Assessing risks of invasion through gamete performance: farm Atlantic salmon sperm and eggs show equivalence in function, fertility, compatibility and competitiveness to wild Atlantic salmon

Adaptations at the gamete level (a) evolve quickly, (b) appear sensitive to inbreeding and outbreeding and (c) have important influences on potential to reproduce. We apply this understanding to problems posed by escaped farm salmon and measure their potential to reproduce in the wild. Farm Atlantic salmon (Salmo salar) are a threat to biodiversity, because they escape in large numbers and can introgress, dilute or disrupt locally adapted wild gene pools. Experiments at the whole fish level have found farm reproductive potential to be significant, but inferior compared to wild adults, especially for males. Here, we assess reproductive performance at the gamete level through detailed in vitro comparisons of the form, function, fertility, compatibility and competitiveness of farm versus wild Atlantic salmon sperm and eggs, in conditions mimicking the natural gametic microenvironment, using fish raised under similar environmental conditions. Despite selective domestication and reduced genetic diversity, we find functional equivalence in all farm fish gamete traits compared with their wild ancestral strain. Our results identify a clear threat of farm salmon reproduction with wild fish and therefore encourage further consideration of using triploid farm strains with optimized traits for aquaculture and fish welfare, as triploid fish remain reproductively sterile following escape

Cryptic choice of conspecific sperm controlled by the impact of ovarian fluid on sperm swimming behavior

Despite evidence that variation in male–female reproductive compatibility exists in many fertilization systems, identifying mechanisms of cryptic female choice at the gamete level has been a challenge. Here, under risks of genetic incompatibility through hybridization, we show how salmon and trout eggs promote fertilization by conspecific sperm. Using in vitro fertilization experiments that replicate the gametic microenvironment, we find complete interfertility between both species. However, if either species’ ova were presented with equivalent numbers of both sperm types, conspecific sperm gained fertilization precedence. Surprisingly, the species’ identity of the eggs did not explain this cryptic female choice, which instead was primarily controlled by conspecific ovarian fluid, a semiviscous, protein-rich solution that bathes the eggs and is released at spawning. Video analyses revealed that ovarian fluid doubled sperm motile life span and straightened swimming trajectory, behaviors allowing chemoattraction up a concentration gradient. To confirm chemoattraction, cell migration tests through membranes containing pores that approximated to the egg micropyle showed that conspecific ovarian fluid attracted many more spermatozoa through the membrane, compared with heterospecific fluid or water. These combined findings together identify how cryptic female choice can evolve at the gamete level and promote reproductive isolation, mediated by a specific chemoattractive influence of ovarian fluid on sperm swimming behavior

Post-copulatory opportunities for sperm competition and cryptic female choice provide no offspring fitness benefits in externally fertilizing salmon

There is increasing evidence that females can somehow improve their offspring fitness by mating with multiple males, but we understand little about the exact stage(s) at which such benefits are gained. Here, we measure whether offspring fitness is influenced by mechanisms operating solely between sperm and egg. Using externally-fertilising and polyandrous Atlantic salmon (Salmo salar), we employed split-clutch and split-ejaculate in vitro fertilisation experiments to generate offspring using designs that either denied or applied opportunities for sperm competition and cryptic female choice. Following fertilisations, we measured 140 days of offspring fitness after hatch, through growth and survival in hatchery and near-natural conditions. Despite an average composite mortality of 61%, offspring fitness at every life stage was near-identical between groups fertilised under the absence versus presence of opportunities for sperm competition and cryptic female choice. Of the 21,551 and 21,771 eggs from 24 females fertilised under monandrous versus polyandrous conditions, 68% versus 67.8% survived to the 100-day juvenile stage; sub-samples showed similar hatching success (73.1% versus 74.3%), had similar survival over 40 days in near-natural streams (57.3% versus 56.2%), and grew at similar rates throughout. We therefore found no evidence that gamete-specific interactions allow offspring fitness benefits when polyandrous fertilisation conditions provide opportunities for sperm competition and cryptic female choice

Cryptic haplotype‐specific gamete selection yields offspring with optimal MHC immune genes

Females choose specific mates in order to produce fitter offspring. However, several factors interfere with females' control over fertilization of their eggs, including sneaker males and phenotypically unpredictable allele segregation during meiosis. Mate choice at the individual level thus provides only a poor approximation for obtaining the best genetic match. Consequently, postcopulatory sperm selection by female oocytes has been proposed as a mechanism to achieve complementary combinations of parental haplotypes. Here, using controlled in vitro fertilization of three‐spined stickleback eggs, we find haplotype‐specific fertilization bias toward gametes with complementary major histocompatibility complex (MHC) immunogenes. The resulting zygote (and thus offspring) genotypes exhibit an intermediate level of individual MHC diversity that was previously shown to confer highest pathogen resistance. Our finding of haplotype‐specific gamete selection thus represents an intriguing mechanism for fine‐tuned optimization of the offspring's immune gene composition and an evolutionary advantage in the Red Queen dynamics of host‐parasite coevolution

A Survey of Photoperiodic Response and Morphological Variation Across a Latitudinal Gradient in Threespine Stickleback

x, 36 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.Natural biological variation exists at different geographic scales. We compared phenotype distribution across latitude, region and habitat type in threespine stickleback (Gasterosteus aculeatus) to determine local adaptation. To quantify variation in photoperiodic response, the day length cue was used to time sexual maturation and morphological characters across these various scales. Using lab-reared lines, we developed an index of sexual maturation and experimentally determined critical photoperiod for Alaskan and Oregon populations. Results showed that photoperiodic response existed in Alaskan but not Oregon populations. We also collected morphological data and made comparisons between wild Alaskan and Oregon populations and found similarities within habitat type across latitude but differences across region and habitat type. These data support the hypothesis that local adaptation results in variation across geography and habitat and, in stickleback, parallel evolution of morphological phenotypes within similar but geographically distant habitats.Committee in Charge: William E. Bradshaw, Chair; William A. Cresko; Christina M. Holzapfe

