Dennis A. Powers

A Molecular Genetic Classification of Zooxanthellae and the Evolution of Animal-Algal Symbioses

Zooxanthellae are unicellular algae that occur as endosymbionts in many hundreds of marine invertebrate species. Because zooxanthellae have traditionally been difficult to classify, little is known about the natural history of these symbioses. Zooxanthellae were isolated from 131 individuals in 22 host taxa and characterized by the use of restriction fragment length polymorphisms (RFLPs) in nuclear genes that encode small ribosomal subunit RNA (ssRNA). Six algal RFLPs, distributed host species specifically, were detected. Individual hosts contained one algal RFLP. Zooxanthella phylogenetic relationships were estimated from 22 algal ssRNA sequences—one from each host species. Closely related algae were found in dissimilar hosts, suggesting that animal and algal lineages have maintained a flexible evolutionary relation with each other.

The gene family encoding the fucoxanthin chlorophyll proteins from the brown alga Macrocystis pyrifera

Six members of a multigene family encoding polypeptide constituents of the fucoxanthin, chlorophyll a/c protein complex from female gametophytes of the brown alga Macrocystis pyrifera have been cloned and characterized. The deduced amino acid sequences are very similar to those of fucoxanthin chlorophyll binding proteins (Fcp) from the diatom Phaeodactylum tricornutum and exhibit limited homology to chlorophyll a/b binding (Cab) polypeptides from higher plants. The primary translation products from the M. pyrifera fcp genes are synthesized as higher molecular weight precursors that are processed prior to their assembly into the Fcp complex. The presumed N-terminal 40-amino acid presequence of the Fcp precursor polypeptide has features resembling that of a signal sequence. This presequence may be required for the protein to transverse the endoplasmic reticulum that surrounds the plastid in brown algae. A subsequent targeting step would be required for the protein to cross the double membrane of the plastid envelope. M. pyrifera fcp transcripts are of two sizes, 1.2 and 1.6 kb. The size difference is accounted for by the length of the 3′ untranslated region, which can be up to 1000 bases. Transcript abundances of members of the fcp gene family are dependent on light quantity, light quality, or both. Transcript levels of one gene increased approximately five- to tenfold in thalli grown in low intensity relative to high intensity white or blue light. Transcripts from this gene also significantly increase in red light relative to blue light at equivalent light intensities.

Biochemical genetics of Fundulus heteroclitus (L.). I. Temporal and spatial variation in gene frequencies of Ldh-B, Mdh-A, Gpi-B, and Pgm-A

Natural populations of Fundulus heteroclitus show extensive spatial variation in gene frequencies at four unlinked polymorphic loci. Large clinal changes in gene frequencies were found for Ldh-B, Mdh-A, and Gpi-B, whereas the spatial variation for the Pgm-B locus was small. Since the geographical area over which these clines are found is characterized by a steep thermal gradient, the clines in gene frequency are correlated with a directional change in mean water temperature. Maximum gene diversity of these four loci was correlated with annual fluctuations in water temperature. Temporal stability of the allelic frequencies was established for a 2–4 year period.

Evolutionary adaptations of gene structure and expression in natural populations in relation to a changing environment: A multidisciplinary approach to address the million‐year saga of a small fish

We have used an experimentally based strategy to address molecular mechanisms underlying adaptation in Fundulus heteroclitus. In an attempt to falsify the hypothesis that selection is a major driving force in the maintenance of genetic diversity, we employed a multidisciplinary approach including allelic isozyme and mtDNA phylogeography, kinetic analyses of allelic isozymes, analysis of variation in coding and regulatory DNA sequences, metabolic biochemistry, organismal physiology, and selection experiments. Observed differences in gene structure and expression led us to make testable predictions about differences in metabolic flux, whole organism performance, and differential survival between allotypes. We have shown that variation in the lactate dehydrogenase-B (Ldh-B) protein results in differences in physiological function and is correlated with differences in survival at high temperatures. Recent work has investigated the role of variation in Ldh-B expression. There are differences in the levels of Ldh-B protein, mRNA, and transcription rate. We have addressed the mechanisms responsible for differences in transcription rate by a combination of sequence comparison, DNase I footprinting, and functional analyses both in vitro and in vivo. We have shown that variation in the regulatory sequence of Ldh-B is responsible for the differences in transcription rate between populations and that the patterns of variation are inconsistent with a neutral model of molecular evolution. This functional differentiation, coupled with departures from neutral expectations, suggests that natural selection has acted on the regulation of Ldh-B. This article illustrates the value of a multidisciplinary approach in addressing problems in gene structure, expression, and evolutionary adaptation.

