Backcrossing as a species restoration technique

Danny Carroll Wharton, Fordham University


A study of the practical results of full species hybridization and backcrossing as a species restoration technique was conducted, observing reciprocal backcrosses of Mus spretus and a laboratory strain of Mus domesticus C57B1/6J. Hybrids, backcrosses and controls were measured in regard to six body characteristics, four pelage coloration characteristics, fourteen behaviors, eight enzyme systems (ten structural gene loci) and fertility as reflected in litter size. Backcrossing was pursued for seven generations to FBC7 where species restoration is estimated to be at 99.7 per cent in mathematical terms. Except for a minority of FBC7 spretus specimens failing to conform completely to one pelage characteristic, FBC7 specimens were essentially indistinguishable from controls both subjectively and in all areas of measurement. The spretus backcross line was followed generation by generation in most areas of measurement and was largely conforming to controls by FBC4 at latest. One sibship of FBC7 in both the spretus and domesticus backcross lines was derived from a backcross sire and pure species female in contrast to all other sibships derived from backcross females. FBC7 backcrosses of paternal derivation conformed well with both controls and FBC7 counterparts of maternal derivation although there were some interesting contrasts in measures of tail length. Discussion is provided on the possible effects of exchanging cytoplasmic genes (e.g. mitochondrial) with another species and its context under natural conditions. It is concluded that backcrossing should be seriously considered as an additional ex situ tool in species and subspecies conservation efforts essentially where (1) only single-sex populations remain; (2) specific survival traits may be missing or lost in the species in question and (3) where inbreeding depression seriously threatens a remnant population's ability to recover.

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Recommended Citation

Wharton, Danny Carroll, "Backcrossing as a species restoration technique" (1990). ETD Collection for Fordham University. AAI9025027.