Cephalic Muscles Research Articles

Variation in the Jaw Musculature of Ratsnakes and Their Allies (Serpentes: Colubridae)

Snakes have a highly modified feeding apparatus. However, its associated musculature is often poorly known. In order to study variation in the cephalic musculature, we dissected specimens representing 28 snake species belonging to the New World clade Lampropeltini and their Old World relatives. The observed variation was analysed using a phylogenetic framework. We found that the pattern of their musculature is conservative. We observed no interspecific variation in the intermandibular muscles or in the posterior jaw adductors. Variation within the dorsal constrictors and lateral jaw adductors is relatively low. This could be explained by morphological (space) limitations and functional constraints.

Morphological, functional, and phylogenetic aspects of the head capsule of the cockroach Ergaula capucina (Insecta/Blattodea).

BackgroundCockroaches are usually typical omnivorous detritivores and their cephalic morphology is considered to be ancestral in various aspects. Thus, several studies addressed the morphology and function of the blattodean head, and the cockroach usually serves as a model for standard mouthparts in text books. However, so far only two of the three major lineages of Blattodea have been studied and no detailed information for the head of any Corydioidea was available. The present study closes this gap by providing a detailed morphological description of the head of Ergaula capucina, studying some important functional parameters of the mandible and discussing it in a phylogenetic framework.MethodsThe cephalic morphology of Ergaula studied in detail using a broad set of different techniques including digital microscopy, µ-computed tomography, and 3-dimensional reconstructions. Concerning the functional morphology of the mandible, we compared the volume and effective cross sections of the eight compartments of the primary mandibular adductor muscle for Ergaula, Blattella germanica, and Salganea rossi and measured the mechanical advantage, i.e., the force transmission ratio for all teeth of the mandible of Ergaula.ResultsThe head capsule of Ergaula is characterized by a strong sexual dimorphism and typical orthopteran mouthparts. It resembles the head capsule of other roaches in several respects and confirms oesotendons, the reduction of the mesal occelus, and bipartite M. verticopharyngealis and M. hypopharyngosalivaris as blattodean apomorphies. But it also shows some unique adaptations. It is the first described cockroach that lacks the dorsal tentorial arms which has various consequences for the cephalic musculature. On the maxillary lacinia, Ergaula is the first described blattodean to show strong and blunt setae instead of a lacinula, which might be homologues to the dentisetae of dragonflies and mayflies. Like other corydiid roaches that inhabit xeric areas, Ergaula has an atmospheric water-vapor absorption mechanism that includes a gland and a ductus on the epipharnyx and bladders on the hypopharynx. The mandibular adductor is in cockroaches asymmetric, a pattern not found in termites, mantids, or other closely related insects.

The impact of Drew Noden's work on our understanding of craniofacial musculoskeletal integration.

The classical anatomist Drew Noden spearheaded craniofacial research, laying the foundation for our modern molecular understanding of development, evolution, and disorders of the craniofacial skeleton. His work revealed the origin of cephalic musculature and the role of cranial neural crest (CNC) in early formation and patterning of the head musculoskeletal structures. Much of modern cranial tendon research advances a foundation of knowledge that Noden built using classical quail-chick transplantation experiments. This elegant avian chimeric system involves grafting of donor quail cells into host chick embryos to identify the cell types they can form and their interactions with the surrounding tissues. In this review, we will give a brief background of vertebrate head formation and the impact of CNC on the patterning, development, and evolution of the head musculoskeletal attachments. Using the zebrafish as a model system, we will discuss examples of modifications of craniofacial structures in evolution with a special focus on the role of tendon and ligaments. Lastly, we will discuss pathologies in craniofacial tendons and the importance of understanding the molecular and cellular dynamics during craniofacial tendon development in human disease.

