Prior mating experience modulates the dispersal of Drosophila in males more than in females

The relationship between morphology and flight in Drosophila: a study of two pairs of sibling species from a natural population

Insect flight is a complex trait involved in different behaviors, from the search for sexual partners, food, or breeding sites. Many studies have postulated the adaptive advantages of certain morphological traits in relation to increased flight capacity, such as low values of wing loading or high values of wing:thorax ratio and wing-aspect ratio. However, few studies have evaluated the relationship between variables related to flight and morphological traits in Drosophila. This work aimed to study morphological traits in males and females of two pairs of sibling species: Drosophila buzzatii Patterson and Wheeler-Drosophila koeferae Fontdevila and Wasserman, and Drosophila melanogaster Meigen-Drosophila simulans Sturtevant, and to analyze its relationship with flight. We detected the highest proportion of flight time in D. koepferae and D. simulans compared to D. buzzatii and D. melanogaster, respectively. Our results also revealed sexual dimorphism, with males exhibiting a higher proportion of flight time than females. Surprisingly, we did not find a general pattern to explain the relationship between morphology and the proportion of flight time because associations varied depending upon the analyses (considering all groups together or each sex-species combination separately). Moreover, these associations explained a low percentage of variation, suggesting that other nonmorphological components related to flight, such as physiological variables, should be taken into account. This work allowed us to show the variability and complexity of an aspect of flight, suggesting that the adaptive role of the morphological traits studied might have been overestimated.

Scared of the dark? Phototaxis as behavioural immunity in a host-parasite system

Behavioural immunity describes suites of behaviours hosts use to minimize the risks of infection by parasites/pathogens. Research has focused primarily on the evasion and physical removal of infectious stages, as well as behavioural fever. However, other behaviours affect infection risk while carrying ecologically significant trade-offs. Phototaxis, in particular, has host fitness implications (e.g. altering feeding and thermoregulation) that also impact infection outcomes. In this study, we hypothesized that a fly host, Drosophila nigrospiracula, employs phototaxis as a form of behavioural immunity to reduce the risk of infection. First, we determined that the risk of infection is lower for flies exposed in the light relative to the dark using micro-arena experiments. Because Drosophila vary in ectoparasite resistance based on mating status we examined parasite-mediated phototaxis in mated and unmated females. We found that female flies spent more time in the light side of phototaxis chambers when mites were present than in the absence of mites. Mating marginally decreased female photophobia independently of mite exposure. Female flies moved to lighter, i.e. less infectious, environments when threatened with mites, suggesting phototaxis is a mechanism of behavioural immunity. We discuss how parasite-mediated phototaxis potentially trades-off with host nutrition and thermoregulation.

Oxygen Dependence of Flight Performance in Ageing Drosophila melanogaster

Similar to humans, insects lose their physical and physiological capacities with age, which makes them a convenient study system for human ageing. Although insects have an efficient oxygen-transport system, we know little about how their flight capacity changes with age and environmental oxygen conditions. We measured two types of locomotor performance in ageing Drosophila melanogaster flies: the frequency of wing beats and the capacity to climb vertical surfaces. Flight performance was measured under normoxia and hypoxia. As anticipated, ageing flies showed systematic deterioration of climbing performance, and low oxygen impeded flight performance. Against predictions, flight performance did not deteriorate with age, and younger and older flies showed similar levels of tolerance to low oxygen during flight. We suggest that among different insect locomotory activities, flight performance deteriorates slowly with age, which is surprising, given that insect flight is one of the most energy-demanding activities in animals. Apparently, the superior capacity of insects to rapidly deliver oxygen to flight muscles remains little altered by ageing, but we showed that insects can become oxygen limited in habitats with a poor oxygen supply (e.g., those at high elevations) during highly oxygen-demanding activities such as flight.

