Restoring ponds for amphibians: a success story

Large-scale restoration of quality habitats is often considered essential for the recovery of threatened pond-breeding amphibians but only a few successful cases are documented, so far. We describe a landscape-scale restoration project targeted at two declining species—the crested newt (Triturus cristatus Laur.) and the common spadefoot toad (Pelobates fuscus Wagler)—in six protected areas in southern and southeastern Estonia. The ponds were restored or created in clusters to (i) increase the density and number of breeding sites at local and landscape levels; (ii) provide adjacent ponds with differing depths, hydroperiods and littoral zones and (iii) restore an array of wetlands connected to appropriate terrestrial habitat. In only 3 years, where 22 of the 405 existing ponds (5%) were restored and 208 new ponds (51%) created, the number of ponds occupied by the common spadefoot toad increased 6.5 times. Concerning the crested newt and the moor frog (Rana arvalis Nilsson), the increase was 2.3 and 2.5 times, respectively. The target species had breeding attempts in most of the colonised ponds—even more frequently than common species. Also, the amphibian species richness was higher in the restored than in the untreated ponds. The crested newt preferably colonised ponds that had some submerged vegetation and were surrounded by forest or a mosaic of forest and open habitats. The common spadefoot toad favoured ponds having clear and transparent water. Our study reveals that habitat restoration for threatened pond-breeding amphibians can rapidly increase their numbers if the restoration is implemented at the landscape scale, taking into account the habitat requirements of target species and the ecological connectivity of populations. When the remnant populations are strong enough, translocation of individuals may not be necessary. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Delineating fine-scale genetic units in amphibians:Probing the primacy of ponds

The population structure of pond-breeding amphibians is shaped by their distinct breeding foci, but it is unclear to what extent this is reflected in the fine-scale distribution of genetic diversity. We used microsatellite genotypes to investigate the genetic signatures of 24 populations of European newts, Triturus cristatus and T. marmoratus, inhabiting 21 ponds in a confined study area (7.5×3.5km) in western France. Employing a Bayesian clustering approach based on individual genotypes that minimises departures from Hardy–Weinberg equilibrium and linkage disequilibrium, no evidence was found for within-pond substructuring. Subjecting all sampled ponds simultaneously to this procedure revealed a clear signal of partitioning, with the most likely number of clusters however below the actual number of ponds (seven in T. cristatus, three in T. marmoratus). A more hierarchical Bayesian approach, with pond as analysis unit, was achieved to separate ponds from genetically more meaningful units, and reduced the T. cristatus populations to 11 clusters, and the T. marmoratus populations to five clusters. We were unable to specify a minimum nearest-neighbour distance where ponds are separate units, probably due to both historical and current demographic processes. The implications for strategies to manage and conserve endangered amphibians in human-altered landscapes are discussed.     

The role of pollutant accumulation in determining the use of stormwater ponds by amphibians

Urbanization often results in the creation of habitats such as stormwater management ponds. Although stormwater ponds are designed to retain runoff and associated pollutants, they are frequently colonized by wildlife including pond-breeding amphibians. Understanding of the ecological function of these created habitats is limited. This study investigated the role of pollutants in shaping use of stormwater ponds by amphibians. A survey of 68 stormwater ponds in Baltimore County, Maryland, and statistical modeling found wood frogs (Rana [= Lithobates] sylvatica) were more likely to breed in ponds with longer hydroperiods and Cl^? concentrations below approximately 250 mg/L. American toad (Bufo [= Anaxyrus] americanus) use of ponds was primarily influenced by hydroperiod; toads were more likely to use longer hydroperiod ponds. To confirm use was a result of toxicity and differential sensitivity among species, wood frog and American toad embryos and larvae were exposed to sediment from six stormwater ponds spanning the range of pollutant conditions documented in the field. Survival of wood frogs through metamorphosis was related to metal and salt levels of pond sediments, but survival of American toads was not. In agreement with the field study, no wood frog larvae survived to metamorphosis when Cl^? levels were above 260 mg/L. The results suggest that pollutants that accumulate in stormwater ponds, specifically road deicing salts, are acting as local filters capable of creating unique assemblages of anuran larvae in urban areas.     

