Hans-Ulrich Thiele

Differences in measurement of day-length and photoperiodism in two stocks from subarctic and temperate climates in the Carabid beetle Pterostichus nigrita F.

SummaryExperiments on the measurement of day-length as a basis for photoperiodism were made with a stock of the carabid Pterostichus nigrita from the Subarctic in Swedish Lapland (64–66° N). Results were compared with those of earlier investigations on a Central European stock (51° N). P. nigrita from Lapland reacted differently from the Central European ones in experiments with abnormal photoperiods (cycle durations from 12 to 72 h; light period in all cases 8 h). Whereas, in the Central European stock, short-day induced reactions (previtellogenesis in the females, maturation of the male gonads) could only be observed if those cycles represented multiples of 24 h in whole numbers, ‘short-day” reactions in the Lapland stock were inducible with all cycles in nearly 100% of the specimens investigated (only in LD 8:4 was this percentage slightly diminished). Experiments with “dark breaks” of 2 h in extreme long-day (LD 20:4) revealed nearly 100% short-day maturation, irrespective of the temporal location of these dark breaks in beetles from the Lapland stock, whereas in Central European beetles only dark breaks during certain scotophile phases had such an effect. In the Central European P. nigrita, two hour light breaks during the night phase of an LD 14:10 had a destructive effect on short-day maturation processes; in the Lapland stock, these were possible in spite of 1 h light breaks during the night of an LD 19:5. In the Lapland stock, developmental processes which in the Central European stock are confined to short-day conditions could occur in all types of experiments, provided that about 3 to 4 h of darkness were given during each 24 h cycle, whether uninterrupted or not.Light break experiments revealed that the long-day process for ovarian development (vitellogenesis) is induced in the same way as with the Central European P. nigrita. It occurs if light falls into a photosensitive phase during the second half of the 24 h cycle.Thus, for the Subarctic population, a model is proposed in which short-day is measured by means of an hour-glass timer, whereas long-day is perceived by means of a circadian oscillator.

Tagesrhythmen der Aktivität bei Carabiden

1. According to our observations in a natural light-dark cycle Molops elatus, M. piceus, Abax ovalis, A. parallelus, Pterostichus oblongopunctatus, P. madidus, and P. nigrita are mainly active in the dark. The start of their nocturnal activity was mostly masked. During the second half of the night the amount of activity decreased more or less, with one exception (the phase angle difference was positive). Even within one species the amount of activity can vary considerably, even if the length of night and all other conditions are kept constant. A slight amount of activity during the day can be interpreted as a flight from strong solar irradiation. 2. Of 22 Carabus species tested in a natural light-dark cycle 1 species is active only during the day, whereas 6 species are active during the night, but show a certain degree of day activity during their breeding time. The other species are active exclusively during the night. 3. According to experiments on Carabus problematicus, a species active only in the dark, conducted in artificial lightdark change the phase angle difference between the period of activity and the period of zeitgcber increases on the whole with the increase of the duration of the dark phase. But for the following reasons the single values deviate widely from their respective mean values: (a) the beginning of activity is usually masked, in short periods of darkness as well as in long ones, (b) the activity in the dark is to a great extent independent from the duration of the dark phase, (c) in the case of a small amount of night activity this activity is concentrated at the beginning of the night. 4. Judging from observations in a natural light-dark cycle Carabus proble. maticus is ready for activity already before nightfall. This holds true for nights of any duration. 5. The autonomous periodicity of carabid beetles seems to be in a lesser degree self-sustained than that of other groups of animals that have so far been thoroughly investigated. This is made probable by an unusually large range of entrainment and an often extremely quick resynchronization after phase shifts of the zcitgeber. The influence of the exogenous factor (i.e. the light-dark-cycle) exceeds that of the autonomous periodicity. In night-active carabid species this is also shown by the fact that the onset of their activity is nearly always masked. 6. So far 67 carabid species have been tested concerning their diurnal pattern of activity, including those investigated in this paper. 60% of them are strictly night-active, while 22% are mainly day-active and 18% show an intermediate

Measurement of day-length as a basis for photoperiodism and annual periodicity in the Carabid beetle Pterostichus nigrita F.

