Morphological Differentiation of Etheostoma olmstedi and E. nigrum (Pisces: Percidae) in Canada

Abstract

Doubts about the validity of the species status of Canadian populations of tessellated darter, Etheostoma olmstedi (Storer) and the johnny darter, E. nigrum (Rafinesque), led to the present examination of 24 meristic and morphometric characters on 767 fishes from 97 locations dispersed over the whole Canadian range of the species complex. Results obtained from a principal components analysis combined with a character index analysis showed that 48.7% of our sample were E. olmstedi and 47.4% were E. nigrum. Of the 30 (3.9%) unidentified fishes, 21 were classified (P < 0.05) within the defined taxa when submitted to a discriminant functions analysis (DFA). In addition, 97.1% of the newly classified fishes were considered correctly identified when submitted to DFA. The major discriminating features for the Canadian populations were an index of scalation of the cheek and nape, the number of dorsal-fin rays and the number of preoperculomandibular and infraorbital pores. Exceptions for the scalation indices in eastern and central Quebec were examined in detail. Clear morphological differences and evidence for a discrete gene pool in an area of sympatry are in accordance with the recognition of the species status in Canada. E. olmstedi is distributed from eastern Quebec to the Lake Ontario region. It is sympatric with E. nigrum over its whole Canadian range. E. nigrum extends its range to eastern Saskatchewan. Finally, because we acknowledge the need to recognize subspecies with unique evolutionary histories, we do not consider it useful to follow the subspecific categorizations suggested by previous taxonomists for the Canadian