HAIM, A; SHANAS, U; SCANTLEBURY, M: COMPARATIVE PHYSIOLOGY OF SPINY MICE POPULATIONS – EFFECTS OF SLOPE FACING MICRO-HABITATS

The common spiny mouse is widely distributed in rocky habitats of Israel from the desert to the Mediterranean ecosystem. A comparative study between mice from a desert population and a Mediterranean population revealed significant differences of thermo and osmo-regulatory abilities. In this study we hypothesized that similar differences may occur in two adjacent populations (from the same locality)inhabiting different micro-habitats on opposite facing slopes. Due to different solar radiation intensity and duration, north-and south-facing slopes (NFS and SFS) of the same valley, represent mesic and xeric habitats respectively. We measured in relation to increasing salinity in summer and winter acclimatized mice the following physiological variables: resting metabolic rates (RMR), daily energy expenditure (DEE), daily rhythms of body temperature, non-shivering thermogenesis (NST), urine volume, concentration, electrolytes and urea. We found that the two populations of mice indeed differed in their thermo- and osmo-regulatory capacities, reflecting their need to cope with the environmental challenges in each habitat. For example RMR was lower in SFS compared with NFS mice. DEE was significantly lower in SFS than in NFS mice. Daily rhythms of body temperature also showed differences between slopes and seasons. Differences in urine osmolarity were revealed only during winter but not in summer. Our results suggest that the two separate populations of mice may have evolved different physiological adaptations to cope with climatic challenges. These differences could be a result of an ongoing adaptive process to different climatic conditions, typical of the Mediterranean region, that are demonstrable example of evolution in action.