Clonality, interspecific hybridisation and inbreeding in a rare mallee eucalypt, Eucalyptus absita (Myrtaceae), and implications for conservation

Abstract

The degree of clonality, interspecific hybridisation and inbreeding in rare species will have significant implications for maintenance of genetic diversity and resilience to environmental change, with related implications for immediate conservation management. Using microsatellites, we detected extensive clonality within the rare mallee, Eucalyptus absita, from a highly disturbed agricultural habitat in southwestern Australia. A total of just 16 unique genets, plus five putative hybrids with E. loxophleba, were detected across the known species range and these genets were estimated to be of considerable age. Each location possessed a unique genotype and overall diversity was moderate (H E = 0.547). The outcrossing rate in seedling progeny was low (t m = 0.281), reflecting a rarity of intraspecific sires and minimal inbreeding depression prior to seed dispersal. Of all seedling progeny, up to 19 % were putative hybrids. Our findings indicate that despite rarity and clonality, moderate levels of genetic diversity and the capacity to produce outcrossed seeds is maintained. However, the ongoing maintenance of E. absita genetic diversity is significantly compromised by a high rate of selfing and potential hybridisation in seedling progeny. Seeds collected for long-term storage or rehabilitation should be screened for inbreeding and hybridisation rates to improve conservation outcomes. All existing adults represent a unique portion of the genepool for conservation.

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

“…Even very small populations of E. caesia that comprised just a few unique genets had surprisingly high levels of heterozygosity (relative to other larger populations). Relatively high levels of heterozygosity also characterize Eucalyptus absita, which has only 16 single unique genets (Bradbury, Grayling, MacDonald, Hankinson, & Byrne, ). Our results demonstrate that individual genet longevity reduces the rate at which heterozygosity is lost and consequently genetic variation may be conserved in very small populations or old individual plants.…”

Landscape and taxon age are associated with differing patterns of hybridization in twoEucalyptus(Myrtaceae) subgenera

“…Widespread clonality detected in the E. erectifolia complex also inflates the apparent frequency of hybridization in this group. Clonal propagation can allow individuals to survive for hundreds to thousands of years and can result in a census population size that is disproportional to the number of distinct genetic individuals (Bradbury et al, 2016). Our data demonstrated that the circular clumps formed by typical E. erectifolia, which was by far the most numerous hybrid combination sampled, were large clonal stands.…”

Genetic and environmental factors in the trade‐off between sexual and asexual reproduction of a rare clonal angiosperm

“…Somatic mutation is, however, difficult to detect (Bradbury et al ). An interesting study by Gross et al () demonstrated somatic mutations in ramet clusters of clonal Grevillea rhizomatosa while a study by van der Merwe et al () revealed a case of somatic mutation in a small population of long isolated clonal heterostylous shrubs.…”