Comparing head muscles among Drusinae clades (Insecta: Trichoptera) reveals high congruence despite strong contrasts in head shape

The subfamily Drusinae (Limnephilidae, Trichoptera) comprises a range of species exhibiting differently shaped head capsules in their larval stages. These correspond to evolutionary lineages pursuing different larval feeding ecologies, each of which uses a different hydraulic niche: scraping grazers and omnivorous shredders sharing rounded head capsules and filtering carnivores with indented and corrugated head capsules. In this study, we assess whether changes in head capsule morphology are reflected by changes in internal anatomy of Drusinae heads. To this end, internal and external head morphology was visualized using µCT methods and histological sections in three Drusinae species—Drusus franzi, D. discolor and D. bosnicus—representing the three evolutionary lineages. Our results indicate that Drusinae head musculature is highly conserved across the evolutionary lineages with only minute changes between taxa. Conversely, the tentorium is reduced in D. discolor, the species with the most aberrant head capsule investigated here. Integrating previous research on Drusinae head anatomy, we propose a fundamental Drusinae blueprint comprising 29 cephalic muscles and discuss significance of larval head capsule corrugation in Trichoptera.

The endoparasitic larval stages of Eoxenos laboulbenei: An atypical holometabolan development (Strepsiptera, Mengenillidae)

Endoparasitic larval stages of Eoxenos laboulbenei were documented with different techniques, with a main focus on the male tertiary larva. Two discrete endoparasitic stages occur, the secondary and the tertiary larva. The presence of large compound eyes and externally visible wing buds in the tertiary larva is a unique feature within Holometabola. The brain with large optic lobes is followed by a single postcephalic ganglionic complex. The cephalic musculature is greatly reduced but pharyngeal dilators and muscles associated with the mouth field are present. Postcephalic sclerites are absent except for the pronotum. The segmented legs bear filiform pretarsal claws. The indirect flight muscles fill up a large part of the metathorax. The 10-segmented abdomen lacks appendages. Pleural folds are present on the thorax and abdomen. The digestive tract is characterized by a very short oesophagus. The large midgut and the narrow hindgut are disconnected. Six short Malpighian tubules are present. Large testes fill out almost the entire abdomen. In contrast to the tertiary larva, the muscles of the secondary larva are not fully differentiated. Cephalic appendages are present as bud-shaped anlagen. The legs lack a pretarsal claw. The developmental transformations are outlined and discussed, also with respect to phylogenetic implications.

Cephalic muscle development in the Australian lungfish, Neoceratodus forsteri.

Lungfishes are the extant sister group of tetrapods. As such, they are important for the study of evolutionary processes involved in the water to land transition of vertebrates. The evolution of a true neck, that is, the complete separation of the pectoral girdle from the cranium, is one of the most intriguing morphological transitions known among vertebrates. Other salient changes involve new adaptations for terrestrial feeding, which involves both the cranium and its associated musculature. Historically, the cranium has been extensively investigated, but the development of the cranial muscles much less so. Here, we present a detailed study of cephalic muscle development in the Australian lungfish, Neoceratodus forsteri, which is considered to be the sister taxon to all other extant lungfishes. Neoceratodus shows several developmental patterns previously described in other taxa; the tendency of muscles to develop from anterior to posterior, from their region of origin toward insertion, and from lateral to ventral/medial (outside-in), at least in the branchial arches. The m.protractor pectoralis appears to develop as an extension of the most posterior m.levatores arcuum branchialium, supporting the hypothesis that the m.cucullaris and its derivatives (protractor pectoralis, levatores arcuum branchialium) are branchial muscles. We present a new hypothesis regarding the homology of the ventral branchial arch muscles (subarcualis recti and obliqui, transversi ventrales) in lungfishes and amphibians. Moreover, the morphology and development of the cephalic muscles confirms that extant lungfishes are neotenic and have been strongly influenced via paedomorphosis during their evolutionary history.

