Seamount coral reefs are egg case nurseries for deep-sea skates.

Egg case nurseries of the boreal skate (Amblyraja hyperborea) and Richardson's skate (Bathyraja richardsoni) were defined and mapped on a bathyal seascape (c. 500-1900 m depths) south of Tasmania, Australia, using 99 towed-camera transects (157 linear km; N = 50,858 images). In total, 738 skate egg cases were observed (present in 240 images, absent in 50,618); among 113 egg cases examined to identify parent species, 70% were A. hyperborea, 10% B. richardsoni and 20% unidentified Bathyraja species. "Recently laid" egg cases were differentiated from "aged" ones by classifying their colour and condition. The great majority (98%) of egg cases were observed in c. 1100-1400 m depths on seamounts (15 of 36 surveyed), not seamount bases or adjacent continental slope. Egg cases were associated with reefs formed by accumulated skeletal matrix of the stony coral Solenosmilia variabilis, with >90% egg cases (including most of those recently laid) observed on living S. variabilis that characterises a "coral zone" in c. 950-1350 m depths. Water in the coral zone is warmer (+0.66 to 2.37°C) than at the deep distributional limits of adult A. hyperborea and B. richardsoni (2000 and 3000 m, respectively), potentially providing for accelerated embryonic development. Co-occurrence with living coral infers an energetically favourable local-scale hydrodynamic environment for egg cases, particularly on seamount peaks, where increased water flow over egg cases would avert smothering by suspended sediment, and compensate for lower oxygen concentration compared to deeper depths occupied by adult skates. Criteria identifying egg case nurseries are strongly met for A. hyperborea at Seamount Z110 (468 egg cases of varied ages, maximum density of 5.47 m-2 ) and to a lesser extent on five others (Seamounts K1, Z16, Hill U, Z5 and Hill V). An abundance (density) criterion for defining nurseries needs to be flexible because it is a spatially scale-dependent measure that differs between surveys according to the tools and design employed. Off Australia, coral reef egg case nursery habitat is restricted to a narrow depth range in temperate latitudes where it is scarce and impacted by historical bottom trawl fishing in many locations. There has been effective conservation of nursery habitat, however, because four of the six nursery sites identified here and extensive coral reef areas are protected within marine parks.

New insights into life-history traits of Mediterranean Electric rays (Torpediniformes: Torpedinidae) as a contribution to their conservation.

Despite being commonly recognized by the general public, knowledge about the biology and life-history of electric rays is still scarce. Globally, according to the International Union for Conservation of Nature, more of the 80% of the species belonging to the Torpedinidae family are, indeed, classified as Data Deficient, so as, in most of the cases, no proper management measures are available for the conservation of these species. For this reason, the main goal of this study is to provide new information on life-history traits of three species inhabiting the Mediterranean Sea. Age and growth were estimated through direct annuli count of 146 vertebral centra sections of Torpedo marmorata. Females' growth pattern was found to be better described by a S-shaped function (Gompertz L∞ = 622mm TL; k = 0.15; IP=2.75 years), while males' by a logarithmic one (von Bertalanffy L∞ = 485mm TL; k = 0.14; t0 = -2.28). The oldest female and male were aged 17 (560mm TL) and 11 (432mm TL), respectively. Females (L50=379mm TL and A50=5.5 years) appeared to mature later than males (L50=272mm TL and A50=3.8 years), also attaining bigger sizes. Despite the observation of late-pregnant females being found only in autumn and regressing ones in autumn and winter, the presence of juveniles during the whole year may indicate a longer reproductive period. The stomach content analysis identified T. marmorata as a top predator (TROPH=4.38) with a very narrow trophic niche (Bi=0.22), extremely specialized in feeding on bony fishes. In addition, this work provides new and updated information on T. torpedo and the rare Tetronarce nobiliana growth, reproductive features and diet. Therefore, offering new essential data to assess the population conditions of all Torpedinidae species that inhabit the Mediterranean Sea, will lead to effective conservation plans.

Description of first nursery area for a pygmy devil ray species (Mobula munkiana) in the Gulf of California, Mexico.

