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Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals

BACKGROUND: Most phylogenetic studies using current methods have focused on primary DNA sequence information. However, RNA secondary structures are particularly useful in systematics because they include characteristics, not found in the primary sequence, that give "morphological" informat...

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Autores principales: Grajales, Alejandro, Aguilar, Catalina, Sánchez, Juan A
Formato: Texto
Lenguaje:English
Publicado: BioMed Central 2007
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913914/
https://www.ncbi.nlm.nih.gov/pubmed/17562014
http://dx.doi.org/10.1186/1471-2148-7-90
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author Grajales, Alejandro
Aguilar, Catalina
Sánchez, Juan A
author_facet Grajales, Alejandro
Aguilar, Catalina
Sánchez, Juan A
author_sort Grajales, Alejandro
collection PubMed
description BACKGROUND: Most phylogenetic studies using current methods have focused on primary DNA sequence information. However, RNA secondary structures are particularly useful in systematics because they include characteristics, not found in the primary sequence, that give "morphological" information. Despite the number of recent molecular studies on octocorals, there is no consensus opinion about a region that carries enough phylogenetic resolution to solve intrageneric or close species relationships. Moreover, intrageneric morphological information by itself does not always produce accurate phylogenies; intra-species comparisons can reveal greater differences than intra-generic ones. The search for new phylogenetic approaches, such as by RNA secondary structure analysis, is therefore a priority in octocoral research. RESULTS: Initially, twelve predicted RNA secondary structures were reconstructed to provide the basic information for phylogenetic analyses; they accorded with the 6 helicoidal ring model, also present in other groups of corals and eukaryotes. We obtained three similar topologies for nine species of the Caribbean gorgonian genus Eunicea (candelabrum corals) with two sister taxa as outgroups (genera Plexaura and Pseudoplexaura) on the basis of molecular morphometrics of ITS2 RNA secondary structures only, traditional primary sequence analyses and maximum likelihood, and a Bayesian analysis of the combined data. The latter approach allowed us to include both primary sequence and RNA molecular morphometrics; each data partition was allowed to have a different evolution rate. In addition, each helix was partitioned as if it had evolved at a distinct rate. Plexaura flexuosa was found to group within Eunicea; this was best supported by both the molecular morphometrics and combined analyses. We suggest Eunicea flexuosa (Lamouroux, 1821) comb. nov., and we present a new species description including Scanning Electron Microscopy (SEM) images of morphological characteristics (sclerites). Eunicea flexuosa, E. pallida, E. laxispica and E. mammosa formed a separate clade in the molecular phylogenies, and were reciprocally monophyletic with respect to other Eunicea (Euniceopsis subgenus, e.g. E. tourneforti and E. laciniata) in the molecular morphometrics tree, with the exception of E. fusca. Moreover, we suggest a new diagnostic character for Eunicea, also present in E. flexuosa: middle layer sclerites > 1 mm in length. CONCLUSION: ITS2 was a reliable sequence for intrageneric studies in gorgonian octocorals because of the amount of phylogenetic signal, and was corroborated against morphological characters separating Eunicea from Plexaura. The ITS2 RNA secondary structure approach to phylogeny presented here did not rely on alignment methods such as INDELS, but provided clearly homologous characters for partition analysis and RNA molecular morphometrics. These approaches support the divergence of Eunicea flexuosa comb. nov. from the outgroup Plexaura, although it has been considered part of this outgroup for nearly two centuries because of morphological resemblance.
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spelling pubmed-19139142007-07-11 Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals Grajales, Alejandro Aguilar, Catalina Sánchez, Juan A BMC Evol Biol Research Article BACKGROUND: Most phylogenetic studies using current methods have focused on primary DNA sequence information. However, RNA secondary structures are particularly useful in systematics because they include characteristics, not found in the primary sequence, that give "morphological" information. Despite the number of recent molecular studies on octocorals, there is no consensus opinion about a region that carries enough phylogenetic resolution to solve intrageneric or close species relationships. Moreover, intrageneric morphological information by itself does not always produce accurate phylogenies; intra-species comparisons can reveal greater differences than intra-generic ones. The search for new phylogenetic approaches, such as by RNA secondary structure analysis, is therefore a priority in octocoral research. RESULTS: Initially, twelve predicted RNA secondary structures were reconstructed to provide the basic information for phylogenetic analyses; they accorded with the 6 helicoidal ring model, also present in other groups of corals and eukaryotes. We obtained three similar topologies for nine species of the Caribbean gorgonian genus Eunicea (candelabrum corals) with two sister taxa as outgroups (genera Plexaura and Pseudoplexaura) on the basis of molecular morphometrics of ITS2 RNA secondary structures only, traditional primary sequence analyses and maximum likelihood, and a Bayesian analysis of the combined data. The latter approach allowed us to include both primary sequence and RNA molecular morphometrics; each data partition was allowed to have a different evolution rate. In addition, each helix was partitioned as if it had evolved at a distinct rate. Plexaura flexuosa was found to group within Eunicea; this was best supported by both the molecular morphometrics and combined analyses. We suggest Eunicea flexuosa (Lamouroux, 1821) comb. nov., and we present a new species description including Scanning Electron Microscopy (SEM) images of morphological characteristics (sclerites). Eunicea flexuosa, E. pallida, E. laxispica and E. mammosa formed a separate clade in the molecular phylogenies, and were reciprocally monophyletic with respect to other Eunicea (Euniceopsis subgenus, e.g. E. tourneforti and E. laciniata) in the molecular morphometrics tree, with the exception of E. fusca. Moreover, we suggest a new diagnostic character for Eunicea, also present in E. flexuosa: middle layer sclerites > 1 mm in length. CONCLUSION: ITS2 was a reliable sequence for intrageneric studies in gorgonian octocorals because of the amount of phylogenetic signal, and was corroborated against morphological characters separating Eunicea from Plexaura. The ITS2 RNA secondary structure approach to phylogeny presented here did not rely on alignment methods such as INDELS, but provided clearly homologous characters for partition analysis and RNA molecular morphometrics. These approaches support the divergence of Eunicea flexuosa comb. nov. from the outgroup Plexaura, although it has been considered part of this outgroup for nearly two centuries because of morphological resemblance. BioMed Central 2007-06-11 /pmc/articles/PMC1913914/ /pubmed/17562014 http://dx.doi.org/10.1186/1471-2148-7-90 Text en Copyright © 2007 Grajales et al; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( (http://creativecommons.org/licenses/by/2.0) ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
spellingShingle Research Article
Grajales, Alejandro
Aguilar, Catalina
Sánchez, Juan A
Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals
title Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals
title_full Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals
title_fullStr Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals
title_full_unstemmed Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals
title_short Phylogenetic reconstruction using secondary structures of Internal Transcribed Spacer 2 (ITS2, rDNA): finding the molecular and morphological gap in Caribbean gorgonian corals
title_sort phylogenetic reconstruction using secondary structures of internal transcribed spacer 2 (its2, rdna): finding the molecular and morphological gap in caribbean gorgonian corals
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913914/
https://www.ncbi.nlm.nih.gov/pubmed/17562014
http://dx.doi.org/10.1186/1471-2148-7-90
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