Influence of methoprene and dietary protein on male Anastrepha suspensa (Diptera:Tephritidae) mating aggregations

The Caribbean fruit fly, Anastrepha suspensa (Loew), like many polyphagous tephritids, exhibits a lek polygyny mating system, and juvenile hormone levels and adult diet are known to have important positive effects on male sexual success. Among the potential components of this success are male lek tenure and female response to the sexual signals of lekking males. Male A. suspensa where submitted to four different treatments: (M⁺P⁺) application of juvenile hormone analog, methoprene (M) and sugar and hydrolyzed yeast as adult food; (M⁺P⁻) application of M and sugar as adult food; (M⁻P⁺) no application of M and sugar and hydrolyzed yeast as adult food; and (M⁻P⁻) no application of M and sugar as adult food. M⁺P⁺ males initiated and participated more in aggregations, mated more frequently, and occupied the lek centers more often. They also had fewer unsuccessful mounting attempts than males in all the other treatments. M⁺P⁺ males also emitted pheromones and acoustically signaled more often and attracted more females than males in other treatments. Male sexual performance was improved due to methoprene, protein supply, and the interaction of methoprene and protein for most of the parameters. Since the success of the sterile insect technique (SIT), a commonly employed technique to control pest tephritids, requires the release of males that can form leks, engage in agonistic sexual interactions, and attract females, these positive effects of protein and methoprene may substantially improve SIT programs.     

Within-nest spawning-site preferences of female bluefin damselfish: the effect of early-stage eggs

In some fish species with exclusive paternal care females prefer to deposit their eggs in nests containing early-stage eggs and avoid those containing only late-stage eggs. Such female preference may also be shown when it comes to deciding where to lay within a given nest; that is, females may prefer to lay contiguously to younger rather than to older eggs. To understand if females benefit from such preferences by obtaining higher offspring survival, we conducted field studies with the bluefin damselfish, Abudefduf luridus. We investigated (1) female between-nest and within-nest spawning-site preferences relative to brood characters and (2) egg-hatching success related to male filial cannibalism. We found evidence that males entirely ate some of their clutches, especially the eggs received near the end of the breeding season. These were also more susceptible to being eaten when laid in nests containing only eggs in a late stage of development. Theoretically, these patterns of clutch loss should result in adaptive female preference for nests containing early-stage eggs, but we found no evidence for such a preference in female A. luridus. However, once females had chosen a nest they strongly preferred to lay contiguously to early-stage eggs than to late-stage eggs. Moreover, females benefited from this decision by obtaining higher survival rates for their clutches. We conclude that within-nest spawning-site preference of the female for early-stage eggs may have evolved as an adaptive response to a dilution effect on the risk of egg loss.     

The hormonal response of female European Stonechats to a territorial intrusion: the role of the male partner

In many bird species, the female participates in defending a pair's breeding territory, however, the endocrine control mechanism of female aggressive behavior is largely unknown. The general statement that androgens are involved in the regulation of aggressive behavior is based on studies conducted only in males. Here, we tested whether paired female stonechats show a hormonal response to a simulated male territorial intruder. Since in males of territorial bird species androgen levels usually increase following a male-male encounter, we measured androgen-levels before and after a simulated male intrusion. In addition, we measured estradiol, the main gonadal hormone in females, and corticosterone, a stress hormone. The results show that a male intruder does not affect any of the measured hormones in females. In a second experiment, we also tested whether the endocrine state of the male partner affects the hormonal response of females to a male intruder by comparing the hormonal response of females paired with pharmacologically castrated males and females paired with control males. Females paired with pharmacologically castrated males had lower corticosterone levels both before and after the intrusion than females paired with control males. Additionally, in both groups, female corticosterone levels were increased following a male intrusion. We suggest that the differences found between females paired with pharmacologically castrated males and females paired with control males are due to differences in intra-pair interactions.     

Female choice linked to male dorsal fin height in a shortfin molly

Sexual selection is a possible mechanism of speciation. This could be true even in systems where female mate choice has not been clearly observed, because pre-existing biases may be expressed if female decision-making results in male trait evolution. In some mollies, males have enlarged dorsal fins and courtship display is the prevailing mating process. In others, male dominance is thought to play a greater role. We tested females of a species in the latter group, Poecilia mexicana, for consistent preference related to dorsal fin morphology. We found that females were biased toward larger dorsal fins. This latent preference could be an important driver in trait evolution.     