Munk's pygmy devil rays (Mobula munkiana) are medium-size, zooplanktivorous filter feeding, elasmobranchs characterized by aggregative behavior, low fecundity and delayed reproduction. These traits make them susceptible to targeted and by-catch fisheries and are listed as Vulnerable on the IUCN Red List. Multiple studies have examined fisheries impacts, but nursery areas or foraging neonate and juvenile concentrations have not been examined. This study describes the first nursery area for M. munkiana at Espiritu Santo Archipelago, Mexico. We examined spatial use of a shallow bay during 22 consecutive months in relation to environmental patterns using traditional tagging (n = 95) and acoustic telemetry (n = 7). Neonates and juveniles comprised 84% of tagged individuals and their residency index was significantly greater inside than outside the bay; spending a maximum of 145 consecutive days within the bay. Observations of near-term pregnant females, mating behavior, and neonates indicate an April to June pupping period. Anecdotal photograph review indicated that the nursery area is used by neonates and juveniles across years. These findings confirm, for the first time, the existence of nursery areas for Munk's pygmy devil rays and the potential importance of shallow bays during early life stages for the conservation of this species.

Adult chondrogenesis and spontaneous cartilage repair in the skate, Leucoraja erinacea.

Mammalian articular cartilage is an avascular tissue with poor capacity for spontaneous repair. Here, we show that embryonic development of cartilage in the skate (Leucoraja erinacea) mirrors that of mammals, with developing chondrocytes co-expressing genes encoding the transcription factors Sox5, Sox6 and Sox9. However, in skate, transcriptional features of developing cartilage persist into adulthood, both in peripheral chondrocytes and in cells of the fibrous perichondrium that ensheaths the skeleton. Using pulse-chase label retention experiments and multiplexed in situ hybridization, we identify a population of cycling Sox5/6/9+ perichondral progenitor cells that generate new cartilage during adult growth, and we show that persistence of chondrogenesis in adult skates correlates with ability to spontaneously repair cartilage injuries. Skates therefore offer a unique model for adult chondrogenesis and cartilage repair and may serve as inspiration for novel cell-based therapies for skeletal pathologies, such as osteoarthritis.

For our joints to move around freely, they are lubricated with cartilage. In growing mammals, this tissue is continuously made by the body. But, by adulthood, this cartilage will have been almost entirely replaced by bone. It is also difficult for adult bodies to replenish what cartilage does remain ­ such as that in the joints. When growing new cartilage, the body uses so-called progenitor cells, which have the ability to turn into different cell types. Progenitor cells are recruited to the joints, where they transform into cartilage cells called chondrocytes, which generate new cartilage. But adults lack these progenitor cells, leaving them unfit to heal damaged cartilage after injury or diseases like osteoarthritis. In contrast, certain groups of fishes, such as skates, sharks and rays, produce cartilage throughout their life ­ indeed their whole skeleton is made of cartilage. So, what is the difference between these cartilaginous fishes and mammals? Why can they generate cartilage throughout their lives, while humans are unable to? And does this mean that these adult fish are better at healing injured cartilage? Marconi et al. used skates (Leucoraja erinacea) to study how cartilage develops, grows and heals in a cartilaginous fish. Progenitor cells were found in a layer that wraps around the cartilage skeleton (called the perichondrium). These cells were also shown to activate genes that control cartilage development. By labelling these progenitor cells, their presence and movements could be tracked around the fish. Marconi et al. found progenitor cells in adult skates that were able to generate chondrocytes. Skates were also shown to spontaneously repair damaged cartilage in experiments where cartilage was injured. Marconi et al. have identified the skate as a new animal model for studying cartilage growth and repair. Studying the mechanisms that skate progenitor cells use for generating cartilage could lead to improvements in current therapies used for repairing cartilage in the joints.

Diurnal activity patterns and habitat use of juvenile Pastinachus ater in a coral reef flat environment.

