Takeoff temperatures in Melitaea cinxia butterflies from latitudinal and elevational range limits: a potential adaptation to solar irradiance

Abstract

1. This study provides evidence that a heliophilic butterfly, the Glanville fritillary (Melitaea cinxia) has adapted differently to environmental variation across latitudes and elevations.2. In cool air, basking M. cinxia orient themselves perpendicular to the sun's rays to gain heat and take off. During flight, solar heating is reduced because orientation perpendicular to the sun is no longer possible and convective cooling occurs. Consequently, M. cinxia have been shown to suffer net heat loss in flight, even in full sunshine. When flight duration is restricted in this way, the takeoff temperature becomes an important thermal adaptation.3. Using a thermal imaging camera, takeoff temperatures were measured in experimental butterflies. Butterflies from the northern range limit in Finland took flight at slightly hotter temperatures than butterflies from the southern limit in Spain, and much hotter than butterflies from the elevational limit (1900-2300 m) in the French Alps. Butterflies from low-elevation populations in southern France also took off much hotter than did the nearby Alpine population.4. These results suggest that the influence of elevation is different from that of latitude in more respects than ambient temperature. Values of solar irradiance in the butterflies' flight season in each region show that insects from the coolest habitats, Finland and the Alps, experienced similar solar irradiance during basking, but that Finns experienced much lower irradiance in flight. This difference may have favored Finnish butterflies evolving higher takeoff temperatures than Alpine butterflies that also flew in cool air but benefited from more intense radiant energy after takeoff.

Cold adaptation across the elevation gradient in an alpine butterfly species complex

“…In contrast to our initial hypothesis, thoracic take-off temperature was not significantly different across species and increased with elevation but only for females. High-elevation butterflies tend to warm up more rapidly and to take off at higher temperatures than low-elevation ones, in contrast with the results obtained by Advani et al (2019) on Melitea cinxia. The ability to warm up quickly could be advantageous at high elevation, where the length of the favourable period for flight is reduced.…”

“…The ability to warm up quickly could be advantageous at high elevation, where the length of the favourable period for flight is reduced. Indeed, not only is the length of the reproductive period reduced at high elevation, but the duration of each flight bout is also more often compromised by clouds and/or wind (Cormont et al, 2011) and heat loss (Advani et al, 2019). In this context, being able to warm up rapidly, as soon as solar radiation increases, might be a prerequisite for butterfly survival at high elevation, as observed in the Lapland butterflies Colias nastes and C. hecla (Majerus, 1998, p. 160).…”

“…E-mail: gabriel.neve@imbe.fr to fly in cold conditions in high-elevation populations (within species), ultimately leading to distinct, specialised alpine species. Under this hypothesis, thermal requirements for flight are expected to be lower at high, than at low, elevation (Advani et al, 2019) and for alpine species compared to low-elevation species (Kingsolver, 1983).…”

Nocturnal dispersal flight of crickets: Behavioural and physiological responses to cool environmental temperatures

“…In contrast to daytime environmental conditions, the cool air and lack of solar radiation at night represent a challenge to dispersal of ectotherms, particularly flying insects that must pre-warm their flight muscles in order to take flight. In temperate latitudes, nighttime temperatures are commonly below the typical lower body temperature threshold of about 30°C required for flight in many insects, even in summer (Advani et al, 2019;Heinrich, 1987;Watt, 1968). By combining laboratory and field studies, we have identified aspects of cricket physiology and behaviour that serve to meet the challenge presented by the nocturnal thermal environment.…”

“…Insects are the only ectothermic animals to have evolved powered flight. Body temperature thresholds for insect flight initiation vary among populations and species, but are relatively high and typically above 30°C (Advani, Parmesan, & Singer, 2019;De Araujo, Karsten, & Terblanche, 2019;Heinrich & Casey, 1973;Keena, 2018;Kingsolver & Watt, 1983;Martini, Rivera, Hoyte, Setamou, & Stelinski, 2018;Neve & Hall, 2016;Watt, 1968).…”