Pattern formation in development of chondrichthyan dentitions: a review of an evolutionary model

The mode of tooth development displayed in Chondrichthyans (sharks, rays and holocephalans), one of frequent tooth replacement, was possible once a dental lamina had evolved, and since 1982 this has been known as the odontode regulation theory after Reif. Today, Reif's concepts need to be transformed into those of modern biology, the crosstalk between epithelium and mesenchyme, for the regulation of timing, spacing and shape of vertebrate teeth. Although Reif's proposed ‘primordial tissue’ may be the only site of progenitor cells, to restrict odontogenic potential to time-specific sites (protogerms), as has been suggested in the sequential addition tooth (SAT) model, very little data are available. Here, his model of alternate tooth replacement files has been interpreted as an integrated tooth addition unit of two adjacent files (SAT) unit for alternate replacement of teeth, regulated by putative, precisely timed gene expression for activation and inhibition. We have provided new data on patterns of tooth succession in dentitions of extant sharks and rays to compare with those of Reif. Using a phylogeny combined from molecular and morphological data, it is suggested that the alternate tooth addition and replacement model is derived within Chondrichthyes, and diversified from single file tooth addition of the stem chondrichthyans.     

Anin vitro,serum-free organ culture technique for the study of development and growth of the dermal skeleton in fish

Summary To develop a serum-free, chemically definedin vitro organ culture system enabling the study of epithelial-mesenchymal interactions in development and growth of fish dermal skeleton, we investigatedin vitro continuation of scale regeneration in the cichlid fishHemichromis bimaculatus. The culture medium in our system is based on Leibovitz medium (L-15) supplemented with vitamin C, additional amino acids and HEPES. With this basis medium, we examined the effects of all trans-retinoic acid, dexamethasone, and prostaglandin-E2 (PG-E2), factors known to exert an effect on development and growth of teeth and bone in mammalian culture systems, on thein vitro regeneration of scales. These effects were compared with those obtained by supplementation of the basis medium with newborn and fetal calf serum. To evaluate our culture system, the medium that allowed to mimick in the best possible way thein vivo regeneration of scales (i.e., the basis medium plus dexamethasone and PG-E2) was also tested on thein vitro development of teeth in the same fish species. Our serum-free, chemically defined organ culture system enablesin vitro development and growth of both scales and teeth. With this model culture system, it is possible to evaluate thein vitro effects of hormones, growth factors, and other substances on growth and development of dermal skeleton in fish.     

Origins of bone repair in the armour of fossil fish: response to a deep wound by cells depositing dentine instead of dermal bone

The outer armour of fossil jawless fishes (Heterostraci) is, predominantly, a bone with a superficial ornament of dentine tubercles surrounded by pores leading to flask-shaped crypts (ampullae). However, despite the extensive bone present in these early dermal skeletons, damage was repaired almost exclusively with dentine. Consolidation of bone, by dentine invading and filling the vascular spaces, was previously recognized in Psammolepis and other heterostracans but was associated with ageing and dermal shield wear (reparative). Here, we describe wound repair by deposition of dentine directly onto a bony scaffold of fragmented bone. An extensive wound response occurred from massive deposition of dentine (reactionary), traced from tubercle pulp cavities and surrounding ampullae. These structures may provide the cells to make reparative and reactionary dentine, as in mammalian teeth today in response to stimuli (functional wear or damage). We suggest in Psammolepis, repair involved mobilization of these cells in response to a local stimulatory mechanism, for example, predator damage. By comparison, almost no new bone is detected in repair of the Psammolepis shield. Dentine infilling bone vascular tissue spaces of both abraded dentine and wounded bone suggests that recruitment of this process has been evolutionarily conserved over 380 Myr and precedes osteogenic skeletal repair.     

A comparative view on mechanisms and functions of skeletal remodelling in teleost fish, with special emphasis on osteoclasts and their function

