Endangered Houston Toad Research Articles

Quantification of chlamydiae in the endangered Houston toad (Anaxyrus houstonensis).

Two primer set/probe combinations targeting variable regions on the 23S rRNA gene were designed to detect and quantify chlamydiae in DNA extracted from brain swabs of the endangered Houston toad (Anaxyrus houstonensis) using SYBRGreen- and Taqman-based quantitative polymerase chain reaction (qPCR). Prevalence and abundance values for samples were generally different between SYBRGreen- and Taqman-based detection methods, with higher specificity observed for Taqman-based detection. Of the 314 samples analyzed, initial screening with SYBRGreen-based qPCR retrieved 138 positive samples, of which 52 were confirmed by Taqman-based analyses as chlamydiae. All of these samples were subsequently identified as C. pneumoniae by specific qPCR and confirmed by comparative sequence analyses of 23S rRNA gene amplicons. These results demonstrate the usefulness of our developed qPCR methods to screen for and verify prevalence of chlamydiae in DNA of brains swabs, and ultimately specifically identify and quantify chlamydiae and specifically C. pneumoniae in these samples.

Acute Bladder Snails, Physa acuta Draparnaud 1805, as ectosymbionts of the endangered Houston Toad, Bufo (Anaxyrus) houstonensis Sanders 1953

Acute Bladder Snails, Physa acuta Draparnaud 1805, as ectosymbionts of the endangered Houston Toad, Bufo (Anaxyrus) houstonensis Sanders 1953

Quantification of members of the Mycobacterium chelonae-abscessus complex in lesions of the endangered houston toad (Anaxyrus houstonensis)

Illumina-based 16S rRNA V3 amplicon sequencing of total DNA obtained from soft tissue lesions (joint granulomas) of the endangered Houston toad (Anaxyrus houstonensis) demonstrated that many reads represented members of the actinobacterial Mycobacterium chelonae-abscessus complex. In order to quantify members of this complex in those lesions, we designed three complex-specific primer set/probe combinations (sets I, II and III) targeting variable regions on the 23S rRNA gene for SybrGreen- and Taqman-based quantitative polymerase chain reaction (qPCR). Both SybrGreen- and Taqman-based analyses specifically detected members of the M. chelonae-abscessus complex in lesion samples, with numbers between 104 and 107 cells per 100-mg sample. Values within individual samples were generally comparable between SybrGreen- and Taqman-based detection methods and between all primer set/probe combinations, except for SybrGreen-based analyses of a few samples analyzed with primer set I that used a less specific forward primer. The development of highly specific detection and quantification methods for members of the M. chelonae-abscessus complex in lesion samples can enable group specific tracking of these organisms, particularly in captive or stewardship settings where source and transmission monitoring are valuable tools to husbandry and species conservation.

Association of Leeches with the Endangered Houston Toad

The prevalence of leech attachment on anuran taxa is largely uncharacterized. When parasitic, such relationships may regulate amphibian populations and function as an obstacle to the recovery of imperiled species. We evaluated the prevalence of leech attachment in a population of endangered Bufo (= Anaxyrus) houstonensis (Houston Toad) in Bastrop County, TX, during the spring of 2021. Of 191 toads examined, 2 (1%) were each infested with a single leech. Molecular analysis of the cytochrome c oxidase subunit I gene identified 1 of those leeches as Helobdella austinensis. This constitutes the first reported association of H. austinensis with a vertebrate host and extends the known range of H. austinensis ∼50 km eastward. Leech attachment in this Houston Toad population is rare and the nature of the association remains unclear.

Near-Infrared Spectroscopy (NIRS) as a Method for Biological Sex Discrimination in the Endangered Houston Toad (Anaxyrus houstonensis).

