Päckert Martin, Martens Jochen, Tietze Dieter Thomas, Dietzen Christian, Wink Michael, Kvist Laura
Staatliche Naturhistorische Sammlungen, Museum für Tierkunde, Dresden, Sachsen, Germany.
Mol Phylogenet Evol. 2007 Jul;44(1):1-14. doi: 10.1016/j.ympev.2007.03.006. Epub 2007 Mar 19.
The ongoing debate on the reliability of avian molecular clocks is actually based on only a small number of calibrations carried out under different assumptions with respect to the choice and constraints of calibration points or to the use of substitution models. In this study, we provide substitution rate estimates for two mitochondrial genes, cytochrome b and the control region, and age estimates for lineage splits within four subgenera of tits (Paridae: Parus, Cyanistes, Poecile and Periparus). Overall sequence divergence between cytochrome b lineages covers a range of 0.4-1.8% per million years and is thus consistent with the frequently adopted approximation for a sequence divergence between avian lineages of 1.6-2% per my. Overall rate variation is high and encompasses the 2% value in a 95% CI for model corrected data. Mean rate estimates for cytochrome b range between 1.9 and 8.9 x 10(-3) substitutions per site per lineage. Local rates differ significantly between taxonomic levels with lowest estimates for haplotype lineages. At the population/subspecies level mean sequence divergence between lineages matches the 2% rule best for most cytochrome b datasets (1.5-1.9% per my) with maximum estimates for small isolated populations like those of the Canarian P. teneriffae complex (up to 3.9% per my). Overall rate estimates for the control region range at similar values like those for cytochrome b (2.7-8.8 x 10(-3), 0.5-1.8% per my), however, within some subgenera mean rates are higher than those for cytochrome b for uncorrected sequence data. The lowest rates for both genes were calculated for coal tits of subgenus Periparus (0.04-0.6% per my). Model-corrected sequence data tend to result in higher rate estimates than uncorrected data. Increase of the gamma shape parameter goes along with a significant decrease of rate and partly age estimates, too. Divergence times for earliest deep splits within tit subgenera Periparus and Parus were dated to the mid Miocene at 10-14my bp. Most recent splits between east and west Palearctic taxa of blue, willow and great tits were dated to the Pliocene/Pleistocene boundary with the earliest estimates based on model-corrected trees. Relaxation of the Messinian calibration point leads to more recent divergence times for North African coal and blue tit populations during the mid Pliocene. Despite a relatively broad age constraint for the split between Nearctic and Palearctic Poecile due to the Pliocene re-opening of the Bering Strait, the split between chickadees and willow tits is dated considerably earlier than in former studies to the upper bound of the age constraint at 7.4 my BP.
关于鸟类分子钟可靠性的持续争论实际上仅基于在不同假设下进行的少量校准，这些假设涉及校准点的选择和限制或替代模型的使用。在本研究中，我们提供了两个线粒体基因（细胞色素b和控制区）的替代率估计值，以及雀形目（山雀科：山雀属、蓝山雀属、丛山雀属和长尾山雀属）四个亚属内谱系分化的时间估计值。细胞色素b谱系之间的总体序列差异范围为每百万年0.4 - 1.8%，因此与鸟类谱系之间每百万年1.6 - 2%的序列差异这一常用近似值一致。总体速率变化很大，在模型校正数据的95%置信区间内包含2%的值。细胞色素b的平均速率估计值在每个位点每个谱系1.9×10⁻³至8.9×10⁻³个替代之间。分类水平之间的局部速率差异显著，单倍型谱系的估计值最低。在种群/亚种水平上，大多数细胞色素b数据集的谱系之间平均序列差异最符合2%规则（每百万年1.5 - 1.9%），对于加那利群岛的特内里费岛山雀复合体等小的隔离种群，最大估计值可达每百万年3.9%。控制区的总体速率估计值与细胞色素b的类似（2.7×10⁻³至8.8×10⁻³，每百万年0.5 - 1.8%），然而，对于未校正的序列数据，在一些亚属中平均速率高于细胞色素b。两个基因中最低的速率是针对长尾山雀属的煤山雀计算的（每百万年0.04 - 0.6%）。模型校正的序列数据往往比未校正的数据产生更高的速率估计值。伽马形状参数的增加也伴随着速率以及部分时间估计值显著下降至。长尾山雀属和山雀属内最早的深度分化时间可追溯到中新世中期，为10 - 14百万年前。蓝山雀、柳山雀和大山雀的东、西古北区分类群之间最近的分化时间可追溯到上新世/更新世边界，最早的估计基于模型校正树。梅西尼校准点的放宽导致北非煤山雀和蓝山雀种群在中新世中期的分化时间更近于。尽管由于上新世白令海峡重新开放，近北极和古北区丛山雀之间的分化存在相对较宽的时间限制，但北美山雀和柳山雀之间的分化时间比以前的研究提前到时间限制的上限，即740万年前。
