Caleb D. McMahan

Field Museum of Natural History · Zoology

Dedicated ichthyological surveys in two karstic caves in Costa Rica resulted in the discovery of hypogean populations from three epigean species of catfishes of the genus Rhamdia. The taxonomic identity of these populations was initially determined based on morphological traits and subsequently corroborated with comparative DNA sequence data in a p...

The application of environmental DNA (eDNA) methods to simultaneously study vertebrate diversity holds promise to accelerate conservation efforts, especially in freshwater systems which are among the most imperiled in the world. Here, using eDNA sampling, we identify patterns of vertebrate biodiversity across different habitats of the Kankakee Rive...

Phylogenetic analyses of mitochondrial and nuclear data of 31 specimens of Cyphocharax from trans‐Andean rivers support the presence of one lineage of Cyphocharax aspilos in Lago Maracaibo and three cryptic lineages of Cyphocharax magdalenae: (1) Cauca‐Magdalena and Ranchería, (2) León and Atrato, and (3) Chucunaque‐Tuira, Santa María, and Chiriquí...

Darwin attributed the absence of species transitions in the fossil record to his hypothesis that speciation occurs within isolated habitat patches too geographically restricted to be captured by fossil sequences. Mayr's peripatric speciation model added that such speciation would be rapid, further explaining missing evidence of diversification. Ind...

Poeciliids (Cyprinodontiformes: Poeciliidae), commonly known as livebearers, are popular fishes in the aquarium trade (e.g., guppies, mollies, swordtails) that are widely distributed in the Americas, with 274 valid species in 27 genera. This group has undergone various taxonomic changes recently, spurred by investigations using traditional genetic...

In biogeography, vicariance and long-distance dispersal are often characterised as competing scenarios. However, they are related concepts, both relying on collective geological, ecological, and phylogenetic evidence. This is illustrated by freshwater fishes, which may immigrate to islands either when freshwater connections are temporarily present...

In biogeography, vicariance and long-distance dispersal are often characterised as competing scenarios. However, they are related concepts, both relying on collective geological, ecological, and phylogenetic evidence. This is illustrated by freshwater fishes, which may immigrate to islands either when freshwater connections are temporarily present...

Based on a combination of intensive literature review, electronic database searches, re-identification of museum specimens, and fieldwork, we provide an updated checklist of the continental fishes of Nicaragua. This checklist, systematically arranged at the ordinal and familial level, includes nomenclatural revisions, distributional information, co...

Natural history museums are vital repositories of specimens, samples and data that inform about the natural world; this Formal Comment revisits a Perspective that advocated for the adoption of compassionate collection practices, querying whether it will ever be possible to completely do away with whole animal specimen collection.

Rocio is a small genus of Neotropical freshwater fishes that is distributed in Atlantic drainages of northern Middle America. Two species of Rocio , R. spinosissima and R . octofasciata, exhibit sympatry in the Río Dulce basin in eastern Guatemala. Rocio spinosissima is endemic to the Río Dulce basin, while R . octofasciata has a larger geographic...

A variety of hierarchical gene flow models have been proposed to explain the distribution of genetic variation in aquatic environments. These models, including the Stream Hierarchy (SH), Death Valley (DV), Headwater (HW), and Widespread Gene flow (WG) models, provide test-able hypotheses that focus on the degree of within-basin or within-stream net...

A variety of hierarchical gene flow models have been proposed to explain the distribution of genetic variation in aquatic environments. These models, including the Stream Hierarchy (SH), Death Valley (DV), Headwater (HW), and Widespread Gene flow (WG) models, provide test-able hypotheses that focus on the degree of within-basin or within-stream net...

Se fotografiaron especímenes recolectados hace más de 46 años en El Salvador, que se encuentran en la colección de peces dulceacuícolas del Museo Field de Chicago, EUA; para estudiar sus condiciones y comparar su distribución geográfica con información actual. Los datos sobre especímenes de las familias Ariidae y Atherinidae, después de 45 años ind...

Hyphessobrycon is one of the most species rich and widely distributed genera in the family Characidae, with more than 160 species ranging from Veracruz, Mexico to Mar Chiquita Lagoon in Buenos Aires, Argentina. The majority of Hyphessobrycon diversity shows a cis-Andean distribution; only nine species are trans-Andean including H. compressus (Meek...

