Aquatic Amphibians Research Articles

Effects of Harmful Algal Blooms on Amphibians and Reptiles are Under-Reported and Under-Represented.

Harmful algal blooms (HABs) are a persistent and increasing problem globally, yet we still have limited knowledge about how they affect wildlife. Although semi-aquatic and aquatic amphibians and reptiles have experienced large declines and occupy environments where HABs are increasingly problematic, their vulnerability to HABs remains unclear. To inform monitoring, management, and future research, we conducted a literature review, synthesized the studies, and report on the mortality events describing effects of cyanotoxins from HABs on freshwater herpetofauna. Our review identified 37 unique studies and 71 endpoints (no-observed-effect and lowest-observed-effect concentrations) involving 11 amphibian and 3 reptile species worldwide. Responses varied widely among studies, species, and exposure concentrations used in experiments. Concentrations causing lethal and sublethal effects in laboratory experiments were generally 1 to 100 µg/L, which contains the mean value of reported HAB events but is 70 times less than the maximum cyanotoxin concentrations reported in the environment. However, one species of amphibian was tolerant to concentrations of 10,000 µg/L, demonstrating potentially immense differences in sensitivities. Most studies focused on microcystin-LR (MC-LR), which can increase systemic inflammation and harm the digestive system, reproductive organs, liver, kidneys, and development. The few studies on other cyanotoxins illustrated that effects resembled those of MC-LR at similar concentrations, but more research is needed to describe effects of other cyanotoxins and mixtures of cyanotoxins that commonly occur in the environment. All experimental studies were on larval and adult amphibians; there were no such studies on reptiles. Experimental work with reptiles and adult amphibians is needed to clarify thresholds of tolerance. Only nine mortality events were reported, mostly for reptiles. Given that amphibians likely decay faster than reptiles, which have tissues that resist decomposition, mass amphibian mortality events from HABs have likely been under-reported. We propose that future efforts should be focused on seven major areas, to enhance our understanding of effects and monitoring of HABs on herpetofauna that fill important roles in freshwater and terrestrial environments. Environ Toxicol Chem 2024;43:1936-1949. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Macroecological correlates of Darwinian shortfalls across terrestrial vertebrates.

Most described species have not been explicitly included in phylogenetic trees-a problem named the Darwinian shortfall-owing to a lack of molecular and/or morphological data, thus hampering the explicit incorporation of evolution into large-scale biodiversity analyses. We investigate potential drivers of the Darwinian shortfall in tetrapods, a group in which at least one-third of described species still lack phylogenetic data, thus necessitating the imputation of their evolutionary relationships in fully sampled phylogenies. We show that the number of preserved specimens in scientific collections is the main driver of phylogenetic knowledge accumulation, highlighting the major role of biological collections in unveiling novel biodiversity data and the importance of continued sampling efforts to reduce knowledge gaps. Additionally, large-bodied and wide-ranged species, as well as terrestrial and aquatic amphibians and reptiles, are phylogenetically better known. Future efforts should prioritize phylogenetic research on organisms that are narrow-ranged, small-bodied and underrepresented in scientific collections, such as fossorial species. Addressing the Darwinian shortfall will be imperative for advancing our understanding of evolutionary drivers shaping biodiversity patterns and implementing comprehensive conservation strategies.

Pond area and availability safeguard amphibian genetic diversity across Iberia's largest protected wetland

Abstract Wetland ecosystems worldwide are threatened by habitat alteration, climate change and the introduction of invasive species, even within protected areas. Unravelling the reliance of sensitive wetland‐dwelling species, such as amphibians, on habitat characteristics is thus essential to identify conservation targets. Here we assess the distribution of genetic diversity of two strongly aquatic amphibians (Pelophylax perezi and Pleurodeles waltl) in association with habitat features across the most extensive, protected wetland of the Iberian Peninsula: Doñana National Park. Despite inhabiting a protected area free from anthropogenic barriers, the genetic diversity of P. perezi and P. waltl is not homogeneously distributed across the wetland, but instead concentrates in core areas, mainly in the northern zone. Both genetic diversity and connectivity (as opposed to genetic differentiation) showed significant positive associations with the area of the breeding sites and the flooded area surrounding the breeding sites within the dispersal potential of either species, that is nearby pond availability. Large water bodies connected to abundant temporary ponds are key for the maintenance of amphibian genetic diversity. Nevertheless, the core populations of our target species, which show markedly aquatic habits, are concentrated in areas colonised by invasive species, which could compromise their long‐term viability. Our results highlight that maintaining widely connected arrays of ponds of different hydroperiods, including large breeding sites free from invasive predators and competitors, is paramount for amphibian conservation in Mediterranean wetlands.

