In this paper we compare the elasmobranch composition, depth-related trends of species and community descriptors (abundance, biomass, mean fish weight, species richness and diversity) of the Balearic ...Islands Archipelago and Algeria (north- and southwestern Mediterranean, respectively). The samples used in this study were collected in bottom trawl surveys between 36 and 779 m depth. Generalized linear models, linear regression, cluster and similarity percentage analyses, and generalized additive models were used to compare the two areas. Twenty-nine elasmobranch species were caught, 12 of them common to both areas, 7 appearing only in the Balearic Islands, and 10 only in Algeria. The bathymetric distributions of species were, in most cases, best fitted to uni-modal response curves. The models for species common to both areas showed similar bathymetric trends, except for Etmopterus spinax, which in Algeria showed a maximum abundance located 154 m shallower than in the Balearic Islands. Four bathymetric assemblages were identified in both areas with similar depth ranges but with different species composition. The mean values of the community descriptors were higher on the shelf in the Balearic Islands, whereas higher values were detected on the slope in Algeria. Different between-area bathymetric trends for all the descriptors were detected, with the exception of mean fish weight. The distinct environmental scenarios and fishing histories of the areas studied are discussed as underlying traits influencing the elasmobranch populations.
The development of luminous structures and the acquisition of luminescence competence during the ontogeny of the velvet belly lantern shark Etmopterus spinax, a deep‐sea squalid species, were ...investigated. The sequential appearance of nine different luminous zones during shark embryogenesis were established, and a new terminology for them given. These zones form the complex luminous pattern observed in free‐swimming animals. The organogenesis of photophores (photogenic organs) from the different luminous zones was followed, and photophore maturation was marked by the appearance of green fluorescent vesicles inside the photocytes (photogenic cells). Peroxide‐induced light emissions as well as spontaneous luminescence analysis indicated that the ability of E. spinax to produce light was linked to the presence of these fluorescent vesicles and occured prior to birth. The size of photogenic organs, as well as the percentage of ventral body surface area occupied by the luminous pattern and covered by photophores increased sharply during embryogenesis but remained relatively stable in free‐swimming animals. All these results strongly suggest camouflage by counter‐illumination in juvenile E. spinax.
Studying an organism’s photogenic structures at the ultrastructural level is a key step in the understanding of its light-emission process. Recently, the photophore ultrastructure of the deep-sea ...lanternshark
Etmopterus spinax
Linnaeus, 1758 was described. The photocytes appeared to be divided into three areas including an apical granular area, which contains inclusions and was hypothesized to be the light-producing reaction site. In this study, we investigated the morphological changes occurring within the granular area during the bioluminescent emissions induced by two hormones: prolactin and melatonin. Prolactin provoked the formation of new structures in the granular area, the “grey particles”, whose number was proportional to the amount of light produced by the reaction. An increase in the number of granular inclusions was also detected at the end of the prolactin-induced light emission. Conversely, melatonin induced a decrease in the number of granular inclusions and an increase in their diameter. An effect of hormones was also observed on the iris-like structure where they triggered pigment retraction and hence an increase in the iris aperture diameter. This is consistent with previous findings and is shown for the first time at the cellular level. The possible role of grey particles in
E. spinax
light-emission mechanism is discussed, while granular inclusion is considered to be
E. spinax
’s intracellular luminescence site. Regarding typical shark long-lasting glows, a new term (“glowon”) is proposed to characterize this novel membrane-free microsource.
Etmopterus spinax
Linnaeus, 1758 is a deep-sea lantern shark that emits blue light thanks to thousands of tiny cup-shaped organs made of a pigmented sheath enclosing light-emitting cells topped by an ...iris-like structure and a lens. In this study, we investigate the ultrastructure of these photophores in order to improve our understanding of the light emission process. The presence of a novel layer, a putative reflector upholstering the pigmented sheath, is highlighted. The intracellular organization of the photocytes is addressed. They appear as regionalized cells: their basal area is occupied by an ovoid nucleus, their medial area is highly vesiculated and their apical area, oriented toward the photophore center, displays small granular inclusions. We hypothesize this granular area to be the intracellular site of photogenesis in
E. spinax
, as it is also the most fluorescent part of the photocyte.
Three species of neonate and juvenile sharks (
Heptranchias perlo
,
Squatina aculeata
,
Etmopterus spinax
) were captured as by-catch from a commercial trawl fishing from depths between 360 and 430 m ...in the North-eastern Mediterranean Sea. Two neonates of
H. perlo
, five neonates of
E. spinax
and one juvenile of
S. aculeata
were for the first time identified in the above region.
