Chromosome evolution in Neotropical Danainae and Ithomiinae (Lepidoptera)

摘要

As part of a broad survey of the genetics, ecology, systematic relationships and evolutionary patterns in butterflies of the Neotropics, the first author has fixed in Bouin/Hollande male gonads from over 2000 populations of these insects over the past 35 years, and the second and third have made chromosome preparations from this material by sectioning and staining with hematoxylin. Earlier papers in the series of reports covering the results of this work (de Lesse and Brown 1971; Suomalainen and Brown 1984; Brown et al. 1992) dealt with members of the Nymphalid tribe Heliconiini, for which the essentially complete data revealed a coherent pattern of chromosome evolution, except in the primitive and still enigmatic genus Philaethria (n=12 to 88). Outside this, only a single derived splinter group (Laparus doris) revealed appreciable variation in chromosome number, paralleling its color-pattern polymorphism. A further paper (Emmel et al. 1995) included incomplete data on the Neotropical Papilionidae (74 populations of 50 species). The modal number n=30 was dominant in all branches of the family, with however some variation in each tribe (n=23 to n=45 in two distasteful species of Troidini, for example).The Ithomiinae (Nymphalidae) are considered as prime movers in most Neotropical mimicry rings (Brown and Benson 1974; Brown 1987) and show great inter- and intraspecific variation in color and pattern (Brown 1979). Early work on their chromosomes (de Lesse 1967, 1970a, 1970b; de Lesse and Brown 1971; Wesley and Emmel 1975) also showed large variations in their number, between subspecies or even within single populations. Although neither the systematic revision, nor the coverage in fixing all major taxa, nor the examination of chromosomes is complete for this subfamily of over 350 species (Brown 1985; Lamas 2004), enough data are now in hand to permit an overview of the patterns of chromosome evolution at the tribal and generic levels, especially in the more basal or isolated groups. These are presented and discussed here, along with preliminary data on all the genera (including new counts on over 1000 populations representing 242 species) and an overall summary of the emergent patterns in this complex group, which includes many large genera with highly variable karyotype. Based on the chromosome patterns, a supplementary revision is presented for the variable genera Melinaea and Mechanitis that form the core of “tiger”-patterned black–yellow–orange mimicry complexes throughout the Neotropics.For comparison, numbers are also reported for Neotropical species in the sister group of the Ithomiinae, the Danainae (Ackery and Vane-Wright 1984). While large in the Old World, this subfamily is small in the Americas (only 14 species); the members also serve as foci for large mimicry rings in all the continents, but tend to join Ithomiinae-based rings in the Neotropics.