Genetic Variation in Cave-dwelling and Deep-sea Organisms, 
with Emphasis on Crangonyx antennatus (Crustacea: 
Amphipoda) in Virginia. 
Gary W. Dickson 1 and John C. Patton 
Department of £ oology , 
University of Georgia, Athens, Georgia 30602 
John R. Holsinger 
Department of Biological Sciences, 
Old Dominion University, Norfolk, Virginia 23508 
AND 
John C. Avise 
Department of £ oology , 
University of Georgia, Athens, Georgia 30602 
ABSTRACT . — Genetic variation was analyzed through electrophoretic 
techniques in six populations of the troglobitic (i.e. obligatory cave- 
dwelling) amphipod Crangonyx antennatus from Lee County, Virginia. 
From the results of this investigation and those tabulated from previous 
studies on a number of cave-dwelling species, genetic variability does 
not appear to be substantially reduced in populations inhabiting sub- 
terranean environments. The origin of normal levels of genetic 
variability in cave-dwelling species may differ from those organisms in- 
habiting another relatively stable environment, the deep-sea. The high 
levels of genetic variability recorded in many deep-sea invertebrates are 
thought to be due in part to the presence of large populations of these 
species. In contrast, the small population sizes observed in cave-dwelling 
organisms may allow species to expand their niches with an associated 
increase in genetic variability. 
INTRODUCTION 
Similarities in the physical environments of caves and the deep-sea 
have led to the suggestion that similar selection pressures may be 
operating on their respective faunas (Poulson 1971). Caves and the deep- 
sea share several important characteristics including absence of light, 
reduced food supply, and relative stability of chemical and physical 
properties. Similar biological adaptations have been observed in 
organisms inhabiting abyssal (Menzies et al. 1973) and subterranean 
Present address: Savannah River Ecology Laboratory, Drawer E, Aiken, S.C. 
29801. 
Brimleyana No. 2: 119-130. November 1979 
119 
