Lithobates Chiricahuensis Research Articles

Successful eradication of invasive American bullfrogs leads to coextirpation of emerging pathogens

AbstractInterventions of the host–pathogen dynamics provide strong tests of relationships, yet they are still rarely applied across multiple populations. After American bullfrogs (Rana catesbeiana) invaded a wildlife refuge where federally threatened Chiricahua leopard frogs (R. chiricahuensis) were reintroduced 12 years prior, managers launched a landscape‐scale eradication effort to help ensure continued recovery of the native species. We used a before‐after‐control‐impact design and environmental DNA sampling of 19 eradication sites and 18 control sites between fall 2016 and winter 2020–2021 to measure community‐level responses to bullfrog eradication, including for two pathogens. Dynamic occupancy models revealed successful eradication from 94% of treatment sites. Native amphibians did not respond to bullfrog eradication, but the pathogens amphibian chytrid fungus (Batrachochytrium dendrobatidis) and ranaviruses were coextirpated with bullfrogs. Our spatially replicated experimental approach provides strong evidence that management of invasive species can simultaneously reduce predation and disease risk for imperiled species.

Hammer Test

Hammer Test Renata Golden (bio) Imagine a spectrum of living creatures. At one end are viruses, bacteria, paramecia. Add invertebrates like worms, snails, octopuses, and shrimp. In the middle, find spiders, crabs, and small animals like frogs, snakes, and songbirds. Somewhere toward the opposite end stand the bigger creatures like prairie dogs, house cats, wolves, alligators, and whales. Holding down the far end are humans—not because of their size or evolutionary superiority, but because of their claim to a moral code. Now picture yourself holding a very large metaphoric hammer that can take many shapes—revulsion, fear, hunger, defense, medical research, vivisection, euthanasia, capital punishment. That hammer represents your willingness to kill. How far along that continuum will you bring your hammer down? Squashing a bug is probably okay, especially if it is a spider or a cockroach or other creepy crawly that freaks you out. And you might be willing to catch a mouse in a snap trap if it’s in your kitchen, eating the crumbs in your dark corners. If you’re an omnivore, you let others butcher your dinner, unless you fish or hunt your own food. Where do you draw the line about killing living things, whether you actually do the deed or support others doing the killing in your name? According to national Gallup and Pew polls, fifty to sixty percent of American adults go all the way to support the death penalty. Where do you stop? [End Page 7] I was unsure of my own answer to that question, especially when I considered threatened species and their preservation. In a natural world made unnatural by human intervention, my ethical responsibilities have grown murky. In my view, a species doesn’t need to provide an obvious benefit to mankind—or even to the rest of the natural world—to be worth saving. Its value lies in the mere fact of its existence. I have heard it said that allowing a species to go extinct is like ripping pages out of a book that you are still reading. What do we lose when a species disappears? What do we suffer when we are the cause of that extinction? And what am I willing to do, either actively or passively, to affect the outcome one way or another? The first good look I had at an American bullfrog in the Chiricahua Mountains was in the sights of a .22 rifle. I had accompanied a biologist and his field technician—let’s call them John and Bob—to a pond that had potential to be a safe harbor for Chiricahua leopard frogs. John and Bob had been monitoring this pond in the flatlands east of Cave Creek Canyon for months. This morning, the two men started at the bottom of a pond and counted eyes as they circled to the top. They estimated more than 500 bullfrogs. They knew the frogs were bullfrogs and not leopard frogs because their size and the chirp they made when they jumped into the water were dead giveaways. John and Bob were on a mission to eradicate some bullfrogs. I found it ironic that they needed to kill a frog to save a frog. With hundreds of bullfrogs living in this flatlands pond, it was obviously not yet ready to receive the leopard frog tadpoles or egg masses that were ready for release. Tasked by U.S. Fish and Wildlife to eradicate the bullfrogs that make life impossible for Chiricahua leopard frogs, John and Bob intended not to kill every American bullfrog in southeastern Arizona, but to establish a buffer zone around Cave Creek where the leopard frogs could thrive. If Chiricahua leopard frogs can’t be returned to their entire previous range, they can at least be saved from extinction. The first step was to give them a suitable home. Before I came to the Southwest Research Station in the Chiricahua Mountains in 2016 to learn about the reintroduction of Chiricahua leopard frogs to their homeland, I had read that Chiricahua leopard frogs and [End Page 8] American bullfrogs are incompatible. Perhaps that’s not the right word—“incompatible” makes it seem like they argue a lot or have...

