Southeastern United States Coastal Research Articles

Snapshots of Coastal Ecology Using Multiproxy Analysis Reveals Insights Into the Preservation of Swamp and Marsh Environments Since the Late Pleistocene

AbstractThe southeastern United States Coastal Plain ecosystem contains baldcypress (Taxodium distichum) swamps and grass‐dominated marshes. These ecosystems also occurred on the exposed continental shelf during lower sea levels but are rarely preserved due to the mechanically erosive nature of transgression and regression. Two presently marine sites on the northeastern Gulf of Mexico's continental shelf contain well‐preserved woody terrestrial sediments that were the subject of previous studies. This study continues the investigation using geochemical (δ13C, δ15N, δ34S) and palynological characteristics of these formerly terrestrial sediments to determine if swamps and/or marshes existed at the time of deposition. The first site is located ∼20 km southeast of Horn Island, Mississippi (MS) and the core has terrestrial sediments radiocarbon dated to 11,066–10,228 (2σ) calibrated years BP (early Holocene). The second site is the “Alabama Underwater Forest” located ∼13 km south of Gulf Shores, Alabama (AL) and the cores have terrestrial sediments optically stimulated luminescence dated to 63 ka (±10 ka, 2σ) to 72 ka (±16 ka, 2σ) (late Pleistocene). Geochemical results for the MS sediments indicate a swamp‐to‐freshwater marsh transitional series, whereas the AL sediments indicate a swamp‐to‐saltwater marsh transitional series, both supported by palynological results. Further exploration of the geochemical results using linear discriminant analysis, trained with published geochemical data, supports the swamp and marsh interpretations. We conclude that the near‐pristine preservation of these woody deposits is not solely due to physical mechanisms, such as rapid burial, but is also coupled with anoxia‐ and euxinia‐driven biogeochemical reactions promoting wood and woody debris preservation in swamp and marsh environments.

Bat winter foraging habitat use in working forests: a multispecies spatial occupancy approach

AbstractInsectivorous bats in temperate zones have evolved strategies such as migration or hibernation to overcome challenges of reduced resource availability and increased energy demand during winter. In the southeastern United States Coastal Plain, bats are either year‐round residents and remain active during winter or are migrants from colder areas seeking milder temperatures. Southeastern Coastal Plain forests also may represent important areas for remnant populations of species impacted by white‐nose syndrome. Working pine (Pinus spp.) forests comprise a large proportion of southeastern Coastal Plain forests, yet winter bat habitat associations and how forest management affects bat use remain understudied. Hence, we used hierarchical multispecies spatial occupancy models to evaluate factors influencing winter bat occupancy and foraging habitat associations in working forests of the southeastern Coastal Plain. From January to March 2020–2022, we deployed Anabat Swift acoustic detectors and measured site‐ and landscape‐level covariates on six working landscapes. We detected five species of bats and three species groups at 93% (224/240) of sites. We observed higher species richness at sites with high proportions of contiguous forest and low levels of basal area. At the species level, occupancy patterns were influenced by site and landscape covariates, which had varying effects on species with distinct foraging strategies. Temperature was an important predictor of detectability. Our findings offer new insights into the ecology of bats in working forest landscapes during winter, where we highlight positive responses in occupancy with contiguous forests and lower levels of basal area, as in previous summer work. By providing valuable information on winter community composition and foraging habitat associations, we hope to guide management decisions for forest attributes important to these species, thus increasing conservation opportunities within working forests.

Unraveling Siren (Caudata: Sirenidae) systematics and description of a small, seepage specialist.

