Geology topics

Research about Hawai'i

Source-linked reports with geographic coverage including Hawai'i.

At least 19 recordsLinked to original sources

USGS2024

Linking avian malaria parasitemia estimates from quantitative PCR and microscopy reveals new infection patterns in Hawai'i

Plasmodium parasites infect thousands of species and provide an exceptional system for studying host-pathogen dynamics, especially for multi-host pathogens. However, understanding these interactions requires an accurate assay of infection. Assessing Plasmodium infections using microscopy on blood smears often misses infections with low parasitemias (the fractions of cells infected), and biases in malaria prevalence estimates will differ among hosts that differ in mean parasitemias. We examined Plasmodium relictum infection and parasitemia using both microscopy of blood smears and quantitative polymerase chain reaction (qPCR) on 299 samples from multiple bird species in Hawai'i and fit models to predict parasitemias from qPCR cycle threshold (Ct) values. We used these models to quantify the extent to which microscopy underestimated infection prevalence and to more accurately estimate infection patterns for each species for a large historical study done by microscopy. We found that most qPCR-positive wild-caught birds in Hawaii had low parasitemias (Ct scores ≥35), which were rarely detected by microscopy. The fraction of infections missed by microscopy differed substantially among eight species due to differences in species’ parasitemia levels. Infection prevalence was likely 4–5-fold higher than previous microscopy estimates for three introduced species, including Zosterops japonicus , Hawaii’s most abundant forest bird, which had low average parasitemias. In contrast, prevalence was likely only 1.5–2.3-fold higher than previous estimates for Himatione sanguinea and Chlorodrepanis virens , two native species with high average parasitemias. Our results indicate that relative patterns of infection among species differ substantially from those observed in previous microscopy studies, and that differences depend on variation in parasitemias among species. Although microscopy of blood smears is useful for estimating the frequency of different Plasmodium stages and host attributes, more sensitive quantitative methods, including qPCR, are needed to accurately estimate and compare infection prevalence among host species.

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USGS2023

Evaluation of replicate sampling using hierarchical spatial modeling of population surveys accounting for imperfect detectability

Effective species management and conservation benefit from knowledge of species distribution and status. Surveys to obtain that information often involve replicate sampling, which increases survey effort and costs. We simultaneously modeled species distribution, abundance and spatial correlation, and compared the uncertainty in replicate abundance estimates of the endangered palila ( Loxioides bailleui ) using hierarchical generalized additive models with a soap film smoother that incorporated random effects for visit. Based on survey coverage and detections, we selected the 2017 point-transect distance sampling survey on Mauna Kea, Hawai‘i Island, for our modeling. Our modeling approach allowed us to account for imperfect detections, control the effects of boundary features, and generate visit-specific density surface maps. We found that visit-specific smooths were nearly identical, indicating that little information was gained from a subsequent visit, and that most of the estimator uncertainty was derived from within-visit variability. Scaling back the palila survey to a single visit would halve the survey effort and logistical costs and increase efficiencies in data management and processing. Changing the sampling protocol warrants careful consideration and our findings may help management and regulatory agencies by maximizing efficiency and minimizing costs of surveying protocols, while providing guidelines on how to best collect information critical to species' conservation.

