Reproduction of wild Mongolian gerbils bred in the laboratory with respect to generation and season 1. Morphological changes and fertility lifespan

Abstract

AbstractA new strain of wild Meriones unguiculatus (strain Ugoe:MU95, named WILD) with high genetic variability was recently established in Germany. A previous study showed that offspring (F-1) of WILD founders (F-0) showed reduced spermatogenesis and testosterone compared to domesticated gerbils (LAB) maintained under similar conditions. We investigated F-0 and subsequent generations in respect to sexual maturation, duration of fertility and gonadal weights of different seasons. Body and reproductive organ weights showed negligible seasonal fluctuations in both strains. Testis and epididymis weights in WILD covered a wide range, which indicates a high reproductive variability. Reproductive organ weights increased in F-3. Less variable and high reproductive organ weights (testis >900 mg, epididymis >200 mg) in almost all LAB illustrate their readiness to reproduce, even in small individuals. Prominent testis (T+) was found in 71% of adult males (F-1, F-2) reflecting the natural portion of T+(63%) found in wild gerbils investigated in Mongolia in 1995 and 2002. Testicular descent was accelerated and pronounced in WILD F-3 (T+, 88%) and LAB (T+, 91%). Time between mating and the first litter was significantly longer in wild F-0 than in their offspring or LAB. The average age in wild F-0 when the last litter was born was 27 months. Breeding went on for 2 to 32 months and was mostly terminated by the death of the females. Relative testis and epididymis weights correspond in young adults and in old males up to 6 years, the total life span of male wild Mongolian gerbils. In summary, the results suggest that laboratory conditions improve the reproductive fitness of wild gerbils.