A Distinctive Chromosomal Race of the Cyprinodontid Fish, Fundulus notatus, from the Upper Tombigbee River System of Alabama and Mississippi

Abstract

Fundulus notatus and F. olivaceus are sibling species which have diploid chromosome numbers of 40 and 48 respectively. However, populations of F. notatus analyzed from the Upper Tombigbee River system of Alabama and Mississippi exhibit a strikingly different karyotype. The Tombigbee population of F. notatus has a modal diploid count of 44, which is intermediate between F. olivaceus and other populations of F. notatus analyzed. Phenotypically and ecologically, the Tombigbee population is essentially identical to other populations of F. notatus. Therefore, the Tombigbee population of F. notatus is considered to represent a variant or chromosomal race of F. notatus. The karyotype of the Tombigbee race could have originated either independently, or through natural hybridization, or by a mechanism involving Robertsonian rearrangements of chromosomes. THE blackstripe topminnow, Fundulus notatus (Rafinesque), and the blackspotted topminnow, F. olivaceus (Storer), are sibling species belonging to the Cyprinodontidae. F. notatus and F. olivaceus are readily distinguished from other members of the genus Fundulus by the presence of a broad black lateral stripe which originates at the tip of the snout and terminates at the caudal fin. F. notatus may be distinguished from F. olivaceus on the basis of dorsolateral spotting. F. notatus has vague indistinct spots while F. olivaceus has distinct spots of at least the same intensity as