Latitudinal gradients in rates of evolution

人们对热带和温带地区的进化速度有何不同知之甚少。一个关键理论将亚马逊和其他热带地区的高度多样性与加速的进化速度联系起来（Rohde 1992，Mittelbach et al. 2007）。或者，进化速度可能不是在多样性最高的地方（热带地区）进行得最快，而是在历史上气候变化最频繁、最强烈的地方（高纬度地区）（Weir & Schluter 2004，2007）。气候变化可能迫使物种适应新的条件，从而加速进化的过程。 区分这些替代预测需要估计不同纬度的进化速率。我之前发表的工作使用间接方法来估计跨纬度梯度新物种形成的速率（Weir & Schluter 2004，2007），并表明物种形成速度最快的不是热带地区，而是两极（图 1 和图 2）。然而，需要直接测量对物种形成重要的性状的进化。鸟类利用发声、羽毛颜色和体形来识别同类成员并吸引配偶。这些特征的进化差异被认为对新物种的形成有重要贡献（Seddon 2005；Edwards et al. 2005；Price 2007）。在这里，我建议量化从亚马逊到新大陆加拿大北极的纬度梯度上的进化分化率，以确定诸如鸣叫、羽毛颜色和形状等特征是否在多样性最高的地方（热带地区）或历史上气候变化最严重的地方（高纬度地区）进化得最快。这些研究将辅之以对加拿大和亚马逊地区杂交区基因渗入的详细分析，以确定交配后生殖隔离在热带或温带地区是否累积最快。

Little is known about how rates of evolution vary between tropical and temperate regions. A key theory links the high diversity of the Amazon and other tropical regions with an accelerated rate of evolution (Rohde 1992, Mittelbach et al. 2007). Alternatively, evolution may proceed fastest not where diversity is highest - the tropics - but where historical episodes of climate change have been most frequent and intense - at high latitudes (Weir & Schluter 2004, 2007). Climate change may force species to adapt to new conditions, thereby accelerating the process of evolution. Distinguishing between these alternative predictions requires estimating the rate of evolution at different latitudes. My previous published work used indirect methods to estimate the rate at which new species form across a latitudinal gradient (Weir & Schluter 2004, 2007) and suggested that species form fastest not in the tropics but towards the poles (Figures 1 and 2). However, direct measurements of evolution in traits important for species formation are required. Vocalizations, plumage colouration and body shape are used by birds to recognize members of their own species and to attract mates. Evolutionary divergence in such traits are believed to contribute importantly to the formation of new species (Seddon 2005; Edwards et al. 2005, Price 2007). Here I propose to quantify rates of evolutionary divergence across a latitudinal gradient stretching from the Amazon to the Canadian arctic in the New World to determine if traits like song, plumage colouration, and shape are evolving fastest where diversity is highest (the tropics) or where historical episodes of climate change have been most severe (high latitudes). These studies will be complemented with detailed analysis of genetic introgression at hybrid zones in Canada and the Amazon to determine if post-mating reproductive isolation accumulated fastest in tropical or temperate regions.