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USGS2023

Microgravity as a tool for eruption forecasting

Detection of gravity change over time has been used to better understand magmatic activity at volcanoes for decades, but the technique is not commonly applied to forecasting eruptions. In contrast, other tools, notably seismic, deformation, and gas monitoring have made exceptional strides in the past several decades and form the foundation for eruption forecasting, especially during the final buildup to an eruption. Reasons for this gap include the high cost and fragile nature of gravity instruments, and the ambiguous nature of many results. But this is changing. Instrumentation is becoming more robust and accurate, expenses may soon diminish thanks to technological advances, and the record of success in tracking subsurface mass change (either from magma or hydrothermal fluids) in volcanic areas is growing. Here we review how gravity change can be applied to forecasting volcanic eruptions across a variety of spatial and temporal scales. We argue that microgravity has untapped potential as a forecasting tool in three specific ways: constraining probabilistic assessments, detecting long-term mass change that may occur prior to the onset of vigorous seismicity and deformation, and identifying transient activity that indicates magma ascent or other changes that immediately precede new eruptions or changes in ongoing eruptions. As with any volcano-monitoring method, microgravity has strengths and weaknesses, but the varied forms of data collection—for instance, campaign versus continuous, and relative versus absolute—offer the potential to record a broad range of signals at volcanoes with a diversity of magmatic systems. The technique is currently underutilized; additional attention, investment, and application at more volcanoes could help to realize its promise.

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USGS2023

Physicochemical coastal groundwater dynamics between Kauhakō Crater lake and Kalaupapa settlement, Moloka‘i, Hawai‘i

Land-based sources of groundwater pollution can be a critical threat to coral reefs, and a better understanding of “ridge-to-reef” water movement is required to advance management and coral survival in the Anthropocene. In this study a more complete understanding of the geological, atmospheric, and oceanic drivers behind coastal groundwater exchange on the Kalaupapa peninsula, on Moloka‘i, Hawai‘i, is obtained by analyzing high resolution geochemical and geophysical time-series data. In concert with multiyear water level analyses, a tidally and precipitation-driven groundwater connection between Kauhakō Crater lake and submarine groundwater discharge (SGD) fluxes are demonstrated. Results include an average discharge rate of 190 cm d −1 and the detection of water-flow pathways past cesspools that likely contribute to higher nutrient loading near the SGD sites. This underlines the importance of managing anthropogenic nutrients that enter the shallow freshwater lens such as through cesspools and are consequently discharged via SGD onto coral reef habitats.

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USGS2022

Microgravity change during the 2008-2018 Kı̄lauea summit eruption: Nearly a decade of subsurface mass accumulation

Results from nine microgravity campaigns from Kı̄lauea, Hawaiʻi, spanning most of the volcano's 2008–2018 summit eruption, indicate persistent mass accumulation at shallow levels. A weighted least squares approach is used to recover microgravity results from a network of benchmarks around Kı̄lauea's summit, eliminate instrumental drift, and restore suspected data tares. A total mass of 1.9 × 10 11 kg was determined from these microgravity campaigns to have accumulated below Kı̄lauea Caldera during 2009–2015 at an estimated depth of 1.3 km below sea level. Only a fraction of this mass is reflected in surface deformation, and this is consistent with previously reported discrepancies between subsurface mass accumulation and observed surface deformation. The discrepancy, amongst other independent evidence from gas emissions, seismicity, and continuous gravimetry, indicate densification of magma in the reservoirs below the volcano summit. This densification may have been driven by degassing through the summit vent. It is hypothesized that during the final years of the summit eruption, magma densification resulted in a buildup of pressure in the reservoirs that may have contributed to the lower East Rift Zone outbreak of 2018. The observed mass accumulation beneath Kı̄lauea could not have been detected through other techniques and illustrates the importance of microgravity measurements in volcano monitoring.

