Effectiveness of antifungal treatments during chytridiomycosis epizootics in populations of an endangered frog

The recently-emerged amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has had an unprecedented impact on global amphibian populations, and highlights the urgent need to develop effective mitigation strategies. We conducted in-situ antifungal treatment experiments in wild populations of the endangered mountain yellow-legged frog during or immediately after Bd-caused mass die-off events. The objective of treatments was to reduce Bd infection intensity (“load”) and in doing so alter frog-Bd dynamics and increase the probability of frog population persistence despite ongoing Bd infection. Experiments included treatment of early life stages (tadpoles and subadults) with the antifungal drug itraconazole, treatment of adults with itraconazole, and augmentation of the skin microbiome of subadults with Janthinobacterium lividum, a commensal bacterium with antifungal properties. All itraconazole treatments caused immediate reductions in Bd load, and produced longer-term effects that differed between life stages. In experiments focused on early life stages, Bd load was reduced in the 2 months immediately following treatment and was associated with increased survival of subadults. However, Bd load and frog survival returned to pre-treatment levels in less than 1 year, and treatment had no effect on population persistence. In adults, treatment reduced Bd load and increased frog survival over the entire 3-year post-treatment period, consistent with frogs having developed an effective adaptive immune response against Bd. Despite this protracted period of reduced impacts of Bd on adults, recruitment into the adult population was limited and the population eventually declined to near-extirpation. In the microbiome augmentation experiment, exposure of subadults to a solution of J. lividum increased concentrations of this potentially protective bacterium on frogs. However, concentrations declined to baseline levels within 1 month and did not have a protective effect against Bd infection. Collectively, these results indicate that our mitigation efforts were ineffective in causing long-term changes in frog-Bd dynamics and increasing population persistence, due largely to the inability of early life stages to mount an effective immune response against Bd. This results in repeated recruitment failure and a low probability of population persistence in the face of ongoing Bd infection.

Effect of UVB and temperature on the invasive algae Undaria pinnatifida

<p>The introduction of non-indigenous species and environmental changes are both important threats to marine ecosystems. Environmental changes occur simultaneously and might impact marine organisms synergically or antagonistly. The success of invasive species has been attributed in part to their greater capacity to acclimate to changing conditions. However, the effect of environmental factors on marine invasive species has been little studied. This thesis studied the tolerance of different life stages of the invasive brown seaweed Undaria pinnatifida to UVB and temperature. Also, the possible interactive effect of an increase of temperature and UVB on U. pinnatifida was evaluated. The tolerance of motile zoospores U. pinnatifida to increasing UVB irradiances was studied in laboratory experiments, and a strong negative effect of UVB on motile zoospores of U. pinnatifida was observed. However, zoospores can recover from UVB stress and the degree of recovery depended on UVB irradiances and exposure time. Their ability to recover could increase the opportunity of zoospores to survive and succeed in the invasion process and shows that U. pinnatifida can survive after UVB stress when environmental conditions improve. The effect of light treatments combined with temperature was also investigated in early life stages of U. pinnatifida. Both treatments affected early life stages independently. Early life stages were particularly sensitive to UVB; more so than the other light treatments and temperature. The tolerance of early life stages to a wide range of light and temperature conditions might allow this species to maintain viable populations where they already exist, but also might permit it to invade other areas if predicted environmental changes occur in the future. The effect of consecutive exposures to PAR and UV treatments at different temperatures on sporophytes of U. pinnatifida and the possible photoprotective role of phlorotannins were investigated. There was an interactive effect of light treatments, temperature during the exposure of sporophytes. Sporophytes were highly sensitive to UVB but not to the other light treatments nor to an increase of water temperature. There was no evidence of induction of phlorotannins by UVB and the other light treatments in U. pinnatifida. The sensitivity of sporophytes of U. pinnatifida to UVB and the lack of photoprotective role of phlorotannins suggests this species might have other strategies for success in the intertidal and might direct its energy mainly to growth and reproduction rather than to photoprotection and repair. The response of the photosynthetic capacity and phlorotannins content to seasonal variations of light and UVB of U. pinnatifida was investigated. A clear seasonal trend in the photosynthetic capacity was observed in sporophytes that were correlated to PAR and UVB irradiances measured in the field. Phlorotannins were variable throughout the sampling period where soluble phlorotannins had seasonal and interannual variation, while there was no clear seasonal variation in cell wall phlorotannins concentration. No correlation between both phlorotannins and PAR and UVB was detected. The response of the photosynthetic apparatus to variations of light illustrates the capacity of this species to acclimate to ambient light conditions. Variation of phlorotannins throughout the year could be attributed to a combination of factors such as grazer and wound healing rather than only to the light conditions. This research contributed to a better understanding of the tolerance of U. pinnatifida to environmental factors. This study showed that the tolerance and response to environmental factors is life stage specific. The major factor affecting U. pinnatifida negatively was UVB, while temperature had little impact on this species. The capacity of U. pinnatifida to inhabit a wide range of light and temperature conditions permits this species to succeed in coastal ecosystems, and these characteristics could permit this species to succeed under future climate change scenarios.</p>

