To remain or leave: Dispersal variation and its genetic consequences in benthic freshwater invertebrates
Authors: Ruggeri Paolo , Pasternak Ellen , Okamura Beth 
Published: October 2019

Variation in dispersal capacity may influence population genetic variation and relatedness of freshwater animals thus demonstrating how life‐history traits influence patterns and processes that in turn influence biodiversity. The majority of studies have focused on the consequences of dispersal variation in taxa inhabiting riverine systems whose dendritic nature and upstream/downstream gradients facilitate characterizing populations along networks. We undertook extensive, large‐scale investigations of the impacts of hydrological connectivity on population genetic variation in two freshwater bryozoan species whose dispersive propagules (statoblasts) are either attached to surfaces (Fredericella sultana) or are released as buoyant stages (Cristatella mucedo) and that live primarily in either lotic (F. sultana) or lentic environments (C. mucedo). Describing population genetic structure in multiple sites characterized by varying degrees of hydrological connectivity within each of three (or four) UK regions enabled us to test the following hypotheses: (1) genetic diversity and gene flow will be more influenced by hydrological connectivity in populations ofC. mucedo(becauseF. sultanadispersal stages are retained); (2) populations ofF. sultanawill be characterized by greater genetic divergence than those ofC. mucedo(reflecting their relative dispersal capacities); and (3) genetic variation will be greatest inF. sultana(reflecting a propensity for genetic divergence as a result of its low dispersal potential). We found that hydrological connectivity enhanced genetic diversity and gene flow amongC. mucedopopulations but not inF. sultanawhile higher overall measures of clonal diversity and greater genetic divergence characterized populations ofF. sultana. We suggest that genetic divergence over time withinF. sultanapopulations reflects a general constraint of releasing propagules that might eventually be swept to sea when taxa inhabit running waters. In contrast, taxa that primarily inhabit lakes and ponds may colonize across hydrologically connected regions, establishing genetically related populations. Our study contributes more nuanced views about drivers of population genetic structures in passively dispersing freshwater invertebrates as outlined by the Monopolization Hypothesis (Acta Oecologica, 23, 2002, 121) by highlighting how a range of demographic and evolutionary processes reflect life‐history attributes of benthic colonial invertebrates (bryozoans) and cyclically parthenogenetic zooplankton. In addition, growing evidence that genetic divergence may commonly characterize populations of diverse groups of riverine taxa suggests that organisms inhabiting lotic systems may be particularly challenged by environmental change. Such change may predispose riverine populations to extinction as a result of genetic divergence combined with limited dispersal and gene flow.

Open Research Badges

This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available athttps://doi.org/10.5061/dryad.1tm8705.