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USGS2022

Magnetotelluric investigations of the Kīlauea Volcano, Hawaii

In 2002 and 2003 a collaborative effort was undertaken between Lawrence Berkeley National Laboratory, Sandia National Laboratories, the U.S. Geological Survey (USGS) Menlo Park, the USGS Hawaiian Volcano Observatory, and Electromagnetic Instruments Inc. to study the Kīlauea volcano in Hawaii using the magnetotelluric (MT) technique. The work was motivated by a desire to improve understanding of the magma reservoirs and conduits within Kīlauea and the East and Southwest Rift zones, which has implications for understanding Kīlauea's plumbing system. An improved understanding of the rift zones has implications in understanding large-scale landslides that are generated in the Hilina Slump, which produce significant impacts on coastal communities. Up to eight stations operated simultaneously, with multiple remote reference sites, and data were processed using multi-station robust processing techniques. In total, data were acquired at 70 sites over the Southwest and East rift zones. Good to excellent quality data were obtained even in the harshest conditions, such as those encountered on the fresh lava flows of the East Rift Zone, where electrical contact resistances are on the order of 100 kΩ. A three-dimensional (3D) MT model study was done to guide interpretation of the observed MT measurements. Synthetic modeling demonstrates that conductive bodies in the upper 3 km can be spatially resolved where MT station sampling is good. Resistivity anomalies in the 3D inversions have a high degree of spatial correlation with previously published seismic velocity anomalies beneath Kīlauea. Melt fractions between 0.096 and 0.117 are calculated for the Kīlauea and Puʻuʻōʻō low resistivity anomalies, respectively.

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USGS2022

Could Kı̄lauea's 2020 post caldera-forming eruption have been anticipated?

In 2018 Kīlauea volcano erupted a decade’s worth of basalt, given estimated magma supply rates, triggering caldera collapse. Yet, less than 2.5 years later Kīlauea re-erupted. At the 2018 eruption onset, pressure within the summit reservoir was ~20 MPa above magmastatic. By the onset of collapse this decreased by ~17 MPa. Analysis of magma surges at the 2018 fissures, following collapse events, implies excess pressure at the eruption end of only ~1 MPa. Given the new vent elevation, ∼11 − 12 MPa pressure increase was required to bring magma to the surface in December 2020. Analysis of GPS data between 8/2018 and 12/2020 shows there was a 73% probability that this condition was met at the onset of the 2020 eruption. Given a plausible range of possible vent elevations, there was a 40 to 88% probability of sufficient pressure to bring magma to the surface 100 days before the eruption.

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USGS2022

Hypotheses and lessons from a native moth outbreak in a low-diversity, tropical rainforest

Outbreaks of defoliating insects in low-diversity tropical forests occur infrequently but provide valuable insights about outbreak ecology in temperate environments and in general. We investigated an extensive outbreak of the endemic koa moth ( Scotorythra paludicola ), which defoliated endemic koa trees ( Acacia koa ) over a third of their range on Hawai‘i Island during 2013 and 2014. At Hakalau Forest National Wildlife Refuge, we observed the dynamics of the outbreak and its effects on host trees, nutrient cycling, and insectivorous consumers in reforestation stands of densely planted koa and in natural forest stands of mixed koa and ‘ōhi‘a ( Metrosideros polymorpha ). Contrary to predictions of the resource concentration hypothesis, caterpillar biomass and defoliation severity were greater in the natural forest sites, where koa density was relatively low. Caterpillars preferentially consumed the most palatable koa foliage type (phyllodes), and koa initially refoliated with the least palatable foliage type (true leaves). Lightly defoliated small trees refoliated more quickly than did heavily defoliated ones but the opposite was true for large trees, which also produced a greater proportion of phyllodes. Mortality was greatest for heavily defoliated small koa. Caterpillar frass caused larger increases in soil nitrogen (N) than phosphorus (P) availability, with the greatest N increases in fine-textured soils. Foliar N increased in alien grasses under koa canopies compared to grasses away from koa and to native woody understory species. Bird activity was influenced by ‘ōhi‘a flower abundance and the severity of koa defoliation; birds switched to outbreaking caterpillar prey, and they gained weight during the outbreak. Bat foraging times decreased during the outbreak, apparently because they became satiated quickly each night. Parasitoid wasps increased with caterpillar abundance but had little influence on outbreak dynamics. Reducing alien grass cover and increasing tree diversity would likely reduce the impacts of insect outbreaks and similar perturbations to native forests.

