Abyssal bioluminescence

Abyssal seafloor is considered to extend from 2000 to 6000m, it is a cold dark place (0 to 4°C no sunlight), it represents more than 70% of the ocean and about 50% of the total planet surface. This vast territory was virtually unknown a century ago and it is only quite recently that during 10 years a systematic exploration was conducted by one international consortium called CeDEMar (Census of the Diversity of Abyssal Marine Life). As a result, an astonishing biodiversity was found and the researchers aimed to describe 500 commonly found species. It is believed that only 1% of this biotope has been sampled and a huge number of organisms remain unknown. Rarely sampled, the abyssal benthic fauna capability to produce light is virtually unknown. Few reports were produced using highly sensitive camera mounted on an autonomous lander send to the seafloor. Abyssal luminous organisms were either not recognized or could not be identified at specific level but most of them belong to the following taxa: Cnidaria, Ctenophora, Copepods and Echinoderms. During a recent expedition on the East coasts of Australia, systematic surveys of abyssal plains from Hobart to the Great Barrier Reef were realized using bottom beam trawls. These brought back at the surface specimens that were observed in a cold dark room enabling us to document for the first time some bioluminescent display of rarely seen organisms using sensitive camera, video recordings, luminometer and microspectrophotometer. Images and data from benthic abyssal organisms revealed the diversity of abyssal bioluminescence. Tissue were frozen and/or fixed for further analysis, work is in progress to describe this fauna. Deep down animals shine light but for what purpose, this remains a mystery, new expeditions will be necessary to try to better understand abyssal bioluminescence

Ten years of shark luminescence study: a synthesis

Marine fishes are the only vertebrates able to produce visible light. For more than two centuries, bioluminescence has been documented in Osteichthyes and a large amount of experimental data are available for these bony fishes. On the contrary, until recently, luminescent sharks (10% of the shark species are luminous) were poorly investigated mainly due to the logistical difficulties to access and maintenance of the species in good physiological conditions. Since 2007 experimental studies on bioluminescent sharks were conducted by researchers of my laboratory. Data presented will summarize ten years of shark luminescence studies from species belonging to two families: Etmopteridae and Dalatidae. Model species, used to understand how, why, with which structures and where sharks are emitting light, are: Etmopterus spinax (velvet belly lantern shark), Etmopterus molleri (slendertail lantern shark), Etmopterus splendidus, (splendid lantern shark) and finally Squaliolus aliae, (pigmy shark). We discovered that light emission is under hormonal control, luminescence control mechanism model was build which also involved neurotransmitters (neuromodulators). Difference in the control mechanisms of light emission between Etmopteridae and Dalatidae as well as recent phylogenetic analysis suggest a unique appearance of bioluminescence during evolution: Dalatidae being the first sharks to glow in the dark. Ontogeny, body pattern, organisation and densities of photophores as well as differential controls suggest that these light organs are involved in various functions such as countershading, aposematic warning, specific recognition, schooling and sexual mating. The nature of the luminous system used by sharks remains unsolved since none positive detections using classical cross-reactions with known luciferin/luciferase were observed; further research should be dedicated to this aspect in order to discover the structure of a putative « sharkline ». Work in progress on the physiology of luminous sharks will be presented during the congress by PhD students of the laboratory

Ecological functions of shark luminescence

Sharks from the Etmopteridae and Dalatiidae families are among the most enigmatic bioluminescent organisms. Although they encompass about 12% of current shark diversity, with over 50 described species, their luminescence is rarely observed. Moreover, contrary to the situation encountered in other animals, their intrinsic light organs (photophores) are primarily controlled by hormones rather than by nerves and form a diversity of patterns whose adaptive advantage has long remained obscure. This work aims to synthetize recent advances made in the field of shark luminescence ecology as well as to present novel experimental data in order to inspire future research. It involves various techniques such as in vivo luminescence measurements [via an optic fibre coupled to a luminometer (Berthold FB12)], spectrophotometry [with a mini-spectrometer (Hamamatsu Photonics C10083CA)], stereology and visual modelling

Bioluminescence of sharks a case study, Etmopterus spinax

Bioluminescence arose independently in a wide range of species, from bacteria to fishes, which are the only luminous vertebrates. Consequently, luminescent species demonstrate a great diversity in the structure, in the control, as well as in the function of their photogenic system. Among luminous organisms, sharks are probably the least investigated group and extremely few information is available concerning their bioluminescence, even though more than 50 shark species, i.e. about 13% of current species, are endowed with the ability to emit light. In this work, we present a synthesis on shark luminescence as well as the first results of a pluri-disciplinary approach of the velvet belly lanternshark, Etmopterus spinax. Light and epifluorescent microscopy, luminometry, as well as digital imaging analysis were used to follow the development of luminous structures during the ontogeny of this species, from embryos to old individuals. The potential functions of bioluminescence were discussed based on light production of the shark and on theoretical optical models. In addition, we provide the first pharmacological analysis of the luminescence control in this animal

Deeper into the mechanistical approach of the shark luminescence control

Slendertail lanternshark, Etmopterus molleri, displays a hormonal control to regulate its bioluminescence. Luminous organs, photophores, are composed of a cup-shaped pigmented cells enclosing the emitting cells, photocytes, surmounted by a multilayer cell zone called the iris-like structure (ILS) and topped by one or several lens cells. ILS cells, acting as a light organ shutter, contains many cells endowed with melanin pigments allowing the modulation of the light output. Previous studies demonstrated that prolactin (PRL) and melatonin (MT) trigger the emission of light, while alpha melanocyte stimulating hormone (α-MSH) inhibits the luminescence. These hormones are known to be involved in the regulation pathway of vertebrate skin pigmentation for shallow-water sharks. In this study, we investigated the effect of proteins involved in the pigmentation pathway on the light emission: adrenocorticotropic hormone (ACTH), cAMP-dependent protein kinase (PKA), protein kinase C (PKC) but also the two main cytoplasmic motor of vesicle movement in cells, dynein and kinesin proteins. ACTH acting as a melanin pigment degranulation factor, active PKA and PKC acting on the pigment granule dispersion by phosphorylating attachment sites of kinesin to microtubules. Kinesin is responsible for intracellular centrifugal movement of pigment granule, conversely to dynein which carry organelles on microtubules to the center of the cells. Results demonstrated, first, that ACTH inhibits the light emission like α-MSH. The implication of pigmentation pathway on the bioluminescence control is highlight by several evidences. These results suggest a functional switch from the skin pigmentation control to the luminescence control mechanism through the melanocyte pigmentation within the ILS cell layer. The ancestral mechanism of countershading to camouflage the body and mimic the background in the shallow-water sharks was hypothetically coopted for the counterillumination system of the lanternshark and possibly bioluminescent sharks in general

First luminescence survey of Okinawa brittle stars

A microprocessor-based system of photoplethysmography and its use in measuring skin blood flow is described. The system was designed specifically for use over long periods and for the analysis of the output to be handled by a personal computer. The photoplethysmograph described in this paper is shown to be a qualitative method for assessment of changes in peripheral skin blood flow. There is potential for use of this instrument in a variety of clinical conditions