Functional morphology of the cuticular terraces in burrowing terrestrial brachyuran decapods

Observations on Gecarcinus lateralis and Ocypode quadrata from Bermuda show that their cuticular terraces are not functional as burrowing sculptures, as previously assumed. Instead, they increase the friction against the walls of the burrow when the animal wedges itself to avoid being extracted by predators. No significant increase in the number of terraces takes place during growth in the size interval available for this study. This is different from the situation described as usual in burrowing decapods, and is rather similar to that of crevice-dwelling crabs. The distribution of terraces and their ontogenetic pattern, therefore, are not reliable indicators of the life habits.     

Activity rhythms in littoral Acari under laboratory conditions

Under experimental conditions, endogenous activity rhythms were found among several species of the terrestrial moiety of the littoral Acari. These rhythms correlated with both circatidal (semidiurnal) and photoperiod/temperature (diurnal) cycles. In non-littoral species, only diurnal cycles were observed. Under similar experimental conditions, members of the aquatic moiety, i.e. the family Halacaridae, showed no activity cycles, and it is thought that in these mites activity may be exogenous. It is suggested that the possession of endogenous activity cycles among the terrestrial moiety is an adaptation to prevent inundation and dislodgement by wave action, and that the aquatic moiety, which are permanently immersed, require no such adaptation, and rely upon exogenously triggered activity patterns.     

Activity rhythms of enzymes in human red blood cell suspensions

Abstract

We have established the presence of a rhythm in the activity of 4 enzymes in in‐vitro cell suspensions of human red blood cells. Glucose 6‐phosphate dehydrogenase and glutamate oxaloacetate transaminase demonstrated semicircadian patterns of activity, while acid phosphatese and acetylcholine esterase exhibited circadian activity rhythms. The ratios between the highest to lowest activities varied from 2:1 to 10:1 among the various enzymes. The affinity of glucose 6 phosphate dehydrogenase to its substrate and coenzyme remained constant throughout the cycle. No evidence was obtained for the presence of a soluble inhibitor at the lower levels of the activity. Sonication of hemolysates with low glucose 6 phosphate dehydrogense activity yielded additional activity comparable to that of the peak activity. Sonication of hemolysates from the time of the peak activity did not change the original activity. The observations point to a role of the cell membrane in the biological clock.     

Circadian performance rhythms: some practical and theoretical implications

Safety and productivity are low at night and this would appear to be because we are a diurnal species. This is reflected not only in our habitual sleep time, but also in our endogenous body clocks that, together with exogenous influences, such as the patterning of meals and activity, result in predictable circadian (24 h) rhythms in our physiological processes. Our performance capabilities also vary over the course of our waking period, with task demands affecting both the precise trend over the day, and the rate at which it adjusts to the changes in sleep timing occasioned by shift work. Studies designed to examine the reasons for this have shown that memory loaded performance may have a quite separate endogenous component to that responsible for more simple performance, suggesting that these two types of performance cannot be causally related. Furthermore, it would appear that the exogenous component of circadian rhythms may also differ across measures, and our attempts to model these endogenous and exogenous components have led us to re-examine the evidence on adjustment to night work. Our findings suggest that shiftworkers merely 'stay up late' on the night shift, rather than adjust to it, and that this is responsible for the reduced safety at night. It would seem that in situations where safety is paramount, the only solution to these problems is the creation of a nocturnal sub-society that not only always works at night but also remains on a nocturnal routine on rest days.     

Daily rhythms of locomotor activity in some Carabidae (Coleoptera)

The daily cycle of activity was investigated in a number of species of Carabidae. Most were either nocturnal or diurnal, but some were plastic and responded to environmental conditions.

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Résumé Le cycle quotidien de l'activité des mouvements fut étudié chez plusieurs espèces de Carabidae par observations d'élevage en insectarium.L'auteur a trouvé que la majorité des espèces pourraient être classées strictement comme nocturnes ou diurnes.Certaines espèces furent classées comme indifférentes, le cycle journalier de leur activité variant en fonction des modifications naturelles du milieu externe.

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This work formed part of a thesis submitted for the degree of Doctor of Philosophy in the University of London.     

Studies in diurnal rhythms ix the water-relations of some nocturnal tropical arthropods

The rate of water-loss from tropical African centipedes (Rbysida nuda and Ethmostigmus trigonopodus) and millipedes (Oxydesmus platycercus and Ophistreptus sp.) is proportional to the saturation deficiency of the atmosphere. These animals therefore resemble forms from temperate and desert regions in this aspect of their physiology. Their nocturnal habits are probably related to their high rate of transpiration. The endogenous 24-hour rhythm shows a slight retardation in constant light and an acceleration in darkness. The probable function of this is to synchronize it with diurnal environmental changes. The West African scorpion, Pandinus imperator, has a critical temperature considerably lower than those of desert species and comparable with that of the Italian Euscorpius germanus.

