Biology subjects

Rojas, B.

Publications and source records attributed to Rojas, B..

15 recordsLinked to original sources

bioRxiv2026

Mercury bioaccumulation varies across breeding-site height and life-history traits in Amazonian phytotelm-breeding frogs

Mercury (Hg) concentrations in the environment have significantly increased in the Amazon. Despite the observed deleterious effects on freshwater wildlife, the impacts of Hg contamination in phytotelmata (i.e., waterbodies contained in plant structures) and the species therein remain undocumented. We investigated the effects of Hg contamination on a phytotelm-breeding frog community in an otherwise pristine rainforest in French Guiana. Total Hg concentrations were measured in 28 pools at different heights (i.e. ground to canopy), and in the bodies of 103 tadpoles from five species with contrasting life histories. Tadpoles from ground pools had higher Hg concentrations than those from arboreal pools, revealing a vertical gradient in Hg contamination; tadpoles from species with slow development and parental care (i.e., tadpole transport) exhibited higher Hg concentrations than those of species with fast development without parental care. Finally, although Hg burdens were not associated with oxidative DNA levels, individuals reaching metamorphosis exhibited lower DNA damage than early-stage tadpoles, possibly reflecting reduced oxidative damage resulting from cellular remodelling undergone during metamorphosis, or selective mortality processes. Our findings highlight the joint influence of habitat type and life-history traits on Hg accumulation and that, even in pristine forests, Hg exposure varies strongly across microhabitats and species.

ecology↗

bioRxiv2026

Chromatic contrasts predict human target detection in a natural search task

Natural scenes are visually complex, with dynamic variation in colour and luminance presenting challenges for detecting salient objects. However, the cues guiding human detection under such natural conditions remain largely untested. We placed custom-built coloured targets in a forest-like setting and quantified their contrasts against natural backgrounds using human visual models. Across human observers (n = 51), detection performance rose sharply with hue and saturation contrast, whereas luminance contrast--long considered a primary driver of visual search--contributed little explanatory power. Strikingly, even large changes in ambient light chromaticity barely altered detection, despite the patchy illumination of the habitat. Under these naturalistic conditions, hue and saturation contrasts were stronger predictors of detection than luminance contrast, providing a rare, field-based test of visual models widely applied across human and animal vision research.

animal behavior and cognition↗

bioRxiv2024

Honest signalling in predator-prey interactions: testing the resource allocation hypothesis

Warning signals are honest if they reliably deliver information about prey unprofitability to predators. One potential mechanism that may create and maintain a positive relationship between the strength of signals and defence is the resource allocation between these costly traits. Here, we test this hypothesis using the wood tiger moth Arctia plantaginis, whose females red hindwings are a warning signal to predators but show considerable variation in colouration within populations. These moths also produce a defensive chemical that is known to influence avian predator attack risk. Using dietary manipulations, image and chemical analyses, and experiments with ecologically relevant predators we demonstrate that protein availability during development can influence the strength of both the primary warning signal and the secondary defence. Our results show that females raised on a high-protein or ad libitum natural diet produced more distasteful defensive fluids than those raised on a low-protein diet or subjected to periodic food deprivation. While the patterning of the warning signal was unaffected by food deprivation, its efficacy was diminished in moths raised on a low-protein diet. However, this change was imperceptible to avian predators. Critically, resource availability influenced the relationship between signal strength and defence: moths on a high-protein diet displayed a positive correlation between warning signal strength and unpalatability, whereas this correlation was absent in moths raised on a natural diet. These findings show that resource availability can weaken the reliability of warning signals as an indicator of an individuals defensive capabilities, highlighting the complex interplay between ecological conditions and the evolution of honest signalling.

evolutionary biology↗

bioRxiv2023

Genome assembly of the dyeing poison frog provides insights into the dynamics of transposable element and genome-size evolution

