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Maternal effects on cloning frequency, larval development, and juvenile size in the seastar Asterias forbesi
Blackburn, Holly N.
Blackburn, Holly N.
Abstract
A fundamental life-history trade-off occurs between the size and number of offspring that a female produces. Traditionally, biologists have assumed that there is a species-specific optimal egg size, the value of which can fluctuate with changing environmental parameters. However, in unpredictable environments a bet-hedging strategy resulting in variable offspring sizes may be favored. The seastar Asterias forbesi can produce viable eggs that vary more than three-fold in volume within a single clutch (141µm - 212µm diameter). Compared to 12 other echinoderm species with similar modes of development (planktotrophic), A. forbesi represents an organism with unusual intra-clutch variation in egg size. In addition, the larvae derived from these eggs have frequently been observed to produce clones. To test for maternal effects on cloning frequency and larval development I reared cultures of large (190µm mean diameter) or small (140µm mean diameter) sibling embryos. Previous studies have shown that exogenous cues can alter the frequency of cloning, but it is unclear whether endogenous reserves might also influence cloning. My results suggest that despite an initial disadvantage in energy reserves, small larvae produced clones at frequencies similar to their larger siblings. Since little is known about the links between maternal investment and juvenile quality in seastars, I continued to follow these larvae and examined the effect of maternal investment on time to and size at metamorphosis. Small larvae took about two additional days to reach metamorphosis compared to large larvae, which was a 6.3% increase in developmental time. Size at metamorphosis did not appear to be affected by maternal investment and varied greatly within size classes. To further examine the costs of delayed metamorphosis, I set up an additional experiment, which examined the effect of time to settlement on post-metamorphic survivability in juveniles. My results indicate that size at settlement, rather than time to settlement, is correlated with survivability.
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Thesis is part of Honors ETD pilot project, 2008-2013. Migrated from Dspace in 2016.
Date
2013-07-09
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Keywords
Cloning, Metamorphosis, Maternal investment, Egg size variation, Bet-hedging
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Department
Biology