Bioluminescence is a common feature in the permanent darkness of the deep-sea. In fishes, light is emitted by organs containing either photogenic cells (intrinsic photophores), which are under direct ...nervous control, or symbiotic luminous bacteria (symbiotic photophores), whose light is controlled by secondary means such as mechanical occlusion or physiological suppression. The intrinsic photophores of the lantern shark Etmopterus spinax were recently shown as an exception to this rule since they appear to be under hormonal control. Here, we show that hormones operate what amounts to a unique light switch, by acting on a chromatophore iris, which regulates light emission by pigment translocation. This result strongly suggests that this shark's luminescence control originates from the mechanism for physiological colour change found in shallow water sharks that also involves hormonally controlled chromatophores: the lantern shark would have turned the initial shallow water crypsis mechanism into a midwater luminous camouflage, more efficient in the deep-sea environment.
Straube, N., Kriwet, J. & Schliewen, U. K. (2010). Cryptic diversity and species assignment of large lantern sharks of the Etmopterus spinax clade from the Southern Hemisphere (Squaliformes, ...Etmopteridae). —Zoologica Scripta, 40, 61–75.
Many species of the speciose deep‐sea shark family Etmopteridae (lantern sharks) are a regular by‐catch component of deepwater trawl and longline commercial fisheries. As for many elasmobranchs, the low fecundity, late sexual maturation and extreme longevity of the lantern sharks increase their susceptibility to overfishing. However, the taxonomic uncertainty within etmopterids and the poorly known patterns of dispersal of these shark species hampers the establishment of reasonable monitoring efforts. Here, we present the first molecular approach to clarify the taxonomy and distribution of a morphologically uniform group of lantern sharks comprising Etmopterus granulosus and closely related congeners by using nucleotide sequence data from the mitochondrial DNA cytochrome oxidase I gene and amplified fragment length polymorphisms. Samples were collected from several locations in the Southern Hemisphere, where the species occur. Our analyses reveal a high level of cryptic diversity. E. granulosus is not endemic to Chile, but instead has a widespread distribution in the Southern Hemisphere being synonymous to New Zealand Etmopterus baxteri. Conversely, specimens previously assigned to E. baxteri from off South Africa apparently represent a distinct species. Our results provide the basis for the re‐description of E. granulosus and E. baxteri which will help in the establishment of useful monitoring and management strategies.
Intraspecific variation in the number of vertebrae is taxonomically widespread, and both genetic and environmental factors are known to contribute to this variation. However, the relative importance ...of genetic versus environmental influences on variation in vertebral number has seldom been investigated with study designs that minimize bias due to non-additive genetic and maternal influences. We used a paternal half-sib design and animal model analysis to estimate heritability and causal components of variance in vertebral number in three-spined sticklebacks (Gasterosteus aculeatus). We found that both the number of vertebrae (h(2) = 0.36) and body size (h(2) = 0.42) were moderately heritable, whereas the influence of maternal effects was estimated to be negligible. While the number of vertebrae had a positive effect on body size, no evidence for a genetic correlation between body size and vertebral number was detected. However, there was a significant positive environmental correlation between these two traits. Our results support the generalization--in accordance with results from a review of heritability estimates for vertebral number in fish, reptiles and mammals--that the number of vertebrae appears to be moderately to highly heritable in a wide array of species. In the case of the three-spined stickleback, independent evolution of body size and number of vertebrae should be possible given the low genetic correlation between the two traits.
The shark genus
Etmopterus encompasses numerous deep-sea species that are widely distributed throughout the world's oceans and share the capability to emit light thanks to numerous tiny epidermal ...photogenic organs called photophores. Despite the potential wide ecological interest of this light emission, it is still a poorly studied aspect of shark biology, mostly due to the challenges inherent to the study of uncommon deep-sea animals. During a collection trip in waters around Okinawa Island, we had the opportunity to collect, maintain and study specimens of
Etmopterus splendidus, a small pelagic lantern shark that was not previously known from this area. Analyses show that (i) the photophore density of this species varies according to the different parts of the body, which led to a heterogeneous photogenic pattern; (ii) photophore harbour the classical structure found in other etmopterid sharks, i.e. a cluster of photocytes enclosed in a pigmented sheath and surmounted by pigmented and lens cells; (iii) the physiological control of these photophores appears similar to what was found in the distantly related
Etmopterus spinax, i.e. including hormonal and neural inputs as well as the action of pigmented cells overlying the photocytes. These results indicate that
E. splendidus luminescence is probably used for more than one purpose, and support the idea that the physiological control of lantern shark photophores was selected early in the evolution of these sharks.
► We investigated living specimens of a rare dwarf pelagic luminous shark. ► We described the organization of its luminescent structures. ► We investigated the physiological control of its luminescence. ► Its luminescence is probably used in camouflage and intraspecific behaviours. ► An early origin of hormonally controlled photogenic organs in sharks is suggested.
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