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USGS2022

The Hawai'i groundwater recharge tool

This article discusses the design and implementation of the Hawai’i Groundwater Recharge Tool, an application for providing data and analyses of the impacts of land-cover modifications and changes in precipitation on groundwater-recharge rates for the island of O’ahu. This application uses simulation data based on a set of 29 land-cover types and 2 precipitation conditions to provide users with real-time recharge calculations for interactively defined land-cover modifications. The tool provides two visualizations, representing the land cover for the island and the resultant groundwater-recharge rates, and a set of metrics indicating the changes to groundwater recharge for relevant areas to present a set of easily interpretable outcomes based on user-defined scenarios. Users have varying degrees of control over the granularity of data input and output, allowing for the quick production of a roughly defined scenario, or more precise land-cover definitions. These modifications can be exported for further analysis. Heuristics are used to provide a responsive user interface and performant integration with the database containing the full set of simulation data. This tool is designed to provide user-friendly access to the information on the impacts of land-cover and precipitation changes on groundwater-recharge rates needed to assist in making data-driven decisions.

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USGS2022

Rapid ʻŌhiʻa Death in Hawaiʻi

Ceratocystis lukuohia and Ceratocystis huliohia are two newly recognized fungi that have arrived in Hawai‘i and are causing a serious vascular wilt and canker disease, respectively, of ‘ōhi‘a trees ( Metrosideros polymorpha ), the most common and important tree species in Hawai‘i. Management of these diseases has presented challenges due to unique etiological aspects and the exceptionally pathogenic nature of one of these fungi ( C. lukuohia ) once it gains access to the tree’s vascular tissue. Careful study of the spread of the pathogens has resulted in an understanding of the role of ambrosia beetles and the frass they produce that carries the pathogen, as well as the wounding of trees by many different agents by which the pathogen can access and infect the vascular tissue. A variety control measures are being used. These include a state-of-the-art monitoring program to detect diseased and recently killed trees and molecular biology approaches that can confirm if a given tree was infected by Ceratocystis . Based on monitoring more than one million trees have been estimated as killed by the diseases to date. A major part of the program includes the deployment of a field crew that seeks out and fells large infected ‘ōhi‘a trees as these trees are the main source of most of the infective Ceratocystis -laden frass. Long-term control measures also include fencing of some forests to reduce the amount of wounding to ‘ōhi‘a trees by feral cattle and pigs that allows entry of the fungi and quarantine restrictions to ensure there will be no inter-island movement of the pathogens in ‘ōhi‘a products. Finally, methods are also being developed to restore ‘ōhi‘a forests affected by these diseases by determining effective regeneration practices and developing genetically resistant ‘ōhi‘a stock. Hawai‘i has an active extension program dedicated to providing information on how residents and visitors can contribute to protecting ‘ōhi‘a trees from these diseases. More than 500,000 people have participated in this program. Hawai‘i residents have a very deep appreciation for this tree species and do what they can to help prevent these diseases from destroying more of their most treasured tree species.

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USGS2022

Evaluation of MPA designs that protect highly mobile megafauna now and under climate change scenarios

