Physiological studies of phototrophy and heterotrophy in two algae with contrasting nutritional characteristics, Pyrenomonas salina (Cryptophyceae) and Poterioochromonas malhamensis (Chrysophyceae)

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1990The ability of algae to take up dissolved organic compounds is well documented for cultured and field populations yet the physiological mechanisms controlling this behavior are largely unknown. The effects of dissolved organic compound additions on the growth and photosynthetic apparatus were examined in two nanophytoplankton with contrasting nutritional characteristics, Pyrenomonas salina (Cryptophyceae) and Poterioochromonas malhamensis (Chrysophyceae). Although both species are capable of chemoheterotrophic nutrition, great differences were found in the relative contribution of heterotrophy to their overall nutrition and the physiological response of their photosynthetic systems to changes in nutritional mode. These differences indicate that the physiological mechanisms involved in integrating autotrophic and heterotrophic nutrition and the environmental control of this integration are distinct in these species. In comparison to other facultatively heterotrophic algae, P. malhamensis is exceptional in the dominant contribution of heterotrophy to its overall nutrition. Growth could be significantly enhanced by organic substrate additions to P. malhamensis at all light intensities and the growth rate on glucose in the dark was equal to the maximum growth rate on glucose in the light. In addition, when organic substrates were available to the alga, chlorophyll a cell-1 was reduced and the extent of this reduction varied with the type of organic substrate. These results support the hypothesis that chloroplast development in P. malhamensis is catabolite-sensitive. The inhibitory effect of organic substrates on chlorophyll production by P. malhamensis was only transitory; i.e., after the initial decline in chlorophyll a cell-1, chlorophyll production increased and the organic substrate uptake rate cell-1 decreased despite the persistence of a relatively high substrate concentration in the culture medium. These results suggest that the accumulation of substance(s) excreted by P. malhamensis conditioned the culture medium and led to a relief of the inhibitory effect of organic substrates on chlorophyll production by the alga. P. salina is typical of most facultatively heterotrophic algae in culture in that phototrophic growth can be enhanced by organic enrichment only at light intensities limiting for photoautotrophic growth. Contrary to P. malhamensis, the effect of organic compounds on the growth rate of P. salina was critically light intensity-dependent under all organic substrate concentrations used in this study. In addition, whereas in P. malhamensis the addition of organic substrates repressed chloroplast development, only selected elements of the photosynthetic system were inhibited by organic substrate additions to P. salina, and the uptake rate of inorganic carbon was not affected. These results indicate that these algae have contrasting metabolic strategies for integrating autotrophic and heterotrophic nutrition for growth. When organic substrates are available to P. malhamensis, the synthesis of the photosynthetic apparatus is repressed and growth and maintenance requirements are met by the catabolism of organic substrates. In contrast, given a sufficient light supply, maximal growth rates can be obtained photoautotrophically by P. salina, but organic substrates can be used to augment the carbon, energy, and/or reductant supply when photosynthetic rates are light-limited. The physiological response of P. salina's photosynthetic system to changes in environmental conditions was further examined by testing two hypotheses. The first hypothesis was that P. salina responds to nitrogen deprivation by mobilizing phycoerythrin in order to help sustain cellular nitrogen requirements. In response to nitrogen depletion from the culture medium, the phycoerythrin content of P. salina cells decreased prior to any changes in growth rate, cell volume, or cellular concentrations of chlorophyll a, carbon, or nitrogen. These results support the hypothesis and suggest that, in addition to its light-harvesting role, phycoerythrin may serve as an important endogenous nitrogen source for this cryptophyte. The second hypothesis was that glycerol uptake selectively inhibits the synthesis of photosynthetic components involved in light-harvesting. Glycerol addition to P. salina cultures grown at a limiting light intensity reduced the cell phycoerythrin content, phycoerythrin to chlorophyll a ratio, thylakoid width, degree of thylakoid packing, number of thylakoids cell-1, and size of photosystem II complexes. These properties were reduced to a similar extent by increasing the light intensity for growth. These results strongly support the hypothesis and indicate that enhancement of heterotrophic potential occurs at the expense of light-harvesting ability in glycerol-grown P. salina.This research was funded by the Massachusetts Institute of Technology /Woods Hole Oceanographic Institution Joint Program, Ocean Ventures Fund Grant 25/85.10 of the Woods Hole Oceanographic Institution Education Program, and NSF Grants BSR-8620443 and BSR- 8919447

An Adaptive Threshold in Mammalian Neocortical Evolution

Expansion of the neocortex is a hallmark of human evolution. However, it remains an open question what adaptive mechanisms facilitated its expansion. Here we show, using gyrencephaly index (GI) and other physiological and life-history data for 102 mammalian species, that gyrencephaly is an ancestral mammalian trait. We provide evidence that the evolution of a highly folded neocortex, as observed in humans, requires the traversal of a threshold of 10^9 neurons, and that species above and below the threshold exhibit a bimodal distribution of physiological and life-history traits, establishing two phenotypic groups. We identify, using discrete mathematical models, proliferative divisions of progenitors in the basal compartment of the developing neocortex as evolutionarily necessary and sufficient for generating a fourteen-fold increase in daily prenatal neuron production and thus traversal of the neuronal threshold. We demonstrate that length of neurogenic period, rather than any novel progenitor-type, is sufficient to distinguish cortical neuron number between species within the same phenotypic group.Comment: Currently under review; 38 pages, 5 Figures, 13 Supplementary Figures, 2 Table