Estimating hydroperiod suitability for breeding amphibians in southern Rhode Island seasonal forest ponds

In New England, seasonal forest ponds provide primary breeding habitat for several amphibian species, including Rana sylvatica (LeConte) and Ambystoma maculatum (Shaw). Because each species requires a minimum duration of inundation to complete its breeding cycle, one of the most important factors determining habitat suitability is a pond’s hydroperiod. The objective of this research was to develop a method for estimating pond hydroperiod from site characteristics such as pond morphology, geology, chemistry, and vegetation structure, and to use the estimates to assess the suitability of individual ponds for breeding amphibians. We monitored the duration of surface inundation in 65 ponds in the Pawcatuck River watershed of southern Rhode Island during 2001 and 2002. Pond hydroperiods, measured from 1 March, ranged from 19 to 44 weeks in 2001 and from 2 to 44 weeks in 2002; mean values were 30 and 21 weeks, respectively. Akaike’s Information Criterion was used to select a multivariate hydroperiod estimation model (R² = 0.59, p < 0.0001) that permitted identification of ponds with hydroperiods suitable for breeding by R. sylvatica (95.4% correct classification rate [CCR]) and A. maculatum (75.4% CCR). Canopy cover, open basin depth, and specific conductance of surface water were among the most useful site characteristics for estimating hydroperiod, while surficial geology and the texture of soil parent material made smaller contributions. The CCR using open basin depth alone was 95.4 and 73.8%, respectively. These findings indicate that it is possible to estimate the hydroperiod of seasonal ponds – and to assess their suitability for individual species of breeding amphibians – without prolonged periods of hydrologic monitoring. Such techniques could have considerable value to wetland regulatory agencies and for planning amphibian habitat management and acquisition at the landscape scale.     

Helminth communities in five species of sympatric amphibians from three adjacent ephemeral ponds in southeastern Wisconsin

Representatives of 5 amphibian species (313 individuals), including eastern American toads (Bufo americanus), wood frogs (Rana sylvatica), spring peepers (Pseudacris crucifer), blue-spotted salamanders (Ambystoma laterale), and central newts (Notophthalmus viridescens louisianensis), were collected from 3 ephemeral ponds during spring 1994, and they were inspected for helminth parasites. The component communities of anurans were more diverse than those of caudates. Infracommunities of all host species were isolationist and depauperate, due mostly to host ectothermy and low vagility. Toad infracommunities were dominated by skin-penetrating nematodes, and they had the highest values of mean total parasite abundance, mean species richness, and overall prevalence. This was likely due to their greater vagility compared with other host species. Infracommunities of wood frogs and blue-spotted salamanders had intermediate values for these measures of parasitism, whereas spring peeper and newt infracommunities had the lowest values. In addition to relative vagility, feeding habits and habitat preference were likely important in helminth community structure. Body size also seemed to play a role because mean wet weight of host species followed the same general trend as values of parasitism. However, effects of size were variable within host species and difficult to separate from other aspects of host ecology.     

Impacts of hydroperiod on growth and survival of larval amphibians in temporary ponds of Central Pennsylvania,USA

The effects of variable hydroperiod (three levels) and initial density of amphibians (two levels) on survival, growth rate, and time to and mass at metamorphosis were studied for wood frogs (Rana sylvatica), Jefferson salamanders (Ambystoma jeffersonianum), and spotted salamanders (A. maculatum). Experiments were carried out in 260-1 mesocosms set up outdoors in a forest. These pond simulations were designed to mimic conditions that occur in palustrine temporary wetlands in central Pennsylvania. No animals reached metamorphosis in the short hydroperiod (56 days). However a greater proportion (66%) of tadpoles of R. sylvatica survived to the end of the 56-day, treatment than the 84- or 158-day treatments (29 and 14%, respectively), from which all survivors metamorphosed. In contrast, neither of the salamanders metamorphosed by 84 days; survival to metamorphosis at 158 days was 15% for A. jeffersonianum and 10% for A. maculatum. Average instantaneous growth rates for A. jeffersonianum decreased with each increase in hydroperiod. Growth of R. sylvatica was greater in the 56-day hydroperiod than in hydroperiods of 84 or 158 days. Initial amphibian density had no effect on growth or survival of any species. It appears that salamander larvae were predatory on tadpoles, since survival of R. sylvatica was negatively correlated with survival of A. jeffersonianum in 84-day treatments and with growth of A. maculatum in 158-day treatments.     

