Scramble competition polygyny in the coreid bug (Colpula lativentris)

The mating system of the coreid bug, Colpula lativentris, was studied, and compared with those in other hemipteran bugs. Copulating pairs formed a compact aggregation on a shoot of the Japanese knotweed, Polygonum cuspidatum, and there continued copulation and feeding for more than one day. This aggregation was defined as “a shoot aggregation”. Other than this aggregation composed of copulating pairs, there were loose aggregations on the ground composed of males and females not in copula. This loose aggregation was defined as “a ground aggregation”. Males searched for receptive females mostly in a ground aggregation. Sex ratio was constant and variance of sex ratio was also very small in any shoot aggregations and in large ground aggregations. However, in small ground aggregations, sex ratio was strongly male biased and variance of sex ratio was fairly large. This was because receptive females tended to leave a small ground aggregation and join a large one. These results suggest that a male can attain higher mating success in a larger ground aggregation.     

Formation and maintenance of mating aggregations in a stink bug,Megacopta punctissimum (Montandon) (Heteroptera: Plataspidae)

Adults of a stink bug,Megacopta punctissimum, formed mating aggregations on their host plants: a few pairs in copula and a few bachelor males (males not in copula) stayed in the aggregation and the bachelor males waited for arriving females to mate with. The processes of formation and maintenance of the aggregations were observed using the individual marking technique. Aggregations initiated by 2 males or by 1 male and 1 female were usually joined by 1 or more individuals and lasted for several days, but aggregations initiated by 2 females broke up within 1 h. Aggregations were not maintained by the same members. The residence time (time from joining an aggregation to leaving the aggregation without copulating) of males was longer than that of females. There was a negative correlation between the residence time of males and the number of bachelor males in an aggregation when bugs joined it, while the residence time of females was positively correlated with the number of bachelor males in the aggregation. When bugs copulated after joining an aggregation, the postcopulatory residence time (time from completing copulation to leaving the aggregation) was longer in males than in females. Thus, males had a stronger tendency to initiate and maintain aggregations than females.     

Female choice for male gregariousness in a Stink bug,Megacopta punctissimum (Montandon) (Heteroptera,Plataspidae)

Adults of a stink bug,Megacopta punctissimum, form mating aggregations on their host plants, based on the gregarious habit of males. A female was released on a stem on which there was an aggregation of 2 mating pairs and 1 bachelor male. Next, the bachelor male was released on a stem on which no bugs were present, and the same female was released there. Sequences of courtship behavior were compared between them. This experiement was repeated for 41 pairs of males and females, and about half (20 cases) of these experiments were made in the reverse order. Males were the active sex in courtship, whilst females either accepted the courtship, or escaped from courting males. Females accepted courtship with a higher probability when males courted in aggregations (73%) compared to solitary conditions (22%). This was because the escape behavior of females from the males was reduced if females detected the presence of other bugs near the males. It was concluded that female choice is a selective force for gregariousness in males.     

Female Leadership During Migration and the Potential for Sex-Specific Benefits of Mass Spawning in the Brown Surgeonfish (Acanthurus nigrofuscus)

Spawning aggregations in coral-reef fishes have been hypothesized to confer any one of several mutually non-exclusive benefits, largely expected to serve the interests of both sexes simultaneously. Here we provide indication that in the brown surgeonfish, Acanthurus nigrofuscus, spawning aggregations may confer a sex-specific benefit. Following tagged individuals en-route to their daily spawning-aggregation site we found that while migrating groups (≤20 fish) consist of both males and females, females tend to occupy the lead position more often than expected by chance. In addition, we found evidence that female A. nigrofuscus divide their daily egg-stock among several spawning bouts within the aggregations. We propose that female leadership en-route to spawning aggregations, together with the potential benefits of multiple female mating, are consistent with a sex-specific benefit to spawning aggregations.     

