Publications

Coral reef recovery could get a boost from an unlikely source: Sea cucumbers, the janitors of the seafloor

Synchronous Spawning—When Timing Is Everything

Some corals release their gametes all at once, dramatically increasing the chances of any one gamete being fertilized. In a report in this issue, Clifton et al . ( 1116 ) demonstrate that a seaweed, Halimeda , also engages in synchronous spawning. Hay's Perspective discusses the natural history of these seaweeds and their efficient use of time in their growth and reproduction.

Propagule pressure of an invasive crab overwhelms native biotic resistance

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 342:191-196 (2007) - doi:10.3354/meps342191 Propagule pressure of an invasive crab overwhelms native biotic resistance A. L. Hollebone, M. E. Hay* School of Biology, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332-0230, USA *Corresponding author. Email: mark.hay@biology.gatech.edu ABSTRACT: Over the last decade, the porcelain crab Petrolisthes armatus invaded oyster reefs of Georgia, USA, at mean densities of up to 11000 adults m–2. Interactions affecting the invasion are undocumented. We tested the effects of native species richness and composition on invasibility by constructing isolated reef communities with 0, 2, or 4 of the most common native species, by seeding adult P. armatus into a subset of the 4 native species communities and by constructing communities with and without native, predatory mud crabs. At 4 wk, recruitment of P. armatus juveniles to oyster shells lacking native species was 2.75 times greater than to the 2 native species treatment and 3.75 times greater than to the 4 native species treatment. The biotic resistance produced by 2 species of native filter feeders may have occurred due to competition with, or predation on, the settling juveniles of the filter feeding invasive crab. Adding adult porcelain crabs to communities with 4 native species enhanced recruitment by a significant 3-fold, and countered the effects of native biotic resistance. Differences in recruitment at Week 4 were lost by Weeks 8 and 12, when densities of recent recruits reached ~17000 to 34000 crabs m–2 across all treatments. Thus, native species richness slows initial invasion, but early colonists stimulate settlement by later ones and produce tremendous propagule pressure that overwhelms the effects of biotic resistance. KEY WORDS: Exotic crab · Invasive species · Marine bioinvasion · Oyster reef · Recruitment · South Atlantic Bight Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Faculty Opinions recommendation of Predator diversity strengthens trophic cascades in kelp forests by modifying herbivore behaviour.

Although human-mediated extinctions disproportionately affect higher trophic levels, the ecosystem consequences of declining diversity are best known for plants and herbivores. We combined field surveys and experimental manipulations to examine the consequences of changing predator diversity for trophic cascades in kelp forests. In field surveys we found that predator diversity was negatively correlated with herbivore abundance and positively correlated with kelp abundance. To assess whether this relationship was causal, we manipulated predator richness in kelp mesocosms, and found that decreasing predator richness increased herbivore grazing, leading to a decrease in the biomass of the giant kelp Macrocystis. The presence of different predators caused different herbivores to alter their behaviour by reducing grazing, such that total grazing was lowest at highest predator diversity. Our results suggest that declining predator diversity can have cascading effects on community structure by reducing the abundance of key habitat-providing species. PMID: 16958869 Funding information This work was supported by: NIGMS NIH HHS, United States Grant ID: K12GM00679

Mystery solved? Disease detectives identify the cause of a mass die-off in the sea

A mass sea urchin die-off in the Caribbean Sea in the 1980s may have resulted from a single-cell protist called a scuticociliate.

Faculty Opinions recommendation of Antimicrobial defences increase with sociality in bees.

Evidence for the antiquity and importance of microbial pathogens as selective agents is found in the proliferation of antimicrobial defences throughout the animal kingdom. Social insects, typified by crowding and often by low genetic variation, have high probabilities of disease transmission and eusocial Hymenoptera may be particularly vulnerable because of haplodiploidy. Mechanisms they employ to reduce the risk of disease include antimicrobial secretions which are particularly important primary barriers to infection. However, until now, whether or not there is selection for stronger antimicrobial secretions when the risk of disease increases because of sociality has not been tested. Here, we present evidence that the production of progressively stronger antimicrobial compounds was critical to the evolution of sociality in bees. We found that increases in group size and genetic relatedness were strongly correlated with increasing antimicrobial strength. The antimicrobials of even the most primitive semi-social species were an order of magnitude stronger that those of solitary species, suggesting a point of no return, beyond which disease control was essential. Our results suggest that selection by microbial pathogens was critical to the evolution of sociality and required the production of strong, front-line antimicrobial defences. PMID: 17504731

Herbivore Preference for Native vs. Exotic Plants: Generalist Herbivores from Multiple Continents Prefer Exotic Plants That Are Evolutionarily Naïve