Resorption and remodelling of skeletal tissues is required for development and growth, mechanical adaptation, repair, and mineral homeostasis of the vertebrate skeleton. Here we review for the first time the current knowledge about resorption and remodelling of the skeleton in teleost fish, the largest and most diverse group of extant vertebrates. Teleost species are increasingly used in aquaculture and as models in biomedical skeletal research. Thus, detailed knowledge is required to establish the differences and similarities between mammalian and teleost skeletal remodelling, and between distantly related species such as zebrafish (Danio rerio) and medaka (Oryzias latipes). The cellular mechanisms of differentiation and activation of osteoclasts and the functions of teleost skeletal remodelling are described. Several characteristics, related to skeletal remodelling, distinguish teleosts from mammals. These characteristics include (a) the absence of osteocytes in most species; (b) the absence of haematopoietic bone marrow tissue; (c) the abundance of small mononucleated osteoclasts performing non‐lacunar (smooth) bone resorption, in addition to or instead of multinucleated osteoclasts; and (d) a phosphorus‐ rather than calcium‐driven mineral homeostasis (mainly affecting the postcranial dermal skeleton). Furthermore, (e) skeletal resorption is often absent from particular sites, due to sparse or lacking endochondral ossification. Based on the mode of skeletal remodelling in early ontogeny of all teleosts and in later stages of development of teleosts with acellular bone we suggest a link between acellular bone and the predominance of mononucleated osteoclasts, on the one hand, and cellular bone and multinucleated osteoclasts on the other. The evolutionary origin of skeletal remodelling is discussed and whether mononucleated osteoclasts represent an ancestral type of resorbing cells. Revealing the differentiation and activation of teleost skeletal resorbing cells, in the absence of several factors that trigger mammalian osteoclast differentiation, is a current challenge. Understanding which characters of teleost bone remodelling are derived and which characters are conserved should enhance our understanding of the process in fish and may provide insights into alternative pathways of bone remodelling in mammals.     

Ontogeny and homology of the skeletal elements that form the sucking disc of remoras (Teleostei,Echeneoidei, Echeneidae)

The sucking disc of the sharksuckers of the family Echeneidae is one of the most remarkable and most highly modified skeletal structures among vertebrates. We studied the development of the sucking disc based on a series of larval, juvenile, and adult echeneids ranging from 9.3 mm to 175 mm standard length. We revisited the question of the homology of the different skeletal parts that form the disc using an ontogenetic approach. We compared the initial stages of development of the disc with early developmental stages of the spinous dorsal fin in a representative of the morphologically basal percomorph Morone. We demonstrate that the “interneural rays” of echeneids are homologous with the proximal‐middle radials of Morone and other teleosts and that the “intercalary bones” of sharksuckers are homologous with the distal radials of Morone and other teleosts. The “intercalary bones” or distal radials develop a pair of large wing‐like lateral extensions in echeneids, not present in this form in any other teleost. Finally the “pectinated lamellae” are homologous with the fin spines of Morone and other acanthomorphs. The main part of each pectinated lamella is formed by bilateral extensions of the base of the fin spine just above its proximal tip, each of which develops a row of spinous projections, or spinules, along its posterior margin. The number of rows and the number of spinules increase with size, and they become autogenous from the body of the lamellae. We also provide a historical review of previous studies on the homology of the echeneid sucking disc and demonstrate that the most recent hypotheses, published in 2002, 2005 and 2006, are erroneous. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Radiolarian skeletons: Formation and morphology of skeletal shells

A new scheme of successive stages in the formation of radiolarian skeletons is proposed. Successive complication of symmetry patterns is considered. The morphology and evolutionary changes of five types of skeletal shells, i.e., latticed, reticulate, spongy, porous, and lamellar, are analyzed.     

Study on properties and regulation peculiarities of glycogenolysis enzymes in fish skeletal muscles depending on peculiarities of the species motor activity

The activity values, properties and peculiarities of activation of glycogen phosphorylase (GP, EC 2.4.1.1) and glycogen phosphorylase kinase (GPK, EC 2.7.138) were studied in the white skeletal muscle of fishes differing in motor behavior. No differences in the GP and GPK activity levels were revealed in porgy Diplodus annularis (L.), horse mackerel Trachurus mediterraneus ponticus, trout Salmo trutta morphario, scorpionfish Scorpaena porcus, flounder Scophtalnus maeoticus maeoticus, and carp Cyprinus carpio; however, properties of the isolated enzymes and peculiarities of formation of their activated forms during swimming in a hydrodynamic tube are determined by functional peculiarities of the muscle tissue and are associated with the motor activity character of the species. The more rapid ion regulation prevails in fishes capable for the burst swimming type (scorpionfish, trout). The glycogenolysis hormonal regulation leading to a change of the GPK activity index has been found in other species.     

Unique evolutionary trajectories in repeated adaptation to hydrogen sulphide‐toxic habitats of a neotropical fish (Poecilia mexicana)

