Mirian David Marques

Circadian Activity Rhythm of the Foragers of a Eusocial Bee (Scaptotrigona aff depilis, Hymenoptera, Apidae, Meliponinae) outside the Nest

In all bee colonies of the Meliponinae subfamily, activity inside the nest is temporally organized around the oviposition by the queen, assisted by nurse bees. This class is constituted by young bees that remain inside the nest. In a colony of Scaptotrigona aff depilis, the oviposition cycle occurs in a 3-hour period. The foragers are older bees that collect food for the colony in the field. Other tasks in the nest are performed by workers of ages intermediate between nurses and foragers. With the aim of studying activity rhythms, foragers were kept under constant light, with food constantly available and no flight restriction. The results showed that, although inside the nest the prevailing period is 3 hours, the activity of the foragers is a circadian rhythm, synchronized by the light/dark cycle and probably influenced by other environmental cycles as temperature and the availability of food sources.

Rhythms and Ecology — Do Chronobiologists Still Remember Nature?

Even a cursory inspection of current chronobiology journals and conferences indicates the remarkable strides that have been made recently in an understanding of the genetic and molecular mechanisms of the endogenous circadian oscillator. However, such advances can sometimes lead the reader to forget the roles of such circadian rhythms in the life of the organism and their adaptive importance. The return to the field after laboratory work (to test theories derived from the laboratory) is rapidly becoming a forgotten practice, although few would deny its importance. The several natural cycles — lunar, tidal, seasonal — and all the strategies that have been selected to enable the species to deal with them represent a wider horizon than the majority of research in biological rhythms is currently focusing upon. Timing mechanisms and temporal adaptation enable the individual to alter its physiology and biochemistry in accord with changes in the environment. Phase-locking — the relationship between the individual’s times of activity and rest and an environmental cycle — is species-specific, and provides one of the most important adaptive characteristics of that species: nocturnality or diurnality. This view must be enlarged, however, since it disregards the interactions between individuals when finding a mate, the timing mechanisms involved when parasites find a host, or the need, amongst those who live in the same environmental niche, to avoid predators and competitors for limited food resources. What role do internal timing mechanisms play in these cases? Biological studies have often been divided into in vivo and in vitro investigations, but this division hides the fact there is a broad spectrum of experiment approaches that ranges from studies of the interactions between species in their natural habitat at one extreme to details of physiological or genetic processes at the other. Those studies dealing with the interaction between the individual and its environment are ‘ecology’, of course, but there are also wide variations in what is encompassed by this term. Increasing control can be exerted by the experimenter in changing the study from one taking place in an unrestricted natural habitat, to one taking place in a natural but physically limited one, to one taking place in a semi-natural environment in the laboratory, and so on. For the ecologist, the priority is to investigate the animal in as natural an environment as is consonant with the aims of the investigation and the measurements that

Reproductive and Post‐Embryonic Daily Rhythm Patterns of the Malaria Vector Anopheles (Kerteszia) cruzii: Aspects of the Life Cycle

Females of Anopheles (Kerteszia) cruzii, a sporadic malaria vector in some areas of the Atlantic Forest in south and southeastern Brazil, were captured and studied under controlled conditions. In the laboratory, daily observations were conducted in natural light‐dark cycles at 25.1±0.6°C and relative humidity 57–81%. Post‐embryonic development, which comprises four larval instars and the pupa, was continuously observed, and its cycles, as well as temporal components of reproduction, were registered. A preliminary study on female longevity was also performed. Oviposition, ecdysis from the third and fourth instars larvae, and pupation were visually monitored over three consecutive days and the emergence of adults over four consecutive days. Results were analyzed by circular statistics, and the null hypothesis of the absence of rhythm was assessed by Rayleighs test at the 5% significance level. From a total of 141 females captured, 113 (80.14%) survived and 79 (69.91%) were successfully fed on blood, offered at one of two time intervals, 09:00–10:30 h (morning) or 18:30–20:00 h (evening). A total of 36 females laid 1063 eggs in 65 oviposition episodes, and 18 females presented fragmented oviposition. The average duration from egg‐laying until adult emergence was 30.71±3.57 days, the larval stage being the longest in the post‐embryonic development. Egg‐laying showed a daily rhythm, with a peak at 23:24±3:47 h, 2 to 5 h after sunset. The time of the blood meal did not shift the phase of the egg‐laying rhythm. The last larval ecdysis, pupation, and adult emergence did not follow a 24 h rhythmic pattern. A description of temporal patterns of post‐embryonic development, particularly in the case of vectors, can be an important tool in research to determine methods of control.

