The Homing Frog: High Homing Performance in a Territorial Dendrobatid Frog Allobates femoralis (Dendrobatidae)

Small population size and possible extirpation of the threatened Malagasy poison frog Mantella cowanii

Amphibians are experiencing severe population declines, requiring targeted conservation action for the most threatened species and habitats. Unfortunately, we do not know the basic demographic traits of most species, which hinders population recovery efforts. We studied one of Madagascar's most threatened frog species, the harlequin mantella (Mantella cowanii), to confirm it is still present at historic localities and estimate annual survival and population sizes. We surveyed eleven of all thirteen known localities and were able to detect the species at eight. Using a naïve estimate of detection probability from sites with confirmed presence, we estimated 1.54 surveys (95% CI [1.10-2.37]) are needed to infer absence with 95% confidence, suggesting the three populations where we did not detect M. cowanii are now extirpated. However, we also report two new populations for the first time. Repeated annual surveys at three sites showed population sizes ranged from 13-137 adults over 3-8 years, with the most intensively surveyed site experiencing a >80% reduction in population size during 2015-2023. Annual adult survival was moderately high (0.529-0.618) and we recaptured five individuals in 2022 and one in 2023 first captured as adults in 2015, revealing the maximum lifespan of the species in nature can reach 9 years and beyond. Our results confirm M. cowanii is characterized by a slower life history pace than other Mantella species, putting it at greater extinction risk. Illegal collection for the international pet trade and continued habitat degradation are the main threats to the species. We recommend conservation efforts continue monitoring M. cowanii populations and reassess the International Union for Conservation of Nature (IUCN) Red List status because the species may be Critically Endangered rather than Endangered based on population size and trends.

Amphibian spatial cognition, medial pallium and other supporting telencephalic structures

Vertebrate hippocampal formation is central to conversations on the comparative analysis of spatial cognition, especially in light of variation found in different vertebrate classes. Assuming the medial pallium (MP) of extant amphibians resembles the hippocampal formation (HF) of ancestral stem tetrapods, we propose that the HF of modern amniotes began with a MP characterized by a relatively undifferentiated cytoarchitecture, more direct thalamic/olfactory sensory inputs, and a more generalized role in associative learning-memory processes. As such, hippocampal evolution in amniotes, especially mammals, can be seen as progressing toward a cytoarchitecture with well-defined subdivisions, regional connectivity, and a functional specialization supporting map-like representations of space. We then summarize a growing literature on amphibian spatial cognition and its underlying brain organization. Emphasizing the MP/HF, we highlight that further research into amphibian spatial cognition would provide novel insight into the role of the HF in spatial memory processes, and their supporting neural mechanisms. A more complete reconstruction of hippocampal evolution would benefit from additional research on non-mammalian vertebrates, with amphibians being of particular interest.

Odor cues rather than personality affect tadpole deposition in a neotropical poison frog

Animals constantly need to evaluate available external and internal information to make appropriate decisions. Identifying, assessing, and acting on relevant cues in contexts such as mate choice, intra-sexual competition, and parental care is particularly important for optimizing individual reproductive success. Several factors can influence decision-making, such as external environmental cues and the animal's own internal state, yet, we have limited knowledge on how animals integrate available information. Here, we used an entire island population (57 males, 53 females, and 1,109 tadpoles) of the neotropical brilliant-thighed poison frog Allobates femoralis to investigate how 2 factors (olfactory cues and personality traits) influence the ability of males to find and use new resources for tadpole deposition. We experimentally manipulated the location of tadpole deposition sites and their associated olfactory cues, and repeatedly measured exploration and boldness in adult males. We further reconstructed tadpole deposition choices via inferred parent-offspring relationships of adult frogs and tadpoles deposited in our experimental pools using molecular parentage analysis. We found that the discovery and use of new rearing sites were heavily influenced by olfactory cues; however, we did not find an effect of the measured behavioral traits on resource discovery and use. We conclude that in highly dynamic environments such as tropical rainforests, reliable external cues likely take priority over personality traits, helping individuals to discover and make use of reproductive resources.