Biological sex is one of the more critically important physiological parameters needed for managing threatened animal species because it is crucial for informing several of the management decisions surrounding conservation breeding programs. Near-infrared spectroscopy (NIRS) is a non-invasive technology that has been recently applied in the field of wildlife science to evaluate various aspects of animal physiology and may have potential as an in vivo technique for determining biological sex in live amphibian species. This study investigated whether NIRS could be used as a rapid and non-invasive method for discriminating biological sex in the endangered Houston toad (Anaxyrus houstonensis). NIR spectra (N = 396) were collected from live A. houstonensis individuals (N = 132), and distinct spectral patterns between males and females were identified using chemometrics. Linear discriminant analysis (PCA-LDA) classified the spectra from each biological sex with accuracy ≥ 98% in the calibration and internal validation datasets and 94% in the external validation process. Through the use of NIRS, we have determined that unique spectral signatures can be holistically captured in the skin of male and female anurans, bringing to light the possibility of further application of this technique for juveniles and sexually monomorphic species, whose sex designation is important for breeding-related decisions.

Determinants influencing recruitment in the Houston toad programmatic safe harbor agreement

ABSTRACT The importance of private lands conservation (PLC) for endangered species continues to grow as habitat is increasingly lost or fragmented. In Texas, nearly 98% of all property is privately owned, rendering PLC critical for protecting endangered species. Despite case studies regarding factors leading to stewardship outcomes for endangered species, a knowledge gap exists regarding PLC for endangered species. To help address this gap, we situate findings from 30 key informant interviews and two focus groups within a novel stewardship framework to understand how PLC interventions for the endangered Houston toad (Anaxyrus houstonensis) appeal to landowners. Our approach revealed that local changes in conservation norms and networks can build relationships between resource-deficient landowners and practitioners that increase awareness and trust, combating barriers to PLC. Enhanced networks and cultural transformation facilitated by demographic changes and decentralized governance can allow stewardship obligations to supersede culturally embedded rural myths and attitudes of anti-government sentiment.

Optimizing the power of human performed audio surveys for monitoring the endangered Houston toad using automated recording devices.

Knowledge regarding the locations of populations of endangered species is a critical part of recovery and facilitates land use planning that avoids unnecessary impacts. Regulatory agencies often support the development of survey guidelines designed to standardize the methods and maximize the probability of detection, thereby avoiding incorrectly concluding a species is absent from a site. Here, using simulations with data collected using automated recording devices (ARDs) we evaluated the efficacy of the existing U.S. Fish and Wildlife Service’s survey requirements for the endangered Houston Toad (Anaxyrus houstonensis). We explored the effect of (1) increasing survey duration, (2) increasing the number of surveys, and (3) combinations of environmental conditions (e.g., temperature, humidity, rainfall) on the detection probability and the number of surveys needed to be 95% confident of absence. We found that increases in both the duration of the survey and the number of surveys conducted decreased the likelihood of incorrectly concluding the species was absent from the site, and that the number of surveys required to be 95% confident greatly exceeded the existing survey requirements. Targeting specific environmental conditions was also an effective way to decrease the number of surveys required but the infrequency in which these conditions occurred might make application difficult in some years. Overall, we suggest that the survey effort necessary to achieve confidence in the absence of Houston Toads at a site is more practically achievable with the use of ARDs, but this may not be suitable in all monitoring scenarios.

MYCOBACTERIA IN SKIN LESIONS AND THE HABITAT OF THE ENDANGERED HOUSTON TOAD (ANAXYRUS HOUSTONENSIS).

