Cold resistance in two species of cave-dwelling beetles (Coleoptera: Cholevidae)

Supercooling points (SCPs), lower lethal temperatures (LLTs), and the effect of short-term exposures (1 min) to low temperatures were examined in the adults of two stenothermal leptodirin species, Neobathyscia mancinii and Neobathyscia pasai (Coleoptera, Cholevidae). Specimens were collected from two caves in the Venetian Prealps (NE-Italy). Inter-species comparison highlighted lower values of SCP in N. mancinii (-7.1+-0.9 °C) than in N. pasai (-6.4+-0.3 °C), with no significant intersexual differences in both species. N. pasai (LLT50+-SE= -16.96 +-2.30 °C; LLT100 -25.41 °C) tolerated short exposures to subzero temperatures better than N. mancinii (LLT50+-SE= -4.89 +-1.08 °C; LLT100 -11.72 °C). According to the mortality and cumulative proportion of individual freezing curves (CPIF), SCPs and LLT100, N. pasai may be defined as ‘‘strongly freeze tolerant’’, N. mancinii as ‘‘moderately freezing tolerant’’. Overall, these results may justify the different in-cave habitat selection showed by the two species (N. pasai was abundant close to the entrance where the temperature is variable whereas N. mancinii was confined to the internal part of the cave where the temperature is constant throughout the year), and suggest hypotheses on the effects of such habitat selection on freeze tolerance strategy adopted. Finally, they give new insights into possible responses to climate changes in cave dwelling species.