Uptake of Spartina-derived humic nitrogen by estuarine phytoplankton in nonaxenic and axenic culture

Humic substances are a collection of colored organic acids characterized by high molecular weight and low nitrogen (N) content that are thought to be biologically recalcitrant. We examined a suite of nonaxenic estuarine phytoplankton isolates to determine their ability to take up N-15-labeled humic substances formed in the laboratory and supplied as the sole N source. All 17 estuarine and coastal strains took up the added humic N, but the one polar isolate did not. Two of the coastal isolates (Heterosigma akashiwo and Fibrocapsa japonica) could take up the humic N in nonaxenic culture but not in axenic culture, suggesting that bacterial remineralization played a role in making humic N accessible to these species. The ability of nonaxenic phytoplankton isolates to use humics of different ages (1 week to 1 yr old) was tested using three strains capable of taking up humic N at high rates. Younger, fresher humics were taken up by the phytoplankton strains at higher rates than older, more fulvic-like compounds, and at rates higher than inorganic N uptake run in parallel. Time-course results indicate that while uptake of the inorganic N forms was sustained, high rates of humic N uptake declined after the first few hours of incubation. Additional humic substances were labeled with both N-15 and C-13, and the relative incorporation of N versus carbon (C) was used to infer potential uptake mechanisms. None of the isolates took up humic C, suggesting that uptake of the humic N followed breakdown of the humic molecule by bacteria or via extracellular enzyme cleavage of humic N. Regardless of the mode of uptake, the observation that humic N can be rapidly used by phytoplankton suggests that the importance of humic N as a source of phytoplankton N nutrition should be reevaluated

Placental morphology and the cellular brain in mammalian evolution

A major focus of evolutionary neurobiology has been on whether different regions of the eutherian brain evolve in concert, and how free the brain is to evolve independently of body plans. Since the eutherian brain is loosely modularized, such that one region is rarely isolated for specialization at the expense of others, but the design of modularization itself can be adapted by tweaking developmental programs, the degree to which brain regions must evolve in concert and can evolve independently may carry a deep phylogenetic signal. Using data collected from preserved brain tissue of 37 primate, 21 carnivore, and 15 other eutherian species (spanning 11 orders), I examined the phylogenetic level at which the proliferation of neurons and glia in the primary visual cortex and hippocampus proper, as well as granular layer volumes of the dentate gyrus and cerebellum, may be constrained by conserved developmental programs. In doing so, I was able to test for cellular signatures of (1) evolutionary changes in metabolic activity, (2) phylogenetic divergences, (3) specializations in behavior, and (4) developmental constraints. The degree to which disparate brain regions evolve in concert is shown to be generally conserved in Eutheria, although a derived ability to evolve regions independently is observed along the primate lineage. Using a separate dataset on placental and life-histroy character states, a comprehensive comparative phylogenetic approach was used to resolve relationships among five aspects of placental structure and to identify syndromes of placental morphology with life-history variables. My results support two discrete biological phenotypes of placental morphology and life-history, which are shown to have an evolutionary affect on allocortical, but not neocortical, brain organization. I have provided a new perspective on exploring how developmental constraints – acting both within and without the brain – may affect brain organization at the cellular level, and the extent to which those constraints have been adapted along certain eutherian lineages

Oceanographic results from the VERTEX 3 Particle Interceptor Trap Experiment off central Mexico,October-December,1982

In this report, we present oceanographic results from VERTEX 3 Particle Interceptor Trap (PIT) experiment conducted off the western-coast of Mexico during October to November 1982. The oceanographic data presented here were obtained during three cruise legs by Moss Landing Marine Laboratory scientists aboard R/V Cayuse while the detailed chemical studies were done by other scientists aboard R/V Wecoma. Only the oceanographic data will be presented in this report. (PDF contains 82 pages

Spectral observations of pigment fluorescence in intermediate depth waters of the North Pacific

Vertical profiles at three stations off the California coast showed spectral differences between fluorescence at the primary fluorescence maxima (near 100 m) and the deeper maximum (near 800 m). Two broad-band excitation and several narrow or high-pass emission filters were used with an in situ fluorometer to 1500 m. Interpretation of these data suggests: (1) chlorophyll a was found throughout the water column, with intermediate depth fluorescence about one-third the intensity of that in the primary maximum; (2) phycobilin fluorescence was stronger at intermediate depths than near the surface; and (3) a pigment which fluoresces beyond 700 nm was also found in the primary fluorescence maximum

A simple and fast method for extraction and quantification of cryptophyte phycoerythrin