Enemy release and biotic resistance are competing, but not mutually exclusive, hypotheses addressing the success or failure of non-native plants entering a new region. Enemy release predicts that exotic plants become invasive by escaping their co-adapted herbivores and by being unrecognized or unpalatable to native herbivores that have not been selected to consume them. In contrast, biotic resistance predicts that native generalist herbivores will suppress exotic plants that will not have been selected to deter these herbivores. We tested these hypotheses using five generalist herbivores from North or South America and nine confamilial pairs of native and exotic aquatic plants. Four of five herbivores showed 2.4-17.3 fold preferences for exotic over native plants. Three species of South American apple snails (Pomacea sp.) preferred North American over South American macrophytes, while a North American crayfish Procambarus spiculifer preferred South American, Asian, and Australian macrophytes over North American relatives. Apple snails have their center of diversity in South America, but a single species (Pomacea paludosa) occurs in North America. This species, with a South American lineage but a North American distribution, did not differentiate between South American and North American plants. Its preferences correlated with preferences of its South American relatives rather than with preferences of the North American crayfish, consistent with evolutionary inertia due to its South American lineage. Tests of plant traits indicated that the crayfish responded primarily to plant structure, the apple snails primarily to plant chemistry, and that plant protein concentration played no detectable role. Generalist herbivores preferred non-native plants, suggesting that intact guilds of native, generalist herbivores may provide biotic resistance to plant invasions. Past invasions may have been facilitated by removal of native herbivores, introduction of non-native herbivores (which commonly prefer native plants), or both.

Novel antineoplastic diterpene-benzoates from the Fijian red alga Callophycus serratus

Red macroalgae are well-known for the production of brominated metabolites, including terpenoids and phenols, yet some taxa within the Rhodophyta remain relatively unstudied. Herein, we report the discovery of unusual diterpene-benzoate natural products representing three novel carbon skeletons, from the red alga Callophycus serratus collected in Fiji. Included among the new compounds were 15- and 16-membered macrolides as well as non-macrocyclic diterpene-benzoic acid structural motifs, all apparently sharing the same 27-carbon biosynthetic precursor. Biological activities of these compounds included moderate antibacterial, antiviral, and antineoplastic effects via specific apoptotic cell death.

CAN QUANTITY REPLACE QUALITY? FOOD CHOICE, COMPENSATORY FEEDING, AND FITNESS OF MARINE MESOGRAZERS

Relationships among food choice, compensatory feeding, and the consequences for consumer fitness rarely have been quantified. We created foods of varying nutritional quality and evaluated the consequences of compensatory feeding for three sympatric species of amphipods by analyzing food choices, feeding rates, and long-term effects on fitness. Nutritional quality was manipulated by creating low-quality diets from algae (low in protein, nitrogen, and total organic carbon), high-quality diets from commercial fish food (high in protein, nitrogen, and total organic carbon), and intermediate-quality diets from mixtures of those two foods. When high- and low-quality diets were simultaneously offered, the more mobile, non-tube-building amphipods, Gammarus mucronatus and Elasmopus levis, both fed preferentially on the high-quality diet. The more sedentary, tube-building amphipod Ampithoe longimana did not discriminate between these foods. When confined to a single food type, all three species exhibited compensatory feeding on the low-quality diet. Despite compensatory feeding, when Elasmopus levis were cultured on the low-quality food, they experienced reduced survivorship, growth, and fecundity during two successive ovulations, compared to individuals feeding on more nutrient-rich foods. Low-nutrient foods caused similar declines in growth and female gonad size for Gammarus mucronatus. In contrast, the survivorship, growth, and fecundity of Ampithoe longimana was not affected by any of the diets tested. Thus, compensatory feeding allowed the more sedentary species, Ampithoe longimana, to completely circumvent the effects of low nutritional quality, but the same behavior was ineffective for both of the more mobile species, Gammarus mucronatus and Elasmopus levis. The ability of A. longimana to achieve equal fitness by substituting food quantity for food quality may allow this sedentary species to form longer associations with individual host plants, minimize movement among hosts, and thus lower its risk of being detected by predators.

Faculty Opinions recommendation of Caribbean-wide decline in carbonate production threatens coral reef growth.

