A new study led by Vetmeduni shows that migratory birds are remarkably well-adapted to the challenges of long flights across the Mediterranean. Even under variable weather conditions, their stress hormone levels remain stable, indicating that they are physiologically well-prepared for these hardships.

The researchers studied two migratory bird species – the Garden Warbler (Sylvia borin) and the Whitethroat (Curruca communis) – during their spring migration. The birds were captured on the Italian island of Ponza after crossing the Mediterranean. The researchers analyzed the concentration of the stress hormone corticosterone (CORT) in the birds' blood, both at rest and under stress conditions.

"It is fascinating to see how well these small birds are prepared for the challenges of their journey. Their ability to maintain a stable stress response even under difficult weather conditions shows how adaptable they are," says lead author Erica Calabretta from the Konrad Lorenz Institute of Comparative Ethology (KLIVV) at Vetmeduni.

Findings on Weather Resilience

The study's findings are surprising: neither wind conditions nor temperatures during the flight affected the baseline levels of the stress hormone. Even with moderate headwinds or cooler temperatures, the birds showed no increased stress reactions. "We had expected adverse weather conditions to increase stress hormone levels, but that was not the case," adds Calabretta.

Strategic Decisions and Adaptability

According to the researchers, birds that successfully reached their destination had sufficient energy and fat reserves and were in good to excellent physical conditions. The study highlights that these birds strategically choose their departure time and condition to successfully cross the Mediterranean. "These birds are true masters of planning," says study senior author Leonida Fusani, head of KLIVV. "They wait for the best conditions before starting their journey and manage their energy well – and it pays off." However, these findings only apply to birds that successfully completed the crossing. "We don’t know how many birds fail to finish the journey," notes Calabretta. "This is an important question that we need to investigate in future studies."

The Mediterranean region has experienced an increase in unpredictable weather events in recent decades, underscoring the importance of this research. "Extreme weather conditions could deplete the birds' energy reserves and impair their ability to cope with stress factors such as predators," says Ivan Maggini from KLIVV.

The research demonstrates how adaptable migratory birds are, but it remains unclear how they would respond to more extreme weather conditions. "We need to better understand the physiological mechanisms that enable these birds to overcome such challenges," says Fusani. The findings aim to improve the protection of migratory birds, especially in the face of climate change.

The article “Passerine stopover physiology: weather variability does not alter corticosterone dynamics after sea crossing” by Erica Calabretta, Virginie Canoine, Massimiliano Cardinale, Ivan Maggini and Leonida Fusani was published in the Journal of Avian Biology.

Scientific article

05-08-2025
 

A recent study by the University of Veterinary Medicine, Vienna, in collaboration with the University of Paris Cité, has investigated the effects of a ketogenic diet (KD) during pregnancy on the development and lifespan of mouse offspring. The results show that even a short, 10-day switch to a high-fat, low-carbohydrate diet during late embryonic development can have sex-specific and long-term effects on the offspring.

The ketogenic diet, which is characterised by a drastic reduction in carbohydrate intake and an increase in the proportion of fat in the diet, is increasingly being used as a therapeutic measure for various diseases such as epilepsy, diabetes and even neurological disorders. However, the effects of such a diet during pregnancy have so far been little researched. This study provides new insights into the potential risks and benefits of a ketogenic diet during prenatal development.

Fewer female offspring and lower birth mass

The ketogenic diet was administered for 10 days during pregnancy (G8.5 to G18.5), a critical phase of organogenesis during which most of the embryo's organs develop. The diet consisted of 84% fat, 11% protein and 5% carbohydrate. After birth, the lactating females and later the offspring after weaning were kept on a standard diet to separate the effects of the prenatal diet from postnatal influences. The study included two cohorts of mice reared under different housing conditions in France and Austria. The results were consistent in both cohorts, which emphasises the robustness of the data.