Stingrays are thought to play important ecological roles in coral reef ecosystems. However, little is known about juvenile stingray movement patterns and habitat use in coral reefs. This study used active acoustic telemetry to determine fine-scale diel movement patterns and habitat use of juvenile cowtail stingrays (Pastinachus ater) in a coral reef flat environment. Seven cowtail stingrays (4 males and 3 females) were manually tracked between April and December 2016. Each individual was tracked over 2 days, generating a total of 14 active tracks ranging from 4.91 to 9 h. Specimens moved at an average speed of 2.44 m min-1 ± 0.87 SE, with minimum distances travelled ranging from 546 to 1446 m. Tracking data showed that juvenile cowtail stingrays move in response to tidal cycles, moving faster and in straighter pathways during incoming and outgoing tides. Juvenile cowtail stingrays also showed a strong affinity to sand flat areas and mangrove edge areas. These areas provide food resources and potential refuges for juvenile rays to avoid predators. Coral reef flats were identified as secondary refuge for juveniles during the lowest tides. Future research is necessary to fully unveil the major drivers of juvenile cowtail stingray seasonal and ontogenetic movement patterns and habitat use within coral reef flat environments. This information is important to establish a full understanding of juvenile cowtail stingray ecology, but could also improve management and conservation policies.

Vertebral growth and band-pair deposition in sexually mature little skates Leucoraja erinacea: is adult band-pair deposition annual?

Mature male and female little skates Leucoraja erinacea were injected with oxytetracycline and maintained in captivity for 13 months to assess centrum growth and the frequency of band-pair deposition. Sixty per cent of the individuals analysed did not deposit a full band pair over the 13 month period. Thus, a majority of captive skates did not exhibit annual band-pair deposition. Previous research confirms annual band-pair deposition in all juvenile and most adult L. erinacea, therefore sexual maturation may lead to decreased frequency of band-pair formation. Age underestimation of larger, older elasmobranchs is being identified in an increasing number of elasmobranch species including L. erinacea as demonstrated in this study. The effect of age underestimation from band-pair counts on studies that use age-based characteristics needs to be addressed.

Age and growth of three endemic threatened guitarfishes Pseudobatos horkelii, P. percellens and Zapteryx brevirostris in the western South Atlantic Ocean.

The age and growth of three endemic threatened guitarfish species were analysed using vertebrae of Pseudobatos horkelii, P. percellens and Zapteryx brevirostris. Edge and marginal-increment analyses were used to evaluate the periodicity of the formation of the band-pairs, suggesting deposition of one band-pair per year, from late winter to late spring. The von Bertalanffy growth model was used to describe the growth of these species with the following parameters, for pooled sexes: P. horkelii L∞ = 126.93, k = 0.19 and t0 = -1.51; P. percellens L∞ = 109.31, k = 0.16 and t0 = -1.78; Z. brevirostris L∞ = 60.37, k = 0.24 and t0 = -1.42. Our results are essential to understanding the resilience and vulnerability of these species to harvest, which can contribute to management and conservation actions of these species.

Higher temperatures increase developmental rate & reduce body size at hatching in the small-eyed skate Raja microocellata: implications for exploitation of an elasmobranch in warming seas.

Effects of temperature on development of Raja microocellata was tested by maintaining embryos in controlled conditions representative of those predicted under current climate scenarios. There was a positive relationship between size of neonates & developmental rate: temperatures 14.5-16.5°C produced skates 3.5-7%, respectively, smaller than those raised at 12.5°C. Developmental rates were also 12-23% faster, with neonates hatching 3-7 weeks earlier.

Age structure and multi-model growth estimation of longnose stingray Hypanus guttatus (Dasyatidae: Myliobatoidei) from north-east Brazil.

We collected 729 Hypanus guttatus from the northern coast of the state of Rio Grande do Norte (RN), of which 196 were used to estimate age and growth. Ninety-five were male (12.7 to 57.0 cm disc width; WD ) and 101 were female (13.0 to 88.5 cm WD ); females were significantly larger than males. Cross sections of vertebrae showed band-pairs ranging from 0 to > 14 in females and from 0 to 9 in males. New-borns presented an opaque edge at birth in vertebrae without a birthmark. The average percentage of error (APE; %E) for the entire sample provided evidence that ages were repeatable. The mean monthly marginal increment (IM ) indicates annual band-pair formation from August to November. The annual cycle model for one band-pair deposition provided the best fit to data based on the AIC, with peaks between August and October, similar to that found in the IM analysis, suggesting an annual formation pattern. A multi-model approach that included four models based on the observed mean WD at age indicated a modified von Bertalanffy growth model as the best for describing the species growth: W0 (WD at birth) = 14.6 cm for both sexes; females W∞ = 98.61 cm (95% CI = 87.34-114.61 cm); k = 0.112 year-1 (CI = 0.086-0.148 year-1 ); males W∞ = 60.22 cm (CI = 55.66-65.35 cm); k = 0.219 year-1 (CI = 0.185-0.276 year-1 ). The age-at-maturity in males and females is 5 years and 7 years, respectively. The age composition shows that most (84%) specimens were aged 0 to 2 years. The information provided here is essential for analytical assessments of H. guttatus, which is subject to significant fishing pressure mainly on new-borns and juveniles.

