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J C Avise

Publications and source records attributed to J C Avise.

At least 19 recordsLinked to original sources
PubMed1992

Balancing selection at allozyme loci in oysters: implications from nuclear RFLPs.

Population genetic analyses that depend on the assumption of neutrality for allozyme markers are used widely. Restriction fragment length polymorphisms in nuclear DNA of the American oyster evidence a pronounced population subdivision concordant with mitochondrial DNA. This finding contrasts with a geographic uniformity in allozyme frequencies previously thought to reflect high gene flow mediated by the pelagic gametes and larvae. The discordance likely is due to selection on protein electrophoretic characters that balances allozyme frequencies in the face of severe constraints to gene flow. These results raise a cautionary note for studies that rely on assumptions of neutrality for allozyme markers.

Alleles↗
PubMed1992

Mode of origin and sources of genotypic diversity in triploid gynogenetic fish clones (Poeciliopsis: Poeciliidae).

Most tributaries of the Río Fuerte in northwestern Mexico contain one or more clones of allotriploid fish of the genus Poeciliopsis. We used multilocus allozyme genotypes and mitochondrial DNA (mtDNA) haplotypes to examine several potential modes of origin of these gynogenetic all-female fish. The allozyme studies corroborated earlier morphological work revealing the hybrid constitution of two triploid biotypes, Poeciliopsis 2 monacha-lucida and Poeciliopsis monacha-2 lucida. Each biotype carries one or two whole genomes from the each of the sexual species P. monacha and P. lucida. Restriction site analysis of mtDNA revealed that P. monacha was the maternal ancestor of five electrophoretically distinguishable triploid clones. Four of five clones were marked by closely related, composite, allozyme/mtDNA genotypes, suggesting they had common origins from an allodiploid clone of the P. monacha-lucida biotype. Genotypic analysis revealed that all five clones arose via the "genome addition" pathway. Fertilization of unreduced ova in P. monacha-lucida females by sperm from P. monacha and P. lucida males, respectively, gave rise to both biotypes.

Animals↗
PubMed1992

Global population genetic structure and male-mediated gene flow in the green turtle (Chelonia mydas): RFLP analyses of anonymous nuclear loci.

We introduce an approach for the analysis of Mendelian polymorphisms in nuclear DNA (nDNA), using restriction fragment patterns from anonymous single-copy regions amplified by the polymerase chain reaction, and apply this method to the elucidation of population structure and gene flow in the endangered green turtle, Chelonia mydas. Seven anonymous clones isolated from a total cell DNA library were sequenced to generate primers for the amplification of nDNA fragments. Nine individuals were screened for restriction site polymorphisms at these seven loci, using 40 endonucleases. Two loci were monomorphic, while the remainder exhibited a total of nine polymorphic restriction sites and three size variants (reflecting 600-base pair (bp) and 20-bp deletions and a 20-bp insertion). A total of 256 turtle specimens from 15 nesting populations worldwide were then scored for these polymorphisms. Genotypic proportions within populations were in accord with Hardy-Weinberg expectations. Strong linkage disequilibrium observed among polymorphic sites within loci enabled multisite haplotype assignments. Estimates of the standardized variance in haplotype frequency among global collections (FST = 0.17), within the Atlantic-Mediterranean (FST = 0.13), and within the Indian-Pacific (FST = 0.13), revealed a moderate degree of population substructure. Although a previous study concluded that nesting populations appear to be highly structured with respect to female (mitochondrial DNA) lineages, estimates of Nm based on nDNA data from this study indicate moderate rates of male-mediated gene flow. A positive relationship between genetic similarity and geographic proximity suggests historical connections and/or contemporary gene flow between particular rookery populations, likely via matings on overlapping feeding grounds, migration corridors or nonnatal rookeries.

Animals↗
PubMed1992

Mitochondrial DNA evolution at a turtle's pace: evidence for low genetic variability and reduced microevolutionary rate in the Testudines.