Head-starting of the federally endangered Houston toad (Anaxyrus houstonensis), that is, the release of egg strands, tadpoles, and metamorphic juveniles produced in captivity into the original breeding ponds, requires assessment of potential threats for the transmission of pathogens from captive to free-ranging toads. We used Illumina-based 16S rRNA V3 amplicon sequencing to investigate the community structure of bacteria from skin lesions of captive Houston toad and habitat (pond) samples. Proteobacteria, alone or together with Actinobacteria and, in some samples, Cyanobacteria represented virtually all reads in tissue lesion samples, whereas pond samples were much more diverse, with Acidobacteria, Actinobacteria, Bacteriodetes, Chloroflexi, Cyanobacteria, Firmicutes, Planctomycetes, Proteobacteria, and Verrucomicrobia present with little variation between samples. If present in lesions, Actinobacteria were largely represented by Mycobacteriaceae, and here mainly by one sequence identical to sequences of members of the Mycobacterium chelonae-abscessus complex. In pond samples, mycobacteria represented only a small portion of the actinobacteria, although at higher diversity with six distinct reads. Sequences for reads obtained from pond samples were identical to those representing the M. chelonae-abscessus complex, a group with Mycobacterium marinum, Mycobacterium kansasii, Mycobacterium avium, a group with Mycobacterium vaccae, Mycobacterium fortuitum, Mycobacterium poriferae, and a group with Mycobacterium elephantis and Mycobacterium celeriflavum, whereas sequences of high similarity were detected for reads related to those of Mycobacterium holsaticum, Mycobacterium pallens, and Mycobacterium obuense, and Mycobacterium goodii. Our results indicated that lesions observed on the Houston toad in captivity are not the result of mycobacteria in every case, and that the presence of mycobacteria in the captive colony does not represent a novel pathogen threat to the wild populations because such bacteria are also seen in the natural pond habitats for the Houston toad.

Development and Validation of Automated Detection Tools for Vocalizations of Rare and Endangered Anurans

AbstractFor many rare or endangered anurans, monitoring is achieved via auditory cues alone. Human-performed audio surveys are inherently biased, and may fail to detect animals when they are present. Automated audio recognition tools offer an alternative mode of observer-free monitoring. Few commercially available platforms for developing these tools exist, and little research has investigated whether these tools are effective at detecting rare vocalization events. We generated a recognizer for detecting the vocalization of the endangered Houston toad Anaxyrus houstonensis using SongScope© bioacoustics software. We developed our recognizer using a large sample of training data that included only the highest quality of recorded audio (i.e., low noise, no interfering vocalizations) divided into small, manageable batches. To track recognizer performance, we generated an independent set of test data through randomly sampling a large population of audio known to possess Houston toad vocalizations. We analyzed training data and test data recursively, using a criterion of zero tolerance for false-negative detections. For each step, we incorporated a new batch of training data into the recognizer. Once we included all training data, we manually verified recognizer performance against one full month (March 2014) of audio taken from a known breeding locality. The recognizer successfully identified 100% of all training data and 97.2% of all test data. However, there is a trade-off between reducing false-negative and increasing false-positive detections, which limited the usefulness of some features of SongScope. Methods of automated detection represent a means by which we may test the efficacy of the manual monitoring techniques currently in use. The ability to search any collection of audio recordings for Houston toad vocalizations has the potential to challenge the paradigms presently placed on monitoring for this species of conservation concern.

Leaping from Awareness to Action: Impacts of an Amphibian Educator Workshop

Abstract Where endangered species occur, recommendations call for conservation education programs that engage local educators; however, few studies have measured the effectiveness of implemented programs. We conducted a multipartner educator workshop for the endangered Houston Toad, Anaxyrus houstonensis, as one local example illustrating the broader issue of globally declining amphibians. We measured the effect of the workshop on participants' (n = 50) awareness/knowledge, values, beliefs, emotions, and intent to take action. We observed significant increases in awareness/knowledge and values regarding general amphibian declines and the focal species. The workshop significantly increased participants' belief that they had necessary resources to teach about the Houston Toad. Ninety-nine percent of participants agreed that they cared more about wild toads after meeting live ambassador toads. Postworkshop, we observed a 33% increase in use of amphibians or Houston Toads in participant learning settings. We ...

