Czechia

The host gut microbiome functions in digestion and immune defense, but additionally influences cognitive behavior. Habitat and diet are strong influencers in shaping the gut microbiome. However, among closely related species, phylogenetic relatedness is a strong predictor of gut microbiome community composition. Although phylogeny is a strong predictor, the impact hybridization has on the gut microbiome is poorly known. To explore this, we sampled feces from nestlings across a hybrid zone transect for black-capped (Poecile atricapillus) and Carolina chickadees (Poecile carolinensis) during the 2021 and 2022 breeding seasons. These nestlings were brought back to the Lehigh University Animal Facility and raised to adulthood under common conditions for cognitive testing. Fecal samples were taken at multiple time points and used to characterize the gut microbiome community composition. To do this, we extracted microbial DNA and sequenced the V3-V4 region of the 16S rRNA gene. Using amplicon sequence variants (ASVs), we compared the abundance and diversity of bacterial taxa across ancestry groups and at different time points after experiencing common conditions. Being raised under common conditions led to a decreased alpha diversity for parental species, but not for hybrids. After standardizing environmental conditions, differences between ancestry groups in abundance of specific gut phyla and specific ASVs suggests that genetic variation also plays a significant role in gut microbial composition. Alpha diversity and abundance of individual ASVs seemed to correlate with cognitive performance as well. Assessing the factors that influence gut microbiome diversity in two closely related sister species and their hybrids helps us to better understand the various factors that shape host-microbiome communities.

SEB Conference 2024

Microbiome Diversity and Cognition in Hybridizing Chickadees

avian

microbiome

hybridization

cognition

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technical paper

Organisms exhibit reversible physiological adjustments as a response to rapidly changing environments. Yet such plasticity of the phenotype is gradual and may lag behind environmental fluctuations, thereby affecting long‐term average performance of the organisms. By supplying energy and essential compounds for optimal tissue building, food determines the range of possible phenotypic changes and potentially the rate at which they occur. Here, we assess how differences in the dietary supply of essential lipids modulate the phenotypic plasticity of an ectotherm facing thermal fluctuations. We use three phytoplankton strains to create a gradient of polyunsaturated fatty acid and sterol supply for Daphnia magna under constant and fluctuating temperatures. We used three different fluctuation periodicities to unravel the temporal dynamics of gradual plasticity and its long‐term consequences for D. magna performance measured as juvenile somatic growth rate. In agreement with gradual plasticity theory, we show that in D. magna, fluctuation periodicity determines the differential between observed growth rates and those expected from constant conditions. Most importantly, we show that diet modulates both the size and the direction of the growth rate differential. Overall, we demonstrate that the nutritional context is essential for predicting ectotherm consumers' performance in fluctuating thermal environments.

Food quality shapes ectotherm gradual phenotypic plasticity

During winter, certain fish species remain active while others become dormant, which is characterized by low metabolic rate, fasting, and negligible or negative growth. We hypothesized that winter dormancy is a survival strategy that arises in poleward species that tolerate severe, uncompensated constraints of cold on physiological performance. To date, we have measured the metabolic, exercise, and digestive performance of cunner (Tautogolabrus adspersus), a model winter-dormant fish, acclimated or acutely exposed to a wide range of temperatures (2-26°C). Contrary to our hypothesis, we found partial cold compensation of nearly all metabolic and exercise performance metrics studied, similar to winter-active species. Further, after bypassing the behavioural fasting response during dormancy using repeated force-feeding during cold acclimation, cunner were able to digest food and subsequently exhibit positive growth compared to negative growth of the voluntarily fasting fish. Only responsiveness to stimuli during the C-start escape response was greatly constrained in the cold even after acclimation, suggesting a thermal sensory limitation that may help explain the need to become dormant. To further explore this idea, we measured the C-start escape performance of six phylogenetically-diverse species along the spectrum of overwintering strategies from winter-dormant to winter-lethargic to winter-active. As we predicted, responsiveness was greater and more plastic in the winter-lethargic and -active species compared to -dormant species. While most physiological performance traits in cold dormant fish remain robust, impaired responsiveness to C-start stimuli may be a weak thermal link driving dormancy as an overwintering strategy among fishes.

Do thermal constraints on physiological performance explain the use of winter dormancy among fishes?

Pollinator behaviour is vital to plant-pollinator interactions, affecting the acquisition of floral rewards, patterns of pollen transfer, and plant reproductive success. During buzz pollination, bees produce vibrations with their indirect flight muscles to extract pollen from tube-like flowers. Vibrations can be transmitted to the flower via the mandibles, abdomen, legs, or thorax directly. Vibration amplitude at the flower determines the rate of pollen release and should vary with the coupling of bee and flower. This coupling often occurs through anther biting, but no studies have quantified how biting affects flower vibration. Here, we used high-speed filmography to investigate how flower vibration amplitude changes during biting in Bombus terrestris visiting two species of buzz-pollinated flowering plants: Solanum dulcamara and S. rostratum (Solanaceae). We found that floral buzzing drives head vibrations up to three times greater than those of the thorax, which doubles the vibration amplitude of the anther during biting compared to indirect vibration transmission when not biting. However, the efficiency of this vibration transmission depends on the angle the bee bites the anther. Variation in transmission mechanism, combined with the diversity of vibrations across bee species, yields a rich assortment of potential strategies that bees could employ to access rewards from buzz pollinated flowers.

