EXAMINING 2 STANDARD ASSUMPTIONS OF ANCESTRAL RECONSTRUCTIONS - REPEATED LOSS OF DICHROMATISM IN DABBLING DUCKS (ANATINI)

Although phylogenetic reconstruction of ancestral character states is becoming an increasingly common technique for studying evolution, few researchers have assessed the reliability of these reconstructions. He re I test for congruence between a phylogenetic reconstruction and a w idely accepted scenario based on independent lines of evidence. I used Livezey's (1991) phylogeny to reconstruct ancestral states of plumage dichromatism in dabbling ducks (Anatini). Character state mapping rec onstructs monochromatic ancestors for the genus A,rns as well as most of its main clades. This reconstruction differs strongly from the wide ly accepted scenario of speciation and plumage evolution in the group (e.g., Delacour and Mayr 1945; Sibley 1957). This incongruence may occ ur because two standard assumptions of character state reconstruction are probably not met in this case. Violating either of these two assum ptions would be a source of error sufficient to create misleading reco nstructions. The first assumption that probably does not apply to duck s is that terminal taxa, in this case species, are monophyletic, Many of the widespread dichromatic species of ducks may be paraphyletic and ancestral to isolated monochromatic species. Three lines of evidence support this scenario: population-level phylogenies, biogeography, and vestigial plumage patterns. The second assumption that probably does not apply to duck plumage color is that gains and losses of character states are equally likely. Four lines of evidence suggest that dichrom atic plumage might be lost more easily than gained: weak female prefer ences for bright male plumage, biases toward the loss of sexually dich romatic characters, biases toward the loss of complex characters, and repeated loss of dichromatism in other groups of birds. These seven li nes of evidence support the accepted scenario that widespread dichroma tic species repeatedly budded off isolated monochromatic species. Drif t and genetic biases probably caused the easy loss of dichromatism in ducks and other birds during peripatric speciation. In order to recove r the accepted scenario using Livezey's tree, losses of dichromatism m ust be five times more likely than gains. The results of this study ca ution against the uncritical use of unordered parsimony as the sole cr iterion for inferring ancestral states, Detailed population-level samp ling is needed and altered transformation weighting may be warranted i n ducks and in many other groups and character types with similar attr ibutes.