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Exclusive: Source of underwater disco light show discovered

What follows is an interview with Lindsey Doughtery, the University of California-Berkley graduate student who recently discovered the source of an amazing underwater light show put off by disco clams. After considerable research and observation, Dougherty and her team discovered that the clam has a highly-reflective lip that mirrors light from its environment. Read more about the discovery and research here.

The news release says that the clam has 40 eyes and may/may not be able to see out of them. Why so many? Especially if they are not visually functioning?

It’s surprising how many organisms have multiple eyes – for example, some species of spiders have up to 8 eyes, chitons have hundreds of eyes, and scallops, which are related to clams, have up to 100 eyes. We know the disco clams can detect light using their eyes, but we don’t know whether they can form images (likely not). The most important question is whether they are sensitive to the display that other disco clams create – after all, the signal an organism produces is only effective when the intended receiver can process and respond to it.

The lips must be incredibly reflective to produce such reflections in low light. What are the reflections like in brighter environments?

The lips are indeed extremely efficient in low-light and blue-green environments. They are very reflective in white light situations as well, as exemplified in the video we’ve taken when shining a dive light on them, but they excel in their natural, dimmer crevice habitats.

Do both male and female members of the species reflect light like this?

Yes, males and females both reflect light. We have not encountered any juveniles smaller than about 1cm across, so we don’t yet know at what developmental stage the display begins. We do see it in both small and large clams, though (we believe the clams are protandrous hermaphrodites, which means they start as juvenile males and mature into females).

What are your theories about why they do this?

Our three main hypotheses are that they are using the light display to:

  1. Lure food (“phototaxic prey luring” as many plankton are attracted to light – we’re testing the flash rate responses to food, as well as testing the food itself (phytoplankton and zooplankton) for phototaxia using the light as a prey lure.
  2. Lure one another (“conspecific recruitment” for settlement and spawning purposes – while diving in the field in Indonesia and Australia, I found that about 60% of the clams were inhabiting holes in 2 or more, and in different class sizes (suggesting asynchronous settlement). This suggests the light display could be a cue for spawning purposes and close proximity in settlement.
  3. Ward off predators (“aposematism” – the disco clams respond to a looming trial, which approximates an approaching predator, by doubling their flash rate temporarily).

It’s obviously the most interesting question, so we’re trying our best to figure it out!

What will this reveal about other aspects of science or discovery? How will your discoveries aid future research?

One of the most interesting aspects of this display is its effectiveness in low-light situations (at depth and within crevices). The silica nanospheres are incredibly effective at broadband scattering, and the combination of the highly absorbent opposite side creates a very dynamic display when the sides are furled and unfurled (which is also interesting, as movement in order to create a dynamic display through scattering is utilized). The other unique aspect is that this is the first instance of the use of silica nanospheres in an animal (diatoms use a hexagonal arrangement and the beetles and butterflies use scales). Similar to Qualcom’s mirasol display that was modeled after the iridescence in butterfly wings, the nanostructure and movement of C. ales could have biomimicry potential in low-light situations or in environments that are dominated by blue-green wavelengths. My work now is centering on:

  • The behavioral purpose of the flashing
  • Their eyes and optical abilities
  • The source of the silica (from diatoms or oceanic uptake)
  • Their phylogenetics.

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