Personality traits differentially affect components of reproductive success in a Neotropical poison frog

Individual reproductive success has several components, including the acquisition of mating partners, offspring production, and offspring survival until adulthood. While the effects of certain personality traits-such as boldness or aggressiveness-on single components of reproductive success are well studied, we know little about the composite and multifaceted effects behavioural traits can have on all the aspects of reproductive success. Behavioural traits positively linked to one component of reproductive success might not be beneficial for other components, and these effects may differ between sexes. We investigated the influence of boldness, aggressiveness, and exploration on the number of mating partners, mating events, and offspring surviving until adulthood in males and females of the Neotropical poison frog Allobates femoralis. Behavioural traits had different-even opposite-effects on distinct components of reproductive success in both males and females. For example, males who displayed high levels of aggressiveness and exploration (or low levels of aggressiveness and exploration) managed to attract high number of mating partners, while males with low levels of boldness, low levels of aggressiveness, and high levels of exploration had the most offspring surviving until adulthood. Our results therefore suggest correlational selection favouring particular combinations of behavioural traits.

Tissue-specific in vivo transformation of plasmid DNA in Neotropical tadpoles using electroporation

Electroporation is an increasingly common technique used for exogenous gene expression in live animals, but protocols are largely limited to traditional laboratory organisms. The goal of this protocol is to test in vivo electroporation techniques in a diverse array of tadpole species. We explore electroporation efficiency in tissue-specific cells of five species from across three families of tropical frogs: poison frogs (Dendrobatidae), cryptic forest/poison frogs (Aromobatidae), and glassfrogs (Centrolenidae). These species are well known for their diverse social behaviors and intriguing physiologies that coordinate chemical defenses, aposematism, and/or tissue transparency. Specifically, we examine the effects of electrical pulse and injection parameters on species- and tissue-specific transfection of plasmid DNA in tadpoles. After electroporation of a plasmid encoding green fluorescent protein (GFP), we found strong GFP fluorescence within brain and muscle cells that increased with the amount of DNA injected and electrical pulse number. We discuss species-related challenges, troubleshooting, and outline ideas for improvement. Extending in vivo electroporation to non-model amphibian species could provide new opportunities for exploring topics in genetics, behavior, and organismal biology.

Exploring links between personality traits and their social and non-social environments in wild poison frogs

An animal's behavioral phenotype comprises several traits, which are hierarchically structured in functional units. This is manifested in measured behaviors often being correlated, partly reflecting the need of a coordinated functional response. Unfortunately, we still have limited understanding whether consistent differences in animal behaviors are due to underlying physiological constraints or a result of plastic adaptation to their current environment. Therefore, characterizing the spatial distribution of behaviors can provide important insights into causes and consequences of behavioral variation. In the present study, we quantified behaviors in a wild, free-ranging population of the Neotropical frog Allobates femoralis. We investigated how these behaviors were linked to the frogs' natural and social environment and quantified the extent to which these behaviors consistently differed among individuals (i.e., animal personality). We assessed levels of aggressiveness, exploration, and boldness by measuring several underlying behaviors expressed in a set of experimental assays, and found evidence for consistent among-individual differences along these axes. Contrary to our expectation, there was no relationship between individual behaviors and their natural environment, but we found a plastic response of males to changes in female density, which might reflect how individuals cope with their socio-ecological environment.

Significance statement

How are behavioral phenotypes distributed across space? Here, we studied an entire free-ranging population of poison frogs, and investigated if the personality traits aggressiveness, exploration, and boldness are linked to the frogs' natural or social environment. We found that behavioral traits were non-randomly distributed across the population, suggesting that the spatial arrangement of behavioral traits reflects how individuals cope with their complex natural and social environment.

Orientation and emigration of larval and juvenile amphibians: selected topics and hypotheses

Most amphibians have a complex life cycle with an aquatic larval and an adult (semi-) terrestrial stage. However, studies concerning spatial behaviour and orientation mainly focus on either the aquatic larvae or the adult animals on land. Consequently, behavioural changes that happen during metamorphosis and the consequences for emigration and population distribution are less understood. This paper aims to summarize the knowledge concerning specific topics of early amphibian life history stages and proposes several testable hypotheses within the following fields of research: larval and juvenile orientation, influences of environmental and genetic factors on juvenile emigration, their habitat choice later in life as well as population biology. I argue that studying larval and juvenile amphibian spatial behaviour is an understudied field of research, however, could considerably improve our understanding of amphibian ecology.

