Pseudacris Crucifer Research Articles

Can alternative mating tactics facilitate introgression across a hybrid zone by circumventing female choice?

Reproductive barriers and divergence in species' mate recognition systems underlie major models of speciation. However, hybridization between divergent species is common, and classic mechanisms to explain permeable reproductive barriers rarely consider how an individual may attain reproductive success. Alternative mating tactics (AMTs) exist in various forms across animal taxa. Such tactics may allow poorer quality individuals to gain mating opportunities and facilitate introgression either through asymmetrical positive selection or by circumventing female choice altogether in areas of secondary contact. One such tactic is satellite behaviour in frogs, where silent males perch near advertisers in an attempt to intercept females. To test whether such satellite male tactics are context-dependent and favoured by hybrids, we genotyped and quantified the morphology of 80 male spring peeper (Pseudacris crucifer) individuals involved in caller-satellite associations from a secondary contact zone between two intraspecific mitochondrial lineages. Irrespective of population, satellite behaviour was best predicted by size but not body condition. Within the contact zone, pure individuals showed a significantly greater probability of being active callers, whereas hybrids of one lineage were more likely to adopt the satellite tactic. We suggest that satellite behaviour in P.crucifer promotes introgression, breaks down reproductive isolating barriers and contributes to asymmetrical introgression in this secondary contact zone. AMTs may thus be an underexplored but important alternative to oft-discussed causes of genetic discordance found in hybrid zones.

Short-Term Exposure to Coal Combustion Waste Has Little Impact on the Skin Microbiome of Adult Spring Peepers (Pseudacris crucifer).

Disruptions to the microbiome can impact host health as can exposure to environmental contaminants. However, few studies have addressed how environmental contaminants impact the microbiome. We explored this question for frogs that breed in wetlands contaminated with fly ash, a by-product of coal combustion that is enriched in trace elements. We found differences in the bacterial communities among a fly ash-contaminated site and several reference wetlands. We then experimentally assessed the impacts of fly ash on the skin microbiome of adult spring peepers (Pseudacris crucifer). Frogs were exposed to fly ash in the laboratory for 12 h, the duration of a typical breeding event, and the skin microbiome was assessed after 5 days (experiment 1) or after 5 and 15 days (experiment 2). We examined bacterial community structure using 16S rRNA gene amplicon sequencing and metabolite profiles using high-pressure liquid chromatography-mass spectrometry (HPLC-MS). We found little impact as the result of acute exposure to fly ash on the bacterial communities or metabolite profiles in either experiment, suggesting that the bacterial symbiont communities of adults may be relatively resistant to brief contaminant exposure. However, housing frogs in the laboratory altered bacterial community structure in the two experiments, which supports prior research suggesting that environmental source pools are important for maintaining the amphibian skin microbiome. Therefore, for contaminants like fly ash that may alter the potential source pool of symbionts, we think it may be important to explore how contaminants affect the initial assembly of the amphibian skin microbiome in larval amphibians that develop within contaminated sites. Animals are hosts to many symbiotic microorganisms, collectively called the microbiome, that play critical roles in host health. Therefore, environmental contaminants that alter the microbiome may impact hosts. Some of the most widespread contaminants, produced worldwide, are derived from the mining, storage, and combustion of coal for energy. Fly ash, for example, is a by-product of coal combustion. It contains compounds such as arsenic, selenium, cadmium, and strontium and is a recognized source of ground and surface water contamination. Here, we experimentally investigated the impacts of short-term fly ash exposure on the skin microbiome of spring peepers, one of many species of amphibian that sometimes breed in open fly ash disposal ponds. This research provides a look into the potential impacts of fly ash on an animal's microbiome and suggests important future directions for research on the effects of environmental contaminants on the microbiome.

