Breeding policies to optimise effective population size in captive populations

Abstract

Preservation of genetic variability has traditionally been faced via the proposal of breeding strategies aiming at the increase of the effective population. Protection provided by zoological reserves and parks may be increasingly necessary for short- and long-term survival. There is consensus on the fact that minimising coancestry in a cohort outperforms other breeding strategies. This research compares via computer simulations the performance of different breeding schemes aiming at limiting the loss of genetic diversity in small captive populations, assessed via fluctuations of the effective population size, at both the short- and the long-term. Nine mating strategies have been assayed: minimum coancestry (F), minimum increase in coancestry (dF), minimum weighted coancestry (mFm; accounting for the actual representation of each individual), minimum weighted increase in coancestry (dmdFdm), minimum offspring coancestry (C), minimum offspring increase in coancestry (dC), minimum offspring coancestry free (Cf; like strategy C, but allowing that females have unbalanced or no offspring), minimum offspring increase in coancestry free (dCf) and combined strategy mixing F and C information of the offspring (mix). Twenty replicates of all simulations were performed during 20 discrete generations. Methods were tested under two different scenarios simulated starting from the actual pedigree of Gazella cuvieri an endangered Sahelo-Saharan gazelle with a relative big population kept in captivity. All strategies tested provided an increase of Ne in the first generation. That increase was higher in those scenarios where not all males were forced to produce offsprings. This was due to the previous unbalance of pedigree depth and to the differential contributions among parents . Ne decreased in all scenarios in the second generation. After third generation, scenarios forcing the use of all males increased Ne. The mix and the dCf strategies gave higher Ne values than the other strategies in the long term. However, dCf gave the worst result in the first generation in cases of poor pedigree depth. The practical use of the methodology depends on the planned horizon that might vary according to generation interval.