Body and wing size, but not wing shape, vary along a large-scale latitudinal gradient in a damselfly

David Outomuro,Maria J Golab,Szymon Sniegula,Frank Johansson

doi:10.1038/s41598-021-97829-9

Abstract

Large-scale latitudinal studies that include both north and south edge populations and address sex differences are needed to understand how selection has shaped trait variation. We quantified the variation of flight-related morphological traits (body size, wing size, ratio between wing size and body size, and wing shape) along the whole latitudinal distribution of the damselfly Lestes sponsa, spanning over 2700 km. We tested predictions of geographic variation in the flight-related traits as a signature of: (1) stronger natural selection to improve dispersal in males and females at edge populations; (2) stronger sexual selection to improve reproduction (fecundity in females and sexual behaviors in males) at edge populations. We found that body size and wing size showed a U-shaped latitudinal pattern, while wing ratio showed the inverse shape. However, wing shape varied very little along the latitudinal gradient. We also detected sex-differences in the latitudinal patterns of variation. We discuss how latitudinal differences in natural and sexual selection regimes can lead to the observed quadratic patterns of variation in body and wing morphology via direct or indirect selection. We also discuss the lack of latitudinal variation in wing shape, possibly due to aerodynamic constraints.

Highlights

Large-scale latitudinal studies that include both north and south edge populations and address sex differences are needed to understand how selection has shaped trait variation
Males of L. sponsa show a mating system known as scramble competition, where males do not defend territories but actively search for females, can engage aggressively towards other males, and in the absence of available females will try to disrupt mating pairs[38]. Males of this species mate more intensively and invest more in armaments related to sexual selection at northern edge populations than in core or southern edge populations, presumably due to constraints imposed by short mating seasons[13,39]
We predicted that edge populations would differ in flight-related traits compared to core populations and that they should show trait values favoring dispersal ability and reproductive investment[7,8,13]

Summary

Introduction

We quantified the variation of flight-related morphological traits (body size, wing size, ratio between wing size and body size, and wing shape) along the whole latitudinal distribution of the damselfly Lestes sponsa, spanning over 2700 km. The flight-related traits should better reflect dispersal ability at the edge p opulations[26], and we predicted, for both sexes, larger body and wing size, larger wing ratio, and longer and narrower wing shapes at the northern and southern edges[40,42,43,44,45,46,47]. At edge populations males would show intermediate body sizes and short and broad forewings, favoring scrambling b ehavior[32,38]

Methods

Results

Conclusion