Individual flight-calling behaviour in wood warblers

Warblers regularly give flight calls during migration, but few studies have addressed flight-calling behaviour by individual birds. In this study, we investigated individual responses to flight calls. We hypothesized that birds would be more likely to give flight calls in response to conspecific flight calls than to heterospecific calls or to other sounds. We studied the flight-calling response of three species of warblers (magnolia warbler, Setophaga magnolia, blackpoll warbler, Setophaga striata, and yellow-rumped warbler, Setophaga coronata) to conspecific calls, calls of one of the other two species or calls of the spring peeper, Pseudacris crucifer, as a control. Additionally, we characterized the proportion of birds calling and the rates of calling (calls/min) for five additional warbler species. We placed each bird individually into an acoustic cone in a soundproof recording studio and recorded its vocalizations before, during and after playing sound cues in the studio. In our experiment, the three species of warblers were more likely to give flight calls in response to flight calls than to the control, and they were more likely to give flight calls to conspecific calls than heterospecific calls. The eight species of warblers that heard conspecific flight calls varied in both the likelihood of giving a response and the rate of calling, and rates of calling also varied between individuals within each species. Most birds that responded gave flight calls soon after hearing flight calls. Our results are some of the first on individual flight-calling responses and flight-calling rates.

A comparison of acoustic monitoring methods for common anurans of the northeastern United States

ABSTRACTMany anuran monitoring programs now include autonomous recording units (ARUs). These devices collect audio data for extended periods of time with little maintenance and at sites where traditional call surveys might be difficult. Additionally, computer software programs have grown increasingly accurate at automatically identifying the calls of species. However, increased automation may cause increased error. We collected 435 min of audio data with 2 types of ARUs at 10 wetland sites in Vermont and New York, USA, from 1 May to 1 July 2010. For each minute, we determined presence or absence of 4 anuran species (Hyla versicolor,Pseudacris crucifer,Anaxyrus americanus, andLithobates clamitans) using 1) traditional human identification versus 2) computer‐mediated identification with software package, Song Scope® (Wildlife Acoustics, Concord, MA). Detections were compared with a data set consisting of verified calls in order to quantify false positive, false negative, true positive, and true negative rates. Multinomial logistic regression analysis revealed a strong (P < 0.001) 3‐way interaction between the ARU recorder type, identification method, and focal species, as well as a trend in the main effect of rain (P = 0.059). Overall, human surveyors had the lowest total error rate (<2%) compared with 18–31% total errors with automated methods. Total error rates varied by species, ranging from 4% forA. americanusto 26% forL. clamitans. The presence of rain may reduce false negative rates. For survey minutes where anurans were known to be calling, the odds of a false negative were increased when fewer individuals of the same species were calling. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Extensive variation in sperm morphology in a frog with no sperm competition.

BackgroundRecent comparative studies of several taxa have found that within-species variation in sperm size decreases with increasing levels of sperm competition, suggesting that male-male gamete competition selects for an optimal sperm phenotype. Previous studies of intraspecific sperm length variation have all involved internal fertilizers where some other factors—e.g., sperm storage and sperm movement along the walls of the female’s reproductive tract—probably also influence and reduce sperm size variation. Thus external fertilizers, where those factors are absent, might be expected to exhibit even more variation when there is little or no sperm competition. To test that idea, we studied the sperm morphology of a North American chorus frog, the spring peeper (Pseudacris crucifer), a species in which males encounter little or no sperm competition.ResultsAs expected, sperm size was highly variable in the spring peeper, largely due to variation in flagellum length within and among individual males, among populations and between mitochondrial lineages in southwestern Ontario. In addition, a large proportion of spermatozoa in all males was abnormal in such a way that the ability of abnormal spermatozoa to fertilize was probably compromised. There were no differences in the frequencies of abnormalities among populations or mitochondrial lineages.ConclusionsIn the absence of sperm competition, we suggest that genetic drift has probably played a role in the generation of diversity in sperm morphology in this species, potentially resulting in the observed differences among populations. Such interpopulation difference in sperm morphology might be expected to increase the degree of reproductive isolation between populations even before other isolating mechanisms evolve.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0601-8) contains supplementary material, which is available to authorized users.

Contact zone dynamics during early stages of speciation in a chorus frog (Pseudacris crucifer).

