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Rapid global warming and increasingly severe heatwaves pose a serious threat to organisms in the Anthropocene. Aquatic ectotherms are especially at risk, as their body temperature generally matches that of the environment. Evolutionary adaptation is one of the few processes which might allow animal populations to better cope with these thermal challenges, yet it is rarely experimentally examined in vertebrates. Our group previously assessed the evolutionary potential for acute upper thermal tolerance by artificially selecting zebrafish on this trait, and found that evolution towards higher tolerance is possible but concerningly slow. We are currently conducting a new selection experiment using the same model species to study the evolution of thermal performance, which is distinct from acute thermal tolerance as it requires survival and resilience under chronic thermal stress. Based on growth performance in the juvenile life stage as the trait, we are selecting zebrafish to increase this performance at warm (34.5°C), control (28°C) or cold (20°C) temperatures. Starting with a genetically diverse ancestral population (6th captive generation offspring of wild-caught zebrafish, n&gt;1000), we produced the F0 generation which was used to establish the respective warm-adapted, control, and cold-adapted lines. Each line consists of two replicates with ~300 fish/replicate, and we select the 33% with the highest growth rate to contribute to the next generation. Although this experiment is still ongoing, we present here the results for the F0 to F2 (n&gt;5400) and place them in the context of key questions about the ability of animals to adapt to climate change.

SEB Conference Prague 2024

Experimental evolution of thermal performance in zebrafish

Rapid global warming and increasingly severe heatwaves pose a serious threat to organisms in the Anthropocene. Aquatic ectotherms are especially at risk, as their body temperature generally matches that of the environment. Evolutionary adaptation is one of the few processes which might allow animal populations to better cope with these thermal challenges, yet it is rarely experimentally examined in vertebrates. Our group previously assessed the evolutionary potential for acute upper thermal tolerance by artificially selecting zebrafish on this trait, and found that evolution towards higher tolerance is possible but concerningly slow. We are currently conducting a new selection experiment using the same model species to study the evolution of thermal performance, which is distinct from acute thermal tolerance as it requires survival and resilience under chronic thermal stress. Based on growth performance in the juvenile life stage as the trait, we are selecting zebrafish to increase this performance at warm (34.5°C), control (28°C) or cold (20°C) temperatures. Starting with a genetically diverse ancestral population (6th captive generation offspring of wild-caught zebrafish, n>1000), we produced the F0 generation which was used to establish the respective warm-adapted, control, and cold-adapted lines. Each line consists of two replicates with ~300 fish/replicate, and we select the 33% with the highest growth rate to contribute to the next generation. Although this experiment is still ongoing, we present here the results for the F0 to F2 (n>5400) and place them in the context of key questions about the ability of animals to adapt to climate change.

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Biodiversity is increasingly under threat due to climate events. Studies examining the impact of climate change on biodiversity often tend to focus on understanding species survival. However, for persistence of species, equal focus requires on reproduction, a process is more vulnerable to heat stress than survival. This vulnerability arises from the susceptibility of gametes and gonads at sublethal temperatures, with sensitivity levels varying across different life stages. Despite this knowledge, majority of existing studies tend to focus on the effects of heatwaves on juvenile or adult stages or/and neglecting the cumulative impact across life stages and potential recovery dynamics. To Address this critical gap, we used Drosophila melanogaster as a model to explore (i) how does heat stress at different life stages affect male reproduction? (ii) how does life stage-specific heatstress affect males’ ability to recover? (iii) What are the mechanisms underlying the reproductive consequences of heat stress? Our findings reveal that gametes and gonads are highly susceptible to heat stress. Cummulative and presistence effect of heat stress can severely damage male reproductive fitness. Such effects could speed up population declines due to loss of fertility, highlighting the need to include effects on reproduction and their recovery in studies of biodiversity loss.

