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During heat exposure, birds face a trade-off between
hyperthermia and dehydration. Numerous studies have
attempted to predict cooling costs for birds, which are expected
to increase with global warming. Although modelling dehydration
risk is important, it does have its limitations, and do not replace
direct measurement of hydration status. In fact, studies
assessing the effects of temperature on the hydration status of
wild birds are surprisingly rare. In this article, we discuss the
experimental evidence for the hyperthermia–dehydration
tradeoff, and the limitations of modelling avian dehydration risk
through set thermal limits. In addition, we present a systematic review of physiological
markers of dehydration for avian species. We find that plasma
osmolarity and plasma concentrations of sodium and chloride
are the most reliable markers of dehydration, and seem to scale
with dehydration severity. Hematocrit appears to predict
dehydration but multiple concerns impede its suitability. Plasma
concentrations of uric acid, urea and creatinine may represent
adequate markers of dehydration. Alternatively, characteristics
of the excreta may represent less-invasive means to assess
hydration status.

SEB Conference 2024

Physiological markers of avian dehydration and perspectives in ecophysiology: assessing the hyperthermia-dehydration tradeoff

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Changed seasonality and increasing temperatures are hallmarks of the ongoing climate change and challenge the viability of individuals, populations, species, and ecosystems. Recent research suggests that aquatic ectotherms such as fish, especially early life-stages are vulnerable to increasing temperatures. To understand, predict, and possibly mitigate the consequences of climate change, it is thus crucial to investigate the causes of variation in early life-stage thermal performance of ectotherms. Egg size has received considerable attention in this context, but previous studies have been limited to species and population comparisons, neglecting the role of egg size variation structuring variation in thermal performance among individuals within populations. This constrains our mechanistic understanding of egg size as a modulator of thermal performance and how organisms may respond to climate change. To test how intraspecific variation in egg size influences thermal performance, we conducted a split-brood experiment where eggs from 64 female pike (Esox lucius) from the same population were fertilized and incubated at four temperatures until hatching. Results showed that larger eggs had higher hatching performance in low temperatures whereas smaller eggs were more successful in higher temperatures. This suggests that fitness advantages associated with larger eggs may change in the future climate.

Smaller pike eggs outperform bigger eggs in a global warming scenario

Wild organisms are usually infected with a whole range of parasites, however, the infection status of organisms is not usually taken into consideration in ecological and food web studies. The impact that parasites can have on their host organisms, affecting their food intake and internal resource use, might drive to differences in the isotopic composition or niche between infected and uninfected organisms, and thus to erroneous conclusions in stable isotope ecology studies. 
This is the first time that controlled diet-switch experiments and stable isotope analyses (whole tissue, bulk SIA, 13C and 15N) have been performed on a host-parasite system comparing infected and uninfected individuals. Our results highlight the importance of accounting for infection status when conducting ecological studies based on stable isotopes, also contributing to fill the gap of parasite contribution to food webs. 


Importance of accounting for the infection status of an organism in isotope ecology studies: Using feeding experiments as an example

Exploration provides information of the environment and its associated points of interest such as food, threats or mates. However, in experimental biology, exploration is vastly described as distance or area covered by the animals (typically rodents). Usually, experimental tests commonly used in laboratories tend to prioritise the minimisation of variables over the complexity of natural environments. While these setups have provided valuable insights, the technological advent of new analysis and 3D printing technologies, allows us to go beyond overly simplistic environments, in order to better understand animal behaviour in contexts that more closely mimic their natural habitats.
We designed an Enriched Open Field (EOF) by including modular plastic structures in a classic squared open field (OF) arena for mice in order to increase the number of environmentally relevant landmarks in the arena, so as the quantity of regions with exploratory salience. We tested CD-1 and C57/BL6 female mice roaming freely in the EOF and OF arenas for 10 minutes. 
As expected, we observed differences between strains, with greater exploration measures in the CD-1 strain. Animals tested in the EOF showed more consistent exploratory patterns, even if they were previously habituated to the modular pieces in the context of a home cage. The average speed of EOF tested animals was greater and the movement more continuous.
Our study suggests that the presence of structures may mimic more naturalistic environments, thereby promoting exploratory behaviours that are closer to those exhibited in the animals' natural habitat when foraging or looking for social cues. 