The attenuation of ultraviolet and visible radiation in Dutch inland waters

The vertical attenuation coefficients (K _d) of downward ultraviolet (UV) and visible irradiance (PAR) were measured in 19 different inland waters in the Netherlands using a scanning spectroradiometer. Water chemistry variables such as dissolved organic carbon (DOC), absorbance of dissolved matter (a _d), chlorophyll-a, and particulate matter were measured to determine the relative contribution of dissolved and particulate components in explaining the variation in K _d. In addition to the field measurements, laboratory measurements were performed to test the relationships between water properties and light attenuation. The attenuation properties of Dutch inland waters vary. In most systems the penetration of UV-B radiation (280–320 nm) is limited to the upper decimetres. Lake Maarsseveen was the clearest waterbody in this study, with K _dUVB of 9.1 (m^–1). The DOC concentration had limited power in predicting UV attenuation in this study (r ²=0.33), because of the large differences in carbon-specific absorption. A _d300 was a much better predictor of UV attenuation (r ²=0.75). The relationships obtained in the laboratory experiments can be used to give a good prediction of in situ K _d values, based on 3 variables (chlorophyll-a, ash weight, and absorption of dissolved matter).     

Melanogenesis in amphibians

Summary The pigmented epithelium of Rana pipiens tadpole eyes normally develops at least two types of melanosomes: (1) an elongated melanin granule of relatively homogeneous electron density, and (2) a complex melanosome which has an outer electrondense area and one or more less dense cores. Evidence indicates that complex melanosomes are formed by new melanin enclosing preexisting melanosomes. An organized fibrillar premelanosome is demonstrated with the aid of the antimelanogenic compound phenylthiourea (PTU). These premelanosomes are the developing forms of the elongated melanosomes. There is evidence that the premelanosomes originate in the smooth endoplasmic reticulum. Phenylthiourea blocks melanin synthesis in the premelanosomes; however, removal of the PTU allows pigment deposition. This finding of an organized, fibrillar premelanosome in an amphibian marks the lowest phylogenetic group in which these organelles have been described.An Oak Ridge Graduate Fellow from Catholic University of America, Washington, D.C., under appointment from Oak Ridge Associated Universities.The MAN Program is supported by the National Cancer Institute, the National Institute of General Medical Sciences, the National Institute of Allergy and Infectious Diseases, and the U.S. Atomic Energy Commission.Oak Ridge National Laboratory is operated by Union Carbide Corporation Nuclear Division for the U.S. Atomic Energy Commission.     

Analyzing the radiation of the melanocortins in amphibians: cloning of POMC cDNAs from the pituitary of the urodele amphibians, Amphiuma means and Necturus maculosus

Proopiomelanocortin (POMC) cDNAs were cloned and sequenced from brain extracts of two species of urodele amphibians: Amphiuma means and Necturus maculosus. Although the two species of urodele amphibians belong to separate families, and do not share a direct common ancestor, the level of primary sequence identity for the open reading of the POMC cDNAs was 90% at the amino acid level and 79% at the nucleotide level. It appears that the POMC gene in these urodele amphibians has been accumulating mutations at the amino acid level at a slower rate than the POMC gene in other sarcopterygian orders.     

Estimates of atmospheric attenuation of solar radiation at specific wave lengths

The Bougner-Lambert law for the attenuation of solar energy was examined for selected wave bands in the visible portion of the solar spectrum: 700, 655, 610, 575, 500, 445 and 400 mµ. The energy reaching the earth's surface for these wave bands was found to follow the law. However, an analysis of the results showed considerable variability in the transmission coefficients even on clear days. This indicates that daily variations in the atmospheric constituents, presumably in the aerosal content, induces a real difference in light quality. When precise estimates of the spectral properties of solar energy are required by biologists, it will be necessary to obtain direct measurements.     

