Strathmann, R. R.. University of Washington, email@example.com
Staver, J. R.. University of Washington, firstname.lastname@example.org
EVOLUTION OF CELL CYCLE DURATIONS AND TIME TO FIRST SWIMMING OF PLANKTONIC EMBRYOS
Planktonic embryos are apparently under selection for rapid development and early locomotion. They have shorter early embryonic cell cycles than brooded or encapsulatedembryos and also swim at earlier stages. If a planktonic embryo is a device for rapidly bridging the gap between zygote and first swimming, how well do different embryos perform this function? For a sample of planktonic embryos from 8 phyla, time to first swimming was not discernibly associated with type of ciliation (uniciliated versus multiciliated cells), cleavage pattern, or processes specifying body axes. Time to swimmming was only weakly correlated with egg size. Time to first swimming was correlated with time from first to second cleavage, an early short cell cycle. Tunicates, though developing the chordate body plan for muscular swimming, achieve swimming as rapidly as ciliated blastulae, although for a given time to first swimming, tunicates have shorter early cell cycles. Overall, times to first swimming are remarkably convergent and remaining differences are partly from differing durations of early cell-cycles. Hypotheses for persistent differences in cell cycle durations for embryos at high risk are numerous and untested. Constraints on cell cycle durations may also affect rates of planktonic larval development at later stages.
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