Social system of an inshore stock of the red hind grouper,Epinephelus guttatus (Pisces: Serranidae)

Synopsis According to sex allocation theory, the decision by a female in protogynous fish species to change sex or not should be influenced by, among other things, the mating sex ratio during spawning periods and/or by factors that vary directly with the spawning sex ratio, such as relative rates of behavioral interaction with males and females outside of spawning periods. In groupers that only spawn during a few weeks of the year in large aggregations, individuals must assess the relative value of changing sex or not entirely within the aggregation unless the social system during the remainder of the year provides a behavioral equivalent of the mating sex ratio. Fifty-five individuals of the red hind,Epinephelus guttatus, were tagged and repeatedly located during a 152-day period within a 100 × 100 m grid on a shallow forereef off southwestern Puerto Rico. The home ranges of 22 tagged individuals sighted 10 or more times were 112–5636 m² in area. Individual home ranges overlapped with the home ranges of 1–18 other individuals. Home ranges of small fish were not clustered within the borders of the home range of larger fish, i.e. fish did not form spatially defined social units. At the end of the study, 31 tagged individuals remained on the grid together with five newly sighted fish. All 36 individuals proved on histological examination to be females similar in size to females in the spawning aggregation of the following year. The sex ratio of this all-female inshore stock differed significantly from the sex ratio of that spawning aggregation. Hence, information predicting the reproductive value of a sex change is not available to females in the inshore stock during nonspawning months.     

Spatial relationships between mate acquisition probability and aggregation size in a gregarious coreid bug, (Colpula lativentris): A case of the ideal free distribution under perceptual constraints

Spatial relationships of mate acquisition probability for individuals of both sexes of a gregariously-mating coreid bug, Colpula lativentris, were studied in relation to aggregation size. Operational sex ratio was always strongly male biased. Mate acquisition probability of females was rather constant and independent of aggregation size, as predicted by an ideal free distribution. Moreover laboratory experiments showed that both multiple mating and rearing density little affected female fecundity, suggesting ideal free distribution of females in terms of reproductive success. On the other hand, mate acquisition probability of males was higher in larger aggregations, where more receptive females were available. This male discrepancy from an ideal free distribution was similar to the patterns predicted by an ideal free distribution under perceptual constraints (Abrahams, 1986), but not by that under unequal competitive ability.     

Mating system of Bracon hebetor (Hymenoptera: Braconidae)

Abstract.

• 1 We report on the mating system of a field population of the parasitic wasp, Bracon hebetor, on a corn pile infested by the Indian meal moth, Plodia interpunctella. We demonstrate that the mating system is based upon male scramble competition polygyny with male aggregations on high places on the corn.
• 2 The sex ratio among adults was greater than 80% males on the surface of the corn, whereas below the surface the sex ratio was less than 45%. Males actively courted females on the surface, but there were no aggressive interactions among males during courtship or mating.
• 3 Approximately 20% of the females found on the surface of the corn had no sperm in their spermathecae, regardless of age, but the numbers of unmated females decreased later during the day.
• 4 In laboratory studies we showed that females from this population oviposit a female biassed sex ratio, and that only 14% of females were mated before dispersing from their place of emergence.
• 5 Thus sib-mating is unlikely in this gregarious parasitoid. This outcrossing mating system probably arose because of severe inbreeding depression that B.hebetor suffers via a sex locus: diploids that are heterozygous at the sex locus develop into females, but homozygous diploids are male and are generally inviable. The female biassed sex ratio may have evolved in B. hebetor in response to males being the more expensive sex, females dispersing more frequently from the population than males, or a fraction of females remaining unmated in the population.

