The comparative morphology of pit organs in elasmobranchs

The pit organs of elasmobranchs (sharks, skates and rays) are free neuromasts of the mechanosensory lateral line system. Pit organs, however, appear to have some structural differences from the free neuromasts of bony fishes and amphibians. In this study, the morphology of pit organs was investigated by scanning electron microscopy in six shark and three ray species. In each species, pit organs contained typical lateral line hair cells with apical stereovilli of different lengths arranged in an “organ‐pipe” configuration. Supporting cells also bore numerous apical microvilli taller than those observed in other vertebrate lateral line organs. Pit organs were either covered by overlapping denticles, located in open grooves bordered by denticles, or in grooves without associated denticles. The possible functional implications of these morphological features, including modification of water flow and sensory filtering properties, are discussed. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Phylogenetic trends in the abundance and distribution of pit organs of elasmobranchs

Pit organs (free neuromasts of the mechanosensory lateral line system) are distributed over the skin of elasmobranchs. To investigate phylogenetic trends in the distribution and abundance of pit organs, 12 relevant morphological characters were added to an existing matrix of morphological data (plus two additional end terminals), which was then re-analysed using cladistic parsimony methods ( paup * 4.0b10). Character transformations were traced onto the most parsimonious phylogenetic trees. The results suggest the following interpretations. First, the distinctive overlapping denticles covering the pit organs in many sharks are a derived feature; plesiomorphic elasmobranchs have pit organs in open slits, with widely spaced accessory denticles. Second, the number of pit organs on the ventral surface of rays has been reduced during evolution, and third, spiracular pit organs have changed position or have been lost on several occasions in elasmobranch evolution. The concentrated-changes test in macclade (version 4.05) was used to investigate the association between a pelagic lifestyle and loss of spiracular pit organs (the only character transformation that occurred more than once within pelagic taxa). Depending on the choice of tree, the association was either nonsignificant at P  = 0.06 or significant at P  < 0.05. Future studies, using species within more restricted elasmobranch clades, are needed to resolve this issue.     

The behavioural role of pit organs in the epaulette shark

Epaulette sharks Hemiscyllium ocellatum in three treatments, pit organs (free neuromasts) ablated, sham-operated and normal ( n  = 8 for each treatment), showed a significant preference for facing upstream in a flume ( P  < 0·05). There were no significant differences in the mean angles or angular variances among treatments. Individuals with ablated pit organs, however, spent significantly less time moving around than controls ( P  < 0·05), suggesting that pit organs contributed to motivation for activity. Pit organs do not appear to make an important contribution to rheotaxis in H. ocellatum . It is suggested that this may be due to structural differences in the pit organs of H. ocellatum compared with other species.     

Morphogenesis of free neuromasts in the larvae of brown-marbled grouper Epinephelus fuscoguttatus

Newly hatched larvae had one pair of free neuromasts behind the eyes. As the larvae grew, free neuromasts increased in number. The apical surface of sensory epithelium widened and subsequently elongated. The number of sensory hair cells increased and the directions of maximum sensitivity became both anteroposterior and dorsoventral on the trunk. Before notochord flexion, only the anteroposterior type was observed. After notochord flexion, two types of neuromasts were observed on the trunk. On the head, the orientation of free neuromasts formed a tangential line to concentric circles around the eyes and nostrils. Free neuromasts on the head could therefore receive stimuli from various angles from predators or zooplanktons. This suggests that these free neuromasts play a role in compensating for a dead angle of vision, and an important role in detecting zooplankton under scotopic vision. Canal organs were observed on the head and operculum in 40-d-old animals.     

Unilateral ablation of trunk superficial neuromasts increases directional instability during steady swimming in the yellowtail kingfish Seriola lalandi

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail‐beat frequency, stride length, caudal fin‐beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A₀) was significantly increased in SN‐disrupted fish compared with sham‐operated controls. In addition, the orientation of caudal fin‐tip relative to the overall swimming direction of SN‐disrupted fish was significantly deflected (two‐fold) in comparison with sham‐operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body‐wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN‐disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (L_F) s^?1. In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion.     

