Action: Can captive breeding have deleterious effects on individual fitness?
- Three studies of wild populations, wild and captive populations and museum specimens, one replicated, found evidence for potentially deleterious physiological or genetic changes due to captive breeding. These studies did not investigate fitness.
- A study of a wild Mauritius kestrel, Falco punctatus, population derived totally from captive individuals found high inbreeding and a loss of genetic diversity, but this was caused more by the very low population size (four wild birds) than by captivity per se.
- The museum-based study found reduced relative brain volume in captive wildfowl, compared with wild birds, whilst a comparison of wild and captive populations of white-headed ducks Oxyura leucocephala found lower genetic diversity in captive populations.
One potential problem with captive breeding is that it limits the effective population of a species to the number of captive individuals that are available to interbreed. This could lead to inbreeding depression and a loss of fitness. Similarly, the different selection pressures on individuals in captivity may alter the physiology of captive populations, as has occurred in domesticated species.
It is important to note that low genetic diversity, inbreeding and changes due to captivity do not necessarily lead to reduced fitness. Care should therefore be taken in interpreting the results from the studies below.
Supporting evidence from individual studies
A study of a population of Mauritius kestrels Falco punctatus in eastern Mauritius (Ewing et al. 2008) found that the population had grown from 12 individuals in 1987 to a minimum of 154 by 2002. Over this time, the degree of inbreeding increased by 2.6% each generation and by 2002, 25% of pairs were either closely or moderately related. Over this period 1.6% of genetic diversity was lost each generation. Effects on reproduction or survival were not monitored.
A replicated study of brain volume in 21 species of wildfowl from museum collections (Guay & Iwaniuk 2008) found that brain volume was lower in captive populations for 16 of the species, with an average decrease of 4.7% (range of 1-33%). Relative brain volume (brain volume in relation to other body measurements) was also lower in captive populations for 20 of the species, with an average reduction of 7.7% (range of 2-30%). A total of 268 skeletons were examined, at least one member of each sex was examined for each species. The effect of these decreases on behaviour, survival or reproduction is not known.
A controlled 2008 study of genetic diversity in white-headed ducks Oxyura leucocephala (Muñoz-Fuentes et al. 2008) found that two captive-bred populations had significantly lower genetic diversity than wild birds from Greece and Spain. A total of 38 captive-bred birds were tested, (27 from a Spanish collection and 11 from a UK collection) and compared with 70 wild birds collected between 1993 and 2003 (63 from Spain, seven from Greece). The captive Spanish birds descended from eight wild birds caught in Spain in 1982, the UK birds from three wild birds caught in Pakistan in 1968. Both microsatellite and mitochondrial DNA were less diverse in captive populations. Effects on reproduction or survival were not monitored.
- Ewing S.R., Nager R.G., Nicoll M.A.C., Jones C. G. & Keller L.F. (2008) Inbreeding and loss of genetic variation in a reintroduced population of Mauritius kestrel. Conservation Biology, 22, 395-404
- Guay P.J. & Iwaniuk A.N. (2008) Captive breeding reduces brain volume in waterfowl (Anseriformes). The Condor, 110, 276-284
- Muñoz-Fuentes V., Green A.J. & Sorenson M.D. (2008) Comparing the genetics of wild and captive populations of White-headed Ducks Oxyura leucocephala: consequences for recovery programmes. Ibis, 150, 807-815