual coercion and heterospecific sexual harassment on the fecundity of a host-specific, seed-eating insect (Neacoryphus bicrucis)

Two species of seed-eating true bugs, Neacoryphus bicrucis (Heteroptera: Lygaeidae) and Margus obscurator (Heteroptera: Coreidae) co-occur on ragwort, Senecio tomentosus, in southern Georgia, USA. Males of both species sometimes engage in chases and protracted grappling with females that flee initial mountings. Sometimes genital coupling occurs while the wriggling female is restrained in the male's grasp. Chases, grappling, and mounting attempts are misdirected toward heterospecific females, heterospecific males, or conspecific males. In a laboratory study, confinement of mated N. bicrucis females with either conspecific or heterospecific males reduced fecundity by approximately one-half relative to mated females confined only with other females. Perhaps as a consequence of this, N. bicrucis females frequently leave areas of high host plant density, where they prefer to oviposit, when males are abundant. The abundance of each species is positively correlated with host plant density but the two species rarely occur together on the same plants. This may be an effect of heterospecific courtship which induces the flight of N. bicrucis more than the flight of M. obscurator. The laboratory results suggest that copulations following chases and grappling represent sexual harassment, not a mechanism of active female choice for a vigorous mate. As sexual harassment imposes high fitness costs that favor abandonment of host plants, it may, when misdirected, incidentally limit habitat use by ecologically similar species. Received: 3 October 1998 / Received in revised form: 21 January 1999 / Accepted: 14 February 1999     

Territory establishment in lekking marine iguanas, Amblyrhynchus cristatus: support for the hotshot mechanism

The territory establishment of male marine iguanas and their subsequent mating success were analysed to identify spatial spillover (hotshot) and temporal spillover effects on lek formation. Males started to establish small display territories 2 months ahead of the mating season. Males did not establish territories in temporal synchrony and did not settle at sites where the probability of encountering females was highest. However, males arriving later preferentially established their territories in the neighbourhood of already established territories independently of the density of female-sized iguanas in these territories. Although settling in close proximity, there were no fights between those males. The number of fights between territorial males increased towards, and peaked during, the mating season. Fights did not result in the transfer of space, indicating that space per se was no resource. Instead, fights were directed towards central (hotshot) males. These central males had higher mating success than marginal males. Female density during the time of territory establishment did not predict the mating success of males, because females changed their spatial preferences between early establishment and mating periods. Similarly, the areas where males achieved the highest numbers of copulations changed during 4 years of our study. Thus, there was no evidence for temporal spillover between subsequent seasons. However, most male-male interactions served to distract successful males and may lead to spatial spillover of females into territories of unsuccessful males. In marine iguanas, territorial establishment appears largely governed by hotshot processes.     

Correlates of male mating success in two species of Anthidium bees (Hymenoptera : Megachilidae)

Summary Field observations were made on the mating behavior of two congeneric species of solitary bees, Anthidium porterae in an arid grassland and A. palliventre in a coastal sand dune habitat. Males of both species exhibited resource defence polygyny and defended hostplants to gain access to females foraging for nectar and pollen. The mating frequencies of marked and measured resident (territorial) males were monitored during periods of continuous observation, following which measurements of territory size and floral resources were obtained. Mating success of A. palliventre males was strongly influenced by territory characteristics: Males that defended small areas with a few rich hostplant patches mated more often than males that held larger territories containing many hostplant patches of low floral density. Large males generally held high-quality sites and thus had a mating advantage over smaller individuals. In A. porterae, on the other hand, male mating success was unrelated to any measure of territory quality. Copulation frequency and male size were positively correlated, however, apparently due to the increased ability of large males to seize and hold females for mating. The two species also differed in the incidence of non-territorial, sneaky males. While absent in A. palliventre, sneaky males accounted for 12% of all mating observed in A. porterae. Males of A. porterae that displayed sneaky tactics mated, on average, as often as resident males. Offprint requests to: E.M. Villalobos     

On the consequences of aggressive male mate-locating behaviour and micro-climate for female host plant use in the butterfly <Emphasis Type="Italic">Lycaena hippothoe</Emphasis>