DAILY RHYTHMS RELATED TO DISTINCT SOCIAL TASKS INSIDE AN EUSOCIAL BEE COLONY

A bee colony is often compared to a multicellular organism, mainly because of its spatial organization. We propose that a temporal organization of equal importance is also present. To support this view, we studied the reproductive processes of two closely related species of stingless bees. Stingless bees enable observations of daily rhythms that are performed by distinct social classes. The emergent process, POP, is cyclic and consists of the building and provisioning of brood cells by the worker bees and egg‐laying by the queen. Colonies were kept in the laboratory under constant conditions with the exit tube opening to the environment; thus, foragers had direct access to environmental cycles. At a later stage of the experiment, the exit tube was closed by a sieve; in this case, bees had their own stock of food, but the environmental LD cycle could still be detected when they were inside the exit tube. Daily POP rhythms were present and showed distinct temporal patterns in each species. A third condition was imposed on one of the species only: the exit tube was closed by a sieve and maintained inside a box that was provided with constant illumination. In this colony, the POP rhythm was perturbed by the destruction of the brood cells. Restoration of POP consisted of a rapid reconstruction of cells followed by a late oviposition in the same day. As different rhythmic patterns were detected, but showed regular timings with respect to one another, an interpretation based upon the concept of an internal temporal order is suggested.

Biological rhythms and vector insects

The adjustment of all species, animals and plants, to the Earth’s cyclic environments is ensured by their temporal organisation. The relationships between parasites, vectors and hosts rely greatly upon the synchronisation of their biological rhythms, especially circadian rhythms. In this short note, parasitic infections by Protozoa and by microfilariae have been chosen as examples of the dependence of successful transmission mechanisms on temporal components.

Using Covariance to Unravel the Effects of Meteorological Factors and Daily and Seasonal Rhythms

Many factors contribute to the activity of animals in the wild. Whilst daily and seasonal rhythms are likely to be present, and to represent underlying biological functions, these will normally be modified by several factors in the environment. Important amongst these are light, temperature, humidity and whether or not it is raining. There is also the problem that the factors might interact, the effect of, say, time of day, being modified by the concomitant temperature. Separating out the effects of these different factors experimentally can be extremely arduous, if not impossible. An alternative approach is to treat the environmental factors as covariants, and then to separate out their effects from the biological ones by statistical means, using Analysis of Covariance, ANCOVA. The potential of this method is illustrated in the current report by a consideration of exits and entries of a colony of bees from their hive. Hourly measurements of this behaviour were taken during the daylight hours for three consecutive days in 11 consecutive months of the year. At the same time, ambient temperature, light intensity, humidity and whether or not it was raining were recorded. ANCOVA enabled the effects of temperature, humidity, light and rainfall upon the exits from the hive and entries back into it to be separated from the effects of time of day and time of the year. The analyses allowed those climatic variables, in addition to time-of-day and time-of-year effects, that influenced behaviour to be identified. Such climatic variables have not been previously isolated, and this might have lead to a misinterpretation of similar results in the past. Having separated out any effects of climatic variables (the covariates), the interaction between time of day and time of the year could then be investigated. Furthermore it has been possible to quantify the effects upon behaviour of each covariate. Rainfall was shown to decrease activity by more than 80%. For the other variables (temperature, humidity and light intensity), the statistical model allowed for the possibility that an increase in the variable initially produced a rise in activity but that this was followed, if the variable continued to rise, by a fall in activity. For light intensity, only a very modest increase in activity was found, and this continued throughout the range of intensities measured. However, for both temperature and humidity, the effects were more marked and showed ‘turning points’. That is, activity increased as the ambient temperature rose until activity peaked at about 33–35°C; after which activity began to fall. Similarly, entries into the hive rose with increasing humidity up to a value of 48%, but fell thereafter. By contrast, exits from the hive increased with increasing humidity throughout the range measured. In the biological system tested, this form of analysis has produced valuable information about the way different factors influence activity in a field study. The results strongly suggest that the proposed methodology has a much wider and more general application. The way in which this type of analysis might be elaborated is discussed.

Sexual behavior elicited in cage-mates of olfactory tubercle stimulated rats.

Fourteen male albino rats kept in pairs were implanted with bipolar electrodes in the olfactory tubercle. Electrical stimulation elicited a behavioral change in the cage-mates of the stimulated rats. This change consisted of increased exploratory activity in six animals. In three of these six rats, sexual behavior with mounting and pelvic thrusting was observed. The changes are described and discussed with special attention to sexual behavior.