Danaus eresimus, ISSUE

Smith, David A. S., Lushai, Gugs & Allen, John A., 2005, A classification of Danaus butterflies (Lepidoptera: Nymphalidae) based upon data from morphology and DNA, Zoological Journal of the Linnean Society 144 (2), pp. 191-212 : 198

THE ERESIMUS ISSUE

The taxon eresimus + plexaure is sympatric with gilippus over 95% of their very extensive combined range, from Texas and Florida in the north to Uruguay and Argentina in the south. Where these two very similar species fly together, the feature that serves best to distinguish them on the wing is a series of pale patches (character 54, Appendix 1A, B) on the hindwing underside of eresimus + plexaure . This character, unique within Danaus , may aid species recognition and, thus, mate selection in sympatry. Because butterfly eyes are sensitive both to ultraviolet ( Silberglied & Taylor, 1978) and polarized light ( Sweeney, Jiggins & Johnsen, 2003) an investigation of the optical properties of these patches could be rewarding. Even to the human eye, the patches serve equally well to distinguish plexaure from gilippus gilippus in Argentina or eresimus tethys from gilippus berenice on Grand Cayman (DASS, unpublished).

The phylogenetic tree derived from mtDNA data ( Fig. 2A ) places the chrysippus + petilia clade as sister to eresimus + gilippus ; with the proviso that dorippus- 1 is excluded from Anosia , the remaining species form a monophyletic group. The Anosia cluster, again excluding dorippus-1, is sister to Salatura and Salatura + Anosia is sister to Danaus . Comparing the topology derived from mtDNA characters ( Fig. 2A ) with that based on morphological characters ( Fig. 2B ), it is clear that the relationships found for eresimus are discordant. Whereas the mitochondrial genomes of eresimus and gilippus are virtually identical ( Lushai et al., 2003a), and the two New World species share a sister relationship with the Old World Anosia species , the nuclear data suggest otherwise. In the latter case, with the substantial caveat that the relevant nodes have weak support, eresimus does not cluster with Anosia , but rather with plexippus + erippus . The analysis of total evidence ( Fig. 3) provides strong support for the eresimus + gilippus clade, but not for its inclusion in Anosia , nor indeed any other subgenus. These anomalies strengthen the case for abandoning the A & V-W subgenera of Danaus s.l. ( Fig. 1 ).

Figures

Figure 1. Cladistic reconstruction of the genus Danaus, after Ackery & Vane-Wright (1984).

Figure 2. A, single most parsimonious tree based on amalgamated mtDNA 12S rRNA (344 bp†) and COI (676 bp†) genes (Appendix 2) for the genus Danaus, rooted by outgroups Tirumala septentrionis and T. limniace (†values before alignment). Tree statistics: characters in matrix 1025, variable informative characters 54, parsimony informative characters 139, heuristic search length 304, consistency index (CI) = 0.80, homoplasy index (HI) = 0.20, retention index (RI) = 0.81, rescaled consistency index (RCI) = 0.65. Bootstrap replicates/Bremer Support values are shown for each node where significant. Branch lengths are drawn proportional to nucleotide changes and indicated in parentheses. The MP topology depicted here is congruent with the MP strict consensus, NJ and ML algorithms not shown. ML branch significance is P <0.01 unless marked *. See Table 1 for provenances and sample sizes. B, single most parsimonious tree based on morphological, biochemical and colour gene characters (Appendix 1A, B) for the genus Danaus, rooted by outgroups T. septentrionis and T. limniace (characters from T. petiverana, T. hamata and T. ishmoides were used to fill gaps); †character alignment was fixed to character). Tree statistics: characters in matrix 67†, variable uninformative characters 8, parsimony informative characters 59, heuristic search length 95, CI = 0.84, HI = 0.16, RI = 0.90, RCI = 0.75. Other notes as in (A). C, one of 11 most parsimonious trees based on amalgamated nDNA 18S rRNA (525 bp†) and EF1-a (400 bp†) genes for the genus Danaus, rooted by outgroups Amauris niavius and A. ellioti (†values before alignment). Tree statistics: characters in matrix 926, variable uninformative characters 19, parsimony informative characters 24, heuristic search length 52, CI = 0.83, HI = 0.17, RI = 0.72, RCI = 0.60. Other notes as in (A).