Comparative analysis of light spectra emitted by two firefly species: Luciola italica and Luciola pedemontana

Abstract

Light plays an important role in fireflies (Coleptera, Lampyridae) and emission spectra and signalling patterns are usually species specific. In Italy there are two species of fireflies belonging to the genus Luciola: Luciola italica and L. pedemontana. No information was available on the light spectrum emitted by L. italica in vivo; moreover, the only data obtained on L. pedemontana dated back more than 50 years and were obtained using outdated measurement equipment. To fill this gap, we studied the spectra of adult males and females of both species. Samples were collected from the western central Po floodplain. Adults were sampled in the early part of the night when they were engaged in mating activity. The next day they were brought to the laboratory and their light emission was analysed using a spectrometer. The maximum emission wavelength (λ max) ranged from 571.8 nm to 584.8 nm. The values of λ max emitted by females of L. italica (581.5±2.4) and L. pedemontana (575.9±2.6) were significantly different. The plots obtained from the light emission measurements show a clear asymmetry, with a shorter tail on the left and a positive skew on the right. As light spectra depend on the structure of luciferases, such differences may indicate ongoing changes in the molecular composition of these enzymes resulting from the genomic divergence of the two species. The spectra of L. italica and L. pedemontana fall in the yellow region and are comparable to those of other Luciola species living in eastern Asia.