The distribution of ecological resources and their significance for males and females may vary considerably. Intersexual behavioural interactions may lead, combined with particular resource configurations, to sexual spatial segregation. We investigated this issue relative to host plant use in females of the purple-edged copper butterfly, Lycaena hippothoe. Males exhibited nectar resource-based territoriality, which is an uncommon mate-locating system in butterflies. They perched and patrolled in large territories harassing every passing female. In our study system, the percentage of spatial dimension shared for adult and larval resources was estimated at 50%, and males monopolised 28% of the nectar-rich zones. Under these conditions of harassment, females travelled between nectar-rich zones for feeding and zones with suitable host plants for egg laying, but often without nectar and hence with low male density. This is likely to limit their time budget and, potentially, their realised fecundity as suggested by the low number of eggs found relative to population size. Females were also highly specialised in selecting host plants under particular environmental conditions. Using test choice in experimental cages, we showed that, in the absence of males, only micro-climatic conditions may significantly influencing egg-laying decisions. Moreover, results of egg-rearing experiments under different temperature treatments suggested that eggs were laid in thermally suitable micro-environments. The highly selective egg-laying behaviour can be viewed as a preference-performance choice. Knowledge of individuals' behaviour, including sexual interactions, can be highly significant for our understanding of habitat use, which in turn can be essential for conservation. We discuss this for L. hippothoe, a species of regional conservation concern.     

Intrasexual competition,territoriality and acoustic communication in male strawberry poison frogs (<Emphasis Type="Italic">Oophaga pumilio</Emphasis>)

In many species male reproductive success is limited by access to females. Territoriality is one behavioural strategy which helps to acquire females. In the present study, we investigated the correlation between territory size and (1) female availability and (2) rate of intrusion by conspecific males in strawberry poison frogs, Oophaga pumilio. Males defended smaller territories in areas with a high female density and high rate of intrusion by conspecific males. Only males with high body condition values were able to establish territories in areas of high female density probably due to better fighting abilities. Moreover, dominant calling frequency was lower during agonistic interactions. Because only males with high body condition values were able to produce very low dominant frequencies, the acoustic properties appear to be an honest signal containing information about fighting abilities. Thus, the negative correlation between dominant frequency and mating success of males found in previous studies seems to be in part the result of intrasexual competition between males.     

Lek structure and territoriality in the chryxus arctic butterfly,Oeneis chryxus (Satyridae)

Summary The territorial and mating systems of the satyrid butterfly Oeneis chryxus were studied for 3 years on individually marked populations in algonquin Provincial Park, Ontario. Males defended territories in a dry open forest clearing by means of chases and spiral flights with conspecifies. Defended areas did not contain food or oviposition sites required by females. Territories were not uniformly distributed over the study area; the highest density of territories was clustered over bare ground covered with sand and small stones rather than areas of vegetation. This pattern of distribution of territories occurred during each year of the study. The patterns of occupancy of territories showed a high degree of consistency from one day to the next, some males defending a given territory for as many as 11 consecutive days. Removal experiments showed that a surplus of non-territorial males did not exist. Vacant territories in the high-density area were absorbed by neighboring males; those in the low-density area remained empty. Male size was not correlated with territory position in the study are. Wing patterning (i.e. size of spots) differed between males occupying territories on sandy/stony versus vegetated areas. The territorial and mating systems of O. chryxus resemble lek polygyny, and are more similar to some vertebrate lek systems than to hilltopping or landmark territoriality.     

Site fidelity and patterns of short- and long-term movement in the brilliant-thighed poison frog <Emphasis Type="Italic">Allobates femoralis</Emphasis> (Aromobatidae)

We studied movement and site fidelity of males and females of the territorial frog Allobates femoralis (Aromobatidae) in a population in the Nature Reserve “Les Nouragues” in French Guiana, South America. Observations during 3 months in 2006 ascertained intra-seasonal site fidelity for males and females. Males actively defend large multi-purpose territories whereas females retreat to small resting sites from where they commute to neighbouring males for courtship and mating. Female short-term movement corroborates the previous assumption of a polygynous or promiscuous resource-defence mating system. Year-to-year recaptures from 2005 until 2008 revealed distinct patterns of inter-annual movement for males and regional site fidelity for females. Males abandon their territories and have to re-negotiate them when reproduction starts again at the end of the dry season. Females are not subject to intra- or inter-sexual territorial competition and as a result move significantly less between reproductive seasons than males. Male long-term movement reflects spatial structure and prevailing social interactions and is a reliable indicator for tadpole deposition sites. The combined effects of intra- and inter-seasonal movement promote the diversity of mates for both sexes.     

