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Banksia seedlings showing different phenotypes with B. robur on the left, B. oblongifolia on the right and intermediate forms in the middle.
Source publication
In perennial plants (especially post-fire resprouters), extant populations may reflect recruitment events in the distant past. This is true of hybrid zones formed by two Banksia species of swamps and woodlands in south-eastern Australia, Banksia robur and B. oblongifolia. Both resprout after fire but recruitment is dependent on periodic fires. Alth...
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We characterised the historical fire regime (1900-2010) in eastern coastal fynbos shrublands, which occur in a poorly studied part of the Cape Floral Kingdom (CFK). Natural (lightning-ignited) fires dominated the fire regime. Fire seasonality decreased from west (Outeniqua region) to east (Tsitsikamma region) within the study area, and between the...
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Citations
... It is assumed that there are firm prezygotic factors in the hairpin banksias due to a lack of observed hybrids between sympatric species, such as at the Vincentia site where B. spinulosa grows near B. vincentia (Stimpson et al., 2016). However, this process might not be visible at the Vincentia site since in some research on Banksia it has only been detected using molecular techniques (Carthew et al., 1988;Henderson, 1991;Maguire et al., 1997;Myerscough et al., 2001;Usher et al., 2010). Finally, despite there being a large ex situ collection from seed and cuttings already established, without an understanding of genetic diversity, the maximum potential of this asset remains unharnessed with regards to the maintenance or improvement of species fitness (Ralls et al., 2020), or building and positioning genetically healthy reserve populations. ...
Premise:
Understanding evolutionary history and classifying discrete units of organisms remains an overwhelming task, and lags in this discipline concomitantly impede an accurate documentation of biodiversity and conservation management. Rapid advances and improved accessibility of sensitive high throughput sequencing tools are fortunately quickening the resolution of morphological complexes that generally are underestimating species diversity. This seems to be the case of the persisting taxonomic quandary of the Hairpin Banksias (B. spinulosa sens. lat.), a group of eastern Australian flowering shrubs demonstrating a continuum of morphological diversity from which the critically endangered B. vincentia has been described.
Methods:
To assist conservation while testing the current taxonomy of this group, high-throughput sequencing was used to infer a population-scale evolutionary scenario for a sample-set comprehensive in its representation of morphological diversity and a two-and-a-half thousand kilometer distribution.
Key results:
Banksia spinulosa sens. lat. represents two clades, each with an internal genetic structure shaped through historical separation by biogeographic barriers. This structure conflicts with the existing taxonomy for the group. Corroboration between phylogeny and population statistics aligns with the hypothesis that B. collina, B. neoanglica, and B. vincentia should not be classified as species.
Conclusions:
The pattern here supports how morphological diversity can be indicative of a locally expressed suite of traits rather than relationship. Over-splitting in the Hairpin Banksias is atypical since genomic analyses often reveal that species diversity is underestimated. However, we show that erring on overestimation can yield negative consequences, such as the disproportionate prioritisation of a geographically anomalous population. This article is protected by copyright. All rights reserved.
... Stochastic fire events are an important feature in the occurrence of hybridization of other species in Australian sclerophyllous environments, such as between Banksia robur and B. oblongifolia (Usher et al., 2010) and Kunzea rupestris and K. capitata (Tierney and Wardle, 2008). In the latter study, Kunzea hybrids did not resprout after fire, and this lower fitness relative to parental plants appeared to restrict the evolutionary potential of hybrids, a trait that should be further investigated in Lomatia hybrids. ...
... Our findings indicate a need to consider the processes by which species maintain distinct morphologies, genotypes, ecological preferences, phenologies and broader geographic distributions, despite ongoing interspecific exchanges of genetic material. Species cohesion in Lomatia is expected to be maintained despite the likelihood of continued gene flow and introgression wherever the species co-occur (Usher et al., 2010). Potential explanations include selective pressures maintaining species-specific character traits, genomic filters reducing introgression at key genomic sites, and adaptive introgression being triggered only when environmental conditions change (Reed et al., 2011). ...
Background and AimsWhen species cohesion is maintained despite ongoing natural hybridization, many questions are raised about the evolutionary processes operating in the species complex. This study examined the extensive natural hybridization between the Australian native shrubs Lomatia myricoides and L. silaifolia (Proteaceae). These species exhibit striking differences in morphology and ecological preferences, exceeding those found in most studies of hybridization to date.Methods
Nuclear microsatellite markers (nSSRs), genotyping methods and morphometric analyses were used to uncover patterns of hybridization and the role of gene flow in morphological differentiation between sympatric species.Key ResultsThe complexity of hybridization patterns differed markedly between sites, however, signals of introgression were present at all sites. One site provided evidence of a large hybrid swarm and the likely presence of multiple hybrid generations and backcrosses, another site a handful of early generational hybrids and a third site only traces of admixture from a past hybridization event. The presence of cryptic hybrids and a pattern of morphological bimodality amongst hybrids often disguised the extent of underlying genetic admixture.Conclusions
Distinct parental habitats and phenotypes are expected to form barriers that contribute to the rapid reversion of hybrid populations to their parental character state, due to limited opportunities for hybrid/intermediate advantage. Furthermore, strong genomic filters may facilitate continued gene flow between species without the danger of assimilation. Stochastic fire events facilitate temporal phenological isolation between species and may partly explain the bi-directional and site-specific patterns of hybridization observed. Furthermore, the findings suggest that F1 hybrids are rare, and backcrosses may occur rapidly following these initial hybridization events.