Environmental DNA and visual encounter surveys for amphibian biomonitoring in aquatic environments of the Ecuadorian Amazon.

The development of anthropogenic activities has generated a decline in aquatic fauna populations, and amphibians have been the most affected. The decline of batrachofauna is concerning, as 41% of all species worldwide are endangered. For this reason, rapid, efficient, and non-invasive biodiversity monitoring techniques are needed, and environmental DNA (eDNA) is one such tool that has been sparsely applied in Ecuador. This technique has allowed scientists generates information on species diversity and amphibian community composition from a water sample. This study applied eDNA-based biomonitoring analyses and visual encounter surveys (VES) as inventory techniques to identify the diversity of aquatic amphibians in the Tena River micro-basin (TRMB). The experimental design was divided into three components: (1) fieldwork: all amphibians were recorded by the VES technique and water samples were collected; (2) laboratory work: DNA isolation from amphibian tissue samples and eDNA-containing filters, amplification, electrophoresis, and sequencing were performed; (3) Data analysis: a local DNA reference database was constructed, and eDNA sequence data were processed for classification, taxonomic assignment, and ecological interpretation. Using both eDNA and VES, we detected 33 amphibian species (13 with eDNA only, five with VES only, and 15 with both methods). These species belonged to six amphibian families: Hylidae being the richest with 14 species (three eDNA, one VES, and 10 with both methods), followed by Strabomantidae with nine species (six eDNA, one VES, and two with both methods). All families were detected with both methods, except for the Aromobatidae, having one single record (Allobates aff. insperatus) by VES. Individually, eDNA detected 28 species and had a detection probability (DP) of 0.42 CI [0.40-0.45], while VES recorded 20 species with a DP of 0.17 CI [0.14-0.20]. Similarly, using VES, Cochranella resplendens was detected for the first time in TRMB, while with eDNA, four mountain frogs Pristimantis acerus, Pristimantis eriphus, Pristimantis mallii, and Pristimantis sp. (INABIO 15591) previously recorded at 1,518 m.a.s.l. at altitudes below 600 m.a.s.l. were detected. Results obtained in this study showed that eDNA-based detection had a greater capacity to detect amphibians in aquatic environments compared to VES. The combination of VES and eDNA improves the sensitivity of species detection and provides more reliable, robust, and detailed information. The latter is essential for developing conservation strategies in the Ecuadorian Amazon.

An assessment of aquatic amphibian biodiversity on the California Lost Coast

One of the most difficult aspects of studying intact amphibian communities is that they tend to occupy isolated areas within inaccessible terrain—factors that both protect watersheds from development and disturbance while also making them difficult to study. We conducted an extensive survey of the freshwater herpetofauna of the remote King Range National Conservation Area in Northern California using a combination of visual encounter surveys and environmental DNA (eDNA) sampling. We found twelve species of native aquatic amphibians and the western pond turtle (Actinemys marmorata), and no introduced amphibians. Detection probabilities for the four most commonly encountered species, giant salamanders (Dicamptodon sp), foothill yellow-legged frogs (Rana boylii), western toads (Anaxyrus boreas), and black salamanders (Aneides flavipunctatus), were affected by substrate and canopy cover, but the effects of these habitat characteristics on detection probability were species specific. Neither survey method, visual encounter surveys nor eDNA sampling, was more effective than the other, and our study suggests that the use of visual encounter surveys in conjunction with eDNA sampling may counteract the shortcomings of either when done individually. Five species were found using both methods, seven were only encountered during visual encounter surveys, and one recorded only from eDNA sampling. DNA samples from two taxa, toads and giant salamanders, could not be resolved to species. Toad species identity was assigned to the only member of the candidate species with a species range known to overlap the study area; the other three candidate species occupy restricted ranges far from the study area. Neither of the two giant salamander candidate species have known species ranges overlapping the study area. One, the California giant salamander (D. ensata), is known to occur within 100 km. However, there is a paucity of genetic material in GenBank DNA library for both the California giant salamander and the coastal giant salamander (D. tenebrosus), a widely distributed species with a range overlapping the study area, which could lead to inaccurate assignment of eDNA fragments.