Northern Middle America (NoMA) is considered a transition zone between the Nearctic and Neotropical biogeographic realms. In this region, Nearctic and Neotropical freshwater fishes create regional faunas of mixed origin, but their general biogeographic patterns have not been quantified. To identify such patterns, we delineate biogeographic regions...

Central America contains a rich diversity of freshwater habitats that support more than 600 species of freshwater fishes. However, despite several perceived threats to the integrity of the freshwater habitats throughout the region, a formal analysis of extinction risk for the region’s ichthyofauna is lacking. In this manuscript, we report an update...

Central America contains a rich diversity of freshwater habitats that support more than 600 species of freshwater fishes. However, despite several perceived threats to the integrity of the freshwater habitats throughout the region, a formal analysis of extinction risk for the region’s ichthyofauna is lacking. In this manuscript, we report an update...

New records of Parascolopsis akatamae Miyamoto, McMahan, & Kaneko, 2020 are reported from India's southeast coast. Three specimens were collected in April 2021 on the Parangipettai coast, Tamil Nadu, India. We examined and compared morphometric and meristic characters of our specimens with published data from the holotype. The new India records exp...

For 175 years, an unremarkable bass, the Grape-eye Seabass (Hemilutjanus macrophthalmos), has been known from coastal waters in the Eastern Pacific. To date, its phylogenetic placement and classification have been ignored. A preliminary osteological examination of Hemilutjanus hinted that it may have affinities with the Acropomatiformes. To test th...

Hyphessobrycon is one of the most species rich and widely distributed genera in the family Characidae, with more than 160 species ranging from Veracruz, Mexico to Argentina. The majority of the diversity of Hyphessobrycon shows a cis -Andean distribution; only nine species are trans -Andean including H. compressus (Meek 1908). It is well establishe...

Body-shape variability may respond to the interaction between history and environment, particularly in species whose range includes known biogeographical barriers. Central America has traditionally been regarded to have functioned as a complete land-bridge connecting two continents since the Plio-Pleistocene and as an incomplete one since much earl...

Poeciliopsis (Cyprinodontiformes: Poeciliidae) is a genus comprised of 25 species of freshwater fishes. Several well-known taxonomic uncertainties exist within the genus, especially in relation to the taxonomic status of Poeciliopsis pleurospilus and P. gracilis. However, to date, no studies have been conducted to specifically address the taxonomic...

Multifunctionality is often framed as a core constraint of evolution, yet many evolutionary transitions involve traits taking on additional functions. Mouthbrooding, a form of parental care where offspring develop inside a parent's mouth, increases multifunctionality by adding a major function (reproduction) to a structure already serving other vit...

The Threadfin Shad (Dorosoma petenense) is a euryhaline fish species that is widely distributed across freshwater systems in the lowlands of the Nearctic and the northern Neotropics with a distributional break at the Easternmost portion of the Trans-Mexican volcanic belt (TMVB). This region has been recognized as a biogeographic barrier for D. pete...

Biological patterns across latitudinal gradients elucidate a number of striking natural clines from which numerous processes can be further explored. The trade‐off between reproduction and somatic maintenance and growth represents a suite of life‐history traits with variable energy allocation and potential latitudinal patterns. Specifically, male s...

Profundulus adani, new species, is described from the upper reaches of the Papaloapan River in the Mexican state of Oaxaca. The uniqueness of this new species is supported by morphological and molecular evidence. A combination of color patterns and counts separate P. adani, new species, from its congeners. Profundulus adani, new species, is disting...

Choosing among types of genomic markers to be used in a phylogenomic study can have a major influence on the cost, design, and results of a study. Yet few attempts have been made to compare categories of next-generation sequence markers limiting our ability to compare the suitability of these different genomic fragment types. Here we explore proper...

Diadromous fishes can exhibit interesting evolutionary and population‐level patterns given their use of freshwater and marine environments as part of their life histories. The River goby genus Awaous are prominent members of riverine ichthyofaunas and occur throughout Atlantic and Pacific slopes of the Americas from the southern United States to Ec...

Introduction: The Cyprinodontiformes are a group of secondary freshwater fishes widely distributed in El Salvador. Currently, many species of this group are usually incorrectly identified for lack of adequate tools. Additionally, their taxonomy and distribution have changed in recent years. Objective: To provide updated information about the taxon...

