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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
(&gt;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.

SEB Conference 2024

Auditory tuning to conspecific acoustic signals in an Eocene katydid

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.

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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.

Long-term weight change measurement of fruit flies using a high-precision force plate

Spiders spin silk into different products, such as fibres, threads and sheets, tailored for specific
functionalities and to fulfil a variety of ecological roles. Examples include draglines and bridging
lines for structural support, as well as webs and sticky threads for prey capture. Most silk products
are made of a combination of different silk fibres with contrasting material properties. The most
common silk types are minor ampullate, major ampullate and aciniform gland silk. Spider silks
exhibit characteristic mechanical properties, including extensibility and tensile strength. How these
properties vary between spider species, gland origins and thread structures as poorly understood.
This study aimed to compare the mechanical properties of different silk products in Pholcidae, with
a particular focus on the cosmopolitan cellar spider (Pholcus phalangioides). P. phalangioides
constructs irregular three-dimensional webs comprising of unique mechanically interesting silk
products. This include capture threads called ‘gumfoots’ which are vertical sticky prey traps
designed to undergo spontaneous deformation and utilizes ‘draglines’ and airborne ‘bridging lines’
which serves for in locomotion and display distinct tensile strength and toughness to hold spider’s
weight. Each of these silk structures were hypothesized to show specific mechanical adaptations.
Preliminary results of tensile test show a significant variety in mechanical properties across
different silk types with varying extensibility, tensile strength and toughness. Further study will
focus on interspecific variation of the structural and mechanical properties of silk products
between pholcid species with different ecology and silk compositions and the composition of fibres
in Pholcidae.

Comparative Analysis of the Mechanical Properties of Silk Products in Pholcidae

Because granivorous birds need to exert bite forces to open seeds, evolution resulted in greater bite forces in species feeding on hard seeds. However, beaks also play a role in sound modulation during singing. They are especially important in song fragments with a high trill rate, which require fast open-close movements of the beak. Studies in canaries showed that females prefer songs with high trill rates, implying an important sexual selection pressure on beak speed in this species. In canaries, beak velocities and frequencies are approximately equal during feeding and singing. However, in finches with strong bite forces, like many Darwin’s finches, beak movements during singing are considerably slower than in canaries. Yet, there is no information about the difference in beak velocities and frequencies between feeding and singing in finches with strong beaks. Here we test the hypothesis that, also in species with a strong bite force, song performance is limited by the beak’s movement capacities. This is done using high-speed video recordings of the Java finch (Lonchura oryzivora) during both singing and feeding on seeds. Contrary to our hypothesis, significantly lower beak frequencies occurred during singing compared to during feeding. Although the beak generally rotates at higher amplitudes during singing, our results nevertheless indicate that Java finches are not producing their potential maximum trill rate. Such usage of the beak below its biomechanical potential in terms of speed and frequency during singing suggests different sexual selection pressures compared to species with considerably higher trill rates like canaries.

Need for speed: are beak speed and frequency similar during singing versus feeding in a strong-biting songbird?

Feeding ecology of carnivorous mammals is highly diverse. It is generally accepted, however, that most primarily employ one of three hunting strategies: pursuit predation, pounce/pursuit predation or ambush predation. Knowledge of how morphology and hunting type relate to each other is imperative for our understanding of the feeding ecology of extinct carnivores. 
Here, we offer a first insight into the relationship between trabecular structure in the distal humerus of carnivorous mammals and their respective hunting types. We analyse μCT-scans with the aim of uncovering morphological correlates to behavioural strategies. Our findings are then compared to results for the extinct thylacine (Thylacinus cynocephalus) to infer its likely hunting behaviour.
Results suggest habitual loading of the distal humerus related to hunting type. Higher values in degree of anisotropy (DA) are uncovered for ambush predators and lower values for pounce/pursuit and pursuit predators respectively. DA remains largely unaffected by phylogeny and body mass, pointing to a functional signal. 
Employing our methodology to the extinct thylacine reveals an overlap with extant pounce/pursuit predators, suggesting a pouncing behaviour.


Trabecular structure of the distal humerus in carnivorous mammals

Muscle is the prime mover of animal locomotion, but muscle force is not usually equal to output force. Instead, the instantaneous ratio between output and input force (the mechanical advantage, MA) is modulated by intervening skeletal elements. Traditional functional analysis, focussing on the instantaneous action of gearing, suggests that smaller MA favours speed, while larger MA favours force. However, mounting evidence suggests that this perspective is too simplistic when considering the outcome of a dynamic muscle contraction. We approach this problem systematically by introducing an analytical framework to study the effect of gearing. This framework reveals two mechanisms by which the output speed of a contraction is affected by gearing. First, gearing can limit muscle work output, because it is bound not only by muscle displacement, but also by muscle shortening velocity. Second, it controls how each unit of muscle work is partitioned into system energies (e.g. kinetic energy vs heat). Consequently, smaller gear ratios do not always result in larger output speeds. No single optimal gear ratio exists for any organism, but rather the optimum depends on internal muscle properties and contraction dynamics, as well as external forces. The analytical framework we propose provides a blueprint to determine optimality conditions across muscle physiology, anatomy, mechanical environment and size, and so to investigate form-function relationships in musculoskeletal gearing.

Musculoskeletal gearing for maximum speed: analytic optimization across mechanical environment and size.

Silicon (Si) is increasingly being recognised as an essential element for plant health to tackle abiotic stresses, and it may also deter herbivores from plant-feeding, as a result of tooth wear caused by silica phytoliths. However, direct quantitative evidence for Si-induced wear is scarce. In this study, we subjected pristine Atta vollenweideri ant mandibles to multiple wear treatments on Hordeum vulgare barley leaves, grown with either 0-, 2- or 4-mM Si-supplemented hydroponic media, resulting in varying Si concentrations in the leaves. Pristine mandibles were collected from freshly eclosed ants that had never engaged in foraging, and wear treatments were conducted by driving isolated mandibles through leaf lamina at a constant speed using custom-built clamps attached to a motor stage. To quantify the effects of mandible wear, before, in between, and after each treatment, the forces required to cut standardised PDMS sheets were measured using a custom-built fibre optic force transducer; after 300 mm barley cut length, the cutting forces on PDMS increased significantly across all Si conditions; this force increase, however, was not consistent across Si concentrations, such that the change in cutting force per leaf length cut was 174% larger on 4 mM compared to 0 mM leaves. These results indicate that mandible abrasion may be facilitated by the mechanical contact between cutting edge and silica phytoliths. As increased mandible wear is likely of significant detriment to lifetime foraging efficiency, targeted Si-supplementation may be an effective yet ‘green’ agricultural strategy to provide protection against insect herbivores.

Next from SEB Conference 2024

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

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