For approximately four decades, scientists have known of the existence of several undescribed species of Siren in the southeastern United States Coastal Plain. One of these species, S. reticulata, was recently described, but a small, seepage-dwelling species has remained undescribed until now. To resolve outstanding questions concerning the phylogeny of Siren, we collected sequence and morphometric data from specimens across the range of Siren. We found S. lacertina and S. reticulata to represent strongly supported monophyletic groups, with S. reticulata having a sister relationship to all other Siren. Additionally, we found five distinct mtDNA lineages within what has been recognized as S. intermedia. Siren lacertina and type-locality S. intermedia (lineage A) are sister mtDNA lineages, whereas S. intermedia lineages B and C show a high level of mitogenomic divergence from type-locality S. intermedia. Analyses of two scnDNA loci revealed that S. lacertina is monophyletic but nested with low positional support in a clade including the three S. intermedia mtDNA lineages. Further study is needed to determine whether S. intermedia lineages A, B, and C represent distinct species or incompletely sorted lineages. We restrict the range of S. intermedia to the region from the Escambia and Perdido river drainages of Florida and Alabama eastward through Virginia (the combined ranges of lineages A, B, and C). We also elevate S. i. nettingi (lineage E) to species status and include the larger S. i. texana form in that taxon, generating a species that occurs from the Mobile Bay drainages westward through the Mississippi Basin and southwest into northeastern Mexico. Lastly, we describe a new miniature species, S. sphagnicola, that ranges from the Florida Parishes of Louisiana eastward to the westernmost tributary creeks of Choctawhatchee Bay in the western Florida panhandle.

The Use of Airborne LiDAR in Assessing Coastal Erosion in the Southeastern USA

Changes in sea level along the coastal southeastern United States (U.S.) influence the dynamic coastal response. In particular, the Southeast Coastal Network (SECN) of the National Park Service (NPS) has exhibited evidence of fluctuations in sea level which caused coastal erosion. Airborne LiDAR acquired from NOAA for Fort Matanzas National Monument, Fort Pulaski National Monument, Charles Pinckney National Historic Site, and Cape Lookout National Seashore were analyzed to identify changes in both elevation and the spatial volume of unconsolidated sedimentary material in the coastal southeast over time. Areas that exhibited an increase (deposited material) or decrease (eroded material) in elevation were mapped across the study area from 2006 to 2018. Results indicate a quasi-cyclic process where unconsolidated sediment distribution and the morphodynamic equilibrium changes with time. The coastal zones are steadily oscillating between the process of erosion and deposition affecting the coastal geomorphological dynamic. The use of LiDAR for evaluating coastal sustainability and resiliency due to this environmental phenomenon is clear.

A new, narrowly endemic species of swamp-dwelling dusky salamander (Plethodontidae: Desmognathus) from the Gulf Coastal Plain of Mississippi and Alabama.

We describe a new, narrowly endemic species of swamp-dwelling dusky salamander (Plethodontidae: Desmognathus pascagoula sp. nov.) from the Gulf Coastal Plain of southeastern Mississippi and southwestern Alabama based on linear morphometrics, mitochondrial DNA, and single nucleotide polymorphisms from 881 loci produced using genotype-by-sequencing. Some populations of the new species were historically referred to as D. auriculatus, a polyphyletic assemblage of at least three species in the Atlantic and Gulf Coastal Plain from Texas to North Carolina. Populations of D. auriculatus from the Gulf Coastal Plain in Louisiana and Mississippi were recently described as D. valentinei. The new species includes populations that were tentatively referred to D. valentinei, but we find it is morphologically, genetically, and geographically distinct. It is smaller, has a more defined dorsal color pattern, more irregular whitish portholes in up to three rows on the lateral surfaces of the body and tail, and a brighter orange or yellowish orange postocular stripe. At present, the new species is known from only six extant populations in the lower Pascagoula, Escatawpa, and Mobile drainages. The latter represents a distinct phylogeographic lineage. We also refer a historical collection from the northeastern side of the Mobile-Tensaw River Delta to this species, suggesting a much broader range in the past. We suspect that more populations remain to be discovered in the area, and their potential species-level distinctiveness should be tested further. This discovery increases knowledge of the biodiversity in the southeastern United States Coastal Plain, a candidate region meeting the global criteria for a biodiversity hotspot, and underscores the amount of cryptic diversity likely remaining to be discovered and described in Nearctic salamanders.

