A study published today in the open access journal BMC Biology reveals that the Oklahoma salamander Eurycea tynerensis metamorphoses into a more terrestrial adult form in streambeds composed of fine, tightly packed gravel but retains its juvenile, or paedomorphic, form in streambeds made of large, loosely packed particles. This study highlights how a simple difference in habitat microstructure can have a major influence on patterns of development, morphology and evolution.
Ronald Bonett and Paul Chippindale from the University of Texas at Arlington, Texas, USA, analysed the type, size and degree of sorting of streambed sediments for 22 populations, 11 paedomorphic and 11 metamorphic, of the plethodontid salamander E. tynerensis living on the Ozark Plateau in south-central North America.
Bonett and Chippindale's results show that paedomorphic salamanders prevailed in streambeds made of large well-sorted gravel, whereas metamorphic salamanders were found where streambeds consisted of small, unsorted sediments. The authors found a strong negative correlation between small streambed sediments and paedomorphosis.
Bonett and Chippindale explain that large gravel creates porous streambeds with large spaces between particles, where aquatic paedomorphic salamanders can access sub-surface water during dry months. However, if these spaces are filled in by small particles, metamorphosis is the only way they can survive when surface streams dry-up.