Empirical evidence for effects of invasive American Bullfrogs on occurrence of native amphibians and emerging pathogens.

Invasive species and emerging infectious diseases are two of the greatest threats to biodiversity. American Bullfrogs (Rana [Lithobates] catesbeiana), which have been introduced to many parts of the world, are often linked with declines in native amphibians via predation and the spread of emerging pathogens such as amphibian chytrid fungus (Batrachochytrium dendrobatidis [Bd]) and ranaviruses. Although many studies have investigated the potential role of bullfrogs in the decline of native amphibians, analyses that account for shared habitat affinities and imperfect detection have found limited support for clear effects. Similarly, the role of bullfrogs in shaping the patch-level distribution of pathogens is unclear. We used eDNA methods to sample 233 sites in the southwestern USA and Sonora, Mexico (2016-2018) to estimate how the presence of bullfrogs affects the occurrence of four native amphibians, Bd, and ranaviruses. Based on two-species, dominant-subordinate occupancy models fitted in a Bayesian context, federally threatened Chiricahua Leopard Frogs (Rana chiricahuensis) and Western Tiger Salamanders (Ambystoma mavortium) were eight times (32% vs. 4%) and two times (36% vs. 18%), respectively, less likely to occur at sites where bullfrogs occurred. Evidence for the negative effects of bullfrogs on Lowland Leopard Frogs (Rana yavapaiensis) and Northern Leopard Frogs (Rana pipiens) was less clear, possibly because of smaller numbers of sites where these native species still occurred and because bullfrogs often occur at lower densities in streams, the primary habitat for Lowland Leopard Frogs. At the community level, Bd was most likely to occur where bullfrogs co-occurred with native amphibians, which could increase the risk to native species. Ranaviruses were estimated to occur at 33% of bullfrog-only sites, 10% of sites where bullfrogs and native amphibians co-occurred, and only 3% of sites where only native amphibians occurred. Of the 85 sites where we did not detect any of the five target amphibian species, we also did not detect Bd or ranaviruses; this suggests other hosts do not drive the distribution of these pathogens in our study area. Our results provide landscape-scale evidence that bullfrogs reduce the occurrence of native amphibians and increase the occurrence of pathogens, information that can clarify risks and aid the prioritization of conservation actions.

Applying sperm collection and cryopreservation protocols developed in a model amphibian to three threatened anuran species targeted for biobanking management

The challenge of replicating environmental cues in amphibian captive assurance colonies has been shown to be one of the contributing factors leading to limited breeding success. To circumvent this challenge, assisted reproductive technologies (ART) have been developed in model organisms and can now be applied to at-risk species. This study tested the transferability of cryopreservation protocols developed in the Fowler's toad (Anaxyrus fowleri) to three threatened anurans, the Chiricahua leopard frog (Lithobates chiricahuensis), Puerto Rican crested toad (Peltophryne lemur), and Houston toad (Anaxyrus houstonensis). Males were administered human chorionic gonadotropin and/or gonadotropin releasing hormone-analog to elicit spermiation, and spermic urine was collected and analyzed for motility. Samples were cryopreserved with 10 % N,N-dimethylformamide + 10 % trehalose + 0.25 % bovine serum albumin and frozen at two rates, −32 to −45 °C/min and − 20 to −29 °C/min. Results show that sperm frozen at −32 to −45 °C/min recovered significantly higher post-thaw sperm motility than −20 to −29 °C/min for P. lemur (p = 0.04) and L. chiricahuensis (p = 0.03). When compared across species, L. chiricahuensis had significantly higher post-thaw motility at both freezing rates (p < 0.05) than the other species, yet there was no difference between sperm motility between the three bufonid species for either freezing rate (p > 0.06). These results indicate that transferability of a cryopreservation protocol between species is possible, and differences in sensitivity and response to cryopreservation may exist between genera.