Age and growth of the endemic Xingu River stingray Potamotrygon leopoldi validated using fluorescent dyes.

Between 2003 and 2005, vertebrae of 151 Xingu River Potamotrygon leopoldi (Potamotrygonidae) (75 males and 76 females) were analysed to derive a growth curve for this species. The disc width (WD ) was significantly different between sexes, with females measuring 149-700 mm WD and males 109-500 mm WD . The average percentage error for vertebrae readings of the whole sample was 2·7%. The marginal increment ratio (RMI ) showed an increasing trend with the highest value in November, decreasing from December on. The majority of vertebrae displaying RMI zero, occurred in September, but the annual periodicity of ring deposition throughout the year was not conclusive. Tetracycline (TCN) injected specimens were held in captivity for 13 months and displayed a fluorescent mark in vertebrae confirming a yearly periodicity of band pair formation with the translucent ring deposited in September-October. The Akaike information criterion (AIC) showed that, among the seven models considered, the best fit was obtained for the von Bertalanffy modified with W0 (where W0 = WD at birth) for both sexes. Growth parameters for females were: W0 = 149 mm; W∞ = 763·06 mm; k = 0·12 year- 1 , whereas for males: W0 = 109 mm; W∞ = 536·4 and k = 0·22 year-1 . Maximal ages were 7·2 years in males and 14·3 years in females. The species shows sexual dimorphism expressed in the growth pattern, size at maturity, longevity and asymptotic sizes. Concern for sustainability is raised due to the construction of the Belo Monte Hydroelectric Power Plant (2015 and 2016) in the State of Pará causing changes to the habitat of this species, which is endemic to the Xingu River and two of its tributaries.

Development and evolution of tooth renewal in neoselachian sharks as a model for transformation in chondrichthyan dentitions.

A defining feature of dentitions in modern sharks and rays is the regulated pattern order that generates multiple replacement teeth. These are arranged in labio-lingual files of replacement teeth that form in sequential time order both along the jaw and within successively initiated teeth in a deep dental lamina. Two distinct adult dentitions have been described: alternate, in which timing of new teeth alternates between two adjacent files, each erupting separately, and the other arranged as single files, where teeth of each file are timed to erupt together, in some taxa facilitating similarly timed teeth to join to form a cutting blade. Both are dependent on spatiotemporally regulated formation of new teeth. The adult Angel shark Squatina (Squalomorphii) exemplifies a single file dentition, but we obtained new data on the developmental order of teeth in the files of Squatina embryos, showing alternate timing of tooth initiation. This was based on micro-CT scans revealing that the earliest mineralised teeth at the jaw margin and their replacements in file pairs (odd and even jaw positions) alternate in their initiation timing. Along with Squatina, new observations from other squalomorphs such as Hexanchus and Chlamydoselachus, together with representatives of the sister group Galeomorphii, have established that the alternate tooth pattern (initiation time and replacement order) characterises the embryonic dentition of extant sharks; however, this can change in adults. These character states were plotted onto a recent phylogeny, demonstrating that the Squalomorphii show considerable plasticity of dental development. We propose a developmental-evolutionary model to allow change from the alternate to a single file alignment of replacement teeth. This establishes new dental morphologies in adult sharks from inherited alternate order.

Growth and reproduction in captivity unveils remarkable life-history plasticity in the smallnose fanskate, Sympterygia bonapartii (Chondrichthyes: Rajiformes)

