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

Randolph Chambers

Chad Vance

Abstract

Marine community structure is dependent on the recruitment of new individuals; an incomplete understanding of life histories, however, hinders the accuracy of recruitment estimates. For example, the assumption that one zygote yields one offspring is violated for many phyla under various conditions. Polyembryony, and specifically larval cloning, is one mechanism by which echinoderms actively refute this assumption. The daisy brittle star, Ophiopholis aculeata, exhibits three different modes of larval cloning. First, as an 8-arm pluteus, the larva autotomizes the distal portion of its posterolateral arm. The second and third modes are related and both occur during metamorphosis and settlement. In the second mode, one half of the posterolateral arm pair is released and the other half is reabsorbed into the juvenile. In the third mode, the full posterolateral arm pair is released from the juvenile body following settlement. I describe these three modes of cloning and provide details of each. First, I tracked the frequency of cloning and regeneration success in a population of O. aculeata from Maine. Larvae of O. aculeata cloned via the first mode 7% of the time and were least likely to regenerate at only 4%. The second mode occurred 6% of the time and 5% of half arm pairs regenerated. Full arm pairs were released 79% of the time and 15% of those regenerated. Only the third mode of cloning via full arm pair release has been reported previously in the literature, but I compare my results to an unpublished data set from a population of the same species in Washington that exhibits the same three cloning modes. Second, I tested whether larvae that were starved had delayed cloning compared to those that were fed. Third, I tested whether the second and third modes of cloning had costs associated with them: a reduction in disc area and decreased time to death from starvation. Lastly, I confirmed that primary larvae that produced clones were asymmetrical and that secondary larvae, which were the products of cloning events were uniquely pigmented. Both of these observations may allow researchers to identify and analyze polyembryony in the field and to estimate cloning frequency in nature.

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