Indiana University, Department of Biology, Bloomington, Indiana 47405 USA.
Am J Bot. 2002 Mar;89(3):472-8. doi: 10.3732/ajb.89.3.472.
The diploid hybrid species Helianthus paradoxus is restricted to salt marshes with sodium concentrations that exceed those found in the habitats of its progenitors, H. annuus and H. petiolaris. The observed association with saline habitats has led to the hypothesis that H. paradoxus is more salt tolerant than its progenitors. This hypothesis was tested by growing all three species in three NaCl treatments (0 mmol/L, 100 mmol/L, and 200 mmol/L). Helianthus paradoxus treated with NaCl was found to be more than five times as fit, in terms of biomass and survivorship, than its progenitors. Selection for salt tolerance in early generation hybrids may have contributed to the formation of H. paradoxus because theory predicts that homoploid hybrid speciation is feasible even when selection favoring hybrid genotypes is much weaker. Additionally, we show that H. paradoxus is significantly different from its parental species for several traits that often distinguish salt-tolerant species and suggest a mechanistic basis for the elevated salt tolerance expressed by H. paradoxus.
二倍体杂种向日葵 Helianthus paradoxus 仅限于盐沼，其盐度超过了其祖先向日葵 H. annuus 和向日葵 H. petiolaris 的栖息地盐度。与盐生栖息地的观察到的关联导致了 H. paradoxus 比其祖先更能耐受盐度的假设。通过在三种 NaCl 处理（0 mmol/L、100 mmol/L 和 200 mmol/L）中生长这三个物种来检验这一假设。结果发现，与盐处理的向日葵相比，H. paradoxus 在生物量和存活率方面的适应能力高出五倍以上。早期杂交种的耐盐性选择可能促成了 H. paradoxus 的形成，因为理论预测，即使有利于杂种基因型的选择弱得多，同倍体杂种物种形成也是可行的。此外，我们还表明，H. paradoxus 在几个特征上与亲本物种有显著差异，这些特征通常可以区分耐盐物种，并为 H. paradoxus 表达的高耐盐性提供了机制基础。