Synthesis ofBatrachochytrium dendrobatidisinfection in South America: amphibian species under risk and areas to focus research and disease mitigation

Amphibian chytridiomycosis, caused byBatrachochytrium dendrobatidis(Bd), has been recognized as the infectious disease causing the most catastrophic loss of biodiversity known to science, with South America being the most impacted region. We tested whetherBdprevalence is distributed among host taxonomy, ecoregion, conservation status and habitat preference in South America. Here we provide a synthesis on the extent ofBdinfection across South America based on 21 648 molecular diagnostic assays, roles of certain species in the epidemiology ofBdand explore its association with the reported amphibian catastrophic declines in the region. We show thatBdis widespread, with a continental prevalence of 23.2%. Its occurrence in the region shows a phylogenetic signal and the probability of infection is determined by ecoregion, preferred habitat and extinction risk hosts' traits. The taxa exhibiting highestBdoccurrence were mostly aquatic amphibians, including Ranidae, Telmatobiidae, Hylodidae, Calyptocephalellidae and Pipidae. Surprisingly, families exhibiting unusually lowBdprevalence included species in which lethal chytridiomycosis and population declines have been described (generaAtelopus,RhinodermaandEleutherodactylus). Higher than expected prevalence ofBdoccurred mainly in amphibians living in association with mountain environments in the Andes and Atlantic forests, reflecting highly favourableBdhabitats in these areas. Invasive amphibian species (e.g.Lithobates catesbeianusandXenopus laevis) exhibited highBdprevalence; thus we suggest using these as sentinels to understand their potential role as reservoirs, vectors or spreaders ofBdthat can be subjected to management. Our results guide on the prioritization of conservation actions to prevent further biodiversity loss due to chytridiomycosis in the world's most amphibian diverse region.

Effects of Copper on the Neuromasts of Xenopus Laevis.

Fish and aquatic amphibians possess neuromasts on the surface of their body that constitute the lateral line, a sensory system used to detect water displacement. Copper is known to inactivate the neuromast organs of this system. Copper-induced neuromast loss in African clawed frogs, Xenopus laevis, was examined by exposing Nieuwkoop-Faber stage 54-55 larvae to copper concentrations of 0, 100, 200, 300, and 400µg/L for 96h, followed by an examination of neuromast counts, staining intensity, and behavioral responses. Neuromasts were counted using a novel imaging method across four different body regions: the whole body, partial body, head, and tail. Neuromast counts showed a decreasing, but nonsignificant, trend across increasing levels of copper exposure. Intensity of neuromast staining showed a stronger concentration-dependent decrease in all four body regions. The decrease in staining intensity, but not neuromast number, may indicate that although neuromasts are still functioning, they have a decreased number of viable hair cells. Potential loss of responsiveness related to neuromast damage was examined via sensitivity to puffs of air at varying distances. We detected little to no difference in response to the air puff stimulus between control tadpoles and tadpoles exposed to 400µg/L of copper. Neuromasts of X. laevis may be more resistant to copper than those of North American tadpole species, possibly suggesting greater tolerance of the lateral line to environmental stressors in species that maintain this sensory system throughout their lifespan as compared with species that only have the lateral line during the larval period.

Differences in Fungal Disease Dynamics in Co-occurring Terrestrial and Aquatic Amphibians.

