You Light Up My World, Photeros annecohenae!

While some may give chocolates to the ones they love, there are some individuals that pull out the fireworks and devote a whole light show to attracting potential mates! Meet Photeros annecohenae, a species of ostracod inhabiting shallow seagrass habitat in the western Caribbean Sea. Male P. annecohenae create a beautifully complex bioluminescent courtship display, emitting flashes of blue in the water during the night in hopes of attracting females to mate.

A female (top left) and male Photerus annecohenae. Note that females are larger than males (sexual dimorphism) and that males have bigger eyes [1]. (Credit: Jim G. Morin).

Ostracods are tiny (from less than a millimeter to a few millimeters long), laterally flattened, crustaceans in the family Cypridinidae, which has several species with a neat skill: they possess a special gland (called the light organ) that allows them to create light by secreting compounds [2]. This form of light production is called bioluminescence. Luminescent cypridinid ostracods can use light to for predator defense and/or for courtship displays. Those that use light to surprise and deter predators emit light when threatened or even when swallowed, causing predators to spit them back out in order to avoid being spotted by their own predators [3]. In some species, bioluminescence can also used for mating displays, but only by males. Depending on the species, males employ different patterns of light pulses (seen as a string of dots) that attract only conspecific females, or females of the same species. In the case of P. annecohenae, males show off just how dazzling they can be by performing little dances in which they emit short bursts of light through reactions by luciferin and luciferase, secreted from their upper lip, as they ascend vertically up the water, all in hopes of finding a mate [3].

Just as a fireworks show takes place during the night when the brilliance of light can really wow the audience, P. annecohenae’s courtship display is performed nightly, in absolute darkness, when males have the best chance of being spotted by females. At this time of the night, they initiate their “dance,” which lasts an average of 45 minutes. Their display begins with a stationary phase, in which they produce second-long (or less) pulses of bright blue light, catching the attention of potential female mates. Then, in the next phase, called the helical phase, males spiral vertically up the water column and create more rapid flashes of light that are less bright, traveling about 60 centimeters (2 feet) total [4]. If a male is successful and an interested female approaches, the male grabs onto his newfound partner with his first antennae and the pair sexually reproduce through internal fertilization.

Male and female P. annecohenae, including several juvenile instars. (Credit: Jim G. Morin).

However, because sexual selection is most likely at play here, competition between males is very common [2, 5]. There are three different types of male contenders, all hoping to find a mate: 1) those that are first to begin their luminescent displays, 2) those that entrain, or synchronize, their displays next to the leading males, and finally, 3) those that do not display at all and instead stealthily sneak into another male’s courtship as a female approaches the displaying male and mate with her surreptitiously [4].

This is a series of images showing how a typical nightly courtship display would look like, where certain males initiate the display (2), others follow (3), and different species display their own unique “light shows” nearby (4 and 5). (Courtesy of Gretchen Gerrish [4])

One can imagine how all these courtship displays can in concert form a larger luminescent display against the black backdrop of the nighttime ocean— P. annecohenae sure know how to impress potential mates! Attracting others with a flashy dance seems to have worked rather well for P. annecohenae, so next time you are out on the dance floor, think about adding some glow sticks or standing right where the disco ball hits you just right!

By Maria Robles Gonzalez. Edited by Liz Boatman. Special thanks to Jim G. Morin, Gretchen A. Gerrish, and Trevor. J. Rivers for providing resources and images.

 

Learn More: 

[1] Gerrish, G. A., and J. G. Morin. “Life cycle of a bioluminescent marine ostracode, Vargula annecohenae (Myodocopida: Cypridinidae).” Journal of Crustacean Biology 28(4). (2008): 669-674.

[2] Rivers, T. J., and J. G. Morin. “Female ostracods respond to and intercept artificial conspecific male luminescent courtship displays.” Behavioral Ecology 24(4). (2013): 877-887.

[3] Rivers, T. J., and J. G. Morin. “Complex sexual courtship displays by luminescent male marine ostracods.” The Journal of Experimental Biology 211. (2008): 2252-2262.

[4] Kramolis, K. “Photeros annecohenae.” University of Wisconsin-La Crosse Organismal Biology. 2011.

[5] Morin, J. G., and A. C. Cohen. “Bioluminescent Displays, Courtship, and Reproduction in Ostracodes.” Crustacean Sexual Biology. (1991): 1-16.