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

Abstract

The Mongolian gerbil has been used as laboratory animal since 1935. Breeding gerbils as an isolated laboratory population for decades may have led to a domestication process whose effects include changes in brain size. Quantitative changes in testicular activity could be assumed. Comparative intraspeci®c measurements were performed in 34 adult males of the laboratory strain (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 examined in January. Testicular spermatozoa were counted, proportions of different cell types were analysed using DNA¯ow cytometry, and mitotic and meiotic activity was calculated from DNA histograms. Intratesticular testosterone concentrations were measured with an enzyme immunoassay. In the WILD, testicular activity was lower and varied more. The overall weight, the ef®ciency of spermatogenesis (sperm/g testis) and resulting total sperm per testis were signi®cantly less in offspring of wild gerbils. This corresponded with lower levels of haploid cells, total germ cell transformation of diploid cells to spermatids and meiotic transformation of spermatocytes to spermatids. 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 F 1 . All parameters changed in WILD F 2 generation compared with F 1 and diminished the differences with LAB. Differences between F 1 and F 2 were signi®cant for testis mass, testis/ body weight ratio, percentages of haploid cells and cells in G 2 /M phase, both germ cell transformations and testosterone concentration. The results suggest rapid, adaptive changes of male reproductive physiology in the early offspring generations from wild populations under laboratory breeding conditions. The breeding of Mongolian gerbils in the laboratory has in¯uenced the testicular function resulting in increased spermatogenic activity and highly stimulated testosterone production.

Intraspecific Allometric comparison of Laboratory gerbils with Mongolian Gerbils Trapped in the Wild Indicates Domestication in Meriones unguiculatus (Milne-Edwards, 1867) (Rodentia: Gerbillinae)

“…Because genetic bottlenecks and domestication affect reproduction in other mammals (O'BRIEN et al 1983;LINCOLN et al 1990), similar changes in laboratory gerbils could be expected, for example, in male reproductive physiology. Raised under identical conditions, offspring (F 1 ) of wild gerbils showed a significantly lower testicular testosterone concentration and reduced rate in spermatogenesis than laboratory males (BLOTTNER et al 2000). Diminishing differences in F 2 wild males suggest rapid, adaptive changes in the early generations of wild offspring bred under human care.…”

Strain-dependence of age-related cochlear hearing loss in wild and domesticated Mongolian gerbils

“…Almost all animals of those colonies descend from a group of 20 founders trapped in 1935 in Mongolia. Due to a long period of inbreeding and domestication in animals descending from those colonies, many changes are reported (Stuermer et al, 2003), like 18% decrease of brain weight (Stuermer et al, 1997), higher testicular activity (Blottner et al, 2000), increased sperm production , and improved reproductive fitness . These domestication effects are an adaptation to the modified living conditions in laboratory breeding colonies.…”