Aposematism is a way animals protect themselves from predators by warning them of their dangerous defenses. These warning signals can be in the form of bright colours or patterns, which often inform about the chemicals, such as alkaloids, that animals have stored in their bodies. Some animals get these chemicals from their food, so the amount and type of defense can vary depending on what they eat and where they live. Examples of animals that use aposematism include colourful frogs and some butterflies. While alkaloid defenses have been the subject of scientific inquiry for decades, their relationship to aposematic signal variation in the colours they are advertised with is less understood. 

An international team of researchers, including Bibiana Rojas from the Konrad Lorenz Institute of Ethology and her team, have studied different populations of the Dyeing Poison Frog in northeastern French Guiana. The Dyeing Poison Frog, is a type of frog species that lives in northern South America. It has many different colours and patterns, and these can vary depending on where the frog lives. Sometimes, even frogs living in the same area can look different from each other. These frogs have distinct alkaloid profiles and varying unpalatability to predators.

In a study conducted with Blue Tits as model predators, the researchers identified 15 alkaloids that are correlated with predator response in one frog population, including three previously undescribed. The study looked at two populations of frogs and found that even though the frogs had different warning signals, there were some key chemicals that were always present and helped to protect the frogs. The researchers hope that by understanding more about how predators respond to these chemicals, they can learn more about the evolution of chemical defenses.

The study provides a novel method for linking unpalatability of skin secretions with the toxins which may contribute to the predator response. This could help explain how varying alkaloid combinations are capable of eliciting consistent behavioural responses, and eventually driving evolutionary change in the characteristics of  aposematic animals.

The article "Linking Predator Responses to Alkaloid Variability in Poison Frogs" by J. P. Lawrence, Bibiana Rojas, Annelise Blanchette, Ralph A. Saporito, Johanna Mappes, Antoine Fouquet, and Brice P. Noonan was published in the Journal of Chemical Ecology.

Scientific article

2023-03-13

Neolamprologus pulcher (N. pulcher) is a species of cichlid found on rocky coasts in East Africa. They are one of only a handful of highly social fish species in the world. Instead of dispersing, they often prefer to stay at home. A research team from the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine, Vienna, has now investigated the reasons for this unusual social behaviour – and thus complements scientific theories explanations for the evolution of complex sociality in fishes. The long-term study has just been published in the top journal "Science Advances".

Extreme pressure from predators has previously been seen by scientists as the main reason for the unusual social behavior of N. pulcher: This is because a fish that wants to leave its home range is likely to be eaten. So it pays to stay at home.

Only particularly strong and fit individuals in good condition can overcome these “ecological constraints” (the name of the corresponding well-known theory). Weaker animals, however, are forced to guard the home and have very little room for self-realization “under their parents´ fins” - the chance of having their own offspring is thus extremely low.

First such long-term study on the cichlid species N. pulcher.

To confirm this common hypothesis, however, measurements of actual reproductive success have been lacking until now. In the world's first long-term study of this kind, a research team from Vetmeduni therefore examined N. pulcher under natural conditions. First author Arne Jungwirth of the Konrad Lorenz Institute of Ethology at the Vetmeduni said: "We measured the lifespan, reproductive success and social status of nearly 500 tagged fish over a period of up to five years.

Both sexes benefit from sedentariness

It turned out that both sexes benefit from staying at home, as survival probability and reproductive success increase. This is not consistent with the predictions of "ecological constraints," but rather with another classic theory - the benefits of sedentariness (benefits of philopatry).

"That both sexes benefit equally from sedentariness is surprising in that they differ both in dispersal behavior - males move around more - and in other aspects of their life history strategies. Females, for example, grow more slowly and to a smaller maximum size, but then live much longer," says Arne Jungwirth.

Polygyny with consequences: Males fight more and therefore have to relocate

According to Arne Jungwirth, the scientists found the following explanation for the fact that males have to move more often: "Competition between males prevents them from settling down more often than females - male cichlids fight more because there are fewer territories for them: There is only about one breeding male for every two breeding females, because the species practices polygyny."         

The article "Philopatry yields higher fitness than dispersal in a cooperative breeder with sex-specific life history trajectories" by Arne Jungwirth, Markus Zöttl, Danielle Bonfils, Dario Josi, Joachim G. Frommen, and Michael Taborsky was published in Science Advances.