Muscle development in the shark Scyliorhinus canicula: implications for the evolution of the gnathostome head and paired appendage musculature

BackgroundThe origin of jawed vertebrates was marked by profound reconfigurations of the skeleton and muscles of the head and by the acquisition of two sets of paired appendages. Extant cartilaginous fish retained numerous plesiomorphic characters of jawed vertebrates, which include several aspects of their musculature. Therefore, myogenic studies on sharks are essential in yielding clues on the developmental processes involved in the origin of the muscular anatomy.ResultsHere we provide a detailed description of the development of specific muscular units integrating the cephalic and appendicular musculature of the shark model, Scyliorhinus canicula. In addition, we analyze the muscle development across gnathostomes by comparing the developmental onset of muscle groups in distinct taxa. Our data reveal that appendicular myogenesis occurs earlier in the pectoral than in the pelvic appendages. Additionally, the pectoral musculature includes muscles that have their primordial developmental origin in the head. This culminates in a tight muscular connection between the pectoral girdle and the cranium, which founds no parallel in the pelvic fins. Moreover, we identified a lateral to ventral pattern of formation of the cephalic muscles, that has been equally documented in osteichthyans but, in contrast with these gnathostomes, the hyoid muscles develop earlier than mandibular muscle in S. canicula.ConclusionOur analyses reveal considerable differences in the formation of the pectoral and pelvic musculatures in S. canicula, reinforcing the idea that head tissues have contributed to the formation of the pectoral appendages in the common ancestor of extant gnathostomes. In addition, temporal differences in the formation of some cranial muscles between chondrichthyans and osteichthyans might support the hypothesis that the similarity between the musculature of the mandibular arch and of the other pharyngeal arches represents a derived feature of jawed vertebrates.

The cephalic morphology of the American cockroach Periplaneta americana (Blattodea)

The skeleto-muscular system of the head of the American cockroach Periplaneta americana is described in detail. The results are compared with previous partial descriptions of the cephalic morphology of this species and other dictyopterans. The head of Periplaneta is, as in other cockroaches, mostly characterized by plesiomorphies such as the typical orthopteroid mouthparts, the lateral position of the compound eyes, 5-segmented maxillary palps and 3-segmented labial palps, as well as long antennae. Periplaneta shows sexual dimorphism with the compound eyes of the males reaching further ventrally. The epistomal ridge is medially interrupted so that the frons and the clypeus are confluent. The cephalic musculature is typical for a polyneopteran insect and includes 59 muscles. Potential apomorphies for Blattodea in the cephalic area include the absence of the median ocellus, the bipartite condition of M. verticopharyngealis (0ph1) and of M. hypopharyngosalivaris (0hy12), and the presence of oesotendons. The lacinula, a subapical lobelet on the lacinia, is present in almost all studied blattodeans but its potential homology to the dentisetae of Palaeoptera or the lamellae of apterygotes cannot be addressed at the moment. A “perforate” tentorium, a membranous postmola, and a lacinia that fits into the concave mesal wall of the galea are confirmed as autapomorphies of Dictyoptera.

Serial block-face scanning electron microscopy sheds new light on the head anatomy of an extremely miniaturized insect larva (Strepsiptera)

Serial cross sections (80 nm) and an image stack (353 sections) of the head of the extremely miniaturized first instar larvae of Stylops ovinae (Stylopidae) were obtained with serial block-face scanning electron microscopy. This approach made it possible for the first time to reconstruct the head anatomy of a strepsipteran larva precisely, partly to cell level. The cephalic anatomy is described in detail, based on a 3D-reconstruction. It was possible to show the proportions of the exo- and endocuticle and the epidermis. Endoskeletal structures are the pharyngeal skeleton and the anterior tentorial arms, which form an articulation with the mandibles. The dorsoventrally flattened mandibles are the only functional mouthparts and used for penetrating the host’s cuticle. The maxillae are fused with the head capsule to form the ventral plate, and the strongly modified and reduced labium functions as a closure of the ventral head opening. The nerves ending at the anterior head margin were reconstructed. The innervation of setae, olfactory pits and the vestigial maxillary palps are also documented for the first time. Five fat body cells are located in the head. Antennae, hypopharynx and labrum are not present as defined structures. A structure resembling a labrum is a secondary formation. Only nine cephalic muscles are present. Muscles of the antennae, hypopharynx, labrum and maxillae are missing. Some of the muscles originate in the thorax. Homology issues, possible phylogenetic implications, functional aspects of head structures, and also possible correlations of structural features with miniaturization and parasitism are discussed.