Evidence is compiled suggesting a slowdown in mean microevolutionary rate for turtle mitochondrial DNA (mtDNA). Within each of six species or species complexes of Testudines, representing six genera and three taxonomic families, sequence divergence estimates derived from restriction assays are consistently lower than expectations based on either (a) the dates of particular geographic barriers with which significant mtDNA genetic clades appear associated or (b) the magnitudes of sequence divergence between mtDNA clades in nonturtle species that otherwise exhibit striking phylogeographic concordance with the genetic partitions in turtles. Magnitudes of the inferred rate slowdowns average eightfold relative to the "conventional" mtDNA clock calibration of 2%/Myr sequence divergence between higher animal lineages. Reasons for the postulated deceleration remain unknown, but two intriguing correlates are (a) the exceptionally long generation length most turtles and (b) turtles' low metabolic rate. Both factors have been suspected of influencing evolutionary rates in the DNA sequences of some other vertebrate groups. Uncertainities about the dates of cladogenetic events in these Testudines leave room for alternatives to the slowdown interpretation, but consistency in the direction of the inferred pattern, across several turtle species and evolutionary settings, suggests the need for caution in acceptance of a universal mtDNA-clock calibration for higher animals.

Animals↗
PubMed1991

Evolutionary distinctiveness of the endangered Kemp's ridley sea turtle.

The endangered Kemp's ridley sea turtle (Lepidochelys kempi) nests almost exclusively at a single locality in the western Gulf of Mexico, whereas the olive ridley (L. olivacea) nests globally in warm oceans. Morphological similarities between kempi and olivacea, and a geographical distribution that "...makes no sense at all under modern conditions of climate and geography", raise questions about the degree of evolutionary divergence between these taxa. Analysis of mitochondrial (mt) DNA restriction sites shows that Kemp's ridley is distinct from the olive ridley in matriarchal phylogeny, and that the two are sister taxa with respect to other marine turtles. Separation of olive and the Kemp's ridley lineages may date to formation of the Isthmus of Panama, whereas the global spread of the olive ridley lineage occurred recently. In contrast to recent examples in which molecular genetic assessments challenged systematic assignments underlying conservation programmes, our mtDNA data corroborate the taxonomy of an endangered form.

Animals↗
PubMed1991

Molecular evidence for multiple origins of hybridogenetic fish clones (Poeciliidae:Poeciliopsis).

Hybrid matings between the sexual species Poeciliopsis monacha and Poeciliopsis lucida produced a series of diploid all-female lineages of P. monacha-lucida that inhabit the Río Fuerte of northwestern Mexico. Restriction site analyses of mitochondrial DNA (mtDNA) clearly revealed that P. monacha was the maternal ancestor of these hybrids. The high level of mtDNA diversity in P. monacha was mirrored by similarly high levels in P. monacha-lucida; thus hybridizations giving rise to unisexual lineages have occurred many times. However, mtDNA variability among P. monacha-lucida lineages revealed a geographical component. Apparently the opportunity for the establishment of unisexual lineages varies among tributaries of the Río Fuerte. We hypothesize that a dynamic complex of sexual and clonal fishes appear to participate in a feedback process that maintains genetic diversity in both the sexual and asexual components.

Animals↗
PubMed1990

A genetic test of the natal homing versus social facilitation models for green turtle migration.

Female green turtles exhibit strong nest-site fidelity as adults, but whether the nesting beach is the natal site is not known. Under the natal homing hypothesis, females return to their natal beach to nest, whereas under the social facilitation model, virgin females follow experienced breeders to nesting beaches and after a "favorable" nesting experience, fix on that site for future nestings. Differences shown in mitochondrial DNA genotype frequency among green turtle colonies in the Caribbean Sea and Atlantic Ocean are consistent with natal homing expectations and indicate that social facilitation to nonnatal sites is rare.

Animals↗
PubMed1990

A genetic discontinuity in a continuously distributed species: mitochondrial DNA in the American oyster, Crassostrea virginica.

