Hurricane-induced disturbance increases genetic diversity and population admixture of the direct-brooding isopod, Gnathia marleyi

Severe hurricanes increase recruitment and gene flow in the clonal sponge Aplysina cauliformis

Upright branching sponges, such as Aplysina cauliformis, provide critical three-dimensional habitat for other organisms and assist in stabilizing coral reef substrata, but are highly susceptible to breakage during storms. Breakage can increase sponge fragmentation, contributing to population clonality and inbreeding. Conversely, storms could provide opportunities for new genotypes to enter populations via larval recruitment, resulting in greater genetic diversity in locations with frequent storms. The unprecedented occurrence of two Category 5 hurricanes in close succession during 2017 in the U.S. Virgin Islands (USVI) provided a unique opportunity to evaluate whether recolonization of newly available substrata on coral reefs was due to local (e.g. re-growth of remnants, fragmentation, larval recruitment) or remote (e.g. larval transport and immigration) sponge genotypes. We sampled A. cauliformis adults and juveniles from four reefs around St. Thomas and two in St. Croix (USVI). Using a 2bRAD protocol, all samples were genotyped for single-nucleotide polymorphisms (SNPs). Results showed that these major storm events favoured sponge larval recruitment but did not increase the genetic diversity of A. cauliformis populations. Recolonization of substratum post-storms via clonality was lower (15%) than expected and instead was mainly due to sexual reproduction (85%) via local larval recruitment. Storms did enhance gene flow among and within reef sites located south of St. Thomas and north of St. Croix. Therefore, populations of clonal marine species with low pelagic dispersion, such as A. cauliformis, may benefit from increased frequency and magnitude of hurricanes for the maintenance of genetic diversity and to combat inbreeding, enhancing the resilience of Caribbean sponge communities to extreme storm events.

Blood meal identification reveals extremely broad host range and host-bias in a temporary ectoparasite of coral reef fishes

Appreciation for the role of cryptofauna in ecological systems has increased dramatically over the past decade. The impacts blood-feeding arthropods, such as ticks and mosquitos, have on terrestrial communities are the subject of hundreds of papers annually. However, blood-feeding arthropods have been largely ignored in marine environments. Gnathiid isopods, often referred to as "ticks of the sea", are temporary external parasites of fishes. They are found in all marine environments and have many consequential impacts on host fitness. Because they are highly mobile and only associated with their hosts while obtaining a blood meal, their broader trophic connections are difficult to discern. Conventional methods rely heavily on detecting gnathiids on wild-caught fishes. However, this approach typically yields few gnathiids and does not account for hosts that avoid capture. To overcome this limitation, we sequenced blood meals of free-living gnathiids collected in light traps to assess the host range and community-dependent exploitation of Caribbean gnathiid isopods. Using fish-specific COI (cox1) primers, sequencing individual blood meals from 1060 gnathiids resulted in the identification of 70 host fish species from 27 families. Comparisons of fish assemblages to blood meal identification frequencies at four collection sites indicated that fishes within the families Haemulidae (grunts) and Lutjanidae (snappers) were exploited more frequently than expected based on their biomass, and Labrid parrotfishes were exploited less frequently than expected. The broad host range along with the biased exploitation of diel-migratory species has important implications for the role gnathiid isopods play in Caribbean coral reef communities.

A major flood caused by a typhoon did not affect the population genetic structure of a river mayfly metapopulation

Floods affect the population structure of organisms that inhabit streams. In recent decades, the scale of floods has become larger due to climate change. Under these circumstances, on 12 October 2019, the largest typhoon in the history of observation in Japan struck the Japanese Archipelago. This typhoon caused heavy rainfall in various places, and the Chikuma-Shinano River System (Japan's largest) suffered great damage. Eight years before the large-scale disturbance in the river system, the population structure of the mayfly Isonychia japonica was studied in detail using quantitative sampling (population numbers and biomass) and by sequencing the mtDNA cytochrome c oxidase subunit I. To understand the impact of the flood on the population and genetic structures, we repeated the same research approximately 1 year after the flood. Direct comparison of sites before and after the flood revealed no significant changes between pre- and post-flood population genetic structure. This indicates high in situ resistance and/or resilience recovery of the populations to the disturbance. We hypothesize that this high resistance/resilience to flood disturbance is a result of strong selection for such traits in the rivers of the Japanese Archipelago, which are short, steep, flow rapidly and violently, and are strongly affected by floods.

