Genetic, vocal, and body size divergence across the Northern Peruvian Low supports two species within the Masked Flowerpiercer (Diglossa cyanea)

Abstract

Populations that become genetically isolated by geographical barriers may express phenotypic divergence more strongly in some traits than in others. Even when genetic differentiation among isolated populations accumulates at a rapid rate, this may not be reflected in phenotypic differentiation. This decoupling of trait divergence from genetic divergence has been found in multiple Andean bird lineages that occupy latitudinally long, linear ranges that are fragmented by ecological and topographic barriers. One of these montane birds is Diglossa cyanea (Thraupidae; Masked Flowerpiercer), a species with a distribution bisected by valleys and lowlands. Across these dispersal barriers one finds subspecies that differ only in subtle but diagnostic phenotypic differences. We evaluated genetic and phenotypic divergence throughout its distribution and found support for two distinct lineages sharply separated by the Maranon River valley at the Northern Peruvian Low (NPL). Specifically, we found that the two populations from the opposite sides of the NPL show deep divergence in mitochondrial DNA (mtDNA; [~]6.7% uncorrected p distance, n = 122), in song structure (exclusive final notes in southern populations, n = 88), and in wing length (longer wings in the southern population, n = 364). No genetic variation or song structure was observed within the large range of the southern group (from the NPL to central Bolivia) or within all northern populations (from the NPL to Venezuela). Moreover, these two lineages are possibly paraphyletic with respect to D. caerulescens (Bluish Flowerpiercer). Our results suggest that the southern taxon, D. c. melanopis, should be recognized as a species-level taxon, distinct from a redefined D. cyanea. We highlight the need to continue amassing complementary suites of datasets from field observations and experiments, laboratory analyses, and collection-based assessments, to better characterize the evolutionary history and taxonomic diversity of Neotropical montane birds. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=184 SRC="FIGDIR/small/492535v2_ufig1.gif" ALT="Figure 1"> View larger version (69K): org.highwire.dtl.DTLVardef@199ddfborg.highwire.dtl.DTLVardef@bc8fb0org.highwire.dtl.DTLVardef@17d7da1org.highwire.dtl.DTLVardef@1c2d9e5_HPS_FORMAT_FIGEXP M_FIG C_FIG LAY SUMMARY We analyzed variation in genetics, songs, and body size among populations of a bird species of the Andean mountains (Masked Flowerpiercer) that shows relatively little plumage variation across its 3800-km long distribution from northern Venezuela to central Bolivia. We found that the Masked Flowerpiercer consists of two divergent populations separated by a deep geographic depression known as the Northern Peruvian Low (NPL) The degree of genetic divergence between them (in terms of mtDNA) is as great as between either of them and another species, the Bluish Flowerpiercer. The two populations also have distinct songs, with the song of the southern group ending with clear whistles that are completely absent in the northern group. The southern group also tend to have longer wings than do populations north of the NPL. The southern population should be treated as a separate species, Diglossa melanopis.