A “Shallow Phylogeny” of Shallow Barnacles (Chthamalus)

Abstract

BackgroundWe present a multi-locus phylogenetic analysis of the shallow water (high intertidal) barnacle genus Chthamalus, focusing on member species in the western hemisphere. Understanding the phylogeny of this group improves interpretation of classical ecological work on competition, distributional changes associated with climate change, and the morphological evolution of complex cirripede phenotypes.Methodology and FindingsWe use traditional and Bayesian phylogenetic and ‘deep coalescent’ approaches to identify a phylogeny that supports the monophyly of the mostly American ‘fissus group’ of Chthamalus, but that also supports a need for taxonomic revision of Chthamalus and Microeuraphia. Two deep phylogeographic breaks were also found within the range of two tropical American taxa (C. angustitergum and C. southwardorum) as well.ConclusionsOur data, which include two novel gene regions for phylogenetic analysis of cirripedes, suggest that much more evaluation of the morphological evolutionary history and taxonomy of Chthamalid barnacles is necessary. These data and associated analyses also indicate that the radiation of species in the late Pliocene and Pleistocene was very rapid, and may provide new insights toward speciation via transient allopatry or ecological barriers.

Estimating the species tree for Hawaiian Schiedea (Caryophyllaceae) from multiple loci in the presence of reticulate evolution

“…This program applies a coalescent framework to estimate the posterior distribution of a species tree jointly with those of the gene trees for each locus, and has been successfully applied to several phylogenetic studies (Belfiore et : prior ages at 7.3, 4.7, and 3.7 (Fig. 6) or at 4.7 and 3.7 ( Linnen and Farrell, 2008;Spinks and Shaffer, 2009), although lack of convergence has been reported (Wares et al, 2009). This version of MB-BEST uses a uniform prior for the species tree and accounts for multiple accessions per species.…”

Genealogical approaches to the temporal origins of the Central American gap: Speciation and divergence in Pacific <i>Chthamalus</i> (Sessilia: Chthamalidae)

“…The "Farfan" form is found in wave-sheltered coastal habitats, solely at Southern locations in this region. Recent data further suggest a difference between the forms (Wares et al 2009), though the nomenclature of the C. southwardorum A and B clades is inconsistent in that source.…”

“…1, Table 1) as part of a global phylogeny of the group (Wares et al 2009). Species in this complex are largely indistinguishable in the field based on external morphology (Pitombo & Burton 2007; P. Dando, pers.…”

“…The widespread barnacle genus Chthamalus has been the subject of several biogeographic studies in the TEP (Laguna 1990, Wares 2001, Pitombo & Burton 2007, Wares et al 2009). Very low levels of morphological variation have made determining species distributions difficult, and until recently many species in the 'fissus group' (defined by two minute but verified synapomorphies) were considered a single species or species complex (Dando 1987).…”

“…This approach enables us to separate the effects of ancestral polymorphism and gene flow at loci where alleles are shared between the two regions. Using substitution rates generated from a phylogenetic analysis of the genus (Wares et al 2009), we have also evaluated the likely time frame at which these regional populations could have become isolated from one another.…”