# Did Cold Resistance Influence the Success of the Halobiont Darkling Beetle Centorus rufipes (Coleoptera, Tenebrionidae) During the Pleistocene?

## TL;DR

This study explores how the darkling beetle Centorus rufipes survived cold Pleistocene climates by measuring its cold resistance and comparing it to other beetles.

## Contribution

The study provides new evidence that C. rufipes had exceptional cold resistance, supporting its success in Pleistocene environments.

## Key findings

- The supercooling point of C. rufipes was around −31 °C, allowing survival in extreme cold.
- The death temperature of 50% of beetles was −27 °C, significantly lower than other darkling beetles.
- C. rufipes did not rely on habitat warming but instead had high cold resistance.

## Abstract

We studied the cold resistance of the darkling beetle Centorus rufipes, the only species of darkling beetle abundant in the late Pleistocene mammoth steppes of western Siberia. In contrast, darkling beetles are one of the leading groups in the modern analog of the mammoth steppes. Insufficient cold resistance has been suggested as the reason for the low prevalence of darkling beetles in the Pleistocene. However, this is insufficiently substantiated without understanding the peculiarities of C. rufipes. Therefore, the following hypotheses were tested: C. rufipes either has high cold resistance that allows it to survive at low temperatures, or it successfully selects microhabitats with relatively mild conditions. The supercooling point for most of the sampled beetles was around −31 °C, and the death temperature of 50% of individuals was approximately −27 °C. These values were at least 5 °C lower than darkling beetle species from the Chuya Depression of the Altai Mountains, known for its extreme winter temperatures. Thus, the hypothesis that increased cold resistance of C. rufipes was important for its success in the Pleistocene was supported.

Centorus rufipes (Gebler, 1833) is the only tenebrionid beetle commonly found in late Pleistocene deposits of southern western Siberia. It is assumed that the reasons for its success during the Last Glacial Maximum could have been its cold resistance and/or the relatively mild conditions of its habitat, the shores of salt lakes. The cold resistance parameters of C. rufipes and their overwintering conditions were studied near Kusgan Lake (Novosibirsk Oblast, Russia). Adults and larvae of this species used a supercooling mechanism to protect themselves from sub-zero temperatures and did not tolerate freezing, just like other steppe species of Tenebrionidae. The supercooling point (SCP) for most of the individuals was around −31 °C. Measurements of low lethal temperatures (LLT) showed that 50% of individuals died after 2 days of exposure to −27 °C. The measured SCP and LLT were at least 5 °C lower than darkling beetle species from the Chuya Depression of the Altai, which is known for its extreme winter temperatures. Thus, the hypothesis of increased cold resistance of C. rufipes was confirmed. No warming effect of its salt lakeside habitats was detected.