Assessing substitution patterns, rates and homoplasy at HVRI of Steller sea lions, Eumetopias jubatus.

Despite the widely recognized incidence of homoplasy characterizing this region, the hypervariable region I (HVRI) of the mitochondrial control region is one of the most frequently used genetic markers for population genetic and phylogeographic studies. We present an evolutionary analysis of HVRI and cytochrome b sequences from a range-wide survey of 1031 Steller sea lions, Eumetopias jubatus, to quantify homoplasy and substitution rate at HVRI. Variation in HVRI was distributed across 41 variable sites in the 238-bp segment examined. All variants at HVR1 were found to be transitions. However, our analyses suggest that a minimum of 101 changes have actually occurred within HVRI with as many as 18 substitutions occurring at a single site. By including this hidden variation into our analyses, several instances of apparent long-range dispersal were resolved to be homoplasies and 8.5-12% of observed HVRI haplotypes were found to have geographic distributions descriptive of convergent molecular evolution rather than identity by descent. We estimate the rate of substitution at HVRI in Steller sea lions to be approximately 24 times that of cytochrome b with an absolute rate of HVRI substitution estimated at 27.45% per million years. These findings have direct implications regarding the utility of HVRI data to generate a variety of evolutionary genetic hypotheses.

Environmental neurotoxic effects: the search for new protocols in functional teratology.

Large quantities of a number of man-made chemicals with the potential to disrupt the developing endocrine and nervous systems in wildlife and humans have been released into the environment. These chemicals are particularly damaging during the embryonic, fetal, and early postnatal periods because they resemble or interfere with the hormones, neurotransmitters, growth factors, and other signaling substances that normally control development. The effects are in many cases irreversible and often are expressed as changes in function rather than as obvious birth defects or clinical diseases. Functional changes pose challenges in documenting the extent of the lesion, especially in the case of neuroendocrinological damage. In the past decade, researchers have added new dimensions to their research strategies in order to compensate for these difficulties. The new approaches reveal more about the extent of the distribution of and exposure to chemicals that interfere with the endocrine and nervous systems and strengthen the links between exposure and damage in developing wildlife and humans. Based on this new knowledge, opportunities abound for extensive multi-disciplinary research involving developmental neurotoxicity.

Epidemiological analysis of persistent organochlorine contaminants in cetaceans.

Information is provided to test the hypothesis that organochlorines introduced into the environment since the early 1940s could threaten the reproductive potential of baleen whales and other cetaceans. Comparisons are made using data on the role of organochlorines in a model system, the Great Lakes region of North America, and in model animals, including humans, pinnipeds, and other wildlife. DDT and PCB are used as model organochlorines with the caveat that there may be thousands of other chemicals in the environment also involved. Improved sensitivity in analytical quantification of synthetic chemicals in biological tissue has been accompanied by an increase in knowledge about biochemical processes that control development and function. The effects described in this review are the result of disrupted gene expression, not damage to the gene. The mechanisms of action of the organochlorines reveal their ability to affect developing organisms at very low concentrations during critical life stages: embryonic, fetal, and early postnatal. Exposure during early development can disrupt the organization of the endocrine, reproductive, immune and nervous systems, effecting irreversible damage that may not be expressed until the individuals reach adulthood. The recent discovery that human sperm count is declining worldwide at a rate of 1 x 10(6) sperm/(mL.yr) suggests common exposure to estrogen-like chemicals during prenatal and early postnatal development. This raises concern for other top predator species that also share the same exposure. Periods of intense feeding followed by long periods of fasting are common among species of baleen whales. This unique strategy places the embryonic and nursing calves in vulnerable positions, because under both situations maternal blood levels are elevated as a result of absorption from food intake or as a result of mobilization as fat is metabolized. Estimates of Toxic Equivalents (TEQs) based on the occurrence of four PCB congeners (118, 183, 153, 180) in sigma PCB reported in whales are highest for St. Lawrence belugas and Faroe Island long-finned pilot whales. This conservative approach reveals that some whale species are within the range of enzyme-induced TEQs at which effects have been associated with adverse health effects in other aquatic species. The epidemiological approach was used for analysis because it was developed to handle multiple exposure scenarios in which direct causal links are virtually impossible to isolate. The analysis includes the tenets of timeorder, strength of association, specificity of cause and effect, consistency, coherence, and predictive performance.

