ALBERT

Notes: Summary 1. ERG S(λ) were determined in darkadapted intact preparations of 6 North American firefly species (Photinus collustrans, marginellus, pyralis, macdermotti, scintillans and Bicellonycha wickershamorum) which restrict their flashing activity to twilight hours. The curves possess narrow (1/2 bandwidth=50–60 nm) peaks in the yellow (560–580 nm) and a shoulder in the violet (370–420 nm), with amarked attenuation (1.4–2.2 log units) of sensitivity in the green (480–530 nm) region of the spectrum (Fig. 1). Two additional species (Photuris potomaca and frontalis) which initiate flashing at twilight and continue on late into the night (twi-night) possess broad sensitivity maxima around 560 nm (Fig. 3). 2. Selective adaptation experiments isolated near-UV and yellow inP. scintillans (Fig. 2). In the dorsal frontal region of the compound eyes inP. frontalis, high sensitivity existed only in the short wavelength region (near-UV and blue) with a maximum in the blue (λ max 435 nm) (Fig. 4). 3. The in situ MSP absorption spectrum of the screening pigments was determined in preparations of firefly retina. a) Two kinds of dark brown granules were found in the clear zone region. These granules absorb all across the spectrum with a gradual increase in optical density in the shorter wavelength region inP. pyralis (Fig. 5). b) Besides dark granules, pink-to-red colored screening pigments were present in the vicinity of the rhabdoms. The absorption spectra of these pigments determined in five species were narrow (1/2 bandwidth=50–80 nm) with species-specific differences in their peak absorption in the green at 525 nm, 510 nm, 512 nm and 517 nm inP. scintillans, macdermotti, collustrans and pyralis, respectively (Fig. 6). A similar pigment was found inP. marginellus with aλ max at 512 nm (Fig. 7). In all cases, transmission increased both at long and short wavelengths, but more sharply in the long wavelength region (Figs. 6 and 7). Hence each twilight-restricted species has its own unique colored screening pigment. A yellow pigment whose absorption spectrum differed from those found in genusPhotinus was found in twi-night activePhoturis potomaca (λ max 461 nm) and night-activeP. versicolor (λ max 456 nm). The transmission of thePhoturis pigment increased sharply only in the long wavelength region (Fig. 8). 4. In the twilight-restricted species, pink-to-red screening pigments modify dramatically the long green wavelength part of S(λ) functions. The calculated effect of the absorption of these screening pigments (O.D.=1.6 to 2.2; ¯X=1.8, n=4) on a theoretical S(λ) curve represented by a green (P550) rhodopsin, match the shape of the experimentally obtained dark-adapted ERG S(λ) in all cases (Figs. 9, 10). These screening pigments (Figs. 6, 7, 8) then would cause attenuation of sensitivity selectively in the green in twilight-restricted fireflies (Fig. 1) with a concomitant shifting of the peak of the sensitivity in the yellow as well as a narrowing of the visual spectral sensitivity. The pink-to-red colored screening pigments presumably would enhance color and/or brightness contrast in the mesopic range of ambient illumination. 5. The presence of the colored screens attenuates absolute sensitivity from 5–25% among different twilight-active species as compared to a night-activePhoturis lucicrescens (Fig. 11).

Notes: Summary The waveform of the electroretinograms (ERGs) recorded from the compound eyes in the dark-active fireflyPhoturis lucicrescens was different in the short (near-UV and violet) and long (green-yellow) wavelengths (Fig. 1). The spectral sensitivity curves in the dark and chromatic adaptation conditions suggested the presence of receptor types in the short (near-UV, Fig. 4, and violet, Fig. 5) and long wavelength (green; λmax 550 nm, Figs. 3–5) regions of the spectrum. The green peak is in correspondence with the species' bioluminescence emission peak at 554 nm (Fig. 3c).

Notes: Summary The electroretinographic visual spectral sensitivity functions in day-active fireflies Lucidota luteicollis and Lucidota atra show a broad green sensitivity and a shoulder in the near-ultraviolet region of the spectrum (Figs. 1, 2) as is commonly found among day-active insects. The nomogram for P530 visual pigment matches the spectral sensitivity curves in the green. The adult L. luteicollis retains its larval bioluminescent light organ which has a peak emission at 562 nm. The λ max of the ERG spectral sensitivity does not match the bioluminescent peak (Fig. 1B) as it does in twilight- and dark-active fireflies. Some relevant behavioural observations with respect to mating are presented.

Notes: Summary Electroretinograms (ERG) were recorded from dark- and chromatic-adapted compound eyes in the dusk-active firefly,Photinus pyralis ♂, at different wavelengths ranging from 320 to 700 run and over 4.5 log units change in stimulus intensity. ERG waveforms differed in the short (near-UV and violet) and long (yellow) wavelengths (Fig. 1). Waveform differences were quantitated by analysis of rise and fall times as a function of the amplitude of the response. Rise times were found to be relatively constant for all stimulus wavelengths. However, variations in the fall times were detected and followed characteristically different functions for short and long wavelengths (Fig. 2). No significant differences in the slopes of the Vlog-I curves at different stimulus wavelengths were observed (Fig. 3). Spectral sensitivity curves obtained from the ventral sector in dark- and chromatic-adapted conditions revealed peaks in the short (λ max 400 nm: Fig. 4;λ max 430 nm: Fig. 5 A; andλ max 380 nm; Fig. 5B) and long (λ max 570 nm: Figs. 4, 5) wavelengths, suggesting the presence of two spectral mechanisms. The long wavelength (yellow) mechanism was in close tune with the species bioluminescence emission spectrum (Fig. 4B).