Influence of the Quaternary Glacial Cycles and the Mountains on the Reticulations in the Subsection Willkommia of the Genus Centaurea

Abstract

Late Neogene and Quaternary climatic oscillations have greatly shaped the genetic structure of the Mediterranean Basin flora, with mountain plant species tracking warm interglacials/cold glacials by means of altitudinal shifts instead of broad latitudinal ones. Such dynamics may have enhanced population divergence but also secondary contacts. In this paper, we use a case example of subsection Willkommia of Centaurea (comprising three narrowly distributed endemic species, Centaurea gadorensis , C. pulvinata , and C. sagredoi ) to test for reticulate evolution and recurrent hybridizations between nearby populations. For this, we combine analyses of genetic diversity and structuring, gene flow and spatial correlation, and ecological niche modeling. Our results support the contention that the current genetic structure of the three species is the result of historical gene flow at sites of secondary contact during the glacial periods, followed by isolation after the retraction of populations to the middle-upper areas of the mountains during the interglacial periods. The extent and direction of the gene flow was determined largely by the location of the populations on mountainsides oriented toward the same valley or toward different valleys, suggesting the intermountain valleys as the areas where secondary contacts occurred.

Molecular insights on the conflicting generic boundaries in the Carduncellus‐Carthamus complex (Compositae)

“…The extensive discordance between plastid and nuclear phylogenetic trees found in the core Carduncellus (Fig. 3B) is compatible with a recurrent pattern of secondary contact induced by the repeat glacial and interglacial cycles of the Pleistocene, which could promote hybridization or introgression between taxa (Thompson, 2005); this pattern is documented in genera close to the complex, such as Centaurea (Garcia‐Jacas & al., 2009; Ben‐Menni Schuler & al., 2019).…”

Localized environmental heterogeneity drives the population differentiation of two endangered and endemic Opisthopappus Shih species

“…Single or simple environmental variations could typically initiate the adaptive divergence between populations, followed by the expansion of accumulating genetic differentiation [ 5 , 50 , 56 ]. The significantly distinct distribution conditions and patterns of the two climate variables in the Taihang Mountains, corresponding to O. longilobus and O. taihangensis , might be regarded as original primordial indicators with driving forces toward causing and promoting the genetic differentiation and diversification of the two species.…”

“…Understanding the processes that drive differentiation between populations and elucidating the mechanisms that underlie the origins and maintenance of genetic variations are major aims and fundamental tasks in evolutionary biology [ 1 – 5 ], which are also core issues in conservation biology [ 6 , 7 ]. Myriad factors may impact the evolution and genetic differentiation of plant populations, where geological events and climate oscillations have been suggested as critical drivers [ 8 – 10 ].…”

“…During this process, intensifying climate change has left an indelible imprint on the composition and divergence of populations or species [ 15 , 16 ], which further greatly influenced the distribution patterns and shaped the genetic structures of populations [ 5 , 17 ]. In general, the geographic processes of mountainous regions may influence the genetic makeup of plant populations over large spatial scales, whereas ecological processes from climate change may impact the genetic structures of plant populations at small spatial scales [ 5 , 18 – 20 ].…”