Hemoglobin heterogeneity in Amazonian fishes

Abstract 1. The hemoglobin patterns of hemolysates from the lungfish,Lepidosiren paradoxa, four species of freshwater rays (Potamotrygon), and actinopterygian teleosts from 77 genera have been characterized by polyacrylamide disc gel electrophoresis. 2. These tropical fishes have hemolysates which are as complex as those reported from temperate zone fishes. 3. There are no obvious correlations between hemoglobin multiplicity and the fish behaviour or habitat preference. 4.Potamotrygon has blurred hemoglobin patterns,Lepidosiren shows a single hemoglobin, and the other teleosts show a mean of 4.0 hemoglobin bands per phenotype. 5. Ostariophysan fishes have a lower mean number of bands per phenotype than acanthopterygian fishes. 6. Patterns of a single hemoglobin band occurred in 8% of the phenotypes. 7. Two or more hemoglobin phenotypes were found in about 10 species. 8. SDS gel electrophoresis showed the fish hemoglobin chains to have molecular weights comparable to those of human Hb A.

MITOCHONDRIAL-DNA RESTRICTION-SITE POLYMORPHISMS IN THE TELEOST FUNDULUS HETEROCLITUS SUPPORT SECONDARY INTERGRADATION

Fundulus heteroclitus is a highly polymorphic fish distributed along the Atlantic coast of North America. Several loci show directional changes in gene frequency with latitude (i.e., clines). Such directional changes have classically been described by two general models: primary and secondary intergradation. Previously, it has not been possible to distinguish between these models for Fundulus heteroclitus on the basis of allelic isozymes or morphological data. However, recent analysis of mitochondrial‐DNA (mtDNA) restriction electromorphs helps resolve this issue.

A comparative study of the oxygen equilibria of blood from 40 genera of Amazonian fishes

Abstract 1. We have examined the oxygen-affinity of the fresh, whole blood from representatives of 40 genera of Amazonian fishes. 2. When all the air-breathing fishes and all the water-breathing fishes were considered, no differentiation in oxygen affinity could be distinguished, although in two cases of closely related species, i.e. Osteoglossum , a water breather, vs Arapaima , an air breather, and Hoplias , a water breather, vs Hoplerythrinus , an air breather; the air breathers have bloods with lower oxygen affinity than do the water breathers. 3. Significant differences in the oxygen affinity were found when fishes were considered by habitat: the oxygen affinities were in general correlated with available environmental oxygen and relative oxygen demand of the fishes.

Time Course of Changes in Enzyme Activities and Blood Respiratory Properties of Killifish during Long-Term Acclimation to Hypoxia

Evidence is presented for quantitative enzymatic changes in fishes in response to the oxygen content of their environment. Fundulus heteroclitus significantly increased the specific activities of lactate dehydrogenase, malate dehydrogenase, and glucose-phosphate isomerase in liver tissue during the first 28 days of acclimation to hypoxia (1.5-2.5 ppm dissolved oxygen). However, the activities of these enzymes returned to control levels after 35 days of hypoxic existence. Unlike liver tissue, white skeletal muscle demonstrated no consistent pattern during hypoxic acclimation. Blood hematocrit increased and red blood cell organic phosphate levels decreased and remained so during the entire acclimation period (35 days). These adaptations facilitate the uptake of oxygen at the gills in an oxygen-poor environment. Serum lactate concentration increased during the first 3 wk of hypoxia. However, this parameter returned to control levels by 28 days of acclimation. These observations, together with behavioral observations, are consistent with an improved delivery and utilization of oxygen after long-term acclimation in a hypoxic environment. The enzymatic changes are thus a short-term response to hypoxic stress.

Body composition of transgenic common carp, Cyprinus carpio, containing rainbow trout growth hormone gene

Abstract F1 transgenic common carp, Cyprinus carpio, containing rainbow trout growth hormone gene, pRSVrtGH1 cDNA were compared to non-transgenic full-siblings for body composition. Percent protein was higher (P A E ratios) of lysine and histidine were higher (P

Genetic bases for protein polymorphism in Fundulus heteroclitus (L.). I. Lactate dehydrogenase (Ldh-B), malate dehydrogenase (Mdh-A), glucosephosphate isomerase (Gpi-B), and phosphoglucomutase (Pgm-A)

Electrophoretic analysis has shown populations of F. heteroclitus to possess variants at four enzyme-coding loci: Ldh-B, Mdh-A, Gpi-B, and Pgm-A. Based on the phenotypic distribution in the F1 generation, each variant segregates as an autosomally inherited codominant allele. A pairwise comparison of the expected phenotypic classes among these loci showed no evidence of strong linkage; however, weak linkage could not be ruled out. Despite the considerable genetic divergence of populations from the geographical extremes of this species, offspring resulting from crosses between individuals from these localities show viabilities similar to those found for crosses of local populations.