John Buck

Synchrony and Flash Entrainment in a New Guinea Firefly

Fireflies can duplicate both faster and slower rhythms of artificial light. Since the interval between the pacer signal and the fireflys flash of the next cycle approximates the fireflys normal free-run period, it is suggested that the pacer signal resets the flash-timing oscillator in the brain, thus providing a mechanism for synchronization.

Toward a Functional Interpretation of Synchronous Flashing by Fireflies

In certain firefly species of tropical Southeast Asia the males habitually congregate in trees in huge numbers and flash in rhythmic synchrony all night, each night. Though females do not synchronize, they are attracted to the trees and mate there. Many fireflies remain in the trees by day. We believe that each display tree approximates a steady-state population in which a constant number of males, stabilized by a balance of inflying and eventual death, is interacting with a constant flux of females, stabilized by a balance of in- and out-migration. There are some very tenuous indications that different tree populations may be partially isolated and somewhat inbred. The mass-display fireflies are unique in possessing a neural mechanism that automatically synchronizes the rhythmic flashing of conspecific males. Mass congregation and mass synchrony are therefore inseparable. All evidence agrees in indicating that the mass synchronized assemblies are exclusively reproductive. In the Thai Pteroptyx malaccae and the Melanesian Pteroptyx cribellata and Luciola pupilla we believe that courtship and mating involve two successive photic interactions. Distant males and females are being attracted indiscriminately into the tree by the massed rhythmic luminescence of the in-tree males. The range and species-specificity of this attraction are enhanced by the flash synchronization. Simultaneously males established individually in the tree and flashing rhythmically in small, defended territories compete for in-tree females. In extension of Lloyds analysis, we postulate mutual recognition via one or more sexual differences in light emission and surmise that the female probably does most of the short-range moving connected with pair formation. We postulate that the female selects her mate on the basis of the intensity of his signal relative to those of other males visible to her simultaneously. As in Lloyds model the selection must depend on a genetic predilection of females for males that are flashing synchronously. Poststimulus refractoriness is suggested as the mechanism for the predilection. The synchronized tree congregation thus performs a long-range attraction of both males and females to the tree and simultaneously operates as a huge permanent lek. In the various in-tree interactions, flash synchronization is thought to improve mating opportunity for all participants and to exclude possible conspecific cheaters. The orthodox view that large-scale synchrony must be only the incidental or statistical consequence of a small-scale adaptive synchrony is questioned on the following bases: 1. From natural selection theory, flash synchronization per se, being a group behavior, cannot serve as the competitive agent for promoting the reproductive fitness of an individual participating male, no matter how small the synchronizing group. 2. Flash synchronization is, for physiological reasons, obligatory between two or more close-together males. Mass synchrony depends on mass congregation. 3. Because most fireflies court by continuous line-of-sight photic contact, environmental obstacles such as abound in the jungly vegetation of Southeast Asia could be a major obstacle to dialogue-type communication. Conversely, the formation by males of a large, concentrated communal light beacon, visible through vegetation for long distances in all directions, might attract more females per unit time than a given male would meet in solo search through a population dispersed in dense vegetation. 4. Such a congregation, it is argued, would benefit all participating males, penalize none, and be safeguarded against nonflashing or nonsynchronizing cheaters by the females requirement for flash coincidence during comparison of male flash intensities. Mass congregation could thus, we suggest, be a group adaptation, made possible by unique physiological and ecological circumstances. The observed evolutionary perpetuation of the behavior is made possible by the fact that flashing-the act that, when synchronized, permits nonspecific sexual gain at two levels (increased mate accessibility for both sexes and eligibility for individual competition between males)-can also be modulated to serve as the competitive instrument between conspecific males vying for selection by females. Any synchronizing male in the congregation who mates will therefore transmit the genetic basis for the flash synchronization as well as that controlling competitive use of flash intensity, and the female will gain by having selected a competitive mate.