Influence of landscape and vegetation characteristics on herpetofaunal assemblages in Gulf Coastal Plain pine forests

AbstractLongleaf pine (Pinus palustris) savanna characterized by open‐canopy, diverse herbaceous vegetation, and high amounts of bare soil once covered much of the southeastern United States Coastal Plain. The unique structural and vegetative conditions of this ecosystem support endemic reptiles and amphibians that have declined as longleaf pine forests have been lost or degraded. Private working pine (Pinusspp.) forests managed for timber production now occur throughout the southeastern United States and have replaced much of the historical longleaf pine savanna. The examination of herpetofaunal (reptile, amphibian) communities in private working loblolly pine (P. taeda) landscapes, particularly in the western Gulf Coastal Plain is lacking. Using repeated field surveys and hierarchical community occupancy models, we examined occupancy and species richness of herpetofauna across 81 sites spanning gradients of management practices, vegetative conditions, and soil composition in northwestern Louisiana, USA, 2017–2019. Young pine stands (<6 yr) exhibited structural characteristics most similar to mature longleaf pine reference sites (>30 yr), while mid‐aged stands (13–26 yr) often featured closed canopy and dense midstory. Vegetation conditions varied widely depending on landscape characteristics and site‐specific disturbance regimes. We documented 43 species of herpetofauna, including 9 open‐pine‐associated species. Occupancy of open‐pine‐associated herpetofauna was positively associated with open‐canopy and understory conditions, and sandy soil area. Sites providing open‐canopy conditions were often occupied by open‐pine‐associated species regardless of overstory type and disturbance method. Overall richness of herpetofauna was greatest at sites with moderate canopy cover outside of sandy soil regions. Working pine landscapes in the western Gulf Coastal Plain can support diverse herpetofaunal assemblages, including open‐pine‐associated species, when management practices maintain open‐canopy conditions on sandy, upland soils. More broadly, our results provide insight into how forest management practices affect herpetofauna and may guide practices that can contribute to conservation value of working pine forests.

Discharge and Temperature Controls of Dissolved Organic Matter (DOM) in a Forested Coastal Plain Stream

Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ~30% of total fluorescence. This observation indicates fluorescent DOM (FDOM) was controlled primarily by soil inputs and not substantially influenced by instream production and processing, suggesting that the bulk of FDOM in these streams is transported to downstream environments with limited in situ modification. Linear regression and redundancy analysis models identified that the seasonal variations in DOM were dictated primarily by hydrology and temperature. Overall, high discharge and shallow flow paths led to the enrichment of less-degraded DOM with higher percentages of microbial humic-like and tyrosine-like compounds, whereas high temperatures favored the accumulation of high-aromaticity, high-molecular-weight, terrestrial, humic-like compounds in stream water. The flux of DOC and four fluorescence components was driven primarily by water discharge. Thus, the instantaneous exports of both refractory humic-like DOM and reactive protein-like DOM were higher in wetter seasons (winter and spring). As high temperatures and severe precipitation are projected to become more prominent in the southeastern U.S. due to climate change, our findings have important implications for future changes in the amount, source, and composition of DOM in Coastal Plain streams and the associated impacts on downstream carbon and nutrient supplies and water quality.

Invasive Wild Pigs: A Significant Disturbance in Coastal Forests

Introduced in ~59 countries and native across Europe and Asia, wild pigs, Sus scrofa, are the most wide-spread swine species in the world. As ecosystem engineers, wild pigs are a significant source of disturbance in introduced ecosystems due to their numerous, complex impacts on ecosystem processes. Wild pigs are often found in the resource-rich habitat of coastal forests. Coastal forests are complex, dynamic systems with tremendous biodiversity. Exposed to recurrent disturbances, the biophysical characteristics of coastal forests contribute to their ability to return to their original state post-disturbance. However, compounding disturbances can weaken this ability and threaten the health and function of the ecosystem. In this review, through the model of the forests of the southeastern United States Coastal Plain, we (1) describe conditions found across the forested coastal landscape, (2) describe wild pig disturbance, and (3) discuss how wild pig impacts can add to significant anthropogenic and climate-related disturbances threatening coastal forests. Through this review, we find that the impacts of wild pig disturbance on coastal forests often have similar effects as anthropogenic and climate change-related disturbances that may enhance these significant threats to coastal forest function and resiliency.

Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018

AbstractHarvest may have myriad effects on target species, including a change in population size structure. To assess whether size shifts have occurred among managed coastal species of shark (superorder Selachimorpha), we examined the population size structure of 12 species caught during a nearly five‐decade‐long fishery‐independent survey conducted in Onslow Bay, North Carolina, using standardized longline gear. We evaluated trends in mean fork length (FL), median FL, and index of maximum FL (L90%) for each species separately across time using linear regression models. We also examined trends in size‐classes (200‐mm bins) and catch per unit effort for each species over time. For 10 of the 12 species (excluding sample‐size‐constrained Tiger Shark Galeocerdo cuvier and Bull Shark Carcharhinus leucas), size structure metrics indicated decreasing sizes over time, although statistical confidence for these patterns varied across species and metrics. Strongest statistical support for declining sizes was observed for Blacknose Shark Carcharhinus acronotus (mean FL, median FL, L90%), Dusky Shark Carcharhinus obscurus (L90%), Smooth Dogfish Mustelus canis (L90%), and Atlantic Sharpnose Shark Rhizoprionodon terraenovae (L90%). Magnitude of decreases in L90% among these 10 species during the survey ranged from roughly 9% (Silky Shark Carcharhinus falciformis; 83‐mm decrease) to 35% (Sandbar Shark Carcharhinus plumbeus; 541‐mm decrease). Our findings indicate a potential for fishing pressure to exert directional selection on these coastal shark species, although further research is needed regarding the nature of size‐dependent catchability and species‐specific vital rates to adequately evaluate these dynamics. Furthermore, in addition to the removal of “great sharks,” decreasing sizes of small coastal sharks, such as Blacknose Shark, Smooth Dogfish, and Atlantic Sharpnose Shark (i.e., “mesopredators”), suggest that harvest may have pervasive effects on species throughout this assemblage.

Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018

Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018

Elasmobranch Use of Nearshore Estuarine Habitats Responds to Fine-Scale, Intra-Seasonal Environmental Variation: Observing Coastal Shark Density in a Temperate Estuary Utilizing Unoccupied Aircraft Systems (UAS)

Many coastal shark species are known to use estuaries of the coastal southeastern United States for essential purposes like foraging, reproducing, and protection from predation. Temperate estuarine landscapes, such as the Rachel Carson Reserve (RCR) in Beaufort, NC, are dynamic habitat mosaics that experience fluctuations in physical and chemical oceanographic properties on various temporal and spatial scales. These patterns in abiotic conditions play an important role in determining species movement. The goal of this study was to understand the impact of environmental conditions around the RCR on shark density within the high-abundance summer season. Unoccupied Aircraft System (UAS) surveys of coastal habitats within the reserve were used to quantify shark density across varying environmental conditions. A combination of correlation analyses and Generalized Linear Modelling (GLM) revealed that density differs substantially across study sites and increases with rising water temperatures, conclusions that are supported by previous work in similar habitats. Additionally, density appears to increase moving towards dawn and dusk, potentially supporting crepuscular activity in coastal estuarine areas. By describing shark density dynamics in the RCR, this study provides new information on this population and presents a novel framework for studying elasmobranchs in temperate estuaries.

Public archaeology at Baynard-Zion: bringing life back to an antebellum cemetery

ABSTRACT Heritage tourism is a driving economic force in much of the coastal southeastern United States, including on Hilton Head Island, South Carolina, one of the most popular destinations for vacationers in the country. Working with local community members in developing a diverse and multipronged public archaeology program, we helped facilitate research and develop programing at the Baynard Mausoleum and Zion Chapel of Ease and Cemetery (Baynard-Zion). Built and used during the late eighteenth through mid-nineteenth centuries, Baynard-Zion includes some of the oldest marked graves on the island as well as its oldest standing architecture. Using a constellation of techniques, including geophysical surveys, genetic testing of human remains, and limited excavations, research conducted at Baynard-Zion provides an opportunity to enhance public perception and understanding of pivotal historic events and people on the island while also assisting in development plans that promote heritage tourism.

