Date Thesis Awarded

5-2022

Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Jonathan Allen

Committee Members

Drew LaMar

Phoebe Williams

Robert Pike

Abstract

Sea stars typically possess a biphasic life cycle, in which they broadcast spawn their gametes into the water to form a planktonic larval stage that eventually metamorphoses into a benthic adult form. During the larval stage, sea stars are capable of fission cloning, a form of asexual reproduction in which a larva splits to create an anterior, or 'head,' clone and a posterior, or 'body' clone. Reproduction via cloning has been considered an adaptation for increasing population size, as it allows larvae to multiply quickly when conditions are favorable. However, data on the survival of clones to metamorphosis are lacking, and there are no accurate estimates of the contribution of larval clones to adult sea star populations. Thus, the effects of cloning on population growth, as well as tradeoffs and potential advantages of cloning apart from increased population size, are unclear. To test whether clones can regenerate and metamorphose, and to shed light on the possible benefits and costs of larval cloning, I tracked the development of body and head clone pairs of the sea star genus Asterias, along with uncloned larvae as controls. While nearly 98% of uncloned individuals grew a juvenile sea star and reached metamorphic competency, only 73% of body clones and 23% of head clones attained competency. Some genotypes exhibited a net gain in the number of juveniles produced due to cloning, while others remained static in the numbers produced and still more exhibited a net loss. Additionally, 96% of body clones and 100% of head clones that began to regenerate their missing structures reached metamorphic competency, indicating that the initiation of the regeneration process is a bottleneck in clone survival rather than an inability to complete regeneration once begun. Lastly, clone size did not play a role in determining whether a clone survived, nor did cloning impact the size of metamorphosed juveniles. My study is the first in which the frequencies of larval clone metamorphosis have been recorded, and my results indicate that there is natural variation in the frequency and metamorphic success of fission clones.

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