Biological and ecological mechanisms for overcoming sperm limitation in invasive dreissenid mussels

Abstract

Many broadcast-spawning benthic invertebrates are subject to sperm limitation yet achieve high population densities, as for example dreissenid mussels (Dreissena polymorpha and Dreisssena bugensis) that were introduced into the Laurentian Great Lakes. The question remains whether biological or ecological/physical mechanisms reduce sperm limitation. Gamete dilution/longevity experiments were undertaken to determine whether dreissenid mussels are subject to sperm limitation, and computational fluid dynamic modeling was used to determine the potential influence of bottom roughness on sperm dilution in nature. Results indicated that dreissenid mussels may be sperm limited, but the extent to which sperm dilution affects them is lower than what was reported for other broadcast spawning invertebrates. Importantly, model mussel clusters influenced external fertilization by retaining sperm in downstream eddies but allowing downstream transport from one cluster to another. This, in addition to high sperm potency at low sperm concentrations, may help to explain the success of dreissenid mussels as invasive species.

The effect of near‐bed turbulence on sperm dilution and fertilization success of broadcast‐spawning bivalves

“…This was the case for both D. polymorpha and D. bugensis in the laboratory and for D. bugensis in the field, and thus we conclude that these dreissenid species are sperm limited. These results are also consistent with computational fluid dynamic models of sperm dilution and transport, which predicted an increase in dilution with distance under the influence of mussel roughness (Quinn and Ackerman 2011). D. polymorpha and D. bugensis are the first freshwater broadcast spawners that have been demonstrated to be sperm limited.…”

“…Bottom roughness influenced the fluid dynamic environment of the near‐bed region, which has been predicted to affect fertilization success as well as larval settlement (Crimaldi et al 2002; Quinn and Ackerman 2011). In this study, it was the abrupt change in bottom roughness (e.g., space between mussel patches) that led to downstream recirculation, which enhanced fertilization success.…”

“…Sperm concentrations were determined through four replicate hemocytometer counts. Fertilization rates were determined by counting the number of eggs with polar bodies on the first 200 eggs encountered under a compound microscope (Quinn and Ackerman 2011), because a polyspermy blocking mechanism has been demonstrated in D. polymorpha (Sprung 1993; Fallis et al 2010).…”

The effect of bottom roughness on scalar transport in aquatic ecosystems: Implications for reproduction and recruitment in the benthos

“…However, it should be noted that an alternate choice of λ and k could have resulted in different λ/k ratios leading to isolated-roughness and wake-interference flows, where settlement would likely increase. Quinn and Ackerman (2011, 2012, 2014, found that mussel shells placed uniformly at high density on the bottom of a flow chamber led to skimming flow, in contrast to wake-interference flow observed under a low mussel-density configuration.…”

“…To the best of our knowledge, this is the first study to examine scalar transport in the near-bed region as it is influenced by bottom roughness of differing geometries and λ/k ratios. This comparison, which is pertinent to benthic organisms in general, builds on results from models of sperm transport over roughness elements of different roughness height, k (Quinn and Ackerman, 2012). In that case, the results indicate that above a certain k, scalar (sperm) released within the space between two roughness elements was retained within the space rather than being transported downstream.…”