Influence of photoperiod on morphological parameters, androgen concentration, haematological indices and serum protein fractions in common vole (Microtus arvalis, pall.).

1. In male voles developed under three different photoperiods (L:D = 24:0, L:D = 18:6, L:D = 6:18) the following results were obtained. 2. Higher variability of most of the parameters (except testes weight and protein fraction levels) was observed in young males. Hormonal synchronization of parameters studied in adult voles was discussed. 3. Sexual activity measured by morphological symptoms was related to increase of body and testes weights, RBC count, alpha 2- and gamma-globulin levels. There was no parallelism between testes weight and androgen concentration. 4. The increasing photoperiod synchronized groups as far as testes weight, WBC count and androgen concentration was concerned. Constant illumination inhibited sexual maturity and probably haemopoesis and androgen secretion. 5. A long "summer" photoperiod was optimal for male vole reproductive form which was related to high body and testes weight as well as value of red blood cell indices. 6. In the shortest "winter" photoperiod puberty was attained more slowly and blood cell counts showed high values. The high level of androgens might play a role in winter reproduction and aggressive behaviour observed in natural vole population. 7. The lowest values of total protein, albumin and alpha 2-globulin levels were observed in the "summer" photoperiod. Constant light and a long photoperiod did not suppress alpha 1- and beta-globulin fractions which showed the lowest level in short photoperiod ("winter"). It was suggested that light was not the most important factor acting on gamma-globulin (immunoglobulin) level in animals developed in laboratory conditions but can act on their heterogeneity in occurrence of the fraction.