Population size, center–periphery, and seed dispersers’ effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon

Abstract

The effect of population size on population genetic diversity and structure has rarely been studied jointly with other factors such as the position of a population within the species’ distribution range or the presence of mutualistic partners influencing dispersal. Understanding these determining factors for genetic variation is critical for conservation of relict plants that are generally suffering from genetic deterioration. Working with 16 populations of the vulnerable relict shrub Cneorum tricoccon throughout the majority of its western Mediterranean distribution range, and using nine polymorphic microsatellite markers, we examined the effects of periphery (peripheral vs. central), population size (large vs. small), and seed disperser (introduced carnivores vs. endemic lizards) on the genetic diversity and population structure of the species. Contrasting genetic variation (H E: 0.04–0.476) was found across populations. Peripheral populations showed lower genetic diversity, but this was dependent on population size. Large peripheral populations showed high levels of genetic diversity, whereas small central populations were less diverse. Significant isolation by distance was detected, indicating that the effect of long‐distance gene flow is limited relative to that of genetic drift, probably due to high selfing rates (FIS = 0.155–0.887), restricted pollen flow, and ineffective seed dispersal. Bayesian clustering also supported the strong population differentiation and highly fragmented structure. Contrary to expectations, the type of disperser showed no significant effect on either population genetic diversity or structure. Our results challenge the idea of an effect of periphery per se that can be mainly explained by population size, drawing attention to the need of integrative approaches considering different determinants of genetic variation. Furthermore, the very low genetic diversity observed in several small populations and the strong among‐population differentiation highlight the conservation value of large populations throughout the species’ range, particularly in light of climate change and direct human threats.

High Genetic Diversity and Low Differentiation in Michelia shiluensis, an Endangered Magnolia Species in South China

“…It is worth noting that the He found in this study is significantly higher than that found in some narrowranging species (He = 0.420) and in some widely distributed species (He = 0.620) [55]. Studies have shown that genetic diversity is positively correlated with population size [56][57][58]. Surprisingly, in this study, neither Ho (P = 0.953) nor He (P = 0.166) was significantly related to the population size (Figure 1).…”

Conflicting selection onCneorum tricoccon(Rutaceae) seed size caused by native and alien seed dispersers

“…; Lázaro‐Nogal et al. ). It produces fleshy fruits consisting of three or (more rarely) four cocci (locules of a syncarpous ovary; Fig.…”

“…The species is considered a relict of the Mediterranean flora that evolved during the early Tertiary (Traveset et al 2012 and references therein). It inhabits southeastern Spain, southeastern France, and western Italy (Sardinia, Giannutri and Tuscany), with the main populations in the Balearic Islands (Traveset et al 2012;Lázaro-Nogal et al 2017). It produces fleshy fruits consisting of three or (more rarely) four cocci (locules of a syncarpous ovary; Fig.…”

Four climate change scenarios for Gypsophila bermejoi G. López (Caryophyllaceae) to address whether bioclimatic and soil suitability will overlap in the future

“…Nevertheless, there is evidence of the effects of connectivity on the fitness of gypsophile species, showing the importance of including habitat connectivity in management and conservation strategies for G . bermejoi , and other species and communities associated with specialist soils [75] .…”