The fungal pathogen, Batrachochytrium dendrobatidis (Bd), has devastated biodiversity and ecosystem health and is implicated as a driver of mass amphibian extinctions. This 100-year study investigates which environmental factors contribute to Bd prevalence in a fully terrestrial species, and determines whether infection patterns differ between a fully terrestrial amphibian and more aquatic host species. We performed a historical survey to quantify Bd prevalence in 1127 Batrachoseps gregarius museum specimens collected from 1920 to 2000, and recent data from 16 contemporary (live-caught) B. gregarius populations from the southwestern slopes of the Sierra Nevada mountains in California, USA. We compared these results to Bd detection rates in 1395 historical and 1033 contemporary specimens from 10 species of anurans and 427 historical Taricha salamander specimens collected throughout the Sierra Nevada mountains. Our results indicate that Bd dynamics in the entirely terrestrial species, B. gregarius, differ from aquatic species in the same region in terms of both seasonal patterns of Bd abundance and in the possible timing of Bd epizootics.

Competitive oxidation and ubiquitylation on the evolutionarily conserved cysteine confer tissue-specific stabilization of Insig-2

Insig-2 is an ER membrane protein negatively controlling lipid biosynthesis. Here, we find that Insig-2 is increased in the tissues, including liver, but unaltered in the muscle of gp78-deficient mice. In hepatocytes and undifferentiated C2C12 myoblasts, Insig-2 is ubiquitylated on Cys215 by gp78 and degraded. However, the C215 residue is oxidized by elevated reactive oxygen species (ROS) during C2C12 myoblasts differentiating into myotubes, preventing Insig-2 from ubiquitylation and degradation. The stabilized Insig-2 downregulates lipogenesis through inhibiting the SREBP pathway, helping to channel the carbon flux to ATP generation and protecting myotubes from lipid over-accumulation. Evolutionary analysis shows that the YECK (in which C represents Cys215 in human Insig-2) tetrapeptide sequence in Insig-2 is highly conserved in amniotes but not in aquatic amphibians and fishes, suggesting it may have been shaped by differential selection. Together, this study suggests that competitive oxidation-ubiquitylation on Cys215 of Insig-2 senses ROS and prevents muscle cells from lipid accumulation.

Pulmonary Smooth Muscle in Vertebrates: A Comparative Review of Structure and Function.

Although the airways of vertebrates are diverse in shape, complexity, and function, they all contain visceral smooth muscle. The morphology, function, and innervation of this tissue in airways is reviewed in actinopterygians, lungfish, amphibians, non-avian reptiles, birds, and mammals. Smooth muscle was likely involved in tension regulation ancestrally, and may serve to assist lung emptying in fishes and aquatic amphibians, as well as maintain internal lung structure. In certain non-avian reptiles and anurans antagonistic smooth muscle fibers may contribute to intrapulmonary gas mixing. In mammals and birds, smooth muscle regulates airway caliber, and may be important in controlling the distribution of ventilation at rest and exercise, or during thermoregulatory and vocal hyperventilation. Airway smooth muscle is controlled by the autonomic nervous system: cranial cholinergic innervation generally causes excitation, cranial non-adrenergic, non-cholinergic innervation causes inhibition, and spinal adrenergic (SA) input causes species-specific, often heterogeneous contractions and relaxations.

Temperature exposure and possible thermoregulation strategies in the Titicaca water frog Telmatobius culeus, a fully aquatic frog of the High Andes

Temperature has an important effect on amphibians, influencing virtually all physio logical systems. Thermoregulation is used to manage unfavourable thermal conditions, but has been poorly studied in aquatic amphibians, and no information is available for adult aquatic anurans. We studied the temperatures to which the Critically Endangered and high Andean fully aquatic Titicaca water frog Telmatobius culeus is exposed and investigated possible thermoregulation strategies of the species in the wild. We measured water temperature in different seasons, microhabitats and depths at which T. culeus is most abundant. We established transects to obtain population densities and activity patterns of the species during the day. Seasonal and daily temperature variations as well as temperature variations among depths and microhabitats were noted. These variations were associated with densities of visible T. culeus, where adult densities were higher at depths with more stable temperatures. T. culeus behaviour associated with thermo regulation strategies in the aquatic habitat included depth selection and movement of individuals between different microhabitats. Selection of microhabitat depended on the temperature at a site and the hour of the day. These results indicate possible behavioural thermoregulation strategies such as movement to different sites or basking used by a highly specialized amphibian, and provide insights into how aquatic benthic organisms use strategies for thermoregulation in aquatic heterogeneous environments. These strategies are probably also used by other aquatic organisms from the tropical Andes. Knowledge of how these organisms respond to temperature could also help to understand the impact of global warming on their status.

