Pfennig David W, Martin Ryan A
Department of Biology, CB#3280, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Evolution. 2009 Apr;63(4):898-909. doi: 10.1111/j.1558-5646.2008.00544.x. Epub 2008 Oct 10.
Despite long-standing interest in character displacement, little is known of its underlying proximate causes. Here, we explore the role of maternal effects in character displacement. We specifically investigated whether differences in maternal body condition mediate divergence in the expression of resource-use traits between populations of spadefoot toads (Spea multiplicata) that occur in sympatry with a heterospecific competitor and those that occur in allopatry. In sympatry, S. multiplicata is forced by its competitor onto a less profitable resource. As a result, sympatric females mature in poorer condition and invest less into offspring. Consequently, their offspring produce a resource-use phenotype that minimizes competition with the other species and that also differs from the phenotype produced in allopatry. These differences in trait expression between allopatry and sympatry disappear once mothers are equilibrated in body condition in the laboratory. Thus, a condition-dependent maternal effect mediates population divergence and character displacement. Such effects potentially buffer populations from extinction (via competitive exclusion) while genetic changes accumulate, which produce divergent traits in the absence of the maternal effect. Maternal effects may therefore often be important in determining the initial direction and rate of evolution during the early stages of character displacement.
尽管长期以来人们对特征取代很感兴趣，但对其潜在的近因却知之甚少。在这里，我们探讨母体效应在特征取代中的作用。我们特别研究了母体身体状况的差异是否介导了与异种竞争者同域分布的北美锄足蟾（Spea multiplicata）种群和异域分布的北美锄足蟾种群之间资源利用性状表达的差异。在同域分布中，北美锄足蟾被其竞争者迫使转向一种获利较少的资源。结果，同域分布的雌性个体在较差的身体状况下成熟，对后代的投入也较少。因此，它们的后代产生一种资源利用表型，这种表型将与其他物种的竞争降至最低，并且也不同于异域分布中产生的表型。一旦在实验室中使母体的身体状况达到平衡，异域分布和同域分布之间的这些性状表达差异就会消失。因此，一种依赖于身体状况的母体效应介导了种群分化和特征取代。在遗传变化积累的过程中，这种效应可能会缓冲种群免于灭绝（通过竞争排斥），而在没有母体效应的情况下，遗传变化会产生不同的性状。因此，母体效应在决定特征取代早期阶段进化的初始方向和速度方面可能常常很重要。