Disturbance decreases genotypic diversity by reducing colonization: Implications for disturbance-diversity feedbacks

One objective of eco-evolutionary dynamics is to understand how the interplay between ecology and evolution on contemporary timescales contributes to the maintenance of biodiversity. Disturbance is an ecological process that can alter species diversity through both ecological and evolutionary effects on colonization and extinction dynamics. While analogous mechanisms likely operate among genotypes within a population, empirical evidence demonstrating the relationship between disturbance and genotypic diversity remains limited. We experimentally tested how disturbance altered the colonization (gain) and extinction (loss) of genets within a population of the marine angiosperm Zostera marina (eelgrass). In a 2-year field experiment conducted in northern California, we mimicked grazing disturbance by migratory geese by clipping leaves at varying frequencies during the winter months. Surprisingly, we found the greatest rates of new colonization in the absence of disturbance and that clipping had negligible effects on extinction. We hypothesize that genet extinction was not driven by selective mortality from clipping or from any stochastic loss resulting from the reduced shoot densities in clipped plots. We also hypothesize that increased flowering effort and facilitation within and among clones drove the increased colonization of new genets in the undisturbed treatment. This balance between colonization and extinction resulted in a negative relationship between clipping frequency and net changes in genotypic richness. We interpret our results in light of prior work showing that genotypic diversity increased resistance to grazing disturbance. We suggest that both directions of a feedback between disturbance and diversity occur in this system with consequences for the maintenance of eelgrass genotypic diversity.

First record and molecular characterisation of two Gnathia species (Crustacea, Isopoda, Gnathiidae) from Philippine coral reefs, including a summary of all Central-Indo Pacific Gnathia species

Due to their unusual life cycle that includes parasitic larval and free living adult stages, gnathiid isopods are typically overlooked in biodiversity surveys, even those that focus on parasites. While the Philippines sits within the region of highest marine biodiversity in the world, the coral triangle, no gnathiid species have been identified or described from that region. Here we present the first records of two gnathiid species collected from the Visayas, central Philippines: Gnathia malaysiensis Müller, 1993, previously described from Malaysia, and G. camuripenis Tanaka, 2004, previously described from southern Japan. This paper provides detailed morphological redescriptions, drawings and scanning electron microscope images as well as the first molecular characterisation of both species, Furthermore, a summary of the Central-Indo Pacific Gnathia species is provided.

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Morphological description of two gnathiid species collected from the central Philippines, along with molecular data, are presented.

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Gnathia malaysiensis was previously described from Malaysia and G. camuripenis was previously described from southern Japan.

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Although the Philippines is in the highly biodiverse coral triangle, this is the first gnathiid description from this region.

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The wide geographic range of G. camuripenis suggests dispersal via large, highly mobile fishes, and/or tropical cyclones.

Molecular detection of apicomplexan blood parasites of coral reef fishes from free-living stages of ectoparasitic gnathiid isopods

Gnathiid isopods are marine ectoparasites that feed on the blood of fishes that have been implicated as vectors of blood parasites, with transmission possibly occurring through biting during their parasitic life-stages, or through ingestion by fishes. However, evidence for their role as vectors is limited, reflecting the small number of research groups working on them. Here, we used a molecular barcode approach to identify fish hosts and apicomplexan parasites in free-living gnathiids from the eastern Caribbean Sea, with the goal of further evaluating their potential role as reservoirs and/or vectors for these parasites. Apicomplexa were only identified in 8% of the Gnathia analyzed, and in four cases we could identify both Apicomplexa and fish host DNA. The results further suggest that Gnathia spp. in this region may serve as reservoirs for Apicomplexa, but whether they are vectors for this parasite remains uncertain.