The homology of cephalic muscles and endoskeletal elements between Diplura and Ectognatha (Insecta)

Diplura (two-pronged bristletails) are key to our understanding of hexapod head evolution. A sister group relationship with Ectognatha (=Insecta), comprising bristletails, silverfish and winged insects, is advocated in most modern studies, however, homologization of head muscles and endoskeletal elements between Diplura and Ectognatha is still lacking. Here, we present the first homologization of a number of head muscles and endoskeletal structures between Diplura and Ectognatha. A homologization of these structures is possible if a range of species, both from Japygidae and Campodeidae, are studied in order to reconstruct the potential groundplan characteristics and account for inner anatomy variations within Diplura. Japygidae and Campodeidae show differences in the origin, insertion, and presence of mandibular and maxillary muscles as well as the shape of the maxillary cardo. Taking into account recent embryological studies on the formation of the endoskeleton in Protura, Collembola and Diplura, we furthermore reconstruct the potential evolution of the endoskeleton in early Hexapoda. The tentorium is a defining feature of dicondylic insects (including Archaeognatha) while anterior and posterior cephalic invaginations (the later tentorial pits of dicondylic insects) are groundplan features of Hexapoda. Additionally, we clarify the composition of the gnathal pouches (i.e. the type of entognathy) in Diplura and Collembola. The pouches in Diplura are posteriorly separated, similar to the state encountered in Collembola. This contrasts to former studies emphasizing the differences in the ellipuran and dipluran type of entognathy.

Development, metamorphosis, morphology, and diversity: The evolution of chordate muscles and the origin of vertebrates.

Recent findings that urochordates are the closest sister-group of vertebrates have dramatically changed our understanding of chordate evolution and vertebrate origins. To continue to deepen our understanding of chordate evolution and diversity, in particular the morphological and taxonomical diversity of the vertebrate clade, one must explore the origin, development, and comparative anatomy of not only hard tissues, but also soft tissues such as muscles. Building on a recent overview of the discovery of a cardiopharyngeal field in urochordates and the profound implications for reconstructing the origin and early evolution of vertebrates, in this study we focus on the broader comparative and developmental anatomy of chordate cephalic muscles and their relation to life history, and to developmental, morphological and taxonomical diversity. We combine our recent findings on cephalochordates, urochordates, and vertebrates with a literature review and suggest that developmental changes related to metamorphosis and/or heterochrony (e.g., peramorphosis) played a crucial role in the early evolution of chordates and vertebrates. Recent studies reviewed here supported de Beer's "law of diversity" that peramorphic animals (e.g., ascidians, lampreys) are taxonomically and morphologically less diverse than nonperamorphic animals (e.g., gnathostomes), probably because their "too specialized" development and adult anatomy constrain further developmental and evolutionary innovations. Developmental Dynamics 244:1046-1057, 2015. © 2014 Wiley Periodicals, Inc.

Coding characters from different life stages for phylogenetic reconstruction: a case study on dragonfly adults and larvae, including a description of the larval head anatomy ofEpiophlebia superstes(Odonata: Epiophlebiidae)

The exclusive use of characters coding for specific life stages may bias tree reconstruction. If characters from several life stages are coded, the type of coding becomes important. Here, we simulate the influence on tree reconstruction of morphological characters of Odonata larvae incorporated into a data matrix based on the adult body under different coding schemes. For testing purposes, our analysis is focused on a well-supported hypothesis: the relationships of the suborders Zygoptera, ‘Anisozygoptera’, and Anisoptera. We studied the cephalic morphology of Epiophlebia, a key taxon among Odonata, and compared it with representatives of Zygoptera and Anisoptera in order to complement the data matrix. Odonate larvae are characterized by a peculiar morphology, such as the specific head form, mouthpart configuration, ridge configuration, cephalic musculature, and leg and gill morphology. Four coding strategies were used to incorporate the larval data: artificial coding (AC), treating larvae as independent terminal taxa; non-multistate coding (NMC), preferring the adult life stage; multistate coding (MC); and coding larval and adult characters separately (SC) within the same taxon. As expected, larvae are ‘monophyletic’ in the AC strategy, but with anisopteran and zygopteran larvae as sister groups. Excluding larvae in the NMC approach leads to strong support for both monophyletic Odonata and Epiprocta, whereas MC erodes phylogenetic signal completely. This is an obvious result of the larval morphology leading to many multistate characters. SC results in the strongest support for Odonata, and Epiprocta receives the same support as with NMC. Our results show the deleterious effects of larval morphology on tree reconstruction when multistate coding is applied. Coding larval characters separately is still the best approach in a phylogenetic framework.