Key roles of paternal care and climate on offspring survival of an Amazonian poison frog

In poison frogs (Dendrobatoidea), usually the males are territorial, care for terrestrial nests and later transport their offspring to waterbodies where they complete larval development. In some species, mothers care for their offspring or may exhibit flexible care to compensate for father absence. We conducted a multi-season field experiment with the Amazonian species Allobates paleovarzensis, in which it was possible to study the joint impact of paternal care and the El Niño climatic anomaly on offspring survival. The experiment consisted of two treatments: non-removal, and removal of the father from their territories. We observed that parental care was performed exclusively by the father, and none of the mothers of the 21 monitored nests transported the tadpoles. We also observed that the severe drought in a year under the influence of the El Niño event caused such a high mortality in all pre-metamorphic stages, that the role of parental care became irrelevant for offspring survival during that season. We found that pre-metamorphic Allobates paleovarzensis are highly vulnerable to the loss of paternal care. In addition, we showed that paternal care, when present, does not prevent offspring death under these increasingly frequent climatic anomalies.

Orientation and navigation in Bufo bufo: a quest for repeatability of arena experiments

Research on navigation in animals is hampered by conflicting results and failed replications. In order to assess the generality of previous results, male Bufo bufo were collected during their breeding migration and translocated to two testing sites, 2.4 and 2.9 km away, respectively, from their breeding pond in the north of Vienna (Austria). There each toad was tested twice for orientation responses in a circular arena, on the night of collection and four days later. On the first test day, the toads showed significant axial orientation along their individual former migration direction. On the second test day, no significant homeward orientation was detected. Both results accord with findings of previous experiments with toads from another population. We analysed the potential influence of environmental factors (temperature, cloud cover and lunar cycle) on toad orientations using a MANOVA approach. Although cloud cover and lunar cycle had small effects on the second test day, they could not explain the absence of homeward orientation. The absence of homing responses in these tests may be either caused by the absence of navigational capabilities of toads beyond their home ranges, or by inadequacies of the applied method. To resolve this question, tracking of freely moving toads should have greater potential than the use of arena experiments.

Reproductive behavior drives female space use in a sedentary Neotropical frog

Longer-range movements of anuran amphibians such as mass migrations and habitat invasion have received a lot of attention, but fine-scale spatial behavior remains largely understudied. This gap is especially striking for species that show long-term site fidelity and display their whole behavioral repertoire in a small area. Studying fine-scale movement with conventional capture-mark-recapture techniques is difficult in inconspicuous amphibians: individuals are hard to find, repeated captures might affect their behavior and the number of data points is too low to allow a detailed interpretation of individual space use and time budgeting. In this study, we overcame these limitations by equipping females of the Brilliant-Thighed Poison Frog (Allobates femoralis) with a tag allowing frequent monitoring of their location and behavior. Neotropical poison frogs are well known for their complex behavior and diverse reproductive and parental care strategies. Although the ecology and behavior of the polygamous leaf-litter frog Allobates femoralis is well studied, little is known about the fine-scale space use of the non-territorial females who do not engage in acoustic and visual displays. We tracked 17 females for 6 to 17 days using a harmonic direction finder to provide the first precise analysis of female space use in this species. Females moved on average 1 m per hour and the fastest movement, over 20 m per hour, was related to a subsequent mating event. Traveled distances and activity patterns on days of courtship and mating differed considerably from days without reproduction. Frogs moved more on days with lower temperature and more precipitation, but mating seemed to be the main trigger for female movement. We observed 21 courtships of 12 tagged females. For seven females, we observed two consecutive mating events. Estimated home ranges after 14 days varied considerably between individuals and courtship and mating associated space use made up for ∼30% of the home range. Allobates femoralis females spent large parts of their time in one to three small centers of use. Females did not adjust their time or space use to the density of males in their surroundings and did not show wide-ranging exploratory behavior. Our study demonstrates how tracking combined with detailed behavioral observations can reveal the patterns and drivers of fine-scale spatial behavior in sedentary species.

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.

The neural basis of tadpole transport in poison frogs

Parental care has evolved repeatedly and independently across animals. While the ecological and evolutionary significance of parental behaviour is well recognized, underlying mechanisms remain poorly understood. We took advantage of behavioural diversity across closely related species of South American poison frogs (Family Dendrobatidae) to identify neural correlates of parental behaviour shared across sexes and species. We characterized differences in neural induction, gene expression in active neurons and activity of specific neuronal types in three species with distinct care patterns: male uniparental, female uniparental and biparental. We identified the medial pallium and preoptic area as core brain regions associated with parental care, independent of sex and species. The identification of neurons active during parental care confirms a role for neuropeptides associated with care in other vertebrates as well as identifying novel candidates. Our work is the first to explore neural and molecular mechanisms of parental care in amphibians and highlights the potential for mechanistic studies in closely related but behaviourally variable species to help build a more complete understanding of how shared principles and species-specific diversity govern parental care and other social behaviour.