Characterizing the genetic and behavioural consequences of contact between previously geographically isolated lineages provides insights into the mechanisms underlying diversification and ultimately speciation. The spring peeper (Pseudacris crucifer) is a widespread Nearctic chorus frog with six divergent mitochondrial DNA (mtDNA) lineages, many of which came into secondary contact during the Holocene. We examined genetics, morphology, advertisement calls and female preference for two lineages that began diverging in allopatry in the Pliocene and now overlap in southwestern Ontario, Canada. We found non-coincident clines in mtDNA and nuclear DNA, mirroring directionality of premating isolation barriers. We also found divergence in a range of traits between these two lineages, displacement in male call attributes and female preference for calls of their natal lineage in sympatry. Hybrids were morphologically distinct from both parental lineages, but hybrid male calls were acoustically intermediate. Female hybrids showed asymmetrical preference for Eastern male calls. These results considered together provide evidence of either unidirectional hybridization or selection against hybrids, potentially implying reproductive character displacement. Our work demonstrates the utility of integrated, multi-character approaches to understanding the processes of divergence and the nature of speciation.

Effects of Pesticide Mixtures on Host-Pathogen Dynamics of the Amphibian Chytrid Fungus.

Anthropogenic and natural stressors often interact to affect organisms. Amphibian populations are undergoing unprecedented declines and extinctions with pesticides and emerging infectious diseases implicated as causal factors. Although these factors often co-occur, their effects on amphibians are usually examined in isolation. We hypothesized that exposure of larval and metamorphic amphibians to ecologically relevant concentrations of pesticide mixtures would increase their post-metamorphic susceptibility to the fungus Batrachochytrium dendrobatidis (Bd), a pathogen that has contributed to amphibian population declines worldwide. We exposed five anuran species (Pacific treefrog, Pseudacris regilla; spring peeper, Pseudacris crucifer; Cascades frog, Rana cascadae; northern leopard frog, Lithobates pipiens; and western toad, Anaxyrus boreas) from three families to mixtures of four common insecticides (chlorpyrifos, carbaryl, permethrin, and endosulfan) or herbicides (glyphosate, acetochlor, atrazine, and 2,4-D) or a control treatment, either as tadpoles or as newly metamorphic individuals (metamorphs). Subsequently, we exposed animals to Bd or a control inoculate after metamorphosis and compared survival and Bd load. Bd exposure significantly increased mortality in Pacific treefrogs, spring peepers, and western toads, but not in Cascades frogs or northern leopard frogs. However, the effects of pesticide exposure on mortality were negligible, regardless of the timing of exposure. Bd load varied considerably across species; Pacific treefrogs, spring peepers, and western toads had the highest loads, whereas Cascades frogs and northern leopard frogs had the lowest loads. The influence of pesticide exposure on Bd load depended on the amphibian species, timing of pesticide exposure, and the particular pesticide treatment. Our results suggest that exposure to realistic pesticide concentrations has minimal effects on Bd-induced mortality, but can alter Bd load. This result could have broad implications for risk assessment of amphibians; the outcome of exposure to multiple stressors may be unpredictable and can differ between species and life stages.

Most of the Dominant Members of Amphibian Skin Bacterial Communities Can Be Readily Cultured.

Currently, it is estimated that only 0.001% to 15% of bacteria in any given system can be cultured by use of commonly used techniques and media, yet culturing is critically important for investigations of bacterial function. Despite this situation, few studies have attempted to link culture-dependent and culture-independent data for a single system to better understand which members of the microbial community are readily cultured. In amphibians, some cutaneous bacterial symbionts can inhibit establishment and growth of the fungal pathogen Batrachochytrium dendrobatidis, and thus there is great interest in using these symbionts as probiotics for the conservation of amphibians threatened by B. dendrobatidis. The present study examined the portion of the culture-independent bacterial community (based on Illumina amplicon sequencing of the 16S rRNA gene) that was cultured with R2A low-nutrient agar and whether the cultured bacteria represented rare or dominant members of the community in the following four amphibian species: bullfrogs (Lithobates catesbeianus), eastern newts (Notophthalmus viridescens), spring peepers (Pseudacris crucifer), and American toads (Anaxyrus americanus). To determine which percentage of the community was cultured, we clustered Illumina sequences at 97% similarity, using the culture sequences as a reference database. For each amphibian species, we cultured, on average, 0.59% to 1.12% of each individual's bacterial community. However, the average percentage of bacteria that were culturable for each amphibian species was higher, with averages ranging from 2.81% to 7.47%. Furthermore, most of the dominant operational taxonomic units (OTUs), families, and phyla were represented in our cultures. These results open up new research avenues for understanding the functional roles of these dominant bacteria in host health.