Asymmetric competition between two tit species: a reciprocal removal experiment

1. In a 5-year field experiment, competition for food was tested between great tit ( Parus major L.) and blue tit ( P. caeruleus L.), two common hole-nesters in Central Europe. Experimental ('allopatric') populations of both species were created during the breeding seasons by preventing the nesting or egg laying of one of the competing species.
2. An asymmetric relationship was found between the two tits; blue tits were more successful in the competitive interaction. Detectable effects were found only in nestling condition. Great tits raised lighter nestlings when breeding sympatrically with blue tits.
3. A possible mechanism is suggested that could be responsible for the different competitive abilities of the two species; blue tits are more effective in utilizing the most abundant size categories of caterpillar food supply than great tits.     

Predators and avian community organization: an experiment in a semi-desert grassland

Summary We provide experimental evidence that predators are a major factor organizing a community of granivorous grassland birds (mostly emberizid finches). Our focus is not on the lethal effects of predators, but on the simple idea that (i) birds will not settle where they perceive a high risk of predation, and (ii) species differ in their perception of the safety of woody vegetative cover due to differences in antipredator escape behavior. Consistent with this idea is the fact that the composition of this grassland community responds markedly to minor manipulations in the distribution of woody cover. In particular, with the addition of cover to open grasslands, species with cover-dependent escape tactics increase in abundance, while the abundance of cover-independent species decreases greatly; this decrease may reflect aggression from cover-dependent species, but evidence suggests that some cover-independent species may actively avoid cover-rich areas per se. Non-predatory effects of cover, most notably those concerning food resources and microclimate, appear unable to explain these results. Predators may influence many communities of terrestrial vertebrates via species-specific responses to cover.     

Spatial organization of a desert rodent community: food addition and species removal

Summary From 1977 through 1983 we conducted experiments on a desert rodent community where supplemental seeds were added or certain rodent species and ants were removed from 0.25-ha fenced plots in a Chihuahuan Desert site in southeastern Arizona, USA. In this paper we examine the patterns of microhabitat use relative to vegetative cover by 11 rodent species. The results show that: i) removal of the largest seed-eating species, Dipodomys spectabilis, produced the most pervasive and dramatic shifts in microhabitat use by the remaining rodent species; ii) adding seeds or removing ants had little effect on the spatial use of microhabitats by rodents in this community; and iii) non-granivores were just as likely as granivores to shift microhabitat use when other granivores were removed. We believe these results indicate that both food and foraging microsites are limited but the relegation of subdominant species to lesspreferred microhabitats by the large Dipodomys spectabilis is the major factor underlying the spatial organization of this community. Results also demonstrate that strong interactions among species increase the probability that pathways of indirect interactions through intermediary species are important; these complex linkages may include species that overlap little in food preferences.     

Acoustic variation of pant hoot calls by male chimpanzees: a playback experiment

Pant hoots, a type of long-distance calls of chimpanzees (Pan troglodytes), were played back to two male chimpanzees in a group of seven captive individuals to determine if chimpanzees would modify those vocalizations in response to strange males. Subjects emitted pant hoots with higher rates of delivery, shorter duration of buildup, and lower minimum fundamental frequency of climax when they were presented with pant hoots of strangers than when they produced the calls spontaneously. Considering the direction of acoustical change, we concluded that the rate of delivery, duration of buildup, and minimum frequency of climax might be associated with the underlying emotional states of the callers rather than call matching. Individual difference between two subject males was significant in minimum frequency and duration of climax and in average frequency of call, which appears to reflect differences of the caller's age and social status. These results suggest that different acoustic variables relate to within- and interindividual differences of these vocalizations. Received: March 7, 2000 / Accepted: May 8, 2000     

Female influences on pair formation, reproduction and male stress responses in a monogamous cavy (Galea monasteriensis)

We examined the possible existence of, and female contributions to, pair bonds, as well as the relation of social preference to mating selectivity, in a recently identified wild guinea pig, the Muenster yellow-toothed cavy (Galea monasteriensis). In Experiment 1, females housed for approximately 20 days in an apparatus in which they could choose to approach and interact with unfamiliar males typically exhibited a robust preference for one of two available males. DNA fingerprinting revealed a strong association between female choice and paternity. Experiment 2 examined the influence of the removal and return of the female on male plasma cortisol levels and behavior in established breeding pairs. A 2-h period of separation in the home enclosure elevated male cortisol levels. Return of the female to the home enclosure reduced male cortisol levels 2 h later, whereas continued separation did not. Reunion in either the home or novel enclosure increased socio-positive and courtship/sexual behavior, as well as time spent in proximity of the partner. Together, these results provide evidence for a substantial female influence on pair bond formation and maintenance in G. monasteriensis and further support for the existence of social and sexual monogamy in this species.     