Marine protected area (MPA) designs, including large-scale MPAs (LSMPAs; >150,000 km 2 ), mobile MPAs (fluid spatiotemporal boundaries), and MPA networks, may offer different benefits to species and could enhance protection by encompassing spatiotemporal scales of animal movement. We sought to understand how well LSMPAs could benefit nine highly-mobile marine species in the tropics now and into the future by: 1) evaluating current range overlap within a LSMPA; 2) evaluating range overlap under climate change projections; and 3) evaluating how well theoretical MPA designs benefit these nine species. We focused on Palmyra Atoll and Kingman Reef, a 2000 km 2 area within the 1.2 million km 2 U.S. Pacific Remote Islands Marine National Monument (PRIMNM) that contains marine megafauna (reef and pelagic fishes; sea turtles; seabirds; cetaceans) reflecting different behaviors and habitat use. Our approach is useful for evaluating the effectiveness of the Palmyra-Kingman MPA and PRIMNM in protecting these species, and tropical LSMPAs in general, and for informing future MPA design. Stationary MPAs provided protection at varying scales. Reef manta rays ( Mobula alfredi ), grey reef sharks ( Carcharhinus amblyrhynchos ), green sea turtles ( Chelonia mydas ), and bottlenose dolphins ( Tursiops truncatus ) had overall small ranges (<100 km from Palmyra-Kingman) and could benefit from stationary MPAs that contained heterogenous reef habitats. Yellowfin tuna ( Thunnus albacares ), sooty terns ( Onychoprion fuscatus ), red-footed boobies ( Sula sula ), great frigatebirds ( Fregata minor ), and melon-headed whales ( Peponocephala electra ) navigated complex oceanographic processes and may benefit most from mobile MPAs that shift with features including thermal fronts, cyclic regions of elevated productivity, and eddies, if relationships with these features are established and predictable. All species had capacity to travel to nearby reef systems, illustrating potential benefits of MPA networks and protected corridors. Suitable habitats will likely contract for all species as warm water expands under climate change scenarios (species habitats were predicted to decrease by 4–49% at Palmyra-Kingman) and MPAs may not protect suitable habitats into the future. Species habitat requirements and movement ecologies are critical aspects of marine spatial planning, especially with respect to dynamic ocean processes and a changing climate.

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USGS2022

Environmental filtering controls soil biodiversity in wet tropical ecosystems

The environmental factors controlling soil biodiversity along resource gradients remain poorly understood in wet tropical ecosystems. Aboveground biodiversity is expected to be driven by changes in nutrient availability in these ecosystems, however, much less is known about the importance of nutrient availability in driving soil biodiversity. Here, we combined a cross-continental soil survey across tropical regions with a three decades' field experiment adding nitrogen (N) and phosphorus (P) (100 kg N ha −1 y −1 and 100 kg P ha −1 y −1 ) to Hawai'ian tropical forests with contrasting substrate ages (300 and 4,100,000 years) to investigate the influence of nutrient availability to explain the biodiversity of soil bacteria, fungi, protists, invertebrates and key functional genes. We found that soil biodiversity was driven by soil acidification during long-term pedogenesis and across environmental gradients, rather than by nutrient limitations. In fact, our results showed that experimental N additions caused substantial acidification in soils from Hawai'i. These declines in pH were related to large decreases in soil biodiversity from tropical ecosystems in four continents. Moreover, the microbial activity did not change in response to long-term N and P additions. We concluded that environmental filtering drives the biodiversity of multiple soil organisms, and that the acidification effects associated with N additions can further create substantial undesired net negative effects on overall soil biodiversity in naturally tropical acid soils. This knowledge is integral for the understanding and management of soil biodiversity in tropical ecosystems globally.

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USGS2022

Distribution and trends of endemic Hawaiian waterbirds

Four endemic species of wetland-dependent waterbirds occur on the main Hawaiian Islands, all of which have experienced sharp population declines and are listed as endangered species. Twice per year, state-wide surveys are conducted to count waterbirds, but these surveys are evaluated only infrequently. We used a state-space approach to evaluate long-term (1986–2016) and short-term (2006–2016) trends and current distribution and abundance of endemic Hawaiian waterbirds. The most numerous species was the Ae‘o, or Hawaiian Stilt ( Himantopus mexicanus knudseni ), with a 5-year estimated average abundance of 1,932 individuals, followed by ‘Alae Ke‘oke‘o, or Hawaiian Coot ( Fulica alai ), with 1,815 individuals, Alae ‘Ula, or Hawaiian Common Gallinule ( Gallinula galeata sandvicensis ) with 927 individuals, and the Koloa Maoli, or Hawaiian Duck ( Anas wyvilliana ) with 931 individuals. All four species had positive trends over the long-term, but short-term and island specific trends were more variable, and in some cases negative. These results provide valuable information to help guide management of Hawaii’s threatened and endangered endemic waterbirds.

