Terrestrial Life Stages Research Articles

Metamorphosis alters concentrations of bioaccumulated pharmaceuticals and endocrine disruptors in caddisflies: Implications for transfer of aquatic–terrestrial subsidies

Abstract Aquatic insects serve as vital inter‐habitat linkages between aquatic and terrestrial ecosystems, as their life cycle includes both aquatic and terrestrial stages. They facilitate the flow of energy and nutrients and play an important role in the transport of waterborne contaminants to terrestrial environments. This study focused on the under‐investigated environmental fate of emerging contaminants (ECs), particularly pharmaceuticals (PhACs) and endocrine‐disrupting compounds (EDCs), which originate from wastewater effluents and accumulate in aquatic insects. Using an in situ study of a highly abundant caddisfly species (Trichoptera), Silo nigricornis (Pictet, 1834), inhabiting a wastewater‐impacted drainage ditch, we examined the bioaccumulation and bioamplification of PhACs and EDCs across the aquatic and terrestrial life stages of the caddisfly. We observed variations in the highest concentrations of PhACs and EDCs in different sample types, including water, biofilm and different life stages of S. nigricornis. Adult S. nigricornis exhibited the highest total concentrations of ECs among the different life stages, with 17 different ECs bioaccumulated in caddisfly tissues. Most of these ECs had higher concentrations in terrestrial adults compared to aquatic larvae and pupae. The total concentration of ECs increased significantly with development, revealing a 41% higher concentration in adult terrestrial caddisflies compared to pupae and larvae. Bioamplification factors provided insights into the increased body burden of the majority of compounds during at least one stage of metamorphosis in S. nigricornis. Evidence of bioamplification was observed in both metamorphosis stages, with certain compounds, such as antibiotics (azithromycin and tilmicosin), endocrine disruptors (TCPP – tris[1‐chloro‐2‐propyl]phosphate and parabens; methylparaben, propylparaben), consistently exhibiting increased concentrations from larval to pupal and from pupal to adult stages. The observed pattern of increasing body burden of contaminants during the caddisfly life cycle emphasises the effects of metamorphosis on the concentration of PhACs and EDCs in adult holometabolous aquatic insects. Our results emphasise the importance of adult caddisflies for the transport of waterborne contaminants such as PhACs and EDCs from aquatic to terrestrial environments. Therefore, our results emphasise the need to include adult trichopterans in the assessment of habitat quality, as their influence extends beyond the boundaries of the aquatic ecosystem.

Occurrence of common frog (Rana temporaria) and common toad (Bufo bufo) adults and metamorphs in agricultural fields in Germany: Potential for exposure to plant protection products.

To characterize the potential for exposure of amphibian terrestrial life stages to plant protection products (PPP), we studied the occurrence and habitat use of adult and metamorph common frogs (Rana temporaria) and common toads (Bufo bufo) in an agricultural landscape in Germany. The four selected study sites were breeding ponds with approximately 80% agricultural land within a 1-km radius. Adults were monitored by radio tracking for two years, and metamorph numbers were assessed for one summer using pitfall traps alongside drift fences. The results demonstrate that adults were rarely present in arable fields at any of the sites (overall 0.5% and 4% of total observations for frogs and toads, respectively). Metamorph captures in arable fields were more variable, ranging from 1.2% to 38.8% (frogs) and from 0.0% to 26.1% (toads) across study sites. Unsurprisingly, most captures in arable fields for both toad and frog metamorphs occurred at the site where the pond was completely surrounded by arable fields. Overall, the presence of adult amphibians in arable fields was limited and, for the metamorphs, occurred primarily when crops were denser and PPP spray interception higher. Diurnal hiding behavior was observed with the highest activity recorded at night, further reducing the risk of dermal exposure from direct PPP overspraying. In addition, it appeared that alternative habitats, such as woody structures or water bodies in the broader surrounding area, were preferred by the animals over the arable areas. The use of buffer zones around water bodies in agricultural areas would be an effective risk mitigation measure to protect terrestrial adults and metamorphs residing there and would reduce spray drift entry into water bodies during PPP application. It is hoped that these results will contribute to the discussion of risk assessment and mitigation options for amphibians. Integr Environ Assess Manag 2024;20:2218-2230. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Utilization of temperature-mediated activation of thyroid hormone-induced molecular memory to evaluate early signaling events in the olfactory epithelium of Rana [Lithobates] catesbeiana tadpoles