We analyzed growth and reproduction of captive-born smallnose fanskates Sympterygia bonapartii. Egg cases were obtained from oviposition of two females caught in the wild and held at Temaikèn Aquarium. Following hatching, growth was analyzed in 13 females and 21 males until sexual maturity. Pattern of oviposition activity and reproductive performance were evaluated in six of the captive-reared females. Four models were fitted to growth data, among which the logistic function was the one attaining the best fit. The highest growth rate for both sexes was recorded during the first year of life, whereas growth was significantly higher in females than in males during the second year. Size at first oviposition was 61.7 ± 3.5 cm TL, similar to wild specimens. However, captive-reared females reached maturity before two years of age, i.e. much earlier than wild skates, implying a significant phenotypic plasticity in this species. The similarity in size at maturity and the difference in age at maturity between captive and wild specimens indicate that there is a decoupling of both parameters mediated through growth rates. Captive-born skates reproduced successfully and yielded viable offspring, indicating that the environment at Temaikèn Aquarium is suitable for S. bonapartii to attain its full life cycle.(AU)

Analizamos el crecimiento y la reproducción de ejemplares de raya marmorada, Sympterygia bonapartii nacidas en cautiverio. Se obtuvieron ovicápsulas a partir de la oviposición de dos hembras capturadas en la naturaleza y mantenidas en el Acuario Temaikèn. Posteriormente a la eclosión, se analizó el crecimiento en 13 hembras y 21 machos hasta la madurez sexual. Se evaluó el patrón de oviposición y la performance reproductiva en seis de las hembras criadas en cautiverio. Se ajustaron cuatro modelos a los datos de crecimiento, entre los cuales la función logística fue la que logró el mejor ajuste. Para ambos sexos, la mayor tasa de crecimiento se registró durante el primer año de vida. Durante el segundo año, la tasa de crecimiento fue significativamente mayor en hembras que en machos. La talla de primera oviposición fue de 61,7 ± 3,5 cm LT, similar a la estimada en rayas silvestres. Sin embargo, las hembras criadas en cautiverio alcanzaron la madurez antes de los dos años de vida, es decir mucho antes que en el ambiente natural, lo que implica una plasticidad fenotípica significativa en esta especie. La similitud en la talla de madurez y la diferencia en la edad de madurez entre individuos cautivos y silvestres indican que hay un desacople de ambos parámetros mediado por la tasa de crecimiento. Los individuos nacidos en cautiverio se reprodujeron exitosamente y dejaron descendencia viable, lo que indica que el ambiente del Acuario Temaikèn es adecuado para que S. bonapartii complete su ciclo de vida.(AU)

Trunk neural crest origin of dermal denticles in a cartilaginous fish.

Cartilaginous fishes (e.g., sharks and skates) possess a postcranial dermal skeleton consisting of tooth-like "denticles" embedded within their skin. As with teeth, the principal skeletal tissue of dermal denticles is dentine. In the head, cranial neural crest cells give rise to the dentine-producing cells (odontoblasts) of teeth. However, trunk neural crest cells are generally regarded as nonskeletogenic, and so the embryonic origin of trunk denticle odontoblasts remains unresolved. Here, we use expression of FoxD3 to pinpoint the specification and emigration of trunk neural crest cells in embryos of a cartilaginous fish, the little skate (Leucoraja erinacea). Using cell lineage tracing, we further demonstrate that trunk neural crest cells do, in fact, give rise to odontoblasts of trunk dermal denticles. These findings expand the repertoire of vertebrate trunk neural crest cell fates during normal development, highlight the likely primitive skeletogenic potential of this cell population, and point to a neural crest origin of dentine throughout the ancestral vertebrate dermal skeleton.

Biological notes on the reef stingray, Urobatis concentricus, an endemic species of Mexico.

This study found that the reef stingray Urobatis concentricus presents a matrotrophic aplacental viviparous reproduction with yolk sac and trophonemata formation. Growth of ovarian follicles occurs asynchronously and continuously with fecundity of three embryos per female. A maximum size of 58·4 cm total length and 37·6 cm disc width was recorded, corresponding to a mature female of 3 or 4 years of age.

Reproductive biology of Psammobatis rutrum (Chondrichthyes: Arhynchobatidae) in south Brazil, south-west Atlantic.

This study presents information on the reproductive biology of Psammobatis rutrum based on 55 males and 53 females obtained as by-catch from bottom trawlers off southern Brazil during July 2013 and September 2014 and includes a detailed description of the egg capsule. Total lengths (LT ) ranged from 22·3 to 31·6 cm and most of the sample comprised larger individuals, although there were no sexual differences in length-frequency distributions. Significant sexual differences were found for total length-disc width, LT -body mass and LT -eviscerated body mass relationships, with females being heavier and larger. Males started to mature at 25·5 cm LT and females, at 25·9 cm LT , while LT at maturity was calculated in 26·67 and 26·81 cm, respectively. Attaining larger sizes and mass may represent a reproductive investment for females, as observed in other rajoid species. Egg bearing females were first observed over 27·1 cm LT and ovarian fecundity was 1-12 vitellogenic follicles. The egg capsules were 2·22-2·62 cm length and had attaching fibrils on both lateral sides. Microscopically, the ventral face of the egg capsule was rougher than the dorsal face.

