Boyle, H.J.*; Graham, J.B.: Acquisition of Characters Facilitating Amphibious Behavior in the Oxudercine Fishes

The evolutionary sequence of character acquisition associated with amphibious air breathing and terrestrial life was examined in the oxudercine fishes (Gobiidae). Included among the 10 genera (35 species) of oxudercines are forms with little to no specializations for amphibious life as well as the four genera (25 species) of the amphibious, air-breathing mudskipper clade. Five characters hypothesized to be associated with amphibious life (presence of a flattened eye lens, reduced gill surface area to mass ratio, increased buccal chamber volume to mass ratio, inability to repay an oxygen debt in water after exercise, and presence of an air phase inside the burrow) are expressed in one mudskipper species, Periophthalmodon schlosseri. Mapping of the character states of six genera (Oxuderces, Pseudapocryptes, Scartelaos, Boleophthalmus, Periophthalmus, and Periophthalmodon) onto a cladogram generated using morphological data indicates the following evolutionary sequence for the transition from an exclusively aquatic existence to amphibious life: deposition of air inside the burrow, increased buccal chamber volume to mass ratio, decreased gill surface area to mass ratio, loss of a round lens, and loss of the capacity to repay an oxygen debt in water after exercise. The hypothesized sequence of acquisition of morphological, behavioral, and physiological characters demonstrates the evolution of progressive specializations for an amphibious existence in the mudskipper clade. (supported by NSF-9604699)