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Zusammenfassung Bie den tropischen afrikanischen Hundertfüßlern Rhysida nuda und Ethmostigmus trigonopodus, den Tausendfüßlern Oxydesmus platycercus und Ophistreptus sp. sowie bei dem Skorpion Pandinus imperator wurden die Wasserverlustraten durch Wägen der Individuen bestimmt, die über Phosphorpentoxyd in konischen Flaschen aufgehängt wurden, die in ein Wasserbad tauchten. Die Tiere wurden jeder Temperatur 20 Minuten lang ausgesetzt, bevor der durch Evaporation bedingte Betrag des Wasserverlustes bestimmt wurde. Es wird gezeigt, daß diese Methode wertvolle Vergleiche zwischen den verschiedenen Arten zu ziehen gestattet. Sowohl bei Hundertfüßlern wie auch bei Tausendfüßlern erwies sich die Transpiration als proportional zum Sättigungsdefizit der Luft. Diese Tiere ähneln deshalb in diesem Punkte ihrer Physiologie Arten aus gemäßigten und Wüsten-Gebieten.Ihre nächtliche Lebensweise, die mittels Aktographen festgestellt wurde, steht wahrscheinlich in Beziehung zu der vergleichsweise hohen Wasserverlustrate. Der endogene diurnale Rhythmus ziegt eine leichte Verzögerung bei Dauerbelechtung und eine Beschleunigung bei Dunkelheit. Auf diese Weise wird wahrscheinlich die Periodizität dieser Tiere mit dem 24-Stunden-Rhythmus der Umgebung synchronisiert.Die kritsche Temperatur des westafrikanischen Skorpions Pandinus imperator liegt beträchtlich niedriger als die der Wüsten-Arten und ähnelt der des italienischen Euscorpius germanus. Es wird vermutet, daß in diesem Falle die nächtliche Lebensweise in Beziehung steht zu der Gefährdung des großen, langsamen Tieres durch räuberische Wirbeltiere.Es wird geschlossen, daß im allgemeinen die Transpirationsrate in Beziehung zum Habitat steht und bei Wüstenbewohnern am niedrigsten ist.

     

Adaptive evolution of crustin antimicrobial peptides in decapods

Antimicrobial peptides (AMPs) are present in a wide range of taxonomic groups and played a crucial role in host adaptation to a diverse array of ever-changing pathogens. Crustin, a cysteine-rich cationic AMP, is known to exhibit antimicrobial activity against Gram-positive and Gram-negative bacteria in decapods. Given their important role in host-immune defense, a large proportion of amino acid substitutions in crustin AMPs are expected to be fixed by natural selection. Utilizing the complete coding nucleotide sequence data of crustin, the present study revealed the pervasive role of positive Darwinian selection in the evolution and divergence of crustin AMPs in decapods. Approximately, 20–35?% of codons in two phylogenetically distinct groups of closely related crustins in Penaeid shrimps are shown to have evolved under positive selection. Interestingly, several of these positively selected sites are located at the carboxyl-terminal region, the region that directly interacts with the invading pathogens. Pathogen-mediated selection pressure could be the likely cause for such an accelerated rate of amino acid substitutions and could have contributed to the structural and functional diversification of crustin AMPs in several taxa.     

Activity of some enzymes in Physarum polycephalum

Summary The activity levels of seven enzymes were studied in growing plasmodia of Physarum polycephalum. The enzymes were isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase, acid phosphatase, phosphodiesterase, -glucosidase, and histidase. Six of the enzymes showed a continuous increase in activity during the mitotic cycle; glutamate dehydrogenase exhibited a stepwise increase about 5 h after mitosis. Cycloheximide immediately inhibited the activity of all enzymes. Actinomycin D was ineffective in inhibiting enzyme activity until after one mitotic cycle had been completed; this indicates that mRNA was stable for all of these enzymes during the G2 period. Attempts to induce enzyme activity were unsuccessful.

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Zusammenfassung Der Aktivitätsverlauf von sieben Enzymen wurde in wachsenden Plasmodien von Physarum polycephalum untersucht. Es handelte sich um die Enzyme: Isocitrat-Dehydrogenase, Glucose-6-Phosphat-Dehydrogenase, Glutamat-Dehydrogenase, saure Phosphatase, Phosphodiesterase, -Glucosidase und Histidase. Sechs dieser Enzyme wiesen einen kontinuierlichen Aktivitätsanstieg während des Mitosecyclus auf; Glutamat-Dehydrogenase zeigte einen stufenförmigen Anstieg etwa 5 Std nach der Kernteilung. Cycloheximid hemmte sofort die Aktivität der Enzyme, während Actinomycin D erst nach Ablauf eines halben Teilungscyclus inhibierend wirkte. Dies deutet auf eine relativ stabile mRNA hin. Versuche, die Aktivität zu induzieren, schlugen fehl.

