Advances in Biology & Earth Sciences

Environmental gradients, especially climatic factors, significantly impact plant distribution and may also affect population genetic diversity and differentiation. Variations in water supply can lead to inter-population discrepancies in ecological processes, hence disrupting connection and resulting in environmental isolation of populations. This study investigates the impact of environmental variability on Oloptum populations and the analysis accounted for variations in geographic location and climate. We employed AFLP markers to examine genetic diversity and differentiation among 10 populations of Oloptum miliaceum from three phytogeographical zones (Mediterranean, Irano-Turanian and Saharo-Arabian), including the species' geographic distribution in Jordan. Flowering phenology has shown variability among populations and areas. The Irano-Turanian and Saharo-Arabian groups exhibited greater genetic diversity than Mediterranean populations and genetic diversity significantly increased with rising temperatures and decreasing precipitation. The Mantel, partial Mantel and distance-based redundancy analyses showed a significant correlation between genetic distances and environmental distances but not with geographic distance, which is consistent with isolation by environment rather than isolation by distance. Marked genetic differentiation was observed, alongside three robustly supported phytogeographical population groups: the first group comprised Mediterranean populations, the second encompassed Irano-Turanian populations and the third included Saharo-Arabian populations, as indicated by PCoA and cluster analysis. Our data suggest that populations from humid and arid regions are ecologically isolated, with environmental gradients influencing their blooming phenology, restricting gene flow and determining their genetic structure. We infer that environmental heterogeneity, particularly moisture availability, temperature and flowering time, may serve as a principal determinant of the observed variation in genetic diversity.