Cephalic muscles of Cyclostomes (hagfishes and lampreys) and Chondrichthyes (sharks, rays and holocephalans): comparative anatomy and early evolution of the vertebrate head muscles

Living vertebrate diversity comprises hagfishes and lampreys (Cyclostomata), elasmobranchs and holocephalans (Chondrichthyes), and bony fish which include tetrapods (Osteichthyes). Based on dissections and an extensive comparative analysis, we provide an updated overview of the anatomy, homologies and evolution of cyclostome and chondrichthyan cephalic muscles, with osteichthyans as primary comparative taxa. The analysis also infers plesiomorphic conditions for vertebrates and gnathostomes. We follow a uniform myological terminology for the Gnathostomata to demonstrate that the last common ancestor of extant vertebrates probably had a single intermandibularis and other mandibular muscles (labial muscles), some constrictores hyoidei and branchiales, and epibranchial and hypobranchial muscle sheets. The division of the cucullaris into levatores arcuum branchialium and protractor pectoralis is an osteichthyan synapomorphy and reflects an evolutionary trend towards a greater separation between the head and pectoral girdle that culminated in the formation of the tetrapod neck. Hence, this paper addresses a long-standing, central issue regarding vertebrate comparative anatomy. It thus provides a valuable basis for future evolutionary, developmental and functional studies of vertebrates and/or of specific vertebrate subgroups/model organisms. © 2014 The Linnean Society of London

Cephalic musculature in five genera of Symphyla (Myriapoda)

The internal anatomy of the head has been investigated in representatives of five genera of Symphyla. Descriptions and schemata of the cephalic musculature, tentorial complex and other structures are displayed for two scutigerellids (Scutigerella and Hanseniella) and three scolopendrellids (Scolopendrella, Symphylella and Scolopendrellopsis). Unexpectedly, the internal anatomy of Scolopendrella corresponds to a higher degree with scutigerellids than with other scolopendrellid representatives. Symphylella and Scolopendrellopsis show features that – compared to the state in other myriapod subgroups – seem to be plesiomorphic, such as the absence of tracheae in the head, the presence of only one tentorial bridge and the presence of large dorsal muscles of the mandibular base. These states are shared with other myriapod subgroups and show that the mandibular mechanisms in Symphyla are not as specialized as previously assumed.

Systematics of the Enigmatic Dipsadine Snake Tropidodipsas perijanensis Alemán (Serpentes: Colubridae) and Review of Morphological Characters of Dipsadini

Abstract On the basis of new material from Colombia, we describe external morphology, the hemipenis, osteology, musculature, and visceral morphology of Tropidodipsas perijanensis, a species previously known from the unique holotype and long assigned to Dipsas. Tropidodipsas perijanensis may be the sister species of all other Dipsadini or the sister species of a clade formed by Dipsas and Sibynomorphus. This distinctive South American species cannot be assigned to Tropidodipsas or to any other genus, and we erect a new genus for it. Our study of cephalic musculature identified a previously unreported division of the m. levator anguli oris and new insertion of the m. intermandibularis posterior superficialis. New characteristics of dipsadine hemipenes were visualized by Alizarin staining. Some osteological characters of Dipsadini support synonymization of Sibon and most species of Tropidodipsas, whereas visceral characters and published molecular data suggest that Dipsas, Sibon, and Sibynomorphus form a clade.

