Chromosome number variation within Philaethria butterflies (Lepidoptera: Nymphalidae, Heliconiini)

Abstract

The haploid chromosome number of the South American butterfly Philaethria dido varies from 12 to 88. Eight different numbers have been found in this species complex. The related Ph. pygmalion and Ph. wernickei usually show only n=29, a very frequent number in the Lepidoptera; numbers of n=15 and n=21 for these species need confirmation. The most common chromosome number for Ph. dido is also the highest, n=88, and is found in many parts of northern and central Brazil on the Amazon river and its tributaries, as well as adjacent parts of other countries. The other numbers were observed mainly in northern South America and along the east coast. Two very different numbers were found together in four localities. We did not find specimens with meiotic features suggesting hybridization between individuals with different chromosome numbers. The diverse numbers in Ph. dido may belong to good sibling species, distinguishable externally by very minor characters. Since Ph. dido is a very primitive species in the tribe Heliconiini, dating probably from the early Tertiary, it probably has had many opportunities to undergo divergent chromosome evolution in isolation. Its strong, high flight and broad ecological valence would then permit rapid spreading out and coexistence of different chromosome forms, which in some cases have been noted to show diverse behaviour in the field.