Multiple reversals of bill length over 1.7 million years in a Hawaiian bird lineage

Evolutionary change has been documented over geological time, but reversals in morphology, from an ancestral state to a derived state and back again, tend to be rare. Multiple reversals along the same lineage are even rarer. We use the chronology of the Hawaiian Islands and an avian example, the Hawaiian honeycreeper ‘amakihi (Hemignathus spp.) lineage, which originated on the oldest main island of Kaua‘i 1.7 million years ago, to examine the process of sequential reversals in bill length. We document three single and two multiple reversals of bill length on six main islands from oldest to youngest, consistent with the phylogeny of the lineage. Longer bills occur on islands with endemic species, including phylogenetically relevant outgroups, that may compete with or dominate the ‘amakihi. On islands without those species, the ‘amakihi had shorter bills of similar length. Both types of reversals in morphology in this lineage integrate microevolutionary processes with macroevolution in th...

地质时间尺度上的演化改变已有诸多实证记录，但形态逆向演化——即从祖先性状状态转变为衍生性状状态后再度逆转——通常较为罕见。同一演化支系（lineage）内的多次逆向演化则更为罕见。本研究依托夏威夷群岛（Hawaiian Islands）的地质年代序列，以鸟类类群——起源于170万年前最古老主岛考艾岛（Kaua‘i）的夏威夷旋蜜雀（Hawaiian honeycreeper）amakihi支系（镰嘴雀属*Hemignathus* spp.）——为研究对象，探究喙长（bill length）的连续逆向演化过程。研究在从老到新的六个主岛上，共记录到三次单次喙长逆向演化与两次多次喙长逆向演化，结果与该支系的系统发育（phylogeny）关系一致。在存在可能与amakihi形成竞争或占据优势地位的特有物种（endemic species，含系统发育相关外类群（outgroup））的岛屿上，amakihi的喙更长；而在无此类物种的岛屿上，amakihi的喙则更短且长度较为均一。该支系的两类形态逆向演化，均将微演化（microevolution）过程与宏演化（macroevolution）过程相整合，相关研究将在