Phylogenetic relationships and systematics of the bamboo-specialist Amaurospiza blue seedeaters

Abstract

The Amaurospiza ‘seedeaters’ are bamboo-specialized mixed strategists, most often found in bamboos in vegetative state, feeding on buds, shoots, petioles and insects. As bamboos die after flowering, birds may wander in search of live vegetative bamboo. The three currently recognized species of Amaurospiza are allopatrically distributed: the Blackish-blue Seedeater Amaurospiza moesta in the Atlantic Forest of Argentina, Brazil and Paraguay, and in forest enclaves in the Cerrado; the recently described Carrizal Seedeater Amaurospiza carrizalensis known from a few localities in southeastern Venezuela; and the Blue Seedeater Amaurospiza concolor distributed patchily from Mexico to Peru. Three subspecies are recognized within A. concolor: relicta in southwest Mexico, concolor from southern Mexico to Panama and aequatorialis from southwest Colombia to northwest Peru. Full species status has been advocated for relicta and aequatorialis but evidence supporting their recognition is weak, while relicta was described in the monospecific genus Amaurospizopsis. Here we (1) test the monophyly of Amaurospiza, (2) reconstruct the phylogenetic relationships of all its constituent taxa using mitochondrial and nuclear markers, (3) re-assess species limits in Amaurospiza with the aid of vocalizations and genetic and plumage data, and (4) discuss the link between bamboo life history, biogeographical patterns and extent of genetic differentiation. Amaurospiza was found to be monophyletic in both the ND2 and multilocus analyses. In the ND2 tree A. moesta and A. carrizalensis were sister to each other, A. concolor was found to be paraphyletic because aequatorialis was placed as sister to moesta–carrizalensis, and a clade including nominate concolor and relicta was sister to all the other taxa. The multilocus tree showed the same relationships, but lacked nuclear samples of relicta. Mean ND2 pairwise distance between concolor and aequatorialis (8.3%) was greater than that between moesta and carrizalensis (5.7%), while relicta diverged on average 1.0% from nominate concolor. The South American clade has more slender bills and white underwing coverts, while the Central American clade has thicker bills and bluish underwing coverts. All taxa exhibited typical Amaurospiza songs with quickly delivered, warbled, pure and fairly high-pitched musical notes. Number of inflections/second exhibited a stepped pattern, with concolor and relicta on the lower end and carrizalensis, aequatorialis and moesta on the upper end. Similarly, moesta, carrizalensis and aequatorialis had overall more inflections per note than concolor and relicta. Linear discriminant analysis using nine acoustic variables correctly assigned all 62 songs to the correct taxon. Morphology, plumage, vocalizations and phylogenetic data indicate that aequatorialis should be afforded full species status as the Ecuadorian Seedeater (A. aequatorialis), suggest keeping relicta as a subspecies of A. concolor and support continued recognition of A. carrizalensis. Our data support merging Amaurospizopsis into Amaurospiza.