Abstract
A description of a G-banded karyotype for Lemur fulvus mayottensiscompletes a sampling of the differentially stained karyotypes of all recognized Lemur fulvussubspecies. The karyotype of two Lemur fulvus mayottensis (one male, one female) contains two pairs of submetacentric autosomes, 27 pairs of acrocentric autosomes, and acrocentric sex chromosomes (2N = 60, N.F. = 64. The karyotype cannot be distinguished from the G-banded karyotypes of Lemur fulvus fulvus, L. f. rufus, L. f. albifrons,or L. f. sanfordi;thus a single G-banded karyotype with a diploid number of 60 characterizes these subspecies. The karyotypes of L. f. collarisand L. f. albocollarisare not like those of other L. fulvussubspecies. They contain a number of biarmed chromosomes derived from a 2N = 60 karyotype via Robertsonian centric fusion of acrocentrics, but retain the N.F. of 64. L. f. collarishas diploid numbers of 52, 51, and 50, with hybridization occurring in wild populations. L. f. albocollaris ischaracterized by 2N =48. Matings of the two subspecies with L. fulvus2N = 60 in captivity regularly produce offspring which are fertile; thus Robertsonian centric fusions per se do not appear to be sufficient to lead to reproductive isolation of sibling populations. Karyotypic studies thus far offer no solution to the question of the relationship between L. f. collaris-albocollarisand any of the living L. fulvus2N = 60 subspecies, but we assume that L. f. collarisand L. f. albocollarisshare a common ancestry because they have two pairs of biarmed fusion products in common. Biarmed chromosomes derived from subsequent fusions involving different acrocentrics (one homologous, the other nonhomologous) serve to distinguish between the collaris-albocollariskaryotypes. The resulting monobrachial homology of one or more biarmed chromosomes may effectively function as a reproductive isolating mechanism, since hybrids between the two should experience difficulties in the synopsis of homologous elements in meiotic prophase.
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