**6. Conclusions**

Luminescence has evolved and been prevalent in a wide variety of marine species being utilised for a number of predative, defensive and communicative functions. Some organisms have developed predator–prey relationships where the predator is able to acquire and utilise luciferin with its own luciferase to emit light. This chapter has reviewed many of the species that exhibit this type of behaviour and utilise semi-intrinsic luminescence, in addition to describing the sources of luciferin in these systems and how this molecule is able to be taken up by consumers. Although this has only been experimentally tested in a few species, it is highly likely that a number of other luminescent organisms utilise this, especially as it is a lot easier from an evolutionary perspective to obtain luciferins from the diet, compared with synthesising them from amino acids or other unknown biosynthetic pathways. This phenomenon raises the question of whether small molecules and enzymes involved in other biological processes are able to be taken up in this manner as well which could provide an evolutionary selection process that is an alternative to molecular evolution.

## **Notes/thanks/other declarations**

This work is supported in part by JST CREST (JPMJCR16N1). We would also like to thank Dr. Ken-ichi Onodera and Okinawa Churaumi Aquarium for providing some photos for this chapter.

*Bioluminescence - Technology and Biology*
