Ontogeny of the Darter Subgenus Doration with Comments on Intrasubgeneric Relationships

Abstract

The darter subgenus Doration has been considered a monophyletic group within the Boleosoma complex. Previous workers combined Etheostoma stigmaeum, the speckled darter, and Etheostomajessiae, the blueside darter, and recognized a single species with several subspecies. Recognition of E. stigmaeum and E. jessiae as distinct species is warranted based on early life-history characters. Etheostoma stigmaeum can be distinguished from E. jessiae by postanal melanophore pattern, precocious ontogenetic development, position of melanophores, and length at which fin elements develop. Etheostoma stigmaeum possesses radiating melanophores at every postanal myoseptum, whereas E. jessiae has several distinct melanophores at the future anal-fin insertion; E. stigmaeum develops fin elements at smaller sizes than E. jessiae. Early lifehistory attributes of Doration are egg-burying, possession of a single, midventral vitelline vein, elevated (18) preanal myomere counts, and absence of pigmentation from the dorsal and lateral body. Larval and early-juvenile apomorphies of Doration include the following: possession of small egg diameters (1.3-1.7 mm); pointed snout; oval-spherical eye shape; small head length/TL; moderate predorsal length/ TL; small pectoral-fin length/TL; narrow shoulder depth/TL; narrow midpostanal depth/TL; laterally compressed, rectangular yolksac; precocious notochord flexion; five predorsal myomeres; 18 presoft dorsal myomeres; 10 preoperculomandibular pores; and presence of midlateral pigmentation.