Unravelling the impact of frequent heatwaves on insect reproduction

First, we used isolated hearts from three teleost species with very different values for maximum heart rate (fHMax: zebrafish, ~300 bpm; Atlantic salmon, ~120 bpm and lumpfish, ~80 bpm) to examine the response of intrinsic fH and atrioventricular delay (AVd) to acute changes in temperature. Heart rate increased linearly with temperature (Q10s of 1.91, 1.50 and 2.67 for zebrafish 16–28℃, salmon 8–20℃ and lumpfish 8–14℃, respectively), whereas AVd decreased (Q10 0.56–0.69). However, the absolute values for AVd showed considerable inter-specific variation. For example, the AVd at 16℃ for 28℃-acclimated zebrafish was ~2 and 3x shorter than that of 8℃-acclimated salmon and lumpfish, respectively. Further, we extrinsically paced their hearts (i.e., at 50, 100 and 150 bpm for zebrafish and 50, 70 and 90 bpm for lumpfish and salmon), and AVd decreased with temperature independent of pacing frequency (i.e., temperature had a direct effect on AV function). Next, we compared 8- vs. 15℃-acclimated salmon, and found that 8℃ fish: 1) exhibited cardiac resetting (i.e., had a higher fH from 12–20℃); 2) experienced 2:1 AV block ~1.7℃ earlier than warm-acclimated fish; and 3) had an ~20% shorter AVd at all test temperatures and pacing frequencies. Finally, we found that although conduction velocity (CV) was consistently ~100–300x faster across the ventricle and atrium than the AV funnel, it also exhibited a plastic thermal response. These data highlight the acclimation capacity of AVd and CV, and suggest that they are key contributors to cardiac thermal compensation and phenotypic plasticity.

Atrioventricular Delay and Cardiac Electrical Conduction Play Important Roles in Determining the Maximum Heart Rate of Fishes

During development, phenotype can be adaptively modulated by environmental conditions. However, as weather variability increases under climate change, the potential for maladaptive responses to environmental variations may increase. In the arid-adapted zebra finch, parents emit “heat-calls” when experiencing heat during incubation, which adaptively affects offspring growth in the heat, and adult heat tolerance. This suggests that heat-call exposure may adjust individual phenotype to hot conditions, potentially compromising individual sensitivity to cool weather conditions. To test this hypothesis, we manipulated individual prenatal acoustic and postnatal thermal experiences during development, and sought to assess subsequent chronic responses to thermal fluctuations at adulthood. We measured heterophil to lymphocyte (H/L) ratios in adults, when held in outdoor aviaries during two summers and two winters. We found that birds exposed to heat-calls as embryos, had consistently lower H/L ratios than controls at adulthood, irrespective of the season. Nonetheless, in all birds, the H/L ratio did vary with short-term weather fluctuations (2, 5 or 7 days), increasing at more extreme (low and high) air temperatures. In addition, the H/L ratio was higher in males than females. Overall, heat-call exposed individuals did not show a stronger chronic response in winter than control individuals, and instead appeared more resilient to thermal variability. Our findings therefore suggest that heat-call exposure did not compromise individual sensitivity to low temperatures at adulthood. Our study also reveals that prenatal sound can lead to long-term differences in individual physiology or quality/condition, which are consistent with previously-demonstrated reproductive fitness differences.

A prenatal acoustic signal of heat reduces a biomarker of chronic stress at adulthood across seasons in an arid-adapted bird