Fragrances, male display and mating behaviour of Euglossa hemichlora: a flight cage experiment

Abstract. Male euglossine bees (Apidae: Euglossini) collect volatile substances (fragrances) from floral and nonfloral sources and store them in hair‐filled cavities in their hind tibiae. Over time, males accumulate large quantities of complex and species‐specific blends of fragrances. Various hypotheses have been put forward to explain this behaviour, including the idea that fragrance stores reflect the genetic quality of individual males and have evolved through sexual selection and female choice. Clear support of this hypothesis is lacking, largely because male–female interactions are both rare and difficult to observe in nature. Here, we report a flight cage experiment performed in Panama that permitted mating between virgin females (raised from brood cells) and males captured in the forest at fragrance baits. In the cage, eight individually marked males defended small territories around vertical perch sites and showed a characteristic display, which included a previously unreported ‘leg‐crossing’ movement, possibly related to fragrance release. A total of six copulations and three copulatory attempts by Euglossa hemichlora were observed and partly recorded on video. The copulations, all of which were initiated by the female landing on a male perch, were short (4–10 s) and showed no signs of the transfer of chemical substances from male to female. In some cases, the male hovered directly over the female before descending to mount her, possibly facilitating fragrance evaluation by the female. After the experiment, the contents of the males' hind legs were analysed by gas chromatography‐mass spectroscopy, which detected complex mixtures of terpenoids and aromatics (totalling 70 different compounds) dominated by hexahydrofarnesyl acetone, farnesene epoxide, ocimene and p‐dimethoxy benzene. Individual total amounts of fragrances were neither related to display activity or perch occupancy by given males, nor to the frequency of matings achieved. Display activity was the only positive correlate of mating frequency. Generally, individuals had uniformly large amounts of stored fragrances in comparison to a previous study of three other species of Panamanian Euglossa.     

Time spent close to a sexual partner as a measure of female mate preference in a sex-role-reversed population of the blenny<Emphasis Type="Italic"> Salaria pavo</Emphasis> (Risso) (Pisces: Blenniidae)

In most species females do not exhibit conspicuous sexual behaviours and female mate preferences are often measured by means of the time spent close to males. In spite of its widespread use, in only a few studies has this measure been validated as a reliable indicator of female mate preference. Sex-role-reversed species offer a better opportunity to test female preferences, as females usually court males. We tested in a sex-role-reversed population of the blenny Salaria pavo (Risso) if the time spent by females close to males related to the number of courtship displays directed towards males, and whether these measures of female preference reliably predicted matings. Females were simultaneously presented with two males behind a glass partition and the time spent close to each male was measured. We then allowed females to have access to the males' compartments and measured the courtship behaviours performed by females towards each male and recorded with which of the males females spawned. Females spent more time close to the male that subsequently received more courtship displays, and the preferred male had a more developed head crest. However, both measures of female preference failed to predict matings. Females were often attacked by males and probably had, in some occasions, to spawn with the less preferred male. Females that spawned with the previously preferred male had more swollen bellies than females that spawned with the less preferred male, suggesting a male preference towards more ripe females. These results validate the use of "time spent close to a sexual partner" as a measure of female preference in S. pavo. We argue that matings may not always reliably indicate mate preferences, particularly in the less choosy sex.Communicated by R. Serrão Santos     

Social organization and food resources availability in primates: a socio-bioenergetic analysis of diet and disease hypotheses.

Data obtained during a field study of two species of nonhuman primates (Alouatta villosa and Ateles geoffroyi) living in the Tikal National Park in Guatemala are used to suggest an answer to the question: To what extent is the existence of a particular form of social organization (group size, structure, and composition) an indication of the amount of energy in the form of food resources available to animals in a particular habitat? Seven researchers working in teams spent 2,318 hours in the field, 1,145 hours of which were in contact with the monkeys. Comparisons of dietary data, estimated energy expenditures, and habitat productivity provide indications of the degree to which a habitat is capable of supporting the energy and other nutritional requirements of howler and spider monkeys living within the study area. These data suggest that much larger populations and different forms of social organizations can be supported by resources available within the habitat.     

