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Mean d2 is a recently devised microsatellite-based measure that is hypothesised to allow the detection of inbreeding depression and heterosis in free-living populations. Two studies that have investigated the measure have both demonstrated an association between mean d2 and traits related to fitness. Here we present an association between mean d1 and an important component of fitness, first-year overwinter survival, in a population of red deer on the Isle of Rum, Scotland. The association between survival and mean d2 differed between males and females. As predicted, outbred female calves (high mean d2 ) survived better than those that were inbred (low mean d2 ). However, the association was in the opposite direction in male calves. We suggest that this difference is due to different early growth strategies between the sexes. The association between mean d2 and survival was not significantly influenced by any single locus. Decomposition of mean d2 into a recent inbreeding component and an outbreeding component showed that it was the degree of outbreeding that influenced survival in males and both the degree of outbreeding and recent inbreeding that influenced survival in females. Our analyses suggest that mean d2 is an easy-to-calculate measure of inbreeding and degree of outbreeding that can reveal interesting interactions between genetics and ecology.

Original publication




Journal article



Publication Date





1951 - 1960


Heterosis, inbreeding depression, juvenile survival, mean d2, population history, red deer