A crab in the lab that identified high and low tides in the sea two miles away: the rediscovery of tidal rhythms in India

The author describes his 'choice' of a Ph.D. dissertation topic in the sixties, the interactions with his advisor, the rhythms of the mole crab and the serendipity of success in research, in a candid and humorous fashion

Persistent tidal and diurnal rhythms of locomotory activity and oxygen consumption in Emerita asiatica (M.-EDW.)

1. The oxygen consumption of the sand crab, Emerita asiatica, when estimated employing solitary specimens showed an unmistakable persistent tidal rhythm. 2. Numbers of 4 and 5 crabs even when huddled together in the respiration chambers showed the rhythmicity in their metabolic rates indicating mutual synchronisation of individual oscillations. 3. In newly moult crabs, in spite of the intensified level of metabolism accompanying the process of moulting, the tidal rhythms were displayed in the metabolic rates. 4. Simultaneous estimations of the swimming activity employing a vertically moving cage device and the oxygen consumption of individual crabs further confirmed the persistence of rhythms. 5. The activity of Emerita coinciding with the high tide at night was considerably enhanced. It was clear that this exaggerated nightly activity was due to the superimposition of a diurnal rhythm an a tidal rhythm. 6. The rhythms in the locomotory activity waned after the crabs had been in the laboratory for 3-4 days. 7. The behaviour of Emerita, as seen in the activity records and oxygen consumption estimations made in the present study, is reminiscent of its behaviour in nature relative to the tide. 8. The adaptive significance of such rhythmic behaviour to the continued existence of littoral animals is evident

Studies on phase-shifts in endogenous rhythms

Cultures of Drosophila pseudoobscura pupae raised in 12:12 hours L/D cycles were subjected to brief light pulses and light steps during early and late subjective night phases.1. A light pulse and a light step during early subjective night evoke dissimilar responses, the pulse effecting a delay phase-shift and the step an advance phaseshift. But a pulse and a step in the latter part of the subjective night evoke a similar response from the system and advance the phase. 2. The results are explained by assuming a differential light sensitivity of the underlying system during the subjective night phase itself, with a phase-point of maximum light sensitivity. 3. It is postulated that the light "off" fraction of a pulse acts as a new "dusk" in the early subjective night and that the "on" fraction acts as a new-"dawn" in the late subjective night. 4. The results of an experiment where a light pulse and a light step combined to form the light treatment bear out the assumptions made above and indicate that the photoinducible phase itself is not phase-locked to environmental time

Erwin Bunning (1906-1990): a centennial homage

This article does not have an abstract

My tryst with the bats of Madurai

I have often been asked by people how I came to work with bats. The story may be well worth recounting, weaving into my account, for the benefit of younger readers, the minor hurdles, the adventure, excitement and thrill of working out in the open at night and inside caves with bats. My affair with the bats of Madurai had lasted two decades and five of my students wrote their PhD theses on the biology, ecology, behaviour and biological clocks of bats. Today the Department of Animal Behaviour & Physiology, Madurai Kamaraj University, has the biggest data base on the biology and behaviour of bats anywhere. In this article I wish to show that first-rate work on animal behaviour can be done in our backyards in India. J B S Haldane felt that the study of animal behaviour was the area in which we are likely to do entirely original research and R.Gadagkar has belaboured this point and, of course, set an example himself with his own researches on the paper wasp. My enterprising first student R Subbaraj had begun field work on bats a year before I had even returned to India from Germany and joined the School of Biological Sciences at the Madurai Kamaraj University in the summer of 1975. Bats were far from my mind, having until then worked for a whole decade on rather abstract concepts such as phase response curves, kinetics of phase shifts of circadian clocks, transient and limit cycles, singularities and light and energy relations of the circadian rhythms in Drosophila. I told Subbaraj that if he wanted to work for a PhD it would have to be based on laboratory work on the biological clock of bats. Subbaraj was intelligent, bright eyed, quick in grasping problems, eager to learn and was a natural talent. He was thrilled that I was opening up a new world, the world of chronobiology, for him. I was glad he was introducing me reciprocally to the exotic world of bats. I told him "The farmer does not eat what the farmer does not know. So let me get to know your bats properly"

Spectral sensitivity of the photoreceptors responsible for phase shifting the circadian rhythm of activity in the bat, Hipposideros speoris