A Carolina Bay in the Land of the Longleaf Pine

A Carolina Bay in the Land of the Longleaf Pine Evan E. Montpellier Unbeknownst to the majority of North Carolina beachgoers, just a few miles away lies a different kind of bay, a Pleistocene Era landform unique to the coastal southeastern United States. Carolina bays were once lakeshores. While their elevational relief is unassuming (~ 1 to 1.5 meters), they are home to a rich and unique anthropogenic, ecological, and climatological history that is worth exploring. Human presence on Carolina bays in North Carolina dates to the Paleoindian and Archaic periods (Brooks et al. 2015). Artifacts gathered at these sites reveal a history of hunting, ritual life, and temporary habitation (Gillam 2015). When Europeans forcibly settled North America, the longleaf pine trees depicted in this issue's cover photo occupied approximately 36.5 million hectares of the southeastern United States and were not exclusive to Carolina bays (Frost 2006). However, longleaf pine ecosystems became the site of the extractive turpentine industry. Raw sap was collected from longleaf pine trees by cutting notches at the base of the tree, removing its bark, and slashing the tree to force its resin to run. This raw resin was distilled to create turpentine. In the 19th century, turpentine was the South's third largest export with North Carolina accounting for approximately 97 percent of the national market (Outland 1996). Continued slashing, along with logging and modern fire suppression techniques have been responsible for a 97 percent decline in native longleaf pine ecosystems (Frost 2006). While many Carolina bay longleaf woodlands were affected by the turpentine and logging industries, others were spared due to inaccessibility. What remains at such sites are relic ecosystems teeming with biodiversity and mature longleaf pine trees. Redcockaded woodpeckers (RCW), a keystone species for longleaf pine ecosystems, are currently listed as an endangered species. RCW nest in hollowed cavities of mature longleaf pines that have historically been found on remote and minimally disturbed Carolina bays (Jose et al. 2007). Trees are marked with a white painted band (as seen on some trees in the cover photo) to indicate the presence of RCW cavities. Venus flytraps, the iconic carnivorous plant species, are endemic to Carolina bay ecosystems and are also currently threatened due to loss of habitat (Luken 2005). In addition, it is estimated that one third of rare flora species in the Southeast can be found in Carolina bays, longleaf pine savannas, and karst ponds (Sharitz 2003). The estimated 10,000 to 20,000 Carolina bays and surrounding pocosin wetlands are integral to the flora and fauna composition of the southeastern United States (Richardson and Gibbons 1993). [End Page 1] Carolina bays have been of interest for recent dendrochronology research that investigates tropical cyclone precipitation (TCP) recorded in the annual rings of longleaf pine trees (Knapp et al. 2016, Montpellier et al. 2019). Accessing Carolina bays with extant old-growth longleaf pines that were not logged or turpentined during the late 19th and early 20th centuries offers the opportunity to survey the 300-year old climatological record stored in their annual rings. Flat tops, flagging branches, gnarled trunks and RCW cavities, some of which can be seen in the issue's cover photo, are all visual indicators of mature longleaf (Harper et al. 1997). The leading hypothesis as to why longleaf pine are sensitive to TCP relates to root structure and water table height fluctuation. When TCP collects in the pocosin wetlands, the water table rises, and longleaf pine roots record this surplus water in their annual rings. This information can be used to assess how TCP has fluctuated over time (Knapp et al. 2016) and allows for the investigation of microelevational influences on tree growth and climate response (Montpellier et al. 2019). Carolina bays are not only a landscape that is unique to the southeastern United States, but they also serve as recorders of anthropogenic and climatological history and provide refuge for species on the brink of extinction. Their research and preservation are vital as historically significant, ecologically vital, and climatologically intriguing locations in the United States are becoming increasingly rare. Evan E. Montpellier University of Minnesota references cited Brooks, Mark J., Barbara E. Taylor, and Andrew H. Ivester. 2010...

