Using environmental DNA and occupancy modelling to identify drivers of eastern hellbender (Cryptobranchus alleganiensis alleganiensis) extirpation

相似文献   

Phylogeography and conservation genetics of the hellbender salamander (Cryptobranchus alleganiensis)

We investigated hellbender phylogeography through phylogenetic analyses of individuals sampled from 16 locations throughout their range in the eastern United States. Analyses were conducted on concatenated cytochrome-oxidase I (COI), cytochrome-b (Cytb) and NADH dehydrogenase subunit 4 (ND4) mtDNA sequence, totaling 2160 nucleotides. Hellbender haplotypes differed by 0.1 to 5.8% maximum likelihood (ML) corrected sequence divergence. Phylogenetic analyses reveal that hellbenders are separated into 8 reciprocally monophyletic populations or clades differentiated by a minimum of 0.7 to 5.4% sequence divergence, each of which constitutes a separate Management Unit (MU). High among population divergence and reciprocal monophyly suggest that female-mediated gene flow is severely restricted or non-existent among each MU. Hellbenders are currently divided into two subspecies, Cryptobranchus alleganiensis alleganiensis and C. a. bishopi based on morphological characters. The phylogenetic analyses presented here strongly indicate that these subspecies are paraphyletic. Management priorities for the hellbender should be reconsidered in light of these new molecular data. Results from Bayesian rooting indicate the root of the hellbender mtDNA tree lies on the branch leading to hellbender haplotypes from the Current, Eleven Point and New Rivers. The rooted tree suggests that a common ancestor in the southern Ozarks and/or southern Appalachians gave rise to northern hellbender populations, consistent with a Pleistocene refuge hypothesis.     

Microsatellite analysis supports mitochondrial phylogeography of the hellbender (Cryptobranchus alleganiensis)

We investigated genetic diversity of the hellbender (Cryptobranchus alleganiensis) throughout its range in the eastern US using nuclear markers and compared our results to a previously published mitochondrial analysis. A variety of nuclear markers, including protein-coding gene introns and microsatellites were tested but only microsatellites were variable enough for population level analysis. Microsatellite loci showed moderate among population sharing of alleles, in contrast to the reciprocal monophyly exhibited by mitochondrial DNA. However, analyses using F-statistics and Bayesian clustering algorithms showed considerable population subdivision and clustered hellbender populations into the same major groups as the mtDNA. The microsatellites combined with the mtDNA data suggest that gene flow is severely restricted or non-existent among eight major groups, and potentially among populations (rivers) within groups. The combined mtDNA and microsatellite data suggest that the currently recognized hellbender subspecies are paraphyletic. We suggest that the eight independent groups identified in our study should be managed as such, rather than basing conservation decisions on the two named subspecies of hellbender.     

Within-river gene flow in the hellbender (Cryptobranchus alleganiensis) and implications for restorative release

Understanding how populations are genetically and demographically connected is beneficial for species management, since gene flow and dispersal contribute to genetic diversity and population persistence. For hellbenders (Cryptobranchus alleganiensis), an aquatic salamander species experiencing dramatic declines in population size, fine-scale (i.e. within river) patterns of genetic diversity and gene flow are not well understood. Previous findings indicate that hellbenders are habitat specialists that exhibit extreme site fidelity and low vagility, suggesting that gene flow is restricted among the several, discrete habitat patches within a river. Using 15 polymorphic microsatellite loci and 497 hellbender samples from four Missouri rivers, we assessed fine-scale patterns of genetic diversity in order to infer population connectivity and aid in population management. Results indicate moderate levels of genetic variation (H_O = 0.66–0.78) with little differentiation among habitat patches (avg. F_ST = 0.002) and no evidence of isolation by distance. Our data suggest that hellbender gene flow has been extensive even among habitat patches separated by distances greater than >100 km. These results are useful for hellbender management, especially in terms of making informed decisions regarding restorative releases of captively propagated individuals.     

Polymorphic microsatellite loci for studies of the Ozark hellbender (Cryptobranchus alleganiensis bishopi)

The hellbender is the only North American member of the aquatic salamander family Cryptobranchidae and is a species of conservation concern across its range. We developed eight polymorphic microsatellite loci for hellbenders using a magnetic bead enrichment protocol and a PCR-based detection technique. Allelic diversity averaged 4.0 (±1.8 SD) per locus and heterozygosity averaged 0.56 (±0.30 SD). The hellbender is rare and difficult to study due to its cryptic life history. These loci will provide a valuable resource for population studies, which could inform future conservation and management decisions.     

