Laboratoire de Morphologie Fonctionnelle et Evolutive, Institut de Chimie (B6c), Université de Liège, Liège, Belgium.
Front Zool. 2012 Apr 25;9(1):8. doi: 10.1186/1742-9994-9-8.
Many coral reef fishes undergo habitat and diet shifts during ontogeny. However, studies focusing on the physiological and morphological adaptations that may prepare them for these transitions are relatively scarce. Here, we explored the body shape variation related to ontogenetic shifts in the ecology of the surgeonfish Acanthurus triostegus (Acanthuridae) from new settler to adult stages at Moorea Island (French Polynesia). Specifically, we tested the relationship between diet and habitat shifts and changes in overall body shape during the ontogeny of A. triostegus using a combination of geometric morphometric methods, stomach contents and stable isotope analysis.
After reef settlement, stable isotope composition of carbon and nitrogen revealed a change from a zooplanktivorous to a benthic algae diet. The large amount of algae (> 75% of stomach contents) found in the digestive tract of small juveniles (25-30 mm SL) suggested the diet shift is rapid. The post-settlement growth of A. triostegus is highly allometric. The allometric shape changes mainly concern cephalic and pectoral regions. The head becomes shorter and more ventrally oriented during growth. Morphological changes are directly related to the diet shift given that a small mouth ventrally oriented is particularly suited for grazing activities at the adult stage. The pectoral fin is more anteriorely and vertically positioned and its basis is larger in adults than in juveniles. This shape variation had implications for swimming performance, manoeuvrability, turning ability and is related to habitat shift. Acanthurus triostegus achieves its main transformation of body shape to an adult-like form at size of 35-40 mm SL.
Most of the shape changes occurred after the reef colonization but before the transition between juvenile habitat (fringing reef) and adult habitat (barrier reef). A large amount of allometric variation was observed after diet shift from zooplankton to benthic algae. Diet shift could act as an environmental factor favouring or inducing morphological changes. On the other hand, the main shape changes have to be achieved before the recruitment to adult populations and start negotiating the biophysical challenges of locomotion and feeding in wave- and current-swept outer reef habitat.
许多珊瑚礁鱼类在个体发育过程中经历生境和食性转变。然而，专门研究可能使它们为这些转变做好准备的生理和形态适应的研究相对较少。在这里，我们探索了莫雷阿岛（法属波利尼西亚）的刺尾鱼（Acanthurus triostegus）（刺尾鱼科）从新定居者到成年阶段的生态发生的与个体发育相关的体型变化。具体来说，我们使用几何形态测量方法、胃内容物和稳定同位素分析相结合，测试了饮食和生境转变与 A. triostegus 个体发育过程中整体体型变化之间的关系。
在珊瑚礁定居后，碳和氮的稳定同位素组成表明，从浮游动物食性转变为底栖藻类食性。在小幼鱼（25-30 毫米 SL）的消化道中发现大量藻类（> 75%的胃内容物），表明这种饮食转变是迅速的。刺尾鱼的定居后生长是高度异速生长的。异速生长的形状变化主要涉及头部和胸鳍区域。在生长过程中，头部变得更短，更朝向腹侧。形态变化与饮食转变直接相关，因为朝向腹侧的小嘴特别适合在成年阶段进行放牧活动。胸鳍更向前和垂直定位，其基部在成鱼中比在幼鱼中大。这种形状变化对游泳性能、机动性、转弯能力有影响，并与生境转变有关。Acanthurus triostegus 在大小为 35-40 毫米 SL 时达到类似成年的主要体型转变。
大多数形状变化发生在珊瑚礁定殖之后，但在幼鱼生境（边缘礁）和成年生境（堡礁）之间的过渡之前。从浮游动物转变为底栖藻类后，观察到大量的异速生长变化。饮食转变可能是一种促进或诱导形态变化的环境因素。另一方面，主要的形状变化必须在成年种群的补充之前完成，并开始应对在波浪和海流冲刷的外礁生境中运动和进食的生物物理挑战。
