No abstract

Environmental DNA (eDNA) quantification and sequencing are emerging techniques for assessing biodiversity in marine ecosystems. Environmental DNA can be transported by ocean currents and may remain at detectable concentrations far from its source depending on how long it persist. Thus, predicting the persistence time of eDNA is crucial to defining the spatial context of the information derived from it. To investigate the physicochemical controls of eDNA persistence, we performed degradation experiments at temperature, pH, and oxygen conditions relevant to the open ocean and the deep sea. The eDNA degradation process was best explained by a model with two phases with different decay rate constants. During the initial phase, eDNA degraded rapidly, and the rate was independent of physicochemical factors. During the second phase, eDNA degraded slowly, and the rate was strongly controlled by temperature, weakly controlled by pH, and not controlled by dissolved oxygen concentration. We demonstrate that marine eDNA can persist at quantifiable concentrations for over 2 weeks at low temperatures (≤10 °C) but for a week or less at ≥20 °C. The relationship between temperature and eDNA persistence is independent of the source species. We propose a general temperature-dependent model to predict the maximum persistence time of eDNA detectable through single-species eDNA quantification methods.

We describe approaches to addressing the perennial challenge of collecting a sufficient diversity of nontarget insects for host-specificity testing of candidate biocontrol agents of invasive wood-borers such as the Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae). Multifunnel and intercept traps, retrofitted to maintain live insects and baited with cerambycid-specific pheromone lures, were deployed in diverse forests in southeastern Massachusetts. We collected 1,288 adult beetles comprising 56 species, mostly from the subfamilies targeted by the lures (Cerambycinae and Lamiinae). The type of trap and tree species in which the trap was hung did not seem to affect the species caught. Methods used to induce egg laying and techniques to rear cerambycid larvae are described. Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is the most common Asian longhorned beetle parasitoid in China; therefore, we conducted tests to determine whether cerambycids native to North America would be at risk should this species be released. D. helophoroides attacked all six species tested: Monochamus scutellatus (Say) (Coleoptera: Cerambycidae: Lamiinae), Monochamus notatus (Drury) (Coleoptera: Cerambycidae: Lamiinae), Apriona rugicollis Chevrolat (Coleoptera: Cerambycidae: Lamiinae), Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae: Cerambycinae), Graphisurus fasciatus (DeGeer) (Coleoptera: Cerambycidae: Lamiinae), and Neoclytus acuminatus (F.) (Coleoptera: Cerambycidae: Cerambycinae). Parasitism of native cerambycids was not statistically different from parasitism of Asian longhorned beetle, except for N. acuminatus, which is a considerably smaller species than Asian longhorned beetle, and for M. notatus and M. scutellatus, which attack pine trees rather than hardwood trees like Asian longhorned beetle and the other native species tested. Our testing indicates that many native cerambycids would be vulnerable to D. helophoroides and we conclude that D. helophoroides should not be considered for release as a biocontrol agent in North America.

Metabarcoding analysis of environmental DNA samples is a promising new tool for marine biodiversity and conservation. Typically, seawater samples are obtained using Niskin bottles and filtered to collect eDNA. However, standard sample volumes are small relative to the scale of the environment, conventional collection strategies are limited, and the filtration process is time consuming. To overcome these limitations, we developed a new large-volume eDNA sampler with in situ filtration, capable of taking up to 12 samples per deployment. We conducted three deployments of our sampler on the robotic vehicle Mesobot in the Flower Garden Banks National Marine Sanctuary in the northwestern Gulf of Mexico and collected samples from 20 to 400 m depth. We compared the large volume (~40-60 liters) samples collected by Mesobot with small volume (~2 liters) samples collected using the conventional CTD-mounted Niskin bottle approach. We sequenced the V9 region of 18S rRNA, which detects a broad range of invertebrate taxa, and found that while both methods detected biodiversity changes associated with depth, our large volume samples detected approximately 66% more taxa than the CTD small volume samples. We found that the fraction of the eDNA signal originating from metazoans relative to the total eDNA signal decreased with sampling depth, indicating that larger volume samples may be especially important for detecting metazoans in mesopelagic and deep ocean environments. We also noted substantial variability in biological replicates from both the large volume Mesobot and small volume CTD sample sets. Both of the sample sets also identified taxa that the other did not; although the number of unique taxa associated with the Mesobot samples was almost four times larger than those from the CTD samples. Large volume eDNA sampling with in situ filtration, particularly when coupled with robotic platforms, has great potential for marine biodiversity surveys, and we discuss practical methodological and sampling considerations for future applications.

In ant-hemipteran mutualisms, ‘tending’ ants indiscriminately defend hemipterans from other arthropods, protecting mutualism-hosting plants from defoliating herbivores in some cases. Censuses of a treehopper, Publilia concava, observations of tending ants, and measurements of leaf area were conducted on tall goldenrod, Solidago altissima, over the course of a summer at a field site in central Vermont. Hosting ant-tended treehopper aggregations had no effect on leaf area or the ability for goldenrod to flower, suggesting that in the absence of an herbivore outbreak this mutualism is neither necessary nor inherently detrimental for goldenrod. These findings support the hypothesis that the net consequence of the ant-hemipteran mutualism for its host plant depends on the costs of hemipteran damage, and the benefits of ant defense from other arthropods.