Prevalence of infection by Batrachochytrium dendrobatidis and Ranavirus in eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) in eastern Tennessee

Hellbenders (n=97) were collected from the Little and Hiwassee Rivers in eastern Tennessee, USA, during 2009 and 2010. Location and morphometrics for each animal were recorded, and nonlethal tissue samples were collected to estimate the prevalence of infection with Batrachochytrium dendrobatidis (Bd) and Ranavirus in each watershed and year. Real-time polymerase chain reaction was performed on skin swabs for Bd and on tail clips for ranaviruses. Overall prevalences of DNA of Bd, Ranavirus, and coinfections (i.e., detectable DNA of both pathogens in the same individual) were 26%, 19%, and 5%, respectively. Differences in infection prevalence were detected between watersheds and years. Gross lesions were observed in 31 animals (32%), but the types of lesions were not consistent with chytridiomycosis or ranaviral disease. This is the first report of infection of eastern hellbenders with Bd and Ranavirus. Despite infection by both pathogens, it is unclear whether chytridiomycosis or ranaviral disease develops in wild populations of hellbenders. More research is needed to determine the susceptibility of hellbenders to Bd and ranaviruses and their role in the epidemiology of these pathogens.     

Projected population persistence of eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) using a stage-structured life-history model and population viability analysis

The population of eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) in the Blue River, Indiana has undergone a dramatic decline over the last decade. Recruitment in these declining populations has been negligible, and populations are now composed almost entirely of older age classes (upwards of 20 years old). Given this dramatic decline, it is imperative to assess the impacts of these demographic patterns on population growth and long-term stability. Therefore, we developed a stage-structured, life-history model to examine the effects of varying levels of egg, juvenile, and adult survivorship on abundance, recruitment, and long-term population projections. We performed a sensitivity analysis of the model and determine which life-history parameters have the greatest potential to increase/stabilise hellbender population growth. Finally, we conducted a population viability analysis to determine the probability of extinction associated with varying management strategies. For eastern hellbender populations in Indiana, adults (especially females) are the most important component of long-term population viability. Sensitivity and elasticity analyses of the Lefkovitch matrix revealed that survival of adult and egg/larvae life-history stages are the most important for focused management efforts. Indeed, adults had the highest elasticity and reproductive value in the matrix model. Increasing survival by as little as 20% corresponded to the turning point at which the population ceased to decline and increased abundance (28% survival of egg/larvae). The importance of the transition from subadult to adult (transitional matrix element) was identified as an additional factor in maintaining abundance based on the relatively long period spent in this life-history stage (seven years for females). A population viability analysis was conducted to assess the likelihood and projected time frame of extinction for this population under no management (～25 years to complete extirpation; probability of extinction = 1) and if management efforts such as captive rearing and headstarting are undertaken (probability of extinction <0.2 at 25–30% survival of egg/larvae). Adult females had the greatest effect in reducing growth rate and population abundance when removed in exploitation simulations (91.3% versus 51.8% reduction in population growth rate), indicating translocation efforts should be designed to maintain females in the breeding pool. These models indicated that conservation management strategies aimed at ensuring the presence of adult females while concomitantly ameliorating survival at early life stages (population augmentation, translocations, introduction of artificial nest structures) are needed to stabilise the Indiana population of eastern hellbenders. This stage-structured model is the first to model eastern hellbenders and has broad implications for use across the geographic range where populations of eastern hellbenders are monitored and vital rates can be estimated.     

Historic occurrence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in hellbender Cryptobranchus alleganiensis populations from Missouri

The pathogenic fungus Batrachochytrium dendrobatidis (Bd) was recently detected in Missouri hellbender Cryptobranchus alleganiensis populations that have declined precipitously for unclear reasons. The objective of this study was to determine whether Bd occurred historically in Missouri hellbender populations or is a relatively novel occurrence. Epidermal tissue was removed from 216 archived hellbenders collected from 7 Missouri streams between 1896 and 1994. Histological techniques and an immunoperoxidase stain were used to confirm historic occurrence of Bd infection in hellbenders from the North Fork of the White (1969, 1973, 1975), Meramec (1975, 1986), Big Piney (1986), and Current rivers (1988). Bd was not detected in hellbenders from the Niangua, Gasconade or Eleven Point rivers. The study detected no evidence for endemism of Bd in Missouri hellbender populations prior to 1969, despite the fact that nearly one third of the hellbenders sampled were collected earlier. Our findings are consistent with the hypothesis that Bd is a non-endemic pathogen in North America that was introduced in the second half of the twentieth century.     