The amphibian olfactory system is highly distinct between aquatic tadpole and terrestrial frog life stages and therefore must remodel extensively during thyroid hormone (TH)-dependent metamorphosis. Developmentally appropriate functioning of the olfactory epithelium is critical for survival. Previous studies in other Rana [Lithobates] catesbeiana premetamorphic tadpole tissues showed that initiation of TH-induced metamorphosis can be uncoupled from execution of TH-dependent programs by holding tadpoles in the cold rather than at warmer permissive temperatures. TH-exposed tadpoles at the nonpermissive (5 °C) temperature do not undergo metamorphosis but retain a “molecular memory” of TH exposure that is activated upon shift to a permissive warm temperature. Herein, premetamorphic tadpoles were held at permissive (24 °C) or nonpermissive (5 °C) temperatures and injected with 10 pmoles/g body weight 3,5,3′-triiodothyronine (T3) or solvent control. Olfactory epithelium was collected at 48 h post-injection. RNA-sequencing (RNA-Seq) and reverse transcriptase quantitative real-time polymerase chain reaction (RT-qPCR) analyses generated differentially expressed transcript profiles of 4328 and 54 contigs for permissive and nonpermissive temperatures, respectively. Translation, rRNA, spliceosome, and proteolytic processes gene ontologies were enriched by T3 treatment at 24 °C while negative regulation of cell proliferation was enriched by T3 at 5 °C. Of note, as found in other tissues, TH-induced basic leucine zipper-containing protein-encoding transcript, thibz, was significantly induced by T3 at both temperatures, suggesting a role in the establishment of molecular memory in the olfactory epithelium. The current study provides critical insights by deconstructing early TH-induced induction of postembryonic processes that may be targets for disruption by environmental contaminants.

Experimental warming and drying act independently on developmental responses for two amphibian species

AbstractClimate change is affecting freshwater habitats worldwide through multiple, interacting pressures that influence the survival, distribution, and persistence of freshwater organisms. Temporary freshwater habitats, or those that dry seasonally, can exhibit wide‐ranging variability in temperature and drying regimes. Aquatic organisms with complex life cycles (e.g., aquatic and terrestrial life stages) often rely on temporary freshwaters to complete their life cycles and have specific adaptations to cope with these dynamic environments. However, climate change is altering the temperature and drying regime of many temporary freshwater habitats worldwide, often resulting in warmer habitats available for shorter durations of time. The ways in which climate‐mediated changes to temporary freshwaters affect development and life history of aquatic organisms, particularly those with complex life cycles, remains poorly understood.We investigated larval development, growth, survival, and relationships among them for two amphibian species, wood frogs (Lithobates sylvaticus) and spring peepers (Pseudacris crucifer), in response to warming and drying in a mesocosm experiment. Over 13 weeks in the spring and summer of 2019, we manipulated temperature and water levels in 48 outdoor pond mesocosms to produce four treatments: control (ambient conditions), drying alone, warming alone, and drying + warming. We predicted reduced survival, body size, and time to metamorphosis for both species in response to warming and drying, with the effect being stronger on wood frogs due to their more specialised habitat use and shorter breeding period.Warming treatments were on average 2°C higher than controls, and drying treatments decreased water depth by 2.5 cm each week. We found that warming temperature shortened larval time to metamorphosis, and drying decreased body size at metamorphosis. Surprisingly, we also found that, across all treatment groups, individuals with early metamorphosis tended to be larger in size and from mesocosms with generally higher survival.Our study indicates that warming and drying may act independently on different developmental responses for amphibians. Our results echo recent calls for a better understanding of the nuanced, often unpredictable, relationships among climate‐mediated environmental pressures and the developmental traits they influence, particularly for organisms with complex life cycles that depend upon dynamic habitat for growth and survival. Understanding these relationships and the mechanisms that drive them will be key to predicting the response of freshwater organisms to climate change.

