Co-occurrence of closely related taxa on islands could be attributed to sympatric speciation or multiple colonization. Sympatric speciation is considered to be rare in small islands, however multiple colonizations are known to be common in both oceanic and continental islands. In this study we investigated the phylogenetic relatedness and means of origin of the two sympatrically co-occurring Zosterops white-eyes, the endemic Zosterops ceylonensis and its widespread regional congener Z. palpebrosus, in the island of Sri Lanka. Sri Lanka is a continental island in the Indian continental shelf of the Northern Indian Ocean. Our multivariate morphometric analyses confirmed the phenotypic distinctness of the two species. Maximum Likelihood and Bayesian phylogenetic analyses with ~2000bp from two mitochondrial (ND2 and ND3) and one nuclear (TGF) gene indicated that they are phylogenetically distinct, and not sister to each other. The two subspecies of the peninsula India; Z. p. egregius of Sri Lanka and India and Z. p. nilgiriensis of Western Ghats (India) clustered within the Z. palpebrosus clade having a common ancestor. In contrast, the divergence of the endemic Z. ceylonensis appears to be much deeper and is basal to the other Zosterops white-eyes. Therefore we conclude that the two Zosterops species originated in the island through independent colonizations from different ancestral lineages, and not through island speciation or multiple colonization from the same continental ancestral population. Despite high endemism, Sri Lankan biodiversity is long considered to be a subset of southern India. This study on a speciose group with high dispersal ability and rapid diversification rate provide evidence for the contribution of multiple colonizations in shaping Sri Lanka’s biodiversity. It also highlights the complex biogeographic patterns of the South Asian region, reflected even in highly vagile groups such as birds.

Hybridization has challenged taxonomy, since hybridizing forms could be stable evolutionary entities or ephemeral forms that are blending together. The island of Sri Lanka has 2 subspecies of the flameback woodpecker D. benghalense: D. b. jaffnense in the north and D. b. psarodes in the south. Red plumage separates the endemic phenotype D. b. psarodes from other subspecies of D. benghalense. Despite these differences, intermediate phenotypes in north-central Sri Lanka discouraged the elevation of D. b. psarodes into a full species. The recent HBW and BirdLife International checklist, however, has elevated D. b. psarodes to a full species (D. psarodes), primarily based on its plumage. To objectively evaluate whether this taxonomic elevation is warranted, we examined the phenotypic and genetic affinities of D. psarodes within the D. benghalense cluster. In doing that we provide the first quantitative phenotypic and genetic analysis across a hybrid zone for an Old World woodpecker group. We sampled woodpeckers along a line transect across the island and measured body shape/size, plumage, and genetic variation in a mitochondrial gene (Cytb). Plumage color ranged from red in the south to yellow in the north, with varying proportions of orange in north-central Sri Lanka (an area of ~66 km). Morphology (body shape/size) and plumage characters showed a clear separation. There are 2 mitochondrial haplotype groups, one in the north and one in the south. A mixture of north and south haplotypes were seen in north-central Sri Lanka. Width of the hybrid zone suggests that some form of selection limits the spread of hybrids into the range of parental forms. Morphological, plumage, and genetic traits are all indicative of limited hybridization in a narrow zone between the 2 taxa, supporting the treatment of D. psarodes as a distinct species. This study provides an illustrative example of extensive hybridization between stable taxonomic entities, discouraging the practice of merging hybridizing forms as single species. La hibridación es desafiante para la taxonomía puesto que las formas que hibridan pueden ser entidades evolutivamente estables o formas efímeras que se están mezclando. La isla de Sri Lanka tiene dos subespecies de Dinopium benghalense; D. b. jaffnense en el norte y D. b. psarodes en el sur. El plumaje rojo separa el fenotipo endémico de D. b. psarodes del de otras subespecies de D. benghalense. A pesar de estas diferencias, la existencia de fenotipos intermedios en el centro-norte de Sri Lanka previno la elevación de D. b. psarodes al estatus de especie. Sin embargo, la lista más reciente del Handbook of Birds of the World y Birdlife International elevó a D. b. psarodes al rango de especie (D. psarodes) basándose principalmente en el plumaje. Para evaluar objetivamente si se justifica este cambio taxonómico, examinamos las afinidades genéticas y fenotípicas de D. psarodes en el grupo de D. benghalense. Al hacerlo, presentamos el primer análisis cuantitativo fenotípico y genético a través de una zona de hibridación de un carpintero del viejo mundo. Muestreamos carpinteros a lo largo de un transecto que atravesaba la isla y medimos el tamaño y la forma del cuerpo, el plumaje y la variación genética en un gen mitocondrial (Cytb). El color del plumaje varió de rojo en el sur a amarillo en el norte, con naranja en diferentes proporciones en el centro-norte de Sri Lanka (un área de ~66 km). Los caracteres morfológicos (tamaño y forma del cuerpo) y del plumaje mostraron una separación clara. Existen dos grupos de haplotipos mitocondriales, uno en el norte y otro en el sur. Se vio una mezcla de haplotipos del norte y del sur en el centro-norte de Sri Lanka. El ancho de la zona de hibridación sugiere que alguna forma de selección limita la dispersión de los híbridos hacia la zona de distribución de las formas parentales. Todos los rasgos morfológicos, genéticos y del plumaje indican que existe hibridación limitada entre los dos taxones en una zona estrecha, lo que apoya el estatus de especie de D. psarodes. Este estudio presenta un ejemplo ilustrativo de hibridación extensa entre entidades taxonómicas estables, lo que desaconseja la práctica de unir formas que hibridan en una sola especie. Palabras clave: Dinopium benghalense, endémicos de islas, especiación, hibridación, Sri Lanka, zona híbrida