In several rodent species, changes in photoperiod are important signals for seasonal acclimatization of thermoregulatory mechanisms. Nocturnal rodents inhabiting extremely hot and arid areas like the Arava (Israeli Rift Valley), may be exposed to very low ambient temperatures, which may be far below their lower critical point. In contrast, nocturnal species from the mesic Mediterranean habitats are not exposed to such dramatic seasonal changes.

In the present study, food consumption was measured as apparent digestible dry matter intake (DDMI), while energy was measured as digestible gross energy intake (DGEI), in four rodent species from different habitats. The studied mice were kept under two different photoperiod regimes 16L:8D long photophase, 8L:16D long scotophase at a constant ambient temperature (T =28°C).

In Meriones crassus, which inhabits extremely arid habitats, apparent DDMI and DGEI were significantly higher in long scotophase acclimated individuals when compared with long photophase acclimated. However, in the mesic species Apodemus flavicollis these parameters were similar under acclimation to the two different photoperiod regimes. These results suggest that, in seasonal acclimatization, species from different habitats may have a different response to photoperiodic cues.

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