Higher testicular activity in laboratory gerbils compared to wild Mongolian gerbils (Meriones unguiculatus)

The Mongolian gerbil has been used as laboratory animal since 1935. Breedin g gerbils as an isolated laboratory population for decades may have led to a domestication process whose effects include changes in brain size. Quanti tative changes in testicular activity could be assumed. Comparative intrasp ecific measurements were performed in 34 adult males of the laboratory stra in (LAB) and in males raised as offspring of wild Mongolian gerbils (WILD) caught in central Mongolia (F-1, n = 16; F-2, n = 17). LAB and WILD were ex amined in January. Testicular spermatozoa were counted, proportions of diff erent cell types were analysed using DNA flow cytometry, and mitotic and me iotic activity was calculated from DNA histograms. Intratesticular testoste rone concentrations were measured with an enzyme immunoassay. In the WILD, testicular activity was lower and varied more. The overall weight, the effi ciency of spermatogenesis (sperm/g testis) and resulting total sperm per te stis were significantly less in offspring of wild gerbils. This corresponde d with lower levels of haploid cells, total germ cell transformation of dip loid cells to spermatids and meiotic transformation of spermatocytes to spe rmatids. The most profound difference was found in testicular testosterone concentration: the mean level was 405.7 +/- 41.2 ng/g testis in LAB vs 6.4 +/- 2.0 ng/g in WILD F1. All parameters changed in WILD Fz generation compa red with F1 and diminished the differences with LAB. Differences between Fl and F2 were significant for testis mass, testis/body weight ratio, percent ages of haploid cells and cells in G(2)/M phase, both germ cell transformat ions and testosterone concentration. The results suggest rapid, adaptive ch anges of male reproductive physiology in the early offspring generations fr om wild populations under laboratory breeding conditions. The breeding of M ongolian gerbils in the laboratory has influenced the testicular function r esulting in increased spermatogenic activity and highly stimulated testoste rone production.