Effect of UVB and temperature on the invasive algae Undaria pinnatifida

<p>The introduction of non-indigenous species and environmental changes are both important threats to marine ecosystems. Environmental changes occur simultaneously and might impact marine organisms synergically or antagonistly. The success of invasive species has been attributed in part to their greater capacity to acclimate to changing conditions. However, the effect of environmental factors on marine invasive species has been little studied. This thesis studied the tolerance of different life stages of the invasive brown seaweed Undaria pinnatifida to UVB and temperature. Also, the possible interactive effect of an increase of temperature and UVB on U. pinnatifida was evaluated. The tolerance of motile zoospores U. pinnatifida to increasing UVB irradiances was studied in laboratory experiments, and a strong negative effect of UVB on motile zoospores of U. pinnatifida was observed. However, zoospores can recover from UVB stress and the degree of recovery depended on UVB irradiances and exposure time. Their ability to recover could increase the opportunity of zoospores to survive and succeed in the invasion process and shows that U. pinnatifida can survive after UVB stress when environmental conditions improve. The effect of light treatments combined with temperature was also investigated in early life stages of U. pinnatifida. Both treatments affected early life stages independently. Early life stages were particularly sensitive to UVB; more so than the other light treatments and temperature. The tolerance of early life stages to a wide range of light and temperature conditions might allow this species to maintain viable populations where they already exist, but also might permit it to invade other areas if predicted environmental changes occur in the future. The effect of consecutive exposures to PAR and UV treatments at different temperatures on sporophytes of U. pinnatifida and the possible photoprotective role of phlorotannins were investigated. There was an interactive effect of light treatments, temperature during the exposure of sporophytes. Sporophytes were highly sensitive to UVB but not to the other light treatments nor to an increase of water temperature. There was no evidence of induction of phlorotannins by UVB and the other light treatments in U. pinnatifida. The sensitivity of sporophytes of U. pinnatifida to UVB and the lack of photoprotective role of phlorotannins suggests this species might have other strategies for success in the intertidal and might direct its energy mainly to growth and reproduction rather than to photoprotection and repair. The response of the photosynthetic capacity and phlorotannins content to seasonal variations of light and UVB of U. pinnatifida was investigated. A clear seasonal trend in the photosynthetic capacity was observed in sporophytes that were correlated to PAR and UVB irradiances measured in the field. Phlorotannins were variable throughout the sampling period where soluble phlorotannins had seasonal and interannual variation, while there was no clear seasonal variation in cell wall phlorotannins concentration. No correlation between both phlorotannins and PAR and UVB was detected. The response of the photosynthetic apparatus to variations of light illustrates the capacity of this species to acclimate to ambient light conditions. Variation of phlorotannins throughout the year could be attributed to a combination of factors such as grazer and wound healing rather than only to the light conditions. This research contributed to a better understanding of the tolerance of U. pinnatifida to environmental factors. This study showed that the tolerance and response to environmental factors is life stage specific. The major factor affecting U. pinnatifida negatively was UVB, while temperature had little impact on this species. The capacity of U. pinnatifida to inhabit a wide range of light and temperature conditions permits this species to succeed in coastal ecosystems, and these characteristics could permit this species to succeed under future climate change scenarios.</p>

Metabarcoding analysis of trophic sources and linkages in the plankton community of the Kuroshio and neighboring waters

Trophic sources and pathways supporting early life stages are crucial for survival of forage fishes recruiting around the oligotrophic and unproductive Kuroshio. However, information is limited for the Kuroshio planktonic food web and its trophodynamics because of its high biodiversity. Here, we explore trophic sources and linkages in the Kuroshio plankton community using metabarcoding analysis of gut-content DNA for 22 mesozooplankton groups. The major prey was dinoflagellates and calanoids for omnivorous groups, and calanoids and gelatinous organisms for carnivorous groups. Larvaceans and hydrozoans were the most frequently appeared prey for both omnivores and carnivores, whereas they were minor constituents of the available prey in water samples. Although calanoids overlapped as major prey items for both omnivores and carnivores because they were the most available, contributions from phytoplankton and gelatinous prey differed among taxonomic groups. Further analysis of the metabarcoding data showed that in addition to omnivorous copepods like calanoids, gelatinous groups like larvaceans and hydrozoans were important hubs in the planktonic food web with their multiple trophic linkages to many components. These findings suggest that gelatinous organisms are important as supplementary prey and provide evidence of niche segregation on trophic sources among mesozooplankton groups in the Kuroshio.

Novel insights into early life stages of finned octopods (Octopoda: Cirrata)

The finned or dumbo octopods (Octopoda: Cirrata) constitute a cephalopod (Mollusca: Cephalopoda) taxon almost exclusively comprising organisms that inhabit the deep-sea. This renders studying the general biology of adult cirrate specimens a difficult task, but even more so when it comes to gathering knowledge on their early life stages. During his comprehensive research exploits on cephalopod development, the late Sigurd von Boletzky (1942–2020) also sought to shed light on specific adaptations that eggs and embryos of these enigmatic deep-sea octopods might show. Based on his seminal work, the present article sets out to provide additional data on a broad range of early cirrate life stages, including egg capsules without any obvious embryonic stage as well as those containing embryos. These previously unreported specimens obtained from museum collections were analyzed using conventional morphological as well as modern three-dimensional imaging techniques. The present overview includes specimens from four of the five oceans, i.e., the Atlantic, Pacific, Indian, and Southern Ocean. Based on information on cirrate ovum, chorion, and egg capsule size as well as shape gathered from the literature, an attempt is made here for the first time to identify von Boletzky's as well as the specimens introduced here down to at least genus level. The combined data provide novel insights into early life stages of finned octopods, aiming to continue von Boletzky's legacy with regard to developmental research on a still largely enigmatic taxon of extant deep-sea cephalopods.