Preoviposition paternal care in a fully aquatic giant salamander: nest cleaning by a den master

AbstractParental care in salamanders is thought to be simple and typically limited to female egg attendance. No elaborate preoviposition parental care had been described from salamanders. Recent studies revealed complex care behaviours by male Japanese giant salamanders (Andrias japonicus), a fully aquatic, secretive species with external fertilization. These studies emphasize behavioural convergence in paternal care between some of the fish species and the giant salamanders. The fish examples further imply the possibility that males of A. japonicus provide preoviposition parental care in the form of nest cleaning and building. We tested this possibility and also predicted that cleaning effort by a male salamander, if exists, would increase as it approaches the spawning event. Prior to the breeding season, large males (i.e. den masters) of A. japonicus occupy and guard suitable burrows well‐hidden along the stream bank. In the falls of 2012, 2013 and 2015, we videotaped and examined a single den master's pre‐ and postoviposition behaviours at Asa Zoological Park in Hiroshima, Japan. The den master repeatedly exhibited vigorous movements of front and hind limbs in a paddling motion at the bottom of the nest every day for the three separate years. The cleaning effort by the den master lineally increased as the spawning event approached, after which the den master completely ceased cleaning. With the cleaning behaviour, the den master made the den filled with debris including leaves and twigs buried in the sand. The floating debris was subsequently removed by the water current flowing through the nest. Water mould infection is a major cause of offspring mortality of aquatic amphibians including A. japonicus. By reducing the amount of organic matter that provides food sources for water mould, the nest cleaning likely reduces the risk of water mould infection among the offspring, serving as an important preoviposition parental care.

High Time for Hair Cells: An Introduction to the Symposium on Sensory Hair Cells.

Sensory hair cells are highly specialized cells that form the basis for our senses of hearing, orientation to gravity, and perception of linear acceleration (head translation in space) and angular acceleration (head rotation). In many species of fish and aquatic amphibians, hair cells mediate perception of water movement through the lateral line system, and electroreceptors derived from hair cell precursors mediate electric field detection. In tunicates, cells of the mechanosensory coronal organ on the incurrent siphon meet the structural, functional, and developmental criteria to be described as hair cells, and they function to deflect large particles from entering the animal. The past two decades have witnessed significant breakthroughs in our understanding of hair cell biology and how their specialized structures influence their functions. This symposium combines the approaches of developmental biology, evolutionary biology, and physiology to share the gains of recent research in understanding hair cell function in different model systems. We brought together researchers working on sensory hair cells in organisms spanning the chordates in order to examine the depth and breadth of hair cell evolution. It is clear that these specialized cells serve a range of functions in different animals, due to evolutionary tinkering with a basic specialized cell type. This collection of papers will serve to mark the progress that has been made in this field and also stimulate the next wave of progress in this exciting field.

Effect of hemin, baicalein and heme oxygenase-1 (HO-1) enzyme activity inhibitors on Cd-induced accumulation of HO-1, HSPs and aggresome-like structures in Xenopus kidney epithelial cells

