Cryptic species in marine polychaete and their independent introduction from North America to Europe

Abstract

The vast body of ballast water carried across oceans by freight ships represents a major source for the introduction of foreign species into marine ecosystems. The worm Marenzelleria viridis, originally found only in North America, appeared in estuaries of the North Sea in 1979 and 6 years later also in the Baltic, where it has developed into a major faunal element. Two competing hypotheses are discussed here: either both populations owe their presence to a single introductory event in the North Sea, or each population originated from a separate introduction. Our phylogeographic analysis of Baltic, North Sea and American Marenzelleria, based on mitochondrial 16S rDNA sequences (326-bp segment) of 98 individuals from 17 localities on the North American, North Sea, and Baltic coasts not only favors the two-event hypothesis, but also separates the locations of origin for the introductions. Eighteen mitochondrial genotypes were identified altogether. In agreement with allozyme data, three lineages were identified: genotypes assigned to the same lineage differed from each other by up to 5 point mutations, and those assigned to different lineages differed by up to 17. The existence of three morphologically indistinguishable, and thus cryptic, species is therefore suggested. The individuals from the Baltic Sea probably originated from the Atlantic coast of the United States between Chesapeake Bay and Georgia, and the North Sea populations may stem from the U.S. coast region north of Chesapeake Bay to Nova Scotia. Despite their similar morphologies, the two European Marenzelleria species may differ ecologically with respect to their preference for habitat salinity. Assuming that transport via ballast water occurs quite frequently, we hypothesize that both European cryptic species of Marenzelleria may originally have been introduced to both the North Sea and the Baltic Sea but that neither of them was able to proliferate in both water bodies owing to their differential physiological performances at high and low salinities.

Vicariance and Dispersal Effects on Phylogeographic Structure and Speciation in a Widespread Estuarine Invertebrate

“…Studies of geographic range and life history may overlook patterns of diversity and underlying evolutionary processes, particularly in diverse marine communities where barriers to gene flow are not readily apparent (Palumbi 1994;Bastrop et al 1998;Knowlton 2000;Rocha-Olivares et al 2001;Hebert et al 2003a). Estuaries are excellent systems with which to address this issue, though studies have failed to explicitly identify the geographic background against which this might occur (Bilton et al 2002).…”

“…3) with the break occurring across Cape Hatteras, where steep temperature gradients and currents converge at the Virginian and Carolinian provincial boundaries (Palumbi 1994; Engle and Summers 1999). Here, breaks or range point ends in other species are linked to dispersal ability and the physical conditions (Saunders et al 1986;Bastrop et al 1998;Jones and Quattro 1999;Collin 2001), which likely preclude gene flow through vicariance or selection (Palumbi 1994;Sotka et al 2004;Stevens and Hogg 2004).…”

“…For example, in the nestbrooding tidewater goby, Eucyclogobbius newberryi, populations along the Californian coast experience little gene flow (Dawson et al 2001). Likewise, studies of sessile estuarine polychaetes demonstrated strong genetic structure along North American and European coasts (Bastrop et al 1998;Virgilio and Abiatti 2004). It should be noted, however, that population structure can evolve even without the prerequisite of low dispersal potential.…”

Cryptic invasion by a non-native genotype of the common reed,Phragmites australis, into North America

“…Both the actual number of invaders and the impacts of these species may be underestimated because of the presence of cryptic invaders, or species that cannot be easily classified as native or introduced (3). Over the past decade, use of PCR-based molecular techniques have revealed repeated occurrences of such invasions in marine ecosystems (4)(5)(6), and studies have demonstrated both genetic and physiological differences between invading and native populations (6). Given that cryptic invaders typically are unrecognized or are mistaken for native species, knowledge of historical trends in geographic distribution and population genetic structure in cases of suspected introductions are of particular interest when trying to reconstruct the invasion history of a species.…”

Genetic evidence for parapatric differentiation of two forms of the brackish-water nereidid polychaete Hediste atoka

“…Many examples of cryptic differentiation have been revealed by molecular techniques in polychaetes (Bastrop et al 1998, Westheide & Hass-Cordes 2001, Jolly et al 2004, Audzijonyte et al 2008, Virgilio et al 2009). …”