SummaryPterostichus nigrita undergoes a gonad dormancy which is overcome by the sequence of short-day/long-day in females and by short-day in males. Experiments with abnormal photoperiods showed that only photoperiods of 24 h and their multiples in whole numbers allowed the processes of gonad maturation, which are normally bound to short-day (i.e., previtellogenesis in the females, bundling of sperms to spermiozeugmata in the males). They were mostly suppressed by photoperiods which represent uneven multiples of 12 h (12, 36, 60). These results permit the conclusion that the short-day measurement is based on an oscillatory (circadian) process. Experiments with “dark breaks” in an extreme long-day (LD 20:4) resulted in two peaks of “short-day” effects. From these findings a model of short-day measurement was derived. It postulates that there are two dark sensitive phases every 24 h during which the beetles require darkness in order for the short-day processes to occur. One of these phases is set by dawn, reaching its peak 15 h thereafter. The other phase is set by dusk and reaches its maximum about 7 h afterwards. Thus, the steps of gonad development bound to short-day are induced if the night is at least about 8–9 h long. The two scotophile phases represent two systems of short-day measurement, which complement each other and strengthen their effects.Light break experiments revealed that the long-day process of ovarian development (vitellogenesis in the females) is induced if light falls into a photosensitive phase during the second half of the day with its maximum about 15 h after “light on.”

Zusammenhnge zwischen Tagesrhythmik, Jahresrhythmik und Habitatbindung bei Carabiden

SummaryCarabid beetles of forest habitats are mostly hygrophilous and darkpreferring species. Nearly all of them are nocturnal, and the majority are autumn breeders. Most carabids from open field habitats are xerophilous, light-preferring and diurnal species, or they are indifferent to humidity and light and can be active by day and night. This group includes markedly more spring breeders than the forest species. The adaptative value of the observed correlations is discussed.

Interactions between photoperiodism and temperature with respect to the control of dormancy in the adult stage of Pterostichus oblongopunctatus F. (Col., Carabidae)

SummaryPterostichus oblongopunctatus belongs to the type of spring breeding carabids with adult hibernation. Ovarian maturation is under the control of photoperiod: the females need a change of day length to mature. The first step of egg maturation (previtellogenesis) is bound to short day, the second step (vitellogenesis) to long day.The short day effect is achieved almost only at temperatures of 10 to 15°C; it is completely suppressed by 20°.The males mature under very different photoperiods and temperatures, but long day diminishes the percentage of mature males slightly, as well as does the higher temperature of 20°C in short day as compared with 15°C.Simulation of climatic conditions as experienced by the beetles from autumn throughout winter until spring in the laboratory showed that a short span of favourable temperatures at short day as experienced in nature in autumn allows the females to accomplish the short day development. But this maturation effect is still more diminished the longer temperatures below 5°C act on the beetles. Following that, a second period of temperatures between 10–15°C must restore the short day maturation effect if full maturity shall be gained in the following long day.The beetles are able to store reserve materials under long day at 20°C. After such a period they are able to have a normal previtellogenesis in spite of a severe shortage of food during short day. These experiments indicate that the failure in short day development outside the temperature range of 10–15°C is not a matter of an especially well balanced over-all metabolism in this favourable temperature range. It seems rather that hormonal systems involved in the short day phase of oogenesis act only within this span of temperature.

Die jahreszeitliche Synchronisation der Gonadenreifung bei Agonum assimile Payk. (Coleopt. Carab.) durch Temperatur und Photoperiode

