Historical faunal exchange between the Pontocaspian Basin and North America

Abstract

Ecrobia is a genus of small brackish‐water mud snails with an amphi‐Atlantic distribution. Interestingly, the species occurring in the northwestern Atlantic, Ecrobia truncata, is more closely related to the Pontocaspian taxa, Ecrobia grimmi and Ecrobia maritima, than to the species occurring in the northeastern Atlantic and Mediterranean Sea. At least three colonization scenarios may account for this peculiar biogeographical pattern: (1) a recent human‐mediated dispersal, (2) a historical transatlantic interchange, and (3) a historical transpolar interchange. To test these three scenarios, we used five operational criteria—time of species divergence, first appearance in the fossil record, dispersal limitation as well as environmental filtering and biotic interactions along the potential migration routes. Specifically, we inferred a time‐calibrated molecular phylogeny for Ecrobia and reconstructed a paleogeographical map of the Arctic Ocean at 2.5 million years ago (Mya). Based on the five operational criteria, scenarios 1 and 2 can likely be rejected. In contrast, all criteria support scenario 3 (historical transpolar interchange). It is therefore suggested that a bird‐mediated and/or ocean current‐mediated faunal interchange via the Arctic Ocean occurred during the Late Pliocene or Early Pleistocene. This dispersal was likely facilitated by reduced distances between the Eurasian and North American/Greenland landmasses, marine introgressions, and/or a stepping‐stone system of brackish‐water habitats in northern Siberia, as well as a lack of competition along the migration route. As for the direction of dispersal, the scientific data presented are not conclusive. However, there is clearly more support for the scenario of dispersal from the Pontocaspian Basin to North America than vice versa. This is the first study providing evidence for a natural faunal exchange between the Pontocaspian Basin and North America via the Arctic Ocean.

Two new genera and three new subterranean species of Hydrobiidae (Caenogastropoda: Truncatelloidea) from Tunisia

“…The two new genera presented in this study raises the number of genera of Hydrobiidae sensu stricto in Tunisia to seven (Pseudamnicola, Hydrobia, Ecrobia Stimpson, 1865, Mercuria, Bullaregia, Belgrandiellopsis gen. nov., Biserta gen. nov.;Wilke et al 2002;Glöer et al 2010;Delicado et al 2015;Khalloufi et al 2017;Vandendorpe et al, 2019) and to eight for North Africa (García et al 2010). The three subterranean genera recovered here as a monophyletic group (i.e., the Tunisian clade) are as genetically divergent (8.0-9.2% COI p-distances) as within other clades of hydrobiid subterranean genera (e.g., 7.8-11.8% COI p-distances; Osikowski et al 2017).…”

Fresh- and Brackish-Water Cold-Tolerant Species of Southern Europe: Migrants from the Paratethys That Colonized the Arctic

“…The gastropod genus Ecrobia has a vast range [112,113]. Ecrobia truncata (Vanatta, 1924) is widespread in the northeast of North America, the range of E. ventrosa (Montagu, 1803) covers Western and Northern Europe and the Mediterranean region.…”

“…Although Ecrobia is not the only representative of aquatic organisms that have spread throughout the Paratethys and the Mediterranean and then crossed the Atlantic Ocean (as noted above, the Atlantic salmon and three-spined stickleback also crossed the Atlantic), the mechanism and route of Ecrobia migration remain unknown. According to Vandendorpe et al [112], genetic data allow three possibilities to be considered: (1) recent human-mediated dispersal, (2) historical transatlantic interchange, and (3) historical transpolar interchange, the last scenario being considered more probable by the authors of the cited paper.…”

“…The migration of cold-water species from the Black Sea basin to the Mediterranean apparently occurred much later and on a limited scale. In particular, the mollusk Ecrobia maritima, typical of the Black Sea [112], and individuals of brown trout carrying the mitochondrial DNA haplotypes typical of the Black Sea basin [76] are quite rare in the Mediterranean basin.…”

“…Most probably, Ecrobia mollusks in North America are also of the Mediterranean origin, their ancestors having migrated there following the path of the ancestors of the Atlantic salmon. This conclusion is based on the fact that E. maritima, a species close to the North American species E. truncata, lives in the Adriatic Sea [112], in the same region as Salmo obtusirostris.…”