Replicated ecological gradients are prime systems to study processes of molecular evolution underlying ecological divergence. Here, we investigated the repeated adaptation of the neotropical fish Poecilia mexicana to habitats containing toxic hydrogen sulphide (H₂S) and compared two population pairs of sulphide‐adapted and ancestral fish by sequencing population pools of >200 individuals (Pool‐Seq). We inferred the evolutionary processes shaping divergence and tested the hypothesis of increase of parallelism from SNPs to molecular pathways. Coalescence analyses showed that the divergence occurred in the face of substantial bidirectional gene flow. Population divergence involved many short, widely dispersed regions across the genome. Analyses of allele frequency spectra suggest that differentiation at most loci was driven by divergent selection, followed by a selection‐mediated reduction of gene flow. Reconstructing allelic state changes suggested that selection acted mainly upon de novo mutations in the sulphide‐adapted populations. Using a corrected Jaccard index to quantify parallel evolution, we found a negligible proportion of statistically significant parallel evolution of J_corr = 0.0032 at the level of SNPs, divergent genome regions (J_corr = 0.0061) and genes therein (J_corr = 0.0091). At the level of metabolic pathways, the overlap was J_corr = 0.2545, indicating increasing parallelism with increasing level of biological integration. The majority of pathways contained positively selected genes in both sulphide populations. Hence, adaptation to sulphidic habitats necessitated adjustments throughout the genome. The largely unique evolutionary trajectories may be explained by a high proportion of de novo mutations driving the divergence. Our findings favour Gould's view that evolution is often the unrepeatable result of stochastic events with highly contingent effects.     

Validation of swabs as a non-destructive and relatively non-invasive DNA sampling method in fish

Non-destructive methods of collecting DNA from small fish species can be problematic, as fin clips can potentially affect behaviour or survivorship in the wild. Swabbing body mucus may provide a less invasive method of DNA collection. However, risk of contamination from other individuals in high density groups could give erroneous genotyping results. We compared multilocus microsatellite genotypes from the same individuals when collected at low and high density and compared this with fin clips. We found no differences between these categories, with a genotyping error rate of 0.42%, validating the use of body mucus swabbing for DNA collection in fish.     

Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis

In this study, we illustrate an exceptionally well-preserved Haikouichthys ercaicunensis from the Lower Cambrian Chengjiang fauna that displays complete single dorsal, ventral and caudal fins. This 530-million-year old vertebrate is fish-shaped and characterized by a single median fin-fold, which is an essential trait of the initial vertebrate chordates. The radially orientated ray-like structures in its dorsal fin somewhat resemble but are probably not real radials seen in basal vertebrates, such as hagfishes and lampreys. The unique design of primitive fins and fin structures provides additional insights into the early evolution of vertebrates.     

Dual role of osteoblastic proenkephalin derived peptides in skeletal tissues

Proenkephalin encodes a group of small peptides with opiate-like activity, the endogenous opioids, known to function as neurohormones, neuromodulators, and neurotransmitters. Recently, we have demonstrated that in addition to its abundance in fetal brain tissue, proenkephalin is highly expressed in nondifferentiated mesodermal cells of developing fetuses. We identified the skeletal tissues, bone, and cartilage as major sites of proenkephalin expression. To examine the possibility that proenkephalin is involved in bone development we have studied the expression of this gene in bone-derived cells, its modulation by bone active hormones, and the effects of enkephalin-derived peptides on osteoblastic phenotype. Our studies revealed that osteoblastic cells synthesize high levels of proenkephalin mRNA which are translated, and the derived peptides are secreted. Reciprocal interrelationships between osteoblast maturation and proenkephalin expression were established. These results together with our observations demonstrating inhibitory effects of proenkephalin-derived peptides on osteoblastic alkaline phosphatase activity, strongly support the notion that proenkephalin is involved in bone development. A different direction of research by other investigators has established the capability of the opioid system in the periphery to participate in the control of pain. On the basis of these two lines of observation, we would like to present the following hypothesis: The potential of embryonic skeletal tissue to synthesize proenkephalin-derived peptides is retained in the adult in small defined undifferentiated cell populations. This potential is realized in certain situations requiring rapid growth, such as remodeling or fracture repair. We suggest that in these processes, similarly to the situation in the embryo, the undifferentiated dividing cells produce the endogenous opioids. In the adult these peptides may have a dual function, namely participating in the control of tissue regeneration and in the control of pain. © 1994 Wiley-Liss, Inc.     

Specificity and host predictability: a comparative analysis among monogenean parasites of fish

1. This article compares generalist (parasite species found on two or more host species) and specialist (found on only one host species) monogenean parasite species of fish. The reduction of the host range – that is an increase in host specificity – may correspond with a better adaptation of the parasite to a more predictable host environment. A more predictable environment may allow the parasite species to develop specific adaptations.
2. We assume that the more predictable host environment can be evaluated by host body size, since numerous life-traits, such as longevity, are positively correlated with size.
3. We found that specialist parasites parasitize larger hosts species than generalist parasites. We also found a good relationship between host body size and parasite body size for specialist parasite species.
4. An adaptation to the mechanical problems encountered in the host's gill chamber may lead to an increase in parasite body size. The infection of a larger part of the host population in order to decrease the chances of local extinction due to fluctuations of host abundance may be another adaptive mechanism.
5. We found a negative correlation between parasite body size and prevalence for generalist parasite species. This relationship disappeared when using the comparative method controlling for phylogeny, which proved that it was a phylogenetic effect.     

