Inbreeding: One word, several meanings, much confusion

Because conservation biologists must frequently deal with small populations, inbreeding (a frequent consequence of small population size) has played a central role in many genetic management programs. However, the word "inbreeding" has several, often contradictory meanings, and a failure to distinguish among these meanings has caused much misunderstanding on the role of inbreeding in genetic management. Three different biological meanings of inbreeding are discussed in this paper: (1) inbreeding as a measure of shared ancestry in the paternal and maternal lineages of an individual; (2) inbreeding as a measure of genetic drift in a finite population, and (3) inbreeding as a measure of system of mating in a reproducing population. The distinction and use of these different measures of inbreeding are discussed and illustrated with a worked example, the North American captive population of Speke's gazelle (Gazella spekei). It is shown that these different meanings of the word inbreeding must be kept separated, otherwise erroneous management recommendations and evaluations can occur. On the positive side, the different measures of inbreeding when used jointly can be a powerful management tool precisely because they measure different biological phenomena.