Biology subjects

Herczeg, D.

Publications and source records attributed to Herczeg, D..

7 recordsLinked to original sources

bioRxiv2026

Microplastics disrupt adaptive predator-induced behavioural plasticity in Rana dalmatina tadpoles

The accumulation of microplastics (MP; plastic particles 1 m - 1 mm in diameter) in the environment is an increasing global concern. Although the physiological effects of MP on organisms, including humans, are increasingly documented, their impacts on behaviour are far less understood. Further, little is known about how MP affect adaptive phenotypic plasticity - the ability of a genotype to adaptively modify its phenotype in response to environmental cues. Anuran tadpoles are key models for studying phenotypic plasticity, with well-established evidence for predator-induced behavioural adjustments. Tadpoles typically reduce their activity and risk-taking when exposed to chemical cues released by predators, which has been proven to be adaptive. We investigated whether MP exposure from the fertilised egg stage alters the behaviour of agile frog (Rana dalmatina) tadpoles, and whether it interferes with their predator-induced behavioural plasticity. Tadpoles exposed to chemical cues from dragonfly larvae showed the expected antipredator response: these larvae showed significantly reduced movement activity and risk-taking. Although exposure to MP did not influence the behaviour of tadpoles that had not been exposed to predator cues, and also did not alter predator-induced changes in movement activity, it entirely abolished the predator-induced reduction in risk-taking. These results indicate that MP can compromise antipredator behaviour, increasing the vulnerability of individuals and natural populations to predation without causing visible developmental abnormalities. We recommend that future MP research targets behavioural traits with direct relevance to survival and reproduction, and examines how adaptive phenotypic plasticity is affected.

animal behavior and cognition↗

bioRxiv2025

Behavioral anapyrexia as a response to virus infection in a poikilothermic vertebrate

Behavioral plasticity may contribute to the ability of wild animals to survive disease outbreaks. In absence of endogen heat control, poikilothermic animals adjust their body temperature behaviorally. While many studies reported behavioral fever, its opposite, behavioral anapyrexia - when infected animals lower their body temperature by using cool microenvironments - remains poorly documented. Here, we report the first evidence of behavioral anapyrexia in a poikilothermic vertebrate as a response to pathogenic infection. We investigated thermoregulatory responses in tadpoles of the agile frog Rana dalmatina, a cool-adapted amphibian, following experimental infection with a warm-adapted ranavirus. Tadpoles were placed either in thermal gradients or homogeneously cool environments for five days post-exposure. In thermal gradients, all tadpoles reduced their preferred temperatures over time, but this decrease was steeper in infected tadpoles, and individuals with higher infection intensities preferred cooler temperatures. Infected tadpoles became increasingly precise in thermoregulation over time, while a similar trend was not detectable in non-infected tadpoles. Infection prevalence was similar between the two thermal environments, yet infection intensities were significantly higher in the thermal gradient. These results suggest fine-tuned thermoregulation by infected tadpoles to balance out the benefits of behavioral anapyrexia for fighting a warm-adapted pathogen versus the immune-suppressive and developmental costs of low temperatures.

ecology↗

bioRxiv2024

Do pyrethroid insecticides influence sex ratios in agile frogs (Rana dalmatina)?

Environmental pollutants have the potential to alter sex ratios in wildlife through sex-biased mortality. Furthermore, endocrine disruptors may cause sex reversal during early ontogeny in ectothermic vertebrates, resulting in a phenotypic sex that is not concordant with the genotypic sex encoded by the sex chromosomes. Despite the wide-ranging implications of these sex-ratio biasing effects, they are rarely studied in ecotoxicology, especially in a way that allows for disentangling the two mechanisms. We investigated these effects of two synthetic pyrethroids, deltamethrin and etofenprox, that are commonly used insecticides and have been linked to adverse effects on fish and amphibian biodiversity. We assessed the effects of environmentally relevant concentrations of these two pyrethroids on phenotypic sex ratio, sex-dependent mortality, and sex reversal in agile frogs (Rana dalmatina). Tadpoles from field-collected eggs were reared in mesocosm until metamorphosis by adding 0.03 or 0.3 g/L of deltamethrin or etofenprox three times to the water. We observed no effect in three of the four treatment groups. However, in the lower-concentration etofenprox treatment, phenotypic sex ratio was male-biased two months post-metamorphosis, and genotypic sexing revealed that this was due to female-biased mortality during metamorphosis and not to sex reversal. Although the estimation certainty of these effects was somewhat limited, they highlight that not all sex-ratio distorting effects are caused by sex reversal. Therefore, ecotoxicological studies aiming to understand the endocrine distruptor effects of environmental contaminants should strive to separate the effects on sex determination and sex-dependent mortality.

ecology↗

bioRxiv2024

Juvenile agile frogs spatially avoid ranavirus-infected conspecifics, but do not show generalized social distancing or self-isolation