Cryptic haplotype‐specific gamete selection yields offspring with optimal MHC immune genes

Females choose specific mates in order to produce fitter offspring. However, several factors interfere with females' control over fertilization of their eggs, including sneaker males and phenotypically unpredictable allele segregation during meiosis. Mate choice at the individual level thus provides only a poor approximation for obtaining the best genetic match. Consequently, postcopulatory sperm selection by female oocytes has been proposed as a mechanism to achieve complementary combinations of parental haplotypes. Here, using controlled in vitro fertilization of three‐spined stickleback eggs, we find haplotype‐specific fertilization bias toward gametes with complementary major histocompatibility complex (MHC) immunogenes. The resulting zygote (and thus offspring) genotypes exhibit an intermediate level of individual MHC diversity that was previously shown to confer highest pathogen resistance. Our finding of haplotype‐specific gamete selection thus represents an intriguing mechanism for fine‐tuned optimization of the offspring's immune gene composition and an evolutionary advantage in the Red Queen dynamics of host‐parasite coevolution

Smart Drugs “As Common As Coffee”: Media Hype about Neuroenhancement

Background: The use of prescription drugs to improve cognitive functioning in normal persons -"neuroenhancement" - has gained recent attention from bioethicists and neuroscientists. Enthusiasts claim that the practice is widespread and increasing, and has many potential benefits; however recent evidence provides weak support for these claims. In this study we explored how the newsprint media portrays neuroenhancement

Migrant health worker deaths during Covid-19: a methodological exploration and initial estimates

Migrants comprise a significant proportion of health workforces that have long been recognised as being at high risk of experiencing adverse outcomes from contracting Covid-19. However, there is a paucity of high-quality research data on the risks of such outcomes faced by migrant health workers compared with non-migrant workers. This paper explores the available data around Covid-19 deaths, health workers, and migration and develops a methodology to estimate how many migrant health workers died due to Covid-19. It presents preliminary assessments of the numbers of such workers based on statistical data from four trial countries chosen for their differences in terms of proportions of foreign-born health workers and development contexts – India, Mexico, Nigeria and the UK. We identify the age-sex standardised approach as the best-available one for this enumerative task. However, the paper identifies the lack of robust data needed to confidently quantify the relative differences in risk of death faced by migrant health workers compared with their non-migrant colleagues. We reaffirm the World Health Organization’s advocacy of standardised measurement and reporting of Covid-19 impacts, and, on the basis of this research, extend its recommendations to improve data on the health workforce to enable disaggregation by sex, age, ethnicity, occupation, health status, migration status, country of origin and whether employed in public or private health care delivery, and to institute better data systems with greater capacity for collecting and analysing disaggregated data. Such advances would go a long way to redressing the near-invisibility of migrant health workers (and migrants more generally) in Covid-19 impact studies and to improving their working conditions

Migrant Health Worker Deaths During Covid-19: a Methodological Exploration and Initial Estimates

Migrants comprise a significant proportion of health workforces that have long been recognised as being at high risk of experiencing adverse outcomes from contracting Covid-19. However, there is a paucity of high-quality research data on the risks of such outcomes faced by migrant health workers compared with non-migrant ones. This paper explores the available data around Covid-19 deaths, health workers, and migration and develops a methodology to estimate how many migrant health workers died due to Covid-19. It presents preliminary assessments of the numbers of such workers based on statistical data from four trial countries chosen for their differences in terms of proportions of foreign-born health workers and development contexts – India, Mexico, Nigeria and the UK. We identify the age-sex standardised approach as the best-available one for this enumerative task. However, the paper identifies the lack of robust data needed to confidently quantify the relative differences in risk of death faced by migrant health workers compared with their non-migrant colleagues. We concur with the WHO’s advocacy of standardised measurement and reporting of Covid-19 impacts, and, on the basis of this research, extend it to recommend: the use of standard country codes, age breaks and formats across global datasets; improved data on the health workforce to enable disaggregation by sex, age, ethnicity, occupation, migration status, country of origin and by public/private health care delivery; and significantly improved data systems with greater capacity for collecting and analysing disaggregated data. Such improvements will go a long way to redressing the near-invisibility of migrant health workers (and migrants more generally) in Covid-19 impact studies and help improve working conditions of the health workforce

Retrospective Observational Study of Atypical Winter Respiratory Illness Season Using Real-Time Syndromic Surveillance, England, 2014-15

During winter 2014–15, England experienced severe strains on acute health services. We investigated whether syndromic surveillance could contribute to understanding of the unusually high level of healthcare needs. We compared trends for several respiratory syndromic indicators from that winter to historical baselines. Cumulative and mean incidence rates were compared by winter and age group. All-age influenza-like illness was at expected levels; however, severe asthma and pneumonia levels were above those expected. Across several respiratory indicators, cumulative incidence rates during 2014–15 were similar to those of previous years, but higher for older persons; we saw increased rates of acute respiratory disease, including influenza like illness, severe asthma, and pneumonia, in the 65–74- and >75-year age groups. Age group–specific statistical algorithms may provide insights into the burden on health services and improve early warning in future winters