Data from: Genetic diversity and differentiation in a wide ranging anadromous fish, American shad (Alosa sapidissima), is correlated with latitude

Studies that span entire species ranges can provide insight into the
relative roles of historical contingency and contemporary factors that
influence population structure and can reveal patterns of genetic
variation that might otherwise go undetected. American shad is a wide
ranging anadromous clupeid fish that exhibits variation in demographic
histories and reproductive strategies (both semelparity and iteroparity)
and provides a unique perspective on the evolutionary processes that
govern the genetic architecture of anadromous fishes. Using 13
microsatellite loci, we examined the magnitude and spatial distribution of
genetic variation among 33 populations across the species' range to
(i) determine whether signals of historical demography persist among
contemporary populations and (ii) assess the effect of different
reproductive strategies on population structure. Patterns of genetic
diversity and differentiation among populations varied widely and reflect
the differential influences of historical demography, microevolutionary
processes and anthropogenic factors across the species' range.
Sequential reductions of diversity with latitude among formerly glaciated
rivers are consistent with stepwise postglacial colonization and
successive population founder events. Weak differentiation among U.S.
iteroparous populations may be a consequence of human-mediated gene flow,
while weak differentiation among semelparous populations probably reflects
natural gene flow. Evidence for an effect of reproductive strategy on
population structure suggests an important role for environmental
variation and suggests that the factors that are responsible for shaping
American shad life history patterns may also influence population genetic
structure.

覆盖物种种群完整分布范围的研究，可揭示影响种群结构的历史偶然性与当代因素的相对作用，还能发掘出否则可能被遗漏的遗传变异模式。
美洲西鲱（American shad）是一种分布广泛的溯河洄游（anadromous）鲱形目鱼类，其种群历史动态与繁殖策略（涵盖一次性生殖（semelparity）与多次生殖（iteroparity）两种模式）存在显著差异，为解析调控溯河洄游鱼类遗传架构的进化过程提供了独特视角。
本研究依托13个微卫星（microsatellite）位点，对该物种种群分布范围内的33个种群展开分析，量化遗传变异的程度与空间分布格局，旨在达成两个研究目标：其一，探明当代种群中是否仍留存有历史种群动态的信号；其二，评估不同繁殖策略对种群结构的影响。
种群间的遗传多样性与遗传分化模式存在显著差异，这反映出历史种群动态、微进化过程以及人为活动因子在该物种种群分布范围内的差异化影响。
在曾受冰川覆盖的河流中，遗传多样性随纬度升高呈逐步降低的趋势，这与冰后逐步拓殖及连续种群奠基事件的理论预期相符。
美国境内多次生殖种群间的遗传分化程度较低，这或许是人类活动介导的基因流所致；而一次性生殖种群间的弱分化，则大概率反映了自然基因流的作用。
繁殖策略对种群结构存在影响的相关证据，表明环境异质性发挥着重要作用，同时也提示，调控美洲西鲱生活史模式的相关因子，同样可能对种群遗传结构产生影响。