Seasonal variation of testicular activity in European brown hare Lepus europaeus

Testicular activity in brown hare Lepus europaeus Pallas, 1778 was studied during the annual cycle. Testicular mass, spermatozoa and testosterone were estimated. Percentages of haploid, diploid and tetraploid cells were monit ored using DNA flow cytometry and the proportions of somatic and spermatoge netic cells were determined after selective labelling of somatic cells. Tes tis mass was high from January to July and declined thereafter to the nadir in September. Testis growth was reactivated significantly in December. Cha nges in testis mass corresponded with the spermatogenic efficacy (spermatoz oa/g testis). High spermatogenic activity was characterized by intensive me iotic transformation of spermatocytes to spermatids, high percentages of ha ploid cells and low proportions of cells in the G2/M phase of mitosis. Prop ortions of haploid cells declined rapidly during the testis involution. Spe rmatogenesis was newly activated from November. The proportions as well as the ratios of spermatogenic and somatic cells differed significantly betwee n the periods of testis involution and recrudescence. Testosterone level sh owed a pronounced increase in autumn preceding the intensification of sperm atogenesis; the lowest concentration was found during prominent testis invo lution in August. The results suggest that the regulation of seasonal testi cular activity is characterized by co-ordinated shifts in the relationships between mitosis, meiosis and testosterone production.