A cognitive map in a poison frog

A fundamental question in cognitive science is whether an animal can use a cognitive map. A cognitive map is a mental representation of the external world, and knowledge of one's place in this world, that can be used to determine efficient routes to any destination. Many birds and mammals are known to employ a cognitive map, but whether other vertebrates can create a cognitive map is less clear. Amphibians are capable of using beacons, gradients and landmarks when navigating, and many are proficient at homing. Yet only one prior study directly tested for a cognitive map in amphibians, with negative results. Poison frogs exhibit unusually complex social and spatial behaviors and are capable of long-distance homing after displacement, suggesting that they may be using complex spatial navigation strategies in nature. Here, we trained the poison frog Dendrobates auratus in a modified Morris water maze that was designed to suppress thigmotaxis to the maze wall, promoting exploration of the arena. In our moat maze, the poison frogs were able to use a configuration of visual cues to find the hidden platform. Moreover, we demonstrate that they chose direct paths to the goal from multiple random initial positions, a hallmark of a cognitive map. The performance of the frogs in the maze was qualitatively similar to that of rodents, suggesting that the potential to evolve a cognitive map is an evolutionarily conserved trait of vertebrates.

Soil and forest structure predicts large-scale patterns of occurrence and local abundance of a widespread Amazonian frog

The distribution of biodiversity within the Amazon basin is often structured by sharp environmental boundaries, such as large rivers. The Amazon region is also characterized by subtle environmental clines, but how they might affect the distributions and abundance of organisms has so far received less attention. Here, we test whether soil and forest characteristics are associated with the occurrence and relative abundance of the forest-floor dwelling Aromobatid frog, Allobates femoralis. We applied a structured sampling regime along an 880 km long transect through forest of different density. High detection probabilities were estimated for A. femoralis in each of the sampling modules. Using generalized linear mixed-effects models and simple linear regressions that take detectability into account, we show that A. femoralis is more abundant in open forests than in dense forests. The presence and relative abundance of A. femoralis is also positively associated with clay-rich soils, which are poorly drained and therefore likely support the standing water bodies required for reproduction. Taken together, we demonstrate that relatively easy-to-measure environmental features can explain the distribution and abundance of a widespread species at different spatial scales. Such proxies are of clear value to ecologists and conservation managers working in large inaccessible areas such as the Amazon basin.

Map-like navigation from distances exceeding routine movements in the three-striped poison frog (Ameerega trivittata)

Most animals move in dense habitats where distant landmarks are limited, but how they find their way around remains poorly understood. Poison frogs inhabit the rainforest understory, where they shuttle tadpoles from small territories to widespread pools. Recent studies revealed their excellent spatial memory and the ability to home back from several hundred meters. It remains unclear whether this homing ability is restricted to the areas that had been previously explored or whether it allows the frogs to navigate from areas outside their direct experience. Here, we used radio-tracking to study the navigational performance of three-striped poison frog translocated outside the area of their routine movements (200-800 m). Translocated frogs returned to their home territory via a direct path from all distances and with little difference in orientation accuracy, suggesting a flexible map-like navigation mechanism. These findings challenge our current understanding of both the mechanisms and the sensory basis of amphibian orientation.

Relying on known or exploring for new? Movement patterns and reproductive resource use in a tadpole-transporting frog