     

Population dynamics of the solitary digger bee<Emphasis Type="Italic"> Andrena vaga</Emphasis> Panzer (Hymenoptera,Andrenidae) studied using mark-recapture and nest counts

The population size of the solitary digger bee Andrena vaga was documented using mark-recapture methods during 4 consecutive years (1996–1999). Additionally, the numbers of the parasitoids Nomada lathburiana and Bombylius major were estimated. For calculations of the daily population size, the Jolly-Seber model for open populations with time-dependent survival and capture rates was used. The mean daily population size corresponded well to the number of nests marked in the aggregation of A. vaga. The method of mark-recapture achieved the most accurate data when the number of sampling periods and the capture probability was high. The results document a decrease in population size of the investigated A. vaga aggregation during 4 successive years. A population increase of its parasitoids B. major is considered to be one reason for the population decline of A. vaga in 1999. The sex ratio of A. vaga was biased toward females, contrary to the expected higher number of males. Results of the mark-recapture studies showed that up to 50% of females left the aggregation or died at the beginning of the season. The females probably colonized new aggregations at distances further than 200 m away from their birth aggregation, as no marked females were observed in the environs of the study area. This behavior is interpreted as a parasite avoidance strategy. The bee populations in the study area form a web of interconnected aggregations. Apparently a flux of extinction and recolonization exists between the different aggregations.     

Coexistence of congeneric spiny lobsters on coral reefs: differences in conspecific aggregation patterns and their potential antipredator benefits

Den sharing by conspecific spiny lobsters (aggregation) is modulated by chemical attraction but may confer several, not necessarily mutually exclusive, antipredator byproduct benefits: a “guide effect”, which only benefits the individual attracted to a sheltered conspecific; a “dilution effect”, which reduces per-capita risk of predation simply through aggregation; or active “group defense”. Each potential benefit has a different set of predictors (relationships between aggregation and conspecific or predator densities), but conflicting results could suggest the simultaneous operation of more than one benefit. These predictions were tested for coexisting Panulirus guttatus (a reef-obligate) and Panulirus argus (a temporary reef-dweller) using data collected during 11 surveys on fixed sites over a coral reef in Mexico. P. guttatus greatly outnumbered P. argus, but P. argus showed a greater tendency to aggregate. All three benefits of den sharing operated for the more social P. argus, with “group defense” being of the most benefit for larger individuals, and the “guide” and “dilution” effects for smaller individuals recently immigrating into the reef habitat and sharing dens with larger conspecifics. P. guttatus did not display “group defense” and its aggregations appeared to be modulated by the interplay between attraction and aggressive behaviors. This species relied more on solitary crypticity, especially at larger sizes, but appeared to benefit from a “guide effect” at high conspecific densities. In experimental tanks, each species tended to aggregate when tested separately, but when tested jointly, aggregation among P. guttatus was significantly reduced. The experimental results reflect the differential patterns of aggregation between the fore-reef, where P. guttatus dominated, and the back-reef, where coexistence of both species was greater.     

AGGREGATION FORMATION AND ASSORTATIVE MATING IN TWO MELOID BEETLES

Males and females of the meloid beetles Lytta magister and Tegrodera aloga form large aggregations in Sonoran Desert habitat. Males and females of L. magister fly to prominent ridgetop landmarks, where they feed on flowering shrubs, mate (probably just once in any one aggregation), and disperse, with the group forming and disbanding in a few days. Males and females of T. aloga form very large, mobile bands that march across the desert flatland feeding and mating; females probably leave after a single copulation, with the result that the group becomes increasingly male-biased in its sex ratio. The aggregations persist for a minimum of 2–3 weeks. Great variation in body size characterizes both species. Positive assortative mating occurs in L. magister but not in T. aloga, possibly because males and females of the two species incur different costs and benefits for selective mating. It is probable that body size in Lytta correlates both with female fecundity and with male spermatophore size or amount of cantharidin contributed during copulation. This should favor males that mate with large females while also favoring females that mate with large males. If large individuals pair off, this will leave smaller individuals to settle for one another, leading to positive assortative mating. The same argument may not apply to T. aloga, perhaps because its copulations are shorter and its aggregations longer-lived, and therefore any one mating does not eliminate chances to copulate again within the band.     