Sex-specific differences in site fidelity and the cost of dispersal in yellow-headed blackbirds

Male migratory birds tend to be more faithful than females to previous breeding sites, suggesting sex differences in costs or benefits of dispersal. In Illinois, greater site fidelity by male yellow-headed blackbirds (Xanthocephalus xanthocephalus) was associated with reduced reproductive success the following year for dispersers relative to non-dispersers. Dispersing females suffered no reduction in reproductive success the following year. Males that attracted few social mates, and thus had low reproductive success, were more likely to disperse, whereas females dispersed in response to low-patch reproductive success, regardless of their individual performance. Males that dispersed appeared to be successful acquiring territories because none was observed as a floater. The rate of dispersal by males in this low-density population was greater than in more dense populations where dispersing males may be less successful at acquiring territories. Despite success at obtaining territories, males that dispersed acquired territories on the periphery of wetlands where fewer females nested, resulting in lower reproductive success. In the second year after dispersing, however, males moved onto more central territories where they acquired larger harems. Thus, dispersal by males may be a long-term strategy requiring at least 2 years for benefits to be realized. Long-term success was enhanced because dispersing males moved to wetlands on which reproductive success was higher than on the wetlands they left. In addition to demonstrating that both individual and patch reproductive success affect dispersal decisions, these data indicate that when evaluating costs and benefits of dispersal, researchers should use a time frame beyond 1 year.     

The influence of temperature on the territorial and mate locating behaviour of the small heath butterfly,Coenonympha pamphilus (L.) (Lepidoptera: Satyridae)

Summary Individual Coenonympha pamphilus males shifted mate locating behaviour depending on temperature. Under low temperature conditions males competed for territories, resulting in a high proportion of potential territories being occupied by stationary males and in long interactions between males in teritories. When temperatures became higher, stationary males tended to leave their territories and travel over a wider area, i.e. become vagrant. This resulted in a low proportion of territories being occupied by stationary males and inshort territorial interactions. Males could stay longer in flight without perching and hence also search a larger area for females within a given time span with increasing temperatures. This may explain why males adopt vagrant behaviour at higher temperatures. Al lower temperatures, on the other hand, when males cannot search effectively for females, waiting for them at a defended territory should be the most successful strategy.     

Nectar dehydration by male carpenter bees as preparation for mating flights

Summary Females of all social and many solitary bees dehydrate nectar before storing it or adding it to larval provisions. Nectar dehydration by males has rarely been documented. We report on the neotropical facultatively social carpenter bee Xylocopa nigrocincta, in which the nest constant males are fed nectar by their female nestmates. Males dehydrate the nectar at the nest entrance before leaving the nest for mating territories. We show that males thereby minimize their water load, resulting in an improvement of their energy budget during hovering flights in their territories. Males can prolong the duration of territorial flights if they cany highly concentrated nectar. We assume that nectar dehydration as a pre-mating behavior is not correlated with the social organization in Xylocopa species. However, the behavior is particularly weil-developed in X. nigrocincta, where during the mating period males remain integrated in the nest society and are fed by their mothers and sisters.     

Female habitat choice as a determinant of the reproductive success of the territorial male marine iguana (Amblyrhynchus cristatus)

Summary The reproductive behaviour of marine iguanas (Amblyrhynchus cristatus) was studied to answer the following questions: Which physical factors determine the number of females found on a male's territory? Do males select territories according to preferences for physical conditions or according to the number of females there? What causes the strong correlation between the number of females on a territory and the number of copulations achieved there? Females preferred as their resting places territories with the following characteristics, in order of importance: High number of shady/shelter places, low temperature of rocks at noon, proximity to the sea, sun-basking places in the afternoon. Other factors measured (probability of being wetted by spray, sun-basking places in the morning and at noon) showed no significant correlation with the number of females. Males, however, preferred territories further from the sea (within about 7 m), with high rock temperatures and a high number of basking places in the morning (in order of importance). Males primarily followed their site preferences and not female density in their choice of a territory. The site choice of females determined the number of copulations achieved on a territory, as females copulated preferentially on their resting places. A shift of females from one territory to another within one colony between two succeeding years was correlated with the change in relative weight of territory owners. This result was interpreted as an indication of female choice. Site preferences of males and females are discussed in relation to the animals' physiological requirements. Possible influences of ecological factors on the evolution of this mating system are considered.     

