Out of Alaska: morphological diversity within the genus Eurytemora from its ancestral Alaskan range (Crustacea, Copepoda)

Abstract

The copepod genus Eurytemora occupies a wide range of habitat types throughout the Northern Hemisphere, with among the broadest salinity ranges of any known copepod. The epicenter of diversity for this genus lies along coastal Alaska, where several species are endemic. Systematic analysis has been difficult, however, because of a tendency toward morphological stasis in this genus, despite large genetic divergences among populations and species. The goals of this study were to (1) analyze patterns of morphological variation and divergence within this genus, focusing on Eurytemora species that occur in North America, and (2) determine patterns of geographic and salinity distribution of Eurytemora species within the ancestral range in Alaska. We applied a comparative multivariate morphological analysis using 16-26 characters from 125 specimens from 20 newly collected sites in Alaska and 15 existing samples predominantly from North America. Results from principal component and hierarchical cluster analyses identified seven distinct morphological species of Eurytemora in North America (E. affinis, E. americana, E. canadensis, E. composita, E. herdmani, E. pacifica, and E. raboti), and identified diagnostic characters that distinguish the species (forming the basis for a new identification key). Several previously named species were regarded as synonyms. The sites we sampled in Alaska were remarkable in the high levels of sympatry of Eurytemora species, to a degree not seen outside of Alaska. Future studies of Eurytemora should shed light on patterns of habitat invasions and physiological evolution within the genus, and yield insights into mechanisms leading to its remarkably broad geographic and habitat range.

Santa Rosalia, the icon of biodiversity

“…The idea that each predator has at least twice the mass (or 1.26 the linear dimensions) of its prey, and that a ratio of sizes varying from 1.1 to 1.4 (with the mean ratio being roughly 1.3) is necessary to permit two species to co-occur in different niches but at the same level of a food web, are further hypotheses contained in the ''Homage.' ' Dodson et al (2010) found this latter ratio consistent with their observations on co-occurring Eurytemora species. However, taking into account that observations of body size from fieldcaught samples cannot reveal whether body size displacement is the result of phenotypic plasticity or selection, the authors underline that body size displacement according to Hutchinson's hypothesis would be a consequence of natural selection acting to reduce competition between species.…”

“…The importance of niche diversity and allopatric speciation (eventually followed by secondary recolonization) for generating species diversity, as expressed by Hutchinson, is the driving hypothesis in the article by Dodson et al (2010) to explain the morphological diversity within the eurihaline genus Eurytemora from its ancestral Alaskan range. The idea that each predator has at least twice the mass (or 1.26 the linear dimensions) of its prey, and that a ratio of sizes varying from 1.1 to 1.4 (with the mean ratio being roughly 1.3) is necessary to permit two species to co-occur in different niches but at the same level of a food web, are further hypotheses contained in the ''Homage.'…”

Feeding, survival, and reproduction of two populations of Eurytemora (Copepoda) exposed to local toxic cyanobacteria

“…Tolerance to abiotic factors may facilitate dispersal success (Dodson et al, 2010;Hirsch et al, 2016), suggesting that tolerance to cyanobacteria could also promote the invasion of Eurytemora to new ecosystems, as seen in Lake Michigan. Lee et al (2013) showed that high food availability and tolerance to lower salinity also promote invasions by Eurytemora to new systems.…”

“…It was later reported in Lake Michigan by Robertson (1966), and since the late 1960s the species is found in both littoral areas and pelagic plankton communities in Green Bay (Gannon, 1974). The species complex has spread multiple times independently from brackish water to freshwater, and established clades in different parts of the world due to its ability to adapt locally (Dodson et al, 2010). There are at least six recognized clades of E. affinis; one clade in Asia, one in Europe, and four in America (Lee, 2000), with recent studies indicating that North American clades represent a separate species (E. carolleeae; Alekseev and Souissi, 2011;Vasquez et al, 2016).…”

New extension range and complementary description of Eurytemora americana (Calanoida: Temoridae) in northern Korea

“…The genus has hitherto been recorded exclusively from subtropical to subarctic, but with the increasing species diversity toward northern latitudes (Dodson et al 2010). Most of the Eurytemora are characterized by a wide habitat distribution ranging from the open ocean waters, coastal marine, hypersaline salt marshes, and brackish estuaries, to completely freshwaters (Heron and Damkaer 1976;Lee 2000;Dodson et al 2010).…”