Effects of wild, semi‐captive, and captive management on male Chiricahua leopard frog sperm quality with implications for conservation breeding programs

AbstractThe Chiricahua leopard frog (Lithobates chiricahuensis) is a threatened species endemic to the southwestern United States and Northern Mexico. Captive breeding programs were established to support reintroduction efforts, yet reproductive output has been lower than needed for recovery of the species. This study aimed to evaluate the effects of captivity on amphibian reproduction by (1) determining if captive, semi‐captive, and wild male L. chiricahuensis produce sperm at similar rates and concentration in response to hormone treatment; and (2) evaluating the quality of sperm obtained over time from these populations. Males from captive, semi‐captive, and wild locations were administered a combination of human chorionic gonadotropin and gonadotropin‐releasing hormone to stimulate sperm production and release. A high percentage of males in the captive (60%), semi‐captive (100%), and wild (95.3%) populations produced sperm following treatment. Sperm quality (forward progressive motility and total sperm motility) did not differ between groups. However, sperm quantity (sperm/ml) differed (p &lt; .05) between populations, with semi‐captive and wild males producing higher concentrations of sperm than captive males. These results suggest that Chiricahua leopard frog sperm quantity, but not quality, may become negatively impacted by long‐term captivity in indoor, controlled settings.

Over 25 Years of Partnering to Conserve Chiricahua Leopard Frogs (Rana chiricahuensis) in Arizona, Combining Ex Situ and In Situ Strategies

The Phoenix Zoo has partnered with US Fish and Wildlife Service, Arizona Game and Fish Department, US Forest Service, and other organizations for more than 25 years to help recover Chiricahua leopard frogs (Rana [=Lithobates] chiricahuensis) in Arizona, USA. This federally threatened species faces declines due to habitat loss and degradation, long-term drought, disease, and invasive species. Over 26,000 larvae, froglets, and adults, as well as 26 egg masses produced by adults held at the Phoenix Zoo have been released to the wild, augmenting and/or re-establishing wild populations. Chiricahua leopard frog-occupied sites in Arizona have increased from 38 in 2007, when the species’ recovery plan was published, to a high of 155 in the last five years, as a result of ex situ and in situ conservation efforts. As one of the longest-running programs of its kind in the United States, communication among partners has been key to sustaining it. Recovery strategies and complex decisions are made as a team and we have worked through numerous management challenges together. Though Chiricahua leopard frogs still face significant threats and a long road to recovery, this program serves as a strong example of the positive effects of conservation partnerships for native wildlife.

Localized carry‐over effects of pond drying on survival, growth, and pathogen defenses in amphibians

AbstractClimate change is increasing variability in precipitation patterns in many parts of the globe. Unpredictable changes in water availability can be particularly challenging for organisms that rely on precipitation‐fed water sources for completing their life cycle, such as many amphibian species. Although developmental plasticity can mitigate the impacts of changing environments for some species, this strategy can come at a cost to other fitness‐linked traits, such as immune function. We investigated localized variation in the capacity to respond to pond drying and evaluated whether developmental responses induced carry‐over effects in disease susceptibility in three leopard frog species (Rana [Lithobates] pipiens and Rana sphenocephala; two populations each, and one population of Rana chiricahuensis). Using mesocosms located near the site of collection (&lt;15 km away) in five regions spanning a latitudinal gradient, we raised tadpoles under simulated fast drying, slow drying, or constant water levels. After metamorphosis, we characterized several aspects of the skin microbiome, immune function, and response to exposure to the fungal pathogen Batrachochytrium dendrobatidis (Bd). Note that for R. chiricahuensis, the only carry‐over effect measured was response to Bd exposure, for which we observed no effects of pond drying. We found that developmental plasticity in response to drying was rare, except in the southernmost population of R. sphenocephala. In this location, tadpoles responded by accelerating development, and frogs with shorter larval periods developed more severe infections following Bd exposure post‐metamorphosis, suggesting a trade‐off between surviving pond drying and pathogen defense investment. In the three other locations, a lack of accelerated metamorphosis in drying treatments was accompanied by increased mortality, decreased anti‐Bd function of the microbiome, and/or greater Bd infection after exposure. Overall, results suggest that faster drying conditions will likely have negative impacts on amphibians with long larval periods, both directly and indirectly via carry‐over effects. Because effects of drying exposure were not uniform within a species, our findings suggest that local responses may not be generalizable to other regions of the range. These multifaceted effects of climate change on pathogen defenses are increasingly relevant as emerging infectious diseases threaten global biodiversity.

