Temperature-driven color lightness and body size variation scale to local assemblages of European Odonata but are modified by propensity for dispersal

Abstract

Previous macrophysiological studies suggested that temperature-driven color lightness and body size variations strongly influence biogeographical patterns in ectotherms. However, these trait-environment relationships scale to local assemblages and the extent to which they can be modified by dispersal remains largely unexplored. We test whether the predictions of the thermal melanism hypothesis and the Bergmann's rule hold for local assemblages. We also assess whether these trait-environment relationships are more important for species adapted to less stable (lentic) habitats, due to their greater dispersal propensity compared to those adapted to stable (lotic) habitats.We quantified the color lightness and body volume of 99 European dragon- and damselflies (Odonata) and combined these trait information with survey data for 518 local assemblages across Europe. Based on this continent-wide yet spatially explicit dataset, we tested for effects temperature and precipitation on the color lightness and body volume of local assemblages and assessed differences in their relative importance and strength between lentic and lotic assemblages, while accounting for spatial and phylogenetic autocorrelation.The color lightness of assemblages of odonates increased, and body size decreased with increasing temperature. Trait-environment relationships in the average and phylogenetic predicted component were equally important for assemblages of both habitat types but were stronger in lentic assemblages when accounting for phylogenetic autocorrelation.Our results show that the mechanism underlying color lightness and body size variations scale to local assemblages, indicating their general importance. These mechanisms were of equal evolutionary significance for lentic and lotic species, but higher dispersal ability seems to enable lentic species to cope better with historical climatic changes. The documented differences between lentic and lotic assemblages also highlight the importance of integrating interactions of thermal adaptations with proxies of the dispersal ability of species into trait-based models, for improving our understanding of climate-driven biological responses.

Keywords: Bergmann's rule; Odonata; dispersal; freshwater insects; habitat–stability–dispersal hypothesis; local assemblages; macrophysiology; thermal adaptation; thermal melanism hypothesis.

FIGURE 1

Distribution of (lentic = 337, lotic = 181) assemblages odonates across Europe. Lentic assemblages are indicated with red circles, lotic assemblages with blue circles, and the main European rivers in gray. The black outlines are country boundaries in the study region. The proportion of lotic habitats is higher in southern and central Europe. The space inside each circle represents the area for which the climate data were aggregated (a radius of ~1 km around the location of each community)

FIGURE 2

Scatterplots of the average (a, b), species‐specific (c, d), and phylogenetic (e, f) components of the average color lightness and body volume of (all habitats = 518, lentic = 337, lotic = 181) assemblages of European odonates and z‐standardized annual mean temperature, and annual precipitation. The color of the dots indicates the habitat type of the assemblages. Lines indicate regression lines of ordinary least‐squares models. The color lightness ranges from 0 (absolute black) to 255 (pure white). The P‐component represents the phylogenetically predicted part of the trait, and S‐component represents the respective deviation of the average trait from the P‐component