Cadmium is a highly toxic environmental pollutant that can cause many adverse effects including cancer, neurological disease and kidney damage. Aquatic amphibians are particularly susceptible to this toxicant as it was shown to cause developmental abnormalities and genotoxic effects. In mammalian cells, the accumulation of heme oxygenase-1 (HO-1), which catalyzes the breakdown of heme into CO, free iron and biliverdin, was reported to protect cells against potentially lethal concentrations of CdCl2. In the present study, CdCl2 treatment of A6 kidney epithelial cells, derived from the frog, Xenopus laevis, induced the accumulation of HO-1, heat shock protein 70 (HSP70) and HSP30 as well as an increase in the production of aggregated protein and aggresome-like structures. Treatment of cells with inhibitors of HO-1 enzyme activity, tin protoporphyrin (SnPP) and zinc protoporphyrin (ZnPP), enhanced CdCl2-induced actin cytoskeletal disorganization and the accumulation of HO-1, HSP70, aggregated protein and aggresome-like structures. Treatment of cells with hemin and baicalein, which were previously shown to provide cytoprotection against various stresses, induced HO-1 accumulation in a concentration-dependent manner. Also, treatment of cells with hemin and baicalein suppressed CdCl2-induced actin dysregulation and the accumulation of aggregated protein and aggresome-like structures. This cytoprotective effect was inhibited by SnPP. These results suggest that HO-1-mediated protection against CdCl2 toxicity includes the maintenance of actin cytoskeletal and microtubular structure and the suppression of aggregated protein and aggresome-like structures.

Artificial lateral line based local sensing between two adjacent robotic fish

The lateral line system (LLS) is a mechanoreceptive organ system with which fish and aquatic amphibians can effectively sense the surrounding flow field. The reverse Kármán vortex street (KVS), known to be a typical thrust-producing wake, is commonly observed in fish-like locomotion and is known to be generated by fish’s tails. The vortex street generally reflects the motion information of the fish. A fish can use LLS to detect such vortex streets generated by its neighboring fish, thus sensing its own state and the states of its neighbors in a school of fish. Inspired by this typical biological phenomenon, we design a robotic fish with an onboard artificial lateral line system (ALLS) composed of pressure sensor arrays and use it to detect the reverse KVS-like vortex wake generated by its adjacent robotic fish. Specifically, the vortex wake results in hydrodynamic pressure variations (HPVs) in the flow field. By measuring the HPV using the ALLS and extracting meaningful information from the pressure sensor readings, the oscillating frequency/amplitude/offset of the adjacent robotic fish, the relative vertical distance and the relative yaw/pitch/roll angle between the robotic fish and its neighbor are sensed efficiently. This work investigates the hydrodynamic characteristics of the reverse KVS-like vortex wake using an ALLS. Furthermore, this work demonstrates the effectiveness and practicability of an artificial lateral line in local sensing for adjacent underwater robots, indicating the potential to improve close-range interaction and cooperation within a group of underwater vehicles through the application of ALLSs in the near future.

Habitat quality affects the incidence of morphological abnormalities in the endangered salamander Ambystoma ordinarium.

Identification of early warning signals previous to the occurrence of population decline or extinction is a major challenge for the conservation of animal species. Prevalence of morphological abnormalities in a population can be one of these signals. We registered morphological abnormalities in the salamander Ambystoma ordinarium. We also evaluated the relation between habitat quality and the prevalence of abnormalities in this species. We used scores from rapid bioassessment protocols (RBPs) to assess the habitat quality of streams inhabited by A. ordinarium. A preliminary survey indicated that of 29 streams where this species has been historically registered, 13 might have few or no A. ordinarium. The association between habitat quality and the incidence of morphological abnormalities was evaluated in these 16 streams. Of 502 sampled individuals, 224 (44.62%) had at least one body abnormality. Of the 224 individuals with body abnormalities, 84 (37.5%) presented more than one abnormality. Of a total of 5,522 evaluated morphological characters, 344 (6.74%) were abnormal. Partial loss of gills and missing digits were the most frequent abnormalities. Results of a binomial logistic regression indicated that the probability of a character of an individual to be abnormal was significantly associated with habitat quality; as the levels of the quality of the habitat increased, the prevalence of morphological abnormalities decreased. These results suggest that RBPs are a quick and useful method for assessing the habitat quality of streams inhabited by A. ordinarium. Given that RBPs provide rapid and cost-effective assessments of the ecological health of aquatic ecosystems, it will be important to test if the RBPs protocols can be used to rapidly assess habitat quality for other species of stream amphibians. The negative association between habitat quality and the prevalence of morpohological abnormalities that we found indicates that habitat condition plays an important role in the high number of abnormalities registered in A. ordinarium. Therefore, our results suggest that one of the several negative effects of habitat degradation on amphibians is an increase in the frequency of morphological abnormalities with marked consequences for the survival and general fitness of aquatic amphibians.