Identifying factors linked with persistence of reintroduced populations: Lessons learned from 25 years of amphibian translocations

Conservation translocations are increasingly used to help recover imperiled species. However, success of establishing populations remains low, especially for amphibians. Identifying factors associated with translocation success can help increase efficiency and efficacy of recovery efforts. Since the 1990s, several captive and semi-captive facilities have produced Chiricahua Leopard Frogs ( Rana chiricahuensis ) to establish or augment wild populations in Arizona and New Mexico, USA. During this same time, personnel associated with several programs surveyed translocation and non-translocation sites for presence of amphibians. We used 25 years (1995–2019) of survey and translocation data for the federally threatened Chiricahua Leopard Frog to identify factors linked with population persistence. Our dataset included approximately 40,642 egg masses or animals translocated in 314 events to 115 distinct sites and > 5800 visual encounter surveys from 641 sites; 120 of these sites were also surveyed with environmental DNA methods in 2018. We used a hierarchical dynamic occupancy model that accounted for imperfect detection to identify patch- and landscape-level attributes associated with site occupancy, and then used predictions from that model to evaluate factors associated with population persistence at translocation sites. Across all sites, extinction probability for Chiricahua Leopard Frogs was higher in lotic (stream) than lentic (pond) habitats and when Western Tiger Salamanders ( Ambystoma mavortium ) were present. Restoration of sites specifically for frog conservation reduced extinction probability. Colonization of unoccupied sites increased moderately with increasing numbers of translocation sites within 2 km, indicating a benefit of translocation efforts beyond sites where frogs were stocked. At translocation sites, persistence was greater in lentic than lotic habitats and was negatively correlated with the proportion of years tiger salamanders were present. Increasing numbers of translocation events, especially of late-stage larvae, increased persistence. There was little difference in population persistence based on whether stock was from captive, semi-captive, or wild sources, but translocations during the dry season (January July) succeeded more than those after the typical arrival of summer rains (August December). Based on the number of years translocation sites were predicted to be occupied, 2 or more translocations produced, on average, a > 4-yr increase in predicted occupancy compared to sites without translocations. While translocations have increased the number of populations across the landscape, continued management of water availability and threats such as invasive predators and disease remain critical to recovery of the Chiricahua Leopard Frog. • Most translocation efforts are unsuccessful, often for unknown reasons. • We assessed factors linked with population persistence for 25 years of translocations. • Local features were paramount, including habitat, predators, and restoration history. • Timing and life stages stocked affected persistence, but rearing environment did not. • ≥ 2 translocations produced a > 4-yr increase in predicted population persistence.

