Pappers Stephanie M, van der Velde Gerard, Ouborg N Joop, van Groenendael Jan M
Department of Aquatic Ecology and Environmental Biology, University of Nijmegen, The Netherlands.
Evolution. 2002 Aug;56(8):1610-21. doi: 10.1111/j.0014-3820.2002.tb01473.x.
A host race is a population that is partially reproductively isolated from other conspecific populations as a direct consequence of adaptation to a specific host. The initial step in host race formation is the establishment of genetically based polymorphisms in, for example, morphology, preference, or performance. In this study we investigated whether polymorphisms observed in Galerucella nymphaeae have a genetic component. Galerucella nymphaeae, the water lily leaf beetle, is a herbivore which feeds and oviposits on the plant hosts Nuphar lutea and Nymphaea alba (both Nymphaeaceae) and Rumex hydrolapathum and Polygonum amphibium (both Polygonaceae). A full reciprocal crossing scheme (16 crosses, each replicated 10 times) and subsequent transplantation of 1,001 egg clutches revealed a genetic basis for differences in body length and mandibular width. The heritability value of these traits, based on midparent-offspring regression, ranged between 0.53 and 0.83 for the different diets. Offspring from Nymphaeaceae parents were on average 12% larger and had on average 18% larger mandibles than offspring from Polygonaceae parents. Furthermore, highly significant correlations were found between feeding preference of the offspring and the feeding preference of their parents. Finally, two fitness components were measured: development time and survival. Development time was influenced by diet, survival both by cross type and diet, the latter of which suggest adaptation of the beetles. This suggestion is strengthened by a highly significant cross x diet interaction effect for development time as well as for survival, which is generally believed to indicate local adaptation. Although no absolute genetic incompatibility among putative host races was observed, survival of the between-host family offspring, on each diet separately, was lower than the survival of the within-host family offspring on that particular host. Survival of offspring of two Nymphaeaceae parents was about two times higher on Nymphaeaceae than on Polygonaceae, whereas survival of offspring of two Polygonaceae parents was 11 times higher on Polygonaceae than on Nymphaeaceae (based on untransformed data). Based on these results, we conclude that genetically determined polymorphisms in morphology and feeding preference exist in G. nymphaeae, resulting in differential performance. Furthermore, in each diet separately, offspring of between-host family crosses were less fit than offspring of within-host family crosses. These results support the hypothesis that within this species two host races can be distinguished.
寄主族是指由于对特定寄主的适应而与其他同种群体部分生殖隔离的种群。寄主族形成的初始步骤是在例如形态、偏好或表现等方面建立基于遗传的多态性。在本研究中，我们调查了睡莲萤叶甲（Galerucella nymphaeae）中观察到的多态性是否具有遗传成分。睡莲萤叶甲是一种食草动物，以植物寄主黄睡莲（Nuphar lutea）和白睡莲（Nymphaea alba，均为睡莲科）以及酸模叶蓼（Rumex hydrolapathum）和两栖蓼（Polygonum amphibium，均为蓼科）为食并在其上产卵。一个完整的正反交实验设计（16个杂交组合，每个组合重复10次）以及随后对1001个卵块的移植揭示了体长和下颚宽度差异的遗传基础。基于中亲-子代回归，这些性状在不同食源下的遗传力值在0.53至0.83之间。睡莲科亲本的后代平均比蓼科亲本的后代大12%，下颚平均大18%。此外，还发现后代的取食偏好与其亲本的取食偏好之间存在高度显著的相关性。最后，测量了两个适合度成分：发育时间和存活率。发育时间受食源影响，存活率受杂交类型和食源影响，后者表明甲虫存在适应性。发育时间和存活率均存在高度显著的杂交×食源交互效应，这通常被认为表明存在局部适应性，这进一步强化了上述适应性的推测。尽管在假定的寄主族之间未观察到绝对的遗传不相容性，但在每种食源下，寄主间杂交组合后代的存活率均低于特定寄主上寄主内杂交组合后代的存活率。两个睡莲科亲本的后代在睡莲科寄主上的存活率比在蓼科寄主上高约两倍，而两个蓼科亲本的后代在蓼科寄主上的存活率比在睡莲科寄主上高11倍（基于未转换的数据）。基于这些结果，我们得出结论，睡莲萤叶甲在形态和取食偏好上存在由遗传决定的多态性，导致了不同的表现。此外，在每种食源下，寄主间杂交组合的后代比寄主内杂交组合的后代适合度更低。这些结果支持了在该物种内可以区分出两个寄主族的假说。
