Emerging infectious disease in sea stars: castrating ciliate parasites in Patiria miniata

Abstract

Orchitophrya stellarum is a holotrich ciliate that facultatively parasitizes and castrates male asteriid sea stars. We discovered a morphologically similar ciliate in testes of an asterinid sea star, the northeastern Pacific bat star Patiria miniata (Brandt, 1835). This parasite may represent a threat to Canadian populations of this iconic sea star. Confirmation that the parasite is O. stellarum would indicate a considerable host range expansion, and suggest that O. stellarum is a generalist sea star pathogen. KEY WORDS: Scuticociliate · Asterias amurensis · Biocontrol · Sperm Resale or republication not permitted without written consent of the publisherDis Aquat Org 81: [173][174][175][176] 2008 parasites strongly argues against their deliberate introduction into other faunas for biocontrol of invasive sea stars. MATERIALS AND METHODSAs part of a continuing study of the reproduction and population structure of Patiria miniata, we routinely collect and spawn adults from 2 intertidal locations at Dixon Island and Grappler Inlet near the Bamfield Marine Sciences Centre (48°50' N, 125°8' W) on Vancouver Island, British Columbia, Canada. In June 2007, we observed several males that responded to a hormonal spawning inducer by producing seminal fluid that had a slightly darker color than the usual milky white appearance of sea star sperm. On examination, these spawns contained abundant small ciliates mixed with sperm. We confirmed these observations with 2 subsequent collections. In August 2007, we searched for ciliates on the external body wall of individuals by gently pipeting from the aboral surface around the gonopores, and then examining this material for ciliates that resembled those found in gonads. We then dissected the gonads to search for ciliates in thin smears of the gonadal tissue. We cultured ciliates collected from gonads at 12°C in 50 ml plastic Falcon tubes containing seawater with pieces of testis or aliquots of sperm from P. miniata. We photographed individual ciliates in thin wet mounts using bright field or differential interference contrast (DIC) microscopy. For DIC, ciliates were fixed in 95% ethanol and immediately photographed. In February 2008, we collected 18 adults from Dixon Island and injected them with 1 to 3 ml of 100 µM 1-methyladenine (1-MA), which induces maturation of oocytes (in females) and spawning (in both sexes, Strathmann 1987). We estimated the prevalence of infection by light microscopy of spawned material in wet mounts. RESULTSIn August 2007, 50% of 12 males sampled from Grappler Inlet had ciliates resembling Orchitophrya stellarum on the external body around the gonopores. Ciliates were also identifiable in gonadal smears in 1 of these samples. In samples from Dixon Island (August 2007), 50% of 14 males and 66% of 9 females had O. stellarum-like ciliates from the aboral body wall. Four of the males sampled from Dixon Island (28%) had ciliate infection in gonadal smears. In a later collection from Dixon Island (February 2008), 8 males spawned in response to 1-M...