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USGS2022

Molt patterns, aging criteria, and molt-breeding seasonality of 8 native forest birds from the Island of Hawaiʻi

Much of our knowledge on the patterns and timing of breeding and molting come from studies of temperate region birds, yet tropical birds can have markedly different phenologies. The Hawaiian Islands support multiple endemic bird species that have evolved for millions of years in isolation to a tropical environment with minimal seasonality. We examined data from multiple studies (1994–2020) conducted across the avian annual cycle, from multiple locations, to evaluate molt patterns and establish criteria for assignment of age and sex based on the WRP, or molt-cycle age classification system designed specifically for tropical species. In addition, we describe the phenologies of molt and breeding and quantify the differences in males and females based on plumage coloration and morphometrics for 8 native species. We were able to validate the WRP tropical bird aging system as an appropriate method for aging forest birds from the Island of Hawaiʻi and separate all 8 species examined into juvenile, formative, and definitive plumages based on feather patterns and molt limits. Additionally, 2 species had distinctive second basic plumages. All 8 species examined also had extended periods of breeding and molting unlike their familial temperate counterparts, but these high energy activities are largely partitioned into separate time periods. Each species had some degree of overlap in breeding and molting, but the frequency of individuals that were simultaneously in breeding condition and molting was low with only 2 species displaying a proportion of overlap greater than 10% among all captures. Accurate aging and sexing techniques improve the quality of data from banding studies and provide important information on how species adapt to their environments.

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USGS2022

Characterization of a small population of the orangeblack Hawaiian damselfly (Megalagrion xanthomelas) in anchialine pools at Kaloko-Honokōhau National Historical Park, Hawai‘i Island

The endangered orangeblack Hawaiian damselfly (Megalagrion xanthomelas) is a lowland inhabitant of freshwater and brackish wetland environments. Formerly one of the most widely distributed native insects in Hawai‘i, it now appears restricted to small populations on the islands of O‘ahu, Moloka‘i, Maui, and Hawai‘i. On Hawai‘i island, anchialine pools provide important habitat for M. xanthomelas, and Kaloko-Honokōhau National Historical Park (Park) supports one of only a few documented populations on the western side of the island. This study aimed to estimate the population size of M. xanthomelas at this Park, characterize its habitat, and identify substrates on which females oviposit eggs. We conducted visual surveys for adult M. xanthomelas at anchialine pools during June 2016–August 2017. On average, the observed population was 10.7 individuals per month (range = 5–20; standard error = 1.3). Males were observed 6.1 times more frequently than females, likely reflecting the less cryptic nature of males compared to females. Females exhibited oviposition behavior on a variety of substrates, but small branches were used most frequently. Factors restricting this population are poorly known, but invasive fish may limit its distribution across the Park. Removal of invasive fishes from anchialine pools and ‘Aimakapā Fishpond may restore much habitat for this rare species in the Park.

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USGS2021

2021 U.S. National Seismic Hazard Model for the State of Hawaii

The 2021 U.S. National Seismic Hazard Model (NSHM) for the State of Hawaii updates the two-decades-old former model by incorporating new data and modeling techniques to improve the underlying ground shaking forecasts of tectonic-fault, tectonic-flexure, volcanic, and caldera collapse earthquakes. Two earthquake ground shaking hazard models (public policy and research) are produced that differ in how they account for declustered catalogs. The earthquake source model is based on (1) declustered earthquake catalogs smoothed with adaptive smoothing methods, (2) earthquake rate forecasts based on three temporally varying 60-year time periods, (3) maximum magnitude models that extend to larger earthquakes than previously considered, (4) a separate Kīlauea-specific seismogenic caldera collapse model which accounts for clustered event behavior observed during the 2018 eruption, and (5) fault ruptures that consider historic seismicity, GPS-based strain rates, and a new Quaternary fault database. Two new Hawaii-specific ground motion models (GMMs) and five additional global models consistent with Hawaii shaking data are used to forecast ground shaking at 23 spectral periods and peak parameters. Site effects are modeled using western U.S. and Hawaii specific empirical equations and provide shaking forecasts for eight site classes. For most sites the new model results in similar spectral accelerations as those in the 2001 NSHM, with a few exceptions caused mostly by GMM changes. Ground motions are highest in the southern portion of the Island of Hawai‘i due to high rates of forecasted earthquakes on décollement faults. Shaking decays to the northwest where lower earthquake rates result from flexure of the tectonic plate. Large epistemic uncertainties in source characterizations and GMMs lead to an overall high uncertainty (more than a factor of 3) in ground shaking at Honolulu and Hilo. The new shaking model indicates significant chances of slight or greater damaging ground motions across most of the island chain.