SummaryThe control of annual rhythmicity in Agonum assimile was investigated by dissections and by breeding experiments both with specimens captured in the field and these reared in the laboratory. A. assimile is a spring breeder with summer larvae. The beetles hatch from the pupa from July until September, hibernate and breed in the following spring from April until June. Only a part of the old generation dies during the winter. Beetles from the previous year form about half of the breeding population. Rearing to the adulthood under laboratory conditions is possible with a success of about 80–90%, depending on the quality of food. Maturation of the sexes in the laboratory is desynchronized when the beetles are kept at 20°C and under “long day” conditions; development of the males is delayed in this case. In both sexes maturation takes place potentially free of dormancy.Development of the female and male gonads is mainly under the control of photoperiod and retarded in different ways by decreasing day length (photoperiodic quiescence). Thereby a maturation of the females is hindered in the autumn, and slow, further development of the males during the winter is made possible. The termination of quiescence by the transition from the “short day” to “long day” in laboratory experiments, or by increasing day length in the spring, synchronizes complete development in both sexes. The females normally produce an offsping of 20–60 larvae. We succeeded in keeping laboratory bred specimens up to 3 years, over this span they could be brought to propagation several times.ZusammenfassungAn Wildfängen und Laboratoriumstieren von Agonum assimile Payk. wurde durch Sektionen und Fortpflanzungsexperimente die Steuerung der Jahresrhythmik untersucht. A. assimile ist ein Frühlingstier mit Sommerlarven. Die Käfer schlüpfen von Juli bis September, überwintern und pflanzen sich im nächsten Frühling von April bis Juni fort. Die alte Generation stirbt im Winter zum Teil ab. Die vorjährigen Tiere machen etwa die Hälfte der sich fortpflanzenden Käfer aus. Die Aufzucht im Laboratorium bis zur Imago gelingt mit etwa 80–90% Zuchterfolg und hängt von der Qualität der Nahrung ab. Im Laboratorium erfolgt die Reifung beider Geschlechter bei 20°C und Langtag dischron (Verzögerung bei den Männchen) und its potentiell dormanzfrei. Die Entwicklung der weiblichen und männlichen Gonaden wird hauptsächlich photoperiodisch gesteuert und bei abnehmender Photoperiode in unterschiedlicher Weise gehemmt (photoperiodische Quieszenz). Dadurch wird im Herbst eine Reifung der Weibchen verhindert und ein langsames Heranreifen der Männchen im Winter ermöglicht. Die Beendigung der Quieszenz durch Übergang von Kurztag zu Langtag im Laboratoriumsexperiment oder bei zunehmender Tageslänge im Frühling läßt beide Geschlechter synchron zur Reife gelangen. Die Weibchen bringen in der Regel 20–60 Larven hervor. Es gelang, Laborzuchttiere bis zu 3 Jahren zu halten und dabei mehrmals zur Fortpflanzung zu bringen.

Versuche zur Schlüpfrhythmik bei Carabiden

SummaryThe emergence times of the following species of Carabid beetles were investigated in a long day of LD 18/6: Agonum assimile Payk., Pterostichus angustatus Dft., P. nigrita F., and P. oblongopunctatus F.The hatching of the beetles was examined by means of an automatically controlled photorecorder.In one series of experiments flash-light was used for taking photographs. In a second series photographs were taken only during the light phase by the light of a fluorescent tube of the same type as used for the illumination of the breeding chamber.Both series of experiments produced no evidence of the existence of a typical emergence rhythm in the four Carabid species. In each species the number of beetles hatched per hour is slightly greater during the phtophase than during the scotophase. This difference was statistically significant only for P. angustatus. From this it is concluded that some Carabid species have a latent capability for synchronization of emergence by a light dark change.The sexes of P. angustatus show no difference in the distribution of their emergence times.ZusammenfassungDie Schlüpfzeiten der Laufkäferarten Agonum assimile Payk., Pterostichus angustatus Dft., Pterostichus nigrita F. und Pterostichus oblongopunctatus F. wurden in 18/6 h-Langtag registriert.Zur Registrierung wurde eine Kamera mit automatischer Auslösesteuerung verwandt.Die Aufnahmen erfolgten in einer Versuchsserie mit Blitzlicht, in einer zweiten Serie nur während der Hellphase beim Licht von Leuchtstoffröhren, wie sie auch zur Beleuchtung des Zuchtraumes dienten.Beide Versuchsserien ergaben keinen Hinweis auf eine typische Schlüpfrhythmik bei den vier Laufkäferarten. Pro Stunde der Hellphase schlüpfen jedoch bei allen Arten etwas mehr Käfer als pro Stunde der Dunkelphase. Dieser Unterschied ließ sich nur für P. angustatus statistisch sichern. Daraus läßt sich auf eine latente Bereitschaft zur Synchronisation des Schlüpfens durch den Licht-Dunkel-Wechsel bei manchen Carabiden schließen.Die Geschlechter von P. angustatus zeigen keine Unterschiede in der Verteilung ihrer Schlüpfzeiten.The emergence times of the following species of Carabid beetles were investigated in a long day of LD 18/6: Agonum assimile Payk., Pterostichus angustatus Dft., P. nigrita F., and P. oblongopunctatus F.The hatching of the beetles was examined by means of an automatically controlled photorecorder.In one series of experiments flash-light was used for taking photographs. In a second series photographs were taken only during the light phase by the light of a fluorescent tube of the same type as used for the illumination of the breeding chamber.Both series of experiments produced no evidence of the existence of a typical emergence rhythm in the four Carabid species. In each species the number of beetles hatched per hour is slightly greater during the phtophase than during the scotophase. This difference was statistically significant only for P. angustatus. From this it is concluded that some Carabid species have a latent capability for synchronization of emergence by a light dark change.The sexes of P. angustatus show no difference in the distribution of their emergence times.