Canopy cover and drought influence the landscape epidemiology of an amphibian chytrid fungus

Batrachochytrium dendrobatidis (Bd) is a globally distributed fungal pathogen of amphibians that has caused amphibian population declines. Prevalence and infection intensity of Bd should vary spatially across heterogeneous landscapes because survival of the pathogen depends on environmental conditions including humidity and temperature. Wetland temperatures should vary with forest canopy cover, but few studies have examined the relationship between Bd prevalence and canopy cover. We sampled anurans for Bd at 33 wetlands in Illinois across a canopy cover gradient during the severe drought of 2012 and during more typical weather in 2013. We hypothesized that anurans from closed canopy wetlands would have higher Bd prevalence than anurans from open canopy wetlands because high canopy cover would prevent temperatures from exceeding Bd's critical maximum temperature as often. We used occupancy modeling to examine how Bd prevalence varied spatially in relation to environmental covariates, and to determine if weather conditions altered such relationships. We analyzed all common species combined and Spring Peepers (Pseudacris crucifer) separately. Bd was widespread among the study wetlands. During the drought year of 2012, however, Bd prevalence and infection intensity were substantially reduced. Although wetland temperatures were related negatively to canopy cover, the influence of canopy cover on Bd was complex. Bd prevalence for Spring Peepers was related positively to canopy cover during the drought, but not in the non‐drought year. Bd prevalence for all common species was not related positively to canopy cover in either year. Effects of other environmental covariates, such as water depth, also differed between years. Weather conditions had a large impact on Bd infection patterns, which makes predicting pathogen dynamics difficult. In the Midwest region of the United States, climate change models predict more frequent droughts, which may generally inhibit Bd while also altering the effect of environmental factors such as canopy cover on Bd prevalence for amphibians.

Spatial arrangement and metrics of freshwater coastal rock pools applied to amphibian conservation

Coastal habitats are an ecotone between aquatic and terrestrial ecosystems. Depressions on volcanic bedrock shores of Lake Superior form small pool habitats that are influenced to various degrees by their spatial context and that relate to differences in mechanisms of disturbance. A total of 71,931 coastal pools were mapped and measured, and amphibian occupants were identified along 48 km of shoreline at Isle Royale National Park, where coastal rock pool habitats were abundant. Generally, mean depth of pools was 0.11 m, with a mean surface area of 0.6 m 2 , although maximum measurements were 1.5 m and 378 m 2 , respectively. Three strongly defined zones occurred, with bedrock near the lake having a low slope and more numerous, smaller, and shallower pools; bedrock near the forest edge had a steeper slope and fewer, larger, and deeper pools; and a median zone occurring between. A single offshore location, Passage Island, had nearly 63% of all pool abundance. Two amphibian species were typical of coastal pools, the chorus frog ( Pseudacris triseriata ) and blue-spotted salamander ( Ambystoma laterale ), while spring peeper ( Pseudacris crucifer ) was uncommon and probably incidental to coastal habitats. These three species were significantly more abundant in mid-shore pools. Four other amphibian species were only rarely detected. Both coastal habitat density and chorus frog abundance were highest at localities directly adjacent to an international shipping lane. As a result of intriguing spatial distributions and potential for impacts from coastal pollution, chorus frog in particular reveals that coastal ecology can be unique from inland contexts and have important management implications at the land–water interface.

Effects of tannin source and concentration from tree leaves on two species of tadpoles.