Somatic and heritable effects of environmental genotoxins and the emergence of evolutionary toxicology.

The genetic effects of environmental pollutants include mutations in somatic cells or germinal cells that are the direct result of exposure to toxicants. Biomarkers that detect such mutagenic effects have been developed and tested in field studies on wildlife populations. However, another class of genetic effects resulting from pollution exposure exists. Specifically, changes in allele frequencies of populations will occur as a result of population bottlenecks, inbreeding, or selection at loci critical for survival in polluted environments. We describe how such genetic alterations can be studied at the population level using the techniques of molecular genetics, and we predict the development of a new field, evolutionary toxicology, that will address such issues.

Chromosomal variation in pocket gophers (Geomys) detected by sequential G-, R-, and C-band analyses.

The chromosomes of six taxa, representing five species of Geomys (G. attwateri, G. breviceps, G. personatus, G. texensis, G. bursarius) were analysed for variation in G-band, R-band, sequential R-/DAPI-AMD, and sequential R-/C-band patterns. Eleven chromosomes had structural rearrangements resulting from deletion/addition events. Fission/fusion rearrangements occurred in two chromosomes, and a pericentric inversion was confirmed in only one chromosome. Eighteen of 34 autosomes had constitutive heterochromatin, with variation in its presence or absence, position, and quantity. The heterochromatic differences were seen both among species and between two subspecies of G. personatus. Chromomycin A3 fluorescent staining identified G-C rich regions in 31 of the autosomes with 29 showing variation in their presence or absence, position, and quantity, and identified a high degree of cryptic variation. The X chromosome was highly variable, with differences attributable to structural rearrangements and variation in chromomycin bright-staining regions.

Further flow cytometric studies of the effects of triethylenemelamine on somatic and testicular tissues of the rat.

Exposure to the mutagen triethylenemelamine on rat bone marrow, blood, and testis was studied using flow cytometry of DAPI-stained nuclei. Increased coefficients of variation (CVs) of the G1 peaks were observed in bone marrow and blood after both 1 d and 5 d exposures. After 5 d exposure and 7 d recovery both tissues had recovered, in some cases to significantly lower CVs. Increased CVs of the 1C peak of testis were observed only after 5 d exposure to the high dose with no subsequently observed recovery. Bone marrow cells also were stained with Hoechst 33258 and Propidium Iodide. No differences among dyes were observed indicating that increased CVs likely are due to DNA damage resulting from interactions with the mutagen rather than differences in how the dyes bind to DNA relative to mutagen binding. This study demonstrates that differences occur among tissues in how quickly they respond and recover from mutagen exposure. Increased CVs, cell cycle alterations, and decreased CVs after recovery are all potentially useful biomarkers of effect for laboratory and field studies in environmental toxicology.

Genetic damage in a population of slider turtles (Trachemys scripta) inhabiting a radioactive reservoir.

Turtles inhabiting a radioactive reservoir appear to experience genetic damage due to environmental exposure to low concentrations of long-lived radionuclides. Total body burdens for the 50 reservoir turtles examined in the survey ranged from 164.7-4679.3 Bq for cesium-137 and from 462.6-5098.3 Bq for strontium-90. Flow cytometric (FCM) assays of red blood cell nuclei demonstrated significantly greater variation in DNA content for the reservoir turtles than for turtles from a nearby, non-radioactive site. Furthermore, two of the reservoir turtles possessed FCM profiles that are indicative of aneuploid mosaicism. These data strongly suggest that exposure to low-level radiation may involve a sensitive genetic response in a natural population.