Department of Integrative Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, CA 94720, USA.
J Exp Biol. 2020 Mar 19;223(Pt 6):jeb217570. doi: 10.1242/jeb.217570.
The origins of novel trophic specialization, in which organisms begin to exploit resources for the first time, may be explained by shifts in behavior such as foraging preferences or feeding kinematics. One way to investigate behavioral mechanisms underlying ecological novelty is by comparing prey capture kinematics among species. We investigated the contribution of kinematics to the origins of a novel ecological niche for scale-eating within a microendemic adaptive radiation of pupfishes on San Salvador Island, Bahamas. We compared prey capture kinematics across three species of pupfish while they consumed shrimp and scales in the lab, and found that scale-eating pupfish exhibited peak gape sizes twice as large as in other species, but also attacked prey with a more obtuse angle between their lower jaw and suspensorium. We then investigated how this variation in feeding kinematics could explain scale-biting performance by measuring bite size (surface area removed) from standardized gelatin cubes. We found that a combination of larger peak gape and more obtuse lower jaw and suspensorium angles resulted in approximately 40% more surface area removed per strike, indicating that scale-eaters may reside on a performance optimum for scale biting. To test whether feeding performance could contribute to reproductive isolation between species, we also measured F1 hybrids and found that their kinematics and performance more closely resembled generalists, suggesting that F1 hybrids may have low fitness in the scale-eating niche. Ultimately, our results suggest that the evolution of strike kinematics in this radiation is an adaptation to the novel niche of scale eating.
新的营养特化的起源，即生物首次开始利用资源，可能可以用行为变化来解释，例如觅食偏好或摄食运动学。一种研究生态新颖性背后的行为机制的方法是比较不同物种的猎物捕获运动学。我们通过比较巴哈马圣萨尔瓦多岛上的一个微地方性适应辐射中的三种小鱼在实验室中捕食虾和鳞片时的运动学，来研究摄食鳞片这一新型生态位的起源。我们发现，摄食鳞片的小鱼的最大张口尺寸是其他物种的两倍，但下颚和悬器之间的夹角也更钝。然后，我们通过测量从标准化明胶立方体上咬下的咬痕面积（去除的表面积）来研究这种摄食运动学的变化如何解释咬鳞的性能。我们发现，较大的最大张口尺寸和更钝的下颚和悬器角度的组合导致每次咬痕的表面积去除增加了约 40%，表明食鳞鱼可能处于最适合咬鳞的性能最佳状态。为了测试摄食性能是否有助于物种间的生殖隔离，我们还测量了 F1 杂种的运动学和性能，发现它们的运动学和性能更接近广食性物种，这表明 F1 杂种在食鳞生态位中的适应度可能较低。最终，我们的结果表明，这一辐射中的攻击运动学的进化是对摄食鳞片这一新型生态位的适应。
