Bucknell University, Lewisburg, PA 17837, USA.
J Exp Biol. 2011 Dec 15;214(Pt 24):4083-91. doi: 10.1242/jeb.060574.
Evolutionary transitions between aquatic and terrestrial environments are common in vertebrate evolution. These transitions require major changes in most physiological functions, including feeding. Emydid turtles are ancestrally aquatic, with most species naturally feeding only in water, but some terrestrial species can modulate their feeding behavior appropriately for both media. In addition, many aquatic species can be induced to feed terrestrially. A comparison of feeding in both aquatic and terrestrial environments presents an excellent opportunity to investigate the evolution of terrestrial feeding from aquatic feeding, as well as a system within which to develop methods for studying major evolutionary transitions between environments. Individuals from eight species of emydid turtles (six aquatic, two terrestrial) were filmed while feeding underwater and on land. Bite kinematics were analyzed to determine whether aquatic turtles modulated their feeding behavior in a consistent and appropriate manner between environments. Aquatic turtles showed consistent changes between environments, taking longer bites and using more extensive motions of the jaw and hyoid when feeding on land. However, these motions differ from those shown by species that naturally feed in both environments and mostly do not seem to be appropriate for terrestrial feeding. For example, more extensive motions of the hyoid are only effective during underwater suction feeding. Emydids evolving to feed on land probably would have needed to evolve or learn to overcome many, but not all, aspects of the intrinsic emydid response to terrestrial feeding. Studies that investigate major evolutionary transitions must determine what responses to the new environment are shown by naïve individuals in order to fully understand the evolutionary patterns and processes associated with these transitions.
水生到陆生环境的进化转变在脊椎动物进化中很常见。这些转变需要大多数生理功能发生重大变化，包括摄食。淡水龟科龟类祖先为水生，多数物种自然只在水中摄食，但一些陆生物种可以适当调整其摄食行为以适应两种介质。此外，许多水生物种可以被诱导在陆地上摄食。在水生和陆生环境中进行摄食比较，为从水生摄食到陆生摄食的进化研究以及研究环境间主要进化转变的方法提供了极好的机会。从 8 种淡水龟科龟类（6 种水生，2 种陆生）个体中拍摄水下和陆地摄食的视频。分析咬合力运动学，以确定水生龟类在环境之间是否以一致和适当的方式调整其摄食行为。水生龟类在环境之间表现出一致的变化，在陆地摄食时，咬的时间更长，颌骨和舌骨的运动范围更广。然而，这些运动与那些自然在两种环境中摄食的物种所表现出的运动不同，而且似乎不太适合陆地摄食。例如，舌骨的更广泛运动仅在水下吸吮摄食期间有效。适应在陆地上摄食的 Emydids 可能需要进化或学习克服许多（但不是全部）与陆生摄食相关的 Emydid 内在反应方面。研究主要进化转变的研究必须确定幼稚个体对新环境表现出哪些反应，以便充分了解与这些转变相关的进化模式和过程。
