Selkoe Kimberly A, Gaines Steven D, Caselle Jennifer E, Warner Robert R
Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California 93106, USA.
Ecology. 2006 Dec;87(12):3082-94. doi: 10.1890/0012-9658(2006)87[3082:csakae]2.0.co;2.
The scales of population structure in marine species depend on the degree to which larvae from different populations are mixed in the plankton. There is an intriguing trend in marine population genetic studies of significant genetic structure for larvae, recruits, or populations at fine scales that is unpatterned across space and changes through time. This "chaotic genetic patchiness" suggests that larval pools are not well mixed in the plankton. However, few studies have been able to distinguish among potential causes of spatial and temporal genetic heterogeneity: changes in larval migration patterns, changes in environmental selection, or stochasticity caused by "sweepstakes" reproductive success of spawners creating detectable family structure. Here we use microsatellite markers to show that significant allele frequency shifts occurred sporadically in space and time for cohorts of recruits of Paralabrax clathratus (kelp bass) collected once every two weeks over two years from five sites in the Santa Barbara Channel, California, USA. We found that the pattern of genetic differentiation among cohorts was explained by a combination of (1) family structure in some cohorts, evidenced by half and full siblings, and (2) an indication of changes in larval delivery. It is unlikely but possible that environmental selection also plays a role. Although sampling of potential source populations was incomplete, cohorts arriving during western current flows show most genetic similarity with a population sample collected in the west, and cohorts arriving during current flows from the southeast show similarity with population samples collected in the south and east. Despite the family structure apparent in some cohorts, these "sweepstakes" events occur on too fine a scale to create lasting year class genetic structure. The results corroborate oceanographic models of larval dispersal, which suggest that larval mixing in the plankton is less extensive than previously believed.
海洋物种的种群结构规模取决于不同种群的幼体在浮游生物中混合的程度。在海洋种群遗传学研究中，存在一种有趣的趋势：在精细尺度上，幼体、新补充个体或种群具有显著的遗传结构，这种结构在空间上无规律可循且随时间变化。这种“混沌遗传斑块性”表明幼体库在浮游生物中并未充分混合。然而，很少有研究能够区分空间和时间遗传异质性的潜在原因：幼体洄游模式的变化、环境选择的变化，或者由产卵者“抽奖式”繁殖成功导致的随机性，进而产生可检测的家族结构。在这里，我们使用微卫星标记表明，对于两年间每两周从美国加利福尼亚州圣巴巴拉海峡的五个地点采集一次的多锯鲈（条纹鲈）新补充个体群体，等位基因频率在空间和时间上偶尔会发生显著变化。我们发现，群体间的遗传分化模式可以由以下因素共同解释：（1）部分群体中的家族结构，表现为半同胞和全同胞；（2）幼体输送变化的迹象。环境选择虽不太可能但也有可能发挥作用。尽管潜在源种群的采样并不完整，但在西向水流期间到达的群体与在西部采集的种群样本遗传相似性最高，而在东南向水流期间到达的群体与在南部和东部采集的种群样本相似。尽管在一些群体中明显存在家族结构，但这些“抽奖式”事件发生的尺度过于精细，无法形成持久的同一年出生群体的遗传结构。这些结果证实了幼体扩散的海洋学模型，该模型表明浮游生物中的幼体混合程度不如先前认为的那么广泛。