Morphology of the mechanosensory lateral line system in the Atlantic Stingray,Dasyatissabina: The mechanotactile hypothesis

The biological function of anatomical specializations in the mechanosensory lateral line of elasmobranch fishes is essentially unknown. The gross and histological features of the lateral line in the Atlantic stingray, Dasyatis sabina, were examined with special reference to its role in the localization and capture of natural invertebrate prey. Superficial neuromasts are arranged in bilateral rows near the dorsal midline from the spiracle to the posterior body disk and in a lateral position along the entire length of the tail. All dorsal lateral line canals are pored, contain sensory neuromasts, and have accessory lateral tubules that most likely function to increase their receptive field. The pored ventral canal system consists of the lateral hyomandibular canal along the disk margin and the short, separate mandibular canal on the lower jaw. The extensive nonpored and relatively compliant ventral infraorbital, supraorbital, and medial hyomandibular canals form a continuous complex on the snout, around the mouth, and along the abdomen. Vesicles of Savi are small mechanosensory subdermal pouches that occur in bilateral rows only along the ventral midline of the rostrum. Superficial neuromasts are best positioned to detect water movements along the transverse body axis such as those produced by tidal currents, conspecifics, or predators. The pored dorsal canal system is positioned to detect water movements created by conspecifics, predators, or possibly distortions in the flow field during swimming. Based upon the stingray lateral line morphology and feeding behavior, we propose the Mechanotactile Hypothesis, which states that the ventral nonpored canals and vesicles of Savi function as specialized tactile mechanoreceptors that facilitate the detection and capture of small benthic invertebrate prey. J. Morphol. 238:1–22, 1998. © 1998 Wiley-Liss, Inc.     

The importance of habitat and life history to extinction risk in sharks, skates, rays and chimaeras

We compared life-history traits and extinction risk of chondrichthyans (sharks, rays and chimaeras), a group of high conservation concern, from the three major marine habitats (continental shelves, open ocean and deep sea), controlling for phylogenetic correlation. Deep-water chondrichthyans had a higher age at maturity and longevity, and a lower growth completion rate than shallow-water species. The average fishing mortality needed to drive a deep-water chondrichthyan species to extinction (Fextinct) was 38-58% of that estimated for oceanic and continental shelf species, respectively. Mean values of Fextinct were 0.149, 0.250 and 0.368 for deep-water, oceanic and continental shelf species, respectively. Reproductive mode was an important determinant of extinction risk, while body size had a weak effect on extinction risk. As extinction risk was highly correlated with phylogeny, the loss of species will be accompanied by a loss of phylogenetic diversity. Conservation priority should not be restricted to large species, as is usually suggested, since many small species, like those inhabiting the deep ocean, are also highly vulnerable to extinction. Fishing mortality of deep-water chondrichthyans already exploited should be minimized, and new deep-water fisheries affecting chondrichthyans should be prevented.     

The lateral line canal sensory organs of the Epaulette Shark (Hemiscyllium ocellatum)

Examination of the lateral line canals in the Epaulette Shark reveals a much more differentiated sensory system than previously reported from any elasmobranch. Two main types of lateral line canals are found. In one type rounded patches of sensory epithelia are separated by elevations of the canal floor. The other type is a straight canal without restrictions and with an almost continuous sensory epithelium. In addition, we found epithelia (type A) with very long apical microvilli on the supporting cells. These microvilli reach beyond the stereovilli of the hair cells. Another type (B) of sensory epithelium has short microvilli on the supporting cells. In this latter type of epithelium the stereovilli of the hair cells are comparatively tall and reach out beyond the supporting cell microvilli.
  New hair cells are found widely in both types of sensory epithelia. These always occur as single cells, unlike those described in teleost lateral line canal sensory epithelia where new hair cells seem to form in pairs. Dying hair cells are also widespread, indicating a continuous turnover of hair cells.     

Intraspecific divergence in the lateral line system in the nine-spined stickleback (Pungitius pungitius)

The mechanosensory lateral line system of fishes is an important organ system conveying information crucial to individual fitness. Yet, our knowledge of lateral line diversity is almost exclusively based on interspecific studies, whereas intraspecific variability and possible population divergence have remained largely unexplored. We investigated lateral line system variability in four marine and five pond populations of nine-spined stickleback (Pungitius pungitius). We found significant differences in neuromast number between pond and marine fish. In particular, three of seventeen lateral line regions (viz. caudal peduncle superficial neuromasts; canal neuromasts from the anterior trunk and caudal peduncle) showed strong divergence between habitats. Similar results were obtained with laboratory-reared individuals from a subset of populations, suggesting that the patterns found in nature likely have a genetic basis. Interestingly, we also found habitat-dependent population divergence in neuromast variability, with pond populations showing greater heterogeneity than marine populations, although only in wild-caught fish. A comparison of neutral genetic (F(ST)) and phenotypic (P(ST)) differentiation suggested that natural selection is likely associated with habitat-dependent divergence in neuromast counts. Hence, the results align with the conclusion that the mechanosensory lateral line system divergence among marine and pond nine-spined sticklebacks is adaptive.     