Scientific article

2023-03-07

The Department for Interdisciplinary Life Sicences has a new Department Speaker: Univ.-Prof. Dr.rer.nat. Ludwig Huber takes over this function from Univ.-Prof. Leonida Fusani, PhD, who held it for three years. Ludwig Huber was suggested by the Department's professors and has now been appointed by the Rector. The term of office is 3 years: March 1, 2023 to February 28, 2026. As his deputies we now have KLIVV head  Leonida Fusani (1st) and FIWI head  Claudia Bieber (2nd). With a planned restructuring of the Vetmeduni, we are facing challenging times. Important groundwork will be laid as early as during the preparation of the development plan (in the summer) and the research priorities and fields defined therein as well as the profile lines. Ludwig Huber plans not only to hold the quarterly department conferences of the professors at the Department, but also to organize an annual Department meeting to which all members of the Department will be invited. These meetings will aim to make structural decisions for the Department and to coordinate between Departments, as well as to inform Department members and decide general matters affecting the Department.

We warmly welcome our new Department Speaker Ludwig Huber and at the same time thank Leonida Fusani for his wonderful services in this function.

Über Ludwig Huber

2023-03-01

Animals often produce honest signals, which is puzzling from an evolutionary perspective. A recent paper provides a new method for constructing mathematical models sufficiently complex to investigate and test theories about the evolution of honest signals. Moreover, this model confirms the authors' argument that the Handicap Principle – the textbook explanation for honest signalling – can be fully rejected.

Animals produce an amazing diversity of signals, which include the colourful plumage of peacocks, the roars of rutting stags, loud begging calls of chicks, stotting of gazelles, and scent marks and pheromones of male mice. These signals are often honest or reliable, which is surprising, because deception can be beneficial. If deception spreads and becomes common, then the signals will be ignored and communication breaks down. So, how does natural selection maintain honesty; what prevents the spread of dishonest signals?

Zahavi argued that signals are honest because they are costly to produce. It is the costs or wastefulness of a signal that makes it impossible to produce a fake signal. He called this idea the "Handicap Principle", and his proposal became widely accepted after Grafen published his 'strategic handicap' model, which he claimed confirmed the Handicap Principle.

Dustin Penn (Konrad Lorenz Institute of Ethology, Vetmeduni Vienna) and Szabolcs Számadó (Budapest University of Technology and Economics) have been collaborating on this theoretical problem for several years. They have previously shown why Grafen's and other previous models have been misinterpreted. They recently teamed up with two other theoreticians to construct a new model to analyze the surprising complexities of signalling games. In addition to providing a new method for constructing more complex and general models, their analyses show why the signal costs are irrelevant to explaining honesty.

Mathematical signalling games were originally adopted from economics, and they have often been used to model the evolution of animal signals and plant-pollinator interactions. These signalling games were far too simple, however, because they only considered the evolution of the sender, who produces the signal; they ignored the receiver, who can evolve decisions for how to respond to the signal. Thus, models are needed to investigate more complex signalling games and include this double-optimization problem.

The new model by Szamado and colleagues provides a novel and general approach for calculating cost functions and for determining how a signal will evolve and reach a stable evolutionary equilibrium. The authors then used their model to re-examine overly simplified signalling games, previously used for studying honesty in sexual signals and offspring begging calls. These are asymmetric signalling models, as the sender has more information about their condition than the receiver (similar to purchasing a used car of unknown quality; which is known as the 'lemon problem' in economics). The results show that an infinite number of signals can evolve that are honest, including signals that have no costs and only benefits. This new model shows that signals do not need to be costly in order to be honest, contrary to the Handicap Principle. This result confirms Penn and Szamado's argument that Grafen's model has been misinterpreted; it is not a model of the Handicap Principle. Honest signals evolve in this model, not because of the costs of the signal, but because of a particular tradeoff, a constraint that makes deceptive signals costly and honesty beneficial.

Thus, this new theoretical model confirms that the Handicap Principle can be fully rejected. Moreover, it provides a new method for testing ideas about the evolution of honest signals. The authors point out that this has become a rather timely topic, given the increasing spread of misinformation, which has become "one of the most important problem facing our species".

The article "Honesty in signalling games is maintained by trade-offs rather than costs" by Szabolcs Számadó, István Zachar, Dániel Czégel, and Dustin J. Penn was published in BMC Biology.