Population Genetics of the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) across Multiple Spatial Scales

Conservation genetics is a powerful tool to assess the population structure of species and provides a framework for informing management of freshwater ecosystems. As lotic habitats become fragmented, the need to assess gene flow for species of conservation management becomes a priority. The eastern hellbender (Cryptobranchus alleganiensis alleganiensis) is a large, fully aquatic paedamorphic salamander. Many populations are experiencing declines throughout their geographic range, yet the genetic ramifications of these declines are currently unknown. To this end, we examined levels of genetic variation and genetic structure at both range-wide and drainage (hierarchical) scales. We collected 1,203 individuals from 77 rivers throughout nine states from June 2007 to August 2011. Levels of genetic diversity were relatively high among all sampling locations. We detected significant genetic structure across populations (F_st values ranged from 0.001 between rivers within a single watershed to 0.218 between states). We identified two genetically differentiated groups at the range-wide scale: 1) the Ohio River drainage and 2) the Tennessee River drainage. An analysis of molecular variance (AMOVA) based on landscape-scale sampling of basins within the Tennessee River drainage revealed the majority of genetic variation (∼94–98%) occurs within rivers. Eastern hellbenders show a strong pattern of isolation by stream distance (IBSD) at the drainage level. Understanding levels of genetic variation and differentiation at multiple spatial and biological scales will enable natural resource managers to make more informed decisions and plan effective conservation strategies for cryptic, lotic species.     

Gas exchange and habitat selection in the aquatic salamanders Necturus maculosus and Cryptobranchus alleganiensis

Summary The standard metabolic rate (SMR) and critical O₂ tension (P_c) of water-breathing mudpuppies and hellbenders were determined at 20° C using open-system respirometry. Both species are metabolic O₂ regulators, although the P_c of hellbenders (90 mmHg) is much higher than that of mudpuppies (40 mmHg). The SMR of the two species in water saturated with air was similar (19.5 and 20.0 l O₂/g·h for Cryptobranchus and Necturus, respectively) and not different from that of salamanders in general. Both species were able to survive for at least 5–11 days in severely hypoxic water (9–10 mmHg) by breathing air, indicating that the lungs are functional accessory respiratory structures.We conclude that hellbenders are restricted to relatively cool and flowing waters because of their limited gas exchange capabilities, particularly with regard to their limited aerobic scope for activity and slow recovery from exercise. Necturus maculosus is much more tolerant of hypoxia, but it is not known if they can inhabit areas were hypoxia is combined with hypercarbia.     

Habitat attributes associated with short‐term settlement of Ozark hellbender (Cryptobranchus alleganiensis bishopi) salamanders following translocation to the wild

1. Organisms associated with lotic systems rank among the most threatened because of global change. Although translocation is being increasingly applied as a conservation strategy, most studies have focused on survival and recruitment of individuals, and few have attempted to identify how habitat attributes influence short‐term settlement of animals during the critical post‐release period. 2. We demonstrate the application of resource selection modelling in an information theoretic framework to identify release‐site characteristics that will increase the likelihood of settlement for a fully aquatic benthic stream salamander, the Ozark hellbender (Cryptobranchus alleganiensis bishopi). We fit discrete choice models using data from 29 radio‐tagged hellbenders that were translocated to two sites in the North Fork of the White River (NFWR), Missouri (U.S.A.). We defined resource availability at two spatial scales (stream reach and home range) and quantified abiotic habitat attributes at 3181 salamander locations and 6329 random available locations collected between May 2008 and August 2009. 3. At both sites and spatial scales, a single model received substantially greater support (0.96–1.00 of total model weight) than all other models, and top‐ranked models were similar in form and predictive ability. At both spatial scales, selection was positively influenced by the presence of cobble‐boulder substratum relative to bedrock and finer substrata. We also noted a negative interactive effect between distance to the nearest substratum particle large enough to provide cover (i.e. at least one axis ≥15 cm in length) and an increase in either a direct or relative (i.e. pool, run, and riffle) measure of water velocity. 4. Collectively, salamanders released in our study selected resources indicative of long‐term benthic microhabitat stability. However, despite strong selection of cobble‐boulder substratum, 8% (282 of 3181) of captive‐reared hellbender locations occurred in bank crevices and root masses. Although several studies have reported the importance of near bed hydraulics in determining occurrence of stream macroinvertebrates, our findings are the first to indicate that spacing among cobble‐boulder substrata may be important for hellbenders. 5. To increase the likelihood of short‐term settlement of captive‐reared hellbenders in the wild, we recommend prioritising release sites where the average distance between cobble‐boulder particles within habitat patches is minimised. In general, average spacing among cobble and boulder substrata should be <1 m in habitat patches where mean benthic water velocity exceeds 0.1 m s^?1, and <0.5 m where water velocity approaches 0.30 m s^?1. Based on home range sizes of captive‐reared Ozark hellbenders, the collective extent of suitable cobble‐boulder habitat patches within release sites should approximate at least 10 m² per salamander released.     

