Behavior of “arvalis” and “obscurus” chromosomal forms of common vole males in the forced swim test

To determine the difference in stress response between two chromosomal forms of a common vole, the “arvalis” and “obscurus”, the behavior of adult (6–12 months) lab-born vole males were evaluated in a forced swim test. During the test, they were carefully placed into glass cylinders (d=12 cm, h=20 cm) filled with water (h=15 cm, 24±1°C) and remained there for up to 6 min. Their behavioral patterns were video recorded and continuously monitored (Ethograph, ver. 2.7, RITEC, Russia) to document the duration of swimming and paddling (orientation), floating (immobility) and climbing (escape). Two series of experiments were performed, in May 2016 and June 2017, with independent groups: “arvalis” (N=9 each year) and “obscurus” (N=9 and 22 each year, respectively). The «arvalis» and «obscurus» significantly differed in their responses to the stress test. Over 35% of obscurus males (2 of 9 in 2016 and 9 of 22 in 2017) failed to complete the test, within 3 min these animals had to be rescued to prevent drowning (significant differences from “arvalis” according to Fisher's exact test). “Arvalis” voles displayed higher duration of escape attempts (F(1.14)=3.5; P=0.08 – for first; F(1.20)=15.6; P<0.001 – for second series of experiment), shorter duration of swimming and paddling (significantly in the first series – F(1.14)=14.3; P<0.005), and shorter duration of immobility (significantly in the second series – (F(1.20)=6.1; P<0.001). The results suggest that two chromosomal forms of common vole have major differences in stress response behavior. In the forced swim test, the “arvalis” voles are displaying higher endurance, associated with active escape behavior, when compared to “obscurus” animals. Further studies need to address their responses to other stress paradigms and to water environment, in general. The latter may play a major role in vole migration when they meet water barriers in their natural environment.