Meeting Abstract
The origin of courtship signals may cause faster speciation and impact biodiversity. But discovering the genetic basis for diversification is usually difficult. Because aspects of the mating signals of cypridinid ostracods (“sea fireflies”) are produced by a simple chemical reaction outside the body, we believe we can discover specific genetic changes that diversified those signals. Male sea fireflies court females by spitting out small boluses of mucus laced with enzyme (luciferase) and substrate (luciferin), which react to make light. Males make trains of glowing dots in different patterns depending on species. While these signals clearly diversified in pulse duration, direction, and inter-pulse distance, previous work suggested the color of luminous displays is invariant across species, and therefore unlikely to be used in mate recognition or species discrimination. However, by measuring the emission spectra of more species’ luminescence, we found significant variation in color. Most strikingly, Photeros species have green-shifted spectra in both lambda max (wavelength with most photons) and FWHM (spectrum width). The lambda max of Photeros is 464 nm, while other signaling species are 458-459 nm. The FWHM of Photeros is 94-97 nm, while that of other signaling species is only 81-87 nm. We speculate the green shift could produce a more conspicuous signal by reflecting off of seagrass in the habitat of most Photeros. Furthermore, based on published mutagenesis of the luciferase of Cypridina (a non-signaling but luminous relative), we know that particular amino acid mutations change the emission spectrum in vitro. Some of the mutations that shifted Cypridina emission toward green are present naturally in Photeros. Therefore, by expressing mutated luciferases in vitro, we will be able to understand the molecular basis of evolved variation in emission spectra of sea fireflies.