1. The spectral sensitivity of the photoreceptors responsible for phase shifting the circadian rhythm of flight activity in the bat,Hipposideros speoris was investigated. For this purpose we studied the phase shifts evoked with 15 min and 2.77 h pulses of monochromatic light at various phases of the rhythm freerunning in DD. 2. A PRC for the circadian rhythm of flight activity inH. speoris was constructed with white light pulses (1,000 lx for 15 min) against DD background (Fig. 1). In the first set of experiments 15 min monochromatic light pulses of varying intensities were administered to two phases of the rhythm: the phase of the rhythm at which maximal phase advances occur CT 4, and the phase of the rhythm at which maximal phase delays occur CT 18. The intensities of the 15 min monochromatic light pulses required to produce 50% of the phase shifts evoked with white light pulses (1,000 lx for 15 min) at these two phases were determined. The spectral sensitivity curve for advance phase shifts has a maximum at the wavelength 520 nm and the spectral sensitivity curve for delay phase shifts has a maximum at the wavelength 430 nm (Fig. 5). 3. In the second set of experiments 2.77 h monochromatic light pulses of equal energy of 100 μW/cm2 were used. We studied the wavelength dependent phase shifts at four phases of the rhythm: CT 2, CT 4, CT 12 and CT 18. The pulses of 430 and 520 nm evoked unequivocal delay and advance phase shifts, respectively, at all four phases (Fig. 7). These results suggest that at this photopic level of pulse energy, there might be a clear antagonism between the two photoreceptor classes, one having a maximum at the wavelength 430 nm and the other having a maximum at the wavelength 520 nm. 4. We suggest that there may exist two different classes of photoreceptors in the retinas ofH. speoris. The S photoreceptors (short wavelength sensitive) having a maximum at the wavelength 430 nm and the M photoreceptors (middle wavelength sensitive) having a maximum at the wavelength 520 nm that mediate delay and advance phase shifts, respectively

Continuous light inside a cave abolishes the social synchronization of the circadian rhythm in a bat

The bat Hipposideros speoris regulates its flight activity rhythm in the absence of time cues in a totally dark natural cave. The flight activity rhythm even of captive bats in total darkness entrained to the social cues available from free flying conspecifics. The social synchronization of the circadian rhythm was abolished in continuous illumination (LL) of 10-20 lx. All the captive bats 'feerun' in LL with τ longer than 24 h. The social entrainment was re-established following a few cycles of transients when total darkness was restored

Mother mouse sets the circadian clock of pups

We report here the ontogeny of a circadian clock of the field mouseMus booduga expressing itself 16 days after parturition in the locomotory activity of neonate pups removed from the mother and held in continuous darkness ever since birth. Locomotion is a 'complex' activity serving such functions as foraging, exploration, and territoriality. Since these functions are not conventionally associated with neonate and altricial animals, it is of interest that this ability has such an early circadian origin. A backward extrapolation of the pups rhythm and the rhythm of the mother strongly implicate maternal synchronization. The period of the circadian rhythm of the pups shortens with age, from birth up to six months

Continuous light abolishes the maternal entrainment of the circadian activity rhythm of the pups in the field mouse

12:12-h cycles of presence and absence of mother mouse act as a 'zeitgeber' and entrain the circadian rhythm of locomotor activity in the pups ofMus booduga under continuous darkness or continuous dim light. Continuous higher illumination of 15-25 lx abolishes this impressive maternal entrainment

Zeitgebers (time cues) for biological clocks

The spatial and temporal aspects of the geophysical environment act as prominent selection forces for the evolution of life on this planet. The spatial features of the environment open up a choice of spatial niches and the temporal aspects on the other hand provide opportunities for adopting different temporal niches. Hence, both the spatial and the temporal properties of the environment together enhance the possibility for living organisms to exploit a given ecological niche at a given time of the day. The temporal selection pressures of the geophysical environment are composed of a number of abiotic factors such as light/dark cycles, temperature cycles, humidity cycles, and a range of biotic factors such as inter-individual interactions, interactions with preys, predators and parasites. Although the study of temporal organization in living organisms is relatively a recent phenomenon in biology, we now have access to a fair amount of knowledge about it in a number organisms ranging from cyanobacteria to humans. In this review, we shall focus mainly on three core questions related to timekeeping in living organisms: How are circadian clocks made to oscillate at desired frequencies?; What are the geophysical cycles that fine-tune circadian clocks?; Why are circadian clocks circadian