Metacommunity dynamics of amphibians in years with differing rainfall

Many studies investigated the habitat preference and behaviour ecology of individual amphibian species while we know less about how their community assembly reflects changes in environmental factors, including the role of climatic extremes. Community-level studies also allow us to apply trait-based analyses that are crucial for a better understanding of the functioning of amphibian communities and metacommunities. In two years with contrasting rainfall (2012 and 2013), we found amphibian species in 85 different waterbodies of a heterogeneous landscape in Central Europe (Hungary). Within the metacommunity framework, the contributions of local, landscape and spatial variables to community assembly were assessed. We also measured the local extinction–colonisation rates in the ponds for all species between the two years. To investigate the role of dispersal traits in explaining the spatial distribution of species, we studied the relationship between body size and the pure spatial fraction of variation. According to our results, the main drivers were the same in both the dry and wet year, but their relative contribution changed. Local variables played a predominant role in the assembly of the amphibian metacommunity. Spatial signals were more evident in the dry year. This implies not only the adverse effect of decreased connectivity due to the drying out of several habitats but also a loss of breeding sites for the studied amphibians. Local colonisation rates were higher in primarily terrestrial species (Hyla arborea, Pelobates fuscus, Bufo bufo) which only visit ponds during breeding. We found a negative relationship between the pure spatial effect and body size, suggesting an increased level of dispersal limitation in small-bodied species. Our results showed that while the strength and relative role of local and spatial processes changed between years, the role of dispersal traits in explaining the spatial distribution of species was similar. Specialisation to different habitats seems to be a major process in determining vertebrate metacommunities in landscapes. Dispersal traits of different species should be taken more into consideration in the practical conservation of amphibian habitats.     

Cancer resistance in amphibians

While spontaneous tumours may occasionally develop in inbred and isogenic strains of Xenopus laevis, the South African clawed toad, they are extremely rare in natural and laboratory populations. Only two amphibian neoplasms, the renal adenocarcinoma of Rana pipiens and the lymphosarcoma of Xenopus laevis, have been extensively explored. Amphibians are resistant to the development of neoplasia, even following exposure to "direct-acting" chemical carcinogens such as N-methyl-N-nitrosourea, that are highly lymphotoxic, thus diminishing immune reactivity. Regenerative capacity in adults, and a dramatic metamorphosis which remodels much of the larval body to produce the adult form, are unique to amphibian vertebrates, and the control mechanisms involved may protect against cancer. For example, naturally rising corticosteroid titres during metamorphosis will impair some T-cell functions, and the removal of T-regulatory (suppressor) functions inhibits the induction of altered-self tolerance. Altered-self tolerance is not as effectively induced in adult Xenopus laevis as in mammals, so cancer cells with new antigenicity are more likely be rejected in amphibians. Amphibian immunocytes tend to undergo apoptosis readily in vitro, and, unlike mammalian immunocytes, undergo apoptosis without entering the cell cycle. Cells not in the cell cycle that die from nuclear damage (apoptosis), will have no opportunity to express genetic instability leading to cell transformation. We suggest that all these factors, rather than any one of them, may reduce susceptibility to cancer in amphibians.     

Diseases of amphibians

The development and refinement of amphibian medicine comprise an ongoing science that reflects the unique life history of these animals and our growing knowledge of amphibian diseases. Amphibians are notoriously fastidious in terms of captive care requirements, and the majority of diseases of amphibians maintained in captivity will relate directly or indirectly to husbandry and management. Investigators have described many infectious and noninfectious diseases that occur among various species of captive and wild amphibians, and there is considerable overlap in the diseases of captive versus free-ranging populations. In this article, some of the more commonly reported infectious and noninfectious diseases as well as their etiological agents and causative factors are reviewed. Some of the more common amphibian diseases with bacterial etiologies include bacterial dermatosepticemia or "red leg syndrome," flavobacteriosis, mycobacteriosis, and chlamydiosis. The most common viral diseases of amphibians are caused by the ranaviruses, which have an impact on many species of anurans and caudates. Mycotic and mycotic-like organisms cause a number of diseases among amphibians, including chytridiomycosis, zygomycoses, chromomycoses, saprolegniasis, and ichthyophoniasis. Protozoan parasites of amphibians include a variety of amoeba, ciliates, flagellates, and sporozoans Common metazoan parasites include various myxozoans, helminths (particularly trematodes and nematodes), and arthropods. Commonly encountered noninfectious disease etiologies for amphibians include neoplasia, absolute or specific nutritional deficiencies or overloads, chemical toxicities, and inadequate husbandry or environmental management.     