Contribution to the Knowledge of Anatomy of Species of Genus Mobula Rafinesque 1810 (Chondricthyes: Mobulinae)

A comparative anatomical study was conducted among four mobulid species (Mobula japanica, M. munkiana, M. tarapacana, and M. thurstoni), from the coasts of the Gulf of California. Characters of the skeleton (neurocranium, mandibles, scapular girdle, pelvic girdle, and synarcual) were described. Mobula species had a wide structural variation. In the skeleton, M. tarapacana displayed the most plesiomorphic characters, mainly at the cranial level (cranium longer than wide, reduced internasal width, fontanelle longer than wide), while M. japanica had the most derived characters (cranium wider than longer, fontanelle wider than longer). Based on the observations, the dorsal cephalic musculature were similar in all species; however, oppositely to other batoid species, the epiaxilis is strongly developed, as it extends toward the cephalic part of the neurocranium, at level of the postorbital processes. In the ventral musculature, ventral constrictor muscles are quite reduced, whereas complex mandibular muscles are very developed. Muscles showing the highest variation are the coracohioideus and the coracoarcual.

Comparative anatomy of the cheek muscles within the Centromochlinae subfamily (Ostariophysi, Siluriformes, Auchenipteridae)

Glanidium melanopterum Miranda Ribeiro, a typical representative of the subfamily Centromochlinae (Siluriformes: Auchenipteridae), is herein described myologically and compared to other representative species within the group, Glanidium ribeiroi, G. leopardum, Tatia neivai, T. intermedia, T. creutzbergi, Centromochlus heckelii, and C. existimatus. The structure of seven pairs of striated cephalic muscles was compared anatomically: adductor mandibulae, levator arcus palatini, dilatator operculi, adductor arcus palatini, extensor tentaculi, retractor tentaculi, and levator operculi. We observed broad adductor mandibulae muscles in both Glanidium and Tatia, catfishes with depressed heads and smaller eyes. Similarities between muscles were observed: the presence of a large aponeurotic insertion for the levator arcus palatini muscle; an adductor arcus palatini muscle whose origin spread over the orbitosphenoid, pterosphenoid, and parasphenoid; and the extensor tentaculi muscle broadly attached to the autopalatine. There is no retractor tentaculi muscle in either the Glanidium or Tatia species. On the other hand, in Centromochlus, with forms having large eyes and the tallest head, the adductor mandibulae muscles are slim; there is a thin aponeurotic or muscular insertion for the levator arcus palatini muscle; the adductor arcus palatini muscle originates from a single osseous process, forming a keel on the parasphenoid; the extensor tentaculi muscle is loosely attached to the autopalatine, permitting exclusive rotating and sliding movements between this bone and the maxillary. The retractor tentaculi muscle is connected to the maxilla through a single tendon, so that both extensor and retractor tentaculi muscles contribute to a wide array of movements of the maxillary barbels. A discussion on the differences in autopalatine-maxillary movements among the analyzed groups is given.

Selective expression of the type 3 isoform of ryanodine receptor Ca 2+ release channel (RyR3) in a subset of slow fibers in diaphragm and cephalic muscles of adult rabbits

The expression pattern of the RyR3 isoform of Ca 2+ release channels was analysed by Western blot in neonatal and adult rabbit skeletal muscles. The results obtained show that the expression of the RyR3 isoform is developmentally regulated. In fact, RyR3 expression was detected in all muscles analysed at 2 and 15 days after birth while, in adult animals, it was restricted to a subset of muscles that includes diaphragm, masseter, pterygoideus, digastricus, and tongue. Interestingly, all of these muscles share a common embryonic origin being derived from the somitomeres or from the cephalic region of the embryo. Immunofluorescence analysis of rabbit skeletal muscle cross-sections showed that RyR3 staining was detected in all fibers of neonatal muscles. In contrast, in those adult muscles expressing RyR3 only a fraction of fibers was labelled. Staining of these muscles with antibodies against fast and slow myosins revealed a close correlation between expression of RyR3 and fibers expressing slow myosin isoform.

