title: Cryptic diversity, geographical endemism and allopolyploidy in NE Pacific seaweeds.
abstract: Molecular markers are revealing a much more diverse and evolutionarily complex picture of marine biodiversity than previously anticipated. Cryptic and/or endemic marine species are continually being found throughout the world oceans, predominantly in inconspicuous tropical groups but also in larger, canopy-forming taxa from well studied temperate regions. Interspecific hybridization has also been found to be prevalent in many marine groups, for instance within dense congeneric assemblages, with introgressive gene-flow being the most common outcome. Here, using a congeneric phylogeographic approach, we investigated two monotypic and geographically complementary sister genera of north-east Pacific intertidal seaweeds (Hesperophycus and Pelvetiopsis), for which preliminary molecular tests revealed unexpected conflicts consistent with unrecognized cryptic diversity and hybridization.
  
  
  
  The three recovered mtDNA clades did not match a priori species delimitations. H. californicus was congruent, whereas widespread P. limitata encompassed two additional narrow-endemic species from California - P. arborescens (here genetically confirmed) and P. hybrida sp. nov. The congruence between the genotypic clusters and the mtDNA clades was absolute. Fixed heterozygosity was apparent in a high proportion of loci in P. limitata and P. hybrida, with genetic analyses showing that the latter was composed of both H. californicus and P. arborescens genomes. All four inferred species could be distinguished based on their general morphology.
  
  
  
  This study confirmed additional diversity and reticulation within NE Pacific Hesperophycus/Pelvetiopsis, including the validity of the much endangered, modern climatic relict P. arborescens, and the identification of a new, stable allopolyploid species (P. hybrida) with clearly discernable ancestry (♀ H. californicus x ♂ P. arborescens), morphology, and geographical distribution. Allopolyploid speciation is otherwise completely unknown in brown seaweeds, and its unique occurrence within this genus (P. limitata possibly representing a second example) remains enigmatic. The taxonomic separation of Hesperophycus and Pelvetiopsis is not supported and the genera should be synonymized; we retain only the latter. The transitional coastline between Point Conception and Monterey Bay represented a diversity hotspot for the genus and the likely sites of extraordinary evolutionary events of allopolyploid speciation at sympatric range contact zones. This study pinpoints how much diversity (and evolutionary processes) potentially remains undiscovered even on a conspicuous seaweed genus from the well-studied Californian intertidal shores let alone in other, less studied marine groups and regions/depths.
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal. jmneiva@ualg.pt.
authors.forename: João
authors.identifier: 0000-0002-5927-4570
authors.initials: J
authors.lastname: Neiva
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
authors.forename: Ester A
authors.initials: EA
authors.lastname: Serrão
authors.affiliation: Long Marine Laboratory, University of California, Santa Cruz, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Anderson
authors.affiliation: Long Marine Laboratory, University of California, Santa Cruz, USA.
authors.forename: Peter T
authors.initials: PT
authors.lastname: Raimondi
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
authors.forename: Neusa
authors.initials: N
authors.lastname: Martins
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
authors.forename: Licínia
authors.initials: L
authors.lastname: Gouveia
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Paulino
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
authors.forename: Nelson C
authors.initials: NC
authors.lastname: Coelho
authors.affiliation: University Herbarium, University of California, Berkeley, USA.
authors.forename: Kathy Ann
authors.initials: KA
authors.lastname: Miller
authors.affiliation: Marine Science Institute, University of California, Santa Barbara, USA.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Reed
authors.affiliation: CICESE - Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California, Mexico.
authors.forename: Lydia B
authors.initials: LB
authors.lastname: Ladah
authors.affiliation: CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
authors.forename: Gareth A
authors.initials: GA
authors.lastname: Pearson
mesh_terms: D000818:Animals; D044822:Biodiversity; D005075:Biological Evolution; D002140:California; D004272:DNA, Mitochondrial / Q000235:genetics; D051456:Gene Flow; D010140:Pacific Ocean; D010802:Phylogeny; D058974:Phylogeography; D011123:Polyploidy; D012624:Seaweed / Q000145:classification / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D004272:DNA, Mitochondrial
keywords: Allopolyploidy; Congeneric phylogeography; Cryptic species; Endemism; Fucaceae; Hesperophycus; Hybridization; Intertidal; NE Pacific; Pelvetiopsis