The fossil record of biodiversity: nutrients, productivity, habitat area and differential preservation

It is hypothesized that the Phanerozoic record of fossil diversity is a function of a secular increase in nutrient availability and productivity (food, energy), and cyclic changes in sea level and habitat area due to supercontinent assembly and rifting. Both variables may have affected biodiversity through the combined variable of {productivity  ×  area}. {Productivity  ×  area} remained relatively constant after the Cambro-Ordovician until the end of the Permian, as did the traditional curve for biodiversity. During assembly of Pangea, decreasing sea level and habitat area were counteracted by increasing nutrient inputs due to uplift and the spread of vascular plants and enhanced continental weathering. As Pangea underwent its final assembly, interior drainage increased, so that by the end of the Permian both habitat area and nutrient runoff decreased. Following the end-Permian extinctions, the traditional curve of diversity began to increase, habitat area, nutrient levels and productivity all increased. Despite the confounding factors of differential preservation and sampling bias toward the present, the fossil record reflects a real response by the marine biosphere to tectonism, sea level, paleoceanographic regime and climate, and the spread of terrestrial floras, and their influence on habitat area, nutrient inputs, and productivity through time.     

Concomitant diel vertical migration of a predatory leech and its amphipod prey

SUMMARY.

• 1 The concomitant diet vertical migrations of the predaceous leech Erpobdella montezuma and its pelagic amphipod prey (Hyalella montezuma) were monitored for 1 year in Montezuma Well, Arizona, U.S.A.
• 2 High densities of H. montezuma occurred in the subsurface strata of the water column during the day, but a substantial portion of the population migrated into the surface 1 m at sunset. E. montezuma remained in the lower water strata during the day, but migrated vertically after sunset to exploit the high densities of H. montezuma near the surface. Densities of E. montezuma progressively increased in the upper strata of the water column after sunset as light energy fell below 1 μEin m^?2 s^?1.
• 3 It is suggested that the synchronized nocturnal migrations of the predator E. montezuma in relation to its prey H. montezuma, increases the foraging efficiency of the leech in the highly predictable environment of Montezuma Well.

     

Abscisic Acid Effects on Growth and Metabolism in the Roots ofLemna minor

The effects of abscisic acid (ABA) on individual plants of Lemna minor L. were studied. The effects on growth and metabolism of the roots were the most noticeable and the most desirable to measure. Two mg/1 of ABA inhibited the root growth rate by 60% and this was accompanied by a 60% deceleration in the rate of uridine incorporation. The uptake of uridine and leucine and the incorporation of leucine were not affected by ABA. The latent period of root growth inhibition was 1 hour, whereas the inhibition of ribonucleic acid (RNA) synthesis occurred 2 to 4 hours after application. The growth inhibition caused an accumulation of starch in the peripheral, differentiated cell layer of the cortex. Apparently, the growth inhibition by ABA was not entirely due to an inhibition of RNA synthesis, and other plausible mechanisms of growth inhibition are discussed.     

Direct Action of Insulin on Plasma Membrane ATPase Activity in Human Lymphocytes

LITTLE is known about the effects of insulin on lymphocytes. Helmreich and Eisen¹ concluded that it has insignificant effects, but others^2–5 have made a case for a role in inflammatory and immunological responses. We^6,7 have demonstrated that noradrenaline enhances the uptake of both glucose and potassium by lymphocytes, as does insulin in several tissues. We have associated this action of noradrenaline with a direct effect on membrane adenosine triphosphatase (ATPase) activity⁷. The observation⁸ that insulin bound to ‘Sepharose’ polymers enhances glucose transport while in contact only with the plasma membrane indicated that insulin might have a direct action similar to that of noradrenaline on membrane ATPase. The observations reported here show that insulin stimulates ATPase activity and glucose uptake in the lymphocyte and suggest a relationship between membrane ATPase activity and glucose transport.     

Chemical Carcinogenesis in Mice inhibited by Interferon

SEVERAL experiments have demonstrated that the anti-viral substance, interferon, can inhibit the growth of spontaneous^1,2, transplanted³ and virus-induced neoplasms in mice^4–7. Lieberman et al.⁵ reported that interferon treatment partially suppressed X-radiation-induced leukaemia in C57B1/6 mice. As they pointed out, the inhibitory effect provided additional evidence for the theory that X-rays cause lymphoma through the activation of a leukaemogenic type C RNA viral intermediate. In this communication, we report studies with CF-1 mice (Carworth Farms, New York City) to determine the effects of interferon on SC tumour induction by 3-methylcholanthrene (3-MC). These mice were previously shown to harbour high levels of type C RNA gs antigen and.infectious virus in normal spleens and in induced tumours, while spontaneous tumours rarely develop until late in life^8–10.     

