Illuminating the Evolutionary Past of Bioluminescent Fish  

In David Attenborough’s documentary episode “Life that Glows”, several different organisms that utilize bioluminescence are featured, and these organisms use bioluminescence to improve fitness in terms of attracting mates or prey. Splitfin flashlightfish (Anomalops katoptron) are a nocturnal deep-sea fish specifically discussed in this documentary. These fish use torch-like organs under their eyes to identify and attract food, communicate with each other, and evade predators [1]. These torch-like organs emit blue light due to the presence of symbiotic bacteria that catalyze luminescent products within the fishes’ organs.

Bioluminescence has evolved independently fifty times, in thousands of species, both on land and under water [2]. Flashlight fish are part of the Anomalopidae family, which makes up the majority of all bioluminescent fish species. Recent research suggests that these bioluminescent bacterial symbionts have an obligate association with specific hosts, suggesting distinct coevolution for each bioluminescent fish. This host specificity of the bacteria suggests coevolution involving the bioluminescent bacteria and splitfin flashlightfish. Coevolution is also suggested by the anatomical adaptations of the host to harbor and control the light of these light-producing bacteria [3]. One such adaptation is the existence of a reflector on the back of the sub ocular light organ (photophore) that enhances the effect of the bacterial luminescence [4]. This symbiotic relationship benefits both organisms: the flashlight fish is benefitted through the various processes previously mentioned, and the luminescent bacteria benefits from an environment provided by the host that gives the bacteria access to nutrients and that promotes bacterial growth. Over its evolutionary history, this symbiotic relationship was strengthened and selected for due to the benefits it confers to both organisms.

by Karunesh Polireddy & Jordan Peyrot Des Gachons

Life that Glows: David Attenborough, starting at approximately 13:28

References

  1. Munz F & W Mcfarland. 1977. Evolutionary adaptations of fishes to the photic environment. The Visual System in Vertebrates Handbook of Sensory Physiology, 193-274.
  2. Widder EA. 2010. Bioluminescence in the ocean: origins of biological, chemical, and ecological diversity. Science 328(5979): 704-708.
  3. Karplus, I. 2014. Symbiosis in fishes: The biology of interspecific partnerships. Wiley Blackwell.
  4. Hellinger, J, Jägers P, Donner M, Sutt F, Mark MD, Senen B, & S Herlitze. 2017. The flashlight fish Anomalops katoptron uses bioluminescent light to detect prey in the dark. Plos One 12(2).

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