Drosophilid species (Insecta, Diptera) in the Brazilian savanna are more symmetric in the dry season

Luciana Costa Nascimento,Rosana Tidon,Francisco Das Chagas Roque Machado

doi:10.17648/heringeriana.v15i1.917941

Abstract

The development of an organism is a controlled process, which can be disrupted by genetic or environmental stress. Although fluctuating asymmetry is widely used as an indicator of developmental instability, its effectiveness has been questioned due to the contradictory results produced by this technique which, at least in part, probably reflects methodological inappropriateness. Here, we investigated if wing asymmetry of drosophilids increases when they develop during the dry season in the Brazilian savanna, considered a stressful season for these insects. Using protocols designed to avoid methodological problems, we analysed the wings of Zaprionus indianus and three species of the genus Drosophila (D. mercatorum, D. simulans, and D. sturtevanti). Surprisingly, the flies were more asymmetrical in the rainy season than in the dry season, although this difference was not always significant. It is suggested that the wings of these insects are submitted to strong natural selection throughout the dry season, when the asymmetric individuals would have less chance of surviving. During the wet season, on the other hand, selective pressures would be more relaxed. Therefore, the results of this study suggest that asymmetry of the wings is not a good indicator of natural environmental stress in drosophilids. Future research should focus on selectively neutral characters.

Highlights

Developmental instability can be described as the predisposition of a developmental system to produce a morphological change in response to random perturbations (Dongen 2006, Klingenberg 2019)
The indexes and asymmetry type for each species in the two seasons are shown in Table 1, where the R and L represent respectively right and left directional asymmetry, and indices without superscript represent fluctuating asymmetry
The visual inspection of the graphs suggests that the wing traits tend to be more asymmetrical in the rainy season (Figure 3), Bonferroni t-tests did not reveal any consistent difference in Fluctuating asymmetry (FA) levels between the seasons

Summary

Introduction

Developmental instability can be described as the predisposition of a developmental system to produce a morphological change in response to random perturbations (Dongen 2006, Klingenberg 2019) Environmental stresses, such as extreme temperatures or shortage of resources, can disrupt the developmental process, increasing developmental instability and altering the morphology of the adult (Markow 1995, Moller & Swaddle 1997). Fluctuating asymmetry (FA) has been widely used as a method to measure developmental instability (Moller & Swaddle 1997, Benítez & Parra 2011, Beasley et al 2013, Klingenberg 2015). Any differences between sides must be the result of errors during development (Clarke 1995, Hosken et al 2000)

Methods

Results

Discussion

Conclusion