Rabu, 27 Maret 2013

Phylogeny of North American Fireflies (Coleoptera:Lampyridae): Implications for the Evolution of Light Signals

More than 2,000 described species of fireflies live around the world, but very little is known of their evolutionary relatedness. Of the approximately 120 species in North America, Dr. James Lloyd at the University of Florida has described three methods of mate attraction: chemical signals (pheromones), glows (continuous light signals), and flashes (short intermittent light signals).

It's well known that fireflies use flashes to find members of the same species when searching for a mate. It has been suggested this luminescence is a carryover from the larval stage where it serves as a warning of bad taste, and has been co-opted in many species of fireflies as a mating signal.
Although all larval fireflies produce a faint glow from paired light organs on their eighth abdominal segment, the presence, location, shape, and use of light organs varies greatly in adults. Only some adult fireflies produce light; others use chemical signals for mate attraction. In addition, only a few fireflies use a similar light organ to the larvae — the light organ of most adult fireflies is located on the sixth and seventh abdominal segment.
In this study, the authors use a phylogenetic approach — comparing DNA as well as morphological characteristics — to illuminate the relationships of North American fireflies and the evolution of their mating signals. The study included 26 species from 16 North American genera and one species (Pterotus) that had recently been removed from the firefly group. To test whether all the North American fireflies evolved from a single ancestor, three European and three Asian fireflies were also studied.
The study results showed that the North American fireflies did not evolve from a common ancestor, but different groups are closely related to fireflies from Europe, Asia and tropical America. Further, in nine difference instances, it was found that the use of light as a mating signal may once have originated among fireflies and was lost.
The use of short flashes independently originated among groups two to three times. Short flashes were replaced at least once by the use of long glows, and light signals as mating signals were lost at least three times in the study group and replaced by pheromones as the main signal.
This chart (PDF) shows the evolutionary relationships — groups of fireflies evolved from a common ancestor and therefore most closely related to each other — of 16 groups or genera of North American fireflies, as well as their method of attracting a mate: do they use a flashing signal (FL), a constant or extended glow (EG), or chemical signals (CH)? The fireflies that we are counting in the Firefly Watch program are the flashing fireflies — particularly Photinus, Pyrctomena, and Photuris.

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