Helminth parasites of eastern box turtles (Terrapene carolina carolina) from southern Indiana, USA

Very little is known about parasitic diseases of eastern box turtles (Terrapene carolina carolina). The objective of this study was to examine the parasitic fauna of eastern box turtles collected from southern Indiana, USA. Turtles (n = 40) were salvaged mostly as road kills from southern Indiana between May and October 2009. Seven species of helminths in total were found parasitizing the gastrointestinal tract, including two digenean trematodes (Brachycoelium salamandrae and Telorchis robustus) and five nematodes (Oswaldocruzia pipiens, Cosmocercoides dukae, Falcaustra affinis, F. chelydrae and Serpinema trispinosus). We report prevalence, abundance and mean intensity of infection for all helminths. Helminths were not found in any other organs examined (heart, gonads, liver, heart, kidney and urinary bladder) and no ectoparasites were found. Overall, mean intensity of infections was low (1-14 parasites/host), suggesting that these parasites are unlikely to be associated with negative health impacts. This constitutes the first study of this kind for Indiana.     

Conservation genetics of eastern hellbenders <Emphasis Type=Italic>Cryptobranchus alleganiensis alleganiensis</Emphasis> in the Tennessee Valley

The eastern hellbender has declined across much of its range and is a candidate for listing under the Endangered Species Act. Some of the most viable remaining populations exist in the Southern Appalachian Region in the Tennessee Valley watershed; however these populations are highly isolated and fragmented, and occupy several physiographic provinces, suggesting they may exhibit significant levels of genetic differentiation. We investigated genetic and phylogeographic relationships among eastern hellbender populations across the Tennessee Valley, using nuclear microsatellite markers and mitochondrial sequence data. Our population genetic analyses of microsatellite data revealed a strong pattern of isolation by stream distance, and 4 genetically distinct populations. These four populations were mainly associated with major watersheds, although middle Tennessee samples were difficult to assign to any particular population. Our phylogeographic analysis of mtDNA resulted in a strongly supported monophyletic ingroup containing nine largely allopatric clades, which also largely corresponded to major watersheds. Our findings suggest that hellbenders from different watersheds in the Tennessee Valley should be recognized as genetically distinct populations, and care should be taken to balance the needs of rescuing declining populations with translocation or headstart programs, while also preserving genetic diversity across the region.     

Morphological and molecular characterization of a new species of leech (Glossiphoniidae,Hirudinida): Implications for the health of its imperiled amphibian host (Cryptobranchus alleganiensis)

The hellbender (Cryptobranchus alleganiensis) is among the most intriguing and imperiled amphibians in North America. Since the 1970s and 80s, western populations of the Ozark and eastern subspecies in Missouri have declined by nearly 80%. As a result of population declines, the Ozark hellbender was recently federally protected as an endangered species, and the eastern subspecies was granted protection under CITES. Although habitat degradation is probably the biggest threat to hellbender populations, recent evidence suggests that pathogens including chytrid fungus and “flesh-eating” bacteria may also contribute to declines in Ozark hellbenders. Leeches, which are very common on Ozark hellbenders, have recently been implicated as possible vectors of disease among Ozark hellbenders but have not been described in eastern hellbenders or outside of Missouri and Arkansas. We discovered a population of leeches on eastern hellbenders in southwest Virginia and confirmed that the species of leech is within the genus Placobdella, but is morphologically and genetically distinct from all previously described leech species. We named the new species Placobdella appalachiensis sp. n. Moser and Hopkins, based on the mountainous region in which it was discovered. Our surveys over a three consecutive year period suggested that this leech species may be patchily distributed and/or have a narrow geographic range. We consistently detected leeches at one site (mean prevalence in 80 hellbenders = 27.5%; median intensity = 3.0 leeches per parasitized hellbender [range 1 – >250 leeches]) during three years of surveys, but we never found leeches in any of our other seven study sites in two streams (mean prevalence in 139 hellbenders = 0%). We found a significant positive relationship between hellbender body size and the intensity of parasitism, and we suggest the possibility that the behavioral ecology of adults leading up to reproduction may increase their encounter rates with parasites. We discuss the potential conservation implications of discovery of leeches in this stream, and make recommendations for future mitigation and monitoring efforts.     

