Casey B. Dillman

Regressive progression, progressive regression or neither? Phylogeny and evolution of the Percopsiformes (Teleostei, Paracanthopterygii)

Dillman, C.B., Bergstrom, D.E., Noltie, D.B., Holtsford, T.P. & Mayden, R.L. (2010). Regressive progression, progressive regression or neither? Phylogeny and evolution of the Percopsiformes (Teleostei, Paracanthopterygii). —Zoologica Scripta, 40, 45–60.

A morphological supermatrix-based phylogeny for the Neotropical fish superfamily Anostomoidea (Ostariophysi: Characiformes): phylogeny, missing data and homoplasy

Although 11 studies have addressed the systematics of the four families and 281 fish species of the ecomorphologically diverse Anostomoidea, none has proposed a global hypothesis of relationships. We synthesized these studies to yield a supermatrix with 463 morphological characters among 174 ingroup species, and inferred phylogeny with parsimony and Bayesian optimization. We evaluated the applicability of the supermatrix approach to morphological datasets, tested its sensitivity to missing data, determined the impact of homoplastic characters on phylogenetic resolution, and determined the distribution of homologies and homoplasies on the topology. Despite more than 60% missing data, analyses supported the monophyly of all families, and phylogenetic structure degraded only with inclusion of species with high percentages of missing data and in analyses limited to homoplasies. The latter differs modestly from the full matrix indicating phylogenetic signal in homoplastic characters. Character distributions differ across the phylogeny, with a greater prevalence of homologies at deeper nodes and homoplasies nearer the tips than expected by chance. This may suggest early diversification into distinct bauplans with subsequent diversification of faster evolving character systems. The morphological supermatrix approach is powerful and allows integration of classical data with modern methods to examine the evolution of multiple character systems.

Genetic introgression of cultured rainbow trout in the Mexican native trout complex

Abstract The Mexican native trout complex is the group of salmonids that naturally has the southernmost distribution in the world. Despite its unique status and evidence of more than 13 distinct lineages, there are only two described species (Oncorhynchus mykiss nelsoni and O. chrysogaster). These fishes are threatened by environmental and anthropogenic factors, most notably the introduction of the exotic species O. mykiss (rainbow trout) for aquaculture. Here we applied population genetics analysis in 1,017 wild and cultured trout to understand the extent of genetic introgression of rainbow trout in Mexican native trout. Present results indicate a high degree of introgression and genetic admixture among introduced rainbow trout and some populations of Mexican native trout, exposing them to loss of genetic diversity. Thus, introduction of exotic trout for aquaculture purposes must be strictly regulated or avoided and we advise the use of native trout for aquaculture.

Anatomy and early development of the pectoral girdle, fin, and fin spine of sturgeons (Actinopterygii: Acipenseridae)

Acipenseriformes hold an important place in the evolutionary history of bony fishes. Given their phylogenetic position as extant basal Actinopterygii, it is generally held that a thorough understanding of their morphology will greatly contribute to the knowledge of the evolutionary history and the origin of diversity for the major osteichthyan clades. To this end, we examined comparative developmental series from the pectoral girdle in Acipenser fulvescens, A. medirostris, A. transmontanus, and Scaphirhynchus albus to document, describe, and compare ontogenetic and allometric differences in the pectoral girdle. We find, not surprisingly, broad congruence between taxa in the basic pattern of development of the dermal and chondral elements of the pectoral girdle. However, we also find clear differences in the details of structure and development among the species examined in the dermal elements, including the clavicle, cleithrum, supracleithrum, posttemporal, and pectoral‐fin spine. We also find differences in the internal fin elements such as the distal radials as well as in the number of fin rays and their association with the propterygium. Further, there are clear ontogenetic differences during development of the dermal and chondral elements in these species and allometric variation in the pectoral‐fin spine. The characters highlighted provide a suite of elements for further examination in studies of the phylogeny of sturgeons. Determining the distribution of these characters in other sturgeons may aid in further resolution of phylogenetic relationships, and these data highlight the role that ontogenetic and comparative developmental studies provide in systematics. J. Morphol. 276:241–260, 2015.

