Meeting Abstract
The paedomorphic Eurycea salamander clade of Central Texas exemplifies a continuum of morphological characteristics associated with aquatic-subterranean living: the surface-dwelling Texas salamander (E. neotenes) exhibits typical optic anatomy and acuity; the intermediate Comal blind salamander (E. tridentifera) maintains reduced but non-functional eyes; and the obligate subterranean Texas blind salamander (E. rathbuni) has an incompletely developed optic system. Together this genus represents a transformation series of karst phenotypes and a potentially exemplar system for using comparative approaches to understanding vertebrate ocular evolution in the face of relaxed selective pressures. More than a century ago Eigenman described ocular histology in E. rathbuni adults as a focal troglodyte; yet, neither the extent of optic-nerve persistence in this taxon nor among its congeners has since been documented. In this study we employed gross and micro-scale imaging techniques to elucidate features of Eurycea optic anatomy with a particular interest in the central nervous system. Specimens from aforementioned taxa were fixed with 100% EtOH, contrast-enhanced with alcoholic iodine (I2E), micro-CT scanned, and digital reconstructed using 3D rendering software for comparison to histological sections. Here we report on the 3D, internal soft-tissue systems of the eye in each taxon, documenting habitat-specific configurations of optic musculature and neuroanatomy for the first time—including for E. rathbuni, which surprisingly appears to retain complete bilateral optic nerves even though it lacks the mid-line decussations associated with an optic chiasm.
