Cave-dwellers: A morphological comparison of allopatric populations of cave-dwelling Gammarus minus

This study examined the external and supraesophageal morphologies of four independently evolved cave-dwelling populations of G. minus from Luddington's (LUC), Organ (ORC), The Hole (THC), and Fallen Rock (FRC) Caves. Since these cave-dwellers display convergent evolution in their external morphological features, the main objective of this study was to determine whether there is a convergence or divergence in the brain (supraesophageal ganglion) morphology of allopatric populations of cave-dwelling G. minus. The heads of G. minus were fixed in a paraformaldehyde-glutaraldehyde mixture, dehydrated in an alcohol series, infiltrated, and embedded in Epon. The tissue was then sectioned and stained with toluidine blue and eosin. External and supraesophageal structures were determined to be similar in the LUC, ORC, and THC populations. The fourth cave population examined from FRC had external and supraesophageal optic structures that were different from the other cave populations, but similar to those of spring animals collected from Burn's #2 (B2S) and Dickson (DKS) springs. This suggests that the FRC population's evolutionary status is between the cave and spring populations.