Genome size varies greatly across the tree of life and transposable elements are an important contributor to this variation. Among vertebrates, amphibians display the greatest variation in genome size, making them ideal models to explore the causes and consequences of genome size variation. However, high-quality genome assemblies for amphibians have, until recently, been rare. Here, we generate a high-quality genome assembly for the dyeing poison frog, Dendrobates tinctorius. We compare this assembly to publicly-available frog genomes and find evidence for both large-scale conserved synteny and widespread rearrangements between frog lineages. Comparing conserved orthologs annotated in these genomes revealed a strong correlation between genome size and gene size. To explore the cause of gene-size variation, we quantified the location of transposable elements relative to gene features and find that the accumulation of transposable elements in introns has played an important role in the evolution of gene size in D. tinctorius, while estimates of insertion times suggest that many insertion events are recent and species-specific. Finally, we show that the diversity and abundance of transposable elements in poison frog genomes can complicate genotyping efforts that rely on repetitive elements as sequence anchors. Our results show that transposable elements have clearly played an important role in the evolution of large genome size in D. tinctorius. Future studies are needed to fully understand the dynamics of transposable element evolution and to optimise primer or bait design for cost-effective population-level genotyping in species with large, repetitive genomes. SignificanceAmphibians display more variation in genome size than any other vertebrate lineage. Complexities associated with large genomes frequently hamper genome assembly and population genetic studies. Here we use long-read HiFi sequences to generate a high-quality 6.3 Gbp genome assembly of the poison frog Dendrobates tinctorius. We use this genome and leverage comparative genomics and de novo annotations to quantify aspects of genome evolution driven by repetitive transposable genetic elements. Our results provide support for the dynamic role that transposable elements play in driving the evolution of "genomic gigantism" in amphibians. We also show how transposable elements can be leveraged for cost-efficient population genetic studies using limited input material.

genetics↗

bioRxiv2023

Visual environment of rearing sites affects larval response to perceived risk

O_LITurbidity challenges the visual performance of aquatic animals. During development, environments with limited visibility may affect the fine-tuning of visual systems and thus the perception of, and response to, risk. While turbidity has frequently been used to characterise permanent aquatic habitats, it has been an overlooked feature of ephemeral ones. C_LIO_LIHere, we use the natural diversity of ephemeral rearing sites (phytotelmata) in which the tadpoles of two poison frog species are deposited and confined until metamorphosis to explore the relationship between environments with limited visibility and response to perceived risk. C_LIO_LIWe sampled wild tadpoles of Dendrobates tinctorius, a rearing-site generalist with facultatively cannibalistic tadpoles, and Oophaga (formerly Dendrobates) pumilio, a small-phytotelm specialist dependent on maternal food-provisioning, to investigate how the visual environment in rearing sites influences tadpole behaviour. We hypothesised that turbid rearing conditions negatively impact both species ability to perceive risk, decreasing response strength to predatory visual stimuli. Using experimental arenas, we measured tadpole activity and space first on a black and white background, and then on either black or white backgrounds where tadpoles were exposed to visual stimuli of (potentially cannibalistic) conspecifics or potential predators. C_LIO_LIWhen placed in a novel arena, the effects of rearing environment on D. tinctorius tadpoles were clear: tadpoles from darker pools were less active than tadpoles from brighter pools, and did not respond to either visual stimuli, whereas tadpoles from brighter pools swam more when paired with conspecifics versus odonate larvae, suggesting that tadpoles can visually discriminate between predators. For O. pumilio, tadpoles were more active on experimental backgrounds that more closely matched the luminosity of their rearing sites, but their responses to the two visual stimuli did not differ. C_LIO_LILarval specialisation associated with species-specific microhabitat use may underlie the observed responses to visual stimuli, which has implications for the stability of species interactions and trophic dynamics in pool communities. Together, our findings demonstrate that light availability of wild larval rearing conditions influences the perception of risk in novel contexts, and provide insight into how visually guided animals may respond to sudden environmental disturbances. C_LI

animal behavior and cognition↗

bioRxiv2023

Diet influences resource allocation in chemical defence but not melanin synthesis in an aposematic moth

