Abstract
Wild bees in natural conditions can develop under various environmental stressors. Heavy metal pollution of the environment is one of the most widely studied stressors in insects, yet its effect is poorly described in bees. We have measured how pollution of the environment along a zinc, cadmium and lead contamination gradient in Poland affects bee development, using red mason bees (Osmia bicornis) as a model and their forewing asymmetry measures to assess possible developmental instabilities. We have also described wing asymmetry measures in the red mason bee—an important managed pollinator species—for the first time. The development of bee larvae in a contaminated environment did not affect forewing asymmetry measures, but it did lead to a negative correlation of wing size with contamination in females. Bees also showed a clear change in their asymmetry measures between various seasons, suggesting other, unknown environmental factors affecting wing asymmetry more than pollution. Sexes were found to have different forewing shape and size, larger females having larger forewings than the smaller males. The direction of size asymmetry was in favour of the left side in both sexes and also shape differences between the left and right wings showed similar tendencies in males and females. The levels of forewing shape and size asymmetry were smaller in females, making them the more symmetrical sex.
Highlights
This correlation was not confirmed in many species and traits, asymmetry cannot be treated as a direct measure of developmental instability (Palmer and Strobeck 2003)
Wing venation length asymmetry did not show any correlation to pollution, but some differences were detected between years, namely one vein in females and one vein in males had different lengths in various years (Table 4)
Wing size was found to be significantly and positively correlated to body size, which is in agreement with the changes in body mass of females reported by Moroń et al (2014)
Summary
Randomly appearing and normally distributed (appearing on both sides) small deviations from perfect symmetry, called fluctuating asymmetry (FA), can be observed, and is suggested that these arise due to developmental instability and random environmental effects on the developing organism (Mather 1953; van Valen 1962; Palmer and Strobeck 1992; Palmer 1994). It is often assumed that more pronounced developmental instability is causing greater degrees of asymmetry in the organism. This correlation was not confirmed in many species and traits, asymmetry cannot be treated as a direct measure of developmental instability (Palmer and Strobeck 2003). Analysis of wing asymmetry is being tested as a possible tool to assess the level of developmental instability caused by various stressors like inbreeding (Brückner 1976), hybridization (Smith et al 1997) or starvation (Szentgyörgyi et al 2016) with varying results
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