Physiological responses of germinant Pinus palustris and P. taeda seedlings to water stress and the significance of the grass-stage

Loblolly pine (Pinus taeda L.) has gradually replaced longleaf pine (P. palustris Mill.) across much of the coastal southeastern United States. Given recent interest in the regeneration of longleaf pine ecosystems, understanding how these two species will respond to drier conditions associated with climate change will be critically important. We conducted a progressive water-stress experiment on germinants of P. palustris and P. taeda over the course of 9 weeks, measuring gas exchange, allometry, water relations, and tracheid anatomy. P. palustris developed more overall biomass, had wider tracheids, allocated more of its biomass into leaf tissue, and maintained a narrower safety margin against hydraulic failure than P. taeda. Both species reduced leaf gas exchange as water stress increased, though P. palustris experienced earlier and greater declines in photosynthetic rates than P. taeda. The greater aboveground growth and narrower hydraulic safety margin observed in P. palustris represents a trade-off between growth and hydraulic safety and is likely related to the species’ defensive strategy against fire. We suggest that this trade-off may limit P. palustris germinant regeneration on sandier, xeric sites as climate change intensifies.

Morphologic and hydrologic distinctions between shallow and deep podzolized carbon in the southeastern United States Coastal Plain

Podzolization imparts soils and landforms of the southeastern United States Coastal Plain with two distinct pools of organic carbon (C), referred to as shallow podzolized C (SPC) and deep podzolized C (DPC). We evaluate podzolization across two catenas, and across the state of Florida, to establish that SPC and DPC are morphologically and hydrologically distinct. We demonstrate that SPC lightens downward (i.e. a Bh horizon with a darker top than bottom) and accumulates below low chroma material, while DPC darkens downward and accumulates below higher chroma material. We interpret these distinct morphologies to be manifestations of separate podzolization processes that are controlled by unique components of soil hydrology. Our analyses support existing notions that SPC is a product of vadose zone hydrology; formed within a pronounced eluvial-illuvial system where C, metals (predominately aluminum), and clay-sized particles are mobilized and immobilized together when near surface saturation thresholds are met. Our work however also identifies DPC to be a product of phreatic zone hydrology; part of an eluvial-illuvial system where C is translocated without metals or clays and immobilized when subsoil saturation thresholds are met. Recognizing the morphologic and hydrologic differences between SPC and DPC not only provides insights into interactions between soil hydrology and terrestrial C cycling in low-relief landforms, but also by incorporating these differences into field-based assessments soil scientists can improve their interpretations and communication of the hydropedology and podzolization.

Myrtle Oak, Quercus myrtifolia

Myrtle oak is one of the three scrub oaks characteristic of scrub communities. It occurs on coastal regions of the Florida Panhandle and throughout the Florida peninsula and coastal southeastern United States west to Mississippi and east to South Carolina. The acorns of myrtle oak are an important food source for wildlife.https://edis.ifas.ufl.edu/sg183
 This publication is derived from information in SGEB-75/SG156, Dune Restoration and Enhancement for the Florida Panhandle, by Debbie Miller, Mack Thetford, Christina Verlinde, Gabriel Campbell, and Ashlynn Smith. https://edis.ifas.ufl.edu/sg156.

Gullah-Geechee settlement patterns from slavery to freedom: Investigation of a Georgia plantation slave quarter

Gullah-Geechee is a creole culture that emerged among enslaved African Americans in the coastal Southeastern United States. Modern material expressions of this culture include a distinctive settlement type, the family compound, consisting of loosely clustered residences and outbuildings. The arrangement of these settlements resembles colonial slave quarters but differs from antebellum “slave rows.” Gullah-Geechee family compounds existed by the mid-20th century, but their origin, time depth, and evolution from linear quarters are unclear. Archaeological study of the Wilson–Miller plantation slave quarter near Savannah, occupied over most of the 19th Century, indicated that the Gullah-Geechee residential compound appeared soon after Emancipation. The study also suggested that communal outdoor space was important in maintaining cultural practices that were expressed in both colonial and post-Emancipation settlement patterns.

Targeted Sampling and Target Capture: Assessing Phylogeographic Concordance with Genome-wide Data.

