Discovery of the female of Pyrocoelia prolongata in Taiwan (Coleoptera, Lampyridae)

Abstract The female of Pyrocoelia prolongata Jeng & Lai, a diurnal lampyrid species from Taiwan, is described for the first time. A single individual was found in a small, shady, dry streambed at the edge of a mixed forest at 2700 m elevation. The individual glowed in darkness and would move its abdomen up and down when disturbed and as a deterring behavior. A key to the females of the species of Pyrocoelia Gorham in Taiwan is provided. The morphology of photogenic organs of females and the function of bioluminescence of day-active species of Pyrocoelia are discussed.


Introduction
The genus Pyrocoelia Gorham is a group of Asian lampyrids including more than 60 known species (McDermott 1966;Jeng et al. 1999b). Males of the genus are alate while, where known, females have vestigial elytra to various degrees and lack hind wings. They can be divided into diurnal and nocturnal groups in which the males possess well-developed photogenic organs in the former but reduced in the latter.
The nomenclature of Pyrocoelia was clarified and the species of Taiwan were revised by Jeng et al. (1999b). Several publications provided additional information and images of the females of Taiwanese species (Ho 1997;Chen 1999Chen , 2003Ho and Chu 2002). Until now, four out of the five species (except P. prolongata Jeng and Lai, a species endemic to Taiwan) have confirmed females. Generally it is difficult to find the flightless females in the field, especially for the diurnal species (Ohba 1983). Because of the limited availability and dramatic sexual dimorphism, many of the females were identified to species by rearing larvae to adults. This has not been achieved for P. prolongata. Fortunately a female of the species was discovered in the field during a collecting trip to high mountains in southern Taiwan in 2004. Herein we describe this individual and its remarkable bionomics, and provide a key to the females of Taiwan's species of the genus.

Material and methods
The only female specimen available for study was collected by the late Japanese coleopterist Dr. M. Satô while digging in a dry streambed for ground beetles at high elevations in southern Taiwan. The female was kept in a transparent plastic cup which was spread with wet tissue paper and moss to maintain suitable humidity and for observation.
Measurements were made by outlining the target structures under a Nikon SMZ-10 microscope with a camera lucida. Body length (BL) was measured as the distance between pronotal and abdominal apices when the body was fully stretched, and body width (BW) as the greatest distance across the abdomen. The abbreviations PL and PW denote pronotal length and width, respectively; while T#, P#, and S# refer to the tergite, pleurite, and sternite of the #th abdominal segment (true segmentation), respectively.
systematics Pyrocoelia prolongata Jeng and Lai http://species-id.net/wiki/Pyrocoelia_prolongata Pyrocoelia prolongata Jeng and Lai, in Jeng et al. 1999b: 358. Diagnosis. The female is characterized by the bell-shaped pronotum which resembles that of the male and is one of the diagnostic characters of the species (Jeng et al. 1999b). No other congeneric species from Taiwan share a similar pronotal morphology and coloration in the female. The temporal and spatial distribution also fits that of P. prolongata.
Material examined. 1♀, S. Taiwan   Sexual dimorphism. Females differ from males by (generic level differences) 1, having shorter and less serrate antennae, much smaller compound eyes, and smaller palpi; 2, the mesoscutellum as broad as long; 3, the highly abbreviated elytra and absence of hind wings; 4, the fusion of metepisternum and metasternum; 5, having an intact abdominal S1; 6, having the hind angles of abdominal T1-7 not very acute; 7, S8 being deeply emarginate (cf., Jeng et al., 1999b); 8, (remainder are species-level differences) the bronze on the metanotum and abdominal T1; and 9, the narrower dark margins on the pronotum. In contrast to known females of Pyrocoelia, the female of P. prolongata is smaller than its respective males. We are not sure if this is simply individual variation or universal to the species.
Habitat and phenology. The female was found in a small, shady, and damp dry streambed at the edge of a mixed forest dominant with Taiwan Red False Cypress [Chamaecyparis formosensis Matsumura (Cupresaceae)] (Fig. 8A). It stayed on the substrate mixed of gravel and sand under a slate stone (Fig. 8B). An Alishan salamander (Hynobius arisanensis Maki) was also found in the microhabitat. Only a few species of Lampyrinae such as Diaphanes nubilus Jeng and Lai, Pyrocoelia formosana Olivier, and P. prolongata have ever been recorded from localities at such high elevations in Taiwan (Jeng et al. 1999a, some of the species denoted as "sp." at that time). No living male of P. prolongata was found in or around the locality during the 3-day duration of our collecting trip, except for an already dead individual. This suggests that the mating season might have come to an end. At that time, a population of the species in central Taiwan (Anmashan, Taichung County, alt. 2300m) was in a peak season of activity (C.F. Lee, pers. comm.).
Behavioral remarks. A male of P. formosana collected from the same locality was put together with the female in a transparent plastic container to observe their interaction. At first the male did not show interest in the female. Later it attempted to copulate with the female but failed due to the female's resistance. They eventually copulated after one day of captivity. The male perished soon after copulation, while the female survived the following week and laid three or four eggs before she died. All eggs failed to hatch and decomposed. The female glowed in darkness via a pair of photogenic organs on abdominal sternite 8. When wagging a finger around the female's head in a dusky environment, the female responded by powerfully raising her abdomen vertically to the body axis then laid down. It was found to be a one-to-one response after several repetitions. Apparently the female can detect the nearby moving subject and the action could be an intimidation to predators.