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USGS2021

Current distribution and abundance of Kohala forest birds in Hawai‘i

The Kohala volcano is home to the most spatially isolated population of Hawaiian forest birds on Hawai‘i Island and contains one of the few native bird populations in the state that has not been monitored since the original Hawai‘i Forest Bird Survey (HFBS) in 1979. We surveyed 143 stations across 13 transects in Pu‘u ‘O ‘Umi Natural Area Reserve on Kohala from February through April 2017 and compared our results to data from the 1979 HFBS conducted at 80 stations across three transects in the same location as our study site. We detected 2806 individuals of 15 species and measured relative abundance, relative occurrence, and density for seven species. We observed changes in species densities ranging from −8.4% (Hawai‘i ‘Elepaio, Chasiempis sandwichensis ) to +714% (‘I‘iwi, Drepanis coccinea ). Equivalence testing showed meaningful increases in population densities for all but one species, the Hawai‘i ‘Elepaio. The increases in population densities on Kohala are in stark contrast to the widespread declines in population densities of native species elsewhere in Hawai‘i. Relative occurrence was greater in 2017 than in 1979 for all species except Hawai‘i ‘Elepaios and House Finches ( Haemorhous mexicanus ), and relative abundance increased for all species except Hawai‘i ‘Elepaios, House Finches, and Melodious Laughing Thrushes ( Garrulax canorus ). We also documented the range expansion of Japanese Bush Warblers ( Cettia diphone ) in Kohala. Our results indicate that this spatially isolated avian community remains biologically diverse, and most population densities are increasing in the study area. Our results provide a framework for future surveys and a baseline for understanding possible changes in population and community dynamics as birds respond to climate change and avian disease on Kohala volcano.

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USGS2021

The roles of phenotypic plasticity and adaptation in morphology and performance of an invasive species in a novel environment

(1) Species introductions provide insights into rapid adaptation and adaptive phenotypic plasticity, as populations encounter and respond to new environments and selection pressures. However, maladaptive responses are increasingly recognized to also be common in nature. The spotted-wing drosophila, Drosophila suzukii , has rapidly invaded divergent environments providing the opportunity to examine adaptive and maladaptive phenotypic and evolutionary responses to its introduced range. (2) We studied how population density in the field and wing size of individuals varied over an elevational gradient on Hawaii. We then conducted a reciprocal common garden experiment to evaluate how temperature influenced wing size and other correlates of fitness. We did this by reciprocally rearing D. suzukii collected from low and high elevations in temperatures representative of low and high elevation. (3) We observed an elevational cline in wing size, in which wing size increased with elevation. Additionally, flies were more abundant at higher elevation. In the reciprocal common garden experiment, flies emerged faster in the warm, low elevation temperature and developed larger wings in the cool, high elevation temperature. Emergence of flies from high and low elevation sites showed a pattern suggesting maladaptation to the temperature representing their home environment. (4) We suggest that opposing selection pressures, the high vagility of flies, and extreme plasticity in body size constrain adaptation to temperature along an elevational gradient. While successful invasive species such as D. suzukii often exhibit local adaptation, this research demonstrates that invasive species can be successful even without such adaptation.

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