Global phylogeography of Oithona similis s.l. (Crustacea, Copepoda, Oithonidae) – A cosmopolitan plankton species or a complex of cryptic lineages?

Abstract

14Traditionally, many small-sized copepod species are considered to be widespread, bipolar or 15 cosmopolitan. However, these large-scale distribution patterns need to be re-examined in 16 view of increasing evidence of cryptic and pseudo-cryptic speciation in pelagic copepods. 17Here, we present a phylogeographic study of Oithona similis s.l. populations from the Arctic Introduction 34The existence of widespread or cosmopolitan species is widely accepted in marine plankton 35 due to the lack of apparent geographic barriers and high dispersal potentials. Thus, it has 36 been assumed that allopatric speciation may be less important in pelagic species than 37 sympatric or parapatric speciation (Norris, 2000). During the past years molecular studies 38 have revealed that many supposedly widespread species are mosaics of several cryptic or 39 pseudocryptic species (Andrews et al., 2014; Burridge et al., 2015; Cornils and Held, 2014; 40 Darling et al., 2007;Halbert et al., 2013; Hunt et al., 2010;Miyamoto et al., 2012). The mode 49The cyclopoid copepod Oithona similis s.l. Claus, 1866 is accepted as a cosmopolitan 50 species, presumably occurring in all oceanic zones (Razouls et al., 2016) and presumably 51 the most abundant copepod species worldwide, although its importance has long been 52 overlooked due to the use of too coarse mesh sizes for plankton hauls (Gallienne and 53 Robins, 2001;Turner, 2004). Previous investigations have stressed that O. similis s.l. is a 54 prominent link between the microbial loop and higher trophic levels (Atkinson, 1995; 55 Castellani et al., 2005; Zamora-Terol et al., 2013). Its preferred habitats are polar and 56 temperate epipelagic marine waters where it is often more abundant than calanoid copepods 57 (Atkinson, 1998; Hopcroft et al., 2010; Pinkerton et al., 2010;Sabatini and Kiørboe, 1994; 58 Zamora-Terol et al., 2014). Furthermore, it has also been found in subtropical and tropical 59 waters (Cepeda et al., 2012; Nishida, 1985), although some of the reported findings seem 60 questionable (Nishida, 1985). Morphological differences have not been detected between O. 61 similis s.l. populations across latitudes, except for morphometric differences in the Northern 62 hemisphere,where prosome length and cephalon shape differed significantly among 63 populations from North Atlantic and Arctic water masses (Shuvalov, 1972). He suspected 64 that O. similis s.l. is "a polytypic species which comprises various subspecies or intraspecific 65 forms and groups with distinct ecological requirements regarding temperature throughout the 66 life cycle." A first attempt to investigate the population structure of O. similis s.l., using the 67 nuclear molecular marker 28S, revealed low levels of intraspecific variety between North and 68 South Atlantic populations (Cepeda et al., 2012). However, the polar habitats of O. similis s.l. 69were not included in that study. 751838, Pseudocalanus spp. or Triconia borealis Sars, 1918 (Ashjian et al., 2003 Hunt et al., 76 2014; Kos...

New insights into global biogeography, population structure and natural selection from the genome of the epipelagic copepod Oithona

“…The study of pelagic copepod populations at the molecular level helps to identify environmental factors that drive the appearance and fixation of adaptive traits. Current approaches applied to pelagic copepods typically use ribosomal genes, mitochondrial cytochrome oxidase subunit I and II genes and microsatellites markers to identify species, genotypes and haplotypes (e.g., Blanco‐Bercial, Álvarez‐Marqués, & Bucklin, ; Blanco‐Bercial, Cornils, Copley, & Bucklin, ; Cornils, Wend‐Heckmann, & Held, ; Goetze, Andrews, Peijnenburg, Portner, & Norton, ; Hirai, Kuriyama, Ichikawa, Hidaka, & Tsuda, ). With appropriate sampling, the calculation of within‐ and between‐population genetic distances can then be used to infer copepod population structure and connectivity (Kozol, Blanco‐Bercial, & Bucklin, ).…”

“…Oithona similis has been identified from all oceans and climate zones (Razouls, de Bovée, Kouwenberg, & Desreumaux, ) and prefers temperatures below 20°C (Castellani, Licandro, Fileman, di Capua, & Grazia Mazzocchi, ), which strengthens the speculation that its occurrence in tropical regions may be based on misidentifications (Nishida, ). A recent finding has also shown that O. similis is a complex of independent lineages with distinct biogeographies linked to climate zones, and not a single cosmopolitan species (Cornils et al., ). Oithona atlantica is also widely distributed and occurs in the temperate and polar oceanic regions of the Atlantic and Pacific Ocean (Cepeda, Blanco‐Bercial, Bucklin, Beron, & Vinas, ; Nishida, ).…”

“…The small size of Oithona (<1 mm) and its subtle morphological species‐specific traits that can only be observed by microscopy (Nishida, Omori, & Tanaka, ) represent a serious difficulty for studies involving a large number of samples. Ribosomal 28S and mitochondrial genes have been successfully used to characterize Oithona species (Cepeda et al., ; Cornils et al., ; Ueda, Yamaguchi, Saitoh, Orui Sakaguchi, & Tachihara, ) but also to identify invasive species (Cornils & Wend‐Heckmann, ). This combination of morphological identification and molecular analyses provides robust molecular resources that can be used as a reference for species identification using molecular analysis‐only approaches including genome‐wide approaches (i.e., metagenomics).…”

Population Genomics of Marine Zooplankton

“…A number of species show large-scale patterns of genetic diversity associated with latitudinal gradients (e.g., Francisco et al 2014) and among ocean basins, including Eukrohnia hamata (Miyamoto et al 2012), Pleuromama abdominalis , and Oithona similis (Cornils et al 2017). …”

“…Results can be interpreted to estimate and understand the age of the lineage in terms of time to coalescence (i.e., the common ancestral gene from which all current copies of the gene are descended), as well as imprints of demographic history on populations and species (Knowles 2009). Among marine zooplankton, mitochondrial markers have been used most regularly to infer demographic history (e.g., Peijnenburg et al 2005;Aarbakke et al 2014;Cornils et al 2017), including marine invasions (Cristescu 2015;Lee 2016;Sherman et al 2016), population expansions and contractions (Edmands 2001), geographic isolation giving rise to speciation events (Lee 2000;Peijnenburg et al 2004;Miyamoto et al 2010), and divergence of genetic lineages following major global climate events (Papadopoulos et al 2005;Blanco-Bercial et al 2011b;Milligan et al 2011). …”