12:00 PM - 12:15 PM
[MIS12-11] Host-parasite relationships between snow algae and chytrids in snow-covered regions of Japan
Keywords:snow algae, chytrids, host-parasite relationships, geographical distribution, snow and ice ecosystems
In glacial and snow-covered ecosystems, environmental DNA analyses have detected diverse novel lineages of chytrids. Our recent research revealed that some of them originate from the chytrids of the order Mesochytriales, which infect snow-inhabiting microalgae (snow algae) (Nakanishi et al. 2023, Front. Microbiol.). However, the host of these chytrids have not yet been identified at the species level, and the host–parasite relationships remain unclear. Although snow environments are regionally isolated, it is unclear whether host–parasite associations are region-specific or shared across distant locations.
This study aimed to elucidate the host-parasite relationships between parasitic chytrids and their snow algal hosts in snow-covered regions of Japan using single-cell analysis. Additionally, DNA metabarcoding analysis was conducted to examine the geographic distribution of host-parasite lineages.
Snow samples from four regions, Tomakomai Experimental Forest (Hokkaido Pref.), Mt. Hakkoda (Aomori Pref.), Mt. Gassan (Yamagata Pref.), and Kanumazawa Riparian Research Forest (Iwate Pref.), were used for single-cell analysis. Hosts (snow algae) and parasites (chytrids) were isolated into pairs, and DNA was extracted. The 18S rDNA regions of both organisms were amplified and sequenced. Phylogenetic analyses were performed to identify host-parasite lineages and their relationships.
To investigate the geographic distribution of snow algae and chytrids, additional snow samples from seven regions were included, totaling 11 regions of Japan. In each snow sample, total DNA was extracted using QIAGEN DNeasy PowerSoil Pro Kit. The barcode region of 18S rDNA was amplified using universal primers 528F and 706R and sequenced using NovaSeq (Illumina). The obtained sequences were analyzed by DADA2 to produce Amplicon Sequence Variants (ASVs). Host-parasite ASVs were identified by BLAST search, and their distributions were analyzed.
In snow samples from the four regions, six lineages of chytrids that infected the green alga Chloromonas were detected. The six lineages belonged to the order Mesochytriales, and five of the six were region-specific. Four chytrid lineages detected in three regions (Mt. Gassan: Mesochytriales sp. 1, sp. 2; Mt. Hakkoda: Mesochytriales sp. 1, sp. 4; Kanumazawa: Mesochytriales sp. 5) infected the same host species, C. miwae. In addition, Mesochytriales sp. 1 detected in two regions (Mt. Gassan and Mt. Hakkoda) also infected C. fuhrii. These findings indicate the presence of region-specific chytrid lineages with overlapping hosts and demonstrate that some chytrids can infect multiple hosts. DNA metabarcoding analysis showed that C. miwae and C. fuhrii were widely distributed whereas Mesochytriales spp. 1–5 had more limited distributions. This suggests that the chytrid lineages have more localized geographic distributions than their hosts and likely complete their life cycles within specific regions, without dispersing widely with their hosts.
In Tomakomai, Mesochytriales sp. 6 infected the novel Chloromonas lineages (Chloromonas spp. A and B), which were not detected in other regions. DNA metabarcoding analysis also showed that these lineages had limited distributions. This suggests that both hosts and parasites in Tomakomai do not disperse widely.
In conclusion, the host-parasite relationships between chytrids and snow Chloromonas in snow-covered regions of Japan vary by region. This suggests that chytrids maintain independent populations in each region rather than dispersing with their hosts over long distances. On the other hand, some chytrids can infect multiple hosts, which means that host range may be different between lineages. Future studies should explore host specificity, regional endemism, and the mechanisms underlying these patterns.
This study aimed to elucidate the host-parasite relationships between parasitic chytrids and their snow algal hosts in snow-covered regions of Japan using single-cell analysis. Additionally, DNA metabarcoding analysis was conducted to examine the geographic distribution of host-parasite lineages.
Snow samples from four regions, Tomakomai Experimental Forest (Hokkaido Pref.), Mt. Hakkoda (Aomori Pref.), Mt. Gassan (Yamagata Pref.), and Kanumazawa Riparian Research Forest (Iwate Pref.), were used for single-cell analysis. Hosts (snow algae) and parasites (chytrids) were isolated into pairs, and DNA was extracted. The 18S rDNA regions of both organisms were amplified and sequenced. Phylogenetic analyses were performed to identify host-parasite lineages and their relationships.
To investigate the geographic distribution of snow algae and chytrids, additional snow samples from seven regions were included, totaling 11 regions of Japan. In each snow sample, total DNA was extracted using QIAGEN DNeasy PowerSoil Pro Kit. The barcode region of 18S rDNA was amplified using universal primers 528F and 706R and sequenced using NovaSeq (Illumina). The obtained sequences were analyzed by DADA2 to produce Amplicon Sequence Variants (ASVs). Host-parasite ASVs were identified by BLAST search, and their distributions were analyzed.
In snow samples from the four regions, six lineages of chytrids that infected the green alga Chloromonas were detected. The six lineages belonged to the order Mesochytriales, and five of the six were region-specific. Four chytrid lineages detected in three regions (Mt. Gassan: Mesochytriales sp. 1, sp. 2; Mt. Hakkoda: Mesochytriales sp. 1, sp. 4; Kanumazawa: Mesochytriales sp. 5) infected the same host species, C. miwae. In addition, Mesochytriales sp. 1 detected in two regions (Mt. Gassan and Mt. Hakkoda) also infected C. fuhrii. These findings indicate the presence of region-specific chytrid lineages with overlapping hosts and demonstrate that some chytrids can infect multiple hosts. DNA metabarcoding analysis showed that C. miwae and C. fuhrii were widely distributed whereas Mesochytriales spp. 1–5 had more limited distributions. This suggests that the chytrid lineages have more localized geographic distributions than their hosts and likely complete their life cycles within specific regions, without dispersing widely with their hosts.
In Tomakomai, Mesochytriales sp. 6 infected the novel Chloromonas lineages (Chloromonas spp. A and B), which were not detected in other regions. DNA metabarcoding analysis also showed that these lineages had limited distributions. This suggests that both hosts and parasites in Tomakomai do not disperse widely.
In conclusion, the host-parasite relationships between chytrids and snow Chloromonas in snow-covered regions of Japan vary by region. This suggests that chytrids maintain independent populations in each region rather than dispersing with their hosts over long distances. On the other hand, some chytrids can infect multiple hosts, which means that host range may be different between lineages. Future studies should explore host specificity, regional endemism, and the mechanisms underlying these patterns.