Increased inbreeding and inter-species gene flow in remnant populations of the rare Eucalyptus benthamii

Abstract

Eucalyptus benthamiiMaiden & Cambage is a forest tree of interest for conservation and plantation forestry. It is vulnerable to extinction, occurring on the alluvial floodplains of the Nepean River and its tributaries, south-west of Sydney, Australia. These floodplains were largely cleared of native vegetation for agriculture by the mid-1800s. Flooding of the Cox Valley for Sydney's water supply further decreased the species distribution. The species is now confined to one population of approximately 6500 trees in the Kedumba valley and three remnant populations on the Nepean River at Bents Basin (about 300 trees), Wallacia (nine trees) and Camden (about 30 trees). Genetic analysis of the four populations using microsatellite markers revealed significant divergence among all populations, despite the Bents Basin, Wallacia and Camden remnants being separated by distances of only a few kilometres. Trees in these populations have been estimated to range from 35 to 200 years old, suggesting genetic divergence among populations occurred prior to land clearing. To investigate the impact of fragmentation on the next generation, outcrossing rates were estimated from 41 families. While no direct relationship was found between population size and outcrossing rates, fragmentation and the isolation of trees appears to have resulted in higher levels of selfing and biparental inbreeding in seed collected from the Camden and Wallacia remnants. There was also evidence from seedling morphology that inter-species gene flow increased with fragmentation since 20% of the progeny from Camden and 30% of the progeny from Wallacia were hybrids. Seed viability and germination rates were significantly lower in the remnant populations, reducing their value as seed sources for regeneration and plantation forestry. To maintain the genetic integrity of the remnant populations, germplasm should be sourced from the local area. Outcrossed, nonhybrid seed could be produced by controlled pollination in ex-situ conservation stands or by using seedling morphology and microsatellites to screen seedlings from the remnant populations.

EFEITO DO HIDROGEL NO CRESCIMENTO DE MUDAS DE Eucalyptus benthamii SUBMETIDAS A DIFERENTES FREQUÊNCIAS DE IRRIGAÇÃO

“…(HIGA;PEREIRA, 2003). Essa espécie é considerada vulnerável ao desaparecimento na região de ocorrência natural, correspondente ao curso do Rio Nepean, a oeste de Sydney, Austrália (BUTCHER et al, 2005).…”

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

“…However, the absence of such a relationship is common in eucalypts (reviewed by Butcher et al 2005), and this was the case for E. cordata. Allelic richness is a highly sensitive genetic diversity parameter and is influenced by the loss of rare alleles following bottlenecks in population size (Maruyama and Fuerst 1985).…”

Altered Soil Properties Inhibit Fruit Set but Increase Progeny Performance for a Foundation Tree in a Highly Fragmented Landscape

“…Mating system studies have shown that increased within-plant foraging and reduced local mate availability appears to affect pollen quality in fragmented populations of many eucalypts and other Myrtaceae, resulting in reduced seed set (Krauss et al, 2007;Yates et al, 2007b;Gauli et al, 2014), while late-acting selfincompatibility mechanisms may have prevented outcrossing rates from being significantly affected by fragmentation in many species (Ottewell et al, 2009;Gauli et al, 2014;Breed et al, 2015), but not all (Butcher et al, 2005;Mimura et al, 2009;Breed et al, 2015). Despite changes in pollen quality, the level of pollination and pollinator abundance was unchanged in Calothamnus quadrifidus (Yates et al, 2007a), while honeybees have increased (González-Varo et al, 2009) or decreased (Hingston et al, 2004) pollination rates in some species of Myrtaceae.…”