Animals relying on uncertain, ephemeral and patchy resources have to regularly update their information about profitable sites. For many tropical amphibians, widespread, scattered breeding pools constitute such fluctuating resources. Among tropical amphibians, poison frogs (Dendrobatidae) exhibit some of the most complex spatial and parental behaviors—including territoriality and tadpole transport from terrestrial clutches to ephemeral aquatic deposition sites. Recent studies have revealed that poison frogs rely on spatial memory to successfully navigate through their environment. This raises the question of when and how these frogs gain information about the area and suitable reproductive resources. To investigate the spatial patterns of pool use and to reveal potential explorative behavior, we used telemetry to follow males of the territorial dendrobatid frog Allobates femoralis during tadpole transport and subsequent homing. To elicit exploration, we reduced resource availability experimentally by simulating desiccated deposition sites. We found that tadpole transport is strongly directed towards known deposition sites and that frogs take similar direct paths when returning to their home territory. Frogs move faster during tadpole transport than when homing after the deposition, which probably reflects different risks and costs during these two movement phases. We found no evidence for exploration, neither during transport nor homing, and independent of the availability of deposition sites. We suggest that prospecting during tadpole transport is too risky for the transported offspring as well as for the transporting male. Relying on spatial memory of multiple previously discovered pools appears to be the predominant and successful strategy for the exploitation of reproductive resources in A. femoralis. Our study provides for the first time a detailed description of poison frog movement patterns during tadpole transport and corroborates recent findings on the significance of spatial memory in poison frogs. When these frogs explore and discover new reproductive resources remains unknown.

Acoustic ranging in poison frogs-it is not about signal amplitude alone

Abstract

Acoustic ranging allows identifying the distance of a sound source and mediates inter-individual spacing and aggression in territorial species. Birds and mammals are known to use more complex cues than only sound pressure level (SPL), which can be influenced by the signaller and signal transmission in non-predictable ways and thus is not reliable by itself. For frogs, only SPL is currently known to mediate inter-individual distances, but we hypothesise that the strong territoriality of Dendrobatids could make the use of complex cues for ranging highly beneficial for this family. Therefore, we tested the ranging abilities of territorial males of Allobates femoralis (Dendrobatidae, Aromobatinae) in playback trials, using amplitude-normalized signals that were naturally degraded over distance, and synthetic signals that were masked with different levels of noise. Frogs responded significantly less to signals recorded from larger distances, regardless of SPL and signal-to-noise ratio (SNR), but showed no differential response to natural minimum and maximum SNRs across the typical communication range in wild populations. This indicates that frogs used signal amplitude and SNR only as ancillary cues when assessing the distance of sound sources and relied instead mainly on more complex cues, such as spectral degradation or reverberation. We suggest that this ability mediates territorial spacing and mate choice in A. femoralis. Good ranging abilities might also play a role in the remarkable orientation performance of this species, probably by enabling the establishment of a mental acoustic map of the habitat.

Significance statement

Acoustic ranging allows the distance of vocalizing competitors and mates to be identified. While birds and mammals are known to use complex cues such as temporal degradation, frequency-dependent attenuation and reverberation for ranging, previous research indicated that frogs rely only on signal amplitude (sound pressure level) to assess the distance of other callers. The present study shows for the first time that also poison frogs can make use of more complex cues, an ability which is likely to be highly beneficial in their territorial social organization and probably can also be used for orientation.

Electronic supplementary material

The online version of this article (doi:10.1007/s00265-017-2340-2) contains supplementary material, which is available to authorized users.

The significance of spatial memory for water finding in a tadpole-transporting frog

The ability to associate environmental cues with valuable resources strongly increases the chances of finding them again, and thus memory often guides animal movement. For example, many temperate region amphibians show strong breeding site fidelity and will return to the same areas even after the ponds have been destroyed. In contrast, many tropical amphibians depend on exploitation of small, scattered and fluctuating resources such as ephemeral pools for reproduction. It remains unknown whether tropical amphibians rely on spatial memory for effective exploitation of their reproductive resources. Poison frogs (Dendrobatidae) routinely shuttle their tadpoles from terrestrial clutches to dispersed aquatic deposition sites. We investigated the role of spatial memory for relocating previously discovered deposition sites in an experimental population of the brilliant-thighed poison frog, Allobates femoralis, a species with predominantly male tadpole transport. We temporarily removed an array of artificial pools that served as the principal tadpole deposition resource for the population. In parallel, we set up an array of sham sites and sites containing conspecific tadpole odour cues. We then quantified the movement patterns and site preferences of tadpole-transporting males by intensive sampling of the area and tracking individual frogs. We found that tadpole-carrier movements were concentrated around the exact locations of removed pools and most individuals visited several removed pool sites. In addition, we found that tadpole-transporting frogs were attracted to novel sites that contained high concentrations of conspecific olfactory tadpole cues. Our results suggest that A. femoralis males rely heavily on spatial memory for efficient exploitation of multiple, widely dispersed deposition sites once they are discovered. Additionally, olfactory cues may facilitate the initial discovery of the new sites.