Savanna vegetation increase triggers freshwater community shifts.

Tropical savannas are globally extensive and ecologically invaluable ecosystems. As most ecosystems however, they are subject to serious anthropogenic stress. Defaunation, and especially the loss of large mammals, is pervasive in tropical savannas and known to trigger wide-ranging ecological effects, from vegetation changes to the loss of ecosystem function. Despite what is currently known about the terrestrial consequences of defaunation, and the potential cross-ecosystem influence of large mammals, virtually no research has investigated associated effects on small adjacent water bodies. This research gap persists because (1) tropical savannas have been historically neglected, (2) the ecological value of small water bodies (e.g. ponds) is only recently being recognized, and (3) empirical baseline data are often lacking. In this paper, we compared a rare pre-change dataset with newly collected data on 213 freshwater assemblages, to investigate community structure and composition before and after a major defaunation event. Our research focused on a diverse species assemblage of amphibian larvae (i.e. tadpoles) in temporary savanna ponds. We found that pond vegetation cover increased from 16.0% to 45.6% post-defaunation, that is, a near three-fold increase. Such habitat changes seemed to have benefitted those species that use vegetation during reproduction (e.g. the leaf-folding Afrixalus spp.), while others have declined. Interestingly, we found a strong correlation between tadpole community shifts and other freshwater organisms, which indicates that habitat changes have affected a wide variety of aquatic organisms. Given that organisms inhabiting temporary aquatic habitats often have complex life histories with terrestrial adult life stages, we propose that the terrestrial effects of defaunation have indirectly led to distinct aquatic communities, in addition to direct habitat effects. These results shed new light on the potential role of large-bodied mammals in shaping adjacent ecosystems, and raise important questions concerning the functioning of temporary aquatic systems in the Anthropocene.

Bioaccumulation and bioamplification of pharmaceuticals and endocrine disruptors in aquatic insects

Environmental fate of emerging contaminants such as pharmaceuticals and endocrine disrupting compounds at the aquatic terrestrial boundary are largely unexplored. Aquatic insects connect aquatic and terrestrial food webs as their life cycle includes aquatic and terrestrial life stages, thus they represent an important inter-habitat linkage not only for energy and nutrient flow, but also for contaminant transfer to terrestrial environments. We measured the concentrations of pharmaceuticals and endocrine disrupting compounds in the larval and adult tissues (last larval stages and teneral adults) of five Odonata species sampled in a wastewater-impacted river, in order to examine their bioaccumulation and bioamplification at different taxonomic levels. Twenty different compounds were bioaccumulated in insect tissues, with majority having higher concentrations (up to 90% higher) in aquatic larvae compared to terrestrial adults (reaching 88 ng/g for 1H-benzotriazole). However, increased concentration in adults was observed for seven compounds in at least one suborder (41% of the accumulated), confirming contaminants bioamplification across the metamorphosis. Both, bioaccumulation and bioamplification differed at various taxa levels; the order (Odonata), suborder (Anisoptera and Zygoptera) and species level. Highest variability was observed between Anisoptera and Zygoptera, due to the underlying differences in their ecology. Generally, Zygoptera had higher concentrations of contaminants in both larvae and adults. Additionally, we aimed at predicting effects of contaminant properties on bioaccumulation and bioamplification patterns using the commonly used physicochemical and pharmacokinetic descriptors on both order and suborder levels, however, neither of the two processes could be consistently predicted with simple linear models. Our study highlights the importance of taxonomy in studies aiming at advancing the understanding of contaminant exchange between aquatic and terrestrial food webs, as higher taxonomic categories include ecologically diverse groups, whose contribution to “the dark side of subsidies” could substantially differ.