Vegetation in and around freshwater ecosystems can affect aquatic organisms through the production of secondary compounds, which are retained in leaves after senescence and are biologically active. Tannins can be toxic to tadpoles, but the plant source of tannins and tannin concentration have been confounded in experimental designs in previous studies. To examine the effects of the concentration and source of tannins (tree species), we examined the effects of 4 factors on tadpole survival, growth, and development: tannin source (red oak [Quercus rubra], white oak [Quercus alba], or sugar maple [Acer saccharum]); tannin concentration (including a control); diet protein level; and tadpole species (American toad [Anaxyrus americanus] and spring peepers [Pseudacris crucifer]). Tannin source and concentration affected spring peeper survival, but American toads had uniformly high survival. Spring peepers had a lower survival rate in high tannin concentrations of oak leachate but a high survival rate in both concentrations of sugar maple leachate. These differences in survival did not correspond with changes in dissolved oxygen, and no effect of dietary protein level on tadpole performance was observed. The presence of plant leachate resulted in increased tadpole growth in both species, but the mechanism for this finding is unclear. The results of the present study show that tannin concentration and source are important factors for tadpole performance, adding further evidence that plant chemistry can affect aquatic organisms.

Landscape context influences the abundance of amphibians and the strength of their food web interactions in small ponds

Many species, including most amphibians, undergo an ontogenetic niche shift (ONS) from an aquatic larval stage to a terrestrial adult stage. We use the ratio of aquatic to terrestrial habitat in a landscape as a tool to understand the influence of landscape context on the population growth of ONS species. The aquatic to terrestrial ratio (ATR) of habitats can be viewed as an analog to the influence of resource ratios on the population growth of consumers and depends on the degree to which each habitat type limits the growth of a given population. Population growth rates of shorter‐lived species tend to be more limited by demographic rates in early (aquatic) life stages. As a result, increasing the ATR should lead to a higher total population size in the landscape (and higher densities in the terrestrial habitat), but have little influence on the density of individuals in any given aquatic habitat. Alternatively, population growth rates of longer‐lived species tend to be more limited by demographic rates in later (terrestrial) life stages and increasing the ATR should have little influence on the total population size in the landscape, but decrease the density of individuals in any given aquatic habitat. We show that among‐landscape variation in the breeding‐pond densities of three widespread amphibians with contrasting life histories is consistent with this framework. Within‐pond densities of Pseudacris crucifer, a species with short‐lived adults, were not influenced by ATR, whereas within‐pond densities of Hyla versicolor, a longer‐lived member of the same family (Hylidae), declined as ATR increased. Ambystoma maculatum, a long‐lived salamander, also had lower densities in ponds with higher ATR. Because A. maculatum larvae are important predators in ponds, we use structural equation modeling to show that landscape context (ATR) can moderate community structure via direct (amphibian abundances) and indirect (prey species richness) effects.

Effects of urbanization on the occurrence of Batrachochytrium dendrobatidis: do urban environments provide refuge from the amphibian chytrid fungus?

Batrachochytrium dendrobatidis (Bd) is a widespread pathogenic fungus that is known to cause the disease, chytridiomycosis, which can be lethal to many amphibians. We compared occurrence rates on spring peepers (Pseudacris crucifer) in urban and forested breeding sites in eastern Texas, USA. All study sites were at approximately the same latitude and altitude, and samples were collected at the same time of year to isolate differences in Bd infection rates between habitat types. We found significant differences (p < 0.001) in the occurrence of Bd between habitats; with dramatically lower rates of occurrence at urban sites (19.5 %), compared to forested sites (62.9 %). The exact reason for the observed differences in the occurrence of Bd is not known, however, we suspect that warmer temperatures or lower population densities and lower species richness at urban sites all could play a role in our results. Our findings suggest that urban environments may provide a refuge for some amphibians from the pathogen.