Take the long way home: Behaviour of a neotropical frog, Allobates femoralis, in a detour task

Detour behaviour, an individual's ability to reach its goal by taking an indirect route, has been used to test spatial cognitive abilities across a variety of taxa. Although many amphibians show a strong homing ability, there is currently little evidence of amphibian spatial cognitive flexibility. We tested whether a territorial frog, Allobates femoralis, can flexibly adjust its homing path when faced with an obstacle. We displaced male frogs from their calling sites into the centre of circular arenas and recorded their escape routes. In the first experiment we provided an arena with equally high walls. In the second experiment we doubled the height of the homeward facing wall. Finally, we provided a tube as a shortcut through the high wall. In the equal-height arena, most frogs chose to escape via the quadrant facing their former calling site. However, when challenged with different heights, nearly all frogs chose the low wall, directing their movements away from the calling site. In the "escape tunnel" experiment most frogs still chose the low wall. Our results show that displaced A. femoralis males can flexibly adjust their homing path and avoid (presumably energetically costly) obstacles, providing experimental evidence of spatial cognitive flexibility in an amphibian.

Sex-specific offspring discrimination reflects respective risks and costs of misdirected care in a poison frog

The ability to differentiate between one's own and foreign offspring ensures the exclusive allocation of costly parental care to only related progeny. The selective pressure to evolve offspring discrimination strategies is largely shaped by the likelihood and costs of offspring confusion. We hypothesize that males and females with different reproductive and spatial behaviours face different risks of confusing their own with others' offspring, and this should favour differential offspring discrimination strategies in the two sexes. In the brilliant-thighed poison frog, Allobates femoralis, males and females are highly polygamous, terrestrial clutches are laid in male territories and females abandon the clutch after oviposition. We investigated whether males and females differentiate between their own offspring and unrelated young, whether they use direct or indirect cues and whether the concurrent presence of their own clutch is essential to elicit parental behaviours. Males transported tadpoles regardless of location or parentage, but to a lesser extent in the absence of their own clutch. Females discriminated between clutches based on exact location and transported tadpoles only in the presence of their own clutch. This sex-specific selectivity of males and females during parental care reflects the differences in their respective costs of offspring confusion, resulting from differences in their spatial and reproductive behaviours.

Poison frogs rely on experience to find the way home in the rainforest

Among vertebrates, comparable spatial learning abilities have been found in birds, mammals, turtles and fishes, but virtually nothing is known about such abilities in amphibians. Overall, amphibians are the most sedentary vertebrates, but poison frogs (Dendrobatidae) routinely shuttle tadpoles from terrestrial territories to dispersed aquatic deposition sites. We hypothesize that dendrobatid frogs rely on learning for flexible navigation. We tested the role of experience with the local cues for poison frog way-finding by (i) experimentally displacing territorial males of Allobates femoralis over several hundred metres, (ii) using a harmonic direction finder with miniature transponders to track these small frogs, and (iii) using a natural river barrier to separate the translocated frogs from any familiar landmarks. We found that homeward orientation was disrupted by the translocation to the unfamiliar area but frogs translocated over similar distances in their local area showed significant homeward orientation and returned to their territories via a direct path. We suggest that poison frogs rely on spatial learning for way-finding in their local area.

Populations, pools, and peccaries: simulating the impact of ecosystem engineers on rainforest frogs

Peccary wallows and footprints are important breeding pools for rainforest frogs. We performed a resource supplementation experiment with artificial pools, simulating peccary actions, in a population of the poison frog Allobates femoralis. The population almost doubled resulting from increased local reproduction, but not from immigration. These findings demonstrate the importance of “ecosystem engineers,” such as peccaries, for other species, the frogs. Our results also indicate that human engineering may help to protect amphibian populations.

“Ecosystem engineering” describes habitat alteration by an organism that affects another organism; such nontrophic interactions between organisms are a current focus in ecological research. Our study quantifies the actual impact an ecosystem engineer can have on another species by using a previously identified model system—peccaries and rainforest frogs. In a 4-year experiment, we simulated the impact of peccaries on a population of Allobates femoralis (Dendrobatidae) by installing an array of artificial pools to mimic a forest patch modified by peccaries. The data were analyzed using a gradual before-after control-impact (gBACI) model. Following the supplementation, population size almost doubled as a result of increased autochthonous recruitment driven by a higher per-capita reproduction of males and a higher proportion of reproducing females. The effect was evenly distributed across the population. The differential response of males and females reflects the reproductive behavior of A. femoralis, as only the males use the aquatic sites for tadpole deposition. Our study shows that management and conservation must consider nontrophic relationships and that human “ecosystem engineering” can play a vital role in efforts against the “global amphibian decline.”