... In general, there are few rules regarding hybrid morphology compared to their parental species. Thus, hybrid individuals can exhibit a mosaic of phenotypes (Rieseberg and Ellstrand 1993) including intermediate morphology (Sanchez and Oyama 2004; Fernández-Manjarres et al. 2006), parental morphology (Craft et al. 2002; Usher et al. 2010), novel and/or extreme morphological traits (Rieseberg and Ellstrand 1993; Johnston et al. 2004). Our results indicated that trees identified as putative hybrids were mainly not first generation hybrids but were more likely advanced backcrosses between the two species. ...
Large-scale reforestation programmes are a major source of unwarranted gene flow and can have profound consequences on local genetic diversity. Recently, ash has been introduced to Ireland from continental Europe to stock plantations but has often exhibited poor stem form. It was not known whether these trees were Fraxinus excelsior, Fraxinus angustifolia or interspecific hybrids that are known to occur in continental Europe. F. excelsior is the only native ash in Ireland, so the introduced populations represent a potential threat for the genetic diversity of native populations. We characterized the introduced trees within two plantations (Clonee and Kildalkey) using morphological characters and six microsatellite markers. Samples from continental Europe were included for comparison. Plantations exhibited higher genetic diversity than control populations because our data suggest they contain a mixture of several provenances. There was a small but significant differentiation between plantations and control populations (ФCT = 0.0211). Bayesian analysis to infer population structure and to assign introduced individuals to reference populations clearly demonstrated the presence of hybrid individuals within the plantations. The percentage of trees detected with potential hybrid origin ranged from 28 to 58 % depending on the plantation and the threshold data analysis level chosen. Most hybrids could be considered cryptic because there was a lack of intermediate morphology for hybrid individuals that mainly clustered with F. excelsior. The results indicated that the source of material at the two plantation sites differed. Management options to minimize the impact of these introduced populations are discussed.
... However, very few studies have been focused on digital image-base procedure to characterize and classify taxa. Usher et al. (2010) recently reported the use of NIH Image software for measuring the quantitative parameters of scanned leaves of Banksia robur and B. oblongifolia species. Here we report digital image-base procedure using ImageJ software for characterization of croton cultivars and classify cultivars qualitatively through visual comparison of leaf base (B1-B2), margin (M1-M3), apices (A1-A3), shape (S1-S7), and coloration and color pattern (C1-C5). ...
Croton Codiaeum variegatum (L.) Blume is a tropical-origin ornamental tree or shrub. Over 300 cultivars are found within this species. The croton cultivars exhibit remarkable leaf phenotypic variety that is apparently ascribed to a high frequency of somatic mutation on the leaves. Until recently, the variation-producing mechanism has yet not been clarified and we do not have a systematic procedure to distinguish the croton cultivars. Even newly developed cultivar has given an attractive trade name. The cultivar names of croton are subjective and may depend on individual preference. Therefore, a new procedure is required to characterize and classify croton cultivars. We investigated 29 croton cultivars found in Okinawa islands, Japan. The cultivars were characterized by 6 quantitative and 7 qualitative leaf parameters. Quantitative leaf parameters were quantified through ImageJ software (NIH), while qualitative characters were assessed through visual comparison. Considerable phenotypic variations were found among the croton cultivars. Scatter plot analysis revealed that leaf length was weakly correlated with leaf width (r = 0.41). Leaf length varied 2.5-fold (12.7 to 26.42 cm), leaf width - 5-fold (2.4 to 12.2 cm), leaf index - 3.7-fold (2.1 to 7.8), petiole length - 8.7-fold (1.1 to 9.8 cm), leaf area - 6.8-fold (30.8 to 209.8 cm2), leaf perimeter - 2.4-fold (34.2 to 81.7 cm). Analysis of variance (ANOVA) suggested that significant variations were observed among the cultivars for all quantitative leaf parameters. These results indicated that croton cultivars can be distinguished by the leaf dimensions. In leaf attachment and arrangement, no difference was observed among the cultivars. However, variations were observed among the cultivars in leaf base, margin, apices, shape and coloration and color patterns. Based on the results we propose a new classification procedure using the five parameters: leaf base (B1-B2), margin (M1-M3), apices (A1-A3), shape (S1-S7) and coloration and color pattern (C1- C5).
... The harvested fresh leaves were scanned with a flatbed scanner (CanoScan LiDE 80) to obtain the digital information in shape and color. NIH ImageJ software (http://rsb.info.nih.gov/ij) was applied to obtain quantitative parameters (Usher et al., 2010). Ratio of leaf length to leaf width (leaf index) and leaf area to leaf perimeter were calculated from the measured parameters. ...
Croton Codiaeum variegatum (L.) Blume is a popular ornamental foliage plant that displays an anomalous range of variations in its leaf size, shape and color pattern. By fixing such leaf variations, more than 300 cultivars have been produced in the world. Until now, however, only a limited number of studies have been made to describe the leaf phenotypic diversity. Here we investigated the diversity of leaf phenotype in croton cultivars with a numerical taxonomic approach. One-way analysis of variance confirmed significant phenotypic variations in the croton cultivars for 12 quantitative leaf parameters. Among the numerical parameter tested, the leaf index that is the ratio of leaf length to leaf width showed the highest variability. High coefficient of variation values were observed in petiole length, leaf area and leaf down quarter width. In contrast with leaf morphology, the composition of leaf pigments that contribute to leaf coloration did not show diversity. Based on the analyses of the leaf parameters, we clustered the croton cultivars into four major groups. The results of this study provide a numerical basis for classification of croton cultivars. A possible involvement of transposon is discussed in terms of somatic mutation that results in the leaf phenotypic diversity.