Discussion
The photogenic organs of females Pyrocoelia vary in number and position. Among the known taxa from Japan and Taiwan, P. analis, P. praetexta, P. rufa Olivier, P. miyako Nakane, and P. atripennis Lewis each have two pairs of morphologically recognizable lanterns on sternites 6 and 7 (Ohba 1983(Ohba , 2004Ho 1997Ho , 2003Chen 1999Chen , 2003; P. prolongata has a significant pair on sternite 8; while P. formosana, P. sanguiniventer, P. discicollis Kiesenwetter, P. matsumurai Nakane, and P. abdominalis Nakane do not have visible lanterns if not glowing (Ohba 1993). However, females of P. praetexta are able to emit six spots of light on sternites 6-8 and at least some species in the last group are confirmed to glow weakly in two spots on sternite 8 (Ho and Chu 2002;Chen 2003;Ohba 2004). It is therefore somewhat risky to interpret glowing behavior based solely on the external morphology of dead, and sometimes dried, specimens. Both sexes of P. prolongata can emit green light from a pair of lanterns on sternite 8. The males are active during the daytime to locate mates by raising their heads and elevating the antennae in a V-shaped position, used to detect female pheromones, as observed for many other diurnal species (Ohba 1983(Ohba , 1997a(Ohba , 1997b(Ohba , 2004. Occasionally they can be found at night owing to their bioluminescence. Ohba (1983Ohba ( , 2004 classified the diurnal species of Pyrocoelia from Japan into the CR system in which males find mates relying mainly on chemical signals and with the aid of relatively weak luminescent signals from mates over a short distance. However, the females of the diurnal species of Pyrocoelia, though able to glow, are extremely rarely seen in the field at night (Ohba 1983). The function of the female bioluminescence is thus questionable. Lall and Lloyd (1989) studied a day-active species, Lucidota luteicollis LeConte, and found that the electroretinographic sensitivity of the male (lamda-maximum= 530 nm) did not match its emission spectrum (lamda-maximum= 562 nm). These authors concluded that the male does not rely on light signals to find a mate, and suggested that the flightless female might be the light receiver. The female could use the male bioluminescence to recognize a mate in the shady, dusky microhabitat in which such long-wavelength light can be transmitted more so than short wavelengths, and thus be detectable by the female. The bioluminescent spectrum and electroretinographic sensitivity of Pyrocoelia are scarcely studied except for a few cases (Eguchi et al. 1984;Ohmiya et al. 1996). The night-active P. miyako Nakane emits green light with a lambda-maximum at 550 nm by males (Ohmiya et al. 1996). The electroretinograph of P. atripennis Nakane, a day-active species from Japan, shows a broad green sensitivity with the lambda-maximum around 540 nm in the male (Eguchi et al. 1984). There is not yet any study on the bioluminescence and visual sensitivity in both sexes of a diurnal species of Pyrocoelia. Whether the bioluminescence is truly functional or merely an evolutionary residual remains open for future study.