Plastic is pervasive in modern economies and ecosystems. Freshwater fish ingest microplastics (i.e., particles <5 mm), but no studies have examined historical patterns of their microplastic consumption. Measuring the patterns of microplastic pollution in the past is critical for predicting future trends and for understanding the relationship betwee...

A new species of dwarf monocle bream, Parascolopsis akatamae n. sp., is described from the Indo-West Pacific. The new species is distinguished from all other species of Parascolopsis in having 16–19 gill rakers on the first arch, length of forked part of caudal fin 5.8–6.5 times in standard length, eye diameter 1.3–1.8 times in length of the longes...

Here we report the first record of the Mayan cichlid, Mayaheros urophthalmus, occurring on an offshore island 70 km from the mainland, the most distant record from the mainland to date. Specimens were collected during several ichthyological surveys on the island of Guanaja, Honduras in November 2019. Mayan cichlids are euryhaline fishes that perfor...

Aim The processes that generate biodiversity occur at finer scales than are often studied, particularly in freshwater systems of the northern Neotropics. We investigate whether fine‐scale biogeographic patterns are present within the larger Grijalva–Usumacinta Area of Endemism (AoE) —a region in Middle America where nearly 60% of freshwater fishes...

Despite their incredible diversity, relatively little work has been done to assess impacts of climate change on tropical freshwater organisms. Chortiheros wesseli is a species of Neotropical cichlid (Cichlidae: Cichlinae) restricted to only a few river drainages in the Caribbean-slope of Honduras. Little is known about this species and few specimen...

THE New Guinea Crocodile (Crocodylus novaeguineae) is a freshwater species of crocodilian endemic to the island of New Guinea in northern Oceania. The species inhabits both the country of Papua New Guinea in the east and Indonesian West Papua. Crocodylus novaeguineae occurs on both the northern and southern side of the Central Highlands, which span...

Pacific and Atlantic-slope rivers of the Isthmus of Tehuantepec in Mexico contain two cichlid species of the genus Vieja relevant to the current study, V. zonata and V. coatlicue, respectively. The Atlantic-slope species was initially considered a population of uncertain taxonomic status and recently described as a distinct species based on three p...

The Middle American killifish genus Profundulus occurs in most Pacific and Atlantic drainages from the Mexican state of Guerrero to the Chamelecón River in Honduras, with highest species diversity in southern Mexico. In this study, we describe a new member of the genus, Profundulus parentiae, new species, from the Mexican state of Oaxaca. It is dis...

Trichomycterus striatus is herein redescribed, based on examination of the types and recently collected specimens, and its geographic distribution is updated. This species can be diagnosed from all other northeastern South American congeners by its variable coloration pattern consisting of a yellowish to light brown background with a black lateral...

Astyanax anai, a new species of characid fish, is described from the Sixaola River basin, eastern Costa Rica–western Panama, Central America. The new species can be distinguished from all other congeners by the following combination of characters: premaxillary teeth 4–5 at the inner series and 4–6 at the outer series; maxillary teeth tricuspid, 2–4...

We documented the first record of the non-native species Piaractus brachypomus (Characiformes: Serrasalmidae) in Lago Petén-Itzá, Petén, Guatemala. One brined specimen was donated by a local fisherman in San Benito, El Petén. The captured specimen was reportedly collected in the southern basin of the lake. We used the mitochondrial gene cytochrome...

Vieja hartwegi was described by Taylor and Miller in 1980 based on 45 juvenile and sub-adult specimens, but this species shows an enormous variation in coloration patterns during ontogenic development and between individuals. Additionally, morphological data have demonstrated the existence of two forms in V. hartwegi: the typical morph of a moderat...

Population-level morphometric variation of the Mountain Mullet (Agonostomus monticola) was assessed in 419 adult specimens from 25 sample sites (river basins) across its Middle American distribution (Pacific and Atlantic-Caribbean drainages). This analysis was based on 36 standardized linear measurements and 19 landmarks on geometric morphometrics...

The distributions of many Northern Hemisphere organisms have been influenced by fluctuations in sea level and climatic conditions during Pleistocene interglacial periods. These cycles are associated with range contraction and refugia for northern-distributed organisms as a response to glaciers. However, lower sea levels in the tropics and sub-tropi...