Ecophysiological interactions and water-related physicochemical parameters among freshwater stingrays / Interações ecofisiológicas e dos parâmetros físico-químico da água em arraias de água doce

Abstract The objective of this study was to compare and correlate the ecology of neonates and young individuals of Potamotrygon wallacei, Potamotrygon motoro and Paratrygon aiereba with regard to their hematological profile and the physicochemical parameters of the water that they inhabit. Principal component analysis (PCA) on the complete blood count revealed total variation of 72.92%, thus demonstrating a differentiation system for oxygen demand. On the other hand, P. motoro was considered to be an intermediate species, given that its complete blood count characteristics interacted with both P. wallacei and with P. aiereba. The interaction among the biochemical variables was shown to total 64.67% of the factors. This allowed differentiation of P. wallacei from P. aiereba, while P. motoro maintained an intermediate position. These characteristics of differentiation within the preferred environment corroborate the PCA of the present study and confirm that these species can be differentiated through considering the complete blood count and biochemical parameters. The PCA on water properties showed 68.57% differentiation, mainly comprising the x axis (49.44%). It can be affirmed that P. motoro has the capacity to inhabit the preferential areas of P. wallacei and P. aiereba, as well as occupying localities in which other stingrays are not found. In conclusion, P. wallacei presents patterns differentiating it from P. aiereba, while P. motoro is a species that presents intermediate characteristics. The latter can be considered to be a more broadly distributed species regarding its ecophysiological characteristics.

Resumo Este trabalho tem por objetivo investigar o perfil hematológico e os parâmetros físico-químicos da água, comparando e correlacionando ecologicamente entre neonatos e jovens de Potamotrygon wallacei (arraia cururu), Potamotrygon motoro e Paratrygon aiereba. A análise de componentes principais (PCA) do hemograma revelou um total 72,92% de variação, constituindo-se em um sistema de diferenciação na demanda por oxigênio. P. wallacei apresenta diferenciação no eixo X quando comparada a P. aiereba, por outro lado P. motoro constitui-se como uma espécie intermediária que apresenta as características do hemograma interagindo tanto com P. wallacei quanto com P. aiereba. A interação entre as variáveis bioquímica demonstram um total de 64,67% dos fatores, no qual foi possível diferenciar, a arraia P. wallacei de P. aiereba, tendo P. motoro uma aspecto de espécie intermediária entre as demais. Esses aspectos de diferenciação de ambiente de preferência corroboraram a PCA obtida no presente estudo e confirmam que essas espécies podem ser diferenciadas quando se considerar as variáveis referentes ao hemograma e a bioquímica. Nos íons, no trombograma e no leucograma, não foi possível diferenciar as espécies. O PCA das propriedades da água foi constituído por 68,57% de diferenciação que se constituiu principalmente no eixo x (49,44%). É possível confirmar que P. motoro tem a capacidade de habitar as áreas preferências de P. wallacei e P. aiereba, além do mais esta possui uma localidade que as demais arraias não são encontradas. Conclui-se que P. wallacei, apresenta padrões diferenciados de P. aiereba, além do mais P. motoro é uma espécie que apresenta características intermediárias entre as descritas, o qual pode ser considerado uma espécie com distribuição mais ampla em seus aspectos ecofisiológicos.

Towards sustainable fishery management for skates in South America: The genetic population structure of Zearaja chilensis and Dipturus trachyderma (Chondrichthyes, Rajiformes) in the south-east Pacific Ocean.

