MOLECULAR SYSTEMATICS AND THE ROLE OF THE “VÁRZEA”–“TERRA-FIRME” ECOTONE IN THE DIVERSIFICATION OF XIPHORHYNCHUS WOODCREEPERS (AVES: DENDROCOLAPTIDAE)

Abstract

The phylogeny of all known Xiphorhynchus (Dendrocolaptidae) species and many of its subspecies was reconstructed to evaluate species limits in this taxonomically challenging genus and investigate the possible role played by the Amazonian ''varzea'' (floodplain forest)-''terra-firme'' (upland forest) ecotone in its diversification. Phylogenies were inferred based on 2,430 bp of the mitochondrial DNA genes ND2, ND3, and cytochrome b. All phylogeny estimates supported the monophyly of all extant Xiphorhynchus species to the exclusion of the sibling species pair Straight-billed (X. picus) and Zimmer's (X. kienerii) woodcreeper. Confirming findings of previous molecular and anatomical studies, strong support was found to include the Lesser Woodcreeper (Lepidocolaptes fuscus )i nXiphorhyn- chus. Levels of sequence divergence among some subspecies of Buff-throated (X. guttatus), Ocellated (X. ocellatus), and Spix's (X. spixii) woodcreepers reached or exceeded those found between closely related, undisputed biological species of Xiphorhynchus. High levels of se- quence differentiation and the paraphyly of some Xiphorhynchus species indicated that the following taxa should be recognized as species: Lafresnaye's (X. guttatoides), Tschudi's (X. chunchotambo), and Elegant (X. elegans) woodcreepers. All Xiphorhynchus species restricted to terra-firme forest in lowland Amazonia formed a well supported monophyletic group, whereas species restricted to varzea forest were either basal to a clade containing species found in a wide variety of habitats (Striped Woodcreeper (X. obsoletus)) or belonged to a distinct lineage likely to be regarded as a separate genus (X. kienerii). These findings falsified an anticipated sister relationship between varzea and terra-firme species, as expected if the varzea-terra-firme ecotone had played a decisive role in population differentiation and spe- ciation within Xiphorhynchus. Instead, phylogeny estimates suggested that the varzea-terra- firme habitat specialization evolved early on in the evolutionary history of Xiphorhynchus and that subsequent differentiation occurred mostly within the terra-firme habitat. Received 15 June 2001, accepted 16 April 2002. RESUMEN.—Se reconstruyola filogenia de todas las especies conocidas y de muchas de las subespecies de Xiphorhynchus (Dendrocolaptidae) para evaluar los limites de las especies en este genero taxonomicamente complejo y para investigar el rol del ecotono entre ''varzea'' (bosque de inundacion) y ''terra-firme'' (bosque de tierras altas) del Amazonas en su diver- sificacion. Las filogenias fueron inferidas a partir de 2,430 pares de bases de los genes de ADN mitocondrial ND2, ND3 y citocromo b. Todas las estimaciones filogeneticas avalaron la monofilia de todas las especies vivientes de Xiphorhynchus, con excepcion del par de es- pecies hermanas X. picus y X. kienerii. Se encontrofuerte respaldo para incluir a Lepidocolaptes fuscus en Xiphorhynchus, confirmando estudios moleculares y anatomicos previos. Los ni- veles de divergencia en las secuencias entre algunas subespecies de X. guttatus, X. ocellatus y X. spixii alcanzaron o excedieron aquellos encontrados entre especies biologicas cercana- mente emparentadas de Xiphorhynchus. Los altos niveles de diferenciacion en las secuencias y la parafilia de algunas especies de Xiphorhynchus indicaron que los siguientes taxones de- berian ser reconocidos como especies: X. guttatoides, X. chunchotambo y X. elegans. Todas las especies de Xiphorhynchus restringidas a las areas de bosque de terra-firme de las tierras bajas del Amazonas formaron un grupo monofiletico fuertemente respaldado, mientras que las especies restringidas a bosques de varzea aparecieron en la base del clado que contenia a aquellas encontradas en una amplia variedad de habitats (X. obsoletus) o pertenecieron a un linaje separado que probablemente pueda ser considerado como un genero separado (X. kie-