Molecular evidence for the hybrid origin of species in the soft coral genusAlcyonium(Cnidaria: Anthozoa: Octocorallia)

Abstract

Several recent studies have suggested that hybridization may play a previously unrecognized and important role in the evolution of corals. Our observations of polymorphic and recombinant sequences in the multicopy ribosomal internal transcribed spacer (ITS) region suggested the possible hybrid origin of two European soft coral species, Alcyonium hibernicum and Bellonella bocagei. To examine this possibility further we cloned and sequenced ITS-1 from multiple individuals and populations of these two species as well as two sympatric congeners, A. coralloides and A. sp. M2. Phylogenetic analyses separated the observed sequence variants into two distinct clades. All A. coralloides sequences belonged to clade A, while A. sp. M2 had only clade B sequences. A majority of A. hibernicum individuals, however, contained both clade A and B sequences that were identical to the predominant sequence variants found in A. coralloides and A. sp. M2, respectively. This pattern of additivity suggests that A. hibernicum originated from a hybrid cross between A. coralloides and A. sp. M2, a hypothesis that is supported by its unusual mode of reproduction (meiotic parthenogenesis). The predominant sequence variant found in B. bocagei was a unique, derived clade B sequence; in addition, however, most individuals of this species also had copies of a sequence identified as a recombinant between clade A and clade B sequence types. The presence of this recombinant sequence in the B. bocagei genome suggests that this species may also be the product of past hybridization events within the clade. Reticulate evolution may explain the failure of several previous studies to resolve the phylogeny of these four species.

Molecular phylogenetics of the genus Physalia (Cnidaria: Siphonophora) in New Zealand coastal waters reveals cryptic diversity

“…Hybridisation is common in cnidarians (van Oppen et al, 2000) and therefore this possibility is worthy of further investigation, particularly in view of the possible hybrid origin of the ITS sequence of the Western Australian specimen (see above). McFadden (1999) and McFadden & Hutchinson (2004) suggested that Octocorallia possess many traits that predispose them to hybridisation including closely related, morphologically similar species with overlapping ranges and reproductive periods. It appears that Physalia share the majority of these traits.…”

Genetic and morphometric evidence for unresolved species boundaries in the coral genus Psammocora (Cnidaria; Scleractinia)

“…As for other taxa in recent years, molecular characterization of species boundaries (Medina et al, 1999;van Oppen et al, 2000van Oppen et al, , 2001Diekmann et al, 2001;Márquez et al, 2002;van Oppen et al, 2002;Wolstenholme et al, 2003;McFadden & Hutchinson, 2004;van Oppen et al, 2004) and of the phylogenetic origin of different lineages of Scleractinia (Chen et al, 1996;Romano & Palumbi, 1996;Le GoffVitry et al, 2004) have evaluated the subsistence of many taxonomic entities, particularly within the genus Acropora.…”

“…The ribosomal DNA unit has been widely used to infer the phylogenetic relationships among different coral species (Van Oppen et al, 2000;Diekmann et al, 2001;Rodriguez-Lanetty & Hoegh-Guldberg, 2002;Van Oppen et al, 2002;McFadden & Hutchinson, 2004). Recently some criticism has been raised on the reliability of Internal Transcribed Spacer sequences as suitable markers for coral phylogenetics (Vollmer & Palumbi, 2004).…”

Next-generation hybridization and introgression

“…To estimate the size of introgressed linkage blocks, low-copy nuclear markers are required. The primer design and cloning required to confirm a single amplified product is time-consuming (Mcfadden and Hutchinson, 2004;Steele et al, 2008). Typically, conserved orthologous markers for amplifying nuclear genes are limited to well-studied families (for example, Asteraceae; Chapman et al, 2007).…”