For animals that synthesise their chemical compounds de novo, resources, particularly proteins, can influence investment in chemical defences and nitrogen-based wing colouration such as melanin. Competing for the same resources often leads to trade-offs in resource allocation. We manipulated protein availability in the larval diet of the wood tiger moth, Arctia plantaginis, to test how early life resource availability influences relevant life history traits, melanin production, and chemical defences. We expected higher dietary protein to result in more effective chemical defences and a higher amount of melanin in the wings. According to the resource allocation hypothesis, we also expected individuals with less melanin to have more resources to allocate to chemical defences. We found that protein-deprived moths had a slower larval development, and their chemical defences were less unpalatable for bird predators, but the expression of melanin in their wings did not differ from that of moths raised on a high-protein diet. The amount of melanin in the wings, however, unexpectedly correlated positively with chemical defences, irrespective of the diet they were raised on. Our findings demonstrate that the resources available in early life have an important role in the efficacy of chemical defences, but melanin-based warning colours are less sensitive to resource variability than other fitness-related traits.

ecology↗

bioRxiv2022

Genetic factors influence behavioural repeatability in juvenile poison frogs

Individual behaviour is a combination of previous experiences and genetic factors whose interaction can be adaptively adjusted to respond to changes in the surrounding environment. Understanding the continuity of behaviours both within and among individuals can help us disentangle the ecological and evolutionary significance underlying patterns of aggression, activity, boldness, and cooperation. In this study, we examined whether there is repeatability in the activity levels of juvenile dyeing poison frogs (Dendrobates tinctorius). This tropical species, known for its striking coloration and skin toxins, changes upon metamorphosis from an aquatic to a terrestrial habitat where individuals must immediately become active foragers to acquire their chemical defences. We did not find individual behaviour to be repeatable, however, we detected repeatability in activity at the family level, suggesting that behavioural variation may be explained, at least partially, by genetic factors in addition to a common environment. The assumption that activity level is very important for the survival of individuals after metamorphosis is supported by our results in that genetic factors seem to play a role in the formation of activity level. Further experiments are needed to investigate to what extent other areas of the individuals lives are affected by the respective activity levels, and what significance this has for the survival of a population.

animal behavior and cognition↗

bioRxiv2022

Not just the sum of its parts: geographic variation and non-additive effects of pyrazines in the chemical defence of an aposematic moth

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. We investigated 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. We expected the variation to reflect populations predation pressures and early-life conditions. To understand the role of the methoxypyrazines, we experimentally manipulated synthetic SBMP and IBMP and tested the birds reactions. We found a considerable variation in methoxypyrazine amounts and composition, both from wild-caught and laboratory-raised male moths. In agreement with the "cost of defence" hypothesis, the moths raised in the laboratory had a higher amount of pyrazines. We found that SBMP is more effective at higher concentrations and that IBMP is more effective only in combination with SBMP and at lower concentrations. Our results fit findings from the wild: the amount of SBMP was higher in the populations with higher predation pressure. Altogether, this suggests that, regarding pyrazine concentration, more is not always better, and highlights the importance of testing the efficacy of chemical defence and its components with relevant predators, rather than relying only on results from chemical analyses.

evolutionary biology↗

bioRxiv2022

Contrasting parental roles shape sex differences in poison frog space use but not navigational performance

