Forpus, Boie, 1858

Smith, Brian Tilston, Thom, Gregory & Joseph, Leo, 2024, Revised Evolutionary And Taxonomic Synthesis For Parrots (Order: Psittaciformes) Guided By Phylogenomic Analysis, Bulletin of the American Museum of Natural History 2024 (468), pp. 1-87 : 23-24

Forpus

Brereton (1963) first published Forpini and Amoropsittacini diagnosed in symbols and let-

Forpus modestus LSUMZB 9635 Forpus cyanopygius UWBM 82383 Forpus crassirostris LSUMZB 7373 Forpus xanthopterygius LSUMZB 6612 Forpus spengeli AMNH 133024 Forpus passerinus LSUMZB 48518 Forpus conspicillatus AMNH 793356 Forpus xanthops FMNH 395954 Forpus coelestis LSUMZB 5221

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MILLION YEARS AGO MYA

FIGURE 4. Time-calibrated phylogeny of Forpini. Support values come from the maximum likelihood tree.

Nodes have ultrafast bootstrap values of ≥95% otherwise noted.

ters in a table with an accompanying legend explaining the meaning of the symbols and letters in words. Schodde et al. (2013) accepted this as validating the names. Sangster et al. (2023) nevertheless disputed it, claiming that Brereton’s descriptions did not conform to the requirements of the current edition of the International Code of Zoological Nomenclature ( ICZN, 1999), and replaced Brereton’s names with their own. Schodde et al. (submitted) have since applied to the International Commission on Zoological Nomenclature to conserve Forpini and Amoropsittacini as published by Brereton (1963). The details of these nomenclatural arguments are to be explained fully in that paper but hinge on due and fully appropriate detail having been given by Brereton (1963). Until this is settled, we consider Forpini and Amoropsittacini as valid family-group names.

The Forpini contains nine small, stockybodied, sexually dimorphic, and largely green species in the genus Forpus . Forpus is currently distributed from Mexico to Argentina, but the fossil record suggests that it occurred in the Bahamas up until at least the Late Pleistocene ( Steadman and Franklin, 2020). Recent molecular ( Smith et al., 2013) and morphological ( Bocalini and Silveira, 2015) data were used to elevate F. spengeli of northwest Colombia and F. crassirostris of western Amazonia to species rank. Bocalini and Silveria (2015) assessed phenotypic variation within F. xanthopterygius and synonymized the remaining taxa ( crassirostris , flavissimus, flavescens, and olallae) within monotypic F. xanthopterygius due to high morphological variation among localities and because plumage patterns did not conform to described subspecies limits. This finding has important implications for species limits in the genus and highlights the limits of using morphological data to assign taxonomic ranks. As recovered in previous work ( Smith et al., 2013), our phylogenomic tree had F. crassirostris as sister to a clade containing all other Forpus except F. modestus and F. cyanopygius . The timing of this divergence (approximately 3.8 Mya; fig 4) was similar to the age estimated using a small number of mtDNA and nuclear DNA loci ( Smith et al., 2013). This deep intraspecific divergence, which was not reflected in the high number of specimens examined by Bocalini and Silveria (2015), indicates that morphological evolution is not tracking population history and is thus not a reliable data source for species delimitation.

The opposite is true for F. passerinus . Forpus spengeli was originally treated at species rank until at least Cory (1918). To the best of our knowledge, it was then placed in F. passerinus by Peters (1937), without comment. At a later date, it was transferred to F. xanthopterygius ( Forshaw, 1973) . Smith et al. (2013) found that spengeli was nested within passerinus differing by only a few base pairs in mtDNA, whereas Bocalini and Silveria (2015) found spengeli to be distinct given its clearly diagnostic turquoise rump on males. They restored the taxon to species rank as F. spengeli . Bocalini and Silveria (2015) included F. passerinus in their study, but did not consider that F. spengeli could be a geographical variant within F. passerinus or, alternatively, its mtDNA may have been introgressed and/or captured by the nearest population of F. passerinus , i.e., F. passerinus cyanophanes . Forpus passerinus , which exhibits a wide variation in rump color in males, ranging from blue to green even with excluding F. spengeli . The molecular changes that result in a shift from a green to turquoise feather patch may be simple, as observed in captive Melopsittacus undulatus , in which a single base-pair change expresses tryptophan, blocking expression of yellow pigment, and so changes green feathers to blue ( Cooke et al., 2017). The identical mutation was also found to produce blue feathers in captive Agapornis ( Ke et al., 2024) , suggesting there may be a single genetic mechanism underlying the green to blue color shift in parrots. While the phylogenomic tree here strongly shows a deep divergence between F. passerinus and F. spengeli (fig. 4), caution is warranted when interpreting this divergence in light of previously characterized shallow mtDNA divergence. The phylogenomic tree is either reflecting discordance between nuclear and mtDNA, possibly due to mitochondrial introgression, or the branch length is artificially long due to the high number of singletons in phylogenomic data. Population-level sampling is necessary to distinguish these scenarios.