Egg fertilisation in a freshwater mussel: effects of distance, flow and male density

  • Authors: Mosley, Tyler L.; Haag, Wendell R.; Stoeckel, James A.
  • Publication Year: 2014
  • Publication Series: Scientific Journal (JRNL)
  • Source: Freshwater Biology 59(10) 2137-2149
  • DOI: 10.1111/fwb.12417


1. Small or sparse populations can experience Allee effects if egg fertilisation is reduced because of a shortage of sperm.
2. Freshwater mussels are spermcasters that often occur as sparse, patchy populations. Previous studies suggested that sperm shortage limits these populations unless facultative hermaphroditism and selffertilisation occur at low density. We conducted experiments in ponds to examine fertilisation in the mussel, Lampsilis straminea, in response to flow, presence of and distance from males, male density, and the presence of upstream females that could compete for sperm with downstream females.
3. Self-fertilisation in the absence of males did not occur in either experiment. Female fertilisation success was uniformly high in most treatments and was not related to flow or distance from males (1–25 m). Fertilisation success was significantly lower at low male density (0.02 m-2, compared with 0.16 m-2) but remained relatively high even in most low male density treatments. The proportion of females that became gravid was higher in the presence of upstream females, but fecundity was significantly lower when upstream females were present; these conflicting results made it difficult to assess the role of competition among females for sperm.
4. Overall, high fertilisation success occurred at densities three orders of magnitude lower than previously proposed thresholds for mussels. Sperm dispersal and acquisition and egg fertilisation appear to be complex processes associated with adaptations for spermcasting. These adaptations are likely to facilitate persistence at low population density and buffer mussels from reproductive Allee effects

  • Citation: Mosley, Tyler L.; Haag, Wendell R.; Stoeckel, James A. 2014. Egg fertilisation in a freshwater mussel: effects of distance, flow and male density. Freshwater Biology. 59(10): 2137-2149. 13 p. 10.1111/fwb.12417
  • Keywords: Allee effects, fertilisation, population density, spermcasting, unionid
  • Posted Date: October 14, 2015
  • Modified Date: October 20, 2015
  • Requesting Print Publications

    Publication requests are subject to availability. Fiscal responsibility limits the hardcopies of publications we produce and distribute. Electronic versions of publications may be downloaded, distributed and printed.

    Please make any requests at

    Publication Notes

    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
    • Our online publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unusable.
    • To view this article, download the latest version of Adobe Acrobat Reader.