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2 Units of Assessment
Pages 29-42

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From page 29...
... A key theme is that population mixing in sea turtles changes with life stage, as juveniles from regional nesting populations may be well mixed, whereas breeding adults may have strong genetic divisions. Population structure also varies among genetic markers, with maternally inherited mitochondrial DNA (mtDNA)
From page 30...
... sometimes showing a strong connection between breeding populations. The major challenges associated with this complex population structure are still being resolved.
From page 31...
... In the current era of genomics, the available classes of genetic markers are now known and largely well characterized. Hence, scientists expect that for at least the coming decade, the workhorse technologies for defining populations will be stable: mtDNA and microsatellites (loci at which short sequences of DNA are repeated in tandem arrays)
From page 32...
... This haploid inheri ­ tance contrasts with the diploid inheritance of nDNA.1 An additional feature is that mtDNA accumulates mutations faster than most nuclear loci, and this makes mtDNA sequences a method of choice for microevolutionary studies, which look at small­scale changes in allele frequencies in a population. mtDNA­sequence information was first used to test the age and isola­ tion of the green­turtle nesting population on Ascension Island (Bowen et al., 1989)
From page 33...
... Those coastlines were almost certainly too cold to support nesting during the last glacial epoch, which ended about 12,000 years ago so loggerhead nesting has spread northward to Virginia, the northernmost nesting site within the thermal regime for embryonic development. Although the nesting populations in northeast Florida, Georgia, South Carolina, and North Carolina are genetically indistinguishable with current mtDNA data, they are almost certainly isolated management units, based on the overall pattern of population genetic separations in loggerheads (Bowen et al., 1993; Bowen and Karl, 2007)
From page 34...
... However, their broadest application may be in defining isolated populations with a biparentally inherited nuclear marker. Microsatellites, in conjunction with maternally inherited mtDNA, allow assessment of the male and female contributions to population structure.
From page 35...
... Complex Population Structure: Life Stages In most marine vertebrates, a survey of adults, preferably at breed­ ing sites, is sufficient to sample the nesting population and thus to define management units. In sea turtles, because of their highly migratory nature and complex population structure, it is necessary to survey every life stage to determine the extent of connectivity among populations (Figure 2.1)
From page 36...
... During the pelagic (open­ocean, juvenile) stage, individuals from the nesting populations intermingle in oceanic habitat, and no population structure is apparent between eastern and western Atlantic.
From page 37...
... showed that contributions from the west Atlantic nesting popula­ tions were roughly proportional to the size of the nesting populations. A similar method showed that juvenile loggerhead turtles from the west Atlantic occupy feeding habitats in the Mediterranean (Laurent et al., 1998)
From page 38...
... However, precise estimates of the contributions of small nesting populations to feeding populations may not be possible, and this uncertainty needs to be built into predictive models used for management decisions. DISTRIBuTION Complex Population Structure: Female versus Male Components of Population Structure Genetic surveys of sea turtles consistently show lower population divergence in nDNA assays than in mtDNA assays (Karl et al., 1992; FitzSimmons et al., 1997b; Roberts et al., 2004)
From page 39...
... shows the effect of males on gene flow and population structure. In some cases, where isolated populations do not overlap on feeding and migratory habitat, the mtDNA and nDNA data can indicate concordant population boundaries (Dutton et al., 2008)
From page 40...
... For this reason, it may not be practical to genotype hatchlings with the expectation of matching these genotypes to turtles recaptured at later life stages. Nonetheless, genetic tags may resolve some aspects of population structure (Lee et al., 2007)
From page 41...
... • mtDNA surveys of nesting populations are useful for defining management units in terms of isolated reproductive populations. • nDNA surveys are useful for resolving the male­mediated connec­ tions between nesting populations and for defining RMUs connected by nuclear gene flow.
From page 42...
... in coastal and oceanic habitats. • Researchers should conduct a sea­turtle genome project for the explicit purpose of developing additional nuclear markers, possibly the next generation of genetic markers for sea turtles (see Appendix A)


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