The Use of Evoked Vocal Responses to Detect Cryptic, Low-Density Frogs in the Field

The protection of rare amphibians depends upon accurate information about their distributions, yet cryptic, low-density populations are easily missed during field surveys. We used sites with known populations of the U.S. federally threatened species Rana chiricahuensis (n = 34) and its congener Rana yavapaiensis (n =11) in Arizona, USA to test whether a conspecific call stimulus can improve detectability of species. We show that the use of the evoked vocal responses technique improves the detectability of initially silent anuran populations of R. chiricahuensis and R. yavapaiensis by 45% and 71%, respectively. Evoked vocal responses, however, were not strictly species specific: 19% of R. chiricahuensis and 45% of R. yavapaiensis populations also increased their vocal activity in response to heterospecific stimuli. The low costs of the material (<50 USD per set) and the short time (1 min) to play a stimulus suggest that the additional costs associated with this technique will be minor relative to existing survey protocols. This technique offers the potential to improve the detection of other frog species, particularly in sites that are difficult to search visually, provided it is carried out by surveyors who can identify species by their calls.

Habitat selection by a threatened desert amphibian.

Habitat degradation and fragmentation are major drivers of amphibian declines. The loss of environmental features that allow for movement between water sources may be particularly detrimental for amphibians in arid environments. Climate changes will increase the importance of microhabitats to amphibians. Enhancing areas to facilitate movement may be a necessary conservation strategy for many animal species that depend on wetlands, including federally threatened Chiricahua leopard frogs (Lithobates chiricahuensis). Habitat preferences of this frog species are not well understood. We sought to better understand fine‐scale habitat selection, to inform conservation of Chiricahua leopard frogs.We conducted our study on the Ladder Ranch, a privately owned working bison ranch in New Mexico, USA that supports a large proportion of the remaining Chiricahua leopard frogs in the state.We attached radio transmitters to 44 frogs during summer 2014. We located each frog daily for up to 8 weeks (median = 30 days). We assessed fine‐scale habitat selection by comparing characteristics at each frog location and a random location 5 m away using conditional logistic regression.Frogs preferred features that likely reduce desiccation, even after accounting for the presence of water. Frogs selected areas with more low‐lying cover, especially aquatic vegetation and woody debris, a tree overstory, and a mud substrate.We recommend managing potential movement corridors for Chiricahua leopard frogs by ensuring the presence of muddy creek bottoms, woody debris, riparian overstory, low‐lying ground cover, and pools. Microclimates created by these features seem especially valuable given warming temperatures and modified precipitation regimes, resulting in decreased surface water, soil moisture, and vegetation cover. Retaining or creating preferred habitat features and microclimates in areas between water sources may increase connectivity among isolated populations of Chiricahua leopard frogs and could improve persistence and recovery of other water‐obligate species in arid landscapes.

Survival estimates for the invasive American bullfrog

Abstract American bullfrogs (Lithobates catesbeianus) are significant invaders in many places and can negatively impact native species. Despite their impact and wide distribution, little is known about their demography. We used five years of capture mark-recapture data to estimate annual apparent survival of post-metamorphic bullfrogs in a population on the Buenos Aires National Wildlife Refuge in their invaded range in Arizona, U.S.A. This population is a potential source of colonists into breeding ponds used by the federally threatened Chiricahua leopard frog (L. chiricahuensis). Results from robust-design Cormack-Jolly-Seber models suggested that survival of bullfrogs was influenced by sex and precipitation but not body condition. Survival was higher for females (mean = 0.37; 95% , 0.72) than males (mean = 0.17; 95% , 0.49), and declined with reduced annual precipitation (mean = −0.36, 95% = −2.09, 0.84). These survival estimates can be incorporated into models of population dynamics and to help predict spread of bullfrogs.

A Statistical Forecasting Approach to Metapopulation Viability Analysis

Conservation efforts are aided by reliable forecasts of extinction risk, under future environmental conditions and management actions. We conducted a statistical metapopulation viability analysis for the federally threatened Chiricahua leopard frog, propagating relevant sources of uncertainty. Our results suggested that without management intervention, extinction risk could be as high as 37% by year 2066. However, pond restoration reduced the upper limit on extinction risk to as low as 2%. Our approach allows management decisions to be made with a more complete understanding of the uncertainty around the intended effect of each management decision. These photographs illustrate the article “A statistical forecasting approach to metapopulation viability analysis” by Paige E. Howell, Blake R. Hossack, Erin Muths, Brent H. Sigafus, Ann Chenevert-Steffler, and Richard B. Chandler published in Ecological Applications. https://doi.org/10.1002/eap.2038

