Andrius Pašukonis

The brain regions supporting spatial navigation are well studied in mammals, but their function in the spatial behavior of other vertebrates is poorly understood, especially in field conditions. Here, we measured the behavior and neural correlates of the initial stages of navigation in a territorial rainforest frog, Allobates femoralis, in its natural environment. Frogs were released in familiar, unfamiliar, or home areas. Only frogs released in a familiar area, but outside their home territory, showed significant orientation towards home and spent more time on elevated structures, presumably orienting in space. In contrast, frogs released back in their home territory tended to move little, whereas those released in an unfamiliar area tended to move more, possibly exploring unfamiliar sites to find familiar landmarks. Contrary to our prediction, the amphibian homolog of the hippocampus (medial pallium) did not show a selective response to the navigational task. When accounting for behavioral differences, most measured pallial and subpallial regions showed increased neural activity during frog orientation home from a familiar environment. Interestingly, despite the behavioral differences, there were few differences in brain activity between the frogs released directly back home and those released in an unfamiliar area. Overall, we find that wild poison frogs respond selectively to environmental familiarity and that most measured brain regions have more translationally-active neurons when challenged to navigate a familiar setting. Our findings support the hypothesis that, in amphibians, brain regions homologous to mammalian centers of spatial processing exhibit more task-general responses.

Understanding animal movement in natural environments is central to research in behavior, ecology, and conservation. However, studying small amphibians in dense habitats presents major logistical challenges. Here, we describe two complementary techniques: harmonic direction finding (HDF) and very high frequency (VHF) radiotelemetry for tracking individual frogs in natural, complex environments. We provide detailed instructions for assembling lightweight HDF transponder tags, preparing VHF transmitters, and attaching both using minimally invasive harness designs. We also note considerations for selecting the appropriate method based on species size, movement behavior, and study goals. Finally, we outline one potential workflow for data collection and post-processing. Together, these techniques allow researchers to collect detailed information on movement patterns, space use, microhabitat use, and individual behavior.

Colubrid snakes are generalist predators and are well documented to predate on adult anurans and their eggs. However, there is limited information on predation of amphibian larvae (tadpoles). This is particularly true for rarely observed species such as arboreal rainforest snakes and frogs. Chlorosoma viridissimum is a common arboreal snake found in the Amazon rainforest. Here, we report multiple events of juvenile C. viridissimum hunting underwater for tadpoles of frogs ( Trachycephalus resinifictrix , T. hadroceps , and Osteocephalus oophagus ) breeding in water‐filled tree cavities. The observations were made through video monitoring and direct observations in the tropical rainforest at Nouragues Nature Reserve, French Guiana. Our observations suggest that juveniles of C. viridissimum are underwater hunters and may be a key predator for canopy‐breeding frog larvae.

The behavioural, sensory and neural bases of vertebrate navigation are primarily described in mammals and birds. While many studies have explored amphibian navigation, none have characterized brain activity associated with navigation in the wild. To address this knowledge gap, we conducted a study on navigation in the cane toad, Rhinella marina . First, we performed a translocation experiment to describe how invasive cane toads in Hawaii navigate home and observed homing following displacements of up to 1 km. Next, we tested the effect of olfactory and magnetosensory manipulations on homing, as these senses are most commonly associated with amphibian navigation. We found that neither ablation alone prevents homing, further supporting that toad navigation is multimodal. Finally, we tested the hypothesis that the medial pallium, the amphibian homologue to the hippocampus, is involved in homing. Our comparisons of neural activity revealed evidence supporting a conservation of neural structures associated with navigation across vertebrates consistent with neural models of amphibian spatial cognition from recent laboratory studies. Our work furthers our evolutionary understanding of spatial behaviour and cognition in vertebrates and lays a foundation for studying the behavioural, sensory and neural bases of navigation in an invasive amphibian.

The behavioral, sensory, and neural bases of vertebrate navigation are primarily described in mammals and birds. However, we know much less about navigational abilities and mechanisms of vertebrates that move on smaller scales, such as amphibians. To address this knowledge gap, we conducted an extensive field study on navigation in the cane toad, Rhinella marina. First, we performed a translocation experiment to describe how invasive toads in Hawaiʻi navigate home following displacements of up to one kilometer. Next, we tested the effect of olfactory and magnetosensory manipulations on homing, as these senses are most commonly associated with amphibian navigation. We found that neither ablation alone prevents homing, suggesting that toad navigation is multimodal. Finally, we tested the hypothesis that the medial pallium, the amphibian homolog to the hippocampus, is involved in homing. By comparing neural activity across homing and non-homing toads, we found evidence supporting the involvement of the medial pallium, lateral pallium, and septum in navigation, suggesting a conservation of neural structures supporting navigation across vertebrates. Our study lays the foundation to understand the behavioral, sensory, and neural bases of navigation in amphibians and to further characterize the evolution of behavior and neural structures in vertebrates.

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 and androgen levels correlated with explorative behavior and homing accuracy. Overall, we reveal that poison frog reproductive strategies shape movement patterns but not necessarily navigational performance. Together this work suggests that prevailing adaptive hypotheses provide an incomplete explanation of sex differences in spatial abilities.

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.

Breeding sites are often a limited and ephemeral resource for rainforest frogs. This resource limitation has driven the evolution of diverse reproductive strategies that increase offspring survival. For example, poison frogs shuttle their tadpoles from terrestrial clutches to aquatic rearing sites, using various cues to assess pool suitability. Yet, how frogs find new pools is unknown. We tested the role of odor cues in the process of finding tadpole deposition sites by the poison frog Allobates femoralis. We created 60 artificial pools grouped into three conditions: stagnant water, tadpole water and clean water control. Fifteen pools were discovered within 6 days, with more tadpoles and more frogs directly observed at pools with stagnant odor cues. Our findings suggest that frogs use odor cues associated with stagnant water for the initial discovery of new breeding pools. These cues may be good indicators of pool stability and increased likelihood of tadpole survival.

Many animals exhibit complex navigation over different scales and environments. Navigation studies in amphibians have largely focused on species with life histories that require advanced spatial capacities, such as territorial poison frogs and migratory pond-breeding amphibians that show fidelity to mating sites. However, other species have remained relatively understudied, leaving the possibility that well-developed navigational abilities are widespread. Here, we measured short-term space use in non-territorial, non-migratory cane toads ( Rhinella marina ) in their native range in French Guiana. After establishing home range, we tested their ability to return to home following translocations of 500 and 1000 meters. Toads were able to travel in straight trajectories back to home areas, suggesting map-like navigational abilities similar to those observed in amphibians with more complex spatial behavior. These observations break with the current paradigm of amphibian navigation and suggest that navigational abilities may be widely shared among amphibians.