The reproductive behavior of Anthidium manicatum (Hymenoptera: Megachilidae) and the significance of size for territorial males

Summary Males of the wool-carder bee, Anthidium manicatum, patrol clumps of garden plants. Females of this species visit these plants for pollen, nectar, and pubescence; they also mate there. Females are polyandrous, with intervals between copulations as short as 35 s. Patrolling males defend their territories (0.1–1.3 m²) against other males and against other species of flower-visiting insects. Honey bees may be rendered unable to fly by the attacks of A. manicatum.Territory owners perform exploratory flights to other males' territories, changing territories often (median ownership 4–7 days; maximum 30 days) and flying up to 450 m to establish new territories. Territorial usurpations are nearly always by larger males.Female visitation rate is significantly correlated with number of flowers on a territory. The head size of territory-owner males shows significant correlation with territorial quality (measured by number of flowers, not area) and thus with number of female visits and copulatory opportunities. Some males fail to maintain territories and instead attempt to forage and copulate in other males' territories while the owners are otherwise occupied. Nonowner males are significantly smaller than owners, forage less often and from fewer flowers, and achieve significantly fewer copulations than owners. Females, however, do not reject smaller, nonowner males at a higher rate than they do larger, owner males; their choice for male size appears to be indirect, based instead on choice of food resource.The interval between a copulation and the male's next attempt with a different female is not shorter than that involving the same female. Males do not escort just-mated females about their teritories, as observed in Anthidium maculosum. Territorial behavior in this species most likely evolved through intrasexual competition for reproductive success which led to sexual dimorphism. The defense of a resourcebased territory is the mechanism used by a male to maximize his reproductive potential.     

Alternative mating strategies in the water strider Gerris elongatus (Heteroptera,Gerridae)

Summary Males of the water strider Gerris elongatus established territories which included copulation and oviposition sites (small pieces of fallen bamboo). Males were aggressive and competition for territory and females was observed frequently. Male midlegs were more developed than female midlegs and were used as weapons. Reproductive behaviour changed as the breeding season advanced. Early in the season immature females were attracted by male surface wave courtship signals, then copulated white floating on the water surface without ovipositing (type 1). In midseason, males established territories, produced calling signals and attracted females which copulated and oviposited there with male postcopulatory guarding (type 2). In late season, many females oviposited without postcopulatory guarding on pondweed mats near fallen bamboo. Non-territorial males waiter for the arrival of these females and copulated without courtship, but mating success was low (type 3). These alternative mating strategies appeared to depend on differences in male size. Larger males were superior to smaller males in many ways (establishing territory, fighting, mating etc.). The largest males defended territories and had higher mating success than small non-territorial males. Medium sized males used all three strategies according to the number of empty territories and seasonal femald distribution.     

Roles of interplant movement,acoustic communication,and phototaxis in mate-location behavior of the leafhopper Graminella nigrifrons

Summary Male Graminella nigrifrons leafhoppers (Cicadellidae: Homoptera) employ a call-fly strategy to find virgin females on oat host plants. Males observed in isolation during daylight hours exhibit a high rate of interplant movement, calling from the lower canopy on each plant visited. Virgin and mated females exhibit little interplant movement. They differ from one another in that virgin females perch on the upper half of plants, whereas mated females perch on the lower half of plants. The positioning of females in the plant canopy is influenced by light. Unlike mated females, virgin females respond to male calls by emitting their own acoustic signals. When virgin females are present on plants visited by males, interplant movement of males ceases, and a localized-upward search of the female bearing plant ensues. Male search is influenced by light. Regardless of whether virgin females were confined to the upper or lower portion of plants, direction of male search was towards a light source used to illuminate above or below the plant canopy. These findings suggest that interplant movement by males and sedentary behavior by females prior to mate recognition and their use of acoustic and phototactic sensory modalities after mate recognition represent previously unrecognized adaptations to problems associated with the use of vibrational signals on plants. Offprint requests to: R.E. Hunt at the current address     

