Climatic factors shape plastic trade‐offs in the polyphenic black scavenger fly Sepsis thoracica (Diptera: Sepsidae)

Abstract

Aim Trade‐offs allow individuals to optimize their fitness by tailoring the investment into different traits to variable environmental conditions, such as along geographical gradients. Trade‐offs thus can help in adjusting to changing thermal and insolation profiles, especially in small ectotherms, whose body temperature typically follows environmental temperatures closely. Two traits usually involved in latitudinal adaptation are body size and melanism. Since both traits are costly, individuals need to optimize investment into each trait. Here, we studied how environmental factors influence this trade‐off in the short and long‐term. Location Europe. Methods We raised flies from 15 latitudinal populations at three constant temperatures in a laboratory common garden to differentiate plastic and evolutionary responses to temperature. We further analysed how the different insolation components of the populations’ habitats influenced the evolution of the trade‐off. Results Male Sepsis thoracica (Diptera: Sepsidae) feature a sigmoid relationship between melanism and body size, defining two strikingly different male morphs: obsidian (small and black) and amber (large and orange). This relationship was altered by the developmental temperature, documenting its plasticity. The relationship further evolved across populations in response to the environmental characteristics of their habitat, notably temperature, insolation and UV radiation, suggesting that plasticity also has an underlying genetic basis. Nevertheless, melanism, but not body size, merely slightly increased with latitude. Main conclusions As the plastic and evolutionary responses of the relationship to temperature differed, plasticity does not necessarily follow the direction of evolution of this trade‐off, but rather adds to it. Our study evinces the role of several environmental factors in shaping the evolution of a plastic melanism—body size relationship defining a rare male polymorphism in temperate sepsid flies.

Sexual size dimorphism is associated with reproductive life history trait differentiation in coexisting sepsid flies

“…As we primarily studied species from north-central Switzerland, latitudinal variation was not an issue here. However, we have previously examined intraspecific latitudinal (and altitudinal) variation across Europe (and North America) of some of these species, and generally found merely minor differentiation (Blanckenhorn 1997;Berger et al 2013;Puniamoorthy et al 2012a,b;Rohner et al 2016;Giesen et al 2017Giesen et al , 2019Busso and Blanckenhorn 2018a;Roy et al 2018). Clinal variation at least in egg size was somewhat more pronounced and in accordance with expectations (larger at higher latitude) in the much larger yellow dung fly (Bauerfeind et al 2018; but see Roy et al 2018 for contrary results for S. fulgens), however also not marked.…”

“…Traits characterizing male and female mating behavior furthermore align well along the slow-fast reproductive continuum (Table 2). The most abundant and relatively large species S. cynipsea, S. punctum and S. thoracica (Rohner et al 2015(Rohner et al , 2019Busso and Blanckenhorn 2018a; Fig. 1) feature clutch sizes of around 45 -60 large eggs (ca.…”

Reconciling ecogeographical rules: rainfall and temperature predict global colour variation in the largest bird radiation

“…; De Keyser et al . ; Busso & Blanckenhorn ). However, previous studies have not explicitly identified the antagonistic or reinforcing effects of different climatic variables.…”

“…Antagonistic climatic effects could provide a general explanation for a lack of agreement between studies. Trade-offs between different selective forces (which may or may not be summarised as ecogeographical rules) are not un-common, and have been used to explain, for example, departures from Bergmann's rule (Medina et al 2007;Guti errez-Pinto et al 2014;De Keyser et al 2015;Busso & Blanckenhorn 2018). However, previous studies have not explicitly identified the antagonistic or reinforcing effects of different climatic variables.…”

Experimental size- and sex-specific predation on dung flies by amphibian and arthropod predators

“…Blanckenhorn, 2007;Blanckenhorn et al, 2010; see http://sepsidnet-rmbr.nus.edu.sg/ for pictures). Sepsis thoracica is the most common sepsid fly around livestock dung in the Mediterranean parts of Europe, but is also frequent north of the Alps (Pont & Meier, 2002;Busso & Blanckenhorn, 2018b).…”