Limits...
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.

Show MeSH

Related in: MedlinePlus

Genome size obtained with PI for three hybridizing species of Epidendrum: E. madsenii ‘MAD’, E. rhopalostele ‘RHO’ and E. falcisepalum ‘FAL’ in three hybrid zones (a-c) and in allopatric populations (d-f) according to the genetic groups detected by NEWHYBRIDS (colors as in Figure 1B). Values are expressed in picograms.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3927766&req=5

Figure 2: Genome size obtained with PI for three hybridizing species of Epidendrum: E. madsenii ‘MAD’, E. rhopalostele ‘RHO’ and E. falcisepalum ‘FAL’ in three hybrid zones (a-c) and in allopatric populations (d-f) according to the genetic groups detected by NEWHYBRIDS (colors as in Figure 1B). Values are expressed in picograms.

Mentions: GS values were significantly different between the three pure parental species and the mean values were 2.69 pg in E. madsenii, 3.13 pg in E. rhopalostele and 4.08 pg in E. falcisepalum (F3,250 = 19.199, P < 0.001). Analyzing the individuals according to the genetic groups assigned by NEWHYBRIDS allowed us to determine that the GS of F1 hybrids conformed to expectations (GS parent1 + GSparent2/2) as they usually showed values intermediate to those of the parental species in all hybrid zones (Figure 2). Backcrossed individuals were usually grouped with the respective backcrossed parental species, and F2 hybrids had GS values higher than those of the remaining genetic groups (Figure 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)

Genome size obtained with PI for three hybridizing species of Epidendrum: E. madsenii ‘MAD’, E. rhopalostele ‘RHO’ and E. falcisepalum ‘FAL’ in three hybrid zones (a-c) and in allopatric populations (d-f) according to the genetic groups detected by NEWHYBRIDS (colors as in Figure 1B). Values are expressed in picograms.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Genome size obtained with PI for three hybridizing species of Epidendrum: E. madsenii ‘MAD’, E. rhopalostele ‘RHO’ and E. falcisepalum ‘FAL’ in three hybrid zones (a-c) and in allopatric populations (d-f) according to the genetic groups detected by NEWHYBRIDS (colors as in Figure 1B). Values are expressed in picograms.
Mentions: GS values were significantly different between the three pure parental species and the mean values were 2.69 pg in E. madsenii, 3.13 pg in E. rhopalostele and 4.08 pg in E. falcisepalum (F3,250 = 19.199, P < 0.001). Analyzing the individuals according to the genetic groups assigned by NEWHYBRIDS allowed us to determine that the GS of F1 hybrids conformed to expectations (GS parent1 + GSparent2/2) as they usually showed values intermediate to those of the parental species in all hybrid zones (Figure 2). Backcrossed individuals were usually grouped with the respective backcrossed parental species, and F2 hybrids had GS values higher than those of the remaining genetic groups (Figure 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