Mating system shift in a pronghorn population

Summary At the National Bison Range (western Montana, USA), pronghorn (Antilocapra american) maintained a territorial mating system from as early as 1965 through 1978. Preliminary observations in 1981 suggested that the mating system had changed. Data from the ruts, 1982–1984 revealed a progressive decay in territoriality. In this paper, data from the territorial years 1969–1978 are contrasted with data from the decay years 1982–1984, with results as follow: 1. In 1982–84, fewer territories were defended than in 1969–78. This was attributable to a smaller proportion of males defending territories in 1982–84, not to a smaller number of males. 2. In 1982–84, most territory owners either abandoned their territories early in ruts, or lost control of females on them following frequent, persistent intrusions by non-territorial males. Abandonment and loss of control did not occur in 1969–78. 3. In 1982–84, territorial males that maintained control of females on their territories did so by shrinking their zones of defense to small areas around female groups. 4. In 1982–84, following the disruption or severe disturbance of all territories, many females left territories, and mated elsewhere, with non-territorial males. In 1969–78, most females remained on territories throughout rut, and mated with territory owners. —The mating system change followed catastrophic winter mortality, 1978–79, that removed 75% of the males, including all males older than 5 years, and all male fawns, from the population. In 1982–84, the number of males present was not different from the number of males in 1969–1978, but the frequency distribution of male ages was strongly shifted toward younger ages. The small number of older males, 1982–84, likely resulted in smaller proportions of males initially defending territories, and in less effective territory defense. When females then clustered on the few territories where defense was at first successful, they attracted large numbers of non-territorial males. The resulting high rates of raids on these territories, coupled with reduced defense radii by territorial males, allowed females only 12% reclining time (summer percentage was 39%). This increased energy cost, plus an apparently greater risk of injury on weakly defended territories, appeared to prompt many females to seek calmer matings elsewhere. Also, if female pronghorn practiced mate selection based upon horn or body size, they may have reduced their efforts to remain on territories in 1982–84. Males from 1969–78 were larger than males from 1982–84, and showed greater variance in horn size. At least two conditions appear to influence the tendency of males to be territorial. First, males must be at least three years old before they attempt to defend a territory. Second, the declining proportion of males defending territories, 1982–84, that coincided with an increasing number of males three years and older, suggests that males also decide whether or not to attempt territory defense based upon the frequency of territorial defense in the population.     

Attraction and learning in mate-finding by solitary bees,Lasioglossum (Dialictus) figueresi Wcislo and Nomia triangulifera Vachal (Hymenoptera : Halictidae)

Summary Males of the solitary sweat bee, Nomia triangulifera, patrol over large areas where thousands of females emerge, searching for receptive females. The daily operational sex ratio is strongly male-biased. Males contact dead, frozen (untreated) females more frequently than they contact females which were washed in hexane, showing that olfactory cues are utilized in mate-finding. A major source of female sex pheromone is in the head. Male pouncing on females is temporally non-random, indicative of group stimulation. Bioassays show that newly emerged females are more attractive to males than are older pollen-collecting females. Female odors are individually distinctive, based on male responses, and there is much variation among females in their attractive properties. Male responses to female odors suggest that learning is important for mating in natural populations. In contrast, the following hypotheses are unlikely to account for the observed behavior: (1) dissipation of female odors; (2) site learning and avoidance behavior by males; (3) decay of male motivation; or (4) male-produced repellents effective against other males. Laboratory and field studies show that female Lasioglossum figueresi produce individually-distinctive odors, which are attractive to males. There is considerable inter-individual variation among females in their attractiveness to males among sexually immature females. Male responses to female odors decay over the course of the presentation, suggesting the importance of learning in natural populations, although several alternatives could not be tested.     

Dispersal: an alternative mating tactic conditional on sex ratio and body size

Summary Small male milkweed beetles are less successful at obtaining mates than are larger males. Larger males usually win fights and prevent smaller males from obtaining mates and from choosing larger more fecund females as mates. When sex ratios are male-biased, smaller males are particularly likely to experience these mating disadvantages. It follows that smaller males should be especially responsive to their local competitive environment and behave so as to minimize the mating disadvantages of their smaller size. This paper tests the hypothesis that smaller males disperse from host plant patches with male-biased sex ratios and remain in patches with female-biased sex ratios more readily than larger males.Results show both larger and smaller males disperse from patches with male-biased sex ratios more frequently than from patches with femalebiased sex ratios. As predicted, however, small males are more likely to disperse from patches with male-biased sex ratios and remain in patches with female-biased sex ratios than are larger males.The data also show that smaller males dispersing from patches with male-biased sex ratios obtain more matings than non-dispersing males.For milkweed beetles, moving between patches can be viewed as an alternative mating tactic conditional on male body size and local sex ratio.