The researchers found that a 10-day ketogenic diet (KD) led to a reduction in litter size and an imbalanced sex ratio, with male offspring surviving more frequently. Female embryos were more susceptible to the negative effects of the diet, possibly leading to increased embryonic mortality. In addition, female offspring in the KD group had a lower birth weight, but this normalised by day 16 of life. ‘Our results show that female offspring are particularly sensitive to the metabolic changes induced by a ketogenic diet during pregnancy,’ explains Sarah M. Zala, lead author of the study and researcher at the Konrad Lorenz Institute of Ethology at the Vetmeduni.

The study emphasises that the increased susceptibility of female embryos may be due to the specific sensitivity of female placentas to dietary changes. Previous studies have shown that female placentas react more strongly to the fat composition of the diet, which could lead to increased vulnerability.

Shortened lifespan in male offspring

In the long term, male offspring in the KD group were found to have increased body mass and a significantly shorter lifespan in later life. Female offspring were less affected. ‘The fact that male offspring had a shorter lifespan in later life is concerning and suggests that the effects of a ketogenic diet during pregnancy may extend well beyond birth,’ says Sarah M. Zala.

The researchers found that the male offspring in the KD group had significantly higher body mass from around two and a half years of age, which persisted until their natural death. Interestingly, this mass gain was not due to obesity, as no excessive fat accumulation was observed. However, the exact causes of the increased body mass remain unclear and require further investigation.

No long-term metabolic or behavioural changes

Despite the differences in lifespan and body mass, the researchers found no evidence of long-term metabolic changes or behavioural abnormalities such as anxiety or depression in the offspring. The offspring's metabolic profiles, including blood glucose and ketone body levels, remained within the normal range, and no differences were found in spontaneous activity or in tests of anxiety and depression susceptibility. ‘Our results suggest that the ketogenic diet during pregnancy has no lasting metabolic or behavioural effects on the offspring, at least not in the parameters tested,’ says Diana Zala, last author of the paper from the Institute of Psychiatry and Neuroscience of Paris, France.

Pathological examinations and reproductive capacity

Pathological examinations showed no differences in the incidence of tumours between the KD and control groups. This is particularly noteworthy as previous studies have indicated that ketogenic diets can reduce the incidence of certain types of tumours in adult mice. The reproductive capacity of the offspring was also unaffected by the diet.

According to the researchers, further studies are needed to better understand the underlying mechanisms and to more accurately assess the risks of a ketogenic diet during pregnancy. In particular, future studies should investigate the epigenetic changes that could be triggered by the diet, as well as the potential effects on brain development and ageing.

The article “Sex-dependent effects of a gestational ketogenic diet on offspring birth and lifespan” by Sarah M. Zala, Renata Santos, Eva Strasser, Alice Schadder, Sarah Kugler, Verena Strauss, Anna Kübber-Heiss and Diana Zala was published in PLOS One.

Scientific Article

31-07-2025

The fire salamander, which is native to Austria, defends itself against predators in two ways: through its conspicuous warning coloration and through a whitish, poisonous secretion that it can secrete from glands on its back. The warning coloration is conspicuous in different ways - which, according to a recently published study by the Konrad Lorenz Institute of Ethology (KLIVV) at the University of Veterinary Medicine, Vienna, only provides salamanders with limited protection from predators. What would provide effective additional protection, however, are non-managed forest areas.

Predator-prey interactions are a kind of evolutionary arms race - influenced by environmental factors. One common strategy to deter predators is aposematism. This involves the coupling of warning signals (e.g. visual) with secondary (e.g. chemical) defense mechanisms for deterrence.

The European fire salamander (Salamandra salamandra) is one such aposematic amphibian. “Their distinctive yellow-black warning coloration and skin toxins protect them from predators, with the yellow on their back correlating negatively with predation attempts. The more yellow they are, the better protected,” explains Carolin Dittrich, one of the lead authors of the study.

