Showing papers by "John C. Avise published in 1995"

Mitochondrial DNA Polymorphism and a Connection Between Genetics and Demography of Relevance to Conservation

Abstract: Molecular markers increasingly are employed to estimate population genetic parameters of relevance to conservation biology, such as within-population heterozygosity, between-population gene flow, and the genetic distinctiveness of taxonomic units. One complication in interpreting empirical results is that alternative markers sometimes yield different outcomes, presumably due to sampling errors associated with the small fraction of the genome represented in any assay, and to the possibility that the genes monitored were influenced by different evolutionary forces (such as selection versus neutral drift). Sometimes a special significance is claimed for particular classes of genetic markers. A recent example was the provocative suggestion by Hughes (1991) that captive breeding programs should be designed with an explicit focus on maintaining allelic diversity in genes of the major histocompatibility complex, a stance that stimulated much controversy and discussion (Gilpin & Wills 1991; Miller & Hedrick 1991; Vrijenhoek & Leberg 1991). In this spirit of provocative thought, I wish to suggest a special demographic significance for the perspectives that have been provided by another genetic systemmitochondrial (mt) DNA (see also Moritz 1994).

Hybridization Among the Ancient Mariners: Characterization of Marine Turtle Hybrids With Molecular Genetic Assays

Abstract: Reports of hybridization between marine turtle species (family Cheloniidae) have been difficult to authenticate based solely on morphological evidence. Here we employ molecular genetic assays to document the sporadic, natural occurrence of viable interspecific hybrids between species representing four of the five genera of cheloniid sea turtles. Using multiple DNA markers from single-copy nuclear loci, eight suspected hybrids (based on morphology) were confirmed to be the products of matings involving the loggerhead turtle (Caretta caretta) x Kemp's ridley (Lepidochelys kempii) (N = 1 specimen), loggerhead turtle x hawksbill (Eretmochelys imbricata) (N = 2), loggerhead turtle x green turtle (Chelonia mydas) (N = 4), and green turtle x hawksbill (N = 1). Molecular markers from mitochondrial DNA permitted identification of the maternal parental species in each cross. The species involved in these hybridization events represent evolutionary lineages thought to have separated 10-75 million years ago (mya) and thus may be among the oldest vertebrate lineages capable of producing viable hybrids in nature. In some cases, human intervention with the life cycles of marine turtles (e.g., through habitat alteration, captive rearing, or attempts to establish new breeding sites) may have increased the opportunities for interspecific hybridization.

A comparison of mtDNA restriction sites vs. control region sequences in phylogeographic assessment of the musk turtle (Sternotherus minor)

Abstract: A total of nearly 800 base pairs of mitochondrial DNA sequence was assayed in each of 52 musk turtles (Sternotherus minor) collected across the species' range in the south-eastern USA. About one-half of the sequence information in effect was accessed by conventional recognition-site assays of the entire mtDNA molecule; the remainder came from direct sequence assays of a normally hypervariable 5' section of the noncoding control region. The two assay methods produced essentially nonoverlapping sets of variable character states that were compared with respect to magnitudes and phylogeographic patterns of mtDNA variation. The two assay procedures yielded nearly identical outcomes with regard to: (a) total levels of species-wide mtDNA genetic variation; (b) mean levels of within-locale variation; (c) extremely high population genetic structure; (d) a phylogenetically significant separation of samples from the north-western half of the species' range vs. those in the south-eastern segment; and (e) considerably lower genetic variability within the north-western clade. The micro- and macro-phylogeographic mtDNA patterns in the musk turtle are consistent with a low-dispersal natural history, and with a suspected longer-term biogeographic history of the species, respectively.