FERTILE HYBRIDS IN 2 GENERA OF WALLABIES - PETROGALE AND THYLOGALE

Breeding trials between karyotypically distinct species of Petrogale p roduced a number of hybrids and backcross hybrids of which same of the females were fertile, The only fertile male hybrid resulted from pare nts currently considered to be conspecific, but with different karyoty pes, To investigate the possibility that hybridizations occur in other genera, we examined three Thylogale species, two of which, T. thetis and T. stigmatica, are sympatric over parts of their range in eastern coastal Australia, while the third, T. billardierii, is now found only in Tasmania, Female hybrids of T. thetis (female) x T. stigmatica (ma le) were fertile when mated with T. stigmatica, but in male hybrids th e testes and seminiferous tubules failed to reach full-blood size and the tubules contained only primary spermatocytes, In contrast, the T. stigmatica (female) x T. thetis (male) crosses failed to produce hybri ds, However, the only female backcross hybrid to produce young to date mated with a 7: thetis. Female T. billardierii have not produced youn g with either T. thetis or T. stigmatica males and T. billardierii mal es could only be caged with conspecifics. Presumably behavioral barrie rs prevent regular gene flow in the wild, but in unusual conditions of habitat change (such as after fire or forest degradation) occasional gene transfers could be expected.