A morphological cline inEucalyptus: a genetic perspective

Abstract

The putative hybrid zone between Eucalyptus populnea and E. brownii is examined using morphological and molecular techniques. This species complex displays continuous morphological variation across the study area, which has been previously interpreted as the product of hybridization between allopatric species. A microsatellite analysis indicates that there was little genetic structuring across the morphological cline and only low levels of population differentiation. The nested clade analysis of the JLA+ region of the chloroplast DNA (cpDNA) indicates that the geographical distribution of cpDNA haplotypes is unlikely to be the result of historical hybridization events, and that restricted seed-mediated gene flow with isolation by distance is responsible for the phylogeographical distribution. A more plausible explanation for the origin and persistence of the morphological cline is that the process of continuous morphological diversification has been promoted by a directional selection gradient. This study addresses species status within Eucalyptus and the belief that hybridization is widespread and is an important process in the group's evolution.

Progress in Myrtaceae genetics and genomics: Eucalyptus as the pivotal genus

“…However, when co-occurring, such closely related species are often poorly differentiated, e.g. Corymbia (Ochieng et al 2010;Shepherd et al 2008a), Eucalyptus (Holman et al 2003;Jones et al 2002), although there are exceptions which argue for barriers to gene flow, e.g. Eucalyptus (McGowen et al 2001) and Melaleuca (Broadhurst et al 2004).…”

“…Evolution at lower taxonomic levels in Eucalyptus-species complexes A number of nuclear microsatellite studies are also revealing an absence of consistent differentiation between closely related, co-occurring species in Corymbia (Ochieng et al 2008(Ochieng et al , 2010Shepherd et al 2008a) and in Eucalyptus (Holman et al 2003;Hudson 2007;Le et al 2009). The spotted gums (genus Corymbia, section Politaria) show a species replacement series along the eastern seaboard of Australia, with distributions marked by regions of disjunction and sympatry.…”

Population genetic analysis and phylogeny reconstruction in Eucalyptus (Myrtaceae) using high-throughput, genome-wide genotyping

“…To further complicate matters, there is incomplete reproductive isolation of morphological species that can produce interspecific hybrids, morphological clines and hybrid swarms Johnson 1971, 1981;Griffin et al 1988), although clines can also be produced by primary differentiation (Holman et al 2003). As a result of these factors, reconstructing the phylogenetic history of Eucalyptus species has been problematic for systematists, even with the application of molecular techniques.…”

“…The development of microsatellite primers for eucalypt taxa (Brondani et al 1998(Brondani et al , 2006Byrne et al 1996;Glaubitz et al 2001;Jones et al 2001;Ottewell et al 2005;Shepherd et al 2006;Steane et al 2001;Thamarus et al 2002) opened the door for reliable genome-wide genotyping of a relatively large number of samples. Microsatellite markers gave researchers the power to examine genetic relationships within and among populations of one (e.g., Butcher et al 2009;Elliott and Byrne 2003;Jones et al 2007;Payn et al 2008;Rathbone et al 2007;Walker et al 2009; see also Byrne 2008 and references therein) or a few closely related species (e.g., Holman et al 2003, Le et al 2009, Shepherd et al 2008. While microsatellites were developed initially for mapping and population genetic studies, Ochieng et al (2007b) found them helpful for phylogenetic resolution of eucalypt genera.…”

Combining citizen science, bioclimatic envelope models and observed habitat preferences to determine the distribution of an inconspicuous, recently detected introduced bee (Halictus smaragdulus Vachal Hymenoptera: Halictidae) in Australia

“…This improvement may be due to less spatial autocorrelation when the number of training points is reduced, but it is also possible that it is due to better taxonomic identification. While there is no firm evidence that the different forms of H. smaragdulus have different environmental requirements, there is a strong chance of ecotypes given the species' broad environmental range and its widespread distribution in its native range (Dillon Jr. 1984;Hájková et al 2008;Holman et al 2003). Models that treat all individuals of a species as genetically and environmentally identical may be suboptimal if there are genotypes or ecotypes with different environmental niches (Boyden et al 2008;Hampe 2004;Lee 2002;Loehle 1998;Randin et al 2006;Wright et al 2006).…”