     

A comparison of adaptations to running, pushing and burrowing in some adult Coleoptera: especially Carabidae

A wide range of compromises between maximum speed attained and pushing force exerted are exhibited by various Coleoptera. Some structural and functional parameters are quoted for two beetles at the extreme ends of this range: the rapid tiger beetle Cicindelu cumpestris and the powerful dung beetle Geotrupes stercorarius. Additionally, maximum sprint speeds and pushing forces were obtained for 105 species selected from 22 families of beetles. To compare the relative speed (u_R) and relative force (F_R) abilities of different sized species, a simple means of scaling was used in which u_R= u/W^0'33 (where u is the maximum sprint speed, and W the weight of a beetle) and F_R= F/W^0'67 (where F is the maximum forçe exerted by the beetle. measured by pulling). The best speed/force adapted species lay along a limiting front where u_R a F_R and u. F/W.k = 1 (where k is a constant). This gave a measure of the locomotory capability of a beetle in terms of I, the index of speed/force specialization. The specialists exhibited an index close to 1·0, but that of most beetles tested lay between 1·0 and 0·01. The Carabidae was analysed more closely as it contains many locomotor specialists. It was possible to define three structural/functional groups which showed different combinations of running and pushing abilities. The possible evolutionary relationships of these habit groups was discussed, and some speed and force comparisons were made between beetles and some other terrestrial arthropods.     

Activity patterns of rodents: the physiological ecology of biological rhythms

To date, most research in the field of biological rhythms has been performed on nocturnal rodents under laboratory conditions. This research has made much progress in recent years. It is now time to investigate the adaptive value of the studied molecular mechanisms under natural conditions. Here we review relevant studies of rodent activity patterns. We also review a case study of temporal partitioning between spiny mice. We conclude that the response to environmental stimuli, using a system composed of a rigid master circadian oscillator and more flexible mechanisms such as peripheral oscillators with weak coupling, masking responses, and downstream switching mechanisms, is adaptive since it enables an animal to reset its activity phase without the cost of shifting the phase of the entire circadian system. We suggest that these mechanisms play a significant role in determining activity patterns under natural conditions, and are important for understanding the ecology and evolution of activity rhythms.     

Haematological correlates of burrowing in Ctenomys

Haematological parameters related to O2 transport and regulation of acid-base equilibrium were determined for two species of Ctenomys. The oxygen capacity values of Ctenomys blood are similar to those of other fossorial mammals. Ctenomys blood has almost half the number of red blood cells of Rattus blood but the amount of Hb in each blood cell is 2-2.5 times higher. Blood pH is within typical mammalian values. Concentration of inorganic phosphate is higher in Ctenomys than in rats while bicarbonate and protein values are within typical mammalian range.     

Optical parameters of the eyes of some benthic decapods as a function of habitat depth (Crustacea,Decapoda)

Summary Eye diameter relative to body length, and interommatidial angle, rhabdom length and rhabdom width as a function of eye size, were determined for specimens of 19 benthic macruran decapod species in 8 genera and 5 families, spanning a wide range of habitat depths. For these species, eye diameter relative to body length tends to increase with adult habitat. In addition, rate of eye growth relative to body growth increases with habitat depth, a trend opposite to that of pelagic crustaceans previously investigated. Interommatidial angle decreases with increasing eye diameter, and therefore with depth for an individual of a particular size. Rhabdom length and width tend to increase with eye diameter. Visual sensitivity may increase with depth among these species as a result of both larger eyes and the associated increase in rhabdom dimensions. Differences in energetic limitations and visual environments might produce the difference in trends of eye size relative to body size between benthic and pelagic crustaceans.     

Pattern of nucleotide substitution and divergence of prophenoloxidase in decapods

Despite the unprecedented development in identification and characterization of prophenoloxidase (proPO) in commercially important decapods, little is known about the evolutionary relationship, rate of amino acid replacement and differential selection pressures operating on proPO of different species of decapods. Here we report the evolutionary relationship among these nine decapod species based on proPO gene and types of selective pressures operating on proPO codon sites. Our analyses revealed that all the nine decapod species shared a common ancestor. The mean percentage sequence divergence at proPO gene was 34.4+/-0.6%. Pairwise estimates of nonsynonymous to synonymous ratio (omega) for Homarus americanus-H. gammarus is greater than one, therefore indicating adaptive evolution (functional diversification) of proPO in these two species. In contrast, strong purifying selection (omega<1) was observed in all other species pairs. However, phylogenetically closely related decapods revealed relatively higher omega value (omega=0.15+/-0.3) than the distantly related species pairs (omega=0.0075+/-0.005). These discrepancies could be due to higher fixation probability of beneficial mutation in closely related species. Maximum likelihood-based codon substitution analyses revealed a strong purifying selection operating on most of the codon sites, therefore suggesting proPO is functionally constrained (purifying selection). Codon substitution analyses have also revealed the evidence of strong purifying selection in haemocyanin subunits of decapods.