Claes, Julien
[UCL]
Delroisse, Jérôme
[Université de Mons]
Mallefet, Jérôme
[UCL]
Etmopterid and dalatiid sharks are among the most enigmatic bioluminescent organisms. They display thousands of epidermal light-producing organs (photophores) that form a diversity of patterns and are primarily controlled by hormones rather than by nerves, the condition in other animals. Various adaptive benefits have been proposed for the light produced by these epidermal organs including camouflage by counterillumination (ventral photophores), intraspecific communication (lateral photophores) and aposematism (dorsal spine-associated photophores). Like other shark species, etmopterids and dalatiids have their skin covered with placoid scales (denticles), which are known to be involved in various tasks including hydrodynamism, protection from predators and ectoparasites and reduction of substrate abrasion. In bioluminescent sharks these denticles have evolved peculiar squamation patterns that are thought to allow photophore accomodation. However, variations in the crown morphology of these structures lead to different degrees of interaction with the photophores and their light emission. Here, we investigated the link between four squamation patterns (internal scales, pavement-like, thorn-like and bristle-like) and several parameters across specimens from 37 shark species (≈75% of current bioluminescent shark diversity) in order to determine if denticle morphology influences photophore organisation and performances. Unexpectedly, pavement-like squamation is linked to higher photophore density and cover (but smaller photophore diameter), and overall photophore performance appears equivalent in external denticles. Future work including optical lithography and computational modelling, will attempt to understand how needle-like denticles, which form a dense external coverage, still allow the delivery of underlying photophore light.
Bibliographic reference |
Claes, Julien ; Delroisse, Jérôme ; Mallefet, Jérôme. Interaction between bioluminescence and denticles in sharks.Living Light: Uniting biology and photonics (Namur, Belgique, du 10/04/2014 au 12/04/2014). |
Permanent URL |
http://hdl.handle.net/2078.1/142345 |