Authors: Richard M Allen and Dustin J Marshall
Published in: PloS ONE, volume 9, issue 7 (July 2014)
The optimal balance of reproductive effort between offspring size and number depends on the fitness of offspring size in a particular environment.
The variable environments offspring experience, both among and within life-history stages, are likely to alter the offspring size/fitness relationship and favor different offspring sizes. Hence, the many environments experienced throughout complex life-histories present mothers with a significant challenge to optimally allocate their reproductive effort.
In a marine annelid, we tested the relationship between egg size and performance across multiple life-history stages, including: fertilization, larval development, and post-metamorphosis survival and size in the field.
We found evidence of conflicting effects of egg size on performance: larger eggs had higher fertilization under sperm-limited conditions, were slightly faster to develop pre-feeding, and were larger post-metamorphosis; however, smaller eggs had higher fertilization when sperm was abundant, and faster planktonic development; and egg size did not affect post-metamorphic survival.
The results indicate that egg size effects are conflicting in H. diramphus depending on the environments within and among life-history stages. We suggest that offspring size in this species may be a compromise between the overall costs and benefits of egg sizes in each stage and that performance in any one stage is not maximized.
Allen RM, Marshall DJ (2014) Egg size effects across multiple life-history stages in the marine annelid Hydroides diramphus. PLoS ONE 9(7): e102253 PDF 250 KB diramphus doi:10.1371/journal.pone.0102253
Authors: Scott C Burgess, Michael Bode and Dustin J Marshall
Published in: Functional Ecology doi: 10.1111/1365-2435.12080
Much of the theory on offspring size focuses on the effects of habitat quality on the relationship between offspring size and fitness. Habitat spacing may be another important factor that affects selection on offspring size when offspring disperse prior to colonization and accrue deferred costs that are mediated by offspring size.
We developed a theoretical model, based on a well-known optimality model, of how selection on offspring size changes with dispersal distance. The model assumes that offspring fitness depends on both offspring size and dispersal duration and that dispersal time and distance are positively related. Such assumptions are based on thousands of marine invertebrate species with non-feeding larvae, but our model also applies more generally to any organism where offspring size modifies the energetic costs of dispersal, and there is a positive relationship between dispersal duration and distance.
Our model predicts that, even when habitat quality does not vary, more isolated habitats may favour the production of fewer, larger offspring if smaller offspring incur greater deferred costs of dispersal. We then empirically demonstrate that offspring size and dispersal duration have interactive effects on post-settlement survival in a marine invertebrate (Bugula neritina), and such size-dependent deferred costs of dispersal are of a magnitude sufficient enough to potentially favour larger offspring in isolated habitats.
Together, our results indicate that the spatial pattern of suitable habitat could impose very different selective regimes on offspring size compared with the effects of habitat quality. Furthermore, our predictions contrast to those predicted for seed size and dispersal in plants, where the production of smaller, more numerous seeds is often a more efficient way for mothers to access distant, suitable habitat.
Burgess SC, Bode M, Marshall DJ (2013) Costs of dispersal alter optimal offspring size in patchy habitats: combining theory and data for a marine invertebrate. Functional Ecology PDF 329 KB doi: 10.1111/1365-2435.12080
Authors: Dustin J Marshall, Patrick J Krug, Elena K Kupriyanova, Maria Byrne and Richard B Emlet
Published in: Annual Review of Ecology, Evolution and Systematics, volume 43, pp. 97–114, doi: 10.1146/annurev-ecolsys-102710-145004
Biologists have long sought to identify and explain patterns in the diverse array of marine life histories. The most famous speculation about such patterns is Gunnar Thorson’s suggestion that species producing planktonic larvae are rarer at higher latitudes (Thorson’s rule). Although some elements of Thorson’s rule have proven incorrect, other elements remain untested.
With a wealth of new life-history data, statistical approaches, and remote-sensing technology, new insights into marine reproduction can be generated.
We gathered life-history data for more than 1,000 marine invertebrates and examined patterns in the prevalence of different life histories. Systematic patterns in marine life histories exist at a range of scales, some of which support Thorson, whereas others suggest previously unrecognized relationships between the marine environment and the life histories of marine invertebrates.
Overall, marine life histories covary strongly with temperature and local ocean productivity, and different regions should be managed accordingly.
Marshall DJ, Krug PJ, Kupriyanova EK, Byrne M, Emlet RB (2012) The biogeography of marine invertebrate life-histories. Annual Review of Ecology, Evolution and Systematics, 43: 97–114 e-print doi: 10.1146/annurev-ecolsys-102710-145004