Sipunculan Larvae and "Cosmopolitan" Species
*Department of Marine Biology, Texas A&M University at Galveston, P.O. Box 1675, Galveston, TX 77553, USAIntegrative and Comparative Biology (Impact Factor: 2.93). 05/2012; 52(4):497-510. DOI: 10.1093/icb/ics082
Sipuncula is a relatively small taxon with roughly 150 recognized species. Many species are geographically widespread or "cosmopolitan." The pelagosphera larvae of some species are estimated to spend several months in the plankton. However, recent molecular evidence suggests that many of the "cosmopolitan" species actually represent species-complexes, some not even monophyletic. Herein, we present data on three sipunculan species with different developmental modes that occur both in the Sea of Japan and in the Northeast Pacific. The development of the three species-Phascolosoma agassizii, Thysanocardia nigra, and Themiste pyroides-is exceptionally well studied in both regions of the Pacific. Significant differences have been observed between the two regions with respect to egg size, developmental mode, and developmental timing. In general, eggs are larger and development slower in the Northeast Pacific when compared with the Sea of Japan. These differences have been explained as a result of phenotypic plasticity exhibited under different environmental conditions, in particular temperature, but we show that the populations of all three species are also remarkably distinct genetically and that gene flow between the two regions is extremely unlikely. In Thysanocardia nigra, we even found two very distinct genetic lineages within the same location in the Northeast Pacific. The amount of genetic divergence between populations from the Sea of Japan and those from the Northeast Pacific is not correlated with developmental mode. Themiste pyroides, the species with the most abbreviated development, actually has the least degree of genetic divergence between the regions. Analyses of molecular variance show that the majority of the observed variation in all three species is between the regions. We conclude that all three "cosmopolitan" species actually represent complexes of cryptic or pseudo-cryptic species. These examples demonstrate that a solid taxonomic framework based on molecular and morphological evidence is a prerequisite for evaluating relationships between dispersal capabilities, species' ranges, and the connectivity of populations.
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[Show abstract] [Hide abstract] ABSTRACT: Sipunculans collected during several European scientific cruises and expeditions (1991–2010) to different regions of the Mediterranean Sea (from depths ranging 1–2287 m) are recorded. A total of 17 species in nine genera are recognized. Only Nephasoma cf. minutum (Keferstein, 1862) could represent a first record for the Mediterranean Sea in the case of further verification of the identification. Three other species, Apionsoma misakianum (Ikeda, 1904), Aspidosiphon mexicanus (Murina, 1967) and Phascolion tuberculosum Théel, 1875, extend their vertical distribution to deeper bottoms. Significant morphological characters are described and illustrated. Juvenile specimens of Phascolosoma stephensoni (Stephen, 1942) and Aspidosiphon misakiensis Ikeda, 1904 are recorded. They show characteristic cuticular pelagosphera-like papillae over the trunk. A distribution map of Aspidosiphon mexicanus is also included. In general, the sipunculan fauna of the Mediterranean Sea is characterized mostly as a part of the warm-temperate Atlantic region, affected by migration of warm-water species mainly from the Red Sea.
- "Finally, a few more sipunculans collected during the scientific cruise DEPRO 96 on board the R/V Phascolosoma (Phascolosoma) perlucens Baird, 1868 16 Phascolosoma (Phascolosoma) scolops (Selenka et al., 1883) 10 16 Phascolosoma (Phascolosoma) stephensoni (Stephen, 1942) required. In recent years, several sipunculan species were identified as complexes of cryptic species ( Giribet 2010, 2014; Schulze et al. 2012 ), although no taxonomic revisions of the respective genera have been followed. Consequently, the species identifications were mainly based on the works by Cutler (1994) and Papadopoulou et al. (1999), but it is possible that some of the common species represent currently unrecognized or cryptic species. "
[Show abstract] [Hide abstract] ABSTRACT: Micrura alaskensis Coe, 1901 is a common intertidal heteronemertean known from eastern and northwest Pacific (Alaska to Ensenada, Mexico and Akkeshi, Japan, respectively). It is an emerging model system in developmental biology research. We present evidence from morphology of the adults, gametes, and sequences of cytochrome c oxidase subunit I and 16S rRNA genes that it is not one, but a complex of five, cryptic species. All five of these species co-occur at least in part of their geographic range (e.g. southern Oregon). Preliminary cross-hybridization experiments suggest that at least some of these species are reproductively isolated. The five species share characteristics of adult morphology (e.g. accessory buccal glands) and at least four are known to possess a unique larval morphotype-pilidium maculosum. We propose that these characters define a new genus, Maculaura gen. nov., which contains the following five species: Maculaura alaskensis comb. nov., Maculaura aquilonia sp. nov., Maculaura cerebrosa sp. nov., Maculaura oregonensis sp. nov., and Maculaura magna sp. nov. It is unclear which of the five species Coe originally encountered and described. We chose to retain the name "alaskensis" for the species that current researchers know as "Micrura alaskensis", although, presently, it is only known from Washington and Oregon, and has not been collected from Alaska. Maculaura aquilonia sp. nov. is the only member of the genus we have encountered in Alaska, and we show that it also occurs in the Sea of Okhotsk, Russia.
- "Maculaura aquilonia was a single species according to 16S data, but was split into two ited to adult morphology, this information typically is not sufficient to differentiate between closely related or cryptic species (e.g. Manchenko and Kulikova, 1996; Hebert et al., 2004; Strand and Sundberg, 2005; Lavoué et al., 2010; Schulze et al., 2012). This, indeed, is the case for the " Micrura alaskensis " species complex. "
[Show abstract] [Hide abstract] ABSTRACT: Sipunculans (also known as peanut worms) are an ancient group of exclusively marine worms with a global distribution and fossil record that dates back to the Early Cambrian. The systematics of sipunculans, now considered a distinct subclade of Annelida, has been studied for decades using morphological and molecular characters, and has reached the limits of Sanger-based approaches. Here, we reevaluate their family-level phylogeny by comparative transcriptomic analysis of eight species representing all known families within Sipuncula. Two data matrices with alternative gene occupancy levels (large matrix with 675 genes and 62% missing data; reduced matrix with 141 genes and 23% missing data) were analysed using concatenation and gene-tree methods, yielding congruent results and resolving each internal node with maximum support. We thus corroborate prior phylogenetic work based on molecular data, resolve outstanding issues with respect to the familial relationships of Aspidosiphonidae, Antillesomatidae and Phascolosomatidae, and highlight the next area of focus for sipunculan systematics. Copyright © 2014. Published by Elsevier Inc.
- "They are also emerging as important non-model organisms for evolutionary and developmental biology, or evo-devo (Schulze and Rice, 2009b; Wanninger et al., 2005, 2009; Wanninger, 2008; Boyle and Seaver, 2010; Boyle and Rice, 2014). Fourth, due to an extended larval phase described for several species within multiple families (Scheltema and Hall, 1965, 1975; Rice, 1976, 1981; Scheltema and Rice, 1990), sipunculans constitute an interesting group for studying dispersal within and between widely separated oceanic regions, which is a topic addressed in several recent studies of cosmopolitanism in the marine realm (Staton and Rice, 1999; Kawauchi and Giribet, 2010; Kawauchi and Giribet, 2013; Schulze et al., 2012; Young et al., 2012; Lemer and Planes, 2014). These and similar studies rely upon robust phylogenetic hypotheses, from species to family-level relationships, to provide a stable evolutionary framework for critical re-interpretation of previous research, and to guide future investigations. "