Kevin W. Conway

Spectacular morphological novelty in a miniature cyprinid fish, Danionella dracula n. sp.

Danionella dracula is a new species of sexually dimorphic, miniature and highly developmentally truncated cyprinid fish. Compared with its close relative, the zebrafish Danio rerio, it lacks 44 bones or parts thereof and represents one of the most developmentally truncated vertebrates. Absence of the majority of bones appears to be due to developmental truncation via terminal deletion. In contrast to these larval-like features, D. dracula also shows several hyperossifications. Uniquely, among carp-like fishes, male D. dracula have a series of long, pointed odontoid processes on the jaws greatly resembling the jaw dentition of teleosts with true teeth. The anterior-most process in each jaw is extended as a canine-like fang projecting through the epithelium. True jaw teeth are absent from all 3700 species of cypriniforms and were lost at least in the Upper Eocene. It remains to be investigated, however, whether the conserved pathways to regulate tooth development in cypriniforms have been used in D. dracula to form and pattern the odontoid processes. This new species represents a remarkable example linking progenetic paedomorphosis via heterochronic change in developmental timing to the evolution of morphological novelties.

Osteology of Paedocypris, a miniature and highly developmentally truncated fish (Teleostei: Ostariophysi: Cyprinidae).

Species of the cyprinid genus Paedocypris are among the smallest and most developmentally truncated fishes and vertebrates. Our analysis of their skeletal structure reveals a puzzling combination of extreme developmental truncation and an increased morphological complexity in sexually dimorphic characters. The skeleton of Paedocypris is characterized by reduction and loss and resembles in many aspects that of a larval/early juvenile stage of its close relatives. We found 61 characters that have been affected by developmental truncation. A comparison with the skeletal development of a close relative, the zebrafish Danio rerio, demonstrates that the majority of the absent bones or skeletal structures in Paedocypris are those that appear late in the ossification trajectory of the zebrafish. Thus, their absence in Paedocypris seems to be due to the simple developmental truncation of terminal stages in the ossification sequence. Our study of the sexually dimorphic structures in Paedocypris demonstrates that predominantly the male exhibits the more complex state. In relation to the female, male Paedocypris uniquely possess a cleithrum with a pointed posterior process that covers the scapula laterally, and a more medially situated posterior flange that contacts the dorsal area of the coracoid; a massive and heavily ossified uppermost pectoral radial tightly bound to the scapula; thickened and enlarged three uppermost pectoral‐fin rays; a large triangular, dorsolaterally directed process on the outer arm of the massive os suspensorium; and a enlarged and shovel‐like anterodorsally directed basipterygium; and a hypertrophied first pelvic‐fin ray with additional anterior flanges that support keratinized pads of skin. Female Paedocypris show only one structure that is better developed than in males: the first proximal‐middle radial and the anteriormost fin ray of the dorsal fin are more massive and more heavily ossified. Although the function and biological role of these dimorphisms is still unknown, we hypothesize that they are related to a special reproductive behavior. Paedocypris is a prime example for the recent claim that miniaturization among cyprinids is associated with evolutionary novelty only in developmentally truncated miniatures and not in proportioned dwarfs. Paedocypris offers a strong challenge to Schindleria as the most extreme example of developmental truncation known among fishes. We highlight the difficulties that developmentally truncated taxa frequently pose to the resolution of their phylogenetic position and propose an approach to overcome this problem. Our phylogenetic comparison to determine the systematic position of Paedocypris among cyprinids reveals that it shares not only a number of unique absences, but also highly unusual progressive characters with Sundadanio and Danionella, two other Asian miniature cyprinids. We hypothesize that the three genera form a monophyletic group. We further found that Paedocypris and Danionella share a number of uniquely derived characters pointing to a sister group relationship of the two. J. Morphol., 2009.

Inferring the Tree of Life of the order Cypriniformes, the earth's most diverse clade of freshwater fishes: Implications of varied taxon and character sampling