Control of flashing in fireflies

SummaryThe restrained male of the fireflyPteroptyx cribellata of Papua New Guinea responds to exogenous light signals with a latency of about one second, which equals the period of the natural spontaneous rhythm of flashing and includes about 800 ms of central nervous delay. The response is cycle-by-cycle and all-or-none and the duration of the response time is independent of the phasing of the driver in relation to the free run rhythm (Figs. 1, 2). The firefly can be entrained to rhythms over a period range of 800 ms to 1,600 ms, during which it leads or lags the concurrent signal by an amount equal to the difference between the driving period and the animals period (Figs. 3, 4). The phase-response line is nearly straight and is inclined 45 ° (Figs. 2, 5). Normally an exogenous signal dictates interflash timing but occasionally may fail to entrain the firefly (Figs. 7B, E) or may fail to evoke a flash (Figs. 7F, G). Persistence of endogenous control of timing period duration even during driving is occasionally seen as spontaneous drift in response time (Fig. 9). It is proposed that during entrainment each exogenous signal resets the pacemaker immediately to the start of its endogenous cycle, from which point it then begins a new series of free run periods. Thus each flash is timed in relation to the signal of the preceding cycle (Fig. 3). We devised a model of the endogenous timing cycle which fits the empirical data and achieves entrainment by a single mechanism involving phase advance or delay rather than change in actual rate of endogenous timing (Fig. 12). The proposed mechanism by which single males entrain to light signals seems compatible also with the mass synchronous flashing which is the characteristic behavior of field congregations.

CONTROL OF FLASHING IN FIREFLIES. II. ROLE OF CENTRAL NERVOUS SYSTEM

1. The central nervous system is shown to be involved in (a) normal spontaneous flashing, both single and multiple, (b) some types of post-stimulatory flashing and scintillation, (c) comatose behavior and refractoriness to stimulation.2. Two and probably three latencies in response to head and anterior cord stimulation exist. At present it is not possible to distinguish between cord pathways (conducting at ca. 15 and 50 cm./sec.) and central delay as possible causes of these latency differences.3. From posterior cord and from lantern surface it is possible to record small and characteristic volleys of action potentials associated 1:1 with spontaneous flashing and involving latencies comparable with those previously found for electrical stimulation. Multiple volleys may invoke multiple flashes. Flash intensity increases with both volley frequency and spike frequency but there is apparently not a close relation between volley structure and flash contour.4. Electrical stimulation in the eye can either inhibi...

CONTROL OF FLASHING IN FIREFLIES. I. THE LANTERN AS A NEUROEFFECTOR ORGAN

1. Records are presented of normal spontaneous flashes and of flashes induced by a variety of electrical stimuli at a variety of anatomical sites in several species of lampyrid firefly.2. The flashes of adult firefly lanterns have long response latencies (25 to 250 mscs. at 25° C. in different species) and durations (100 to 1000 mscs.) and can be repeated many hundred times with only slight fatigue. The response itself shows strength-duration relations and frequency responses (summation, treppe, tetany) which are similar to those of more conventional neuroeffector systems. A striking long-lasting neuroeffector facilitation is also evident.3. Response latency lengthens with falling temperature, Q10 values for the 10°-30° range varying from about 2.4 to 1.4. Extreme temperatures slow the decay phase of luminescence preferentially, as does hypoxia.4. The flashes of most species differ characteristically in time course, response latency and other electrophysiological properties.5. The responses of the Photuri...

Respiration of phormia regina in relation to temperature and oxygen

Abstract Respiratory rates of larvae, pupae, and adults of Phormia regina in general follow a sigmoid curve with respect to temperatures from 0 to 45°C. One exception is an unexplained plateau between 10 and 15° in the curve for intact larvae. At 25° respiration of larvae and pupae is somewhat more dependent on ambient O2 concentration than that of adults, the dependence of the former being limited at concentrations between 10 and 15%, and the latter at concentrations below 5%. The contributions of ‘resting’ and ‘activity’ respiration with respect to temperature and O2 concentration are evaluated by comparing deganglionated larvae and headless flies with intact ones. The role of spiracular area as a respiration-limiting factor is explored in experiments with artificially enlarged larval spiracles. The bearing of this work on the mechanism of gas transfer in insects is briefly considered.