CO-OCCURRENCE OF CHIRICAHUA LEOPARD FROGS (LITHOBATES CHIRICAHUENSIS) WITH SUNFISH (LEPOMIS)

Invasive species are a major threat to the persistence of native species, particularly in systems where ephemeral aquatic habitats have been replaced by permanent water and predators, such as fish, have been introduced. Within the Altar Valley, Arizona, the invasive American bullfrog, Lithobates catesbeianus (formerly Rana catesbeianus), has been successfully eradicated to help recover Chiricahua leopard frogs (Lithobates chiricahuensis). However, other nonnative predators including sunfish (Lepomis) are present in some permanent water bodies. During four consecutive years (2014–2017), we detected both the federally threatened Chiricahua leopard frog and sunfish at one permanent water body in the Altar Valley. This suggests that despite the potential negative effect of predatory fish on amphibians, there may be conditions where the Chiricahua leopard frog can co-occur with this nonnative predator. A better understanding of rare situations of co-occurrence with nonnative predators may contribute to our understanding of why co-occurrence happens in some, but not all, systems and whether conservation strategies can be developed in situations where eradication of nonnative predators is infeasible.

Informing Amphibian Conservation Efforts with Abundance-Based Metapopulation Models

Science-based management strategies are needed to halt or reverse the global decline of amphibians. In many cases, sound management requires reliable models built using monitoring data. Historically, monitoring and statistical modeling efforts have focused on estimating occupancy using detection–nondetection data. Spatial occupancy models are useful for studying colonization–extinction dynamics, but richer insights can be gained from estimating abundance and density-dependent demographic rates. We developed an integrated abundance-based metapopulation model of the processes contributing to spatiotemporal variation in patch population density. We fit our model to a combination of detection–nondetection and count data from a 14-yr study of a reintroduced metapopulation of federally threatened Chiricahua Leopard Frogs (Lithobates chiricahuensis). Pond-specific population growth rate was influenced by pond hydroperiod and frog density, such that permanent and semipermanent ponds with low densities of adult frogs experienced the highest annual population growth rates. Immigration rate declined as the distance among ponds increased. After reintroduction in 2003, metapopulation-level abundance increased and appeared to stabilize around 1300 adult frogs (95% CI = 1192–1471) by year 2015. Further, changes in metapopulation abundance were driven mostly by changes in abundance at a few ponds. These high-density populations, which would not have been identifiable with traditional occupancy-based metapopulation models, are likely especially important for species recovery in the area. Abundance-based metapopulation models can be widely applied to inform conservation efforts, by providing higher quality information needed to prioritize habitat patches for management and can be used to make more accurate predictions of metapopulation extinction risk.

A statistical forecasting approach to metapopulation viability analysis.

Conservation of at-risk species is aided by reliable forecasts of the consequences of environmental change and management actions on population viability. Forecasts from conventional population viability analysis (PVA) are made using a two-step procedure in which parameters are estimated, or elicited from expert opinion, and then plugged into a stochastic population model without accounting for parameter uncertainty. Recently developed statistical PVAs differ because forecasts are made conditional on models fitted to empirical data. The statistical forecasting approach allows for uncertainty about parameters, but it has rarely been applied in metapopulation contexts where spatially explicit inference is needed about colonization and extinction dynamics and other forms of stochasticity that influence metapopulation viability. We conducted a statistical metapopulation viability analysis (MPVA) using 11yr of data on the federally threatened Chiricahua leopard frog (Lithobates chiricahuensis) to forecast responses to landscape heterogeneity, drought, environmental stochasticity, and management. We evaluated several future environmental scenarios and pond restoration options designed to reduce extinction risk. Forecasts over a 50-yr time horizon indicated that metapopulation extinction risk was <4% for all scenarios, but uncertainty was high. Without pond restoration, extinction risk is forecasted to be 3.9% (95% CI 0-37%) by year 2066. Restoring six ponds by increasing their hydroperiod reduced extinction risk to <1% and greatly reduced uncertainty (95% CI 0-2%). Our results suggest that managers can mitigate the impacts of drought and environmental stochasticity on metapopulation viability by maintaining ponds that hold water throughout the year and keeping them free of invasive predators. Our study illustrates the utility of the spatially explicit statistical forecasting approach to MPVA in conservation planning efforts.