Exposure to contagious pathogens can result in behavioural changes, which can alter the spread of infectious diseases. Healthy individuals can express generalized social distancing or actively avoid the sources of infection, while infected individuals can show passive or active self-isolation. Amphibians are globally threatened by serious contagious diseases, yet their behavioural responses to infections are very scarcely known. We studied behavioural changes in agile frog (Rana dalmatina) juveniles upon exposure to a Ranavirus (Rv). We performed classic choice tests in chambers containing a conspecific infected with Rv in one end compartment and a non-infected conspecific in the other end, with an Rv-infected or non-infected focal individual in the central compartment. We found that both non-infected and Rv- infected focal individuals spatially avoided infected conspecifics, while there were no signs of generalized social distancing, nor self-isolation. Spatial avoidance of infected conspecifics may effectively hinder disease transmission. On the other hand, the absence of self-isolation by infected individuals may facilitate it. Our finding that infected individuals spent more time near the non-infected than infected conspecifics suggests that the strong behavioural drive to avoid infected conspecifics may not be silenced by infection, possibly to prevent secondary infections. The observation that infected focal individuals did not spend more time near conspecifics than non-infected focals renders it unlikely that the pathogen manipulated host behaviour to aid disease spread. More research is urgently needed to understand under what circumstances behavioural responses can help amphibians cope with infections, and how that affects disease dynamics in natural populations. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=68 SRC="FIGDIR/small/588850v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@59b5a9org.highwire.dtl.DTLVardef@1a59896org.highwire.dtl.DTLVardef@c4bc64org.highwire.dtl.DTLVardef@2c76c3_HPS_FORMAT_FIGEXP M_FIG C_FIG

animal behavior and cognition↗

bioRxiv2023

Effects of mild winter conditions and two pyrethroid insecticides on the development and survival of juvenile common toads (Bufo bufo)

Combined effects of pollutants and climate change can have long-term negative effects on Earths biodiversity. We tested how amphibians are affected by exposure to pesticides around metamorphosis in combination with current winter conditions or those projected to become the norm by 2100. We applied two pyrethroid insecticides, cypermethrin or deltamethrin, to newly metamorphosed common toads (Bufo bufo) via spraying, thereafter reared animals in outdoor enclosures, and finally exposed them either to a long&cold winter (1.5 {degrees}C for 91 days) or to a short&mild one (4.5 {degrees}C for 61 days). After hibernation, we examined changes in body mass, size and gross morphology of parotoid glands and visceral organs, and determined the phenotypic sex of the surviving toadlets. In the long&cold winter scenario, we observed high mortality rate, regardless of the chemical treatment (control: 82%, cypermethrin: 78%, deltamethrin: 70%). At the same time, mortality was significantly lower in the short&mild winter scenario (control: 33%, cypermethrin: 41%, deltamethrin: 26%). The decrease in body mass during overwintering did not differ among treatment groups. Our results contradict the hypothesis of sex-biased mortality caused by chemical pollutants, harsh or mild winter conditions or by their combination. No significant deformations of the internal organs were found in either group. Our results suggest that winter conditions becoming ever milder in the temperate zone may prove beneficial for amphibian overwinter survival, and that exposure to the tested pyrethroids at ecologically relevant concentrations after metamorphosis does not interfere with the fitness of juvenile common toads.

zoology↗

bioRxiv2022

Amphibian larvae benefit from a warm environment under simultaneous threat from chytridiomycosis and ranavirosis

Rising temperatures can facilitate epizootic outbreaks, but disease outbreaks may be suppressed if temperatures increase beyond the optimum of the pathogens while still within the temperature range that allows for effective immune function in hosts. The two most devastating pathogens of wild amphibians, Batrachochytrium dendrobatidis (Bd) and ranaviruses (Rv), co-occur in large areas, yet little is known about the consequences of their co-infection and how these consequences depend on temperature. Here we tested how co-infection and elevated temperatures (28 and 30{degrees}C vs. 22{degrees}C) affected Bd and Rv prevalence, infection intensities, and resulting mortalities in larval agile frogs and common toads. We found multiple pieces of evidence that the presence of one pathogen influenced the prevalence and/or infection intensity of the other pathogen in both species, depending on temperature and initial Rv concentration. Generally, the 30{degrees}C treatment lowered the prevalence and infection intensity of both pathogens, and, in agile frogs, this was mirrored by higher survival. These results suggest that if temperatures naturally increase or are artificially elevated beyond what is ideal for both Bd and Rv, amphibians may be able to control infections and survive even the simultaneous presence of their most dangerous pathogenic enemies.

evolutionary biology↗

bioRxiv2021

"Heat waves" experienced during larval life have species-specific consequences on life-history traits and sexual development in anuran amphibians

Extreme temperatures during heat waves can induce mass-mortality events, but can also exert sublethal negative effects by compromising life-history traits and derailing sexual development. Ectothermic animals may, however, also benefit from increased temperatures via enhanced physiological performance and the suppression of cold-adapted pathogens. Therefore, it is crucial to address how the intensity and timing of naturally occurring or human-induced heat waves affect life-history traits and sexual development in amphibians, to predict future effects of climate change and to minimise risks arising from the application of elevated temperature in disease mitigation. We raised agile frog (Rana dalmatina) and common toad (Bufo bufo) tadpoles at 19 {degrees}C and exposed them to a simulated heat wave of 28 or 30 {degrees}C for six days during one of three ontogenetic periods (early, mid or late larval development). In agile frogs, exposure to 30 {degrees}C during early larval development increased mortality. Regardless of timing, all heat-treatments delayed metamorphosis, and exposure to 30 {degrees}C decreased body mass at metamorphosis. Furthermore, exposure to 30 {degrees}C during any period and to 28 {degrees}C late in development caused female-to-male sex reversal, skewing sex ratios strongly towards males. In common toads, high temperature only slightly decreased survival and did not influence phenotypic sex ratio, while it reduced metamorph mass and length of larval development. Juvenile body mass measured two months after metamorphosis was not adversely affected by temperature treatments in either species. Our results indicate that heat waves may have devastating effects on amphibian populations, and the severity of these negative consequences, and sensitivity can vary greatly between species and with the timing and intensity of heat. Finally, thermal treatments against cold-adapted pathogens have to be executed with caution, taking into account the thermo-sensitivity of the species and the life stage of animals to be treated.

ecology↗