Towards a more naturalistic perspective: Enriched open field as an ethologically-relevant exploratory paradigm

The depletion of dissolved oxygen (DO) in global oceans is a growing concern. This phenomenon is observed in coastal and oceanic waters, where different mechanisms contribute. In the Estuary and Gulf of Saint Lawrence (SL), this process of deoxygenation has been documented and is mainly attributed to a greater inflow of the warm, DO-poor North American Central Waters deeper in the water column, isolated by a persistent pycnocline. The responses of organisms chronically under these conditions, particularly benthic invertebrates with low to no mobility, usually encompass molecular modifications (thus complex physiological changes), to cope with environmental hypoxia. Such changes might also be reflected on the proteome, given the range of functions of these molecules on cell structure and metabolism. However, the characterisation of complex proteomic responses in situ is not yet fully addressed. Therefore, the aim of this work is to describe and compare the proteomic profile of a benthic invertebrate across the natural deoxygenation gradient of the SL. We sampled individuals of the annelid Neloeanira tetragona from four subregions across the gradient of the SL and on a well oxygenated outgroup region, the Saguenay Fjord. Proteins were identified and quantified by high resolution LC-MS/MS on whole body samples. The profiles obtained were tested both via pairwise comparisons and multivariate modelling using environmental data. These analyses ultimately highlighted site-specific responses, particularly linked to DO levels, with an overrepresentation of energy metabolism, cell signalling and protein homeostasis pathways. N. tetragona exhibits a compensatory accumulation strategy to cope with environmental chronic hypoxia.

Proteomic profiling across the St. Lawrence River hypoxia gradient: a tale of the worm Neoleanira tetragona

Hearing has evolved independently many times in the animal kingdomand is prominent in various insects and
vertebrates for conspecific communication and predator detection. Among insects, katydid (Orthoptera: Tettigoniidae)
ears are unique, as they have evolved outer,middle, and inner ear components, analogous in their
biophysical principles to the mammalian ear. The katydid ear consists of two paired tympana located in each
foreleg. These tympana receive sound externally on the tympanum surface (usually via pinnae) or internally
via an ear canal (EC). The EC functions to capture conspecific calls and low frequencies, while the pinnae
passively amplify higher-frequency ultrasounds including bat echolocation. Together, these outer ear components
provide enhanced hearing sensitivity across a dynamic range of over 100 kHz. However, despite a
growing understanding of the biophysics and function of the katydid ear, its precise emergence and evolutionary
history remains elusive. Here, using microcomputed tomography (mCT) scanning, we recovered geometries
of the outer ear components and wings of an exceptionally well-preserved katydid fossilized in
Baltic amber (44 million years old). Using numerical and theoretical modeling of the wings, we show
that this species was communicating at a peak frequency of 31.62 (± 2.27) kHz, and we demonstrate that
the ear was biophysically tuned to this signal and to providing hearing at higher-frequency ultrasounds
(>80 kHz), likely for enhanced predator detection. The results indicate that the evolution of the unique ear
of the katydid, with its broadband ultrasonic sensitivity and analogous biophysical properties to the ears
of mammals, emerged in the Eocene.

Auditory tuning to conspecific acoustic signals in an Eocene katydid

Jumping is one of the most commonly used forms of locomotion by insects, and a characteristic trait of the Orthoptera (locusts, crickets, and allies). Their specialised jumping behaviours have evolved for many functions, including traversing long distances, evading predators, and initiation of flight. Although lots of work has been conducted on jumping behaviour across these contexts, jumps which rely on target perception, such as those used for navigating complex environments and hunting prey, have received little attention. In this study, we document a sophisticated vertical jumping behaviour in a neotropical predatory bush-cricket (Tettigoniidae: Meconematinae), whereby visual cues are utilised to aid in perception of target distance. We found that across different target heights (50, 75, and 100 mm), the insect adjusted the properties of its jump to ensure landing. As jump height increased, there was a significant increase in linear velocity (m/s) and decrease in angular velocity (rad/s). This decoupling between linear and angular velocity suggests that the animal is able to perceive the difference in height and establish the jump path prior to take-off. Despite jumping faster to the higher targets, the speed of rotation is adjusted during the jump, allowing the animal to land parallel to the target surface. This study offers evidence that some orthopterans can independently control both the speed at which they take off, and their rate of rotation, based on the visual cue of target distance to achieve a precise and controlled landing.