High-resolution forest mapping for behavioural studies in the Nature Reserve 'Les Nouragues', French Guiana

For animals with spatially complex behaviours at relatively small scales, the resolution of a global positioning system (GPS) receiver location is often below the resolution needed to correctly map animals' spatial behaviour. Natural conditions such as canopy cover, canyons or clouds can further degrade GPS receiver reception. Here we present a detailed, high-resolution map of a 4.6 ha Neotropical river island and a 8.3 ha mainland plot with the location of every tree >5 cm DBH and all structures on the forest floor, which are relevant to our study species, the territorial frog Allobates femoralis (Dendrobatidae). The map was derived using distance- and compass-based survey techniques, rooted on dGPS reference points, and incorporates altitudinal information based on a LiDAR survey of the area.

Homing trajectories and initial orientation in a Neotropical territorial frog, Allobates femoralis (Dendrobatidae)

Introduction

The ability to relocate home or breeding sites after experimental removal has been observed in several amphibians and the sensory basis of this behavior has been studied in some temperate-region species. However, the actual return trajectories have rarely been quantified in these studies and it remains unknown how different cues guide the homing behavior. Dendrobatidae (dart-poison frogs) exhibit some of the most complex spatial behaviors among amphibians, such as territoriality and tadpole transport. Recent data showed that Allobates femoralis, a frog with paternal tadpole transport, successfully returns to the home territories after experimental translocations of up to 400 m. In the present study, we used harmonic direction finding to obtain homing trajectories. Additionally, we quantified the initial orientation of individuals, translocated 10 m to 105 m, in an arena assay.

Results

Tracking experiments revealed that homing trajectories are characterized by long periods of immobility (up to several days) and short periods (several hours) of rapid movement, closely fitting a straight line towards the home territory. In the arena assay, the frogs showed significant homeward orientation for translocation distances of 35 m to 70 m but not for longer and shorter distances.

Conclusions

Our results describe a very accurate homing behavior in male A. femoralis. The straightness of trajectories and initial homeward orientation suggest integration of learned landmarks providing a map position for translocated individuals. Future research should focus on the role of learning in homing behavior and the exact nature of cues being used.

Tadpole transport logistics in a Neotropical poison frog: indications for strategic planning and adaptive plasticity in anuran parental care

Introduction

Individuals should aim to adjust their parental behaviours in order to maximize the success of their offspring but minimize associated costs. Plasticity in parental care is well documented from various bird, mammal and fish species, whereas amphibians were traditionally assumed as being highly instinct-bound. Therefore, little is known about ‘higher’ cognitive abilities of amphibians, such as strategic planning and behavioural flexibility. Dendrobatid frogs have evolved a remarkable diversity of parental behaviours. The most noticeable of these behaviours is tadpole transport, which is obligatory in almost all species. Nonetheless, there is limited knowledge about spatial and temporal patterns of tadpole transport and the possible existence of behavioural plasticity on the individual level. In this study, we investigated correlates of tadpole transport behaviour in a natural population of the dendrobatid frog Allobates femoralis during five years.

Results

Tadpole transport was predominantly observed during morning hours. Although tadpoles were carried almost exclusively by males (N = 119), we also observed ten females performing this task. The parentage analysis revealed that in all cases females transported their own offspring. In contrast, four tadpole-carrying males were not the genetic fathers of the larvae they were transporting. The average clutch size of 20 eggs and our observation of an average of 8 tadpoles on the back of transporting individuals indicate that frogs do not carry entire clutches at once, and/or that they distribute their larvae across several water bodies. Contrary to the predictions from a hypothetical random search for deposition sites, the number of transported tadpoles was higher in males that travelled over longer distances.

Conclusions

Our results suggest a strong selective pressure on males to shift the time invested in tadpole transport to periods of low intra-specific competition. The number of tadpoles on the back of the males significantly correlated with displacement distance from the respective home territories, indicating a strategic non-random tadpole transport rather than random search for suitable tadpole deposition sites during tadpole transport. The observation of females who occasionally transported larvae supports the prevalence of adaptive plasticity in parental behaviours even in a species with a rather low level of parental care.