Abstract

Metabarcoding datasets targeting protists in marine environments are often dominated by a group of dinoflagellates referred to as the Marine Alveolates (MALVs). Despite a global distribution, considerable sequence diversity, and significant prevalence and abundance in various hosts and environments, MAL Vs include just a handful of characterised lineages. They largely represent a vast collection of uncharacterised 18S barcodes. Known lineages, however, are important parasites that can impact fish and crustacean farming or even harmful algal bloom proliferation. Dinoflagellate genomes are notoriously large and complex. With only two comprehensive MALV genomes available, inferring robust evolutionary histories based solely on 18S phylogenies remains challenging. To overcome this issue, we are manually isolating and sequencing individual MALV cells to generate transcriptomes for phylogenomics, increasing the number of characterised MALV lineages and improving our understanding of dinoflagellate evolution in the process. Using this approach, we demonstrated that MAL Vs originated from two distinct, free-living ancestors, indicating multiple transitions to parasitism and challenging prevailing assumptions about MAL Vs as a whole. More recently, we have isolated several new genera, one of which appears to represent an entirely new MALV group. Going forward, we aim to use metabarcoding datasets to guide the targeted isolation of uncharacterised MALV lineages, filling in critical gaps in our understanding of these important regulators of both animal and environmental health.