Comparative phylogeography provides the necessary framework to examine the factors influencing population divergence, persistence, and change over time. Avise (2000) outlined four aspects of concordance that result when data exhibit significant phylogeographic signal: concordance among sites within a locus, among multiple loci within a species, among multiple species within a region, and between genetic patterns and established biogeographic provinces. To fully address each aspect of concordance, we combined target capture of a set of orthologous loci with targeted geographic sampling of multiple species, thus removing any variability introduced by using different genetic markers and heterogeneous sampling distributions. We used hybrid enrichment and high-throughput sequencing of four anuran species sampled from 36 congruent localities in the Southeastern United States Coastal Plain, a region that represents one of the classic systems in phylogeography. In total, we recovered > 375 of the same nuclear loci across species and assembled mitochondrial genomes, resulting in one of the most comprehensive comparative phylogeographic datasets in any region or taxon to date. We used these data to evaluate concordance, compare genetic structure across species, and test previously described biogeographic features in the region including major river drainages and suture zones. We then applied a recently-developed framework to quantify concordance across species using phylogeographic concordance factors. For the four species examined, which have higher dispersal and potentially limited structure compared to many amphibians, we found poor resolution in individual nuclear gene trees even with long (~ 1400 bp) nuclear sequences. The mitochondrial and multi-locus nuclear datasets, however, produced similar patterns within species, indicated high discordance among species, and suggested little correspondence of genetic patterns with putative biogeographic barriers. Variation in the phylogeographic structure detected may be related to differences in natural history, in that the two habitat generalists exhibited less structure. Our study demonstrates the utility of combining target capture, which is highly repeatable and produces comparable datasets, with a targeted sampling strategy to quantify phylogeographic concordance across diverse taxa in a region with a complex history.

Host and parasite thermal ecology jointly determine the effect of climate warming on epidemic dynamics

Host-parasite systems have intricately coupled life cycles, but each interactor can respond differently to changes in environmental variables like temperature. Although vital to predicting how parasitism will respond to climate change, thermal responses of both host and parasite in key traits affecting infection dynamics have rarely been quantified. Through temperature-controlled experiments on an ectothermic host-parasite system, we demonstrate an offset in the thermal optima for survival of infected and uninfected hosts and parasite production. We combine experimentally derived thermal performance curves with field data on seasonal host abundance and parasite prevalence to parameterize an epidemiological model and forecast the dynamical responses to plausible future climate-warming scenarios. In warming scenarios within the coastal southeastern United States, the model predicts sharp declines in parasite prevalence, with local parasite extinction occurring with as little as 2 °C warming. The northern portion of the parasite's current range could experience local increases in transmission, but assuming no thermal adaptation of the parasite, we find no evidence that the parasite will expand its range northward under warming. This work exemplifies that some host populations may experience reduced parasitism in a warming world and highlights the need to measure host and parasite thermal performance to predict infection responses to climate change.

The Impact of Late Holocene Land Use Change, Climate Variability, and Sea Level Rise on Carbon Storage in Tidal Freshwater Wetlands on the Southeastern United States Coastal Plain

AbstractThis study examines Holocene impacts of changes in climate, land use, and sea level rise (SLR) on sediment accretion, carbon accumulation rates (CAR), and vegetation along a transect of tidal freshwater forested wetlands (TFFW) to oligohaline marsh along the Waccamaw River, South Carolina (four sites) and along the Savannah River, Georgia (four sites). We use pollen, plant macrofossils, accretion, and CAR from cores, spanning the last 1,500–6,000 years to test the hypothesis that TFFW have remained stable throughout the late Holocene and that marshes transitioned from TFFW during elevated SLR during the Medieval Climate Anomaly, with further transformation resulting from colonial land use change. Results show low and stable accretion and CAR through much of the Holocene, despite moderate changes associated with Holocene paleoclimate. In all records, the largest observed change occurred within the last ~400 years, driven by colonial land clearance, shifting terrigenous sediment into riparian wetlands, resulting in order‐of‐magnitude increases in accretion and C accumulation. The oligohaline marshes transitioned from TFFW ~300–500 years ago, coincident with colonial land clearance. Postcolonial decreases in CAR and accretion occur because of watershed reforestation over the last century. All sites show evidence of recent (decades to century) swamp forest decline due to increasing salinity and tidal inundation from SLR. This study suggests that allochthonous sediment input during colonialization helped maintain TFFW but that current SLR rates are too high for TFFW to persist, although higher accretion rates in oligohaline marshes increase the resilience of tidal wetlands as they transition from TFFW to marsh.