Sex differences in vertebrate spatial abilities are typically interpreted under the adaptive specialization hypothesis, which posits that male reproductive success is linked to larger home ranges and better navigational skills. The androgen spillover hypothesis counters that enhanced male spatial performance may be a byproduct of higher androgen levels. Animal groups that include species where females are expected to outperform males based on life-history traits are key for disentangling these hypotheses. We investigated the association between sex differences in reproductive strategies, spatial behavior, and androgen levels in three species of poison frogs. We tracked individuals in natural environments to show that contrasting parental sex roles shape sex differences in space use, where the sex performing parental duties shows wider-ranging movements. We then translocated frogs from their home areas to test their navigational performance and found that the caring sex outperformed the non-caring sex only in one out of three species. In addition, males across species displayed more explorative behavior than females. Furthermore, androgen levels correlated with explorative behavior and homing accuracy. Our findings suggest that poison frog reproductive strategies shape space use patterns but not navigational performance, providing counterevidence to the prevailing view of adaptive sex differences in spatial abilities.

animal behavior and cognition↗

bioRxiv2021

Pool choice in a vertical landscape: tadpole rearing site flexibility in phytotelm-breeding frogs

Many species of Neotropical frogs have evolved to deposit their tadpoles in small water bodies inside plant structures called phytotelmata. These pools are small enough to exclude large predators but have limited nutrients and high desiccation risk. Here, we explore phytotelm use by three common Neotropical species: Osteocephalus oophagus, an arboreal frog that periodically feeds eggs to its tadpoles; Dendrobates tinctorius, a tadpole-transporting poison frog with cannibalistic tadpoles; and Allobates femoralis, a terrestrial tadpole-transporting poison frog with omnivorous tadpoles. We found that D. tinctorius occupies pools across the chemical and vertical gradient, whereas A. femoralis and O. oophagus appear to have narrower niches that are restricted primarily by pool height, water capacity, alkalinity, and salinity. Dendrobates tinctorius tadpoles are particularly flexible, and can survive in a wide range of chemical, physical, and biological conditions, whereas O. oophagus seems to prefer small, clear pools and A. femoralis occupies medium-sized pools with abundant leaf litter and low salinity. Together, these results show the possible niche partitioning of phytotelmata among frogs, and provide insight into stressors and resilience of phytotelm breeders.

ecology↗

bioRxiv2020

Size-dependent tradeoffs in aggressive behavior towards kin

Aggression between juveniles can be unexpected, as their primary motivation is to survive until their reproductive stage. However, instances of aggression, which may escalate to cannibalism, can be vital for survival, although the factors (e.g. genetic or environmental) leading to cannibalism vary across taxa. While cannibalism can greatly accelerate individual growth, it may also reduce inclusive fitness when kin are consumed. As a solution to this problem, some cannibals demonstrate kin discrimination and preferentially attack unrelated individuals. Here, we used both experimental and modeling approaches to consider how physical traits (e.g. size in relation to opponent) and genetic relatedness mediate aggressive behavior in dyads of cannibalistic Dendrobates tinctorius tadpoles. We paired sibling, half-sibling, and non-sibling tadpoles of different sizes together in an arena and recorded their aggression and activity. We found that the interaction between size and relatedness predicts aggressive behavior: large non-siblings are significantly more aggressive than large siblings. Unexpectedly, although siblings tended to attack less overall, in size mismatched pairs they attacked faster than in non-sibling treatments. Ultimately, it appears that larval aggression reflects a balance between relatedness and size where individuals trade-off their own fitness with that of their relatives.

animal behavior and cognition↗

bioRxiv2020

Visible implant elastomer (VIE) success in early larval stages of a tropical amphibian species

Animals are often difficult to distinguish at an individual level, but being able to identify individuals can be crucial in ecological or behavioral studies. In response to this challenge, biologists have developed a range of marking (tattoos, brands, toe-clips) and tagging (PIT, VIA, VIE) methods to identify individuals and cohorts. Animals with complex life cycles are notoriously hard to mark because of the distortion or loss of the tag across metamorphosis. In frogs, few studies have attempted larval tagging and none have been conducted on a tropical species. Here, we present the first successful account of VIE tagging in early larval stages (Gosner stage 25) of the dyeing poison frog (Dendrobates tinctorius) coupled with a novel anaesthetic (2-PHE) application for tadpoles that does not require buffering. Mean weight of individuals at time of tagging was 0.12g, which is the smallest and developmentally youngest anuran larvae tagged to date. We report 81% tag detection over the first month of development, as well as the persistence of tags across metamorphosis in this species. Cumulative tag retention versus tag observation differed by approximately 15% across larval development demonstrating that “lost” tags can be found later in development. Tagging had no effect on tadpole growth rate or survival. Successful application of VIE tags on D. tinctorius tadpoles introduces a new method that can be applied to better understand early life development and dispersal in various tropical species.Competing Interest StatementThe authors have declared no competing interest.View Full Text

