Chromosome polymorphism and Fanconi-like instability in the scarabaeid beetle Macraspis tristis from Guadeloupe

The karyotype of Macraspis tristis Laporte is described. It is composed of 18 chromosomes. C-band positive heterochromatin is very abundant and is located at centromeric regions and, for some chromosomes, at telomeric regions. There is a high inter-individual chromosomal polymorphism for the presence and extension of telomeric heterochromatin. In one of the 8 specimens studied, 2 populations were observed in testicular cells. Besides groups of normal metaphases, other groups displayed multiple chromatid and chromosome alterations such as breaks, exchanges (radials), deletions and translocations, resembling those described in Fanconi anemia. The insect had a normal phenotype, but its gametogenesis did not reach the spermatocyte II stage, and was quite poor in spermatocytes I. The clonal character of the chromosome instability was obvious owing to the incomplete cytodiaeresis of germ cells which remain associated by cytoplasmic bridges. This may be the first example of chromosome instability observed in animals from nature.