Quantitative and molecular genetic variation in sympatric populations ofMedicago laciniataandM. truncatula(Fabaceae): relationships with eco-geographical factors

Abstract

SummaryMedicago laciniatais restricted to south of the Mediterranean basin and it extends in Tunisia from the inferior semi-arid to Saharan stages, whereasM. truncatulais a widespread species in such areas. The genetic variability in four Tunisian sympatric populations ofM. laciniataandM. truncatulawas analysed using 19 quantitative traits and 20 microsatellites. We investigated the amplification transferability of 52 microsatellites developed inM. truncatulatoM. laciniata. Results indicate that about 78·85% of used markers are valuable genetic markers forM. laciniata.M. laciniatadisplayed significantly lower quantitative differentiation among populations (QST=0·12) than didM. truncatula(QST=0·45). However, high molecular differentiations, with no significant difference, were observed inM. laciniata(FST=0·48) andM. truncatula(FST=0·47). Several quantitative traits exhibited significantly smallerQSTthanFSTforM. laciniata, consistent with constraining selection. ForM. truncatula, the majority of traits displayed no statistical difference in the level ofQSTandFST. Furthermore, these traits are significantly associated with eco-geographical factors, consistent with selection for local adaptation rather than genetic drift. In both species, there was no significant correlation between genetic variation at quantitative traits and molecular markers. The site-of-origin explains about 5·85% and 11·27% of total quantitative genetic variability among populations ofM. laciniataandM. truncatula, respectively. Established correlations between quantitative traits and eco-geographical factors were generally more moderate forM. laciniatathan forM. truncatula, suggesting that the two species exhibit different genetic bases of local adaptation to varying environmental conditions. Nevertheless, no consistent patterns of associations were found between gene diversity (He) and environmental factors in either species.