Pteropsora sp.

A Pterospora-like gregarine apicomplexan
Haplozoon, a parasitic dinoflagellate

Apicomplexans are notorious parasites, and have a significance in the veterinarian and agricultural sciences (e.g., Toxoplasma, Sarcocystis, Cryptosporidium). We are currently working to explore the diversity of early-branching apicomplexan parasites, and those associated with fisheries. This data will be paramount for understanding some of the earliest stages of apicomplexan evolution, and shed light on the economic importance of these parasites. Our hope is that this work will help lay a foundation for future work with non-model apicomplexans, and grow aspects of the field of parasitology that have been hitherto neglected.

I. Marine gregarine apicomplexans: evolutionary change and patterns of speciation

Evolution in early alveolates – Gregarine apicomplexans are exclusive parasites of invertebrates. From an evolutionary perspective this is interesting because these lineages appear at the nexus between lineages of alveolates that are free-living or obligate parasites (i.e., those that would later comprise the Apicomplexa). In this way, the study of marine gregarines (some of the earliest of these apicomplexan lineages) is likely to be informative, as we seek to understand these fundamental evolutionary shifts.

Patterns of speciation among gregarine apicomplexans – Another topic we are interested in exploring is the ways in which these parasites have diversified and spread throughout invertebrates. Marine gregarines are by no means rare, and can be quite common in some marine inverts (e.g., polychaetes and tunicates). Gregarines are homozygous, meaning they only need one host to complete their lifecycle, and typically each host tends to have their own loyal gregarine parasites.

Gregarine apicomplexans and their close relatives (other alveolates)

II. Marine apicomplexans and their impact on global fisheries

We started collaborating with a group of New Zealand researchers examining some bizarre apicomplexans that parasitize New Zealand shellfish. Currently, we are examining the unexplored diversity of apicomplexan parasites of bivalve shellfish, with the goal of using novel methods such as laser capture microscopy and metagenomic sequencing to gain a better picture of the diversity of parasites and their impacts on fisheries.

Photos of the NZ-collaboration. Some photos from Suong et al., 2017, 2018
Laser capture microscopy system — attempting to isolate apicomplexans from their host tissue!

Dinoflagellates are aquatic microalgae. Although they are mainly single-celled and microscopic, many people know of their effects. Some dinoflagellates can grow rapidly to form large blooms, often referred to as ‘red tide’ (akashio in Japanese). Other dinoflagellates bioluminescence, causing spectacular ‘light shows’ in the water at night. As a group, dinoflagellates are quite diverse. A large portion of dinoflagellates use the sun to produce their own energy (photosynthetic). Another portion eat other microorganisms (heterotrophic), and some live off of a host organism (parasitic).

I. Diversity and toxicity of dinoflagellates

Some dinoflagellates produce toxins, and the growth of dense accumulation of these algae in aquatic habitats are known as “red tide” or “harmful algal blooms”. These blooms can pose a significant risk to ecosystems, poisoning sea life such as fish. These toxins are a public health risk because they can bioaccumulate in organisms such as shellfish, and can potentially kill people if eaten (e.g., paralytic shellfish poison or diuretic shellfish poison – PSP or DSP, respectively).

II. Primary endosymbiosis, and the independent evolution of photosynthesis in Sinophysis (dinoflagellata)

This project is a recent theme in my lab, being led by a student. Here, we are studying Sinophysis, a dinoflagellate lineage that is known to be heterotrophic. In this particular species, which is found in Southern Japan, cyanobacteria are maintained in a symbiotic (photosynthetic) relationship with the dinoflagellate. Currently, we are analyzing genomic and transcriptomic data from single-cells to assess the relationship between the cyanobacteria and the Sinophysis. This topic is of interest because it represents a new, yet to be characterized, relationship that represents the early stages of primary endosymbiosis in dinoflagellates.

Fluorescence in situ hybridization staining for cyanobacteria DNA (left); negative (right)

III. Innovative complexity and the independent origin of multicellularity in parasitic dinoflagellates

Parasitic dinoflagellates are notably understudied, compared to their photosynthetic and heterotrophic counterparts. This is because photosynthetic and heterotrophic dinoflagellates tend to grow in large numbers, forming easy-to-spot blooms; they also look like other dinoflagellates, making them easier to identify. In comparison, parasitic dinoflagellates have been traditionally overlooked. Due to selective pressure, some have even been misclassified into other groups altogether. Here, we are examining a specific dinoflagellate lineage, Haplozoon, that has independence developed a multicellular stage (unprecedented among other dinoflagellates, and rare in other eukaryotic groups).

One of the least-studied groups of parasitic dinoflagellates is Haplozoon. It was initially discovered over 120 years ago but was misclassified as a primitive animal and other parasitic groups because of its weird appearance. It was not until sometime later that Haplozoon was recognized as a dinoflagellate. Still, a basic understanding regarding the biology of Haplozoon such as its lifecycle, distribution, and pathology remain largely unstudied. Additionally, this particular dinoflagellate parasite is interesting, as it has independently developed a life stage that is multicellular, with regions specialization. This represents a very unique opportunity to study the independent origin of a major biological event: the evolution of multicellularity from a single cell.

IV. Diversity of benthic dinoflagellates

Hokkaido University
Tel: +81 11 706 7241

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