Browsing by Author "WALKER, LI"

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    CYTOGENETIC AND REPRODUCTIVE STUDIES OF 2 NOMINAL SUBSPECIES OF PHYLLOTIS-DARWINI AND THEIR EXPERIMENTAL HYBRIDS
    (1984) WALKER, LI; SPOTORNO, AE; ARRAU, J
    P. darwini vaccarum and P. d. darwini live contiguously in central Chile, the former in the high Andes an the latter in the Central Valley and on the coast. All individuals examined of both kinds had 38 chromosomes of similar shape, but P. d. vaccarum always showed large paracentromeric C-bands on all chromososmes: P. d. darwini showed none or only small ones. Pairings (56) between the 2 forms were made in the laboratory. They resulted in 23 hybrids produced by 4 P. d. vaccarum females and 4 P. d. darwini females. A higher incidence of aggression and mortality was observed in the cross-pairings, as well as a lower incidence of birth (14.3%) and a lower mean litter size (2.9), in comparison with 117 pairings within forms (65.0% and 4.2%, respectively). C-banded hybrid metaphases showed 19 chromosomes with large paracentromeric C-bands and 19 with none or only small ones. In the G-banded hybrid karyotypes, it was possible to identify 8 chromosome pairs with total correspondence of band patterns, 5 pairs with correspondence only at their long arms and 10 autosomes and the X chromosomes with no correspondence at all. Hybrids were completely sterile; adults had incomplete germinal lines and a lack of differentiated gametes in their gonads. There results and the presence of individuals of both chromosomal forms in the same trap line with no traces of mixing, provide strong evidence of complete genetic isolation of the 2 forms; they should be considered as separate species. Gene flow is suggested between P. d. vaccarum and the other Andean forms living in northern Chile and probably with those from southern Chile; the oldest species-group name available for all of these is P. d. xanthopygus.