Ultrasonic Vocalizations in Rat Sexual Behavior

Ultrasonic vocalizations are very conspicuous during rat matingactivity. Two types of calls are produced by both sexes. Thefirst, brief complex calls with the main frequency centeredabout 50 kHz, occur primarily in conjunction with solicitationand mounting activity. The second type of call is the long,22 kHz whistle which is emitted mainly by the male during thepostejaculatory refractory period, but also by both male andfemale at other times during the copulatory sequence. The occurrenceof ultrasonic vocalizations is correlated with sexual motivationof rats. Males emit more 50 kHz calls before successful matingtests than before tests in which they fail to ejaculate. Furthermore,more vocalizations are emitted by the pair prior to intromissionsthan prior to mounts without intromission. Just before ejaculationthere is a large increase in the rate of calling and, at times,transition by the male to calling at 22 kHz. This latter eventmay represent physiological dearousal by the male. Followingejaculation, the male characteristically emits 22 kHz vocalizationsand exhibits a sleep-like EEG pattern. The function of the postejaculatoryvocalization may be to enforce separation between the matingpair, while at the same lime maintaining contact between thepartners. Fifty kHz calls, on the other hand, prime and facilitatesexual responsiveness of the female. Tape recorded vocalizationsof mating rats facilitate solicitation behavior of estrous femalesin the presence of castrated males, and such females also showa preference for these sounds in a "Y" maze. Deafening of femalesdoes not affect their normal pacing of copulatory contacts,but it drastically reduces their solicitation behavior. Thestudies summarized in this paper lead us to conclude that ultrasonicvocalizations play a major role in the integration of reproductiveactivity in the Norway rat, Rattus norvegicus.     

CANNABINOID ENANTIOMER ACTION ON THE CYTOARCHITECTURE

The negative and positive enantiomers of 7-hydroxy- Δ⁶-tetrahydrocannabinol-dimethylheptyl (designated HU-210 and HU-211 respectively) differentially affect undifferentiated and differentiating cultured pheochromocytoma cells (PC-12 cells). In general, cell viability and cell proliferation were suppressed to a much greater extent with HU-210 than with HU-211 in differentiating cells. The effects of these synthetic cannabinoids on the cytoskeleton of PC-12 cells were examined by epifluorescence and confocal microscopy. In both undifferentiated and differentiating PC-12 cells, HU-211 has little effect on the cytoarchitecture whereas HU-210 disrupts the distribution of microtubules and microfilaments. Vacuoles (2–4 μm) were evident in the cytoplasm of HU-210-treated cells but not in the cytoplasm of HU-211-treated cells or in vehicle controls. Tubulin and actin mRNA levels were reduced to 5 and 40 %, respectively (relative to untreated controls) in 10 μmHU-210-treated cells whereas the same concentration of HU-211 reduced tubulin and actin mRNA levels to 90 and 95 %, respectively. A comparison of the effects of the paired enantiomers and Δ¹-THC on the cellular parameters studied reveals that in differentiating cells the action of Δ¹-THC is intermediate between that of HU-210 and HU-211. This study demonstrates that compared to HU-210 and Δ¹-THC the positive enantiomer HU-211 has little cellular activity.     

Modeling a Neural Oscillator that Paces Heartbeat in the Medicinal Leech

SYNOPSIS. Heartbeat in the medicinal leech is paced by a neuraloscillator comprising two elemental oscillators whose activityis coordinated intersegmental coordinating fibers. The elementaloscillators each consist of a bilateral pair of heart interneuronslinked by reciprocal inhibitory synapses. The activity cycleof each elemental oscillator consists of alternating burstsof action potentials (plateau/burst phase) and periods inhibition(inactive phase). Oscillation ensues in the reciprocally inhibitorypairs because each neuron is able to escape from the inhibitionits contralateral partner and thus move on to the plateau/burstphase. We have identified and described membrane currents thatcontribute to oscillation and studied graded synaptic transmissionbetween the neurons, using discontinuous current clamp and switchingsingle electrode voltage clamp techniques. A hyperpolarization-activatedinward current, Ih, plays a major role in escape from inhibition,and Ca²⁺ currents produce plateau potentials that support burstformation and mediate graded synaptic transmission. To consolidate our knowledge and guide future research, we haveconstructed a first generation computer model of a neural oscillatorbased on reciprocal inhibition, using Hodgkin-Huxley equationsand a synaptic transfer model, derived from our biophysicalstudies, with Nodus software (De Schutter, 1989). This modelhas confirmed an important role for I_h in sustaining oscillationand has implicated a similarly important role for outward currents(particularly I_A), which remain to be studied. Neural oscillatorsbased on reciprocal inhibition appear to be ubiquitous, andour studies, biophysical and computational, provide insightsinto how they may operate.