Geographic coordinate data. Latitude and longitude data for collection localities for Vieja maculicauda. (XLS)

Ostariophysi is a superorder of bony fishes including more than 10,300 species in 1100 genera and 70 families. This superorder is traditionally divided into five major groups (orders): Gonorynchiformes (milkfishes and sandfishes), Cypriniformes (carps and minnows), Characiformes (tetras and their allies), Siluriformes (catfishes), and Gymnotiformes...

Vieja melanura is a Neotropical cichlid occurring in the Petén-lake district systems of Guatemala, as well as the Río Grijalva-Usumacinta basin, and other systems in Southern México, Belize, and Guatemala. A caudal stripe, extending forward from the caudal peduncle, is characteristic of this species. This stripe is sloped downward in nearly all ind...

Winnowing is a foraging strategy common in geophagine cichlids (Cichlidae), in which sediment is sifted for food in the oral cavity. Geophagines have modified pharyngeal structures that function in winnowing, although detailed anatomical and functional information is still needed to clarify the mechanisms by which these fishes obtain food by siftin...

The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009;...

This plot is not part of the published stance but derives from it. The plot shows the number of authors by geographic region (courtesy of Dr. Diego Astua).

We investigate phylogeographic patterns and delimit species boundaries within Amatitlania, a genus of CentralAmerican cichlid fishes. Phylogenetic analyses of mitochondrial DNA sequences from 318 individuals spanningthe geographical ranges of all three currently recognized Amatitlania species strongly supported one major clade,with a relatively dive...

Profundulus balsanus was described by Ahl in 1935 and later placed in synonymy with P. punctatus. Recent molecular studies have demonstrated that specimens identified as P. balsanus belong to a distinct taxon. Herein we used a combination of morphometric, meristic, coloration and osteological data in order to demonstrate the distinctiveness of P. b...

Two species and one subspecies of the genus Osteochilus (Cypriniformes: Cyprinidae) were described from Borneo in a revision of the group by Karnasuta in 1993. Examination of type material has illuminated points of conflict regarding some of the type specimens listed in original descriptions. Based on archived correspondence and the author's origin...

Incongruence between morphological and molecular-based phylogenetic hypotheses has been reported across a wide range of taxa. Specifically, morphological and molecular hypotheses of squamate phylogeny have been consistently incongruent and have been notoriously difficult to reconcile. With the ever-rising popular view of the superiority of molecula...

In recent years great strides have been made for improving our understanding of the evolutionary relationships among neo-tropical cichlids, particularly within the clade Heroini and its crown clade the herichthyins. Most phylogenetic studies have largely converged on congruent topologies for relationships among species and major lineages within the...

As part of a revision of the cichlid genus Archocentrus, a new genus, Amatitlania, was erected comprising four species: A. nigrofasciata (the type species), A. siquia, A. kanna, and A. coatepeque. Amatitlania coatepeque is an endemic and an eponym of Lago Coatepeque in the interior highlands of western El Salvador. This species was diagnosed by a Y...

Recent interest in diagnoses and relationships between lineages of the alligator snapping turtle (Macrochelys temminckii) present conflicting patterns of molecular variation across the taxon's range. This study uses geometric morphometric techniques to test molecular hypotheses. We analyse alligator snapping turtle cranial variation amongst populat...

Although attempts to understand Central American freshwater fish provincialism date to the 1960s, early efforts lacked the wealth of distributional data now available. Biogeographic work on Central American freshwater fishes has been largely descriptive and regional, and lacked a broader synthesis. Here we use parsimony analysis of endemicity (PAE)...

Due to recent population declines in tropical gar (Atractosteus tropicus), a greater understanding of its population structure is needed. A key step in gaining this understanding is the development of microsatellite loci for use in this species. For this purpose, 33 microsatellite loci from alligator gar (A. spatula) were screened in 52 individuals...

The contrasting distribution of species diversity across the major lineages of cichlids makes them an ideal group for investigating macroevolutionary processes. In this study, we investigate whether different rates of diversification may explain the disparity in species richness across cichlid lineages globally. We present the most taxonomically ro...

Strict consensus of seven most parsimonious trees (16549 steps, CI: 0.30, RI: 0.35) resolved for the 54-taxon cichline phylogeny that includes all 51 extant terminals, † Plesioheros, and both species of † Tremembichthys . (PDF)

List of cichlid taxa used in supplemental cichlid phylogenetic analysis. (PDF)