Leuciscus (Pisces, Cyprinidae) karyotypes: Transect of Portuguese populations

Abstract

The presently described Iberian chubs - Leuciscus carolitertii and L. pyrenaicus - sampled throughout their distribution ranges in Portugal were cytogenetically analyzed. Their chromosome numbers were consistently 2n = 50, except for two specimens of L. carolitertii, which exhibited a supernumerary chromosome in some of the metaphases. The karyotypes were found to be highly typical for other Leuciscus taxa, as well as for European leuciscine cyprinids: the chromosome sets are dominated by metacentric and submetacentric elements with a reduced number of acrocentric pairs (three to four); the largest pair of the complements belongs typically to this latter category. The chubs from northern drainages, assignable to L. carolitertii, have apparently a more stable karyotype structure (12M:30S:8A) than the chubs from L. pyrenaicus, which have 12M:32S:6A, but may exhibit in the most southern river basins (Guadiana, Mira, Aljezur, Bordeira and Arade) more variable karyotypes. Besides, these data support the very recent discovery of two genetically distinct Leuciscus taxa in this region of the Iberian Peninsula, suggesting the stochastic fixation of structural chromosome rearrangements in these small and isolated drainages, which may be affected by bottlenecks due to significant variations in hydrological regimes. The NORs were apparently located in one small submetacentric pair of chromosomes and the presence of a heteromorphic sex chromosome system of the ZW/ZZ type was also evidenced for the Iberian endemic chubs.