Long-term effect of inbreeding in the yellow steppe lemming, Eolagurus luteus, captive colony

In the current research, we investigated the impact of gradually increasing inbreeding on the life span and reproductive rate of yellow steppe lemmings, Eolagurus luteus, that reproduced in the Moscow Zoo. The focal captive colony existed from 2017 to 2021. The studied animals belonged to the second to tenth generations. The founders of the colony were 5 females and 5 males originating from 3 females and 4 males livetrapped in the Zaisan basin (Kazakhstan). The degree of their descendant relatedness progressively increased. The animals intended to be used for reproduction were distributed to pairs with unfamiliar partners. We constructed the pedigree of 177 individuals and calculated their inbreeding coefficients. This parameter varied from 0 to 0.29, and the maximum values were registered in the lemmings of the seventh to tenth generations. We measured the life span of 61 individuals and used information about the reproduction or its absence in 45 pairs. A substantial decline in individual life span and reproductive parameters in the breeding pairs, along with a progressive increase in the inbreeding coefficients, was registered. The number of delivered litters, born pups, and young lived up to the age of puberty significantly depended on the level of mother inbreeding. The noticeable traits of inbreeding depression in the colony appeared in 2019-2020 when the offspring inbreeding coefficients reached approximately 0.2. Therefore, we assume that if the E. luteus population originates from a relatively small number of noninbred and unfamiliar individuals, then successful reproduction without significant inbreeding depression will continue for several generations of offspring.