Presenter Information

Zoe ZilzFollow

Presentation Title

How do mass die-off events affect host-parasite dynamics? An examination of the relationship between the ochre sea star and its sperm-eating parasite.

Presentation Type

Oral Presentation

Abstract

The recent massive sea star die-off event, linked to sea star wasting disease (SSWD), provides researchers with an opportunity to examine how parasite prevalence and abundance responds to changes in host populations. This study determined if North American populations of the sea star Pisaster ochraceus, host a castrating ciliate parasite, Orchitophyra stellarum, and if this host-parasite relationship has shifted in the wake of sea star wasting disease. I surveyed 16 sites in three regions: Washington State, Oregon State, and Northern California, sampling from the epidermis of P. ochraceus as well as removing their gonads in search for O. stellarum. We found no evidence of parasitism in the gonads of P. ochraceus, but did find that 51% of sea stars were associated with the ciliate on their epidermis. We compared current percent prevalence of epidermal association with O. stellarum with data from Stickle & Kozloff 2001, 2007 and 2008 and found that, at the three sites they surveyed, percent prevalence has not changed. Current prevalence was highly variable from site to site, but not due to region, suggesting that other variables affect the prevalence of this parasite. I found a significant negative relationship between host population size and O. stellarum prevalence. There may be a high parasite to host ratio in smaller populations because of the facultative nature of this parasite. There was a positive relationship between percent males and parasite prevalence, which is in contrast to previous studies but suggests that O. stellarum thrives in male-biased populations.

Start Date

10-5-2018 11:00 AM

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May 10th, 11:00 AM

How do mass die-off events affect host-parasite dynamics? An examination of the relationship between the ochre sea star and its sperm-eating parasite.

The recent massive sea star die-off event, linked to sea star wasting disease (SSWD), provides researchers with an opportunity to examine how parasite prevalence and abundance responds to changes in host populations. This study determined if North American populations of the sea star Pisaster ochraceus, host a castrating ciliate parasite, Orchitophyra stellarum, and if this host-parasite relationship has shifted in the wake of sea star wasting disease. I surveyed 16 sites in three regions: Washington State, Oregon State, and Northern California, sampling from the epidermis of P. ochraceus as well as removing their gonads in search for O. stellarum. We found no evidence of parasitism in the gonads of P. ochraceus, but did find that 51% of sea stars were associated with the ciliate on their epidermis. We compared current percent prevalence of epidermal association with O. stellarum with data from Stickle & Kozloff 2001, 2007 and 2008 and found that, at the three sites they surveyed, percent prevalence has not changed. Current prevalence was highly variable from site to site, but not due to region, suggesting that other variables affect the prevalence of this parasite. I found a significant negative relationship between host population size and O. stellarum prevalence. There may be a high parasite to host ratio in smaller populations because of the facultative nature of this parasite. There was a positive relationship between percent males and parasite prevalence, which is in contrast to previous studies but suggests that O. stellarum thrives in male-biased populations.