Buzz-pollinating bees deliver thoracic vibrations to flowers through periodic biting

The Atlantic bluefin tuna Thunnus thynnus (ABFT) is an extremely valuable marine fish, a pelagic predator with physiological adaptations to a lifestyle of ceaseless swimming, notably partial endothermy and obligatory ram ventilation. Very little is known about ABFT energetics but, by comparison to ‘normal’ teleosts, they are expected to have elevated standard and routine metabolic rates (SMR and RMR) and aerobic metabolic scope (AS), and high aerobic swimming performance. We used swim tunnel respirometry to investigate this in age 0+ juveniles (mass 550g, forklength 30cm) held at 19 °C. The tuna did not enjoy the tunnel, they lost equilibrium and became agitated below 1.4 bodylengths per second (BL s-1), refused to swim faster than 2.2 BL s-1, and had their highest metabolic rates when agitated. Their SMR was about 1.5 times those of other Mediterranean fishes at similar sizes and temperatures, whereas their AS was two to threefold higher. Video analysis of the juveniles in their rearing tank revealed they were actually cruising spontaneously at speeds between 2.5 and 3.5 BL s-1. Extrapolation of respirometry data to 3 BL s-1 indicated an RMR about fourfold higher than direct measures, by tank respirometry, in other Mediterranean species. These preliminary observations would confirm longstanding predictions about the comparative energetics of ABFT but more work is clearly needed and some is ongoing.

Insights into the in-vivo physiological energetics of juvenile Atlantic bluefin tuna

The transition from water to air, or terrestrialization, is a key event in the evolution of many marine organisms to exploit new ecological niches for food, stress buffers, and to access higher and temperature-independent air oxygen concentrations. Microorganisms are pivotal for host adaptation, however their contribution to overcoming the challenges posed by the lifestyle changes from water to land is not well understood. In this study, we examined how microbial associations with a key multifunctional organ, the gill, is involved in the intertidal adaptation of mangrove dwelling fiddler crabs, which are dual-breathing organisms. Electron microscopy revealed a rod-shaped bacterial layer tightly connected to the gill lamellae of five crab species sampled across a latitudinal gradient spanning the central Red Sea to the southern Indian Ocean. The gill bacterial community diversity assessed with 16S rRNA gene amplicon sequencing was consistently low across crab species, and the same actinobacterial group, namely Ilumatobacter, was dominant regardless of the geographic location of the host. Using metagenomics and metatranscriptomics, these members of actinobacteria were found to potentially be able to convert ammonia to amino acids and could help eliminate the toxic sulphur compounds and carbon monoxide to which crabs are constantly exposed. These results indicate that gill bacteria can play a role in the adaptation of animals in dynamic intertidal ecosystems. Hence, this relationship is likely to be important in the ecological and evolutionary processes of the transition from water to air and deserves further attention, including the ontogenetic onset of this association.

The role of gill-associated bacteria in the adaptation to terrestrial environments of mangrove crabs

Variation in animal behaviour has recently gained traction in understanding variation within physiological traits. Integrating animal behaviour may be particularly important for measuring metabolism as oxygen demand is sensitive to the behavioural state of the individual. For example, a fish exposed to a novel environment may exhibit individual differences in metabolic oxygen demand as a consequence of behavioural responses, such as activity and exploration related to anxiety in an unfamiliar context. On this background, we sought to explore variation in routine metabolism (RMR) as a consequence of novelty to the testing chamber and substrate color – with black representing a low anxiety state and white a high anxiety state – using a repeated measures experimental design to track differences in individual traits across treatments. Finally, as shoaling is thought to reduce predation risk and therefore may influence stress-related responses, we tested a subset of individuals in a third iteration of respirometry with a size-matched conspecific. Contrary to our predictions, we found no difference in RMR with black vs. white substrate; whereas, RMR was significantly higher during the second iteration of respirometry, independent of substrate color. Interestingly, the total oxygen consumption in our paired fish tests was not significantly different from the mean RMR in the initial run, potentially indicating a mollifying social effect. Behavioural data suggests differences in activity/exploration that complement metabolic patterns. Our data indicates individual variation in behaviour, especially in response to novelty, and its impacts on the stability of metabolic measurements.