In a global change scenario, emerging infectious diseases are becoming more frequent and harder to prevent or control. In birds, malaria parasites are responsible for wildlife population declines of many species worldwide. Despite being exposed to the same risk, there is a clear inter-individual variation in the susceptibility to malaria. As hormone-mediated maternal effects may act as mechanisms of phenotypic plasticity facilitating the offspring's adaptation to new environments, here, we explored the dose-dependent response to maternal yolk hormones by experimentally injecting two different testosterone (T) doses into the egg yolks of wild great tits. High prenatal T levels could carry short-term benefits (i.e. accelerated metabolism and growth) but carry long-term costs including accelerated telomere shortening (i.e. a hallmark of ageing) and depressed immunity that could both increase susceptibility to malaria. Our preliminary results show no effects of T-treatment on body size or condition of nestlings, but chicks treated with the higher T-dose had higher breathing rates. Nestling survival to fledging was positively influenced by prenatal T (higher T-dose > control and lower T-dose), while we found no evidence of an effect on hatching success or post-fledging survival. The medium to long-term costs of prenatal T are currently investigated through post-natal telomere dynamics and malaria susceptibility measurements at the post-fledging stage, with the prediction that the short-term benefit of prenatal T should lead to shorter telomeres and accentuated malaria susceptibility. Future studies should carefully consider a range of concentrations, as the balance of costs and benefits of prenatal hormones may be dose-dependent.

Effects of elevated yolk testosterone levels on malaria susceptibility, aging, growth, and survival in a wild passerine

Climate change causes significant changes in aquatic and terrestrial habitats, making them more susceptible to invasive species relative to native ones. However, our understanding of how metabolic responses to environmental stressors facilitate biological invasions is limited. In this study, we measured the metabolism of native (Gammarus pulex) and invasive (Dikerogammarus villosus) amphipods under different thermal and predation risk conditions to determine the plasticity of each species. We discovered an interactive and species-dependent effect of temperature and predation risk on the body-mass scaling of metabolic rate. The metabolic scaling relationship of the invasive species was insensitive to temperature changes, in contrast to that of the native species. Our results suggest that invasive species are less sensitive to increasing temperature, which may facilitate their invasion success in habitats vulnerable to global warming or at thermally polluted locations. Moreover, both species limited their metabolic responses to predation risk when the temperature increased, which may have negative implications for their defensive responses. Thus, attempts to understand effects of global warming in isolation from additional factors, such as predation pressure or taxonomic identity of species dominating in local communities, may lead to underestimation of its true ecological consequences

“Too hot to fear?” Metabolic response of ectothermic prey to predation risk is modulated by global warming.

European green crabs (Carcinus maenas) are a prolific non-indigenous species (NIS) in North America that negatively impacts local species important for Indigenous food sovereignty and commercial shellfish production. Despite the low genetic diversity due to serial bottlenecks, green crab spread in North America is likely facilitated by high thermal tolerance and plasticity. How do C. maenas maintain thermal tolerance with seemingly low adaptive potential? To answer this question, this talk will explore environmental and genetic contributions to C. maenas thermal tolerance, and compare physiological and molecular mechanisms of plasticity between non-native populations in Massachusetts and Washington, USA. Crabs were exposed to cold (5ºC), ambient (15ºC), or warm (25ºC or 30ºC) temperatures for at least one month, and monitored weekly using time-to-right and respirometry. In both populations, crab righting response and rate of oxygen consumption slowed at 5ºC and sped up at 25ºC or 30ºC when compared to 15ºC. Metabolome and lipidome analyses elucidated biochemical pathways used to maintain homeostasis at experimental temperatures, with broad molecular shifts occurring as early as three days after exposure began. Crabs were also genotyped at a putative chromosomal inversion that contains a high proportion of amino acid-changing mutations and is strongly associated with sea surface temperature. Interrogation of individual crab responses to temperature revealed within-treatment physiological differences influenced by genotype, suggesting a genetic contribution to thermal plasticity. This work illustrates the importance of understanding factors that contribute to inter-individual variation in thermal tolerance, which may improve overall population fitness and influence spread of NIS.

