Yamamoto Yoshiyuki, Espinasa Luis, Stock David W, Jeffery William R
Department of Biology, University of Maryland, College Park, MD 20742-4415, USA.
Evol Dev. 2003 Sep-Oct;5(5):435-46. doi: 10.1046/j.1525-142x.2003.03050.x.
We studied the development and evolution of craniofacial features in the teleost fish, Astyanax mexicanus. This species has an eyed surface dwelling form (surface fish) and many different cave dwelling forms (cavefish) with various degrees of reduced eyes and pigmentation. The craniofacial features we examined are the tooth-bearing maxillary bones, the nasal and antorbital bones, the circumorbital bones, and the opercular bones, all of which show evolutionary modifications in different cavefish populations. Manipulations of eye formation by transplantation of the embryonic lens, by lentectomy, or by removing the optic vesicle showed that eye-dependent and -independent processes change both the surface fish and cavefish craniofacial skeletons. The size of the olfactory pits, which the nasal and antorbital bones define, and the size and positioning of the circumorbital bones were found to correlate with eye development. For the six suborbital bones (SO1-6), the relationship with the developing eye appears to be due to ossification initiated from foci in the suborbital canal of cranial neuromasts, whose patterning is also highly correlated with the presence or absence of an eye. By contrast, we found that the number of maxillary teeth, the number of SO3 bone elements, the positioning of SO4-6 with respect to the opercular bone, and the shape of the opercular bone are not dependent on eye formation and vary among different cavefish populations. The results suggest that evolution of the cavefish craniofacial skeleton is controlled by multiple developmental events, some a direct consequence of eye degeneration and others unrelated to loss of the eye.
我们研究了辐鳍鱼墨西哥丽脂鲤颅面特征的发育与演化。该物种有眼睛外露的表层生活形态（表层鱼）以及许多不同的洞穴生活形态（穴居鱼），其眼睛和色素沉着程度不同程度地退化。我们研究的颅面特征包括含牙的上颌骨、鼻骨和眶前骨、眶周骨以及鳃盖骨，所有这些在不同穴居鱼种群中都显示出进化上的改变。通过移植胚胎晶状体、晶状体切除术或移除视泡来操纵眼睛形成，结果表明依赖眼睛和不依赖眼睛的过程都会改变表层鱼和穴居鱼的颅面骨骼。发现由鼻骨和眶前骨界定的嗅窝大小以及眶周骨的大小和位置与眼睛发育相关。对于六块眶下骨（SO1 - 6），其与发育中眼睛的关系似乎是由于颅神经丘眶下管内的骨化中心引发的骨化，其模式也与眼睛的有无高度相关。相比之下，我们发现上颌牙齿数量、SO3骨元件数量、SO4 - 6相对于鳃盖骨的位置以及鳃盖骨的形状不依赖于眼睛形成，并且在不同穴居鱼种群中有所不同。结果表明，穴居鱼颅面骨骼的演化受多种发育事件控制，其中一些是眼睛退化的直接后果，另一些与眼睛缺失无关。