The longnose skates (Zearaja chilensis and Dipturus trachyderma) are the main component of the elasmobranch fisheries in the south-east Pacific Ocean. Both species are considered to be a single stock by the fishery management in Chile however, little is known about the level of demographic connectivity within the fishery. In this study, we used a genetic variation (560 bp of the control region of the mitochondrial genome and ten microsatellite loci) to explore population connectivity at five locations along the Chilean coast. Analysis of Z. chilensis populations revealed significant genetic structure among off-shore locations (San Antonio, Valdivia), two locations in the Chiloé Interior Sea (Puerto Montt and Aysén) and Punta Arenas in southern Chile. For example, mtDNA haplotype diversity was similar across off-shore locations and Punta Arenas (h = 0.46-0.50), it was significantly different to those in the Chiloé Interior Sea (h = 0.08). These results raise concerns about the long-term survival of the species within the interior sea, as population resilience will rely almost exclusively on self-recruitment. In contrast, little evidence of genetic structure was found for D. trachyderma. Our results provide evidence for three management units for Z. chilensis, and we recommend that separate management arrangements are required for each of these units. However, there is no evidence to discriminate the extant population of Dipturus trachyderma as separate management units. The lack of genetic population subdivision for D. trachyderma appears to correspond with their higher dispersal ability and more offshore habitat preference.

Clasper gland morphology and development in Potamotrygon magdalenae (Elasmobranchii: Potamotrygonidae).

Clasper gland morphology and development in Potamotrygon magdalenae and its relation with the acquisition of reproductive maturity is described in males of different developmental stages (embryos, neonates, juveniles, and reproductively active and resting adults). The glands are subcutaneous masses in the proximal base of each clasper. They are partially bilobate organs with a ventral groove that bears a row of papillae. Glands tend to be asymmetric, the left gland has a larger size, a trend that has been observed in other organs of elasmobranchs. Glands are formed by radially organized tubular secretory units lined with a simple columnar epithelium with basal nuclei and granular eosinophilic cytoplasm; vascularized loose connective tissue surrounds the gland units. The gland is covered by two layers of striated muscle tissue in circular and longitudinal arrangement. The clasper glands begin to develop in neonates and their secretory activity begins in juveniles. The active secretion of the clasper gland is observed in mature males, it includes glycoproteins and sulfated mucopolysaccharides. The size of the glands has a positive and direct relationship with body size, measured as disc width. Significant differences in clasper gland size were found between mature (active and resting) and immature (neonates and juveniles) males, suggesting that the acquisition of the sexual maturity involves the increase in the size of the gland due to a highly augmented secretory activity. Therefore, clasper glands are clearly associated with the reproductive activity of males and their secretion should have an endocrine control as other sexual secondary organs. J. Morphol. 278:369-379, 2017. © 2017 Wiley Periodicals, Inc.

Life-history traits of the long-nosed skate Dipturus oxyrinchus.

This work investigates life-history traits of the long-nosed skate Dipturus oxyrinchus, which is a common by-catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4-117·5 cm total length, LT ) attained larger sizes than males (14·5-99·5 cm LT ). To evaluate age and growth, a sub-sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length-at-age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L∞ mean ± s.e.: 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm LT ) and 15 years (96·0 cm LT ), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado-somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.

Ecophysiological interactions and water-related physicochemical parameters among freshwater stingrays.

The objective of this study was to compare and correlate the ecology of neonates and young individuals of Potamotrygon wallacei, Potamotrygon motoro and Paratrygon aiereba with regard to their hematological profile and the physicochemical parameters of the water that they inhabit. Principal component analysis (PCA) on the complete blood count revealed total variation of 72.92%, thus demonstrating a differentiation system for oxygen demand. On the other hand, P. motoro was considered to be an intermediate species, given that its complete blood count characteristics interacted with both P. wallacei and with P. aiereba. The interaction among the biochemical variables was shown to total 64.67% of the factors. This allowed differentiation of P. wallacei from P. aiereba, while P. motoro maintained an intermediate position. These characteristics of differentiation within the preferred environment corroborate the PCA of the present study and confirm that these species can be differentiated through considering the complete blood count and biochemical parameters. The PCA on water properties showed 68.57% differentiation, mainly comprising the x axis (49.44%). It can be affirmed that P. motoro has the capacity to inhabit the preferential areas of P. wallacei and P. aiereba, as well as occupying localities in which other stingrays are not found. In conclusion, P. wallacei presents patterns differentiating it from P. aiereba, while P. motoro is a species that presents intermediate characteristics. The latter can be considered to be a more broadly distributed species regarding its ecophysiological characteristics.