Restriction site variation in mitochondrial DNA (mtDNA) of the American oyster (Crassostrea virginica) was surveyed in continuously distributed populations sampled from the Gulf of St. Lawrence, Canada, to Brownsville, Texas. mtDNA clonal diversity was high, with 82 different haplotypes revealed among 212 oysters with 13 endonucleases. The mtDNA clones grouped into two distinct genetic arrays (estimated to differ by about 2.6% in nucleotide sequence) that characterized oysters collected north vs. south of a region on the Atlantic mid-coast of Florida. The population genetic "break" in mtDNA contrasts with previous reports of near uniformity of nuclear (allozyme) allele frequencies throughout the range of the species, but agrees closely with the magnitude and pattern of mtDNA differentiation reported in other estuarine species in the southeastern United States. This concordance of mtDNA phylogenetic pattern across independently evolving species provides strong evidence for vicariant biogeographic processes in initiating intraspecific population structure. The post-Miocene ecological history of the region suggests that reduced precipitation levels in an enlarged Floridian peninsula may have created discontinuities in suitable estuarine habitat for oysters during glacial periods, and that today such population separations are maintained by the combined influence of ecological gradients and oceanic currents on larval dispersal. The results are consistent with the hypothesis that historical vicariant events, in conjunction with contemporary environmental influences on gene flow, can result in genetic discontinuities in continuously distributed species with high dispersal capability.

Alleles↗
PubMed1989

The effects of assortative mating and migration on cytonuclear associations in hybrid zones.

We examine the influence of nonrandom mating and immigration on the evolutionary dynamics of cytonuclear associations in hybrid zones. Recursion equations for allelic and genotypic cytonuclear disequilibria were generated under models of (1) migration alone, assuming hybrid zone matings are random with respect to cytonuclear genotype; and (2) migration in conjunction with refined epistatic mating, in which females of the pure parental species preferentially mate with conspecific males. Major results are as follows: (a) even the slightest migration removes the dependency of the final outcome on initial conditions, producing a unique equilibrium in which both pure parental genotypes are maintained in the hybrid zone; (b) in contrast to nuclear genes, the dynamics of cytoplasmic allele frequencies appear robust to changes in the assumed mating system, yet are particularly sensitive to gene flow; (c) continued immigration can generate permanent cytonuclear disequilibria, whether mating is random or assortative; and (d) the order of population censusing (before versus after reproduction by immigrants) can have a dramatic effect on the magnitude but not the pattern of cytonuclear disequilibria. Using the maximum likelihood method, the parameter space of migration rates and assortative mating rates was examined for best fit to observed cytonuclear disequilibria data in a hybrid population of Hyla tree frogs. An epistatic mating model with a total immigration rate of about 32% per generation produces equilibrium gene frequencies and cytonuclear disequilibria consistent with the empirical observations.

Animals↗
PubMed1989

DNA fingerprints from hypervariable mitochondrial genotypes.

Conventional surveys of restriction-fragment polymorphisms in mitochondrial DNA of menhaden fish (Brevoortia tyrannus/patronus complex) and chuckwalla lizards (Sauromalus obesus) revealed exceptionally high levels of genetic variation, attributable to differences in mtDNA size as well as in restriction sites. The observed probabilities that any two randomly drawn individuals differed detectably in mtDNA genotype were 0.998 and 0.983 in the two species, respectively. Thus, the variable gel profiles provided unique mtDNA "fingerprints" for most conspecific animals assayed. mtDNA fingerprints differ from nuclear DNA fingerprints in several empirical respects and should find special application in the genetic assessment of maternity.

Animals↗
PubMed1986

Mitochondrial DNA and the evolutionary genetics of higher animals.

