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Multiple hybridization events, polyploidy and low postmating isolation entangle the evolution of neotropical species of Epidendrum (Orchidaceae).

Marques I, Draper D, Riofrío L, Naranjo C - BMC Evol. Biol. (2014)

Bottom Line: In addition, future ecological niche models were constructed to predict the outcomes of hybridization between these species.The process of hybridization was highly asymmetric and followed in some cases by polyploidy.The recurrent process of hybridization has compromised the genetic integrity of the parental species.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Agriculture (Botany), High Polytechnic School of Huesca, University of Zaragoza, C/ Carretera de Cuarte Km 1, Huesca E22071, Spain. isabel.ic@gmail.com.

ABSTRACT

Background: Hybridization and polyploidy are central processes in evolution and speciation. These mechanisms often lead to complex patterns of genetic variation and the creation of novel genotypes, which may establish if they become isolated from gene flow. However, in the absence of reproductive isolation, species boundaries might easily be disrupted. Here, we used a combination of AFLPs, chloroplast DNA markers and flow cytometry to investigate the evolutionary outcomes of hybridization between two endemic Ecuadorian species of Epidendrum (E. madsenii and E. rhopalostele) in three hybrid zones. Postmating isolation was also quantified to determine the role of this barrier in restraining gene flow between hybrids and the parental species. In addition, future ecological niche models were constructed to predict the outcomes of hybridization between these species.

Results: Our results confirmed the presence of hybrids in all hybrid zones, but revealed that a third parental species (E. falcisepalum) has contributed to one of the hybrid zones studied. Backcross genotypes were frequent in all hybrid zones, which was in accordance with the absence of strong reproductive barriers. The process of hybridization was highly asymmetric and followed in some cases by polyploidy. The projection of future niche models predicted a severe reduction in the area suitable for the occurrence of these species, although favorable conditions will still occur for the existence of the current hybrid zones.

Conclusions: The recurrent process of hybridization has compromised the genetic integrity of the parental species. Most individuals of the parental species can no longer be considered as pure-bred individuals because most were classified as backcrossed hybrids. Novel genetic lineages occur in all hybrid zones implying that hybrids are fertile and can compete with the parental species. These results, together with the prediction of suitable conditions for the future occurrence of these hybrid zones, highlight the importance of conserving these geographic areas as sources of novel taxonomic entities.

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Related in: MedlinePlus

Mean fruit set in experimental crosses within (grey bars) and between (white bars) the studied species of Epidendrum. Values represent the mean ± SD (N = 100 plants⁄cross). The first letters indicates the identity of the maternal species: FAL = E. falcisepalum; MAD = E. madsenii; RHO = E. rhopalostele. Crosses with the same letter do not differ significantly (P > 0.05).
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Figure 3: Mean fruit set in experimental crosses within (grey bars) and between (white bars) the studied species of Epidendrum. Values represent the mean ± SD (N = 100 plants⁄cross). The first letters indicates the identity of the maternal species: FAL = E. falcisepalum; MAD = E. madsenii; RHO = E. rhopalostele. Crosses with the same letter do not differ significantly (P > 0.05).

Mentions: Experimental pollinations between the pure parental individuals assigned by NEWHYBRIDS yielded different results among the three hybrid zones. In HZ1, interspecific fruit set was lower than intraspecific fruit set, especially when E. madsenii was the ovule donor (Figure 3, Table 1). In HZ2 and HZ3, no differences were observed between intra- and interspecific crosses when E. rhopalostele was the ovule donor, whereas interspecific fruit set was slightly lower than intraspecific fruit set when E. madsenii was the ovule donor (Figure 3, Table 1). No differences were observed between populations in the interaction of population × treatment (Table 1). The strength of postmating prezygotic isolation (RIpostmating/prezygotic) was therefore very low, but variable among species (Table 2).


Multiple hybridization events, polyploidy and low postmating isolation entangle the evolution of neotropical species of Epidendrum (Orchidaceae).

Marques I, Draper D, Riofrío L, Naranjo C - BMC Evol. Biol. (2014)

Mean fruit set in experimental crosses within (grey bars) and between (white bars) the studied species of Epidendrum. Values represent the mean ± SD (N = 100 plants⁄cross). The first letters indicates the identity of the maternal species: FAL = E. falcisepalum; MAD = E. madsenii; RHO = E. rhopalostele. Crosses with the same letter do not differ significantly (P > 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3927766&req=5

Figure 3: Mean fruit set in experimental crosses within (grey bars) and between (white bars) the studied species of Epidendrum. Values represent the mean ± SD (N = 100 plants⁄cross). The first letters indicates the identity of the maternal species: FAL = E. falcisepalum; MAD = E. madsenii; RHO = E. rhopalostele. Crosses with the same letter do not differ significantly (P > 0.05).
Mentions: Experimental pollinations between the pure parental individuals assigned by NEWHYBRIDS yielded different results among the three hybrid zones. In HZ1, interspecific fruit set was lower than intraspecific fruit set, especially when E. madsenii was the ovule donor (Figure 3, Table 1). In HZ2 and HZ3, no differences were observed between intra- and interspecific crosses when E. rhopalostele was the ovule donor, whereas interspecific fruit set was slightly lower than intraspecific fruit set when E. madsenii was the ovule donor (Figure 3, Table 1). No differences were observed between populations in the interaction of population × treatment (Table 1). The strength of postmating prezygotic isolation (RIpostmating/prezygotic) was therefore very low, but variable among species (Table 2).

Bottom Line: In addition, future ecological niche models were constructed to predict the outcomes of hybridization between these species.The process of hybridization was highly asymmetric and followed in some cases by polyploidy.The recurrent process of hybridization has compromised the genetic integrity of the parental species.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Agriculture (Botany), High Polytechnic School of Huesca, University of Zaragoza, C/ Carretera de Cuarte Km 1, Huesca E22071, Spain. isabel.ic@gmail.com.

ABSTRACT

Background: Hybridization and polyploidy are central processes in evolution and speciation. These mechanisms often lead to complex patterns of genetic variation and the creation of novel genotypes, which may establish if they become isolated from gene flow. However, in the absence of reproductive isolation, species boundaries might easily be disrupted. Here, we used a combination of AFLPs, chloroplast DNA markers and flow cytometry to investigate the evolutionary outcomes of hybridization between two endemic Ecuadorian species of Epidendrum (E. madsenii and E. rhopalostele) in three hybrid zones. Postmating isolation was also quantified to determine the role of this barrier in restraining gene flow between hybrids and the parental species. In addition, future ecological niche models were constructed to predict the outcomes of hybridization between these species.

Results: Our results confirmed the presence of hybrids in all hybrid zones, but revealed that a third parental species (E. falcisepalum) has contributed to one of the hybrid zones studied. Backcross genotypes were frequent in all hybrid zones, which was in accordance with the absence of strong reproductive barriers. The process of hybridization was highly asymmetric and followed in some cases by polyploidy. The projection of future niche models predicted a severe reduction in the area suitable for the occurrence of these species, although favorable conditions will still occur for the existence of the current hybrid zones.

Conclusions: The recurrent process of hybridization has compromised the genetic integrity of the parental species. Most individuals of the parental species can no longer be considered as pure-bred individuals because most were classified as backcrossed hybrids. Novel genetic lineages occur in all hybrid zones implying that hybrids are fertile and can compete with the parental species. These results, together with the prediction of suitable conditions for the future occurrence of these hybrid zones, highlight the importance of conserving these geographic areas as sources of novel taxonomic entities.

Show MeSH
Related in: MedlinePlus