The risk of predation differs across forest zones

An important habitat of the fire salamander is the Vienna Woods Biosphere Reserve, a forest region in which both protected areas and areas with forest management can be found. In this natural habitat, the researchers compared the predation rates on fire salamanders. The plasticine salamander models used for this purpose had the same amount of yellow dorsal coloration, but differed in how this color was distributed, either over many small or few large markings, and were placed in either protected or managed forest zones. “We observed no differences based on the size of the markings, as all models were attacked similarly often. However, attacks by birds were more frequent in managed forest areas than in protected areas,” says Bibiana Rojas (KLIVV) about the results.

Complexity of forest structure and tree diversity make the difference

The main difference between these forest zones relates to tree diversity. “We suspect that forest structure and complexity may lead to differences in the abundance or composition of predator communities, which in turn could influence attack rates,” explains Rojas. The study authors therefore emphasize the importance of protected areas as potential refuges for fire salamanders and see a great need for further research, “especially to investigate the effects of differences in predator community composition on predation risk in different forest areas. Furthermore, our study highlights the intricate relationships between evolutionary strategies, ecological interactions and human land use. And it underlines the need for an integrated approach to forest management that considers the complex balance of natural ecosystems.”

The article „Habitat alteration impacts predation risk in an aposematic amphibian“ by Doriane Hagnier, Carolin Dittrich, Myrna Van den Bos and Bibiana Rojas was published in „Journal of Zoology“.

Scientific article

03-07-2025

A recently published study by the Konrad Lorenz Institute of Ethology (KLIVV) at the University of Veterinary Medicine, Vienna, investigated whether dogs judge human social behavior. Using a controlled feeding experiment, the researchers examined whether dogs react differently to “nice” or “nasty” behavior displayed by humans towards themselves or another dog, and whether the age of the dogs plays a role. According to the researchers, there is no evidence that dogs make such distinctions.

Some animal species, such as chimpanzees, can form impressions of humans through direct interactions or by observing how humans interact with others – a phenomenon known as “Eavesdropping.” Given their close cooperative relationship with humans, dogs (Canis lupus familiaris) have been the focus of much research investigating whether they can socially evaluate people. However, the findings so far have been inconsistent, with studies pointing in different directions.

Do dogs form a reputation of humans?

To explore whether this potential ability develops over a dog’s lifetime (ontogeny), the researchers investigated whether dogs of different ages – young, adult, and senior – can judge people, since older dogs have more life experience with humans. The dogs were tested after either observing humans interact with a conspecific (another dog) or engaging in direct interactions with the humans in a food-giving situation.

Forty domestic dogs took part in the experiment. In the eavesdropping phase, the dogs watched two humans interacting with a dog demonstrator – one human was nice and fed the dog, while the other was nasty and withheld the food. In the direct experience phase, the dogs interacted with both humans themselves.

Hoi-Lam Jim from KLIVV, first author of the study, explains how the experiment proceeded: “We analyzed the dogs' first choice and the time they spent showing affiliative behaviors (e.g., proximity, jumping up) towards each partner. The results showed that dogs of all ages did not significantly favor the nice partner over the nasty partner. Their behavior was also not above chance level, whether after observing the interactions or experiencing it directly.”

No evidence for reputation formation in domestic dogs, regardless of age

According to the researchers, the study does not support the idea that domestic dogs are capable of forming reputations, regardless of their age. “These findings add to the growing literature suggesting that social evaluation is a challenge for animals,” emphasizes senior author Sarah Marshall-Pescini from KLIVV. “To better understand how and whether ontogeny influences dogs’ sociocognitive abilities, future research should systematically compare dogs from different populations (e.g., free-ranging dogs), age groups, and life experiences (e.g., dogs with specialized training such as police or service dogs). Furthermore, our study underscores the importance of refining methodological approaches, as there may be limitations in current experimental designs that prevent dogs from demonstrating this ability,” Marshall-Pescini adds.

The article „Do dogs form reputations of humans? No effect of age after indirect and direct experience in a food-giving situation“ by Hoi-Lam Jim, Kadisha Belfiore, Eva B. Martinelli, Mayte Martínez, Friederike Range and Sarah Marshall-Pescini was published in Animal Cognition.