Sexual Selection of Zorion guttigerum Westwood (Coleoptera: Cerambycidae: Cerambycinae) in Relation to Body Size and Color

Zorion guttigerum is a flower-visiting longhorned beetle endemic to New Zealand. Sexual selection of this species in relation to the body size and color form of different sexes was investigated in the field. The population sex ratio, based on censuses of feeding and mating sites (flowers), is male-biased. Females are significantly larger than males. Both sexes have antennae of similar length but the antennal length relative to the elytral length is greater in males than in females, and the antennal length of males increases more with an increase in body size than that of females. Both sexes have dark blue (DB) and yellowish-brown (YB) individuals. Both pair-bonded and solitary males are similar in elytral and antennal length. In pair-bonded males, DB individuals are significantly more numerous than YB ones, but in solitary males, the number of both color forms is similar. Males tend to have territory protection behavior, fighting with and chasing away rival males from feeding and mating sites. Larger males usually win the fight but the size-dependent fighting advantage does not translate into mating success. Male color plays an important role in mating success, with DB males having a significantly better chance to mate than YB males. Furthermore, male body size and color also have interactions in mating success: males of DB color morph obtain a greater mating advantage according to body size. Pair-bonded females are significantly larger and have longer antennae than solitary females, suggesting that males prefer larger females for mating. In addition, females of DB color morph with longer antennae are also preferred by males for mating. The significance of these findings is discussed.     

Mating Aggregations and Mating Success in the Flower Thrips, Frankliniella schultzei (Thysanoptera: Thripidae), and a Possible Role for Pheromones

Aggregations of Frankliniella schultzei males were observed on the corollas of Hibiscus rosasinensis and Gossypium hirsutum flowers in southeast Queensland. Aggregations were seen only on the upper surfaces of corollas but may have occurred on other flower parts, which were hidden from view. Conspecific females entered aggregations and a small proportion of them mated [18% (n = 163), H. rosasinensis; 30% (n = 181), G. hirsutum]. Most females (87 and 72%, respectively) that did not mate in aggregations walked to other flower parts. Behavior was difficult to observe on these parts, but mating was sometimes observed there. The number of females that landed within aggregations on the upper surfaces of both H. rosasinensis and G. hirsutum corollas was highly correlated with the number of males (r = 0.88, r = 0.93, respectively; P < 0.001). Significantly more mating pairs were observed in high-density aggregations (mean ± SE, 1.10 ± 0.22 and 4.44 ± 0.48, respectively) than in low-density aggregations (0.37 ± 0.11 and 1.67 ± 0.29, respectively) (P < 0.05) on flowers of both species. More F. schultzei females were attracted to sticky traps baited with live conspecific males set among flowering Ipomoea indica (mean ± SE, 8.83 ± 0.32) and G. hirsutum (10.90 ± 0.79) plants than to control traps (0.10 ± 0.05 and 0.70 ± 0.25, respectively) (P < 0.05), presumably in response to male-produced pheromones. Significantly more females were attracted to traps with high male densities than to traps with low densities. We found no statistical evidence that aggregation size influenced mating success (proportion males that mated). Mating success, however, should be evaluated with respect to mating on all flower parts and not just the upper surfaces of corollas. The results of this study constitute the first behavioral evidence for an attractant sex pheromone in thrips.     

Attraction of the sexes inFormica lugubris Zett (Hymenoptera: Formicidae)

Summary Sexuals ofFormica lugubris fly to mating places, where females attract males by using a sex pheromone. Females collected on the nest surface before departing on a mating flight are much less attractive than those collected on the mating place after the mating flight, suggesting that the mating flight triggers the release of the sex pheromone. Olfactory cues are essential for males to locate females while they patrol. Males probably use visual cues to locate females once they have alighted nearby them. Males are also attracted by aggregations of other males on the ground, probably because one or several females are likely to be close to male aggregations.     