Patterns of individual variation in metabolism and behavioural responses in the sheepshead minnow (Cyprinodon variegatus)

Risk assessments have identified prey limitation as one of the strongest risk factors for juvenile salmon migration survival under climate change. In British Columbia, Canada, juvenile Chinook salmon (Oncorhynchus tshawytscha) may experience prolonged periods of food deprivation during their marine entry and first marine winter. In this study we conducted a lab-based food deprivation and refeeding experiment to assess the physiological consequences of starvation and
identify transcriptional responses to develop mRNA-based biomarkers for food limitation in the gill of juvenile Chinook salmon. Throughout the experiment, fish were held at both summer (16oC; marine entry) and winter (8oC; overwintering) temperatures and were sampled at least every 2 weeks collecting physiological data (condition factor, hepatosomatic index, morphometrics) as well as liver and gill tissue for RNA-sequencing. As expected, both food-deprivation treatments demonstrated significant differences from their fed counterparts with decreases in condition factor and hepatosomatic index with 14 to 28 days, respectively. The 16oC acclimation treatment was the first to reach a starvation endpoint (10% mortality) by 35 days,
with the 8oC treatment persisting until 56 days (20% reduced condition factor). During refeeding, condition factor returned rapidly in both acclimation treatments, 9-12 days post feed introduction. Further, hepatosomatic index recovered within 3 days and increased up to 2.5-fold when compared to unfasted counterparts by days 12-21 of the refeeding process. Conserved transcriptional responses between 8oC and 16oC treatments will be discussed in the context ofpathways modified by starvation, and candidate biomarkers for nonlethal screening in wild
juvenile Chinook salmon.

 Food deprivation, physiological impacts, and associated transcriptional responses in juvenile Chinook salmon

Aquatic animals including fish species are being exposed to climate-related stressors such as temperature and hypoxia with increasing severity and frequency. Group living is an adaptive behaviour found in many species, including the majority of fish species, and associated with improved foraging success and protection from predators. As conditions change, however, individual motivations for group living may also change. Individual behaviours such as sociability, exploratory behaviour (boldness), and activity level, may be affected by climate-related stressors. This may lead to changes in group dynamics and shoal disruption. This study used rummy-nose tetra Hemigrammus rhodostomus as a model species, and tested boldness, sociability, and activity level in individuals under three conditions of temperature, and three conditions of oxygen level. Fish were then placed in groups of six under the same set of treatments, and group behaviour monitored for each individual. In this way, we hope to elucidate how individual changes in behaviour will impact group dynamics. We predict that individual sociability will be reduced, and boldness and activity increased, under increased temperature and low oxygen levels and that this will translate to reduced group cohesion under climate stressor conditions. We also predict significant interindividual variation in sociability, boldness, and activity level, and that this will impact the tendency of different individuals to associate together. Our study is the first, to our knowledge, to incorporate climate-related stressors into the study of effects of individual behaviour on group dynamics, and will provide much-needed information on a key adaptive behaviour in a changing world.

Effects of temperature and hypoxia on the role of individual behaviour in shaping group dynamics in a freshwater fish

‘Now we’re going to work in groups’ is often a phrase which causes a feeling of dread and anxiety in students, but it doesn’t need to. There is a plethora of advantages to structured group work, including the skills that students can develop, but also for authenticity in learning and assessment for learning. Teaching in groups can facilitate peer-peer feedback and subsequently independence from lecturers, leading ultimately to more independent and collegial graduates. Students supporting one another as the first port of call enhances efficiency for lecturers. Group work can also help to reduce the costs of the hidden curriculum: students who haven’t developed those skills can learn them from peers.
The advantages are also numerous for lecturers. In large modules, marking can be a significant workload and due to large volumes of marking, it can be impossible to provide truly meaningful feedback, without losing consistency by splitting the marking between staff. Incorporating group submissions means that there are fewer items to mark and therefore, feedback can be much more in depth and useful. The reduced number of submissions has enabled the design of an assessment which is significantly more authentic, efficiently addresses learning outcomes, and provides a learning experience for the students.
This talk will illustrate how I have introduced groupwork to be a significant part of my large first year module in a way that the students have enjoyed and benefitted from and the vital considerations to ensure success when designing similar schemes of work.

Working together: The use of groupwork to enhance authenticity in assessment and feedback.

Steadily more extreme heatwaves threaten crop production worldwide, primarily through reduced viability of gametes. The formation of male gametophytes is particularly susceptible to temperatures above ~36°C. We report here on molecular events that characterise male gametophytes as they develop under specific heat regimes and identify potential approaches for crop improvement. Cotton was used as a relatively heat-tolerant species to demonstrate compromised pollen function. Gametophytes were exposed to moderate (36/25°C, day/night) and extreme heat (38/28°C and 40/30°C) for five days, coinciding with meiosis (tetrads) and mitosis (uninucleate and binucleate microspores) and pollen maturation. Morphological and physiological changes were analysed alongside molecular responses in each developmental stage.
Severe cell damage was observed when tetrads were exposed to 40/30°C, resulting in failed dehiscence, smaller pollen grains, and yield loss. Molecular analysis demonstrated that each stage of pollen development has qualitatively distinct transcriptome and proteome profiles. Notably, extreme heat induced unique expression patterns in tetrads, in contrast with the relatively heat-tolerant mature pollen and leaves. We demonstrated that although molecular chaperones were abundant during meiosis, where they putatively refold aggregated proteins, they were not highly up-regulated in the late stages of pollen development. We speculate that accelerated metabolism contributes to the susceptibility of meiotic cells to heat. Identifying the precise molecular events underlying the susceptibility of gamete formation to heat is a challenging but vital goal for plant (and animal) research.

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Food quality shapes ectotherm gradual phenotypic plasticity

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