Biology subjects

Armbruster, J. W.

Publications and source records attributed to Armbruster, J. W..

3 recordsLinked to original sources

bioRxiv2026

Ecological axes of skull diversification in a massive 1 vertebrate radiation

Eupercarian spiny-rayed fishes are one of the largest vertebrate radiations, rivaling mammals and occupying nearly every aquatic habitat. We present a densely sampled, time-calibrated phylogenomic framework for Eupercaria, supporting a revised classification, combined with the largest cranial phenomics dataset for fishes. Habitat and trophic ecology make independent, complementary contributions to skull shape. Most species cluster around a conserved generalized architecture, the Percomorph Pile, from which one clade of pufferfishes, anglerfishes, butterflyfishes, and surgeonfishes repeatedly invaded novel morphospace; exceptionally high rates on its deep branches indicate that rapid skull evolution arose early in this clade. Freshwater lineages converge on the ancestral condition, reflecting late arrival into systems occupied by older otophysans, whereas durophages show the greatest disparity and converge on derived forms. Cranial diversity was partitioned among subclades during the Cretaceous and later within them across the Cenozoic, showing that clade-level differences in evolutionary rates and ecological opportunity jointly shaped skull diversification.

evolutionary biology↗

bioRxiv2026

Competition among freshwater clades explains cave colonization in blind cavefishes

Flatfishes display the most dramatic asymmetric body plan in vertebrates, yet whether this rare innovation evolved once (flatfish monophyly, FM) or multiple times (flatfish polyphyly, FP) has remained contentious. A recent genome-wide study supported FP by placing Psettodes, the earliest-diverging flatfish lineage, among symmetric relatives within Carangaria, the clade that also includes billfishes, jacks, mahi-mahi, and barracudas. Subsequent work traced this to base-composition artifacts and inadequate substitution modeling. Here we revisit the question using whole-genome phylogenomic and synteny data from 17 carangarian species spanning flatfishes and carangarian relatives. We contribute three new chromosome-level assemblies, including the first for Psettodes. Nucleotide-based coalescent analyses (e.g., ROADIES, CASTER) yield strong support for FM, with Psettodes sister to all other flatfishes. Microsynteny analyses built from conserved gene-order blocks corroborate this result: topology tests, cluster-profile counts, and rearrangement-based trees favor FM over two competing FP topologies. Macrosynteny, based on chromosome-scale rearrangements, yields a more mixed signal, with support for FM depending on the metric and taxon-sampling scheme. We interpret this scale-dependent pattern in the context of the explosive post-Cretaceous radiation of Carangaria. The short intervals between speciation events that characterize rapid radiations appear to have left sufficient signal in fine-grained microsyntenic rearrangements, while chromosome-scale rearrangements were too rare to consistently resolve these closely spaced splits. When integrated with evidence from conserved developmental mechanisms active during metamorphosis, the stage at which flatfish asymmetry first emerges, and from the exceptionally complete fossil record, our multi-scale genomic evidence supports a single evolutionary origin of flatfish asymmetry.

evolutionary biology↗

bioRxiv2019

A Hotspot Atop: Rivers of the Guyana Highlands Hold High Diversity of Endemic Pencil Catfish

AimThe Pakaraima Mountains are an ancient mountain range along the borders of Guyana, Brazil, and Venezuela. The high plateau is drained by multiple river systems in all directions. Although hypotheses have been presented for the biogeographic relationships of lowland rivers, the interconnectivity of rivers on the top of the plateau is unknown. With multiple complex rivers in a small, upland area we predicted a high level of endemism for stream fishes and complex biogeographic relationships. We explore this with the incredibly diverse pencil catfish genus Trichomycterus. Only two species are known from the region. In this study, we 1) confirm the discovery of multiple endemic Trichomycterus species in the region, 2) determine the phylogenetic placement of our samples to posit biogeographical scenarios, and 3) provide clarification for the identification of T. guianensis based on morphology.\n\nLocationPakaraima Mountains, a part of the Guiana Shield in Guyana, South America\n\nTaxonPencil catfish genus Trichomycterus\n\nMethodsUsing collections from recent expeditions to the Pakaraima Mountains of Guyana, we amplified three mitochondrial (16S, COI, and cytb) and two nuclear markers (myh6 and RAG2). We constructed individual gene trees as well as a concatenated tree to determine the placement of these taxa within the Trichomycterus of the Trans-andean/Amazonian clade.\n\nResultsOur results identify six unique lineages in the highlands of Guyana. Only two species, Trichomycterus guianensis and T. conradi, were previously known to science.\n\nMain ConclusionsThe Pakaraima Mountains of South America are a region of high endemism, as demonstrated here in Trichomycterus catfishes. We find two species occupying multiple basins, suggesting that Pakaraima streams either maintain or had some degree of recent connectivity. We identify six endemic lineages of Trichomycterus from the highlands of the Pakaraima Mountains. The upper portions of the study rivers have been connected either through surface flow or by stream capture. Both processes have occurred on multiple time scales and are independent of the patterns seen in the lowlands.

zoology↗