Behavioral Ecology and Sociobiology

, Volume 57, Issue 1, pp 17–22 | Cite as

Apparent sibling rivalry in the freshwater fingernail clam Sphaerium striatinum

  • Mark A. BeekeyEmail author
  • Ronald H. Karlson
Original Article


In Sphaerium striatinum, a freshwater brooding bivalve, up to 97.5% of offspring that adults initially produce fail to reach independence. Marsupial sacs, specialized extensions of gill filaments that act as nurseries, initially contain multiple offspring in various sizes and stages of development. However, by the time offspring reach later stages of development, marsupial sacs typically contain only one offspring. Brood mortality is hypothesized to be the result of competition among embryos for nutrients and/or space. Sphaeriid eggs do not contain enough yolk for offspring to complete development. Adults supply additional nutrients required to reach independence. Brood capacity is limited by adult size. Adults cannot physically brood all offspring they produce. Here, we examine the validity of the competition hypothesis for brood mortality. We reared offspring, in vitro, through metamorphosis under varying nutrient levels and embryo densities. While hatching success and time to hatching were not influenced by nutrients or density, both factors had significant effects on the percentage of embryos completing metamorphosis and timing of metamorphosis. A higher percentage of offspring completed metamorphosis in higher nutrient levels and lower densities. Offspring reared with higher nutrient levels and lower densities also completed metamorphosis more rapidly. We discuss these results in relation to hypotheses for the overproduction of offspring, sibling rivalries, as well as factors that might explain brood mortality in this species.


Bivalves Brooding Brood mortality Sibling rivalry 



We would like to thank Daniel Carson and the Department of Biological Sciences for supporting this research through a small departmental supplementation grant, Cindy Farrach-Carson for the use of laboratory facilities, Melinda Duncan for suggestions on rearing and observing embryos in vitro, Ed Walls and the Maryland Department of Natural Resources for allowing us to collect specimens in the Fair Hill Natural Resources Management Area, and Mike Hadfield for aiding us in our identification of embryonic stages. We would also like to thank three anonymous reviewers whose comments greatly improved the theoretical context of this manuscript. Lastly we would like to thank Daniel Hornbach, Gerald Mackie, and William Heard for their helpful suggestions and comments with regard to brood mortality in sphaeriids. All experiments comply with U.S. laws regarding animals.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Department of Biological SciencesUniversity of DelawareNewarkUSA
  2. 2.Department of BiologyUniversity of PennsylvaniaPhiladelphiaUSA

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