Navigating the trade‐offs between environmental DNA and conventional field surveys for improved amphibian monitoring

AbstractThe need for efficient, accurate biodiversity monitoring is growing, especially for globally imperiled taxa, such as amphibians. Environmental DNA (eDNA) analysis holds enormous potential for enhancing monitoring programs, but as this tool is increasingly adopted, it is imperative for users to understand its potential benefits and shortcomings. We conducted a comparative study to evaluate the efficacy of two eDNA methodologies (quantitative (q)PCR and metabarcoding) and conventional field sampling approaches (seining, dipnetting, and visual encounter surveys) in a system of 20 ponds containing six different amphibian species. Using an occupancy modeling framework, we estimated differences in detection sensitivity across methods, with a focus on how eDNA survey design could be further optimized. Overall, both metabarcoding and qPCR were competitive with or improved upon conventional methods. Specifically, qPCR (species‐specific approach) was the most effective technique for detecting two rare species, the California tiger salamander (Ambystoma californiense) and California red‐legged frog (Rana draytonii), with a detection probability of >0.80 per survey. Metabarcoding (community approach) estimated amphibian diversity with comparable rates to field techniques on average, and detected an additional 41 vertebrate taxa. However, for two abundant species (western toads, Anaxyrus boreas, and Pacific chorus frogs, Pseudacris regilla), field techniques outperformed metabarcoding, especially as individuals metamorphosed. Our results indicate that eDNA approaches would be most effective when paired with visual encounter surveys to detect terrestrial life stages, and that more optimization, specifically primer choice and validation, is needed. By comparing methods across a diverse set of ponds and species, we provide guidance for future studies integrating eDNA approaches into amphibian monitoring.

Skin Wound Healing of the Adult Newt, Cynops pyrrhogaster: A Unique Re-Epithelialization and Scarless Model.

In surgical and cosmetic studies, scarless regeneration is an ideal method to heal skin wounds. To study the technologies that enable scarless skin wound healing in medicine, animal models are useful. However, four-limbed vertebrates, including humans, generally lose their competency of scarless regeneration as they transit to their terrestrial life-stages through metamorphosis, hatching or birth. Therefore, animals that serve as a model for postnatal humans must be an exception to this rule, such as the newt. Here, we evaluated the adult newt in detail for the first time. Using a Japanese fire-bellied newt, Cynops pyrrhogaster, we excised the full-thickness skin at various locations on the body, and surveyed their re-epithelialization, granulation or dermal fibrosis, and recovery of texture and appendages as well as color (hue, tone and pattern) for more than two years. We found that the skin of adult newts eventually regenerated exceptionally well through unique processes of re-epithelialization and the absence of fibrotic scar formation, except for the dorsal-lateral to ventral skin whose unique color patterns never recovered. Color pattern is species-specific. Consequently, the adult C. pyrrhogaster provides an ideal model system for studies aimed at perfect skin wound healing and regeneration in postnatal humans.

Conservation Implications of Spatiotemporal Variation in the Terrestrial Ecology of Western Spadefoots

ABSTRACTConservation of species reliant on ephemeral resources can be especially challenging in the face of a changing climate. Western spadefoots (Spea hammondii) are small burrowing anurans that breed in ephemeral pools, but adults spend the majority of their lives underground in adjacent terrestrial habitat. Western spadefoots are of conservation concern throughout their range because of habitat loss, but little is known about the activity patterns and ecology of their terrestrial life stage. We conducted a radio‐telemetry study of adult western spadefoots at 2 sites in southern California, USA, from December 2018 to November 2019 to characterize their survival, behavior, and movements from breeding through aestivation to refine conservation and management for the species. Western spadefoot survival varied seasonally, with risk of mortality higher in the active season than during aestivation. The probability of movement between successive observations was higher during the winter and spring and when atmospheric moisture was high and soil water content at 10‐cm depth was low. The amount of rain between observations had the strongest effect on the probability of movement between observations; for every 20 mm of rainfall between observations, western spadefoots were 2.4 times more likely to move. When movements occurred, movement rates were highest when both relative humidity and soil water content at 10‐cm depth were high. The conditions under which western spadefoots were likely active on the surface, likely to have moved, and moved at the highest rates are conditions that reduce the risk of desiccation of surface‐active spadefoots. Western spadefoot home range areas varied between study sites and were mostly <1 ha, although 1 individual's home range area was >6 ha. Western spadefoots rapidly dispersed from the breeding pools, and asymptotic distances from the breeding pool were generally reached by June. The asymptotic distance from the breeding pool varied between sites, with the 95th percentile of the posterior predictive distribution reaching 486 m at 1 site and 187 m at the other. Western spadefoots did not select most habitat components disproportionately to their availability, but at Crystal Cove State Park, they avoided most evaluated vegetation types (graminoids, forbs, and shrubs). Spatial variation was evident in most evaluated western spadefoot behaviors; context‐dependent behavior suggests that site‐specific management is likely necessary for western spadefoots. Furthermore, comparison with an earlier study of western spadefoots at Crystal Cove State Park indicated substantial temporal variation in western spadefoot behavior. Therefore, basing management decisions on short‐term studies might fail to meet conservation objectives. Better understanding the influences of spatial context and climatic variation on western spadefoot behavior will improve conservation efforts for this species. © 2021 This article is a U.S. Government work and is in the public domain in the USA. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.