Invasive Silver Carp movement patterns in the predominantly free-flowing Wabash River (Indiana,USA)

Many organisms must move among habitats to fulfill life history requirements. Fish movements have been widely studied and tend to be either fine-scale (i.e., routine) and governed by factors such as food availability and cover, or broad-scale and associated with spawning migrations. However, movements of invasive fishes in non-native ecosystems are comparatively poorly understood despite the often critical importance of fish movement and dispersal for invasion success. We examined invasive Silver Carp (Hypophthalmichthys molitrix) movements using acoustic telemetry to monitor the timing, distance, and direction of fish movements and assessed movements in relation to seasonal, annual, environmental, and individual factors in the Wabash River (Indiana, USA), a largely unregulated Midwestern river. Silver Carp exhibited highly variable movements that could be rapid and large in magnitude; however, tagged individuals remained stationary most of the time. Despite high variability, several trends emerged, indicating the importance of backwater habitats, avoidance of small tributaries, and tendencies of tagged fish to exhibit directed spring and fall broad-scale movements. Summer movements were smaller in magnitude, characterized by lower movement rates, and evenly split between upstream and downstream directions, although tagged Silver Carp moved more frequently during summer months. Our results indicate that specific seasons (i.e., spring and early fall) and locations (i.e., backwaters) are likely targets for Silver Carp control in the Wabash River and should also be useful targets for early detection and control in other largely unconstrained rivers over a broad geographic range (e.g., Great Lakes tributaries and upper Mississippi River mainstem and tributaries).     

Canada geese (Branta canadensis) nesting on elevated structures in urban Indiana,USA

The Canada goose (Branta canadensis) population has radically changed over the past 60 years—from once being extirpated in the state of Indiana to the current level of approximately 113,000. High urban densities have resulted in persistent human–wildlife conflicts and novel interactions between geese and their physical environment. Canada geese typically choose nest sites that are on the ground or slightly elevated sites such as muskrat lodge, but we report observations of Canada geese nesting on rooftops 2.6–12.2 m above ground level in central Indiana. These observations suggest that alternative, unpredicted nesting sites are being chosen over more traditional sites, in a likely attempt to reduce risks of disturbance and predation. This atypical nest‐site selection may pose new management challenges, but further research is needed.     

Invasive shrub distribution varies with distance to roads and stand age in eastern deciduous forests in Indiana, USA

We documented the relationship between densities of invasive exotic shrubs, distance to road, and successional age of the forest in 14 forested sites throughout central and southern Indiana. Roadways are increasingly abundant, human-made features that can be conduits for the spread of invasive exotic plants in a number of ecosystems. Little is known, however, about the role of roads in eastern deciduous forest ecosystems where road density is high. Further, it is not known whether the distribution of exotic plants along roads depends on the successional age of the forest. In this study, densities of four of seven exotic shrub species declined with increasing distance to the nearest road across all successional ages. Greater densities of exotic shrubs were found in young and mid-successional forests than mature forests. However, there was no interaction between distance to road and forest age, suggesting that the role of roads in the invasion process does not change across forest successional ages. We outline several potential mechanisms that may drive patterns of shrub distribution along roadside edges as a guide for future research.     

Brown trout (Salmo trutta,Linnaeus, 1758) spawning habitat improvement in the Ebro River Basin (eastern Spain)

Limestone streams in Spain are subject to calcium carbonate precipitation processes, which make the substrate very cohesive. Many populations of brown trout (Salmo trutta, Linnaeus, 1758) in those rivers show reduced production due to unsuitable spawning habitats. This study presents data on S. trutta spawning habitat improvement in the Guadalope River Basin during 2011. The main objectives of this study were to (i) modify the substrate in order to make it easier for S. trutta females to dig when spawning, (ii) test the effect of the gravel quality improvement on the habitat, (iii) analyse the effect of habitat improvement on S. trutta recruitment, and (iv) monitor habitat improvement effectiveness in the long term. Three manual measures were adopted to make the gravel suitable for S. trutta breeding: the separation of the embedded gravel using an iron bar by hitting it with a mace‐hammer (‘substrate breaking’), the spreading out of the gravel loosened by the previous action with a rake (‘raking up’), and thirdly the elimination of fine sediment depositions (‘substrate cleaning’). Results of the first year of monitoring (2012) in improved and control areas were compared. Methodology effectiveness assessment requires monitoring over a longer period, but the data from the first year after habitat improvement provide encouraging results, mainly dealing with changes in spawning habitat parameters and an increase in the S. trutta age‐0 class in the improved areas.