Scientific article

02-07-2025

Researchers at the Konrad Lorenz Institute of Ethology (KLIVV) at the University of Veterinary Medicine, Vienna recently published a study in which they investigated two common hypotheses on primary and secondary sexual traits using male wild-caught house mice (Mus musculus musculus). They found that inbreeding influences the expression of primary and secondary sexual traits. According to the scientists, this is the first experimental evidence that the courtship songs and sperm quality of house mice are both influenced by inbreeding, though, contrary to what they expected, that these sexual traits were not positively or negatively correlated, i.e., male courtship song did not provide an honest indicator of their fertility nor was there a trade-offs between these traits.

Two hypotheses on the evolution of sexual traits

The Fertility Indicator Hypothesis states that the expression of secondary (pre-copulatory) sexual traits, such as courtship behavior or songs, by males provides reliable indicators of their sperm traits (primary or post-copulatory traits) and predicts positive correlations between these pre- and post-copulatory traits. In contrast, the sexual allocation trade-off hypothesis claims that males make trade-offs between investments in primary and secondary sexual traits. However, whether or not males face such trade-offs may depend on their quality or condition. ‘If the sexual traits of males are condition-dependent, and males in good condition are thus better able to invest into both pre- and post-copulatory traits than males in lower condition, then both hypotheses are possible,’ says study co-author Dustin J. Penn.

Only two generations of inbreeding change sperm quality and courtship behavior

To test these hypotheses, the researchers manipulated the genetic quality of wild-caught male house mice through experimental inbreeding and tested whether inbreeding affects primary or secondary sexual traits. "First, we recorded the courtship behavior and vocalizations of the males when they were in contact with females, Then we measured the males' reproductive organs and the quality of their sperm, as well as the expression of four genes associated with spermatogenesis. We then tested whether these pre- and post-copulatory traits correlate," reports study first author Doris Nicolakis.

The scientists found no difference in the number of courtship calls, but inbreeding altered the vocal repertoire and reduced other courtship behaviors in male house mice. ‘Inbreeding also had a negative effect on testes mass as well as on sperm quantity and quality,’ says Nicolakis.

However, the scientists found no evidence to support either the fertility indicator hypothesis or the sexual allocation trade-off hypotheses. Study last author, Sarah M. Zala comments: ‘We saw no consistent correlations between pre- and post-copulatory traits, either positive or negative, independent of inbreeding.’ However, the authors explained why studies are needed in the wild or naturalistic conditions, as the expected correlations may not occur in laboratory settings.

The study “Pre- and post-copulatory traits are affected by experimental inbreeding, but they are not correlated” by Doris Nicolakis, Maria Adelaide Marconi, Kerstin E. Auer, Dustin J. Penn und Sarah M. Zala was published in “BMC Biology”.


Scientific article

25-06-2025

From April 22^nd to 25^th 2025, the Lorentz Center in Leiden (Netherlands), hosted an interdisciplinary workshop titled "Honest Signalling and Communication: From Microbes to Humans." The event brought together experts from biology, sociology, anthropology, and economics to examine the mechanisms and evolution of honest communication across diverse life forms.

The workshop addressed fundamental questions about why and how honest communication persists despite prevalent conflicts of interest and opportunities for deception, even among organisms lacking cognition. Participants discussed the limitations of traditional theories like the Handicap Principle and explored alternative models that account for honest signalling through condition-dependent trade-offs and evolutionary constraints.

Sarah Zala from the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine in Vienna was part of the scientific organisation team which also included Szabolcs Számadó (HUN-REN Centre for Social Sciences), István Zachar (HUN-REN Centre for Ecological Research), Károly Takács (Linköping University), and Bianca Beersma (VU University Amsterdam).

