Evolution and nature of the dense bodies in the chicken pinealocytes.

The acid phosphatase reaction, applied to light and electron microscopy, was studied in the chicken pineal gland from the moment of hatching until 2 months of age. From the moment of hatching there is a great amount of acid phosphatase, which is mainly found in the vicinity of the lumen of both the recess and large follicles. Acid phosphatase is poor in the parafollicular layer. From day 30 onwards, there is an obvious fragmentation of the recess and of large follicles. Also, the parafollicular layer differentiates to form new follicles. The dense polymorphous bodies of the B pinealocytes are ultrastructurally identified as lysosomes.     

Evolution and nature of science instruction

In this article, I provide an analysis of my work (1985–present) with non-major biology students and science teacher candidates in developing strategies for teaching and enhancing learning with respect to evolutionary science. This first-person account describes changes in evolution instruction over the course of a career based on personal experiences, research-informed practices, and a critical collaboration with colleague Mike U. Smith. I assert four insights concerning the influence and efficacy of teaching nature of science (NOS) prior to the introduction of evolution within college courses for science non-majors and science teacher candidates. These insights are: (a) teach explicit NOS principles first; (b) integrate evolution as a theme throughout a course in introductory biology (but after NOS principles have been introduced); (c) use active learning pedagogies; and (d) use non-threatening alternative assessments to enhance student learning and acceptance of evolutionary science. Together, these insights establish a pedagogy that I (and my colleagues) have found to be efficacious for supporting novice students as they engage in the study of evolutionary science.     

Heterochronic genes and the nature of developmental time

Timing is a fundamental issue in development, with a range of implications from birth defects to evolution. In the roundworm Caenorhabditis elegans, the heterochronic genes encode components of a molecular developmental timing mechanism. This mechanism functions in diverse cell types throughout the animal to specify cell fates at each larval stage. MicroRNAs play an important role in this mechanism by stage-specifically repressing cell-fate regulators. Recent studies reveal the surprising complexity surrounding this regulation--for example, a positive feedback loop may make the regulation more robust, and certain components of the mechanism are expressed in brief periods at each stage. Other factors reveal the potential for important roles of steroid hormones and targeted proteolysis. Investigation of the heterochronic genes has revealed a mechanism composed of precisely timed switches linked to discrete developmental stages. Timing is a dimension of developmental regulation that may be difficult to witness in vertebrates because developmental stages are not as discrete as in C. elegans, each tissue is likely to be independently regulated. Homologs of certain heterochronic genes of vertebrates show temporally regulated expression patterns, and may ultimately reveal timing mechanisms not previously known to exist.     

Evolution of ontogeny and nature of heterochronies

Every aspect of biological orderliness is a result of evolution, which expresses the systemic reorganization of organismal body plan, along with the way of its ontogenetic formation. Phyletic changes in the developmental rates (heterochronies) experienced by the organism or its structures exemplify just a kind of such consequences. The current belief that heterochronies are the causes of evolutionary events is based on the assumption that evolution of ontogeny proceeds in the same way as the ontogeny itself, i.e., from a germ cell to adult state. This premise (termed here “the central dogma”) is the cornerstone of traditional ideas of the evolutionary mechanism, regardless of whether it is perceived in terms of gene mutations or “embryonic modes.” In fact, the directions of two transformations compared are opposite each other. An evolutionary change in the body plan results from reorganization of the developmental system, which comes in response to disturbance of stability of the system’s terminal (adult) state. Realized by selection, this change starts immediately from the terminal state and then spreads in generations towards early ontogenetic stages. Heterochronies show just the same dynamics of events irrespective of whether they reflect the acceleration or delay of development. Empirically, such course of evolutionary changes was grounded most evidently by Severtsov in the early version of his concept of the phylembryogenesis. The theoretical basis of the same regularity is provided by the Schmalhausen–Waddington’s theory.     

Evolution and development of time coding systems

Precise temporal coding is a hallmark of both the electrosensory and auditory systems. Selective pressures to improve accuracy or encode more rapid changes have produced a suite of convergent physiological and morphological features that contribute to temporal coding. Comparative studies of temporal coding can also point to shared computational strategies, and suggest how selection might act to improve coding.     

Evolution of codon usage patterns: the extent and nature of divergence between Candida albicans and Saccharomyces cerevisiae.

Codon usage in a sample of 28 genes from the pathogenic yeast Candida albicans has been analysed using multivariate statistical analysis. A major trend among genes, correlated with gene expression level, was identified. We have focussed on the extent and nature of divergence between C.albicans and the closely related yeast Saccharomyces cerevisiae. It was recently suggested that significant differences exist between the subsets of preferred codons in these two species [Brown et al. (1991) Nucleic Acids Res. 19, 4293]. Overall, the genes of C.albicans are more A + T-rich, reflecting the lower genomic G + C content of that species, and presumably resulting from a different pattern of mutational bias. However, in both species highly expressed genes preferentially use the same subset of 'optimal' codons. A suggestion that the low frequency of NCG codons in both yeast species results from selection against the presence of codons that are potentially highly mutable is discounted. Codon usage in C.albicans, as in other unicellular species, can be interpreted as the result of a balance between the processes of mutational bias and translational selection. Codon usage in two related Candida species, C.maltosa and C.tropicalis, is briefly discussed.     

