Abstract
Unraveling the relationships between ecological, functional traits and genetic diversity of narrow endemic plants provide opportunities for understanding how evolutionary processes operate over local spatial scales and ultimately how diversity is created and maintained. To explore these aspects in Sierra Nevada, the core of the Mediterranean Betic‐Rifean hotspot, we have analyzed nuclear DNA microsatellite diversity and a set of biological and environmental factors (physicochemical soil parameters, floral traits, and community composition) in two strictly endemic taxa from dolomite outcrops of Sierra Nevada (Helianthemum pannosum and H. apenninum subsp. estevei) and two congeneric widespread taxa (H. cinereum subsp. rotundifolium and H. apenninum subsp. apenninum) that further belong to two different lineages (subgenera) of Helianthemum. We obtained rather unexpected results contrasting with the theory: (a) The narrow endemic taxa showed higher values of genetic diversity as well as higher average values of pollen production per flower and pollen‐to‐ovule ratio than their widespread relatives; and (b) the two taxa of subg. Helianthemum, with larger corollas, approach herkogamy and higher pollen production than the two taxa of subg. Plectolobum, displayed lower genetic diversity and higher values of inbreeding. Altogether, these results disclose how genetic diversity may be affected simultaneously by a large number of intrinsic and extrinsic factors, especially in Pleistocene glacial refugia in mountains where the spatial context harbors a great ecological heterogeneity. On the other hand, differences in mating system and the significant effect of the substrate profile, both being highly diverse in the genus Helianthemum, in the genetic variability illustrate about the importance of these two factors in the diversification and species differentiation of this paradigmatic genus in the Mediterranean and open the field to formulate and test new hypotheses of local adaptation, trait evolution, and habitat diversification.
Highlights
It is well known that biological diversity is concentrated in particular regions around the world, so-called biodiversity hotspots
TA B L E 3 Mean values (± SE) of petal length, number of stamens, number of ovules, number of pollen grains per flower, pollen-to-ovule ratio (P/O), tallest stamen height, stigma height, and stigma-anther separation measured for the study taxa of Helianthemum: H. apenninumsubsp. apenninum (Ha), H. apenninumsubsp. estevei (He), H. cinereumsubsp. rotundifolium (Hc), and H. pannosum (Hp)
| 3025 mating system rather than geographic distribution is driving the differences in genetic variability between the two pairs of relatives in this study and the existence of a significant effect of the substrate profile in the genetic variability of the dolomite specialist H. apenninum subsp. estevei may be further indicating the important role of these factors on the diversification and species differentiation in Helianthemum, showing that proneness to endemism in the genus is associated with ecological specialization, given the apparent distinct distribution and habitat types of many endemics (López-González, 1992)
Summary
It is well known that biological diversity is concentrated in particular regions around the world, so-called biodiversity hotspots. Its woody flora has been subjected to an evolutionary account of biodiversity using barcoding techniques and the construction of megaphylogenies, and it has been possible to determine the effects of elevation and substrate mosaicism on the phylogenetic structure of its species assemblages (Molina-Venegas, Aparicio, Lavergne, & Arroyo, 2015; Simón-Porcar et al, 2018) Whereas these studies have allowed detecting the prevailing evolutionary patterns, further insight requires scaling down to particular lineages diversified in the region, and even to species and population level of taxa subjected to systematic discussion, to disentangle how diversity in this hotspot is created and maintained, and the drivers involved. Beyond deriving possible implications for the implementation of conservation action plans for the two stenochorous taxa in the Sierra Nevada National Park involved in this study, the assessment of the microevolutionary forces that drive the species divergence and differentiation in Helianthemum in a context of recent radiation can further shed light on why many species in this genus are prone to endemism
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