Modes of spontaneous chromosomal mutation and karyotype evolution in ants with reference to the minimum interaction hypothesis.

Abstract

Aspects of chromosomal mutation and karyotype evolution in ants are discussed with reference to recently accumulated karyological data, and to detailed karyotype analyses of several species or species complexes with low chromosome number and unusual chromosomal mutations (the complexes of Myrmecia pilosula (Smith) (n=1, 5 or 9 to 16); M. piliventris Smith (n=2, 3-4, 17 or 32), and Ponera scabra Wheeler (n=3 or 4, 2n=7 or 8)). Translocations and Robertsonian polymorphisms are confirmed to be non-randomly distributed among ants -the former are found at high frequencies in species with low chromosome numbers (n<_ 12), while the latter predominate in those with high numbers (n> 12). This situation is consistent with the minimum interaction hypothesis of , under which translocations are expected to occur most frequently in low-numbered karyotypes, and that the resulting genetic risks are minimized by increases in chromosome and/or arm numbers through centric fission and pericentric inversion. Centric fusion is considered to be a transient event in karyotype evolution, resulting from telomere instability in acrocentric chromosomes.

Notes on the Remarkable Karyology of the Primitive Ant Nothomyrmecia Macrops, and of the Related Genus Myrmecia (Hymenoptera: Formicidae)

“…and M.Y.W. Chromosomal details of another of these species, now believed nomenclaturally to be "true"pilosula (2n=17-32), were reported by Imai et al (1988).…”

“…In addition Myrmecia piliventris Smith is known to have the chromosome complement n--2, 2n--4, and to have closely similar relatives with much higher counts (2n--6, n--3 or 4; 2n--34; 2n--64 respectively; Imai and Taylor, 1986;Imai et al, 1988 We expect, however, that the pilosula complex will prove to be more chromosomally diverse and species-rich than presently indicated, and this would have the effect of increasing the value of the maximum multiplier used above.…”

Estudos citogenéticos em formigas neotropicais do gênero Gnamptogenys Roger (Hymenoptera, Formicidae, Ectatomminae)

“…Já foram analisados os cariótipos de mais de 500 espécies na família Formicidae, a mais estudada do ponto de vista citogenético entre os Hymenoptera (IMAI et al 1988;1994, MARIANO et al 2003a (CROZIER 1969(CROZIER , 1975. Também são conhecidos os números cromossômicos de quatro espécies orientais do gênero Gnamptogenys, que são Gnamptogenys menadensis (Mayr, 1887) (2n=42), Gnamptogenys binghamii (Forel, 1900) (n=22) (IMAI et al 1983) da Malásia, Gnamptogenys sp.1 (2n=42), Gnamptogenys sp.2 (2n=36), ambas do oeste da Malásia e Cingapura (GÕNI et al 1982;IMAI 1983).…”

“…A análise citogenética foi feita a partir de gânglios cerebrais destas prépupas, seguindo a metodologia de IMAI et al (1988), cujo resultado consegue informar a distribuição de heterocromatina, não sendo necessária a utilização de técnica de banda-C (IMAI et al 1988). Em média, foram analisadas 10 lâminas por colônia, que foram coradas com Giemsa diluído em tampão Sörensen na proporção de 1:30 por 20 minutos.…”

Location of ribosomal genes in the chromosomes of Anopheles darlingi and Anopheles nuneztovari (Diptera, Culicidae) from the Brazilian Amazon

“…Preparations of mitotic chromosomes -Mitotic chromosomes in air-dried neuroblast preparations from fourth instar larvae (early and middle stages) and prepupae (F1) were examined using the techniques described by Imai et al (1988). Thirty-nine treated and fixed slide preparations containing 4 to 5 well-spread metaphase plates of A. darlingi and A. nuneztovari were used in the fluorescence in situ hybridization assays.…”