Mechanical properties of the integument of the common gartersnake,Thamnophis sirtalis(Serpentes: Colubridae)

The evolution of the ophidian feeding mechanism has involved substantial morphological restructuring associated with the ability to ingest relatively large prey. Previous studies examining the morphological consequences of macrophagy have concentrated on modifications of the skull and cephalic musculature. Although it is evident that macrophagy requires highly compliant skin, the mechanical properties of the ophidian integument have received limited attention, particularly in the context of feeding. We examined mechanical properties of skin along the body axis in Thamnophis sirtalis (Colubridae). Data were collected from tensile tests and were analyzed using a multivariate analysis of variance (MANOVA) and post-hoc multiple comparison tests. Significant differences in mechanical properties were detected among regions of the body. In general, prepyloric skin is more compliant than postpyloric skin, consistent with the demands of macrophagy.

Threatened Fishes of the World: Noturus placidus Taylor, 1969 (Ictaluridae)

Common names: Neosho madtom (T). Conservation status: Listed federally as threatened 22 May 1990 (USFWS 1991). Identification: One of 25 madtom species, distinguished from four madtoms in its range by two distinct crescent-shaped bands of pigment on caudal fin and lack of dark pigment extending to edge of adipose fin (Taylor 1969). Pectoral spines have poorly developed saw-like teeth on front margin. Fin ray counts: anal rays 13–16 (14.72); pelvic rays 8–12 (9.06), soft pelvic rays 7–9 (7.99); caudal rays 49–59 (54.32); vertebrae: 32–36 (33.62). Adults typically greater than 50 mm TL (Bulger & Edds 2001). Males in spawning condition exhibit swollen cephalic epaxial muscles and elongated genital papillae; both sexes exhibit reddened tooth patches during spawning season. Photograph by Janice L. Bryan. Distribution: Endemic to Neosho River basin in Kansas, Missouri, and Oklahoma (Taylor 1969). Species’ range historically extended south to Illinois River in Oklahoma; currently restricted by reservoirs to approximately two-thirds of original range (Moss 1981). Abundance: Large population fluctuations occur seasonally and annually (Moss 1981). In 1 year, Wilkinson et al. (1996) reported a mean summer density of occurrence in the Spring River of 11.3 fish versus 30.0 per 100 m in the autumn when generational overlap ocurrs. Higher mean autumn densities found in the Neosho River compared to the Spring River (Wildhaber et al. 2000a). Habitat and ecology: Occur over gravel bars and riffles in fourth to sixth order streams having moderate current, permanent flow, and unconsolidated gravel (Fuselier & Edds 1994; Bulger & Edds 2001). Nocturnal benthic insectivores gathering prey from gravel interstices (Moss 1981). In nature, young-of-the-year (YOY) 15–49 mm TL; mature individuals reach 33–82 mm TL by end of first year (Fuselier & Edds 1994; Bulger & Edds 2001). Suspected life span 1–2 years. Reproduction: Sexual maturity reached during first year (Bulger & Edds 2001). Spawning occurs mid-summer; YOY found July–August. Nests excavated beneath large rocks in unconsolidated gravel. Male parental care lasts 18–19 days (Bulger et al. 2002). Clutch size 60; mean chorion diameter 3.1 mm. Threats: Impoundments restrict migration, alter natural hydrograph, and with gravel mining, eliminate preferred habitat (USFWS 1991). Water quality and quantity impacted by municipalities, agriculture, zinc–lead mining, urbanization, and industrialization (Wildhaber et al. 2000a). Conservation actions: Federally listed as threatened in 1990; threatened status in Kansas and endangered in Missouri and Oklahoma. Recovery plan published in 1991 (USFWS 1991). Five-year moratorium on gravel mining in Neosho River instituted spring 1991. Annual population monitoring conducted since 1991 (Wildhaber et al. 2000b). Recent and ongoing research efforts focused on Neosho madtom ecology. Conservation recommendations: Continue to limit gravel mining, prohibit dam construction, and encourage removal of unused dams. Further research needed on life history. Remarks: Cooperation of government agencies and private landowners crucial to recovery.