Peroxisomes of the firefly lantern.

Photocyte granules, very abundant 1- to 2-μm particulates of photocytes of adult firefly light organs, were studied morphologically and in relation to their reaction to diaminobenzidine. The content of these granules is uniform except for a dense “nucleoid” or “core” and occasionally a vacuole or a sheaf of straight tubules. All these inclusions are near the periphery of the granule, which is bounded by a single membrane. Occasionally the membrane or the tubules appear to merge with the general cytoplasm or with the endoplasmic reticulum of the photocyte. The photocyte granule reacts positively to the diaminobenzidine tests for peroxidatic catalase activity. Significant catalase activity was demonstrated in the photogenic tissue by direct biochemical assay. The photocyte granule thus appears to be a peroxisome (microbody), present in remarkable concentration. Relations between peroxidatic activity and firefly luminescence are discussed.

The relation of oxygen consumption to ambient oxygen concentration during metamorphosis of the blowfly, Phormia regina

Abstract At 1–5 days of pupal life in Phormia regina at 25°C, respiration becomes oxygen-limited at ambient oxygen concentrations between 15 and 10 per cent. In 1 per cent O 2 it is reduced to about one-fifth of the corresponding control levels. One and 5 day pupae tend to be somewhat more sensitive to hypoxia than other ages. Pupae exposed to pure nitrogen for 4 hr show a subsequent respiratory overshoot in air as compared with controls. Considering the overshoot as repayment of oxygen debt, the theoretical extent of repayment in 7 hr is 14 or 26+ per cent, depending on whether development is considered to stop or to continue during anoxia. The corresponding repayments in pure oxygen are 26 and 33+ per cent, suggesting that the rate of postanoxic respiration in air is physically limited.

Cyclic CO2 release in diapausing pupae—II: Tracheal anatomy, volume and pCO2; Blood volume; Interburst CO2 release rate

An average one gram cyclically-respiring diapausing pupa of the saturniid moth Agapema galbina has a tracheal volume of about 60 μl and a tracheal pCO2 of 45 mm Hg. This shows that nearly 90 per cent of the approximately 30 μl of gaseous CO2 released during a “burst” must come out of solution and combination in tissue stores. Body water per g is distributed: blood, 330 μl; tissues, 180 μl; gut lumen, 100 μl; and cuticle 110 μl. Dimensions of the major parts of the tracheal path from environment to tissues are given, and it is shown by computation that the spiracular valve is the only site where significant resistance to diffusion could occur. It is shown statistically that the rate of CO2 release increases gradually during the interburst period, as it should if CO2 is being impounded in body buffers. Arguments are advanced for cyclic CO2 release being potentially widespread in insects under conditions where O2 supply is high relative to demand.

Light organ fine structure in certain Asiatic fireflies.

Control of effector activity by nerve has been studied exhaustively in muscle and to a lesser extent in glands and in electric organs. Coordinated light production by congregations of specialized photocytes represents an entirely different kind of effector activity, in which neural control, though long suspected, has only recently been established directly. Thus far it is only in the light organ or lantern of certain fireflies of the beetle family Lampyridae that nerve endings have been demonstrated (Smith, 1963), excitatory volleys in peripheral lantern nerves recorded (Case and Buck, 1963; Buonamici and Magni, 1967; Magni, 1967) and pharmacological evidence of neurosecretory excitation adduced (Smalley, 1965). However, the firefly lantern is a particularly favorable material in which to study excitation-effector coupling because it excels all other photophores in versatility and precision of control and because there exists a large body of detailed information about the biochemistry, physiology and morphology of the light-emitting system. Recently recordings have been made of the flashing of fireflies of the genus Pteroptyx in Bornea and Thailand (Buck and Buck, 1968). These insects can produce flashes lasting only about 30 msec. and can flash repetitively at frequencies of more than 30 per second. Because this is at least three times as sharp a control as in any previously studied firefly, and because electron microscopic studies on species from the tropical orient have not previously been reported, the fine structure of the Pteroptyx lantern was studied. For comparison we present also some data for the firefly genera Luciola and Pyrophanes from the same regions.