A keynote lecture was given by Dustin Penn (Konrad Lorenz Institute of Ethology, Vetmed) titled “The demise of the handicap principle and alternative explanations for honest signals and deception” in which he debunked the notion that animals signal honestly—like showing off bright colours or loud calls—because those signals are costly, an idea known as the Handicap Principle. He argued that these signals aren't honest because they're expensive, but because of trade-offs: being honest often benefits the signaller, while lying can have negative effects. The talk highlighted how past models could have been misinterpreted and introduced newer theories that may better explain both honest and deceptive communication in nature.

The endocrine systems that regulate hunger, food intake and fat deposition are well conserved in vertebrates. In mammals, for example, the hormone leptin reduces appetite, and disruption of this feedback system can lead to metabolic disease and obesity. A few years ago, researchers discovered that birds have lost this leptin system in the course of evolution. Now, a study funded by the Austrian Science Fund FWF and led by Leonida Fusani from the Konrad Lorenz Institute of Ethology (KLIVV) at the University of Veterinary Medicine, Vienna and the Department of Behavioral and Cognitive Biology at the University of Vienna (lead author Stefan Prost) has found that songbirds have also lost the other main hormone of this system, ghrelin. A discovery that is also exciting for humans, especially in regard to obesity and eating disorders.

In their study, the researchers focused on ghrelin. This peptide - also known as the “hunger hormone” - is secreted by the gastrointestinal tract to regulate food intake and body mass in vertebrates. However, studies on domestic birds had shown that ghrelin has the opposite effect in birds than in mammals, inhibiting food intake rather than promoting it. According to Leonida Fusani, “some of our team's studies also suggested that ghrelin might play a key role in the control of migratory behavior. We were therefore puzzled when we could not find ghrelin in the genome of the garden warbler, a passerine bird.” 

Searching for the hunger hormone ghrelin in songbirds - and finding it nowhere

Based on this finding, the research team conducted a thorough search for ghrelin using both bioinformatic tools, by searching the genomes of other bird species, and biochemical tools, by analyzing samples from passerine birds and comparing them to those of quail and pigeons, which possess ghrelin. “We were very surprised to find that the Passerine birds, that is songbirds - the largest group of birds, comprising 60% of all bird species - have also lost this hormone,” says Fusani. Using all available sources and research methods, the scientists were unable to find the genes coding for ghrelin in the DNA of all songbirds for which information is available.

Groundbreaking work on bird physiology with important findings for humans

According to Fusani, these study results are a breakthrough in the study of bird physiology and open up important new avenues for biomedical research: “Songbirds are unique in that they can increase their body weight by up to 100% by accumulating enormous amounts of fat before migration, but return to their normal weight within a few days after the end of their long journeys,” explains Fusani. The loss of leptin and ghrelin seems to be related to this extraordinary plasticity, according to Fusani. Thus,  “understanding how birds manage to control their body fat could be very useful for humans to tackle common health problems such as obesity and eating disorders,” emphasizes Fusani.

The article „The unexpected loss of the ‚hunger hormone‘ ghrelin in true passerines: a game changer in migration physiology“ by Stefan Prost, Jean P. Elbers, Julia Slezacek, Alba Hykollari, Silvia Fuselli, Steve Smith and Leonida Fusani was published in „Royal Society Open Science“.

Scientific article
 

Understanding intraspecific variation in habitat selection of polytypic species, where different variants occur in different populations, can improve knowledge of population-specific selection pressures. This knowledge can also provide useful information in the context of conservation measures. An international research team involving Vetmeduni Vienna has now investigated the differences in habitat selection in six populations of the dyer's poison frog (Dendrobates tinctorius).

