Gibb Alice C, Liu Corina, Swanson Brook O
Department of Biology, Northern Arizona University, Flagstaff, Arizona 86011-5640, USA.
J Exp Zool A Ecol Genet Physiol. 2007 Oct 1;307(10):556-67. doi: 10.1002/jez.409.
Teleost fishes produce coordinated escape responses (C-starts) at hatching. This implies that essential swimming morphologies and motor behaviors develop during the incubation interval while the embryo is in the chorion. We examined prehatching motor behaviors in rainbow trout Oncorhycus mykiss (considered morphologically mature at hatching) and compared this species with zebrafish Danio rerio (considered morphologically immature) and assessed two hypotheses concerning the development of escape behavior. (1) Escape behavior is associated with the formation of key elements of the musculoskeletal and nervous systems; thus, the escape response appears early in ontogeny, when these elements form. (2) Escape behavior is not directly associated with the formation of underlying morphological elements; instead, it appears at hatching (i.e. when needed). We find that rainbow trout, like zebrafish, respond to touch early in the incubation interval, but do not demonstrate a complete C-start (including the second, propulsive stage) until shortly before hatching. At hatching, rainbow trout and zebrafish are similar in the degree of development of the chondocranium, paired fins and visceral arches (which comprise the larval jaw and gill support); however, rainbow trout have incipient rays in their unpaired fins (dorsal, anal and caudal), whereas zebrafish retain the embryonic fin fold. Although rainbow trout are more mature in axial swimming morphology at hatching, the essential neural and musculoskeletal systems that produce a coordinated escape response are functional at hatching in both species. This finding supports the evolutionary hypothesis that an effective escape response is critical for the survival of newly hatched teleost fishes.
硬骨鱼在孵化时会产生协调的逃避反应（C型启动）。这意味着在胚胎处于卵膜内的孵化期时，基本的游泳形态和运动行为就已经发育形成。我们研究了虹鳟（Oncorhycus mykiss，在孵化时被认为形态成熟）孵化前的运动行为，并将该物种与斑马鱼（Danio rerio，被认为形态未成熟）进行比较，同时评估了两个关于逃避行为发育的假说。（1）逃避行为与肌肉骨骼系统和神经系统关键要素的形成有关；因此，逃避反应在个体发育早期，即这些要素形成时就会出现。（2）逃避行为与潜在形态要素的形成没有直接关联；相反，它在孵化时（即需要时）出现。我们发现，虹鳟和斑马鱼一样，在孵化期早期对触摸有反应，但直到孵化前不久才表现出完整的C型启动（包括第二个推进阶段）。在孵化时，虹鳟和斑马鱼在软骨颅、成对鳍和内脏弓（构成幼体颌骨和鳃支撑结构）的发育程度上相似；然而，虹鳟的不成对鳍（背鳍、臀鳍和尾鳍）有雏形鳍条，而斑马鱼保留着胚胎鳍褶。尽管虹鳟在孵化时轴向游泳形态更成熟，但在这两个物种中，产生协调逃避反应的基本神经和肌肉骨骼系统在孵化时都是有功能的。这一发现支持了进化假说，即有效的逃避反应对新孵化的硬骨鱼的生存至关重要。