Scientific article

Also see the commentary in Proceedings of the National Academy of Sciences (PNAS): "The peacock’s tail and other flashy ornaments don’t have to come at a cost"

2023-01-30

Chemical defences often vary within and between populations both in quantity and quality, which is puzzling if prey survival is dependent on the strength of the defence.

An international team of researchers led by Cristina Ottocento from the Department of Biology and Environmental Science, University of Jyväskylä, Finland, with participation of Bibiana Rojas from the Konrad Lorenz Institute of Ethology and others, studied the within- and between-population variability in chemical defence of the wood tiger moth (Arctia plantaginis). The major components of its defences, SBMP (2-sec-butyl-3-methoxypyrazine) and IBMP (2-isobutyl-3-methoxypyrazine), are volatiles that deter bird attacks.

They hypothesized that (1) variation in the chemical defences of male wood tiger moths reflects the local predation pressure; (2) observed differences in quantity and quality of defence among populations have a genetic basis; and (3) increasing concentrations of SBMP and IBMP will elicit greater aversive reactions in predators, with the two pyrazines having an additive effect on predators' avoidance.

They found that the chemical defence of wild moths partly reflects local predator selection: high predation pressure populations (Scotland and Georgia) had stronger chemical defences, but not lower variance, than the low-predation populations (Estonia and Finland). Based on the common garden results, both genetic and environmental components seem to influence the strength of chemical defence in moth populations. Furthermore, they found that IBMP alone did not provide protection against bird predators, but worked against bird attacks only when combined with SBMP, and while SBMP was more effective at higher concentrations, IBMP was not.

Altogether this suggests that, when it comes to pyrazine concentration, more is not always better, highlighting the importance of testing the efficacy of chemical defence and its components with relevant predators, as extrapolating from chemical data may be less than straightforward.

The article "Not just the sum of its parts: Geographic variation and nonadditive effects of pyrazines in the chemical defence of an aposematic moth" by Cristina Ottocento, Anne E. Winters, Bibiana Rojas, Johanna Mappes, and Emily Burdfield-Steel was published in the Journal of Evolutionary Biology.

Scientific article

2023-01-17

The long seasonal travels of migratory birds are a well-known phenomenon. But what hormonal processes are involved? A recent study by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine Vienna identifies sharply rising levels of the hormone ghrelin as a key trigger of migratory restlessness. The recently published research could not, however, confirm a connection with the hormone corticosterone as shown in other studies.

Migratory birds have spectacular physiological adaptations to accommodate the long-distance flights between their breeding and wintering grounds. The animals use fat reserves built up prior to migration as their main source of energy. In both captive and free-flying birds, the migratory phenotype – the physical changes that occur prior to and during migration – is signalled by rapid and marked increases in food and energy intake as well as by changes in nocturnal activity and by migratory restlessness. However, there has been little scientific evidence to date on the exact hormonal mechanisms underlying this process.

Hormone ghrelin makes quail fit for long flights

An international research team led by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine used common quails (Coturnix coturnix) to assess if  the hormone corticosterone and the gut-derived hormone ghrelin play a role in the seasonal expression of migratory behaviour. For their experiment, the researchers exposed quails to controlled changes in day length  to simulate autumn migration, followed by a wintering period. The researchers then compared corticosterone and ghrelin concentrations and assessed whether these two metabolic hormones varied between migratory states.

“In accordance with our predictions, we found that the emergence of the migratory phenotype was associated with higher concentrations of ghrelin. In addition, ghrelin correlated with changes in body mass of birds as they transitioned into their autumnal migratory state and as they entered the wintering state,” explains the study’s first author, Valeria Marasco from the Konrad Lorenz Institute of Ethology at Vetmeduni.

No correlation between corticosterone levels and migratory restlessness

Contrary to their predictions, however, the researchers observed no correlation between circulating levels of ghrelin and corticosterone. The scientists were also unable to detect elevated levels of corticosterone in the migratory phenotype. “There was no significant correlation between baseline corticosterone levels and changes in body mass, levels of food intake or migratory restlessness (the urge of captive birds to migrate at night)” says the study’s senior author Leonida Fusani, head of the Unit of Ornithology at the Konrad Lorenz Institute of Ethology.

The article "Ghrelin, not corticosterone, is associated with transitioning of phenotypic states in a migratory Galliform“ von Valeria Marasco, Hiroyuki Kaiya, Gianni Pola, and Leonida Fusani was publised in „frontiers“.

Scientific article

2023-01-11