The dyeing poison frog is an aposematic (warningly coloured, toxix) species in which individuals from different populations look very different (coloration, body size, etc.). For their study, the researchers recorded the locations and associated habitat of the frogs in each population and systematically assessed the available habitat. Study lead author Bibiana Rojas from the Konrad Lorenz Institute of Ecology at Vetmeduni (KLIVV) explains: “We hypothesized that habitat selection differs between populations with different variants. We assumed that larger frogs are less dependent on moisture-retaining habitat structure, e.g. fallen trees and dead wood. Second, we hypothesized differences between human-disturbed and largely undisturbed areas, assuming that frogs in disturbed areas are more dependent on structural diversity and water bodies. We also predicted differences between males and females, with stronger differences in habitat selection in populations with more pronounced sexual size dimorphism.”

Researchers identify strong general patterns of habitat selection

Contrary to these assumptions, the research team found only slight differences in habitat selection between populations or between human-influenced and untouched areas. In general, however, frogs of all populations relied on fallen trees, dead wood and small water sources. In addition, males tended to be closer to water (to which they transport newly hatched tadpoles) and females closer to dead wood, where they often lay their eggs.

Important new information for future conservation measures

Taken together, the results suggest that habitat selection in aposematic species may be constant across populations, possibly due to reduced susceptibility to localized risks from predators. Study co-author Lia Schlippe Justicia from KLIVV emphasizes the importance of the research: “Our study is the first to investigate the habitat selection of D. tinctorius across a large part of its range, including human-influenced sites. As it is a polytypic species (individuals from different populations have different appearances), understanding whether different population variants have different habitat requirements is crucial for effective conservation planning and prioritization. Our results provide important baseline data on the habitat requirements of this fascinating species, which may be important for efficient conservation measures in the future.”

The article „Phenotypic divergence across populations does not affect habitat selection in an Amazonian poison frog“ von Martin Mayer, Lia Schlippe Justicia and Bibiana Rojas was published in „Global Ecology and Conservation“ .

Scientifc article

19.02.2025

The ruff (Calidris pugnax) is a migratory bird that breeds in marshes and wet meadows across northern Europe and Asia and winter in large flocks across the world. In ruffs, there are three male phenotypes – also called ‘morphs’ – that are genetically determined and differ in their sexual behaviour. The ‘independent’ males are territorial and perform courtship, the ‘satellites’ are not aggressive but participate in courtship’, whereas the ‘faeders’ look like females and attempt to sneak copulations whenever possible. An international study published in "Science" with the participation of the University of Veterinary Medicine Vienna has now discovered that a gene that regulates the metabolism of the main androgen, testosterone, is responsible for the differences between male phenotypes in this species of snipe.

Androgens are pleiotropic - i.e. they orchestrate several physiological processes - and play a central role in the development and modification of sexual phenotypes. In their study, the scientists have now been able to show that the differences in the circulating androgens of the three male mating morphs in ruffs are linked to the enzyme 17-beta-hydroxysteroid dehydrogenase 2 (HSD17B2), which is encoded by a gene within the supergene that determines the morphs.

A single gene leads to numerous variations

"A combination of evolutionary changes in the regulation, sequence and structure of a single gene leads to endocrine variations that underlie reproductive phenotypes," emphasises study co-author Leonida Fusani, head of the Konrad Lorenz Institute of Ethology (KLIVV) at the Vetmeduni. Overall, according to Fusani, the results indicate that a combination of changes in the regulation and the coding sequence of the HSD17B2 gene leads to increased testosterone conversion in the  two non-aggressive morphs. Furthermore, the suppression of recombination caused by the supergene presumably accelerated the evolution of these two derived morphs.

Clear correlation: Expression of HSD17B2 and testosterone levels

Males with low testosterone levels had higher HSD17B2 expression in the blood and in brain areas associated with social behaviour and testosterone production than males with high testosterone levels. Derived HSD17B2 isoenzymes, which are absent in high testosterone males but preferentially expressed in low testosterone males, also converted testosterone to androstenedione - a steroid that is a weaker androgen than testosterone - faster than the original isoenzyme.

The article „A single gene orchestrates androgen variation underlying male mating morphs in ruffs“ by Jasmine L. Loveland, Leonida Fusani, Clemens Küpper et al. was published in „Science“.

Scientific article

17.02.2025