Diurnal and Seasonal Activity Patterns of Drosophilid Species (Diptera: Drosophilidae) Present in Blackberry Agroecosystems With a Focus on Spotted-Wing Drosophila

Drosophilid species with different life histories have been shown to exhibit similar behavioral patterns related to locating and utilizing resources such as hosts, mates, and food sources. Drosophila suzukii (Matsumura) is an invasive species that differs from other frugivorous drosophilids in that females lay eggs in ripe and ripening fruits instead of overripe or rotten fruits. We hypothesized that there may be diurnal and/or seasonal patterns associated with the movement of drosophilid species into and out of crop fields and their attraction to fermentation-odor-based monitoring traps, and that D. suzukii would conform to similar patterns. To test these hypotheses, we deployed passive, 2-headed Malaise traps between crop fields and wooded edges to simultaneously catch flies moving into and out of crop fields. We also deployed monitoring traps with a fermentation-based bait between crop fields and wooded edges and within crop rows. Traps were deployed weekly in June-August in 2014 and 2015 at two commercial blackberry farm in Cleveland County, NC, and were checked hourly for 24 h, except during darkness. Both D. suzukii and other drosophilid species moved between crop fields and wooded edges and were attracted to monitoring traps primarily during the morning and evening hours. Whereas other drosophilids were captured in traps throughout the season, few D. suzukii were caught in traps until early to mid-July in both years and increased as the season progressed. Understanding D. suzukii movement and activity patterns is essential for the development of effective management strategies.

A Review of the Phenotypic Traits Associated with Insect Dispersal Polymorphism, and Experimental Designs for Sorting out Resident and Disperser Phenotypes

Dispersal represents a key life-history trait with several implications for the fitness of organisms, population dynamics and resilience, local adaptation, meta-population dynamics, range shifting, and biological invasions. Plastic and evolutionary changes of dispersal traits have been intensively studied over the past decades in entomology, in particular in wing-dimorphic insects for which literature reviews are available. Importantly, dispersal polymorphism also exists in wing-monomorphic and wingless insects, and except for butterflies, fewer syntheses are available. In this perspective, by integrating the very latest research in the fast moving field of insect dispersal ecology, this review article provides an overview of our current knowledge of dispersal polymorphism in insects. In a first part, some of the most often used experimental methodologies for the separation of dispersers and residents in wing-monomorphic and wingless insects are presented. Then, the existing knowledge on the morphological and life-history trait differences between resident and disperser phenotypes is synthetized. In a last part, the effects of range expansion on dispersal traits and performance is examined, in particular for insects from range edges and invasion fronts. Finally, some research perspectives are proposed in the last part of the review.

Individual, but not population asymmetries, are modulated by social environment and genotype in Drosophila melanogaster

Theory predicts that social interactions can induce an alignment of behavioral asymmetries between individuals (i.e., population-level lateralization), but evidence for this effect is mixed. To understand how interaction with other individuals affects behavioral asymmetries, we systematically manipulated the social environment of Drosophila melanogaster, testing individual flies and dyads (female-male, female-female and male-male pairs). In these social contexts we measured individual and population asymmetries in individual behaviors (circling asymmetry, wing use) and dyadic behaviors (relative position and orientation between two flies) in five different genotypes. We reasoned that if coordination between individuals drives alignment of behavioral asymmetries, greater alignment at the population-level should be observed in social contexts compared to solitary individuals. We observed that the presence of other individuals influenced the behavior and position of flies but had unexpected effects on individual and population asymmetries: individual-level asymmetries were strong and modulated by the social context but population-level asymmetries were mild or absent. Moreover, the strength of individual-level asymmetries differed between strains, but this was not the case for population-level asymmetries. These findings suggest that the degree of social interaction found in Drosophila is insufficient to drive population-level behavioral asymmetries.

Does kin selection moderate sexual conflict in Drosophila?

