Brown trout in the Falkland Islands: invasion ecology, population structure and genetic diversity

Biological invasions are important causes of biodiversity loss, particularly in remote islands. Non-native salmonids, such as brown trout (Salmo trutta), have been widely introduced throughout the Southern Hemisphere, impacting endangered native fauna, particularly galaxiid fishes, through predation and competition. However, due to their importance for sport fishing and aquaculture, they are often protected, and any attempts to curtail their impacts are generally met with limited support, which poses a conservation conundrum. The best prospect of protecting native galaxiids is to predict where and how salmonids might disperse. This thesis aims to answer three main questions about brown trout in the Falkland Islands in order to provide resource managers with information to facilitate conservation planning to minimize the impacts of brown trout on native galaxiids. (1) determine the distribution of invasive brown trout and native zebra trout, Aplochiton zebra and Aplochiton taeniatus. (2) estimate patterns of movement and (3) assess the population structuring and estimate levels of gene flow between different rivers and populations of brown trout in the Falklands. To meet these aims, I used state-of-the-art methods, including SNP genotyping, stable isotope analysis, acoustic tagging, and environmental DNA (eDNA) analysis. The results of this thesis suggest that establishment success (calculated as the proportion of historical introductions where brown trout became established) was ~88% and that brown trout are continuing to spread from their original sites of introduction. The native Aplochiton species have disappeared from most rivers invaded by brown trout. Four genetically distinct clusters of brown trout were identified, with high levels of gene flow indicating widespread dispersal of brown trout across the Falkland Islands. Without strong containment, brown trout are predicted to invaded nearly all suitable freshwater habitats in the Falklands within the next ~70 years, which might put native galaxiids at a high risk of extinction

SNP analyses and acoustic tagging reveal multiple origins and widespread dispersal of invasive brown trout in the Falkland Islands

Biological invasions are important causes of biodiversity loss, particularly in remote islands. Brown trout (Salmo trutta) have been widely introduced throughout the Southern Hemisphere, impacting endangered native fauna, particularly galaxiid fishes, through predation and competition. However, due to their importance for sport fishing and aquaculture farming, attempts to curtail the impacts of invasive salmonids have generally been met with limited support and the best prospects for protecting native galaxiids is to predict where and how salmonids might disperse. We analysed 266 invasive brown trout from 14 rivers and ponds across the Falkland Islands as well as 32 trout from three potential source populations, using a panel of 592 single nucleotide polymorphisms (SNPs) and acoustic tagging, to ascertain their origins and current patterns of dispersal. We identified four genetically distinct clusters with high levels of genetic diversity and low admixture, likely reflecting the different origins of the invasive brown trout populations. Our analysis suggests that many trout populations in the Falklands may have originated from one of the donor populations analysed (River Wey). The highest genetic diversity was observed in the rivers with the greatest number of introductions and diverse origins, while the lowest diversity corresponded to a location without documented introductions, likely colonized by natural dispersal. High levels of gene flow indicated widespread migration of brown trout across the Falkland Islands, likely aided by anadromous dispersal. This is supported by data from acoustically tagged fish, three of which were detected frequently moving between two rivers ~26 km apart. Our results suggest that, without containment measures, brown trout may invade the last remaining refuges for the native endangered Aplochiton spp. We provide new insights into the origin and dispersal of invasive brown trout in the Falkland Islands that can pave the way for a targeted approach to limit their impact on native fish fauna

Addressing the welfare needs of farmed lumpfish: knowledge gaps, challenges and solutions

Lumpfish (Cyclopterus lumpus L.) are increasingly being used as cleaner fish to control parasitic sea lice, one of the most important threats to salmon farming. However, lumpfish cannot survive feeding solely on sea lice, and their mortality in salmon net pens can be high, which has welfare, ethical and economic implications. The industry is under increasing pressure to improve the welfare of lumpfish, but little guidance exists on how this can be achieved. We undertook a knowledge gap and prioritisa tion exercise using a Delphi approach with participants from the fish farming sector, animal welfare, academia and regulators to assess consensus on the main challenges and potential solutions for improving lumpfish welfare. Consensus among participants on the utility of 5 behavioural and 12 physical welfare indicators was high (87–89%), reliable (Cronbach's alpha = 0.79, 95CI = 0.69–0.92) and independent of participant background. Participants highlighted fin erosion and body damage as the most use ful and practical operational welfare indicators, and blood parameters and behav ioural indicators as the least practical. Species profiling revealed profound differences between Atlantic salmon and lumpfish in relation to behaviour, habitat preferences, nutritional needs and response to stress, suggesting that applying a common set of welfare standards to both species cohabiting in salmon net-pens may not work well for lumpfish. Our study offers 16 practical solutions for improving the welfare of lumpfish and illustrates the merits of the Delphi approach for achieving consensus among stakeholders on welfare needs, targeting research where is most needed and generating workable solutions.info:eu-repo/semantics/publishedVersio

Addressing the welfare needs of farmed lumpfish: knowledge gaps, challenges and solutions