Houston Toad (Bufo(Anaxyrus)houstonensis) Tadpoles Decrease Their Activity in Response to Chemical Cues Produced from the Predation of Conspecifics and Congeneric (Bufo(Incilius)nebulifer) Tadpoles

Abstract Anurans have been shown to reduce their activity in the presence of predation-related chemical cues. We exposed tadpoles of the federally endangered Houston Toad, Bufo (Anaxyrus) houstonensis, to three chemical cues: A no-predation cue produced by the presence of only predatory anisopteran nymphs (Anax junius), a conspecific-predation cue produced from the consumption of conspecific tadpoles by A. junius nymphs, and a heterospecific-predation cue produced from the consumption of coastal plain toad (Bufo (Incilius) nebulifer) tadpoles by A. junius nymphs. We measured tadpole activity levels before and after exposure to the cues. Tadpole activity was not influenced by the no-predation cue, but it decreased significantly during exposure to either predation cue. The reduction in activity did not differ significantly between predation cue treatments. These data suggest that: 1) B. houstonensis tadpoles will respond to predation, but not the presence of a predator alone. 2) There may be a chemical homo...

USING CALLING ACTIVITY TO PREDICT CALLING ACTIVITY

Understanding anuran calling activity patterns is important for maximizing efficiency and value of call survey data collection and analyses. Previous studies have primarily focused on identifying and quantifying abiotic variables that influence anuran calling activity, and investigating relationships between calling activity and population estimates. In this study we investigated the use of a predictor pond approach to guide call survey effort. In this approach, calling activity at a subset of breeding sites (e.g., ponds) is used as a predictor of calling activity at additional breeding sites, with the goal being to minimize sampling effort while simultaneously maximizing sampling efficiency. We explored the efficiency of this approach using call survey data collected on the endangered Houston Toad (Bufo [Anaxyrus] houstonensis) at 15 known breeding ponds over 9 survey years. We found that if calling activity at 3 predictor ponds was used to decide if additional call surveys would occur at the remaining 12 ponds, we would have hypothetically correctly assumed calling activity was not occurring at non-predictor ponds on 92.1% of survey nights, and we would have hypothetically detected 93.9% of the total number of detected individuals over the 9 survey years. We found the predictor pond approach performed well in our case study, and believe it could be a valuable tool for many anuran monitoring programs.

Wildfire and Postfire Restoration Action Effects on Microclimate and Seedling Pine Tree Survivorship

AbstractThrough modification of structural characteristics, ecological processes such as fire can affect microhabitat parameters, which in turn can influence community composition dynamics. The prevalence of high-severity forest fires is increasing in the southern and western United States, creating the necessity to better understand effects of high-severity fire, and subsequent postfire management actions, on forest ecosystems. In this study we used a recent high-severity wildfire in the Lost Pines ecoregion of Texas to assess effects of the wildfire and postfire clearcutting on six microclimate parameters: air temperature, absolute humidity, mean wind speed, maximum wind speed, soil temperature, and soil moisture. We also assessed differences between burned areas and burned and subsequently clearcut areas for short-term survivorship of loblolly pine Pinus taeda seedling trees. We found that during the summer months approximately 2 y after the wildfire, mean and maximum wind speed differed between unburned and burned areas, as well as burned and burned and subsequently clearcut areas. Our results indicated air temperature, absolute humidity, soil temperature, and soil moisture did not differ between unburned and burned areas, or burned and burned and subsequently clearcut areas, during the study period. We found that short-term survivorship of loblolly pine seedling trees was influenced primarily by soil type, but was also lower in clearcut habitat compared with habitat containing dead standing trees. Ultimately, however, the outcome of the reforestation initiative will likely depend primarily on whether or not the trees can survive drought conditions in the future, and this study indicates there is flexibility in postfire management options prior to reseeding. Further, concerns about negative wildfire effects on microclimate parameters important to the endangered Houston toad Bufo (Anaxyrus) houstonensis were not supported in this study.