Female‐biased sleeping aggregations of Amegilla florea urens (Hymenoptera: Apidae)

Although male bees and wasps aggregate in specific sites overnight, few studies have addressed the behaviors of female hymenopterans during the night. It is generally understood that they spend the night in a burrow or nest structure. We found female‐biased sleeping aggregations of Amegilla florea urens in populations on Iriomote Island. The sex ratio and number of sleeping individuals in the sex‐mixed aggregations changed daily. This species used dead branches as its main sleeping places, and the maximum number of individuals observed per place was 15. Females arrived at the aggregation place later and left it earlier in the morning than did males. Our result suggests that females used the sleeping place regularly but avoided a long stay with males. The use of the same sleeping place by the two sexes may be due to a limited number of sites suitable for sleeping in the forest.     

Observations of spawning in the Leather Bass, <Emphasis Type="Italic">Dermatolepis dermatolepis</Emphasis> (Teleostei: Epinephelidae), at Cocos Island,Costa Rica

Courtship and spawning behavior is described for the Leather Bass, Dermatolepis dermatolepis, from observations made from a manned submersible at Cocos Island, Costa Rica on 19 days between November 2006 and February 2007. Spawning occurred in the evening (16:00–18:30 h) in subgroups of 10–32 individuals that formed within aggregations of 50–70 individuals. The mating sequence was characterized by subgroup formation and crowding behavior followed by a brief vertical spawning rush, gamete release, and the rapid separation of participants. The aggregation was present on all dives, and spawning was not restricted to specific lunar phases.     

Male-biased sex ratios,female promiscuity,and copulatory mate guarding in an aggregating tropical bug,Dysdercus bimaculatus

The ecological and social bases of the mating system of the seed-feeding bug, Dysdercus bimaculatus(Hemiptera: Pyrrhocoridae), were studied in the lab and in aggregations at the host tree, Sterculia apetala(Malvales: Malvaceae), in Panama. On theoretical grounds, two factors are predicted to be of importance in determining the evolution of male mating tactics in Ms species: the operational sex ratio and the probability that undefended females will mate with other males, subjecting the gametes of deserters to sperm competition. Results of a study of a related species suggested that sperm displacement is probably substantial. Adult sex ratios at numerous sites were significantly male biased, and females whose mates were removed remated before oviposition (i. e., sperm utilization). These results predict that a mate defense tactic is likely to be superior to a nondefense tactic. The biological significance of the parameters is supported by observations that captive pairs often remained in copulafor several days, until just before oviposition. However, substantial variation in copulation duration was also observed, and possible causes of this variation are considered. Causes of male biased adult sex ratios were investigated by monitoring demographic changes within a single aggregation over 2 months. Both female juvenile and adult mortality rates were greater than male. In addition, dissections of reproductive adults showed that the flight muscles of females, but not males, had histolyzed, so that female reproduction is physiologically limited to a single site. Greater rates of immigration among both mature and young males suggests that an excess of males may also be found in the populations of bugs that subsequently colonize other host plants, so that female scarcity is typical of aggregations in all stages of development. The evolution of sex-limtied flight muscle histolysis may be explained by greater patchiness of females than males as mating resources, plus a lower energetic benefit/cost ratio of histolysis for males.     

Grouping behavior of Sumatran orangutans (Pongo abelii) and Tapanuli orangutans (Pongo tapanuliensis) living in forest with low fruit abundance

In contrast to the African great apes, orangutans (Pongo spp.) are semisolitary: Individuals are often on their own, but form aggregations more often than expected by chance. These temporary aggregations provide social benefits such as mating opportunities. When fruit availability is high, costs of aggregating should be lower, because competition is less pronounced. Therefore, average party size is expected to be higher when fruit availability is high. This hypothesis would also explain why orangutans in highly fruit-productive habitats on Sumatra are more gregarious than in the usually less productive habitats of Borneo. Here, we describe the aggregation behavior of orangutans in less productive Sumatran habitats (Sikundur and Batang Toru), and compare results with those of previously surveyed field sites. Orangutans in Sikundur were more likely to form parties when fruit availability was higher, but the size of daily parties was not significantly affected by fruit availability. With regard to between-site comparisons, average party sizes of females and alone time of parous females in Sikundur and Batang Toru were substantially lower than those for two previously surveyed Sumatran sites, and both fall in the range of values for Bornean sites. Our results indicate that the assessment of orangutans on Sumatra as being more social than those on Borneo needs revision. Instead, between-site differences in sociality seem to reflect differences in average fruit availability.     