Male and female preference for conspecifics in a fish with male parental care (Percidae: Catonotus)

Speciation by sexual selection is commonly modeled as the divergent co-evolution of male signals and female preferences in geographically isolated populations. Upon secondary contact, females fail to recognize divergent males as suitable mates and exhibit a strong preference for their own type. The result is behavioral isolation and, if behavioral isolation is strong enough, there is an absence of gene flow between two species. Growing evidence of both mutual and male choice challenges the conventional role of females as primary regulators of species boundaries; however, to date, few studies have explicitly compared males and females for conspecific preference. The relative contribution of the two sexes to species boundaries therefore remains poorly understood. We examined the strength of preference for conspecifics in both males and females using two closely related species of darters. Males in these species exhibit substantial parental investment; therefore, we hypothesized that selection for male choosiness would result in male preference for conspecifics comparable to females’. Results show that females exhibited strong and significant preference for conspecific males; whereas, male preference for conspecific females was highly variable. Some males showed a strong preference for conspecifics while others preferred heterospecifics or showed no preference, resulting in a non-significant mean preference for conspecifics. Therefore, despite considerable parental investment by males in this system, our results suggest females play a larger role in regulating species boundaries.     

Different nest predator faunas and nest predation risk on ground and shrub nests at forest ecotones: an experiment and a review

This study examined predator faunas of artificial ground and shrub nests and whether nest predation risk was influenced by nest site, proximity to forest edge, and habitat structure in 38 grassland plots in south-central Sweden. There was a clear separation of predator faunas between shrub and ground nests as identified from marks in plasticine eggs. Corvids accounted for almost all predation on shrub nests whereas mammals mainly depredated ground nests. Nest predation risk was significantly greater for shrub than for ground nests at all distances (i.e. 0, 15 and 30 m) from the forest edge. However, nest predation risk was not significantly related to distance to forest edge, but significantly increased with decreasing distance to the nearest tree. Different corvid species robbed nests at different distances from the forest edge, with jays robbing nests closest to edges. We conclude that the relationship between the predation risk of grassland bird nests and distance to the forest edge mainly depends on the relative importance of different nest predator species and on the structure of the forest edge zone. A review of published articles on artificial shrub and ground nest predation in the temperate zone corroborated the results of our own study, namely that shrub nests experienced higher rates of depredation in open habitats close to the forest edge and that avian predators predominantly robbed shrub nests. Furthermore, the review results showed that predation rates on nests in general are highest <50 m inside the forest and lower in open as well as forest interior habitats (≥50 m from the edge). Received: 16 March 1998 / Accepted: 30 July 1998     

Oviposition Deterrence Is Likely an Effect,Not a Mechanism,in the Leaf Beetle <Emphasis Type="Italic">Chrysophtharta bimaculata</Emphasis> (Olivier) (Coleoptera: Chrysomelidae)

Oviposition deterrence is common in many insects as an evolutionary mechanism to reduce subsequent larval competition. We investigated a suspected case of oviposition deterrence by the paropsine chrysomelid, Chrysophtharta bimaculata. In paired choice tests, gravid females were found to prefer ovipositing on host leaves without conspecific eggs, confirming the presence of an apparent oviposition deterrence mechanism. Washing egg batches in water, hexane, or ethanol did not change this preference, suggesting that a soluble marking pheromone was not involved. Furthermore, it is unlikely that a plant-derived oviposition deterring substance is produced as beetles showed no significant oviposition preference between leaves which had been oviposited upon, but then had the eggs removed, and those that had never been oviposited upon. In trials using artificial leaves and mimic egg batches, “leaves” with “egg batches” placed near the tip of the leaf (the preferred site of oviposition in this species) were significantly less likely to be laid upon than artificial leaves where mimic eggs were placed away from the tip. In combination, the results strongly infer that oviposition deterrence in C. bimaculata is due to the mechanical blocking of the oviposition site by the first laid egg-batch, rather than a specific oviposition deterring cue. The apparent oviposition deterrence in this insect may well be an outcome or evolutionary effect of oviposition-site selection, rather than a clear adaptive mechanism to decrease larval competition.