Neoselachian sharks and rays from the British Bathonian (Middle Jurassic)

Extensive sampling of Bathonian sediments from localities across southern and central England has produced over 8000 neoselachian teeth. These comprise diverse faunas, with over 25 species being represented in total, most of them previously undescribed. Seventeen new species and seven new genera are named: Palaeoscyllium tenuidens sp. nov., Praeproscyllium oxoniensis gen. et sp. nov., Eypea leesi gen. et sp. nov., Proheterodontus sylvestris gen. et sp. nov., Paracestracion bellis sp. nov., Palaeobrachaelurus mussetti sp. nov., Heterophorcynus microdon gen. et sp. nov., Dorsetoscyllium terraefullonicum gen. et sp. nov., Ornatoscyllium freemani gen. et sp. nov., Pseudonotidanus semirugosus gen. et sp. nov., Synechodus duffini sp. nov., Protospinax magnus sp. nov., P. bilobatus sp. nov., P. carvalhoi sp. nov., Belemnobatis kermacki sp. nov., B. stahli sp. nov. and Spathobatis delsatei sp. nov. In addition, a new family, the Pseudonotidanidae fam. nov., is defined and the status of Paranotidanus Ward and Thies, 1987, Hybodus levis Woodward, 1889 and Breviacanthus brevis (Phillips, 1871) are discussed. These taxa show strong facies specificity, with different species being restricted to different palaeoenvironments.     

Post‐embryonic development of canal and superficial neuromasts and the generation of two cranial lateral line phenotypes

The relatively simple structural organization of the cranial lateral line system of bony fishes provides a valuable context in which to explore the ways in which variation in post‐embryonic development results in functionally distinct phenotypes, thus providing a link between development, evolution, and behavior. Vital fluorescent staining, histology, and scanning electron microscopy were used to describe the distribution, morphology, and ontogeny of the canal and superficial neuromasts on the head of two Lake Malawi cichlids with contrasting lateral line canal phenotypes (Tramitichromis sp. [narrow‐simple, well‐ossified canals with small pores] and Aulonocara stuartgranti [widened, more weakly ossified canals with large pores]). This work showed that: 1) the patterning (number, distribution) of canal neuromasts, and the process of canal morphogenesis typical of bony fishes was the same in the two species, 2) two sub‐populations of neuromasts (presumptive canal neuromasts and superficial neuromasts) are already distinguishable in small larvae and demonstrate distinctive ontogenetic trajectories in both species, 3) canal neuromasts differ with respect to ontogenetic trends in size and proportions between canals and between species, 4) the size, shape, configuration, physiological orientation, and overall rate of proliferation varies among the nine series of superficial neuromasts, which are found in both species, and 5) in Aulonocara, in particular, a consistent number of canal neuromasts accompanied by variability in the formation of canal pores during canal morphogenesis demonstrates independence of early and late phases of lateral line development. This work provides a new perspective on the contributions of post‐embryonic phases of lateral line development and to the generation of distinct phenotypes in the lateral line system of bony fishes. J. Morphol. 277:1273–1291, 2016. © 2016 Wiley Periodicals, Inc.     