Ingestion of suspended bacteria by fish: a modified approach

The ingestion of suspended bacteria by common carp larvae and juvenile tilapias was quantified by counting of fluorescently labelled bacteria (FLB) in guts of experimental fish under an epifluorescence microscope.     

Chromosomes, RAPDs and evolutionary trends of the Neotropical fish Mimagoniates microlepis (Teleostei: Characidae: Glandulocaudinae) from coastal and continental regions of the Atlantic forest, Southern Brazil

Chromosome and random amplified polymorphic DNA (RAPD) markers of samples of Mimagoniates microlepis were studied to test the hypothesis that a vicariant event occurred as the result of the orogeny of the coastal mountain range (Serra do Mar; southeastern and southern Brazil). Conventional karyotypes and nucleolar organizer region (Ag-NOR) phenotypes of two samples of M. microlepis from the headwaters of the Iguaçu River (southern Brazil) were compared both with each other and with other local populations of the species in the coastal drainage of southeastern Brazil. Additional molecular data (RAPD markers and genetic diversity) were obtained from specimens from coastal and continental regions of southern Brazil. The same diploid number (52 chromosomes), karyotypic formula and Ag-NOR phenotype were found for both analysed samples from the Iguaçu River. A genetic discontinuity was discovered in the comparison of the karyotypical formula of the Iguaçu samples with those from coastal drainages of the region. Polymerase chain reaction-RAPD markers revealed strikingly different molecular profiles between coastal and continental samples and indications of a high degree of genetic variation. Based on these results, we provide some comments on the biogeographical patterns and evolutionary trends for M. microlepis from coastal and continental regions of southeastern/southern Brazil.     

Osteoderm histology of Proterochampsia and Doswelliidae (Reptilia: Archosauriformes) and their evolutionary and paleobiological implications

Postcranial osteoderms are commonly developed in the major lineages of Archosauriformes, including forms such as proterochampsids and doswelliids. Here, we survey the histology of osteoderms of the doswelliids Archeopelta arborensis and Tarjadia ruthae, and the proterochampsids Chanaresuchus bonapartei and Pseudochampsa ischigualastensis to understand better the morphogenesis of these skeletal elements. Whereas, the Doswelliid osteoderms possess a trilaminar organization, in which two cortices (external and basal) can be differentiated from an internal core of cancellous bone, these elements are compact structures in proterochampsids. The osteoderms of P. ischigualastensis are avascular and they consist entirely of parallel‐fibered bone. Conversely, the osteoderms of C. bonapartei are well vascularized structures composed of zones of woven‐fibered bone and annuli of parallel‐fibered bone. The rather simple microstructure observed in P. ischigualastensis osteoderms suggests that these elements grew at a constant, low rate. Compared with proterochampsids, doswelliid osteoderms possess a more complex histology, which appears to be linked to variations in the growth rate during the osteoderm formation and also to the development of the external ornamentation. A comparison of our findings with the results of earlier studies on other archosauriforms (phytosaurs and pseudosuchians) reveals that the general osteoderm histology of doswelliids bears a closer resemblance to that of phytosaurs and pseudosuchians than the proterochampsid osteoderm microstructure. If all archosauriform osteoderms are homologous structures, the closer resemblance of doswellid osteoderm microstructures to that of phytosaurs and pseudosuchians is in agreement with the hypothesis that doswellids are more closely related to archosaurs than proterochampsids. J. Morphol. 276:385–402, 2015. © 2015 Wiley Periodicals, Inc.     

Confocal immunohistochemistry of the dermal glands and evolutionary considerations in the caecilian,Typhlonectes natans (Amphibia: Gymnophiona)

An immunohistochemical study of the cutaneous glands of the caecilian Typhlonectes natans was conducted. Analyses of nerve fibres revealed that adrenergic and galanin‐positive axons innervate the MECs and mediate their contraction. These glands may represent one of the main targets of the adrenergic ganglion cells and reflect the prominent preganglionic cell columns of the species studied. But neurochemical features of the sympathetic ganglia and retrograde tract‐tracing studies are necessary to study the morphology and organization of the sympathetic nervous system of studied species.     

Pike Esox lucius as an emerging model organism for studies in ecology and evolutionary biology: a review

The pike Esox lucius is a large, long‐lived, iteroparous, top‐ predator fish species with a circumpolar distribution that occupies a broad range of aquatic environments. This study reports on a literature search and demonstrates that the publication rate of E. lucius research increases both in absolute terms and relative to total scientific output, and that the focus of investigation has changed over time from being dominated by studies on physiology and disease to being gradually replaced by studies on ecology and evolution. Esox lucius can be exploited as a model in future research for identifying causes and consequences of phenotypic and genetic variation at the levels of individuals, populations and species as well as for investigating community processes.