zoology↗

bioRxiv2020

Geographic mosaic of selection by avian predators on hindwing warning colour in a polymorphic aposematic moth

Warning signals are predicted to develop signal monomorphism via positive frequency-dependent selection (+FDS) albeit many aposematic systems exhibit signal polymorphism. To understand this mismatch, we conducted a large-scale predation experiment in four locations, among which the frequencies of hindwing warning coloration of aposematic Arctia plantaginis differ. Here we show that selection by avian predators on warning colour is predicted by local morph frequency and predator community composition. We found +FDS to be strongest in monomorphic Scotland, and in contrast, lowest in polymorphic Finland, where different predators favour different male morphs. +FDS was also found in Georgia, where the predator community was the least diverse, whereas in the most diverse avian community in Estonia, hardly any models were attacked. Our results support the idea that spatial variation in predator and prey communities alters the strength or direction of selection on warning signals, thus facilitating a geographic mosaic of selection.

ecology↗

bioRxiv2019

Much more than a clasp: Evolutionary pattern of amplexus diversity in anurans

The evolution and diversification of animal reproductive modes have been pivotal questions in behavioral ecology. Amphibians present the highest diversity of reproductive modes among vertebrates, involving various behavioral, physiological and morphological traits. One of such features is the amplexus, the clasp or embrace of males on females during reproduction, which is almost universal to anurans. Hypotheses about the origin amplexus are limited and have not been thoroughly tested, nor had they taken into account evolutionary relationships in most comparative studies. However, these considerations are crucial to understand the evolution of reproductive modes. Here, using an evolutionary framework, we reconstruct the ancestral state of amplexus in 686 anuran species; investigate whether the amplexus type is a conserved trait; and test whether sexual size dimorphism (SSD) could have influenced the amplexus type or male performance while clasping females. Overall, we found evidence of at least 35 evolutionary transitions in amplexus type across anurans. We also found that amplexus exhibits a high phylogenetic signal (it is conserved across Anura evolutionary history) and the amplexus type does not evolve in association with SSD. We discuss the implications of our findings on the diversity of amplexus types across anurans.

evolutionary biology↗

bioRxiv2019

From Habitat Use to Social Behavior: Natural History of a Voiceless Poison Frog, Dendrobates tinctorius

Descriptive studies of natural history have always been a source of knowledge on which experimental work and scientific progress rely. Poison frogs are a well-studied group of small Neotropical frogs with diverse parental behaviors, distinct calls, and bright colors that warn predators about their toxicity; and a showcase of advances in fundamental biology through natural history observations. The dyeing poison frog, Dendrobates tinctorius, is emblematic of the Guianas region, widespread in the pet-trade, and increasingly popular in research. This species shows several unusual behaviors, such as the lack of advertisement calls and the aggregation around tree-fall gaps, which remain poorly described and understood. Here, we summarize our observations from a natural population of D. tinctorius in French Guiana collected over various field trips between 2009 and 2017; our aim is to provide groundwork for future fundamental and applied research spanning parental care, animal dispersal, disease spread, habitat use in relation to color patterns, and intra specific communication, to name a few. We report sex differences in habitat use and the striking invasion of tree-fall gaps; describe their courtship and aggressive behaviors; document egg development and tadpole transport; and discuss how the knowledge generated by this study could set the grounds for further research on the behavior, ecology, and conservation of this species.

animal behavior and cognition↗