Geographical variation of some taxonomically important characters in fishes: the case of the bitterling Rhodeus sericeus

Abstract

Geographical variation of three meristic characters, the number of pored scales in lateral line (LL), the number of branchial spines on the first gill arch (SPBR) and the number of transverse scale rows (SQU), were studied in the cyprinid fish Rhodeus sericeus and their validity for subspecific discrimination was tested. Counts investigated were taken from population samples at 23 localities covering an area of about 68° geographical longitude (2°40 W -49°30 E and 128°00 E -143°00 E), and about 15° geographical latitude (37°30 N -52°00 N). All three characters manifested a distinct clinal variation. LL, SQU and SPBR closely followed the species’ essentially longitudinal distribution. The number of segments was also related to latitude, elevation, mean annual air temperature and fish size. Bergmann’s rule was fully demonstrated for fishes and at the species level. Local regional differences were found within particular regions, indicating the existence of subclines. Variation of truly isolated populations seems to be predictable and dependent on the clines found in adjacent populations. None of the counts investigated, including a key character (number of pored scales in LL), can be used to distinguish amarus from sericeus. Owing to sufficient evidence that meristic and morphometric characters used to distinguish fish subspecies succumb to the clinal variation controlled by various factors, the concept of subspecies and trinomial nomenclature is inefficient, superfluous and misleading, and should be excluded from taxonomy, nomenclature and ecology.