Colour and size variation in Junonia villida (Lepidoptera, Nymphalidae): subspecies or phenotypic plasticity?

Abstract

Colour pattern and size variation in the widespread Indo-Pacific Meadow Argus butterfly, Junonia villida (Fabricius, 1787), are reviewed based largely on examination of c. 1500 museum specimens from across its entire geographical range. Including villida, 14 available species-group names for this taxon are documented. The butterfly is recorded from some 200 islands or island groups. Larvae are reported to feed on 24 genera of flowering plants from 12 families. While the suggestion of H.T.G. Watkins that geographical variation in villida can be summarized by four segregates (eastern Pacific, Maluku–Papuan, Sunda–Australian, Chagos Islands) is found to have some validity, there are numerous exceptions. Based on a discussion of biological factors that may be responsible for the pattern of variation observed, it is concluded that, with the exception of J. villida chagoensis, a geographical isolate with a recognisable and constant phenotype not seen in any other population, any attempt at further formal division of this butterfly into subspecies is at present difficult or impossible to support. Reaching this conclusion has only been possible through the use of major museum collections. This leads to the perspective that variable species exhibiting seasonal polyphenism and migration, such as J. villida, need to be studied using a variety of techniques to explore their phenotypic plasticity before attempts are made to recognise numerous subspecies.