Male aggregation behaviour in the fireflies Photinus ignitus and Pteroptyx malaccae

Abstract

Apart from the bioluminescence involved, the remarkable synchronously flashing aggregations formed by males of some Pteroptyx species bear little resemblance to the roving male flash behaviour observed in Photinus and many other firefly species. However, synchrony has been documented in some Photinus species and could be an emergent property of competitive flash behaviour among males at high male densities. We used “virtual fireflies” (VFIs), programmable microcomputers driving LEDs, in order to explore how males aggregate into potentially high density groups in both Photinus ignitus and Pteroptyx malaccae. We observed the frequency of flashes from roving male P. ignitus fireflies at the sites of VFIs programmed to conspecific and heterospecific flash patterns as well as in the absence of flash patterns in Lancaster, Massachusetts, USA. We found roving males were more frequent and flashed more frequently at sites with conspecific male flash patterns. To explore the role of flash synchrony and conspecific signals in male P. malaccae, we varied VFI flash treatments each night at two sites along a jetty on the Chao Phraya River in Samut Prakarn, Thailand. These treatments included conspecific and heterospecific synchronous flash patterns as well as conspecific flash patterns produced asynchronously. We found that there were significant differences across treatments in terms of the number of fireflies approaching and synchronising with the virtual fireflies. In each case we observed the greatest number of fireflies approaching, landing near, or synchronizing with the synchronous species-specific flash pattern. Our research illustrates that males approach conspecific flash patterns while searching in both Photinus and Pteroptyx fireflies, but that P. malaccae males only approach synchronously flashing groups of males. While it remains unclear how synchrony has evolved in Pteroptyx, it seems likely that male competition for access to females has played a role in selecting for the evolution of both loose roving aggregation behaviour in P. ignitus as well as in the more dense stationary leks observed in synchronous P. malaccae.