Meiotic behavior and karyotypic variation in Acledra (Pentatomidae, Heteroptera).

ABSTRACT

Acledra comprises 15 taxonomically identified species, most of which are crop pests. This is the first cytogenetic study of species of this genus. Acledra kinbergii and A. modesta showed the modal number of the Pentatomidae (2n = 14 = 12 + XY), while A. bonariensis had a reduced complement (2n = 12 = 10 + XY), with a markedly larger autosomal pair. Meiotic behavior follows the general pattern of the family; the autosomes divide pre-reductionally, the sex chromosomes are achiasmatic and divide post-reductionally, and at metaphase II the autosomes show a ring-shaped configuration with the pseudobivalent at the center. However, the configuration at metaphase I varies; A. modesta shows the typical arrangement (ring of bivalents with the sex chromosomes lying at its center). In A. kinbergii, the sex chromosomes are part of the ring or only the Y chromosome is at the center. In A. bonariensis, the ring arrangement is not well defined. There are also differences at the diffuse stage; chromatin strands of different width are observed in A. bonariensis and A. modesta, whereas bivalents do not entirely lose their identity in A. kinbergii. In A. bonariensis, the reduced complement may have originated from the fusion of the two larger non-homologous autosomes, which could characterize the ancestral karyotype of this genus. The presence of secondary constrictions in the larger pair of A. modesta and A. bonariensis may support this hypothesis. Since secondary constrictions are uncommon in the holokinetic chromosomes of heteropterans, their presence in these species may indicate that it is a plesiomorphic character of the genus.