Is Lotus zhegulensis Klok. (Fabaceae) a separate species endemic of the Middle Volga Region or just a variety of a widespread L. corniculatus L.?

Abstract

We have studied several samples from Lotus corniculatus s. l. and L. zhegulensis populations with the use of SSR and sequenced nuclear (ITS) and plastid (atpB-rbcL, ndhC-trnV, rpl32-trnL(UAG), trnH-psbA, trnL-trnF) markers. We analysed 9 local populations from the Volga River valley ranging from Ulyanovsk in the north to Volgograd in the south, as well as two local populations from Moscow and Lipetsk Provinces. Analyses of SSR markers using the STRUCRURE program divided the sample into three genetic clusters. Populations from Moscow and Lipetsk Provinces, and three local populations from the ‘locus classicus’ location of L. zhegulensis in Samara Province appeared to be the most genetically differentiated while all the other populations were variously genetically admixed. Low pairwise Fst values indicate low genetic differentiation of Lotus populations and the intraspecific nature of the revealed diversity. The nuclear and plastid DNA sequences analyzed yielded little information. Substitutions and indels revealed were mostly autapomorphies characteristic of separate specimens or small groups of specimens but not of populations. Our study enables to firmly conclude that Lotus populations from the right bank of the Volga River in vicinity of Zhiguli upland described as L. zhegulensis are weakly genetically differentiated from other populations of Lotus corniculatus s. l. and, hence, cannot be regarded as a separate species.