Mitochondrial DNA (mtDNA) in higher animals is rapidly becoming a well characterized genetic system at the molecular level. In this paper, I shift the focus to consider questions in organismal evolution that can be addressed by mtDNA assay. For the first time, it is possible to estimate empirically matriarchal phylogeny; to determine directionality in crosses producing hybrids; and to study the population genetic consequences of varying female demographies and life histories. The data obtainable from mtDNA may be especially well suited for studies of population genetic structure, dispersal, and historical zoogeography. The female-mediated, clonal transmission of mtDNA is also stimulating new ways of thinking about times to common ancestry of asexual lineages within otherwise sexually reproducing populations; about the possible relevance of mtDNA-nuclear DNA interactions to reproductive isolation; and about the very meaning of the phylogenetic status of related species with respect to particular kinds of genetic characters. These and other topics are reviewed.

Animals↗
PubMed1979

Mitochondrial DNA clones and matriarchal phylogeny within and among geographic populations of the pocket gopher, Geomys pinetis.

Restriction endonuclease assay of mitochondria DNA (mtDNA) and standard starch-gel electrophoresis of proteins encoded by nuclear genes have been used to analyze phylogenetic relatedness among a large number of pocket gophers (Geomys pinetis) collected throughout the range of the species. The restriction analysis clearly distinguishes two populations within the species, an eastern and a western form, which differ by at least 3% in mtDNA sequence. Qualitative comparisons of the restriction phenotypes can also be used to identify mtDNA "clones" within each form. The mtDNA clones interconnect in a phylogenetic network which represents an estimate of matriarchal phylogeny for G. pinetis. Although the protein electrophoretic data also differentiate the eastern and western forms, the data are of limited usefulness in establishing relationships among more local subpopulations. The comparison between these two data sets suggests that restriction analysis of mtDNA is probably unequalled by other techniques currently available for determining phylogenetic relationships among conspecific organisms.

Albumins↗
PubMed1979

The use of restriction endonucleases to measure mitochondrial DNA sequence relatedness in natural populations. I. Population structure and evolution in the genus Peromyscus.

In this study we introduce to natural population analysis a molecular technique that involves the use of restriction endonucleases to compare mitochondrial DNA (mtDNA) sequences. We have examined the fragment patterns produced by six restriction endonucleases acting upon mtDNA isolated from 23 samples of three species of the rodent Peromyscus. Our observations confirm the following conclusions derived from previous experiments with laboratory animals: (1) mtDNA within an individual homogeneous; (2) at least the majority of mtDNA present in an individual is inherited from the female parent. Our experiments demonstrate for the first time that there is detectable heterogeneity in mtDNA sequences within and among natural geographic populations of a species and that this heterogeneity can readily be used to estimate relatedness between individuals and populations. Individuals collected within a single locale show less than 0.5% sequence divergence, while those collected from conspecific populations separated by 50 ti 500 miles differ by approximately 1.5%. The mtDNAs of the closely related sibling species P. polionotus and P. maniculatus differ from each other by 13 to 17%; nonsibling species differ by more than 20%. Qualitative and quantitative approaches to analysis of digestion patterns are suggested. The results indicate that restriction analysis of mtNDA may become the most sensitive and powerful technique yet available for reconstructing evolutionary relationships among conspecific organisms.

Animals↗
PubMed1977

Is evolution gradual or rectangular? Evidence from living fishes.

The traditional view that most evolutionary change is gradual and cumulative within lineages (phyletic gradualism) has recently been challenged by the proposition that the majority of evolutionary change is concentrated within speciation events (rectangular evolution). The logical implications of these competing hypotheses for the means and variances of genetic distance among living members of rapidly and slowly speciating phylads are examined. An example of a critical test of gradual versus rectangular evolution is provided by electrophoretic analyses of genic composition in 69 species of North American Cyprinidae (minnows), and 19 species of Centrarchidae (sunfish). Rate of protein evolution appears somewhat decelerated, if anything, in the rapidly speciating minnows. Results are inconsistent with predictions of rectangular evolution, but are not demonstrably incongruent with predictions of phyletic gradualism.

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