Spatial and temporal distribution and microhabitat use of aquatic breeding amphibians (Anura) in a seasonally dry tropical forest in Chamela, Mexico

The distribution of amphibians is affected by abiotic and biotic factors, availability of resources and the characteristics of reproductive sites. In particular, reproductive activity of aquatic-breeding anurans that inhabit tropical dry areas is affected by rainfall, which determines the availability and quality of reproductive sites. In this study, we analyzed the spatial and temporal distribution of anurans with indirect development in a tropical dry forest in Western Mexico, during two rainy seasons (July 10-October 4, 2013, and June 26-September 26, 2014). We collected data on the occupancy and reproductive activity of 15 species in four temporary streams, and evaluated their relationship with precipitation, humidity and temperature. We determined richness, abundance and diversity of species in each stream; we also identified differences in the reproductive strategies and microhabitats used by the species. The most abundant species were: Tlalocohyla smithii and Exerodonta smaragdina , whereas the least abundant were Leptodactylus melanonotus and Incilius mazatlanensis . Species richness, abundance and reproductive activity peaked alongside the stream with the greatest number of breeding sites (e.g. pools). We found temporal segregation in the occupancy and reproductive activity of species in all streams which were mainly associated with precipitation. However, occupancy and reproductive activity of some species overlapped up to four weeks during part of the breeding season. Most species used specific substrates for particular reproductive activities (e.g. oviposition), but used a range of microhabitats (leaf-litter, water, rocks, branches, leaves, logs, etc.) for others (e.g. calling). We discuss these behavioral differences as factors that facilitate coexistence of species in this environment in the rainy season.

Structure and function of the mechanosensory lateral line system in fish and biomimetic

As an adaptation to their environment, fishes and some aquatic amphibians have developed a hydrodynamic receptor system, the lateral line mechanosensory system, which enables them to detect minute water motion, and provide information that can apply for feeding, avoidance, schooling, navigation, and intraspecific communication. This system consists of individual sensory receptors, neuromasts, that either lie within lateral line canals along the body (canal neuromasts, CNM) or occur freestanding on the surface of the skin (superficial neuromasts, SNM). These CNM and SNM act as acceleration (higher frequency response, 60–120 Hz) or velocity receptors (lower frequency response, 20–60 Hz), respectively, which can also provide the signal location and fluidic direction to the central nervous system (CNS). The neuromast consists of discrete clusters of sensory hair cells, support cells and mantle cells. On the apical of hair cell, a bundle of several stereocilia and one kinocilium that protrudes from of the hair cell into a gelatinous cupula. The cupula covers entire neuromast apical and connects the ciliary bundles with surrounding water. Deflection of the cupula induces the directional movement of the hair bundles that results in opening or closing of the transduction channels on the kinocilium, affecting the release of neurotransmitter that conveys the hair cell’s relative excitation to the afferent neuron (in the lateral line ganglion), then, travels to the target areas in the CNS. Between CNM and SNM, there are several morphological differences such as diameter of sensory epithelium, number of hair cells, orientation of axis, and peripheral innervation pattern. They also demonstrate with different biomechanical properties in detecting different types of hydrodynamic signals and play different roles in responding to the various water motion patterns (including micro fluid). All the peripheral information that is integrated at different levels of the CNS centers before guiding the proper behavior of fish. The CNM appears to provide information about fine spatial details that lead to the ability of fish to segregate the fine turbulence signal in near field while towards discrete sources or under rapidly changing water motions surrounding. SNM appears to provide peripheral spatial information of large-scale stimuli, such as rheotaxis to slow motion currents. As a delicate hydrodynamic detector system, a well functioned lateral line system that only consists of two types of peripheral receptor plus their architectural design of arrangement and canal pattern modifications that is far advanced than, up to date, any of the man-made underwater detector in the world. Even more, the system provides a high efficient computing model that is from the peripheral innervation pattern designed for major collection of temporal and spatial hydrodynamic information, the integration of data processing structure, and to the action assignment in the CNS. The mechanosensory lateral line system in fish is starting attracted by research approaches in biomimetic, mathematics, physical and computing sciences, in addition to the biology and neurosciences. The participating of integrative study on the lateral line system, that is not only help developing of new applications but also enhanced biological understand of the system. The biologists have been speculated the function of the CNM, the co-relationship of the canal morphology and fish habits over decades. Until recently, the mathematic model and the device of artificial lateral line receptor established by Klein and Bleckmann (2015), demonstrate that “it is possible to change the transfer function of an artificial line by changing its canal shape, dimensions and pore pattern”. Moreover, their research evident indicate that the lateral line is able to “detect and localize vibrating sources, detect and monitor vortices, localize upstream objects, discriminate between upsteam objects (size and shape), estimate bulk flow velocity in turbulent environment, and measure small amounts of liquid” (Klein, 2016 personal communication). This review paper intends to introduce the fish mechanosensory lateral line system from several aspects that include the studies of morphological characteristics, biological origin of the system, development of the pattern formation, functional properties, behavioral neurophysiology and neural control mechanisms, finally, the biomimetic application and perspectives. We combine both of our knowledge in lateral line and recent research results in the non-canal lateral line system with broad collections of the references in the lateral line studies, especially, the new publications. We hope to provide information to readers across different disciplines, not only for theoretical consideration but also for the application in biomimetic, civic engineering, and the aquatic animal protection /biodiversity program.

