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Aphrastura subantarctica Rozzi, Quilodrán, Botero-Delgadillo, Crego, Napolitano, Barroso, Torres-Mura & Vásquez, in Rozzi, Quilodrán, Botero-Delgadillo, Napolitano, ... et Vásquez, 2022 Illustrations by Mauricio Alvarez Abel. Images by Omar Barroso. |
Abstract
We describe a new taxon of terrestrial bird of the genus Aphrastura (rayaditos) inhabiting the Diego Ramírez Archipelago, the southernmost point of the American continent. This archipelago is geographically isolated and lacks terrestrial mammalian predators as well as woody plants, providing a contrasted habitat to the forests inhabited by the other two Aphrastura spp. Individuals of Diego Ramírez differ morphologically from Aphrastura spinicauda, the taxonomic group they were originally attributed to, by their larger beaks, longer tarsi, shorter tails, and larger body mass. These birds move at shorter distances from ground level, and instead of nesting in cavities in trees, they breed in cavities in the ground, reflecting different life-histories. Both taxa are genetically differentiated based on mitochondrial and autosomal markers, with no evidence of current gene flow. Although further research is required to define how far divergence has proceeded along the speciation continuum, we propose A. subantarctica as a new taxonomic unit, given its unique morphological, genetic, and behavioral attributes in a non-forested habitat. The discovery of this endemic passerine highlights the need to monitor and conserve this still-pristine archipelago devoid of exotic species, which is now protected by the recently created Diego Ramírez Islands-Drake Passage Marine Park.
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| Study areas for the morphological and genetic characterization of Aphrastura spinicauda and A. subantarctica. The distribution range of the nominal species is shown in light green, and the new taxonomic group from the Diego Ramírez Archipelago in light blue. (A) Sampling sites for morphology. (B) Sampling sites for mtDNA. (C) Sampling sites for microsatellite markers. The numbers correspond to the sample size. The names of the colored sites follow the methods description, and Tables 1 and 2. Bird illustrations by Mauricio Alvarez Abel. |
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| Habitat characteristics and individual appearance of two populations of Aphrastura. (A) Forest habitat on Navarino Island. (B) An individual of the thorn-tailed rayadito (Aphrastura spinicauda) from Navarino Island. (C) Tussock (Poa flabellata) habitat on Gonzalo Island, Diego Ramírez Archipelago, with a mist net. (D,E) Individuals of the proposed new species Aphrastura subantarctica from Gonzalo Island. Images by Omar Barroso. |
Order: Passeriformes (Linnaeus, 1758)
Family: Furnariidae (Gray, 1840)
Genus: Aphrastura (Oberholser, 1899)
Aphrastura subantarctica, sp. nov. R Rozzi, CS Quilodrán, E Botero-Delgadillo, RD Crego, C Napolitano, O Barroso, JC Torres-Mura & RA Vásquez.
Common name (English): Subantarctic Rayadito.
Common name (Spanish): Rayadito Subantártico.
Diagnosis: Morphology.—Typical Aphrastura structure with rounded wings, and an idiosyncratic tail morphology. Aphrastura’s distal third of the inner web of the rectrices is abruptly and deeply excised, giving the tips of the feathers a thornlike appearance. No other genus in the family has a similar tail structure. Aphrastura differs in these morphological characters from the phylogenetically closest related genera in the subfamily Synallaxinae present in southwestern South America: Leptasthenura and Sylviorthorhynchus. In contrast to Aphrastura, Leptasthenura’s tail is not abruptly and deeply excised at the distal portion of the inner web of the rectrices; in Sylviorthorhynchus, the rectrices are denuded of barbs1. A. subantarctica differs from A. spinicauda, in having on average a larger and heavier body (~ 25%), a larger beak (~ 15%), a larger tarsus (~ 5%), and a shorter tail (~ 16%) (Fig. 3; Supplementary Information Appendix 5 and 6). The primaries and secondaries are greyish on the ventral side with whitish edges; the central rectrices are dark grey on the ventral side, but do not differ between the two species. Color terms using Munsell Color’s52 notation are shown in Appendix 7 (Supplementary Information).
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Concluding remarks:
We propose A. subantartica as a new species. The genetic, morphological, and ecological divergence of this population, which may have resulted from isolation on an island with a distinct habitat, is probably an ongoing evolutionary process. Because of the small size of the Diego Ramírez islands and the potential arrival of exotic mammal predators, it is pressing to protect this new endemic species from extinction. The Diego Ramírez Archipelago encompasses the southernmost extreme islands of the American continent and is free of invasive alien species. Measures should be put into place to keep exotic mammals, such as rats (Rattus rattus), domestic cats (Felis catus), and American minks (Neovison vison)–which are all present on other islands of the Cape Horn Biosphere Reserve–off the Diego Ramírez islands. In particular, the rapid expansion of the American mink has impacted bird populations on other subantarctic islands that have evolved in the absence of terrestrial mammal predators. Collaboration between the scientific community and other institutions, in particular the Chilean Navy, which has been regularly present on this archipelago since the establishment of the lighthouse on Gonzalo island in 1951, is critical for the success of scientific long-term monitoring and conservation programs. In 2019, the Diego Ramírez-Drake Passage Marine Park was created by the Chilean government to protect one of the few archipelagos that is still free from the arrival of exotic species worldwide. The description of A. subantarctica is also an appeal to the community to protect not only a population of a new species, but also to protect a remote natural laboratory that represents an opportunity to preserve the diversity of nature and its ecological and evolutionary processes.
Ricardo Rozzi, Claudio S. Quilodrán, Esteban Botero-Delgadillo, Constanza Napolitano, Juan C. Torres-Mura, Omar Barroso, Ramiro D. Crego, Camila Bravo, Silvina Ippi, Verónica Quirici, Roy Mackenzie, Cristián G. Suazo, Juan Rivero-de-Aguilar, Bernard Goffinet, Bart Kempenaers, Elie Poulin and Rodrigo A. Vásquez. 2022. The Subantarctic Rayadito (Aphrastura subantarctica), A New Bird Species on the Southernmost Islands of the Americas. Scientific Reports. 12, 13957. DOI: 10.1038/s41598-022-17985-4
