[HELICONIUS] Ithomia paper in "Evolution" journal

[Jim Mallet]

Dear All,

I thought you might like to see this new paper in Evolution.

Available for download at: 
http://heliconius.cap.ed.ac.uk/butterfly/publications/Jiggins_Evol2006.pdf

THE PHYLOGENETIC PATTERN OF SPECIATION AND WING PATTERN CHANGE IN 
NEOTROPICAL ITHOMIA BUTTERFLIES (LEPIDOPTERA: NYMPHALIDAE), by Chris D. 
Jiggins,  Ricardo Mallarino, , Keith R. Willmott, Eldredge Bermingham

Species level phylogenetic hypotheses can be used to explore patterns of 
divergence and speciation. In the tropics, speciation is commonly 
attributed to either vicariance, perhaps within climate-induced forest 
refugia, or ecological speciation caused by niche adaptation. Mimetic 
butterflies have been used to identify forest refugia as well as in studies 
of ecological speciation, so they are ideal for discriminating between 
these two models. The genus Ithomia contains 24 species of warningly 
colored mimetic butterflies found in South and Central America, and here we 
use a phylogenetic hypothesis based on seven genes for 23 species to 
investigate speciation in this group. The history of wing color pattern 
evolution in the genus was reconstructed using both parsimony and 
likelihood. The ancestral pattern for the group was almost certainly a 
transparent butterfly, and there is strong evidence for convergent 
evolution due to mimicry. A punctuationist model of pattern evolution was a 
significantly better fit to the data than a gradualist model, demonstrating 
that pattern changes above the species level were associated with 
cladogenesis and supporting a model of ecological speciation driven by 
mimicry adaptation. However, there was only one case of sister species 
unambiguously differing in pattern, suggesting that some recent speciation 
events have occurred without pattern shifts. The pattern of geographic 
overlap between clades over time shows that closely related species are 
mostly sympatric or, in one case, parapatric. This is consistent with modes 
of speciation with ongoing gene flow, although rapid range changes 
following allopatric speciation could give a similar pattern. Patterns of 
lineage accumulation through time differed significantly from that expected 
at random, and show that most of the extant species were present by the 
beginning of the Pleistocene at the latest. Hence Pleistocene refugia are 
unlikely to have played a major role in Ithomia diversification.


James Mallet
http://www.ucl.ac.uk/taxome/jim/