Territorial behavior of the plethodontid salamander Plethodon kentucki: influence of habitat structure and population density

To investigate the possible influence of variation in ecological and demographic factors on the spatial organization of the terrestrial plethodontid salamander Plethodon kentucki, I conducted a 3-year capture-recapture study and determined home-range characteristics and spatial relationships of individuals at two field sites that differed in predominant cover type and population density. Home ranges of adults were fixed and the home ranges of same-sex adult neighbors were mostly exclusive. The spatial arrangement of adult home ranges exhibited overall regularity or regularity within aggregations, whereas the distribution of juvenile home ranges was usually random. Analysis of nearest-neighbor sex indicated a positive intersexual association of adult home ranges. Removal studies provided evidence for defense of adult home ranges only at the high-density site. The distribution of home ranges was influenced by the presence of cover objects, but there was no significant relationship between adult body size and percent of home-range area with cover. Males overlapped the home ranges of gravid females significantly more often than those of non-gravid females, indicating that the distribution of gravid females had a strong influence on the distribution of male home ranges. In laboratory tests, increased male-male aggression during the breeding season suggests that males may compete for access to mates. At the high-density site, larger males may have benefited by having greater reproductive success than smaller males because they were more dominant and their home ranges overlapped a greater number of gravid-female home ranges. My results indicate that habitat structure and population density may influence the spatial organization and mating system of P. kentucki. Received: 26 May 1997 / Accepted: 9 October 1997     

Studies on the mating system of the winter cherry bug,Acanthocoris sordidus Thunberg (Heteroptera: Coreidae) II. Harem defence polygyny

The mating system of the winter cherry bug, Acanthocoris sordidus, was analyzed precisely. As a result, it was found that male adults of this species establish a small territory for mating on the stem of host plant which harbors females. These males abandoned their territories soon after the disappearance of monopolized females. Thus it was confirned that the cue for the territorial establishment of males is the presence of females per se on the host plant. Moreover, most aggregations of adults observed on the host plant contained only a single male. This one-male unit in the mating was named a harem. Harem holding males were usually big in body-size and had a high chance of copulations. The defence behaviors of harem holding males, the mating disparity among males, and the oviposition habit of females in relation to the mating system, were observed. The results obtained were discussed in relation to the sexual selection theories.     

Mating tactics and courtship behavior inCleogonus rubetra (Fabricius) (Coleoptera: Curculionidae)

Females of the tropical weevilCleogonus rubetra oviposit into fruits of the leguminous treeAndira inermis, and larvae develop in the pulp and seed of these fruits. We hypothesized three alternative tactics by which males might secure matings. By using focal observations of males and by evaluating predictions specific to each hypothesis, we demonstrate that males search within aggregations of conspecifics for receptive females, and upon finding a suitable partner, males mount and perform courtship behavior consisting of stroking the eyes and sides of the female's abdomen. Males also stridulate and emit a sequence of short buzzing sounds. While mounted, males actively prevent rival males from mating with their partner. Males defend their mates for a mean duration of 3.7 h (including copulation). As predicted, paired males were larger than solitary individuals, although the difference was marginally nonsignificant. The overabundance of fruits relative to males, the prolonged period during which females are active, and the probability of last male sperm precedence are factors that may have contributed to the evolution of this female-defense tactic by males. Paired females were significantly larger than solitary females. We observed no competition among females for mates, and the correlation between elytron length of paired males and females was not significant.