Introduction: This blog examines the relationship between the Hawaiian Bobtail Squid and a bioluminescent bacterium. The Hawaiian Bobtail squid acquires an enhanced ability to capture prey and avoid predators, while the bacterium receives key nutrients from residing within the squid . Distribution of this aquatic relationship is limited by the habitat of the squid (Hawaii). Several bioluminescent bacteria cycle through a single squid daily.
Description of Relationship: The type of relationship observed between Euprymna scolope(Hawaiian Bobtail squid) and Vibrio fischeri(bioluminescent bacterium) is unique to organisms with specialized structures called light organs. These light organs are specialized structures that have evolved to allow the organisms that house them to create light. While the evolutionary reason for this structure is unknown, many individuals hypothesize that certain marine organisms form these light organs through adaptation from dark environments in order to increase vision. By using Combes’ logic, this is a textbook example of a symbiosis (when individuals of two species whose evolution has previously been independent associate with one another so that each benefits) . Justification for this statement will be discussed in the cost/benefit analysis section. The life cycle or interaction between these two partners is interesting. Each morning, a squid will eject the bacteria from the previous day and take in new/infant bacteria of that same species. Over the course of the day, the bacteria will multiply and be utilized by the squid at night. The next day the squid repeats this peculiar behavior of ejecting old bacteria and absorbing new bacteria .
Cost/Benefit Analysis: In this relationship, both organisms seem to benefit one another. By properly utilizing the bacteria to reduce its shadow from the moonlight, the Euprymna scolope is able to become a better predator to the prey below and evade its own predators through camouflage. Vibrio fischeri receive a special source of nutrition in the form of amino acids and other essential compounds that are provided to them via the Euprymna scolope’s light organ and bacteria are provided with shelter . The extra weight the squid obtains from housing these bacteria, thus reducing their speed and more likely to be eaten by a predator, is a questionable cost. This cost seems to be outweighed by the beneficial ability the bacteria provide to squid. The squid does not appear to exert any recognizable cost on the bacteria.
 Art of Being a Parasite, Claude Combs