The phylogenetic relationships of species are fundamental to any biological investigation, including all evolutionary studies. Accurate inferences of sister group relationships provide the researcher with an historical framework within which the attributes or geographic origin of species (or supraspecific groups) evolved. Taken out of this phylogenetic context, interpretations of evolutionary processes or origins, geographic distributions, or speciation rates and mechanisms, are subject to nothing less than a biological experiment without controls. Cypriniformes is the most diverse clade of freshwater fishes with estimates of diversity of nearly 3,500 species. These fishes display an amazing array of morphological, ecological, behavioral, and geographic diversity and offer a tremendous opportunity to enhance our understanding of the biotic and abiotic factors associated with diversification and adaptation to environments. Given the nearly global distribution of these fishes, they serve as an important model group for a plethora of biological investigations, including indicator species for future cli- matic changes. The occurrence of the zebrafish, Danio rerio, in this order makes this clade a critical component in understanding and predicting the relationship between mutagenesis and phenotypic expressions in vertebrates, including humans. With the tremendous diversity in Cypriniformes, our understanding of their phylogenetic relationships has not proceeded at an acceptable rate, despite a plethora of morphological and more recent mo- lecular studies. Most studies are pre-Hennigian in origin or include relatively small numbers of taxa. Given that analyses of small numbers of taxa for molecular characters can be compromised by peculiarities of long-branch attraction and nodal-density effect, it is critical that significant progress in our understanding of the relationships of these important fishes occurs with increasing sampling of species to mitigate these potential problems. The recent Cypriniformes Tree of Life initiative is an effort to achieve this goal with morphological and molecular (mitochondrial and nuclear) data. In this early synthesis of our understanding of the phylogenetic relationships of these fishes, all types of data have contributed historically to improving our understanding, but not all analyses are complementary in taxon sampling, thus precluding direct understanding of the impact of taxon sampling on achieving accurate phylogenetic inferences. However, recent molecular studies do provide some insight and in some instances taxon sampling can be implicated as a variable that can influence sister group relationships. Other instances may also exist but without inclusion of more taxa for both mitochondrial and nuclear genes, one cannot distinguish between inferences being dictated by taxon sampling or the origins of the molecular data.

The Gill Arches of Psilorhynchus (Ostariophysi: Psilorhynchidae)

Abstract Members of the genus Psilorhynchus are small cypriniform fishes adapted for life in the fast flowing streams of the Ganga–Brahmaputra drainage of India and Eastern Nepal and the Ayeyarwady drainage of Northern Myanmar and adjacent China. The systematic placement of Psilorhynchus within existing cypriniform classification schemes has been controversial since the creation of this genus by McClelland in 1839. Over the last 150 years Psilorhynchus has been assigned to, and removed from, the Cyprinidae, Balitoridae, and Cobitidae at least once and has even been placed in its own family, Psilorhynchidae. In this paper we investigate the gill-arch osteology of two species of Psilorhynchus (P. sucatio and P. balitora) and compare their general features to those of a ‘typical’ member of the Cyprinidae. Additionally, we reassess the most recent testable phylogenetic analyses to include species of Psilorhynchus. We conclude based on evidence from gill-arch osteology that Psilorhynchus is more closely related to non-cyprinid cypriniforms than to members of the Cyprinidae.

Microanatomy of the paired-fin pads of ostariophysan fishes (Teleostei: Ostariophysi).

Members of the teleost superorder Ostariophysi dominate freshwater habitats on all continents except Antarctica and Australia. Obligate benthic and rheophilic taxa from four different orders of the Ostariophysi (Gonorynchiformes, Cypriniformes, Characiformes, and Siluriformes) frequently exhibit thickened pads of skin along the ventral surface of the anteriormost ray or rays of horizontally orientated paired (pectoral and pelvic) fins. Such paired‐fin pads, though convergent, are externally homogenous across ostariophysan groups (particularly nonsiluriform taxa) and have been considered previously to be the result of epidermal modification. Histological examination of the pectoral and/or pelvic fins of 44 species of ostariophysans (including members of the Gonorynchiforms, Cypriniformes, Characiformes, and Siluriformes) revealed a tremendous and previously unrecognized diversity in the cellular arrangement of the skin layers (epidermis and subdermis) contributing to the paired‐fin pads. Three types of paired‐fin pads (Types 1–3) are identified in nonsiluriform ostariophysan fishes, based on differences in the cellular arrangement of the epidermis and subdermis. The paired‐fin pads of siluriforms may or may not exhibit a deep series of ridges and grooves across the surface. Two distinct patterns of unculus producing cells are identified in the epidermis of the paired‐fin pads of siluriforms, one of which is characterized by distinct bands of keratinization throughout the epidermis and is described in Amphilius platychir (Amphiliidae) for the first time. General histological comparisons between the paired fins of benthic and rheophilic ostariophysan and nonostariophysan percomorph fishes are provided, and the possible function(s) of the paired‐fin pads of ostariophysan fish are discussed. J. Morphol. 2012.

Cryptic diversity and venom glands in Western atlantic clingfishes of the genus acyrtus (Teleostei: Gobiesocidae).

Examination of genetic data (mitochondrial cytochrome c oxidase I) for western Atlantic clingfishes revealed two distinct lineages within a group of individuals originally identified as Acyrtus artius. Subsequent investigation of preserved voucher specimens was conducted to reconcile the genetic data and the existing classification, which is based on morphology. In addition to discovering that one of the genetic lineages is an undescribed species, which we describe as Acyrtus lanthanum, new species, we found that the nominal species Acyrtus artius has a putative venom gland associated with the subopercle that has been overlooked since the species was described nearly 60 years ago. The new species lacks the subopercular gland as does Acyrtus rubiginosus, but one is present in the related Arcos nudus. Venom glands have not been reported previously for the Gobiesocidae, and the venom gland described herein for Acyrtus and Arcos represents the first example in teleost fishes of a venom gland associated with the subopercle.