Resource selection and movement of the coastal tailed frog in response to forest harvesting

The coastal tailed frog (Ascaphus truei) has a biphasic life-history that includes the use of montane streams adjacent to mature old growth forests. This species is at risk from a variety of land-use activities, including forest harvesting, that results in younger and more fragmented terrestrial habitats. Post-metamorphic tailed frogs are cryptic and difficult to capture, making for few studies of the terrestrial life stage of the species. At the northern extent of the species’ range, we investigated the spatial ecology of tailed frogs across riparian and adjacent upland forest in three forest types: mature to old unharvested, streamside forest retention, and clearcut. Post-metamorphic frogs were fitted with Very High Frequency radio transmitters and monitored for an average of 10.75 days (SE 0.89). Females moved further from their origin of capture during the monitoring period (x¯= 68.89 m, SE 16.3) when compared to males (x¯= 36.85 m, SE 7.9). We used Resource Selection Functions to quantify habitat selection of female and male tailed frogs. Monitored frogs were positively associated with habitats containing well-decayed coarse woody debris (≥ 7.5 cm diameter), less ambient light, adjacency to the larval stream, hygric and subhygric microsites, and cool temperatures (11–12 °C). Females were more selective in their choice of habitat than males. Overall, the relationship between distribution and activity of tailed frogs was reflective of the sex of the frog in combination with microsite or broader climatic conditions ameliorated by stand-level habitat conditions. Our data suggest that habitat management for post-metamorphic tailed frogs focus on the retention of both streamside (within 40 m) and upland forest (> 50 m from larval stream), as well as stand-level attributes such as hygric and subhygric microsites, and coarse woody debris with advanced decay.

Vulnerability of Aquatic Insect Species to Insecticides, Depending on Their Flight Period and Adult Life Span.

Effects of insecticides on terrestrial adult life stages of otherwise aquatic insects, such as mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera), are largely unknown. In the present study, a risk model was used to pinpoint the species most likely to experience effects due to spray drift exposure during the adult life stage. Using data from an earlier case study with lambda-cyhalothrin, 6 species with different life cycle traits were used to explore how life cycle characteristics may influence vulnerability. In addition, we performed a generic calculation of the potential effect on the terrestrial life stages of 53 species (including 47 species with unknown sensitivity). Our approach incorporated temporal and spatial distribution of both the insect and the insecticide, creating different exposure conditions among species due to variation in the relative proportion of the populations present at the time of insecticide spraying. The Ephemeroptera species represented were least vulnerable due to their extremely short adult life span and relatively short flight period. Based on their life cycle characteristics, Plecoptera and Trichoptera species were more vulnerable. These vulnerable species segregated into 2 distinct groups; one with a long adult life span to emergent period ratio and another with a high overlap between emergent period and spraying season. We therefore recommend that future ecotoxicological tests be done on species with these life cycle characteristics. Environ Toxicol Chem 2021;40:1778-1787. © 2021 SETAC.