Two recent studies provide provocative experimental findings about the potential influence of kin recognition and cooperation on the level of sexual conflict in Drosophila melanogaster. In both studies, male fruit flies apparently curbed their mate-harming behaviours in the presence of a few familiar or related males, suggesting some form of cooperation mediated by kin selection. In one study, the reduction in agonistic behaviour by brothers apparently rendered them vulnerable to dramatic loss of paternity share when competing with an unrelated male. If these results are robust and generalizable, fruit flies could be a major new focus for the experimental study of kin selection and social evolution. In our opinion, however, the restrictive conditions required for male cooperation to be adaptive in this species make it unlikely to evolve. We investigated these phenomena in two different populations of D. melanogaster using protocols very similar to those in the two previous studies. Our experiments show no evidence for a reduction in mate harm based upon either relatedness or familiarity between males, and no reduction in male reproductive success when two brothers are in the presence of an unfamiliar, unrelated, 'foreign' male. Thus, the reduction of sexual conflict owing to male cooperation does not appear to be a general feature of the species, at least under domestication, and these contrasting results call for further investigation: in new populations, in the field and in the laboratory populations in which these phenomena have been reported.

Mating experience and food deprivation modulate odor preference and dispersal in Drosophila melanogaster males

Rotting fruits offer all of the known resources required for the livelihood of Drosophila melanogaster Meigen (Diptera: Drosophilidae). During fruit fermentation, carbohydrates and proteins are decomposed to produce volatile alcohols and amines, respectively. It is hypothesized that D. melanogaster adults can detect these chemical cues at a distance to identify and locate the decaying fruits. In the present paper, we compared the olfactory responses and movement of male flies varying in mating status and nutritional state to methanol, ethanol, and ammonia sources using a glass Y-tube olfactometer. In general, ethanol vapor at low to moderate concentrations repelled more hungry mated males than satiated ones. In contrast, methanol showed little difference in the attractiveness to males at different nutritional states and mating status. Moreover, ammonia attracted more hungry mated males. The attractiveness increased almost linearly with ammonia concentration from lowest to highest. When ammonia and artificial diet were put together in the odor arm, the responses of male flies to mixed odor mimicked the response to ammonia. Furthermore, odorant concentration, mating status, and nutritional state affected the flies' dispersal. Mated and starved males dispersed at a higher rate than virgin and satiated ones. Thus, our results showed that starved, mated males increased dispersal and preferred ammonia that originated from protein.

Genetics and evolution of function-valued traits: understanding environmentally responsive phenotypes

Many central questions in ecology and evolutionary biology require characterizing phenotypes that change with time and environmental conditions. Such traits are inherently functions, and new 'function-valued' methods use the order, spacing, and functional nature of the data typically ignored by traditional univariate and multivariate analyses. These rapidly developing methods account for the continuous change in traits of interest in response to other variables, and are superior to traditional summary-based analyses for growth trajectories, morphological shapes, and environmentally sensitive phenotypes. Here, we explain how function-valued methods make flexible use of data and lead to new biological insights. These approaches frequently offer enhanced statistical power, a natural basis of interpretation, and are applicable to many existing data sets. We also illustrate applications of function-valued methods to address ecological, evolutionary, and behavioral hypotheses, and highlight future directions.

Lipid profiles as indicators of functional senescence in the medfly

Changes associated with the age-related decline of physiological functions, and their relation with mortality rates, are thoroughly being investigated in the aging research field. We used the Mediterranean fruit fly Ceratitis capitata, largely studied by biodemographers, as a model for functional senescence studies. The aim of our work was to find novel combinatorial indicators able to reflect the functional state of adult insects, regardless of chronological age. We studied the profiles of neutral and polar lipids of head, thorax and abdomen of standard populations kept at 23 °C, at different ages. Lipid classes were separated by thin layer chromatography, and the quantitative values were used to find patterns of change using a multivariate principal component analysis approach. The lipid-dependent principal components obtained correlated with age, and differences between sexes were consistent with differences in the shape of the survival curves and the mortality parameters. These same components were able to discriminate populations with a behavioral decline due to a mild 28 °C thermal stress. Thus, young populations at 28 °C showed similar lipid profiles than old populations at 23 °C. The results indicated that the lipid-dependent components reflect the functional state of the flies, and so were named functional state components (FSCs). It is proposed that FSCs may be used as functional senescence indicators.