Changing climate and increasing anthropogenic impact affect the diversity of marine invertebrates, particularly mollusks. This diversity originated mostly from the historical migration and formation of adapted populations in the previous periods of climate change. Sea vessels also play a certain role in dispersal of some species, which survive in new locations under favorable conditions.

Gantsevich M, Strelkov P (2017) Dynamics of Genetic and Morphological Diversity of Marine Mollusks Related to Climate and Human-Caused Environmental Changes. Ann Aquac Res 4(1): 1028.

•    Diversity
•    Marine mollusks
•    Migrations
•    Climate

The analysis of ecological and genetic plasticity of species related to the factors that determine the limits of species distribution is considered to be one of the fundamental problems of biogeography [1-3]. Global climatic changes have a great effect the dynamics of species distribution. The long-term climate change, which is more pronounced in the temperate zone, affects physiology and population structure of many marine species, particularly mollusks. For example, the average annual water temperature in the North Sea has increased by 1°C over the past two decades, which probably led to reduction of the reproductive potential, survival rate, and retardation of the population growth in Macoma balthica in the Danish Wadden Sea – the area of the longest continuous intertidal monitoring in Northern Europe [4]. It is important now to understand the origin of genetic and morphological diversity, because of its decisive effect on the distribution of species in changing environmental conditions.

The development of the modern fauna in seas of Northern Europe began in the Pliocene (3.5 million years ago), when the opening of the Bering Strait allowed further exchange between the Pacific and Atlantic marine faunas after a long period of isolation. Such common North Atlantic species, as Macoma, Mya, Mytilus, Asterias, and some other used the strait to migrate to Europe via the Arctic [5-7]. During the most Pleistocene, the Pacific and Atlantic basins were once again isolated, which resulted in divergence between the Atlantic and Pacific populations of these species [8]. During the period of warming that began in the late Pleistocene, trans-Arctic migrations of boreal species started again, which caused their secondary contacts and hybridization in formerly isolated populations. The evidence of such secondary contacts in the Holocene is the presence of hybrid zones, where “pure” Atlantic and Pacific forms (species) coexist now with hybrids.

During the Pleistocene isolation, some species inhabiting both Atlantic and Pacific in the Pliocene diverged, which can be traced on morphological and genetic levels. The other species, particularly the majority of bivalves retained similar morphological characteristics, but diverged genetically [8,9].

Morphological diversity of individuals in different populations is determined by numerous factors and can be observed at different geographic scales [6]. Scientific discussions on the mechanism of latitudinal diversity of species are usually focused on physiological and ecological aspects. Thus, many hypotheses on changes in the body size of both invertebrates and vertebrates along latitudinal gradients are based on availability of food/energy resources (species-energy hypothesis, [10]). Biogeographical and evolutionary contexts of existing morphological diversity are often neglected [6].

Phylogeographic research confirms the fact that genetic diversity within the species range develops historically as a result of changes in spatial distribution induced by climatic factors [11]. In unfavorable and unstable habitats at the edge of the species range, increased phenotypic and genetic diversity could be caused by disruptive selection [12]. Thus, extreme conditions could promote intensification of selection [13]. On the other hand, at the edge of the range populations are often “ephemeral”, they arise due to immigration of individuals from the central parts of the range and die out at times under the impact of stochastic environmental and (or) demographic factors. Genetic drift proved to be the prevailing factor in genetic dynamics of these populations, which are also characterized by reduced intra-population and increased inter-population genetic diversity [3,5].

Finally, human-caused environmental changes also affect phenotypic and genetic diversity. Well-developed sea transport routes promote dispersal of opportunistic species, because larvae of marine invertebrates can survive for a long time in the water pumped into ballast tanks of sea vessels and thus be carried a long way to new localities close to the destination seaport. More than 7000 species of marine invertebrates, including Macoma balthica, Mytilus edulis, and Cerastoderma edule travel every day across the world ocean in ballast waters. Well-known introduced species are Dreissena polymorpha, Carcinus maenas, and Rapana venosa [14].

Authors are grateful to Marina Katolikova and Larisa Basova from Department of Ichthyology and Hydrobiology, Faculty of Biology, Saint-Petersburg State University for help in analyzing literature data.

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