Conservation Across Aquatic-Terrestrial Boundaries: Linking Continental-Scale Water Quality to Emergent Aquatic Insects and Declining Aerial Insectivorous Birds

Larval aquatic insects are used to assess water quality, but less attention is paid to their adult, terrestrial life stage, which is an important food resource for declining aerial insectivorous birds. We used open-access water-quality, aquatic-invertebrate, and bird-survey data to study how impaired water quality can emanate from streams and lakes through changes in aquatic insect communities across the contiguous United States. Emergent insect relative abundance was highest across the West, in northern New England, and the Carolinas in streams, and highest near the Great Lakes, parts of the Southwest, and northern New England for lakes. Emergent insects declined with sedimentation, roads, and elevated ammonium concentrations in streams, but not lakes. The odds that a given taxon would be non-emergent increased by up to 2.0× as a function of pollution tolerance, underscoring the sensitivity of emergent aquatic insects to water-quality impairment. However, relationships between bird populations and emergent insects were generally weak for both streams and lakes. For streams, we observed the strongest positive relationships for a mixture of upland and riparian aerial insectivorous birds such as Western Wood-Pewee, Olive-sided Flycatcher, and Acadian Flycatcher and the strongest negative association for Purple Martin. Different avian insectivores responded to emergent insect abundances in lakes (e.g., Barn Swallow, Chimney Swift, Eastern Wood-Pewee, Common Nighthawk). In both streams and lakes, we observed stronger, but opposing, relationships between several aerial insectivores and the relative abundance of sensitive insect orders (E)phemeroptera, (P)lecoptera, and (T)richoptera (positive), and pollution tolerant individuals (negative). Overall, our findings indicate that emergent insects are negatively correlated with pollution tolerance, suggesting a large-scale loss of this nutritional subsidy to terrestrial environments from impaired aquatic ecosystems. While some bird populations tracked scarcities of emergent aquatic insects, especially EPT taxa, responses varied among species, suggesting that unique habitat and foraging behaviors likely complicated these relationships. Strengthening spatial and temporal concordance between emergent-insect and bird-survey data will improve our ability to interpret species-level responses over time. Thus, our analysis highlights the need for developing conservation and biomonitoring strategies that consider the cross-ecosystem effects of water quality declines for threatened insectivorous avifauna and other terrestrial wildlife.

Holo- and hemimetabolism of aquatic insects: Implications for a differential cross-ecosystem flux of metals.

Increased metal concentrations in aquatic habitats come as a result of both anthropogenic and natural sources. Emerging aquatic insects that play an indispensable role in these environments, transferring resources and energy to higher trophic levels in both aquatic and terrestrial habitats, may inadvertently also act as biovectors for metals and other contaminants. This study measured levels of 22 different metals detected in biofilm, aquatic and terrestrial life stages of Trichoptera and Odonata, as well as riparian spiders, to examine the uptake and transfer from freshwater to terrestrial ecosystems. We show that emerging insects transfer metals from aquatic to terrestrial ecosystems, however with large losses observed on the boundary of these two environments. Significantly lower concentrations of most metals in adult insects were observed in both hemimetabolous (Odonata) and holometabolous insect orders (Trichoptera). In holometabolous Trichoptera, however, this difference was greater between aquatic life stages (larvae to pupae) compared to that between pupae and adults. Trophic transfer may have also played a role in decreasing metal concentrations, as metal concentrations generally adhered to the following pattern: biofilm>aquatic insects>terrestrial invertebrates. Exceptions to this observation were detected with a handful of essential (Cu, Zn, Se) and non-essential metals (Cd, Ag), which measured higher concentrations in adult aquatic insects compared to their larval counterparts, as well as in aquatic and terrestrial predators compared to their prey. Overall, all metals were found to be bioavailable and biotransferred from contaminated waters to terrestrial invertebrates to some degree, suggesting that risks associated with metal-contaminated freshwaters could extend to terrestrial systems through the emergence of these potential invertebrate biovectors.

Plants, water quality and land cover as drivers of Odonata assemblages in urban ponds

As cities expand, urban ecosystems could either contribute to or impede conservation efforts. To maximize the potential for urban areas to support biodiversity, there is a need to understand how systems in an urban environment can sustain the natural history requirements of species. This study compared the relative importance of local-scale factors (plant communities and water quality) to landscape factors (surrounding land cover) in structuring assemblages of a recognized group of wetland bioindicators. Odonata (dragonflies and damselflies), at both the adult and larval life stages, along with plant communities, pond water quality and surrounding land cover types were sampled at 51 ponds across a north temperate metropolitan area. Plant communities (particularly of wetland species) consistently explained the largest amount of variation in both dragonfly and damselfly community structure at all life stages. Pond water quality was of secondary importance for both aquatic and terrestrial life stages, with dragonflies more negatively affected by urban contaminants than damselflies. Overall, surrounding land cover types in pond catchments explained less variation in Odonata community structure, especially in the case of damselflies. However, the presence of adjacent ponds and wetlands had a measurable effect. Plant, water quality and land cover variables together explained as much as half of the variation in Odonata community structure at ponds. Urban ponds could potentially provide high quality habitat for species when designed and managed to promote native wetland plant communities and water quality is maintained.