Pheromonal communication in amphibians

Pheromonal communication is widespread in salamanders and newts and may also be important in some frogs and toads. Several amphibian pheromones have been behaviorally, biochemically and molecularly identified. These pheromones are typically peptides or proteins. Study of pheromone evolution in plethodontid salamanders has revealed that courtship pheromones have been subject to continual evolutionary change, perhaps as a result of co-evolution between the pheromonal ligand and its receptor. Pheromones are detected by the vomeronasal organ and main olfactory epithelium. Chemosensory neurons express vomeronasal receptors or olfactory receptors. Frogs have relatively large numbers of vomeronasal receptors that are transcribed in both the vomeronasal organ and the main olfactory epithelium. Salamander vomeronasal receptors apparently are restricted to the vomeronasal organ. To date, no chemosensory ligands have been matched to vomeronasal receptors or olfactory receptors so it is unknown whether particular receptor types are (1) specialized for detection of pheromones versus other chemosignals, or (2) specialized for detection of volatile, nonvolatile, or water-borne chemosignals. Despite progress in understanding amphibian pheromonal communication, only a small fraction of amphibian species have been examined. Study of additional species of amphibians will indicate which traits related to pheromonal communication are evolutionarily conserved and which traits have diverged over time.     

Studies on the effects of UV-B radiation on phytoplankton of sub-antarctic lakes and ponds

Summary Experiments were performed to determine the effects of UV-B (ultraviolet, 280–320 nm) radiation on motility and growth of phytoplankton from lakes and ponds in South Georgia. After 4 h of solar radiation and 4h artificial radiation (UV-B_BE 11.6 kJ m^-2 day^-1, UV-B lamps) the swimming velocity of Cryptomonas sp. decreased. The growth rate of Botryococcus, Lyngbya sp. and Stauraslrum sp. did not show any significant variations between the different light conditions. The UV-B component was reduced by filtering solar radiation through glass bottles und cellulose acetate. Cloudy days had only 30% of the radiation of clear days in both the PAR (photosynthetic active radiation) and UV-B regions. The ponds contained large amounts of humic substances, which are responsible for the absorbance in the UV region.     

Assessment of radiation exposure level for hydrobionts in some special industrial ponds at the Mayak PA

Evaluation of the radionuclide content in the ecosystem components (water, sediments, aquatic organisms) of industrial reservoirs-storages of liquid radioactive waste of the Mayak PA (reservoirs R-4, R-10, R-11, R-17, R-9) and the estimation of the absorbed dose rate in aquatic organisms of these reservoirs using the software package ERICA Assessment Tool 1.0 May 2009 have been performed. Gradient of the absorbed dose rate for the detected taxonomic groups of hydrobionts in the series of the studied reservoirs R-11 --> R-10 --> R-4 --> R-17 --> R-9 was almost equal to one order of magnitude. The estimated absorbed dose rate for phytoplankton ranged from 5.4 x 10(0) mGy/day (R-11) to 4.0 x 10(4) mGy/day (R-9), for zooplankton--from 6.4 x 10(-1) mGy/day (R-11) to 3.8 x 10(3) mGy/day (R-9), for zoobenthos (chironomids)--from 5.6 x 10(0) mGy/day (R-11) to 1.1 x 10(3) mGy/day (R-17), for fish (roach)--from 8.0 x 10(-1) mGy/day (R-11) to 1.9 x 10(1) mGy/day (R-4).     

Multiple overseas dispersal in amphibians

Amphibians are thought to be unable to disperse over ocean barriers because they do not tolerate the osmotic stress of salt water. Their distribution patterns have therefore generally been explained by vicariance biogeography. Here, we present compelling evidence for overseas dispersal of frogs in the Indian Ocean region based on the discovery of two endemic species on Mayotte. This island belongs to the Comoro archipelago, which is entirely volcanic and surrounded by sea depths of more than 3500 m. This constitutes the first observation of endemic amphibians on oceanic islands that did not have any past physical contact to other land masses. The two species of frogs had previously been thought to be nonendemic and introduced from Madagascar, but clearly represent new species based on their morphological and genetic differentiation. They belong to the genera Mantidactylus and Boophis in the family Mantellidae that is otherwise restricted to Madagascar, and are distinguished by morphology and mitochondrial and nuclear DNA sequences from mantellid species occurring in Madagascar. This discovery permits us to update and test molecular clocks for frogs distributed in this region. The new calibrations are in agreement with previous rate estimates and indicate two further Cenozoic transmarine dispersal events that had previously been interpreted as vicariance: hyperoliid frogs from Africa to Madagascar (Heterixalus) and from Madagascar to the Seychelles islands (Tachycnemis). Our results provide the strongest evidence so far that overseas dispersal of amphibians exists and is no rare exception, although vicariance certainly retains much of its importance in explaining amphibian biogeography.