The Fitzcarrald Arch: A Vicariant Event for Chaetostoma (Siluriformes: Loricariidae) Speciation?
The genus Chaetostoma is a species-rich group of armored catfishes that inhabits rivers and streams in montane forests of South America. Most species of Chaetostoma have been described based on only one or a few specimens from a single river system. Our aim was to determine if the lifting of the Fitzcarrald Arch, 4 Ma, triggered speciation between the disjunct populations of Chaetostoma lineopunctatum in two isolated river drainages: the Río Ucayali and the Río Madre de Dios. We addressed this question by quantifying morphological and molecular divergence among samples of C. lineopunctatum from four river systems, three of which drain into the Río Ucayali drainage, including the type locality for the species, and one river system which drains into the Río Madre de Dios drainage. Morphological divergence, based on measurements, was statistically significant in the MANOVAs for the samples grouped by locality (P < 0.025) and by river system (P < 0.025). However, neighbor-joining trees of specimens grouped by locality (based on Mahalanobis distances) did not show group patterns according to river system. Morphologically, the specimens can be discriminated by river system with up to 88.7% confidence based on size-free discriminant analysis. Furthermore, the divergence values among haplotypes from the Río Ucayali and the Río Madre de Dios drainages, based on partial cytochrome b sequences (801 bp), ranged from 1.1% to 1.5%, which overlaps the 1.2% divergence between haplotypes from the Río Ucayali drainage. Based on the available morphological and molecular data, we conclude that there are not significant differences among populations of C. lineopunctatum from the Río Ucayali and the Río Madre de Dios drainages, and thus the Fitzcarrald Arch uplift did not cause speciation in this taxon. Alternatively, we suggest that isochronous tectonic events prior to the uplift of the Fitzcarrald Arch could have triggered genetic isolation of populations of C. lineopunctatum.Abstract
Map of Peru showing localities from where specimens of Chaetostoma lineopunctatum included in the present study were collected. Open symbols, specimens with no associated tissue samples; solid symbols, specimens with associated tissue samples. Type locality (star); Río Pachitea system (squares); Río Tambo system (diamonds); Río Urubamba system (circles); and Río Inambari system (triangles).
Landmarks for morphometric analysis. (A) Lateral view: 1, anterior tip of the mesethmoid; 2, posterior margin of bony nostril; 3, anterior margin of bony orbit; 4, posterior margin of bony orbit; 5, posterior tip of supraoccipital; 6, anterior margin of first dorsal-fin ray at base; 7, tip of first dorsal-fin ray; 8, posterior margin of last dorsal- fin ray at dorsal-fin base; 9, tip of last dorsal-fin ray; 10, posterior margin of preadipose plate; 11, tip of adipose spine; 12, anterior margin of last dorsal procurrent ray; 13, posterior margin of the last median lateral plate; 14, posterior margin of last anal-fin ray at base. (B) Dorsal view: 15, medial margin of bony nostril; 16, medial margin of bony orbit; 17, lateral margin of exposed cleithrum. (C) Ventral view: 18, medial margin of premaxilla; 19, lateral margin of premaxilla; 20, medial margin of dentary; 21, lateral margin of dentary; 22, medial edge of branchial opening; 23, anterior margin of pectoral spine at base; 24, bony tip of pectoral spine; 25, anterior margin of first pelvic-fin ray; 26, tip of first pelvic-fin ray; 27, base of urogenital papilla; 28, anterior margin of first anal-fin ray at base; 29, anterior margin of last ventral procurrent ray.
Neighbor-joining tree based on Mahalanobis distance values of size-free data for specimens of Chaetostoma lineopunctatum from eight localities in four river systems.
Plots of scores for the first two discriminant functions for size-free data (SF-DF1 vs. SF-DF2) for specimens of Chaetostoma lineopunctatum grouped by (A) locality and (B) system.
Haplotype network of cytochrome b sequences from specimens of Chaetostoma lineopunctatum collected from three river systems in central and southeastern Peru. Nodes sizes are proportional to haplotype frequency.
Maximum likelihood tree based on cytochrome b sequences from specimens of Chaetostoma lineopunctatum from three river systems in central and southeastern Peru. Lnl = −1192.8221; Ti/tv ratio = 17.1371; ΠA = 0.2995; ΠC = 0.2796; ΠG = 0.1288; ΠT = 0.2921; Pinv = 0; equal rates for all sites. Numbers on branches denote bootstrap values. Bootstrap values are only shown when ≥50%.
Contributor Notes
Associate Editor: R. E. Reis.