The Geography of Morphological Convergence in the Radiations of Pacific Sebastes Rockfishes
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vol. 184, no. 5 the american naturalist november 2014 E-Article The Geography of Morphological Convergence in the Radiations of Pacific Sebastes Rockfishes Travis Ingram1,* and Yoshiaki Kai2 1. Department of Zoology, University of Otago, Dunedin 9054, New Zealand; 2. Maizuru Fisheries Research Station, Field Science Education and Research Center, Kyoto University, Nagahama, Maizuru, Kyoto 625-0086, Japan Submitted August 15, 2013; Accepted May 8, 2014; Electronically published October 6, 2014 Online enhancement: appendix. Dryad data: http://dx.doi.org/10.5061/dryad.s5s3s. strong deterministic component (Schluter 1990, 2000). The abstract: The evolution of convergent phenotypes in lineages subject study of replicated radiation has focused on islands and to similar selective pressures is a common feature of adaptive radiation. In geographically replicated radiations, repeated convergence occurs island-like habitats such as young lakes, where similar en- between clades occupying distinct regions or islands. Alternatively, a vironments and a wealth of available resources relative to clade may repeatedly reach the same adaptive peaks in broadscale the number of competing species can set the stage for col- sympatry, resulting in extensive convergence within a region. Rockfish onizing lineages to diversify into the same niches on each (Sebastes sp.) have radiated in both the northeast and northwest Pacific, island (Kocher et al. 1993; Losos et al. 1998; Chiba 2004; allowing tests of the extent and geographic pattern of convergence in Gillespie 2004; Mahler et al. 2013). Convergence between a marine environment. We used a suite of phylogenetically informed lineages occupying larger regions such as continents or methods to test for morphological convergence in rockfish. We ex- amined patterns of faunal similarity using nearest neighbor distances oceans, including classic examples of matched pairs of mar- in morphospace and the frequency of morphologically similar yet dis- supial and eutherian mammals (Springer et al. 2004), is well tantly related species pairs. The extent of convergence both between established, but replicated radiation across entire clades has regions and within the northeast Pacific exceeds the expectation under rarely been tested or demonstrated in continental or marine a Brownian motion null model, although constraints on trait space faunas. Instead, an alternative outcome—convergence of could account for the similarity. We then used a recently developed multiple lineages within a shared region—has recently been method (SURFACE) to identify adaptive peak shifts in Sebastes evo- demonstrated in continental (Kozak et al. 2009), marine lutionary history. We found that the majority of convergent peak shifts occur within the northeast Pacific rather than between regions and (Rutschmann et al. 2011; Fre´de´rich et al. 2013), and large that the signal of peak shifts is strongest for traits related to trophic lacustrine (Muschick et al. 2012) radiations, with pheno- morphology. Pacific rockfish thus demonstrate a tendency toward mor- typically similar lineages often occurring in broad sympatry. phological convergence within one of the two broad geographic regions These outcomes—clade-wide convergence between or in which they have diversified. within regions—present alternative geographic contexts in Keywords: adaptive radiation, clade-wide convergence, Hansen which convergence can take place. model, Ornstein-Uhlenbeck model, replicated radiation, SURFACE. Advances in comparative methods and increased avail- ability of molecular phylogenetic trees are making possible targeted tests for convergence in clades undergoing adap- Introduction tive radiation. Historically, phylogenetic approaches have compared the statistical pattern of faunal similarity to null The convergent evolution of similar phenotypes in response distributions, initially obtained by randomization and later to shared ecological conditions provides powerful evidence by simulation under evolutionary null models such as for natural selection and is a hallmark of many adaptive Brownian motion (e.g., Cody and Mooney 1978; Ricklefs radiations (Schluter 2000; Losos 2010). In extreme cases, and Travis 1980; Muschick et al. 2012). These methods do replicated adaptive radiation occurs when clades diversifying not incorporate processes that can result in deterministic independently in multiple regions produce similar sets of convergence, such as adaptation toward the same opti- convergent species, implying that the radiations have a mum trait values, often represented as multivariate peaks * Corresponding author; e-mail: [email protected]. on a macroevolutionary adaptive landscape (Simpson Am. Nat. 2014. Vol. 184, pp. E115–E131. ᭧ 2014 by The University of Chicago. 