Predictive Models for Calling and Movement Activity of the Endangered Houston Toad

Anuran monitoring has increased in recent years in response to global population declines. Delineating abiotic factors that influence anuran activity patterns is important for maximizing monitoring and research efficiency. The Houston toad (Bufo (Anaxyrus)houstonensis) was the first amphibian to be listed as federally endangered in the United States, and populations have continued to decline since it was listed. In this study we investigated the influence of six abiotic factors and one biotic factor on Houston toad calling activity and terrestrial movement in the Lost Pines ecoregion of Texas. Using program PRESENCE, we treated the factors as survey-specific covariates to determine their influence on detection probabilities, and thus presumably activity levels. We found that average daily absolute humidity, average daily wind speed, and presence/absence of Houston toad calling activity the previous night were important factors influencing calling activity, and average daily absolute humidity and detection/non-detection of Houston toad movement activity the previous night were important factors influencing movement activity. We also found that multiple survey years were necessary to delineate influential factors for this species, a result with implications for activity patterns of other rare anurans. The results of this study contribute to our understanding of amphibian activity patterns, and will improve the efficiency of future Houston toad research and monitoring efforts.

Assessment of Public Knowledge and Support for Recovery of the Endangered Houston Toad (Bufo houstonensis) in Bastrop, Texas

Community support is critical to recovery success of endangered species. Education can cultivate positive attitudes and actions toward species recovery. The federally endangered Houston toad (Bufo houstonensis) is endemic to east-central Texas and the largest population is currently located near the City of Bastrop in Bastrop County. This study quantified the level of knowledge about the Houston toad for residents of the City of Bastrop, explored reasons behind expressed opinions of residents, and determined current and future education outlets. Nearly two thirds of respondents had heard of the Houston toad. Of the 83 surveyed residents who had heard of the species, 94% knew the Houston toad was endangered. Most respondents believed the Houston toad was an important part of the Lost Pines ecosystem and cared if it goes extinct. Survey responses did not vary by sex or age. This article will hopefully guide future education and collaborative recovery initiatives.

Estimating Abundance of the Endangered Houston Toad on a Primary Recovery Site

Abstract The Griffith League Ranch is one of the primary recovery sites for the endangered Houston toad Bufo (Anaxyrus) houstonensis. New recovery initiatives have recently been implemented to increase Houston toad abundance; however, no robust estimate of population size has been conducted in the last decade of study, nor from this recovery site. To assist with inferences regarding efficacy of current and future management actions, we estimated adult Houston toad abundance on the Griffith League Ranch. Houston toads were sampled at breeding ponds during the 2010 breeding season using a mark–recapture methodology. We analyzed the data using a modified Jolly–Seber open population model in Program MARK. Models were built whereby the probability of capture remained constant, the apparent survival varied with time or was constant, and the probability of entry varied with time. Model averaging was used to account for uncertainty and the derived adult male Houston toad abundance ranged from 201 to 307 individuals. Using a previously determined Griffith League Ranch Houston toad functional sex ratio of 5∶1, we estimated the abundance of the total adult Houston toad population on this primary recovery site to be from 241 to 368 individuals. This study is the first to report a robust abundance estimate of a Houston toad population and provides a foundation for further research to quantify the impact of current and future management actions.

Is Bigger Always Better? Mate Selection in the Houston Toad (Bufo houstonensis)

Abstract Sexually dimorphic traits are used for mate selection either by female choice (intersexual selection) or male–male competition (intrasexual selection). In anurans, both types of selection mechanisms, especially intersexual selection, generally will favor large males. In bufonids, however, male size does not seem to be a factor in mate selection. Very little is known about the mating preferences of the endangered Houston Toad (Bufo houstonensis). Studies examining the breeding dynamics of B. houstonensis were conducted during the early 1980s, with conflicting results. To further examine mate selection, 329 Houston Toads were collected from Bastrop State Park, Texas, and the snout–urostyle length (SUL) was measured. There was no significant difference in size for males found in amplexus, suggesting females may not select larger males.

