Low internal transcribed spacer rDNA variation in New Zealand Bonamia ostreae: evidence for a recent arrival

Abstract

Bonamia ostreaeis a haplosporidian parasite of oysters that was first reported to occur in the Southern Hemisphere in 2015 in the New Zealand flat oysterOstrea chilensis.Until that report,B. ostreaehad been restricted to populations ofO. eduliswithin the Northern Hemisphere. This large range extension raised questions regardingB. ostreaedispersal, including whetherB. ostreaeis a recent introduction and from where it originated. The whole 18S rRNA gene of New ZealandB. ostreaerevealed 99.9-100% sequence homology to other publishedB. ostreae18S rDNA sequences. Internal transcribed spacer (ITS) rDNA sequences (n = 29) were generated from New ZealandB. ostreaeand compared to publishedB. ostreaesequences from 3 Northern Hemisphere sites: California, USA (n = 18), Maine, USA (n = 7), and the Netherlands (n = 6) to investigate intraspecific variation. Low ITS rDNA variation was observed from New ZealandB. ostreaeisolates, and high levels of variation were observed from Northern HemisphereB. ostreaesequences. We hypothesise that the low ITS rDNA diversity found in New ZealandB. ostreaeis the result of a founder effect resulting from a single introduction from a limited number of propagules. The high level of ITS rDNA variation from the Northern Hemisphere prevented inferences of dispersal origins. New ZealandB. ostreaewere genetically differentiated from all sites, and additional genetic data are required to better determine the origin ofB. ostreaein New Zealand.