Investigating genomic and plastic contributions to thermal tolerance in a non-indigenous crab

An exceptionally species-rich endemic fauna lives in the freshwater subarctic Lake Baikal in Siberia. The most diverse taxonomic group in the lake's benthic communities are amphipods (Crustacea), which play a significant role in the functioning of the ecosystem and constitute 45.3% of all freshwater epigean amphipod species in the world. The Baikal endemic amphipod fauna is represented mainly by specialists, narrowly adapted to low temperatures and ultra-oligotrophic conditions of the lake. The aim of this work was to study the physiological, biochemical, and molecular adaptation to cold in the Baikal endemic amphipod species Eulimnogammarus verrucosus (Gerstfeldt, 1858), which reproduces in winter at temperatures close to zero.
We analyzed changes in the proteome and biochemical markers of metabolism and stress in successive field samplings in autumn, winter, and summer. In addition, we conducted a laboratory experiment to study the effect of cooling on the proteome and biochemical markers of this species. The comparative field-laboratory approach made it possible to reveal the adaptive capacities of this species to cooling and to investigate how these capacities are realized during the reproduction cycle in the field. 


Adaptations to low temperatures in winter-reproducing Baikal endemic amphipod Eulimnogammarus verrucosus - insights from the field sampling and laboratory experiments

This work examined the role of central venous pressure (CVP), an understudied component of cardiac regulation in fishes, in tilapia faced with a number of environmental challenges. First, we measured the heart rate (fH), cardiac output (Q), stroke volume (SV) and CVP of 30℃-acclimated fish, and those acutely exposed to 24℃, following titrations of zatebradine hydrocholoride (i.e., a pharmacological agent that decreases intrinsic fH). As predicted, fH and Q were ~40% lower in the acutely cooled fish (Q10 ~ 2.3) and both groups had very comparable (i.e., within 10%) values for SV (i.e., SV was temperature insensitive). Interestingly, the CVP of fish at 24℃ was higher than that in 30℃-acclimated fish across all concentrations of zatebradine (i.e., CVP increased from 0.04–0.11 kPa vs. -0.09–0.07 kPa, respectively, as fH was reduced), and this was reflected in a right-shifted relationship between CVP and SV for the 24℃ fish. These data suggest that the acutely cooled tilapia required a higher CVP to attain a similar SV as compared to 30℃ conspecifics. Ongoing experiments are now being performed on 25℃-acclimated tilapia to measure the same cardiovascular parameters (with the addition of oxygen consumption and tissue-oxygen extraction) when: i) exposed to critical thermal maximum (CTMax) and minimum (CTMin) tests at normoxia (100% air sat.); and ii) when exposed to acute/severe hypoxia (30% air sat.) followed by a CTMax test. These data will also be presented at the SEB 2024 conference in Prague.

What Role Does Central Venous Pressure Play in Supporting Cardiac Function in Nile Tilapia (Oreochromis niloticus) Exposed to Environmental Challenges?

Thrombosis and thromboembolic complications are the dominant pathology in the general structure of mortality and mortality in the adult population. For this reason, the development of new potential drugs with antithrombotic effects with a low risk of side effects is one of the promising areas of modern science.

Preclinical evaluation of the effectiveness of antithrombotic drugs

In a 10-month experimental study, we assessed the combined impact of warming and acidification on critical life stages of small-spotted catshark (Scyliorhinus canicula). Using recently developed frameworks, we disentangled individual and group responses to two climate scenarios projected for 2100 (SSP2-4.5: Middle of the road and SSP5-8.5: Fossil-fueled Development). Seasonal temperature fluctuations revealed the acute vulnerability of embryos to summer temperatures, with hatching success ranging from 82% for the control and SSP2-4.5 treatments to only 11% for the SSP5-8.5 treatment. The death of embryos was preceded by distinct individual growth trajectories between the treatments, and also revealed inter-individual variations within treatments. Embryos with the lowest hatching success had lower yolk consumption rates, and growth rates associated with a lower energy assimilation, and almost all of them failed to transition to internal gills. Within 6 months after hatching, no additional mortality was observed due to cooler temperatures.

Experimental evolution of thermal performance in zebrafish

Next from SEB Conference Prague 2024

Unravelling the impact of frequent heatwaves on insect reproduction

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