Gamete plasticity in a broadcast spawning marine invertebrate

Crean, A. and Marshall, D. (2008) Gamete plasticity in a broadcast spawning marine invertebrate. Proceedings of the National Academy of Sciences of the United States of America, 105 36: 13508-13513. doi:10.1073/pnas.0806590105


Author Crean, A.
Marshall, D.
Title Gamete plasticity in a broadcast spawning marine invertebrate
Journal name Proceedings of the National Academy of Sciences of the United States of America   Check publisher's open access policy
ISSN 0027-8424
Publication date 2008-09
Sub-type Article (original research)
DOI 10.1073/pnas.0806590105
Open Access Status Not Open Access
Volume 105
Issue 36
Start page 13508
End page 13513
Total pages 6
Place of publication United States
Publisher National Academy of Sciences
Collection year 2009
Language eng
Subject C1
9608 Flora, Fauna and Biodiversity
0602 Ecology
06 Biological Sciences
Abstract Sperm competition has classically been thought to maintain anisogamy (large eggs and smaller sperm) because males are thought to maximize their chance of winning fertilizations by trading sperm size for number. More recently it has been recognized that sperm quality (e.g., size, velocity) can also influence sperm competition, although studies have yielded conflicting results. Because sex evolved in the sea, debate has continued over the role of sperm competition and sperm environment in determining both sperm and egg size in externally fertilizing broadcast spawners. Remarkably, however, there have been no direct tests of whether broadcast spawners change the traits of their gametes depending on the likelihood of sperm competition. We manipulated the density (and thus, sperm environment) of a broadcast spawning ascidian (Styela plicata) in the field and then determined whether the phenotype of eggs and sperm changed. We found that sperm from adults kept at high density were larger and more motile than sperm from low-density adults. In vitro fertilizations revealed that sperm from high-density adults also lived longer and induced less polyspermy. Adult density also affected egg traits: eggs from high-density adults were smaller targets for sperm overall but produced larger ovicells than eggs from low-density adults. This suggests that broadcast spawning mothers balance (potentially conflicting) pre- and postzygotic selection pressures on egg size. Overall, our results suggest that sperm competition does not represent a strong force maintaining anisogamy in broadcast spawners. Instead, sperm limitation seems to select for large eggs and smaller, more numerous sperm.
Formatted abstract
Sperm competition has classically been thought to maintain anisogamy (large eggs and smaller sperm) because males are thought to maximize their chance of winning fertilizations by trading sperm size for number. More recently it has been recognized that sperm quality (e.g., size, velocity) can also influence sperm competition, although studies have yielded conflicting results. Because sex evolved in the sea, debate has continued over the role of sperm competition and sperm environment in determining both sperm and egg size in externally fertilizing broadcast spawners. Remarkably, however, there have been no direct tests of whether broadcast spawners change the traits of their gametes depending on the likelihood of sperm competition. We manipulated the density (and thus, sperm environment) of a broadcast spawning ascidian (Styela plicata) in the field and then determined whether the phenotype of eggs and sperm changed. We found that sperm from adults kept at high density were larger and more motile than sperm from low-density adults. In vitro fertilizations revealed that sperm from high-density adults also lived longer and induced less polyspermy. Adult density also affected egg traits: eggs from high-density adults were smaller targets for sperm overall but produced larger ovicells than eggs from low-density adults. This suggests that broadcast spawning mothers balance (potentially conflicting) pre- and postzygotic selection pressures on egg size. Overall, our results suggest that sperm competition does not represent a strong force maintaining anisogamy in broadcast spawners. Instead, sperm limitation seems to select for large eggs and smaller, more numerous sperm.
Keyword anisogamy
sperm competition
adaptive maternal effect
transgenerational plasticity
Q-Index Code C1
Q-Index Status Confirmed Code

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2009 Higher Education Research Data Collection
School of Biological Sciences Publications
Ecology Centre Publications
 
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Citation counts: TR Web of Science Citation Count  Cited 51 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 51 times in Scopus Article | Citations
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Created: Wed, 10 Dec 2008, 11:33:49 EST by Gail Walter on behalf of School of Biological Sciences