Department of Earth and Environmental Sciences, Palaeontology and Geobiology, Ludwig-Maximilians-University Munich, Germany.
Zoology (Jena). 2011 Dec;114(6):321-34. doi: 10.1016/j.zool.2011.07.004. Epub 2011 Oct 14.
Our study was designed to evaluate if, and to what extent, restrictive environmental conditions affect otolith morphology. As a model, we chose two extremophile livebearing fishes: (i) Poecilia mexicana, a widespread species in various Mexican freshwater habitats, with locally adapted populations thriving in habitats characterized by the presence of one (or both) of the natural stressors hydrogen sulphide and darkness, and (ii) the closely related Poecilia sulphuraria living in a highly sulphidic habitat (Baños del Azufre). All three otolith types (lapilli, sagittae, and asterisci) of P. mexicana showed a decrease in size ranging from the non-sulphidic cave habitat (Cueva Luna Azufre), to non-sulphidic surface habitats, to the sulphidic cave (Cueva del Azufre), to sulphidic surface habitats (El Azufre), to P. sulphuraria. Although we found a distinct differentiation between ecotypes with respect to their otolith morphology, no clear-cut pattern of trait evolution along the two ecological gradients was discernible. Otoliths from extremophiles captured in the wild revealed only slight similarities to aberrant otoliths found in captive-bred fish. We therefore hypothesize that extremophile fishes have developed coping mechanisms enabling them to avoid aberrant otolith growth - an otherwise common phenomenon in fishes reared under stressful conditions.
我们的研究旨在评估限制环境条件是否以及在何种程度上影响耳石形态。我们选择了两种极端生境的胎生鱼类作为模型：（i）广泛分布于墨西哥各种淡水生境的墨西哥丽鱼（Poecilia mexicana），其具有局部适应性的种群在存在一种（或两种）自然胁迫物（硫化氢和黑暗）的生境中繁盛，以及（ii）生活在高度硫化环境中的亲缘种墨西哥丽鱼（Poecilia sulphuraria）。墨西哥丽鱼的所有三种耳石类型（小石砾、矢耳石和星耳石）的大小均减小，范围从无硫洞穴生境（Cueva Luna Azufre）到非硫化表面生境，再到硫化洞穴（Cueva del Azufre），再到硫化表面生境（El Azufre），再到墨西哥丽鱼。尽管我们发现不同生态型在耳石形态上存在明显的分化，但沿着两条生态梯度的特征进化没有明显的模式。从野外捕获的极端鱼类的耳石与在圈养条件下饲养的鱼类中发现的异常耳石仅存在轻微的相似之处。因此，我们假设极端鱼类已经发展出应对机制，使它们能够避免异常的耳石生长，这是在应激条件下饲养的鱼类中常见的现象。