Captive parturition and neonatal growth of the dwarf ornate wobbegong (Orectolobus ornatus de Vis, 1883)

Neonatal predation in multispecies aquarium exhibits can prevent detection of captive breeding by wobbegong sharks. We used ultrasonography and isolation strategies to prevent neonatal predation and maximize survival/growth of the dwarf ornate wobbegong (Orectolobus ornatus de Vis, 1883). We captured seven free‐living wobbegongs (two males and five females) and subjected each animal to a health assessment which led to the euthanasia of one female with a retained hook. Ultrasonography showed that females were pregnant, one was preovulatory, and one was in a resting phase. Two females (one pregnant) and one male were placed in isolation in each of two tanks. In October 2006, 25 neonates were born overnight with the two litters placed into separate neonate tanks. Over the ～6.5‐month monitoring period, four neonates with reduced body condition died without premonitory signs resulting in a 63.0% annual survival rate. Finite growth rates did not differ between sexes or litters and averaged (±SE) 12.2 (1.5) cm/year and 156.4 (26.4) g/year. At the cessation of monitoring, total length had increased by ～30%, whereas total weight had almost doubled with neonatal body condition in line with free‐living wobbegongs. Our efficacious, six‐step manipulative, the approach should be applicable with all wobbegongs given their reproductive similarities, but we recommend that efforts focus on the dwarf ornate, tasselled and Japanese wobbegongs because all are small in size and have bred in aquaria. Ultimately, this approach should produce self‐sustaining aquarium populations, place less reliance on the wild acquisition and provide animals for other aquaria, population restocking, or scientific research.     

Inter- and intraspecific variation of nuclear DNA reassociation kinetics in the Gracilariales (Rhodophyta)

DNA reassociation kinetics were used to determine inter- and intraspecific variation in genome organization and complexities in species ofGracilaria andGracilariopsis. Results indicate the presence of three second order components corresponding to fast, intermediate and slow fractions. Repeated sequences varied from 13–95%. Three geographic populations ofGracilaria tikvahiae were similar with 13–27% repeated sequences.Gracilaria sp. cultivars G-1 and G-6 with 35% and 95% repeated sequences, respectively, were distinct from each other andG. tikvahiae. No pattern of genome organization and complexity was found which permitted a distinction betweenGracilaria andGracilariopsis. Comparison of the percent of unique and repetitive sequences (U/R) indicated a wide range of ratios, withGracilaria tikvahiae populations having the highest values (2.7–7.3) andGracilaria sp. cultivar G-6,G. blodgettii andGracilariopsis lemanieformis the lowest (0.05–1.80). Unique component complexities varied one order of magnitude, from 10⁸ forGracilaria takvahiae to 10⁷ forGracilaria sp. cultivar G-6,G. blodgettii andGracilariopsis lemanieformis. Information for genome size, organization and complexity is used to develop a nuclear genome profile forGracilaria blodgettii andGracilariopsis lemanieformis which are characterized by commercial grade agars having high gel strengths (> 700 g cm^?2) and elevated melting temperatures (99 °C).     

Evaluation of intramuscular ketoprofen and butorphanol as analgesics in chain dogfish (Scyliorhinus retifer)

The mediation of nociception with analgesic medications has not been well documented in elasmobranchs. The purpose of this study was to determine effective analgesic doses of the opioid agonist‐antagonist, butorphanol, and the non‐steroidal anti‐inflammatory drug, ketoprofen, in an elasmobranch. This was evaluated by repetitively assessing minimum anesthetic concentrations of the immersion anesthetic, tricaine methanesulfonate (MS‐222), required to prevent response to noxious stimuli in chain dogfish (Scyliorhinus retifer) when administered multiple doses of each of the analgesics (0.25, 0.5, 1.0, 2.5, and 5.0 mg/kg butorphanol and 1.0, 1.5, 2.0, and 4.0 mg/kg ketoprofen). Baseline concentrations of MS‐222 required to prevent a response to a noxious stimulus were determined for each animal and served as the controls. Although individual animals displayed a reduction in MS‐222 concentration with various doses of both analgesics, no statistically significant difference was noted between control animals and animals given analgesics. It is plausible that unique elasmobranch anatomy, lack of appropriate medication dose or timing of administration, and other physiological factors not yet identified may have contributed to the lack of apparent efficacy of the analgesics evaluated in this study. Zoo Biol 0:1–10, 2006. © 2006 Wiley‐Liss, Inc.     