Potential Component Allee Effects and Their Impact on Wetland Management in the Conservation of Endangered Anurans

Effective management of wetland quantity and quality is crucial for effective conservation of declining amphibian populations. In particular, frogs and toads that employ aggregative breeding strategies may suffer negative population impacts in response to changes in availability of aquatic breeding habitat, including overabundance of suitable habitat, if density of conspecifics attending aggregations is positively correlated with reproductive success. Here we document such a positive relationship, potentially the first example of a component Allee effect in an anuran, in the critically endangered Houston toad (Bufo houstonensis). We assessed the relationship between mean yearly chorus size and reproductive success of males at the pond level using an information theoretic model selection approach and a two-sample t-test. The chosen model contained the single variable of mean yearly chorus size to predict probability of reproduction, as selected using the Akaike Information Criterion corrected for small sample size and Akaike weight. Mean chorus sizes were significantly higher among ponds exhibiting evidence of reproduction than in those that showed no evidence of reproduction. Our results suggest that chorusing alone is a poor proxy for inference of population stability and highlight a need for reassessment of widely-used amphibian monitoring protocols. Further, amphibian conservation efforts should account for potential Allee effects in order to optimize benefits and avoid underestimating critical population thresholds, particularly in species exhibiting rapid population declines.

Projecting population trends of endangered amphibian species in the face of uncertainty: A pattern-oriented approach

Amphibian populations have been declining worldwide for the last three decades. Determining the risk of extinction is one of the major goals of amphibian conservation, yet few quantitative models have been developed for amphibian populations. Like most rare or threatened populations, there is a paucity of life history data available for most amphibian populations. Data on the critical juvenile life stage are particularly lacking. Pattern oriented modeling (POM) has been used successfully to estimate life history parameters indirectly when critical data lacking, but has not been applied to amphibian populations. We describe a spatially explicit, individual-based, stochastic simulation model developed to project population dynamics of pond-breeding amphibian populations. We parameterized the model with life history and habitat data collected for the endangered Houston toad ( Bufo houstonensis), a species for which there is a high degree of uncertainty for juvenile and adult male survival. During model evaluation, we focused on explicitly reducing this uncertainty, evaluating 16 different versions of the model that represented the range of parametric uncertainty for juvenile and adult male survival. Following POM protocol, we compared simulation results to four population-level patterns observed in the field: population size, adult sex ratio, proportion of toads returning to their natal pond, and mean maximum distance moved. Based on these comparisons, we rejected 11 of the 16 model versions. Results of the remaining versions confirmed that population persistence depends heavily on juvenile survival, and further suggested that probability of juvenile survival is likely between 0.0075 and 0.015 (previous estimates ranged from 0.003 to 0.02), and that annual male survival is near 0.15 (previous estimates ranged up to 0.43). Thus, although the uncertainty associated with population projections for the Houston toad remains large, we were able, via the POM approach, to (1) narrow the range of plausible survival estimates, (2) calculate a first estimate of over-wintering metamorph survival, and (3) provide a set of alternative model versions that quantifies the current level of uncertainty associated with population projections. These results suggest that POM is particularly well suited for modeling amphibian systems, and other ecological systems characterized by low structural uncertainty and high parametric uncertainty.

Arthropod Abundance Following a Prescribed Burn in the Lost Pines Forest of Central Texas

Abstract A Berlese-sample survey was conducted over an 8-month period to determine the manner in which a prescribed burn affected arthropod abundance in a relict pine-oak forest of central Texas. One arthropod taxon (i. e., Diplopoda) was more abundant in the burned section than in the control, one (i. e., Psocoptera) was less abundant, and juvenile stages of holometabolous taxa in general were found in much lower numbers in the burned section, but there was no significant difference between numbers of adults of most taxa even during this nearly immediate post-burn analysis. Such findings are of interest to those concerned with the preservation of the endangered Houston toad, Bufo houstonenis Sanders, and to those who wish to restore the forest to a more natural condition with increased plant and animal diversity through the agency of prescribed burns.