Biology subjects

Okamura, B.

Publications and source records attributed to Okamura, B..

3 recordsLinked to original sources

bioRxiv2026

Transmission strategy modulates parasite biogeography in an island-colonising bird

Parasites occur in every ecosystem, although their dispersal is often constrained by the availability of hosts or vectors. Here, we explore how variation in parasite life history traits, particularly transmission strategy, may influence their distributions. Specifically, we test whether a variety of parasites ad-here to the rules of island biogeography, and whether their distributions vary with transmission strategy. We utilised broad-spectrum parasite detection from existing Whole Genome Sequence (WGS) data to characterise parasites with varying transmission strategies from the blood of a passerine bird, the silvereye (Zosterops lateralis), sampled across 25 islands in the South Pacific and from five of the states in mainland Australia. Overall, parasite richness was higher on mainland Australia compared to islands and decreased with distance of islands from the Australian continent. However, these patterns were dependent on transmission strategy. For parasites transmitted by flying insect vectors, richness decreased on islands compared to the mainland. However, increasing isolation from the mainland among islands had little further impact. On the other hand, richness of directly transmitted parasites and those requiring another intermediate host declined sharply with increasing distance from the mainland. While islands may act as an initial barrier to colonisation for parasites relying on flying insect vectors, their highly dispersive vectors may subsequently reduce the impact of increasing isolation distance on richness. Our work underscores the importance of considering parasite life-histories and their transmission strategies for understanding the processes that shape parasite communities on islands.

ecology↗

bioRxiv2026

Life cycle complexity shapes parasite sharing amongst migratory and resident hosts

Migratory animals are potentially important parasite dispersers. However, understanding the impact of host migration on parasite distributions is challenging because variation in parasite life histories can mediate dispersal potential. Furthermore, studies of parasite dispersal via host migration often compare parasites in different species of migrant and resident hosts, despite differences in host phylogeny, ecology, and exposure history, which can complicate ascertaining the impact of migration. The Tasmanian population of silvereye (Zosterops lateralis lateralis) exhibits partial migration. Some members of the population overwinter on the Australian mainland, where they co-occur with residents of another silvereye subspecies (Z. l. cornwalli). Utilising targeted PCR, metabarcoding and high-throughput sequencing, we characterise a range of parasite genera from blood and faecal samples in Tasmanian resident, migrant and mainland resident birds. Greater parasite richness was documented in migrant individuals, possibly reflecting exposure to varied parasite faunas at stopovers or during overwintering. The increased richness was primarily driven by parasites with simple life cycles. Reduced sharing of parasites with complex life cycles amongst migratory and resident host populations may be explained by ecological constraints in establishing transmission, such as vector or secondary host availability. Our study exemplifies the utility of molecular methods for characterising multi-parasite systems and makes use of a single host species to provide insights on patterns of parasite distributions that result from migratory movements. Knowing how parasite life histories constrain or promote dispersal via regular host migration will be essential for predicting future patterns of pathogen dispersal under climate change and shifting migratory regimes.

ecology↗

bioRxiv2020

Comparative transcriptomics and host-specific parasite gene expression profiles inform on drivers of proliferative kidney disease

The myxozoan parasite, Tetracapsuloides bryosalmonae has a two-host life cycle alternating between freshwater bryozoans and salmonid fish. Infected fish can develop Proliferative Kidney Disease (PKD), characterised by a gross lymphoid-driven kidney pathology in wild and farmed salmonids. To facilitate an in-depth understanding of T. bryosalmonae-host interactions, we have adopted a two-host parasite transcriptome sequencing approach to minimize host contamination in the absence of a complete T. bryosalmonae genome. Parasite contigs common to both infected hosts (the intersect transcriptome; 7,362 contigs) were typically AT-rich (60-75% AT). 5,432 contigs within the intersect were annotated with 1,930 unannotatde contigs encoding for unknown transcripts. We have focused on transcripts encoding proteins involved in; nutrient acquisition, host-parasite interactions, development, and cell-to-cell communication or proteins of unknown function, establishing their potential importance in each host by RT-qPCR. Host-specific expression profiles were evident, particularly in transcripts encoding proteases and proteins involved in lipid metabolism, cell adhesion, and development. We confirm for the first time the presence of homeobox proteins and a frizzled homologue in myxozoan parasites. The novel insights into myxozoan biology that this study reveals will help to focus research in developing future disease control strategies.

genomics↗