Spring peepers Pseudacris crucifer modify their call structure in response to noise

Abstract Acoustic interference can impede effective communication that is important for survival and reproduction of animals. In response to acoustic interference, some animals can improve signalling efficacy by altering the structure of their signals. In this study, we played artificial noise to 46 male spring peepers Pseudacris crucifer, on their breeding grounds, and tested whether the noise affected the duration, call rate, and peak frequency of their advertisement calls. We used two experimental noise treatments that masked either the high- or low-frequency components of an average advertisement call; this allowed us to evaluate whether frogs adaptively shift the peak frequency of their calls away from both types of interference. Our playback treatments caused spring peepers to produce shorter calls, and the high-frequency noise treatment caused them to lower the frequency of their calls immediately after the noise ceased. Call rate did not change in response to playback. Consistent with previous studies, ambient temperature was inversely related to call duration and positively related to call rate. We conclude that noise affects the structure of spring peeper advertisement calls, and that spring peepers therefore have a mechanism for altering signal structure in response to noise. Future studies should test if other types of noise, such as biotic or anthropogenic noise, have similar effects on call structure, and if the observed changes to call structure enhance or impair communication in noisy environments [Current Zoology 60 (4): 438–448, 2014].

White-throated sparrows alter songs differentially in response to chorusing anurans and other background noise

Animals can use acoustic signals to attract mates and defend territories. As a consequence, background noise that interferes with signal transmission has the potential to reduce fitness, especially in birds that rely on song. While much research on bird song has investigated vocal flexibility in response to urban noise, weather and other birds, the possibility of inter-class acoustic competition from anurans has not been previously studied. Using sound recordings from central Ontario wetlands, we tested if white-throated sparrows (Zonotrichia albicolis) make short-term changes to their singing behaviour in response to chorusing spring peepers (Pseudacris crucifer), as well as to car noise, wind and other bird vocalizations. White-throated sparrow songs that were sung during the spring peeper chorus were shorter with higher minimum frequencies and narrower bandwidths resulting in reduced frequency overlap. Additionally, sparrows were less likely to sing when car noise and the vocalizations of other birds were present. These patterns suggest that birds use multiple adjustment strategies. This is the first report to demonstrate that birds may alter their songs differentially in response to different sources of noise.This article is part of a Special Issue entitled: insert SI title.

Proportion of Hosts CarryingBatrachochytrium dendrobatidis, Causal Agent of Amphibian Chytridiomycosis, in Oswego County, NY in 2012

Abstract Although the fungus Batrachochytrium dendrobatidis is a causal agent behind precipitous amphibian declines globally, little is known about its regional distribution in New York State (NYS). With an aim toward increased understanding of B. dendrobatidis prevalence locally, we collected amphibians between April through November 2012 at the Rice Creek Field Station in Oswego County, NY, and took swabs of the ventral surfaces of all individuals caught. Polymerase chain reaction on DNA extracted from swabs and comparison with B. dendrobatidis control DNA showed that 30% of amphibians sampled carried the fungus, with prevalence ranging between 20–50%) for Lithobates catesbeianus (Bull Frogs), Lithobates clamitans (Green Frogs), Pseudacris crucifer (Spring Peepers), and Eurycea bislineata (Two-lined Salamanders). We detected Batrachochytrium dendrobatidis only during the months of April, May, June, August, and September of the sampling period. June and September had the highest percentage of amphibians ...

Testing for intraspecific postzygotic isolation between cryptic lineages ofPseudacris crucifer

Phenotypically cryptic lineages appear common in nature, yet little is known about the mechanisms that initiate and/or maintain barriers to gene flow, or how secondary contact between them might influence evolutionary trajectories. The consequences of such contact between diverging lineages depend on hybrid fitness, highlighting the potential for postzygotic isolating barriers to play a role in the origins of biological species. Previous research shows that two cryptic, deeply diverged intraspecific mitochondrial lineages of a North American chorus frog, the spring peeper (Pseudacris crucifer), meet in secondary contact in Southwestern Ontario, Canada. Our study quantified hatching success, tadpole survival, size at metamorphosis, and development time for experimentally generated pure lineage and hybrid tadpoles. Results suggest that lineages differ in tadpole survival and that F1 hybrids may have equal fitness and higher than average mass at metamorphosis compared with pure parental crosses. These findings imply hybrid early life viability may not be the pivotal reproductive isolation barrier helping to maintain lineage boundaries. However, we observed instances of tadpole gigantism, failure to metamorphose, and bent tails in some tadpoles from hybrid families. We also speculate and provide some evidence that apparent advantages or similarities of hybrids compared with pure lineage tadpoles may disappear when tadpoles are raised with competitors of different genetic makeup. This pilot study implies that ecological context and consideration of extrinsic factors may be a key to revealing mechanisms causing negative hybrid fitness during early life stages, a provocative avenue for future investigations on barriers to gene flow among these intraspecific lineages.

