Differential accumulation and localization of maternal poly(A)-containing RNA during early development of the ascidian,Styela

The regional distribution of poly(A)⁺ RNA was examined in sections of Styela oocytes and fertilized eggs by in situ hybridization with [³H]poly(U). The nucleus and cytoplasm of previtellogenic oocytes contain equivalent densities of [³H]poly(U) binding sites. The concentration of these sites is reduced in the cytoplasm, but not the nucleus, during vitellogenesis. Consequently, the germinal vesicle (GV) plasm of mature oocytes is characterized by an eightfold elevation in [³H]poly(U) binding activity relative to the surrounding cytoplasm. The distinctive cytoplasmic regions of the mature oocyte do not exhibit differential concentrations of [³H]poly(U) binding sites. Following fertilization which triggers GV breakdown, meiosis, and ooplasmic segregation, the high density of [³H]poly(U) binding sites characteristic of the GV plasm is conserved in the basophilic cytoplasm during its extensive migration and eventual accumulation in the animal hemisphere of the egg. The insensitivity of the [³H]poly(U) binding sites of the basophilic cytoplasm to actinomycin D suggests that they are of maternal origin. It is concluded that maternal poly(A)⁺ RNA is subject to differential accumulation in the GV plasm and its derivative ooplasm during the early development of Styela.     

Immunofluorescent and ultrastructural studies of “sarcomeric” units in stress fibers of cultured non-muscle cells

Immunofluorescence and electron microscopy were used to study the organization of actin, myosin and α-actinin in the “sarcomeric” units of the stress fibers of a selected non-muscle cell type. The results of indirect immunofluorescence confirm that myosin and α-actinin are periodically distributed in discrete units along stress fibers and demonstrate that they are alternately spaced. This relationship is required by a sarcomere model of stress fiber construction. A comparison between immunofluorescent and EM images of stress fibers confirms that α-actinin is confined to Z line-like dense bodies, myosin to the spaces in between. The most intriguing result is that by immunofluorescence a periodic distribution of actin can be detected in some fibers. This may indicate that even actin is periodically distributed in non-muscle “sarcomeres”.     

Complementarity of thermoregulatory rhythms in Micropterus salmoides and M. dolomieui

Largemouth (Micropterus salmoide) and smallmouth (M. dolomieui) blackbasses tested in an electronic shuttlebox exhibited behavioral thermoregulatory rhythms which were temporally complementary. With a LD 12 : 12 photoperiod, M. dolomieui exhibited a preferred-temperature peak of 30.1°C during the latter portion of the photophase, when M. salmoides reached a minimum of 27.1°C. M. dolomieui exhibited a minimum of 26.6°C during the latter portion of scotophase, while M. salmoides remained at a significantly higher plateau of about 29°C, with a peak of 29.5°C at the midpoint of scotophase. The phase relations of the thermoregulatory rhythms relative to photoperiod suggest that they are endogenously timed circadian rhythms entrained by photoperiod. The thermotemporal complementarity of these rhythms suggests an aspect of niche segregation between these largely sympatric congeneric species.     

Behavioral thermoregulation by Ammocoete larvae of the sea lamprey (Petromyzon marinus) in an electronic shuttlebox

Ammocoete larvae of the sea lamprey Petromyzon marinus, a member of the primitive vertebrate class Agnatha, were tested for thermoregulatory behavior in an electronic shuttlebox (ichthyotron). The final preferendum derived from pooled data for 24 individually tested ammocoetes was characterized by a mean of 13.6 ± 0.17 (s.e.m.)°C, a mode and median of 140°C, and a range of voluntarily occupied temperatures from 10–19°C over a 3-day period.     

The natural history of a fugitive prairie plant (Mirabilis hirsuta (Pursh) MacM.)

Summary Some perennial fugitive plants that colonize badger disturbances in xeric prairies have a limited dispersal capacity, and consequently propagules are dispersed over a small area. I hypothesized that high density-dependent mortality might occur early in the life history of such species, and thus increased survival might occur in subsequent age classes because intraspecific competition would be reduced. These hypotheses were tested using natural and experimental cohorts of Mirabilis hirsuta (Pursh) MacM. From these data and field observations, inferences were obtained concerning selective forces operating upon life history characteristics of this species.The distance between individuals of M. hirsuta increases in successive age classes; the greatest decrease in density occurs between the propagule and seedling age classes. Mortality of propagules due to predation by ants and mice was density-dependent. Predation rates were highest at high propagule densities and predation upon propagules located on badger disturbances was higher than the mortality of propagules at similar densities in undisturbed prairie. The results of mortality in the propagule age class are seedlings present only at low densities and located away from parent plants. Seedlings survive to maturity only if they are located on badger disturbances; this species apparently can not successfully compete with plants present in undistrubed prairie. On badger disturbances seedlings present at low densities have much higher survival (roughly 50%) to maturity than do seedlings present at high densities (essentially zero). Thus, if high densities of propagules occur on a disturbance, predation upon propagules results, indirectly, in increased survival of seedlings to maturity. Such predation potentially could have important effects upon interspecific competition of M. hirsuta with other fugitives also colonizing badger disturbances.Reproductive success of M. hirsuta on the Cayler Prairie Preserve is contingent upon successful colonization of disturbance sites. It would appear that selection has operated upon the life history characteristics to favor both successful immigration onto new sites and establishment of seedlings on those sites. Relatively few, but large propagules are produced annually over a long adult life span. While large propagules enhance seedling establishment on xeric sites, production of few propagules annually for a number of years increases the likelihood of immigration onto sites that are variable in the time of appearance within the dispersal range of the plant.     

The condensed tannins of pasture legume species

Condensed tannins have been isolated from legume pasture species and purified by gel chromatography on Sephadex G-50 and LH-20 media. Molecular size di     

The molecular structure of (10R)-17β-hydroxy-5-methylene-4,10-cyclo-19-nor-4,5-seco-17α-pregn-20-YN-1-one

The crystal and molecular structure of (10R)-17β-hydroxy-5-methylene-4,10-cyclo-19-nor-4,5-seco-17α -pregn-20-YN-1-one has been determined by X-ray analysis in order to ascertain the configuration at C(10). As observed in most other 17α-pregn-20-yn-17β-ol structures, atom 0(17B) participates as a donor in a hydrogen bond trans to the C(16)-C(17) bond, and there is a short C(21)…0 intermolecular contact.