Ecology and demography of the Critically Endangered Kandian torrent toadAdenomus kandianus: a long-lost endemic species of Sri Lanka

AbstractThe tropical island nation of Sri Lanka is a biodiversity hotspot with a high diversity and endemism of amphibians. The endemic, stream-dwelling Kandian torrent toadAdenomus kandianusis Critically Endangered and was considered to be extinct until its rediscovery in 2012. The species is now known from two localities in tropical montane forests. We conducted a 4-year study using transect surveys and opportunistic excursions to assess habitat associations, demographics and abundance ofA. kandianusin and around Pidurutalagala Conservation Forest. We recorded a mean of 44.25 post-metamorphs per year, with a density of < 1 individual per 100 m2, with occurrence within a narrow extent (c. 0.005 km2) of the stream channel. Behaviour and microhabitat selection varied depending on sex and stage of maturity. The species preferred moderately sized montane streams with rocky substrates and woody debris, colder temperatures, and closed-canopy, intact riparian forests. We noted size-based reversed sexual dimorphism and a strong ontogenetic relationship between snout–vent length and body weight. Anthropogenic activities such as intensive crop farming deterred the species; proximity to croplands had a negative influence on abundance. We recommend re-delineation of the boundary of Pidurutalagala Conservation Forest to incorporate the toad's habitat into the core of the reserve and thus limit the impacts of human activities. Conservation and management actions such as ex-situ breeding, population monitoring, and restoration of degraded habitats could also contribute towards the persistence of this toad. Our findings provide useful insights into ecological research on and conservation of range-restricted aquatic amphibians.

An Evolutionarily Conserved Mechanism for Activity-Dependent Visual Circuit Development.

Neural circuit development is an activity-dependent process. This activity can be spontaneous, such as the retinal waves that course across the mammalian embryonic retina, or it can be sensory-driven, such as the activation of retinal ganglion cells (RGCs) by visual stimuli. Whichever the source, neural activity provides essential instruction to the developing circuit. Indeed, experimentally altering activity has been shown to impact circuit development and function in many different ways and in many different model systems. In this review, we contemplate the idea that retinal waves in amniotes, the animals that develop either in ovo or utero (namely reptiles, birds and mammals) could be an evolutionary adaptation to life on land, and that the anamniotes, animals whose development is entirely external (namely the aquatic amphibians and fish), do not display retinal waves, most likely because they simply don’t need them. We then review what is known about the function of both retinal waves and visual stimuli on their respective downstream targets, and predict that the experience-dependent development of the tadpole visual system is a blueprint of what will be found in future studies of the effects of spontaneous retinal waves on instructing development of retinorecipient targets such as the superior colliculus (SC) and the lateral geniculate nucleus.