Added Value: Gopher Tortoise Surveys Provide Estimates of Gopher Frog Abundance in Tortoise Burrows

AbstractThe gopher frog Lithobates capito is one of the most terrestrial frogs in the southeastern United States and often inhabits gopher tortoise burrows Gopherus polyphemus outside of the breeding season. Gopher frog populations have declined, and the species is under review for listing as threatened or endangered under the U.S. Endangered Species Act. Much of our knowledge on the status of gopher frogs is based on detections of larvae at breeding wetlands, which can be challenging because of environmental variability and provides no information on the terrestrial life stages of the species. Therefore, an alternative method is called for. We recorded observations of gopher frogs during gopher tortoise surveys at four conservation lands in Florida and used line-transect distance sampling to estimate frog abundance. We also recorded burrow size, incidence of frog co-occupancy with tortoises, and distance from frog-occupied burrows to breeding wetlands. We observed 274 gopher frogs in 1,097 tortoise burrows at the four sites. The proportion of burrows occupied by gopher frogs among sites ranged from 0.17 to 0.25. Gopher frog abundance in tortoise burrows was 742 (512–1,076 95% CL) at Etoniah Creek State Forest, 465 (352–615) at Ft. White Wildlife Environmental Area, 411 (283–595) at Mike Roess Gold Head Branch State Park, and 134 (97–186) at Watermelon Pond Wildlife Environmental Area. We observed up to four frogs in a single burrow. The proportion of frogs detected in burrows occupied by a gopher tortoise ranged from 0.46 to 0.79 among sites, and overall, gopher frogs preferred burrows occupied by tortoises over unoccupied burrows (χ2 = 15.875; df = 3; P = 0.001). Gopher frogs used burrows from 7 to 43 cm in width; mean width of frog-occupied burrows did not differ from that of unoccupied burrows (F1,3 = 0.049, P = 0.825). Distance from frog-occupied tortoise burrows to the nearest breeding wetland ranged from 141 to 3,402 m. Our data on gopher frogs collected in conjunction with gopher tortoise monitoring efforts using line-transect distance sampling and burrow cameras provided novel information on frog abundance in their terrestrial habitat and required no additional effort. However, the extent to which frogs use tortoise burrows relative to other available refuges (small mammal burrows, stumps, or other structures) is unknown; thus, our estimates should be considered conservative. We suggest that terrestrial abundance estimates for gopher frogs can complement efforts to monitor breeding activity to provide a more comprehensive means of monitoring population trends in this cryptic species.

Pesticide risk indicator for terrestrial adult stages of aquatic insects

Many taxonomic groups of freshwater insects have a reproductive terrestrial life stage, and some are highly sensitive to insecticides. In agricultural landscapes, it is likely that streams and rivers often run along agricultural fields treated with pesticides, but the risk to insects with a reproductive terrestrial life stage due to pesticide exposure is not well-covered by existing risk indicators. Different aquatic insect species may have different strategies for feeding and mating and, thus, different spatial and temporal distribution of the terrestrial abundance. This influences the fraction of individuals that can suffer from pesticide exposure, and thus the risk indicator in this paper includes spatial and temporal distributions of both insect abundance and air born pesticide deposition, in this case multiplied together and weighted with toxicity. The indicator is denoted Adult Stage Risk Indicator, ASRIi,j, and can be calculated for every combination of insect taxon i, and pesticide active ingredient j. An Excel/VBA based model is available as Supplementary material. However, setting up the indicator using another platform is simple, and for any application please refer to this paper.

Cross-ecosystem bottlenecks alter reciprocal subsidies within meta-ecosystems.

