Comparative analysis of overwintering physiology in nine species of semi‐aquatic bugs (Heteroptera: Gerromorpha)

Abstract

In semi‐aquatic bugs (Heteroptera: Gerromorpha), the strategies of overwintering in a cryothermic state (i.e. at body temperatures below the equilibrium freezing point) remain largely unexplored. The present study provides an analysis of the ecophysiological aspects of overwintering in nine gerromorphan species. All nine species avoid ice formation by means of a more or less extensive supercooling of their body fluids. There is a tight correlation between the supercooling point (SCP) and the lower lethal temperature. Different species use different physiological adjustments to increase the likelihood of survival in a supercooled state. These include stabilization of the supercooled state by active antifreeze factors that cause thermal hysteresis between equilibrium melting and freezing points, the accumulation of low‐molecular weight sugars and polyols with putative cryoprotective functions, or by having a relatively high body fluid osmolality, combined with a low level of hydration. The majority of species under study overwinter only as adults, whereas Velia caprai Tamanini can overwinter either as an adult or in the egg stage. The supercooling capacity of V. caprai adults is insufficient to prevent the risk of lethal freezing. The adults therefore survive only opportunistically in suitable microhabitats, and/or during mild winters. The survival of V. caprai in winter is assured by extensive supercooling and having overwintering eggs that are highly cold tolerant.

Differences in prey capture in semiaquatic bugs (Heteroptera:Gerromorpha)

“…The significant differences between promptness and efficiency of prey capture in gerrids and veliids can be explained at least in part in relation to their adaptations to different habitats. The behavior, life cycle and dispersal pattern of V. caprai make this species highly adapted to changing environmental conditions (Ditrich & Papáček 2009a,b; Ditrich & Koštál ). Both investigated Velia species colonize small forest streams, whereas the gerrid species used in our experiments are found mainly in lentic habitats.…”

Exploring the plastic response to cold acclimation through metabolomics

“…This carbohydrate cryoprotectant is also known to accumulate in various overwintering insects (e.g. Baust & Edwards 1979; Ditrich & Koštál 2011). While our data, together with earlier studies, support a growing consensus regarding the implication of sugars in the cold tolerance of D. melanogaster , it is also conceivable that differential rate of ingestion/digestion during acclimation might affect sugar levels.…”

The role of ecology, neutral processes and antagonistic coevolution in an apparent sexual arms race

“…Season length: mean number of frost‐free days annually; associated with larger bodies in Aquarius remigis water striders (Blanckenhorn & Fairbairn ). Winter severity: mean number of days annually in which temperature <−10 °C, close to the lower lethal limit of −15 °C (Ditrich & Koštál ; <−15 °C data unavailable); winter mortality is severe in water striders (Fairbairn ). Snow protection from winter cold: mean depth of snow, December to February; protects overwintering adults against cold (Ditrich & Koštál ).…”

“…Winter severity: mean number of days annually in which temperature <−10 °C, close to the lower lethal limit of −15 °C (Ditrich & Koštál ; <−15 °C data unavailable); winter mortality is severe in water striders (Fairbairn ). Snow protection from winter cold: mean depth of snow, December to February; protects overwintering adults against cold (Ditrich & Koštál ). Emergent vegetation index: from 0 to 5 (0, none; 1, 0–20%; 2, 21–40%; 3, 41–60%; 4: 61–80%; 5: 81–100%); associated with Gerris spp.…”