Increasing connectivity between metapopulation ecology and landscape ecology.

Metapopulation ecology and landscape ecology aim to understand how spatial structure influences ecological processes, yet these disciplines address the problem using fundamentally different modeling approaches. Metapopulation models describe how the spatial distribution of patches affects colonization and extinction, but often do not account for the heterogeneity in the landscape between patches. Models in landscape ecology use detailed descriptions of landscape structure, but often without considering colonization and extinction dynamics. We present a novel spatially explicit modeling framework for narrowing the divide between these disciplines to advance understanding of the effects of landscape structure on metapopulation dynamics. Unlike previous efforts, this framework allows for statistical inference on landscape resistance to colonization using empirical data. We demonstrate the approach using 11yr of data on a threatened amphibian in a desert ecosystem. Occupancy data for Lithobates chiricahuensis (Chiricahua leopard frog) were collected on the Buenos Aires National Wildlife Refuge (BANWR), Arizona, USA from 2007 to 2017 following a reintroduction in 2003. Results indicated that colonization dynamics were influenced by both patch characteristics and landscape structure. Landscape resistance increased with increasing elevation and distance to the nearest streambed. Colonization rate was also influenced by patch quality, with semi-permanent and permanent ponds contributing substantially more to the colonization of neighboring ponds relative to intermittent ponds. Ponds that only hold water intermittently also had the highest extinction rate. Our modeling framework can be widely applied to understand metapopulation dynamics in complex landscapes, particularly in systems in which the environment between habitat patches influences the colonization process.

Movement of Imperiled Chiricahua Leopard Frogs during Summer Monsoons

Abstract Habitat fragmentation and subsequent disruption of animal movement are responsible for extinctions in some species, including amphibians. Amphibians that can travel across fragmented landscapes may be at lower risk of extinction. Chiricahua Leopard Frogs are threatened because of fragmentation associated with habitat loss and degradation. We sought to identify cues leading frogs to leave perennial ponds and factors related to movement ability of Chiricahua Leopard Frogs in New Mexico during the summers of 2013 and 2014. Using pitfall traps, we captured frogs leaving ponds and radio-tracked 30 individuals to characterize overland movements. We checked traps and located frogs daily for up to eight weeks. We assessed factors related to the number of frogs leaving ponds using linear models and to distances moved by frogs using linear mixed models. The number of frogs caught was related to rainfall, but not water temperature, and more frogs were found outside ponds at an intermediate level of rainfall...

Toxicity of Cadmium, Copper, and Zinc to the Threatened Chiricahua Leopard Frog (Lithobates [Rana] chiricahuensis)

The Chiricahua leopard frog (Lithobates chiricahuensis) is in decline throughout the western United States, and is particularly sensitive to physical, chemical and biotic changes in their habitat. Acute toxicity tests revealed that among the metals detected in Chiricahua leopard frog habitat, copper was toxic at concentrations lower than those observed in the environment. Developing tadpoles were chronically exposed for 60 days to cadmium, copper and zinc because of the potential for long term exposure to these metals during early development. Cadmium was toxic, but at concentrations above observed environmental levels. Copper was especially toxic to this species at concentrations of about 10% of concentrations observed in their habitats. The onset of toxicity occurred within a few days of exposure, thus pulsed exposures from rain events could potentially be acutely toxic to tadpoles of this species. Zinc did not appear to have a negative impact during the acute or chronic exposures.