1953; Hansen 2012). Comparative methods based on the 0003-0147/2014/18405-54903$15.00. All rights reserved. Ornstein-Uhlenbeck model have been used to represent DOI: 10.1086/678053 evolutionary dynamics that include a stochastic compo- E116 The American Naturalist nent and deterministic adaptation toward one or more were polyphyletic, consisting of NEP and NWP species peaks (Hansen 1997; Butler and King 2004; Beaulieu et that were distantly related despite their phenotypic resem- al. 2012). Most such approaches require an a priori hy- blance (Kai et al. 2003; Hyde and Vetter 2007), and that pothesis about which lineages are convergent, but exten- dispersal between regions was relatively rare. Each region sions of this method allow convergent peak shifts to be is home to substantial clades that have diversified in situ, identified using only a tree and data for multiple phe- and the NEP in particular contains multiple lineages that notypic traits (Ingram and Mahler 2013; Mahler et al. have independently arrived at similar ecological strategies 2013). The resulting model includes estimates of the po- (such as benthic vs. open-water habitat use; Love et al. sitions of the multivariate trait optima and can thus be 2002). This makes clade-wide convergence both between regarded as an approximation of a macroevolutionary and within oceanic regions plausible outcomes in the ra- adaptive landscape. The inferred positions of peak shifts diations of Sebastes in the North Pacific. on the tree can be combined with reconstructed biogeo- Here, we use molecular phylogenies, measurements of graphic histories of the clade to infer the geographic con- morphological traits with putative links to ecology, and text of convergence (Mahler and Ingram 2014) and to test statistical and model-based comparative analyses to ask to for clade-wide convergence either between geographically what extent convergence has occurred between and within replicated radiations or within regions. regions in Pacific Sebastes. We show that while some con- Rockfish of the genus Sebastes living in the North Pacific vergence between regions is evident, most cases of con- Ocean are an excellent system in which to test for clade- vergence occur between lineages within the northeast wide convergence between and within regions in a marine Pacific. environment. With approximately 110 species worldwide, including 96 described species in the northern Pacific Ocean, this diverse genus is a dominant component of the Methods northern temperate ichthyofauna (Nakabo and Kai 2013). Phylogeny Reconstruction At least 62 species occur exclusively in the northeast Pacific (NEP), while 28 are restricted to the northwest Pacific The most complete phylogenetic treatment of Sebastes to (NWP), and 5 have a trans-Pacific (TP) distribution. Dis- date was presented by Hyde and Vetter (2007), who se- persal out of the North Pacific has resulted in small num- quenced seven mitochondrial (cytochrome b [cyt b], cy- bers of species endemic to the Gulf of California (treated tochrome oxidase 1 [cox1], 12S rRNA, 16S rRNA, tRNA here as distinct from the NEP), the Atlantic Ocean, and proline, tRNA threonine, and the control region) and two the Southern Hemisphere. Since their Miocene origin nuclear (RAG2 and ITS1) genes from 99 Sebastes species (Hyde and Vetter 2007), rockfish have undergone rapid and four outgroup taxa. To this alignment, we added nine lineage diversification, accompanied by extensive diversi- additional species from the NWP, four of which are mem- fication in resource use, habitat, and ecologically relevant bers of species complexes that were only recently resolved morphology. Species vary in adult depth habitat (shallow as valid species (Sebastes cheni, Sebastes ventricosus, Sebastes subtidal to 1500 m), in the use of benthic habitats versus nudus, and Sebastes zonatus; Kai and Nakabo 2008, 2013; the water column, and in the extent of feeding on zoo- Muto et al. 2011) and five of which had not been included plankton, larger invertebrates, or fishes (reflected in in previous treatments (Sebastes koreanus, Sebastes nivosus, trophic position inferred using stable nitrogen isotope ra- Sebastes longispinis, Sebastes itinus, and Sebastes wakiyai). tios). This ecological variation is accompanied by variation We used existing mitochondrial DNA sequences for most in body size (17–108 cm maximum total length), trophic of these additional species (Kai and Nakabo 2008, 2013; morphology such as gill raker number and length, and Muto et al. 2011) and added new sequences for S. itinus elements of body and fin shapes (Love et al. 2002; Ingram (gene, GenBank accession no.: cyt b, AB826452; cox1, and Shurin 2009; Ingram 2011). AB826455; 12S rRNA, AB826456; 16S rRNA, AB826453; While a quantitative appraisal