Heterodonty in the New World: An SEM Investigation of Oral Jaw Dentition in the Clingfishes of the Subfamily Gobiesocinae (Teleostei: Gobiesocidae)

New World members of the Gobiesocinae (including Acyrtops, Acyrtus, Arcos, Derilissus, Gobiesox, Pherallodiscus, Rimicola, Sicyases, and Tomicodon) exhibit a heterodont oral dentition comprising two, and in some cases three, different types of teeth. The oral jaw teeth of New World gobiesocines are arranged in a series of 2–4 short staggered rows along the anterolateral margin of the premaxilla and dentary, to which new teeth are added posteriorly (rows 1–4) via shallow open crypts located along the labial margin of the jaw bones and medially (row 1 only) via one or two shallow open crypts located adjacent to the jaw symphysis. A putative monophyletic group comprising solely the New World genera of the Gobiesocinae is hypothesized based on characters of tooth arrangement and replacement in the oral jaws. The phylogenetic position of Eckloniaichthys, a homodont and the only Old World member of the Gobiesocinae, is discussed. The mode of tooth attachment in the Gobiesocidae is Type 2 (i.e., ring of collagen between tooth base and bone of attachment), and the mode of tooth replacement in the oral jaws is interpreted as intermediate between intraosseus and extraosseus replacement (sensu Trapani) and to take place in association with an internal cavity along the jaw bones.

Phylogenetic diagnosis of the African cyprinid genus Clypeobarbus (Ostariophysi: Cyprinidae), with the rehabilitation of Clypeobarbus bomokandi

The subgenus Clypeobarbus Fowler 1936 is elevated to generic rank and distinguished from African “Barbus” by the derived presence of a midlateral row of greatly enlarged, shield-like scales edged with dark pigment and deepest and widest below the dorsal fin, a dark pigment streak situated posterodorsal to the cleithrum, and the presence of a large occipital fontanel, border laterally by the frontals and parietals and posteriorly by the supraoccipital bone of the neurocranial vault. Seven species are placed within Clypeobarbus, C. pleuropholis (Boulenger 1899), C. congicus (Boulenger 1899), C. pseudognathodon (Boulenger 1915), C. bomokandi (Myers 1924), C. hypsolepis (Daget 1959), C. schoutedeni (Poll and Lambert 1961), and C. bellcrossi (Jubb 1965), and a redescription is provided for C. bomokandi, which is rehabilitated as a valid species.

Life in the Fast Lane: A Review of Rheophily in Freshwater Fishes

Ecological opportunities and physical challenges of fast-water habitats have dramatically shaped the evolution of freshwater fish lineages from a broad diversity of clades globally, often leading to the convergent or parallel evolution of highly similar morphologies. In this chapter, we present a patch dynamics model of how longitudinal shifts in geomorphological and ecological processes from small headwater torrents to large river rapids may differentially affect gene flow among, and evolutionary specialization within, resident rheophilic fish populations. Fast-water habitats offer ecological advantages including predator avoidance and increased foraging efficiency, but require that organisms resist downstream displacement and avoid shifting, crushing substrates. We review the specialized morphological and behavioral characteristics associated with life in fast waters and the taxonomic distribution of these specializations across fishes. We also report results of specific functional studies where available and summarize empirical evolutionary, phylogenetic support for our model and for specific mechanisms or pathways by which rheophilic specializations may arise.

Danionella dracula, an escape from the cypriniform Bauplan via developmental truncation?

We provide a detailed account of the osteology of the miniature Asian freshwater cyprinid fish Danionella dracula. The skeleton of D. dracula shows a high degree of developmental truncation when compared to most other cyprinids, including its close relative the zebrafish Danio rerio. Sixty‐one bones, parts thereof or cartilages present in most other cyprinids are missing in D. dracula. This impressive organism‐wide case of progenesis renders it one of the most developmentally truncated bony fishes or even vertebrates. Danionella dracula lacks six of the eight unique synapomorphies that define the order Cypriniformes and has, thus, departed from the cypriniform Bauplan more dramatically than any other member of this group. This escape from one of the most successful Baupläne among bony fishes may have been facilitated by the organism‐wide progenesis encountered in D. dracula. By returning in its skeletal structure to the early developmental condition of other cypriniforms, D. dracula may have managed to overcome the evolutionary constraints associated with this Bauplan and opened up new evolutionary avenues that enabled it to evolve a number of striking morphological novelties, including its tooth‐like odontoid processes and a complex drumming apparatus. J. Morphol. 277:147–166, 2016.