Dispersal activities of the sibling species Drosophila melanogaster and Drosophila simulans

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.

Non-independence of individuals in a population of Drosophila melanogaster: effects on spatial distribution and dispersal

We used a simple quadrat analysis to globally categorise the spatial distribution of Drosophila melanogaster individuals. Individuals were spatially aggregated and this was not only due to sexual attraction. This aggregation seemed to be maintained during dispersal, hence explaining the great variability of this behaviour observed in our work and by other authors. Thus, individuals are expected to arrive as small groups into a new patch. This may induce costs through competition and benefits by ensuring the presence of reproductive mates and/or if there is a phenomenon of local resource enhancement by the presence of conspecifics, hence influencing the evolution of dispersal.

Inter- and intrapopulational variation in digging in Drosophila melanagaster larvae

The digging behavior of larvae from the following strains of Drosophila melanogaster was studied: Oregon R-c, taxi, yellow, and vestigial. It was found that the time of stay of preadults in the culture medium, the number of larvae, and the illumination conditions can modify this behavior. The presence of this characteristic depends on the genetic composition of the population: the larvae of each strain used exhibited their own particular pattern of dispersal throughout the culture medium, independent of the experimental conditions under which this behavior was surveyed.

Phototactic responses along a gradient of light intensities for the sibling species Drosophila melanogaster and Drosophila simulans

The phototactic responses of four recently collected isofemale strains of Drosophila melanogaster and Drosophila simulans were measured in a light gradient from 590 to 10 lux. High light intensities were preferred by most flies, but a small proportion of flies preferred the lowest light intensity. Based on the strains tested, D. simulans showed greater phototaxis than D. melanogaster, and within each species variability was found. The niche breadth of D. melanogaster appears likely to be greater than that of D. simulans for phototaxis in the light gradient. These results are in general qualitative agreement with earlier results published on dispersal activities from the same populations.