Evolution of handling time can destroy the coexistence of cycling predators

Several consumers (predators) with Holling type II functional response may robustly coexist even if they utilize the same resource (prey), provided that the population exhibits nonequilibrium dynamics and the handling time of predators is sufficiently different. We investigate the evolution of handling time and, in particular, its effect on coexistence. Longer handling time is costly in terms of lost foraging time, but allows more nutrients to be extracted from a captured prey individual. Assuming a hyperbolically saturating relationship between handling time and the number of new predators produced per prey consumed, we obtain three results: (i) There is a globally evolutionarily stable handling time; (ii) At most two predator strategies can coexist in this model; (iii) When two predators coexist, a mutant with intermediate handling time can always invade. This implies that there is no evolutionarily stable coexistence, and the evolution of handling time eventually leads to a single evolutionarily stable predator. These results are proven analytically and are valid for arbitrary (not only small) mutations; they however depend on the relationship between handling time and offspring production and on the assumption that predators differ only in their prey handling strategy.     

Effect of the nature of dietary fibre on transit time and faecal excretion in the growing pig

When added to a fibre-free diet, polyethylene, a substance not modified in the digestive tract and devoid of water-holding capacity, reduces mean transit time (MTT) in the gut of the growing pig from 101.3 to 88.8 h and increases faecal water excretion from 2 to 43 g day⁻¹. It does not modify the digestibility of the other components of the diet.

However, with the same amount of added wheat bran, more pronounced effects (MTT: 75.7 h; daily faecal water output: 119 g) are observed. The mechanical properties of indigestible material, therefore, only partly explain its effect on transit time and faecal excretion in the pig.     

The mechanism of the synthesis of enzymes. II. Further observations with particular reference to the linear nature of the time course of enzyme formation

1. The pretreatment induction method of studying the formation of beta-galactosidase in E. coli B has been described. 2. It has been found that E. coli B cells have their maximum capacity to form beta-galactosidase, in response to a constant induction stimulus, when they are in the stationary phase of the growth cycle. 3. The concentration of inductor, the nature of the nitrogen source, the duration of the assimilatory phase, oxygen tension, and temperature are factors which affect, and may limit, the rate of beta-galactosidase formation. 4. When limitations imposed by these factors were removed, the time course of induced beta-galactosidase formation was strictly linear from the onset. 5. The implications of this finding were discussed and a new theory of the mechanism of enzyme formation has been proposed. 6. A very satisfactory method of synthesis of ortho-nitrophenol-alpha-D-galactoside has been described. This substance is a suitable chromogenic substrate for the specific determination of alpha-galactosidase activity. 7. Preliminary experiments using this substrate have confirmed the results of respiration studies and shown that in E. coli B alpha-galactosidase formation may be induced by beta- as well as by alpha-galactosides.     

Evolution of fringing reefs: space and time constraints from the Gulf of Aqaba

This study documents the pattern and rate of reef growth during the late Holocene as revealed by unique geological conditions at the subsiding NW Gulf of Aqaba. We discovered that the modern fringing reef near the city Elat grows on top of a fossil submerged mid-Holocene reef platform. Four coral cores from the fossil platform were dated using the radiocarbon and U-Th methods. The fossil corals range from 5.6±0.1 to 2.4±0.03 ka, constraining the initiation of the modern reef to 2,400 years ago at most. We documented the detailed morphology of the reef using aerial photographs and scuba diving. The survey shows that at its northern end, growth of the 2-km-long reef is inhibited by an active alluvial fan, and it is composed of isolated knolls that are just approaching the sea surface. Towards the south, the knolls are progressively larger and closer together, until they form a continuous reef platform. Along this north-to-south trend we follow the evolution of reef morphology, changes in coral distribution, and the development of a lagoon separated from the open sea. Based on these observations, we suggest a four-stage reef growth model: (a) the reef initiates as coral colonies, forms knolls, and begins to grow upward, limited by the sea surface. (b) Upon reaching the surface, the knolls spread laterally, preferentially parallel to the dominant wave direction assuming an elongated morphology. (c) Continued growth results in adjacent knolls eventually coalescing to form a continuous jagged reef. We interpret the spurs-and-grooves morphology that can be traced across the reef at Elat as remnants of the original trends of knolls. (d) While reef expansion continues, the original knoll trends may be obscured as a massive reef front takes shape. Considering reef growth rates and observations from the modern reef at Elat, this evolution scheme predicts an age range of 10³ years for corals on the reef platform. The range and distribution of radiometric ages we obtained from the fossil reef platform underlying the living Elat reef confirm this hypothesis.