Conservation of old individual trees and small populations is integral to maintain species' genetic diversity of a historically fragmented woody perennial

Abstract

Historically fragmented and specialized habitats such as granite outcrops are understudied globally unique hot spots of plant evolution. In contrast to predictions based on mainstream population genetic theory, some granite outcrop plants appear to have persisted as very small populations despite prolonged geographic and genetic isolation. Eucalyptus caesia Benth. is a long‐lived lignotuberous tree endemic with a naturally fragmented distribution on granite outcrops in south‐western Australia. To quantify population to landscape‐level genetic structure, we employed microsatellite genotyping at 14 loci of all plants in 18 stands of E. caesia. Sampled stands were characterized by low levels of genetic diversity, small absolute population sizes, localized clonality and strong fine‐scale genetic subdivision. There was no significant relationship between population size and levels of heterozygosity. At the landscape scale, high levels of population genetic differentiation were most pronounced among representatives of the two subspecies in E. caesia as originally circumscribed. Past genetic interconnection was evident between some geographic neighbours separated by up to 20 km. Paradoxically, other pairs of neighbouring stands as little as 7 km apart were genetically distinct. There was no consistent pattern of isolation by distance across the 280 km range of E. caesia. Low levels of gene flow, together with strong drift within stands, provide some explanation of the patterns of genetic differentiation we observed. Individual genet longevity via the ability to repeatedly resprout and expand from a lignotuber may enhance the persistence of some woody perennial endemic plants despite small population size, minimal genetic interconnection and low heterozygosity.

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

“…Surprisingly, in this study, neither Ho (P = 0.953) nor He (P = 0.166) was significantly related to the population size (Figure 1). This outcome has been found in some special cases [59,60]. However, because the population size in this study has remained relatively uniform, this result might require further The results of the correlation between geographic distance and genetic distance (Mantel test; Figure 8) show no significant correlation between the genetic distance and geographic distance of the M. shiluensis population at the cpDNA level (R = 0.01, p = 0.96), regardless of whether YC is removed (R = 0.63, p = 0.13).…”

“…Surprisingly, in this study, neither Ho (p = 0.953) nor He (p = 0.166) was significantly related to the population size (Figure 1). This outcome has been found in some special cases [59,60]. However, because the population size in this study has remained relatively uniform, this result might require further consideration.…”

Primary pollinator exclusion has divergent consequences for pollen dispersal and mating in different populations of a bird‐pollinated tree

“…In comparison, Chiddarcooping covers an area of 5,400 hectares and is surrounded by relatively large tracts of native vegetation (see maps in Figure ). These two populations are among the largest known of E. caesia and have been comprehensively mapped and genotyped (Bezemer, Krauss, Roberts, & Hopper, ). Most populations of E. caesia are characterized by strong genetic substructuring, with genetic differentiation of subpopulations over a few hundred metres (Bezemer et al, ).…”

“…These two populations are among the largest known of E. caesia and have been comprehensively mapped and genotyped (Bezemer, Krauss, Roberts, & Hopper, ). Most populations of E. caesia are characterized by strong genetic substructuring, with genetic differentiation of subpopulations over a few hundred metres (Bezemer et al, ). High levels of differentiation are also evident across the species' landscape distribution on isolated granite rocks over ca.…”

“…High levels of differentiation are also evident across the species' landscape distribution on isolated granite rocks over ca. 300 km (Bezemer et al, ; Byrne & Hopper, ).…”