Morphological and molecular evidence supports recognition of <i>Danaus petilia</i> (Stoll, 1790) (Lepidoptera: Nymphalidae) as a species distinct from <i>D. chrysippus</i> (Linnaeus, 1758)

Abstract

<div><p>The danaine butterfly <i>Danaus chrysippus</i> (Linnaeus, 1758) occurs widely in the Afrotropical, Oriental and Australian regions and comprises a taxonomic complex, with recent authors recognizing between one and three species. <i>Danaus petilia</i> (Stoll, 1790) has previously been considered to be a subspecies of <i>D. chrysippus</i>, but we present evidence from wing colour pattern, morphological characters and molecular data that support a recent proposal to treat <i>D. petilia</i> as a separate, parapatric species. The subspecies <i>D. chrysippus cratippus</i> (C. Felder 1860) has a limited range in Indonesia, and was until recently known in Australia from only two specimens. However, on Cobourg Peninsula in the Northern Territory of Australia, <i>D. chrysippus cratippus</i> and <i>D. petilia</i> were observed flying together in <i>Melaleuca</i> swampland. Comparative analysis of wing colour pattern and quantitative morphological characters of material of both taxa sampled from this geographical region of sympatry indicates at least six diagnostic features that distinguish <i>D. petilia</i> from <i>D. chrysippus cratippus</i>. Moreover, a well-sampled molecular phylogeny of the <i>D. chrysippus</i> complex based on sequence data from mitochondrial (<i>cytochrome oxidase subunit 1</i>, <i>cytochrome b</i>) and nuclear (<i>wingless</i>, <i>elongation factor 1 alpha</i>) genes, demonstrates that <i>D. petilia</i> and <i>D. chrysippus</i> are reciprocally monophyletic, suggesting that the two species maintain their distinctiveness even when given the spatiotemporal opportunity for interbreeding. Phylogenetic reconstruction based on molecular data and extensive sampling of the <i>D. chrysippus</i> complex confirms that: (1) samples of <i>D. chrysippus cratippus</i> from Indonesia and Australia and <i>D. chrysippus bataviana</i> (Moore, 1883) from Indonesia are indeed <i>D. chrysippus</i>; (2) specimens from India (incorrect type locality of <i>D. petilia</i>) are <i>D. chrysippus</i>; and (3) the taxon <i>D. chrysippus dorippus</i> (Klug, 1845) (type locality Dongala, Sudan) is not a distinct species as has recently been proposed, and is best treated either as a subspecies of <i>D. chrysippus</i> restricted to Africa or a genetic colour morph of <i>D. chrysippus</i> that extends more widely into Asia. A lectotype designation is made for <i>Danais cratippus</i> C. Felder, 1860, and the status of the type material and application of the name <i>Papilio petilia</i> is discussed. Attention is drawn to the likely clinal variation (an east–west morphocline) of the <i>D. chrysippus</i> complex in Southeast Asia and Australia, and the dubious utility of attempting to discriminate subspecies within <i>D. chrysippus</i>.</p></div