Determination of Clone Size and Age in a Mallee Eucalypt Using RAPDs

Abstract

Fragmentation of lignotubers and the consequent problems in genotype identification make demographic studies of mallee eucalypts unreliable. DNA fingerprinting using Random Amplification of Polymorphic DNA (RAPD) markers was employed to determine if a hybrid copse between Eucalyptus risdonii and E. amygdalina was clonal. Based on lignotuber morphology this copse appeared to be composed of approximately 20 separate individuals. No variation in RAPD genotype was observed for 67 bands scored from nine primers among the 20 individuals. In contrast, variation was observed between individuals sampled from outside the copse (average 28.6 band differences between any two individuals) and within full sibling families (average 12.9 band differences between individuals). On this basis the copse was considered to be clonal (one genet), originating from lignotuber fragmentation, and measured 5.5 × 3.5 m. The rate of radial expansion in 15-year-old seedling and lignotuber cohorts was measured and used to estimate the age of the hybrid copse. The hybrid genet appeared to be at least 900 years old. While such estimates must be viewed with caution they strongly support the suggestion that mallee eucalypts may attain ages far in excess of single-stemmed eucalypts.

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

“…However, it is possible that these figures are an overestimate if clonality is also achieved by epicormic resprouting from fallen stems, which we have observed in some E. absita individuals. Further, all estimates must be viewed with caution as lignotuber growth can be variable according to species, environment and genotype, and growth rates can change during the life of individuals (Tyson et al 1998). Nonetheless, the mallee clumps of E. absita, including the clonal hybrid clumps, can be considered to be of great age and a long-standing feature of the landscape.…”

“…The large size of some mallee clumps suggests that individual genets of E. absita are of great age. Based on radial growth rate of the lignotuber, which has been estimated at 1.5-3.4 mm per year by Tyson et al (1998), and up to 5 mm per year by Head and Lacey (1988), the approximate age of the largest E. absita genet (L5) with 17 m approximate radius (based on mean clump length and width) is 3000-11,000 years. This estimate is comparable to, and among the highest of, those made for the mallees E. bennettiae (590-1700 years) (Walker et al 2009), E. argutifolia (2000 years) (Kennington and James 1997a), E. phylacis (6380 years) (Rossetto et al 1999) and E. curtisii (4000-9000 years) (Smith et al 2003), suggesting that this genet of E. absita may be among the oldest mallee eucalypt ''Family'' refers to genets at the locations described in Table 1 Standard errors in parentheses a This family represents the only family from the three available from the L2 clump that did not possess any mismatched progeny and therefore segregated as expected and outcrossed seedlings based on allele counts; with outcrossing distinguished into known, detectable E. absita outcrosses (black bars) and putative hybrid outcrosses (hashed bars).…”

“…Population size and potential level of genetic diversity may be overestimated, leading to underestimation of perceived threats to persistence and priority for ongoing conservation action (Tyson et al 1998;Millar et al 2010). Further, the genetic diversity of seed collections made for long-term storage or rehabilitation will be dramatically reduced if seeds are unknowingly collected from multiple ramets (individuals with identical genotypes) rather than those with distinct genotypes from different genets.…”

Unravelling the evolutionary history of Eucalyptus cordata (Myrtaceae) using molecular markers

“…Many of the E. cordata populations (particularly of subspecies cordata) similarly comprise individuals that have regenerated vegetatively from large basal lignotubers (Potts 1989). Applying the rate of radial growth of lignotubers reported by Tyson et al (1998) to the isolated clonal stems detected at Chimney Pot Hill (3), which were separated by 3.6 m, suggests that a single genotype can be at least 529-857 years old. This evidence argues that individuals within many populations of E. cordata could be very long lived, and represent genotypes remaining from previously larger populations that were not affected by small population processes.…”

“…Eucalypts can have long generational times because of regeneration from underground lignotubers, which can fragment with time and result in disconnected, clonal patches (Tyson et al 1998;Byrne 2008). In the case of E. morrisbyi, Jones et al (2005) estimated that clonal patches in the Risdon Hill (22) population were at least 670-1523 years old.…”