Lost but not forgotten: MHC genotypes predict overwinter survival despite depauperate MHC diversity in a declining frog

The amphibian disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has contributed to the decline of Chiricahua leopard frogs (Rana chiricahuensis), a federally threatened species native to the Southwestern United States. We characterized immunogenetic variability in R. chiricahuensis by sequencing an expressed Major Histocompatibility Complex (MHC) class IIβ gene across 13 natural populations in Arizona, USA, as well as 283 individuals that were captive reared from two egg masses. We recovered a total of five class IIβ MHC alleles compared to 84 alleles previously characterized in eight natural populations of the Arizona congener R. yavapaiensis, demonstrating reduced MHC diversity in R. chiricahuensis. One allele was fixed in five populations but none of the R. chiricahuensis alleles were closely related to R. yavapaiensis allele Q, which is significantly associated with chytridiomycosis resistance in laboratory trials. Nine of 13 R. chiricahuensis population localities were Bd positive, and bearing allele RachDRB*04 was the best genetic predictor of an individual being infected with Bd. A total of three class IIβ alleles were recovered from captive reared individuals, which were released to two natural population localities followed by recapture surveys to assess MHC-based survival over winter, the time when chytridiomycosis outbreaks are most severe. At one site, all released animals were fixed for a single allele and MHC-based survival could not be assessed. At the second site, fewer than half of the released but all of the recaptured individuals were homozygous for RachDRB*05, indicating that MHC genotype is important in determining Bd survival under natural field conditions. We conclude that the limited MHC variation in R. chiricahuensis is likely the consequence rather than the cause of natural selection favoring alleles that promote survival in the face of Bd. Our study highlights that preserving even low levels of functional genetic variation may be essential for population persistence, and that local disease adaptation may present as a reduction in genetic diversity. These finding also suggest that for populations that have declined due to a specific infectious pathogen, MHC-based genetically-informed reintroduction approaches may enhance species recovery efforts.

Effects of CFT Legumine (5% Rotenone) on Tadpole Survival and Metamorphosis of Chiricahua Leopard Frogs Lithobates chiricahuensis, Northern Leopard Frogs L. pipiens, and American Bullfrogs L. catesbeianus

AbstractAmphibians may experience collateral effects if exposed to CFT Legumine (5% rotenone), a piscicide that is used to remove invasive fish. A series of 48‐h static toxicity tests assessed the acute effects of CFT Legumine on multi‐aged tadpoles of the federally listed Chiricahua leopard frog Lithobates chiricahuensis, the widespread northern leopard frog L. pipiens, and the increasingly invasive American bullfrog L. catesbeianus. At the earliest Gosner stages (GS 21–25), Chiricahua leopard frogs were more sensitive to CFT Legumine (median lethal concentration [LC50] = 0.41–0.58 mg/L) than American bullfrogs (LC50 = 0.63–0.69 mg/L) and northern leopard frogs (LC50 = 0.91 and 1.17 mg/L). As tadpoles developed (i.e., increase in GS), their sensitivity to rotenone decreased. In a separate series of 48‐h static nonrenewal toxicity tests, tadpoles (GS 21–25 and GS 31–36) of all three species were exposed to piscicidal concentrations of CFT Legumine (0.5, 1.0, and 2.0 mg/L) to assess postexposure effects on metamorphosis. In survivors of all three species at both life stages, the time to tail resorption was nearly doubled in comparison with that of controls. For example, mid‐age (GS 31–36) Chiricahua leopard frog tadpoles required 210.7 h to complete tail resorption, whereas controls required 108.5 h. However, because tail resorption is a relatively short period in metamorphosis, the total duration of development (days from posthatch to complete metamorphosis) and the final weight did not differ in either age‐group surviving nominal concentrations of 0.5‐, 1.0‐, and 2.0‐mg/L CFT Legumine relative to controls. This research demonstrates that the CFT Legumine concentrations commonly used in field applications to remove unwanted fish could result in considerable mortality of the earliest stages of Lithobates species. In addition to acute lethality, piscicide treatments may result in delayed tail resorption, which places the tadpoles at risk by increasing their vulnerability to predation and pathogens.Received October 1, 2016; accepted January 17, 2017 Published online March 30, 2017