An important adaptation of Photeros annecohenae is its ability to be bioluminescent. This ability is not only crucial for mating but also extremely important for the organism in deterring predators. When preyed on by plankton-consuming fish or crustaceans, such as the Cardinalfish, these ostracods emit a cloud of luminescence lasting as long as a minute both around and within the predator (James G. Morin 2011). This often  results in the regurgitation of the ostracod (See below video.) as well as startles and potentially temporarily blinds the predator. Most importantly, this sudden luminescence attracts the predator’s predators (the secondary predators). Because of this, the ability of Photeros annecohenae to release luminescence when attacked is termed the “burglar alarm effect" (Morin 1986). Because the “burglar alarm effect" causes predators of Photeros annecohenae to be more conspicuous to their own predators, they avoid consuming the ostracods as well as other organisms that are “ostracod-sized.” Because male ostracods are luminescent when displaying, they are invulnerable to predation at these times. The above photo displays a predator of ostracods.


     It is thought that the protein luciferin, a component of bioluminescence in ostracods, initially evolved as a defense (warning to predators that the ostracod will taste bad). Then, its "matching" enzyme, luciferase, evolved, allowing for the production of bioluminescence (Gerrish Personal Communication). This bioluminescence worked better for predatory defense as well as courtship displays. (Gerrish and Morin 2008) This could be seen as an adaptation to darkness and has lead to species-specific displays (See photo to left.) that allow for communication about reproductive status and the presence of a given species. The mating displays are thought to be an adaptation to the effect of sexual selection: They allow for competing males to “wow” potential female mates that are capable of choosing their male partner (Cohen and Morin 1990).

      This leads to the species-specific habitats discussed on the Habitat page. It is thought that species of bioluminescent ostracods reside in distinct habitats to make it easier for females to distinguish their own species' displays (Gerrish Personal Communication). If many species of bioluminescent ostracod were displaying in the exact same place at the exact same time, there would be a clutter of displays, and one species of female may be distracted by another species' display. Overall, the courtship routines and, therefore, mating would not be as a effective or efficient. This issue is also avoided by the fact that each given species begins displaying at a distinct time (Rivers and Morin 2009).

     Another adaptation involving Photeros annecohenae’s bioluminescent displays is the species' ability to exhibit “phenotypic plasticity.” (Rivers and Morin 2009) This means that the organism can quickly adapt physically to changes in the environment. In bioluminescent ostracods, especially in Photeros annecohenae, this is seen in the shift of ostracods acting as “leading” signalers ("leaders"), that begin their mating displays first, entrainers, or signaling ostracods that begin their displays next to another species member’s display, and “sneakers,” who do not demonstrate luminescence but follow closely next to a luminescent male in hopes of grabbing a female mate (See Reproduction page for more information.).

      Many morphological adaptations of Photeros annecohenae revolve around the process of mating. Males possess a pair of antennae (first antennae) used to grasp a receptive female and grip her during mating. It has also been discovered that many of these adaptations enforce mating only within a given species. For example, a male’s copulatory organ (eighth limb) only fits comfortably inside a female of its own species. Also, spermatophores, sacs or sperm which males deposit onto female genitalia to ensure she cannot mate with another male, are species-specific, meaning the spermatophores of one species of male will not fit into the genitalia of a different species of female.     

     Other physical adaptations include the presence of a pair of second antennae, with setae attached to the ends, that aid in locomotion, especially that of swimming. These appendages extend through an opening in the carapace called the incisur. The pair of first antennae (used to grasp females during mating) may also be used as sensory structures to detect chemicals in the current from decaying fish or other food sources as well as the general environment around the ostracod. These ostracods react well to stimuli. As mentioned on the Classification and Nutrition pages, the second antennae are also used to distinguish food from other substances the ostracod comes across. The  complexity of the compound eye is also an extremely important morphological adaptation for Photeros annecohenae. Eyes this complex are only seen in ostracods that exhibit bioluminescent courtship behavior and help the species see and distinguish the displays. They are good detectors of not only light but distance and contain many ommatidia. The medial eye detects light levels as well, including distinguishing between day and night. All ostracods' carapaces are streamlined to allow for easy movement through the water and contain a keel at the back to help them stay upright. This chitinous carapace is an adaptation that protects an ostracod from its predators by making it more difficult to consume. The light organ as well as the nozzles present on the organism's upper lip make bioluminescence possible.

     Molting is an adaptation of all arthropods. Because all arthropods have a chitinous exoskeleton that covers all of their extremities, they must shed this through the process of molting in order to get to the next developmental stage.

To learn more about how the adaptation of bioluminescence is used, visit the Reproduction page!