When Do Peepers Peep? Climate and the Date of First Calling in the Spring Peeper(Pseudacris crucifer)in Southeastern New York State

The date of first calling (DFC) of Pseudacris crucifer (Spring Peeper) was recorded over 15 years between 1997 and 2012 in a small vernal pond in southeastern New York State. There was no statistically significant trend in temperature or in the DFC over this period. To determine what temperature cues best predicted DFC, 20 potential temperature indices (daily mean, minimum and maximum temperatures averaged over several different time periods, and thermal sums using several different base temperatures) and five precipitation indices (precipitation on the DFC and for four time windows prior to the DFC) were calculated, and predicted DFCs were compared to observed DFCs. The thermal sum with a base of 3 °C (TS3) was the best predictor but overestimated DFC slightly at high values of DFC. In evaluating impacts of climate change on the calling of this frog, the TS3 index may provide a more accurate metric than the daily temperature statistics that have been used in previous studies. In a 63-year record from a nearby weather station, the TS3 index declined significantly, suggesting that Spring Peepers may be calling earlier now than they were in the mid-20th century.

Pre-existing sensory biases in the spectral domain in frogs: empirical results and methodological considerations

In many species of anurans, advertisement calls excite only one of the two inner-ear organs. One prediction of the pre-existing bias hypothesis is that signal innovations that additionally excite the "untapped" organ will be more behaviorally effective than normal calls. However, recent studies have shown that females of three species with single-peaked calls that stimulate only the basilar papilla (BP) preferred single-peaked synthetic calls with a frequency typical of conspecific calls to two-peaked calls that also stimulated the amphibian papilla (AP). We report that in spring peepers (Pseudacris crucifer) that also produce single-peaked calls, females did not show a preference in choices between single-peaked and two-peaked synthetic calls. Thus, the addition of energy exciting the AP had a neutral effect on signal attractiveness. Together, these results are unsupportive of the pre-existing bias hypothesis. An alternative hypothesis is that positive fitness consequences of responding to sounds providing extraordinary spectral stimulation are required for a novel call to become established as a mate-attracting signal. Testing these ideas requires a taxonomically broader examination of responses to sounds with novel spectral complexity, and attention to some methodological details will improve the comparability of such studies.

Effects of leachate from tree leaves and grass litter on tadpoles

Tree species composition can change as a result of succession, climate change, fire suppression, and invasive species. These changes clearly affect forests, but they can also affect aquatic ecosystems based on differences in the input quality of leaf litter, such as plant secondary compounds. These compounds vary in type and concentration depending on species and can be toxic to aquatic organisms. To examine toxic effects on Pseudacris maculata and Pseudacris crucifer tadpoles, we conducted 60-d laboratory experiments to compare leaf litter leachate from a dominant canopy species (red oak) and nonnative species (white pine) with an aquatic grass (prairie cordgrass) and plain water control. An additional experiment examined the effects of white pine on Bufo americanus, Hyla versicolor, and tannin concentrations in natural ponds. Compared with the control and grass, tree leaf extracts resulted in reduced tadpole survival. Leached compounds from pine reduced tadpole survival to 3 d or less. Tadpoles were able to metamorphose in significant numbers only from the two controls. The lowered survival with the red oak treatment might have been caused by lowered dissolved oxygen or high tannin concentrations. However, pine is known to have high concentrations of toxic monoterpenes, which should be investigated further. We found that tannin concentrations in natural ponds were much lower than the test concentrations, indicating that these results may represent worst-case scenarios or unrealistic concentrations.