Taxonomic assessment of sharks,rays and guitarfishes (Chondrichthyes: Elasmobranchii) from south‐eastern Arabia,using the NADH dehydrogenase subunit 2 (NADH2) gene

An 829‐bp fragment of the NADH dehydrogenase subunit 2 (NADH2) gene was used to assess the taxonomic status of 1487 elasmobranch specimens, representing 52 putative species. Strong evidence was found for the existence of an undescribed Echinorhinus species and for cryptic speciation within Rhynchobatus djiddensis. The results also provide strong molecular support for the existence of two previously reported, but undescribed, guitarfish species. Potential, but less conclusive, cryptic lineage diversification was also noted in Carcharhinus leucas, Loxodon macrorhinus, Iago omanensis and Gymnura poecilura. A complex situation was found in the genus Himantura, with potentially three distinct lineages evident, one of which is probably an undescribed species, in the H. gerrardi complex. One dasyatid specimen could not be identified, but appears to be closely related to Dasyatis ushiei, while Himantura leoparda and Carcharhinus longimanus are reported from Oman for the first time. The results of the present study also reinforce previously reported geographical divisions within certain putative species, which has important implications for fishery management and conservation. © 2015 The Linnean Society of London     

Inter- and intraspecific alarm response in the termiteMacrotermes subhyalinus (Rambur)

Summary In laboratory studies we analysed the reaction of aMacrotermes subhyalinus (Rambur) colony in contact with a small group of test termites placed at the head of a gallery system. As test termites we usedMacrotermes subhyalinus of the same nest,Macrotermes subhyalinus of a foreign nest and the related sympatric speciesMacrotermes bellicosus (Smeathman).Contact with an introduced group of foragers evokes a significant recruitment of workers and minor soldiers. The intensity of the response depends on the test groups we introduced. The highest recruitment results withM. bellicosus andM. subhyalinus from a foreign nest. During the recruitment the increase in the number of minor soldiers is greater than the increase in the number of workers, and as a result, the relative proportion of the soldiers in the population leaving the nest is significantly higher than before.Direct observations at the place of contact show thatM. bellicosus individuals are immediately attacked and killed. In the case ofM. subhyalinus from a foreign nest, not all individuals are killed; some are only intensively examined with the antennae or seized with the mandibles.M. subhyalinus from the same nest are rarely attacked. Mostly they are antennally inspected or enter the gallery system unhindered.The recruitment of termites from the nest is released by major workers which, after contact with the test termites, run back into the nest and provoke an alarm by tactile stimuli. On their way back into the nest the major workers, in all probability, lay a pheromone trail which leads the outgoing alarmed termites towards the place of contact.     

Inter- and intraspecific variation in the genitalia of the ‘Melitaea phoebe group’ (Lepidoptera, Nymphalidae)

The ecology and phylogeny of the Melitaeini butterflies have received considerable attention in the last few years. Several publications have been based on research using molecular methods. Genital morphometry has already been published on two sibling species but without any accompanying taxonomic revision of related species or their intraspecific taxonomy. In this study the morphology of genitalia was analysed by landmark-based geometric morphometrics in males and by traditional morphometrics in females. Based on these morphological characters, the whole M. phoebe group (subg. Cinclidia) was revised. According to our results M. telona Fruhstorfer, 1908 is conspecific with M. ‘phoebe’ ornata Christoph, 1893. Thus, we consider M. telona a junior synonym of M. ornata, and we propose new combinations: M. ornata ornata Christoph, 1893, M. ornata telona Fruhstorfer, 1908, M. ornata amanica Rebel, 1917, M. ornata capreola Varga, 1967, M. ornata emipunica Verity, 1919, M. ornata enoch Higgins, 1941, M. ornata kovacsi Varga, 1967, M. ornata nigrogygia Verity, 1938, M. ornata ogygia Fruhstorfer, 1907 and M. ornata totila Stauder, 1914 based on the rule of priority. The validity of the species status of M. punica and M. scotosia was confirmed, whereas M. sibina and M. pseudosibina could not be separated from M. phoebe using morphometrics. A new species from Iran (Zagros Mts.) was described as M. zagrosi sp. n. In addition, the whole geographical range of M. ornata was reconsidered and some biogeographical connections were discussed. In M. ornata four morphotypes were found based on genitalia: 1. ‘Western type’: including the Italian, Hungarian and SW Ukrainian populations; 2. ‘Eastern type’: with a much extended distribution ranging from the Balkan Peninsula through Asia Minor to Kazakhstan; 3. ‘The Levant type’ (=M. ornata telona comb. nov.); 4. ‘Northern Iranian type’ (Kopeth Dagh and Elburz Mts.). The distribution of these morphotypes can be attributed to historic separation in distinct glacial refugia.