Lumpfish (Cyclopterus lumpus L.) are increasingly being used as cleaner fish to control parasitic sea lice, one of most important threats to salmon farming. However, lumpfish cannot survive feeding solely on sea lice, and their mortality in salmon net-pens can be high, which has welfare, ethical and economic implications. The industry is under increasing pressure to improve the welfare of lumpfish, but little guidance exists on how this can be achieved. We undertook a knowledge gap and prioritization exercise using a Delphi approach with participants from the fish farming sector, animal welfare, academia, and regulators to assess consensus on the main challenges and potential solutions for improving lumpfish welfare. Consensus among participants on the utility of 5 behavioural and 12 physical welfare indicators was high (87-89%), reliable (Cronbach’s alpha = 0.79, 95CI = 0.69-0.92), and independent of participant background. Participants highlighted fin erosion and body damage as the most useful and practical operational welfare indicators, and blood parameters and behavioural indicators as the least practical. Species profiling revealed profound differences between Atlantic salmon and lumpfish in relation to behaviour, habitat preferences, nutritional needs and response to stress, suggesting that applying a common set of welfare standards to both species cohabiting in salmon net-pens may not work well for lumpfish. Our study offers 16 practical solutions for improving the welfare of lumpfish, and illustrates the merits of the Delphi approach for achieving consensus among stakeholders on welfare needs, targeting research where is most needed, and generating workable solutions.Additional authors: P.T.J. Deacon, B.T. Jennings, A. Deakin, A.I. Moore, D. Phillips, G. Bardera, M.F. Castanheira, M. Scolamacchia, N. Clarke, O. Parker, J. Avizienius, M. Johnstone & M. Pavlidi

A new high‐resolution melt curve eDNA assay to monitor the simultaneous presence of invasive brown trout ( <i>Salmo trutta</i> ) and endangered galaxiids

Brown trout are highly invasive in the Southern Hemisphere where they support important sport fisheries and aquaculture activities, which may impact endangered native galaxiid fishes and cause conflicts. To protect native galaxiids it is essential to monitor changes in species distributions, but this can be difficult when species are rare or difficult to sample. We developed and validated, both in the laboratory and in the field, a new assay using a high-resolution melt curve (HRM)-eDNA approach to simultaneously detect the presence of two threatened native galaxiids (Aplochiton zebra and Aplochiton taeniatus) and the invasive brown trout (Salmo trutta). Using this method, we found brown trout in 30% of the sampled waterbodies and Aplochiton sp. in 15% of them. Galaxiids were solely identified as being present in rivers that lacked brown trout, with both native species coexisting in two of the three rivers where they were detected, despite their different niche preferences. These assays can be used to monitor threatened zebra trout as well as invasive brown trout populations, allowing conservation managers to target areas for intervention

Overcoming resistance to STING agonist therapy to incite durable protective antitumor immunity

Background Activating the Stimulator of Interferon Genes (STING) adaptor incites antitumor immunity against immunogenic tumors in mice, prompting clinical trials to test STING activators. However, STING signaling in the tumor microenvironment (TME) during development of Lewis lung carcinoma (LLC) suppresses antitumor immunity to promote tumor growth. We hypothesized that local immune balance favoring suppression of antitumor immunity also attenuates antitumor responses following STING activation. The purpose of this study was to evaluate how STING activation impacts antitumor responses in mice bearing LLC tumors.Methods Mice bearing established LLC tumors were treated with synthetic cyclic diadenyl monophosphate (CDA) to activate STING. Mice were monitored to assess LLC tumor growth, survival and protective antitumor immunity. Transcriptional and metabolic analyses were used to identify pathways responsive to CDA, and mice were co-treated with CDA and drugs that disrupt these pathways.Results CDA slowed LLC tumor growth but most CDA-treated mice (77%) succumbed to tumor growth. No evidence of tumor relapse was found in surviving CDA-treated mice at experimental end points but mice were not immune to LLC challenge. CDA induced rapid increase in immune regulatory pathways involving programmed death-1 (PD-1), indoleamine 2,3 dioxygenase (IDO) and cyclooxygenase-2 (COX2) in the TME. PD-1 blockade enhanced antitumor responses to CDA and increased mouse survival but mice did not eliminate primary tumor burdens. Two IDO inhibitor drugs had little or no beneficial effects on antitumor responses to CDA. A third IDO inhibitor drug synergized with CDA to enhance tumor control and survival but mice did not eliminate primary tumor burdens. In contrast, co-treatments with CDA and the COX2-selective inhibitor celecoxib controlled tumor growth, leading to uniform survival without relapse, and mice acquired resistance to LLC re-challenge and growth of distal tumors not exposed directly to CDA. Thus, mice co-treated with CDA and celecoxib acquired stable and systemic antitumor immunity.Conclusions STING activation incites potent antitumor responses and boosts local immune regulation to attenuate antitumor responses. Blocking STING-responsive regulatory pathways synergizes with CDA to enhance antitumor responses, particularly COX2 inhibition. Thus, therapy-induced resistance to STING may necessitate co-treatments to disrupt regulatory pathways responsive to STING in patients with cancer