The microalgal pigment phycoerythrin (PE) is of commercial interest as natural colorant in food and cosmetics, as well as fluoroprobes for laboratory analysis. Several methods for extraction and quantification of PE are available but they comprise typically various extraction buffers, repetitive freeze-thaw cycles and liquid nitrogen, making extraction procedures more complicated. A simple method for extraction of PE from cryptophytes is described using standard laboratory materials and equipment. The cryptophyte cells on the filters were disrupted at −80 °C and added phosphate buffer for extraction at 4 °C followed by absorbance measurement. The cryptophyte Rhodomonas salina was used as a model organism. • Simple method for extraction and quantification of phycoerythrin from cryptophytes. • Minimal usage of equipment and chemicals, and low labor costs. • Applicable for industrial and biological purposes

RPANDA: an R package for macroevolutionary analyses on phylogenetic trees

A number of approaches for studying macroevolution using phylogenetic trees have been developed in the last few years. Here, we present RPANDA, an R package that implements model‐free and model‐based phylogenetic comparative methods for macroevolutionary analyses. The model‐free approaches implemented in RPANDA are recently developed approaches stemming from graph theory that allow summarizing the information contained in phylogenetic trees, computing distances between trees, and clustering them accordingly. They also allow identifying distinct branching patterns within single trees. RPANDA also implements likelihood‐based models for fitting various diversification models to phylogenetic trees. It includes birth–death models with i) constant, ii) time‐dependent and iii) environmental‐dependent speciation and extinction rates. It also includes models with equilibrium diversity derived from the coalescent process, as well as a likelihood‐based inference framework to fit the individual‐based model of Speciation by Genetic Differentiation, which is an extension of Hubbell's neutral theory of biodiversity. RPANDA can be used to (i) characterize trees by plotting their spectral density profiles (ii) compare trees and cluster them according to their similarities, (iii) identify and plot distinct branching patterns within trees, (iv) compare the fit of alternative diversification models to phylogenetic trees, (v) estimate rates of speciation and extinction, (vi) estimate and plot how these rates have varied with time and environmental variables and (vii) deduce and plot estimates of species richness through geological time. RPANDA provides investigators with a set of tools for exploring patterns in phylogenetic trees and fitting various models to these trees, thereby contributing to the ongoing development of phylogenetics in the life sciences

Two-Thirds Favor President to Be Chosen Based on National Popular Vote

Two-thirds of American voters prefer for the US president to be chosen based on the national popular vote, according to a new survey consultation by the Program for Public Consultation at the University of Maryland and released today by the nonpartisan Voice of the People. However, two-thirds of Republicans (65%) would like to keep the current system for electing the president. This Compact has already been adopted in 15 states plus the District of Columbia, which brings the total of electoral votes currently to 196. It has also passed in one legislative chamber in eight states with a total of 75 electoral votes. If all of these eight states were to adopt the Compact, it would go into effect

Americans on Police Reform

A policymaking simulation is an online process that puts citizens in the shoes of elected officials by simulating the process they go through in making policy decisions. Each simulation introduces a broader policy topic and then presents a series of modules that address a specific policy option that is currently under consideration in the current discourse. For each module, respondents: 1) receive a short briefing on a policy issue and the option or options for addressing it; 2) evaluate arguments for and against the policy options; and 3) finally, make their recommendation for what their elected officials should do.For decades now, there have been periodic efforts to reform police practices and laws regarding the use of force, especially deadly force, by law enforcement officers. The recent deaths of George Floyd and Breonna Taylor and other incidents of law enforcement officers using deadly force have stimulated protest and demands for policing reforms. The U.S. House of Representatives recently passed the George Floyd Justice in Policing Act (H.R. 7120), sponsored by Rep. Karen Bass (D-CA), The JUSTICE Act (S. 3985), sponsored by Sen. Tim Scott (R-SC), failed to get cloture in the U.S. Senate, meaning the measure could not proceed for debate or a vote. . The provisions in these two bills continue to the basis for ongoing debates over police reform, including: ● when police officers should use deadly force; ● what types of force police officers should be able to use, such as chokeholds; ● the use of no-knock warrants; ● the standards by which officers are held accountable for their use of excessive force; ● whether racial bias among police is a problem to be addressed; and ● how much regulation there should be of military equipment transferred to the police. Both bills address these issues, to different extents. The most significant difference between the House bill and the Senate bill is how mandatory the proposed reforms are. The House bill would require that police departments and local governments implement new policies or be denied access to federal funding for police departments. The Senate bill would offer police departments new funding for training and data collection, and only in a few cases requires that police departments adopt new policies. The House bill also includes provisions to change the standards by which officers are criminally convicted and held civilly liable, which the Senate bill does not. To bring the American people a voice at the table of the current debate on this legislation, the Program for Public Consultation (PPC) has conducted an in-depth on-line survey of over 3,000 registered voters with a probability-based sample provided by Nielsen Scarborough. Unlike standard polls that rely on respondents’ existing impressions and information, PPC took respondents through a process called a ‘policymaking simulation’ that seeks to put respondents in the shoes of a policymaker. Respondents: ● are given a briefing on policy options under consideration ● evaluate strongly stated arguments both for and against each option ● make their final recommendation. The content of the process is thoroughly reviewed by experts across the spectrum of opinion on the policy options to ensure that the briefing is accurate and balanced and that the arguments are the strongest ones being made by proponents and opponents