Occurrence of Juvenile Paralichthys lethostigma (Southern Flounder) in Tributaries of Chesapeake Bay

Abstract Paralichthys lethostigma (Southern Flounder) inhabits the continental shelf and estuarine waters of the Gulf of Mexico and the east coast of the North Atlantic, from peninsular Florida to Albemarle Sound in North Carolina. Between 30 May and 20 August 2012, we collected 15 juvenile (71–192 mm) Southern Flounder in fyke nets in the Mattaponi River, a tributary of the York River, in southeastern Virginia. This is the first known documentation of juvenile Southern Flounder in any tributary of Chesapeake Bay. We confirmed our identification of the specimens as Southern Flounder morphologically and genetically by counting gill rakers and sequencing cytochrome oxidase subunit I, respectively.

Identity of a Unique Cartilage in the Buccal Cavity of Gars (Neopterygii: Lepisosteiformes: Lepisosteidae)

The lower jaw of Lepisosteus osseus has been described as containing a U-shaped cartilaginous structure identified as a detached portion of Meckels cartilage. We investigated this structure through study of a growth series of L. osseus, including cleared-and-stained specimens and histological preparations. Meckels cartilage is well developed by 17.2 mm SL, and is formed by typical hyaline cartilage. The left and right Meckels cartilage are continuous across the anterior midline in most small specimens (<35 mm SL), although the robustness of this continuity is variable and in some specimens the two sides are separate. In larger individuals (>85 mm SL) the left and right sides are separate from one another and end far posterior to the tip of the dentaries. In specimens between 17.6–22.1 mm SL, there is a diffuse, V-shaped patch of connective tissue between the rami of the lower jaws. By 35 mm SL this patch becomes more consolidated and in histological sections of a 44.6 mm SL specimen, it is revealed to contain chondrocytes. In even larger individuals, this becomes a well-defined U-shaped structure. Because both this structure and a Meckels cartilage that crosses the anterior midline are present in the same individuals, we conclude that this cartilage is not homologous to the anterior portion of Meckels cartilage (i.e., it fails the test of conjunction) but is rather a neomorphic structure, herein termed the rostrohyal.

Molecular phylogenetics of Neotropical detritivorous fishes of the family Curimatidae (Teleostei: Characiformes)

Curimatidae, the fourth largest family of detritivorous Neotropical characiform fishes, encompasses eight extant genera and over 110 species dwelling in diverse freshwater habitats from Costa Rica to Argentina. Extensive phylogenetic analyses of soft anatomy and osteology provided evidence for intergeneric and most interspecific relationships, and formed the basis of curimatid taxonomy for nearly 40 years. However, that morphological phylogeny demonstrated incomplete phylogenetic resolution at various scales and has never been tested with extensive molecular data. Herein, we infer molecular phylogenies spanning ∼70% of the known species diversity using three nuclear and three mitochondrial loci. Topologies from concatenated likelihood and Bayesian analyses and coalescent Bayesian species trees agree broadly with each other, and with the prior morphological hypothesis in many, but not all respects. All molecular analyses support the monophyly of Curimatidae and of six of its constituent genera, and agree on the placement of Curimatopsis as sister to all other curimatids. DNA-based intergeneric relationships differ substantially from prior morphological hypotheses by placing Curimata sister to Potamorhina and Psectrogaster sister to Pseudocurimata, rather than in a ladderized arrangement. Our results also resolve a major uncertainty in the morphological tree by revealing Cyphocharax, a genus for which no anatomical synapomorphy has ever been proposed, as a paraphyletic assemblage containing a monophyletic Steindachnerina and a polyphyletic Curimatella. Overall, the phylogeny expands substantially our understanding of the morphology, phylogenetics and evolution of the Curimatidae, and will guide future intrageneric studies by improving precision in the choice of comparative taxa.