Jumping up a level: Target distance and angle estimation facilitates successful landing in a jumping glass katydid

Silk Production is one of the most prominent characteristics of spiders. The silk is extruded through spigots located on the spinnerets, which are single- to multimembered paired appendages at the end of the abdomen. Most extant spiders have three pairs of spinnerets, and in between either a cribellum (spinning plate) or a colulus (defunct vestigial organ), dividing these spiders into cribellate and ecribellate species. Previous research has shown that cribellate and ecribellate spiders differ not only in the composition of their spinning apparatus but also in the kinematics of spinneret movements during silk spinning. The objective of this study was to determine whether the differences in spinneret movements are solely due to variations in the degrees of freedom of the spinnerets or whether they are based on differences in muscular anatomy. This was accomplished by analyzing micro-computed tomography scans of the posterior abdomen of each three cribellate and ecribellate species. It was found that the number of muscles did not differ between cribellate and ecribellate species, but there were distinct differences between the species within each group. Muscle thickness, particularly of the posterior median spinneret, varied slightly between groups, with cribellate spiders exhibiting more robust muscles, possibly to aid in the combing process during cribellar thread production. Interestingly, the vestigial colulus still possessed muscles, that could be homologized with those of the cribellum. This initial exploration into spinneret anatomy using micro-CT data reveals that despite being small appendages, the spider spinnerets are equipped with a complex musculature that enables them to perform fine-scaled maneuvers to construct different fibre-based materials.


Comparative anatomy of the spinneret musculature in cribellate and ecribellate spiders (Aranea)

Boobies have the habit of plunging into the sea at high speeds over 90 km/h to capture fish. Their head shape has changed over the history of evolution and this change may have benefitted boobies by the mitigation of impact on the plunge into the water. In this study, we focused on this possibility and investigated a head shape suitable for water plunging from the viewpoint of shock mitigation as well as the evolutional meanings of head shape change. In this research, booby’s head were modeled on the computer based on the CT scanned data of the scull of current and ancestral boobies and the models were printed by 3D printer to be used for the water plunging experiments. The fossil head of the ancestor was deformed during the fossilization process, so it was restored using modeling software. The completed model was plunged into the water surface at a speed of approximately 5.8 m/s, and the impact force was compared by measuring the acceleration at the time of water surface plunge. As a result, it was confirmed that the model based on the head of the present species had a smaller shock per unit volume and had an impact mitigation effect.

Relationship between Head Shape and Impact Mitigation in Plunge Diving Behavior of Boobies

Different bird species exhibit substantial variation in flight behaviour. Flight behaviours are often associated with specific ecological niches and the unique demands that a given habitat or lifestyle imparts. One of the main ways in which niches differ is in how often a bird must use non-steady flight behaviours, such as take-off, landing, or manoeuvring. Due to the link between locomotion and morphology it follows that wing morphology should vary with the relative use of non-steady flight. We here investigated the wing morphology properties that underlay variation in flight behaviour by looking at how external and internal wing morphology relates to ecological parameters that vary in non-steady flight use. We focused on the radius and ulna for our analyses because many of the muscles that are essential for non-steady flight originate or insert on these bones. We hypothesized that the morphology of the radius and ulna varies among bird species in a pattern consistent with how often the species use non-steady flight as predicted by their ecology. We quantified variation in ulna and radius morphology using 3-dimensional geometric morphometrics and used phylogenetic comparative methods to uncover relationships among skeletal morphology, wing shape, and a suite of ecological variables that are linked to non-steady flight use. Our findings suggest that overall curvature and stoutness are major axes of variation for both radius and ulna shape. Furthermore, this morphological variation is potentially related to ecology and non-steady flight use.

Morphological variation of the radius and ulna among raptor (Accipitriformes) species in relation to ecology and unsteady flight behaviours

Fruit flies have been served as a great animal because of its rich genetics. In this research, we monitor weight changes and real-time activities of a fruit fly simultaneously using a force plate. The force plate has a large plate with a diameter of 35 mm which is over 11 times longer than its body length, and a spring structure consisting of four spirals. The force plate uses a glass wafer for preventing strain due to the passage of time, and four spiral cuts are simply fabricated by UV laser marker. The vertical displacement of the center plate is measured by a laser displacement meter fixed under the force plate and converted into the force. The resolution of the force plate is 0.1 µN, which is equivalent to 1/100 of the fruit fly’s weight. In the experiment, a fruit fly is placed in the center of the force plate, and a chamber is covered on top of it. The chamber prevents the force plate from vibrating due to airflow, making it possible to observe changes in fruit fly activity with high precision. Then, measurement is carried out until it stops moving. As it moves on the force plate multiple times, it can be observed that its weight gradually decreases over time. We have confirmed that its weight decreased by approximately 2.3% per hour. It is expected to lead to quantitative evaluation of water evaporation and metabolism from measuring its weight loss.

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Smaller pike eggs outperform bigger eggs in a global warming scenario

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