Reciprocal subsidies link ecosystems into meta-ecosystems, but energy transfer to organisms that do not cross boundaries may create sinks, reducing reciprocal subsidy transfer. We investigated how the type of subsidy and top predator presence influenced reciprocal flows of energy, by manipulating the addition of terrestrial leaf and terrestrial insect subsidies to experimental freshwater pond mesocosms with and without predatory fish. Over 18 months, fortnightly addition of subsidies (terrestrial beetle larvae) to top-predators was crossed with monthly addition of subsidies (willow leaves) to primary consumers in mesocosms with and without top predators (upland bullies) in a 2 × 2 × 2 factorial design in four replicate blocks. Terrestrial insect subsidies increased reciprocal flows, measured as the emergence of aquatic insects out of mesocosms, but leaf subsidies dampened those effects. However, the presence of fish and snails, consumers with no terrestrial life stage, usurped and retained the energy within in the aquatic ecosystem, creating a cross-ecosystem bottleneck to energy flow. Thus, changes in species composition of donor or recipient food webs within a meta-ecosystems can alter reciprocal subsidies through cross-ecosystem bottlenecks.

Microcystin in multiple life stages of Hexagenia limbata, with implications for toxin transfer

Microcystins are present in some aquatic organisms, but the potential transfer to and accumulation in terrestrial organisms is less understood. We measured microcystin concentrations in multiple terrestrial life stages of Hexagenia limbata to determine whether this cyanotoxin is transferred from one life stage to another and if H. limbata subimagos and imagos transport the algal toxin microcystin into terrestrial systems. Hexagenia limbata (n = 43) were hand collected from the shore of a low-nutrient lake with a history of Microcystis aeruginosa, located in Michigan’s Lower Peninsula. We quantified microcystin concentrations in H. limbata with enzyme linked immunosorbent assay (n = 39), with a subset verified with high performance liquid chromatography tandem mass spectrometry (n = 8, including duplicates). Microcystin ranged from the method limit of detection (MLOD) to 0.64 µg/g dry weight with detectable concentrations in subimagos, imagos, and spent females, indicating a potential for transport of this toxin to terrestrial systems. These data indicate that emerging aquatic insects are a potential vector for the transfer of microcystins from aquatic to terrestrial food webs and may pose a threat in and around systems with both H. limbata and more extensive blooms of M. aeruginosa.

Nanoparticles transported from aquatic to terrestrial ecosystems via emerging aquatic insects compromise subsidy quality

Nanoparticle contaminants enter aquatic ecosystems and are transported along the stream network. Here, we demonstrate a novel pathway for the return of nanoparticles from aquatic to terrestrial ecosystems via cross-boundary subsidies. During their emergence, trichopteran caddisflies carried titanium dioxide and gold nanoparticles into their terrestrial life stages. Moreover, their emergence was delayed by ≤30 days, and their energy reserves were depleted by ≤25%. Based on worst case estimates, it is suggested that terrestrial predators, such as bats feeding on aquatic prey, may ingest up to three orders of magnitude higher gold levels than anticipated for humans. Additionally, terrestrial predator species may suffer from alterations in the temporal availability and nutritional quality of their prey. Considering the substantial transfer of insect biomass to terrestrial ecosystems, nanoparticles may decouple aquatic and terrestrial food webs with important (meta-)ecosystem level consequences.

Retention of cervical and abdominal gills in the adult of a new fossil stonefly (Insecta, Plecoptera, Petroperlidae) from mid-Cretacous Burmese amber

A new stonefly genus and species, Branchioperla ianstewarti gen. et sp. nov., is described based on a single adult female specimen from mid-Cretaceous Burmese amber, and attributed to the extinct family Petroperlidae. Its high extent of adult gill retention is a remarkable morphological trait exhibited by the new species. Although the specimen described herein represents a winged terrestrial life stage, it retains tufts of branched gill filaments similar to larval gills on several body parts, including the first eight abdominal segments; a pattern which is unique within the order Plecoptera. The extent of adult gill remnants is evaluated as highly variable within Petroperlidae, probably subject to selective pressures resulting from microhabitat partitioning among various species of this Cretaceous family.