Stream mosses as chemically-defended refugia for freshwater macroinvertebrates

Additional file 4 of Parasite-host ecology: the limited impacts of an intimate enemy on host microbiomes

Additional file 4. Exact sequence variants (ESVs) differing significantly in proportional abundance between sampling locations on outplanted corals: scar vs. distal microbiomes (Sheet 1), scar vs. basal microbiomes (Sheet 2), and distal vs. basal microbiomes. Differentially abundant ESVs were identified by DESeq, with significance assessed by a Wald test. The fold change in abundance (expressed as log2) reflects abundance in natural colonies relative to abundance in outplanted corals. ESV classifications are provided at the highest possible taxonomic resolution.

ChemInform Abstract: Habenariol, a Freshwater Feeding Deterrent from the Aquatic Orchid Habenaria repens (Orchidaceae).

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Appendix C. Results of regression analyses testing for relationships between mean effect size and experimental plot size.

Results of regression analyses testing for relationships between mean effect size and experimental plot size.

Faculty Opinions recommendation of Symbiont-mediated insecticide resistance.

Coastal Ecology

STRONG IMPACTS OF GRAZING AMPHIPODS ON THE ORGANIZATION OF A BENTHIC COMMUNITY

Large brown seaweeds dominate coastal hard substrata throughout many of the world's oceans. In coastal North Carolina, USA, this dominance by brown seaweeds is facilitated by omnivorous fishes, which feed both on red and green algae and on herbivorous amphipods that graze brown algae. When fish are removed in the field, brown seaweeds are replaced by red seaweeds, and herbivorous amphipods are more abundant. Using an array of large (∼4000 L) outdoor mesocosms, we tested three mechanistic hypotheses for this pattern: fish feeding facilitates brown algal dominance (1) by removing red and green algal competitors, (2) by removing amphipods and reducing their feeding on brown seaweeds, or (3) through an interaction of these mechanisms. Our experiments revealed strong impacts of both fish and amphipods, and a key role for the interaction, in structuring this community. When both fish and amphipods were removed (the latter with dilute insecticide), space was rapidly dominated and held for 17 weeks by fast-growing, primarily filamentous green algae. In contrast, when either fish, amphipods, or both were present, green algae were cropped to a sparse turf, and space was more rapidly dominated by larger macroalgae. The impacts of amphipods and fish on late-successional macroalgal assemblages were comparable in magnitude, but different in sign: red seaweeds prevailed in the amphipod-dominated treatment, whereas browns dominated in the presence of fish. Laboratory feeding assays and amphipod densities in the tanks suggested that the significant effects of amphipods were attributable largely, if not exclusively, to the single amphipod species Ampithoe longimana, which fed heavily on brown macroalgae. Our experimental removal of red and green algae failed to enhance cover of brown algae significantly; however, the latter reached substantially lower cover in the grazer-removal treatment, where green algae were very abundant, than in the fish-only treatment, where green algae were sparse. Thus, our results support the third hypothesis: fish-mediated dominance of brown algae involves both suppression of grazing amphipods and removal of algal competitors. Although collective impacts of fish and amphipods on this benthic community were generally comparable in magnitude, impacts normalized to each grazer's aggregate biomass were consistently higher for amphipods than for fish, sometimes by 1–2 orders of magnitude. Thus, the impacts of grazing amphipods (specifically A. longimana) on the benthic community were both strong and disproportionate to their biomass. These experimental results imply that grazing amphipods, which are ubiquitous in marine vegetation but poorly understood ecologically, may play important roles in the organization of benthic communities, particularly where predation pressure is low.

Faculty Opinions recommendation of Biodiversity enhances ecosystem multifunctionality across trophic levels and habitats.

Are lower‐latitude plants better defended? Palatability of freshwater macrophytes

Increased herbivory at lower latitudes is hypothesized to select for more effective plant defenses. Feeding assays with seaweeds and salt marsh plants support this hypothesis, with low‐latitude plants experiencing greater damage in the field and being less palatable than higher‐latitude plants. We tested this hypothesis for freshwater macrophytes because they offered an independent plant lineage and habitat type for testing this general hypothesis and because the patchiness of consumer occupancy across isolated water bodies might produce local variance in herbivory that would override geographic variance and produce different results for this habitat type. When we fed eight congeneric pairs of live plants from four sites in Indiana vs. four sites in South Florida (∼215 and 0 frost days/yr respectively) to three species of crayfishes and one species of snail, three of the four herbivores significantly preferred high‐latitude to low‐latitude plants. For two crayfishes that differed in feeding on live plants (one favoring high‐latitude plants and one not), we retested feeding using foods composed of freeze‐dried and finely ground plants, thus removing structural characteristics while retaining most chemical/nutritional traits. In this assay, both herbivores strongly preferred high‐latitude plants, suggesting that lower‐latitude plants had been selected for more deterrent chemical traits. When we collected 22 pairs of congeneric plants from 9 sites throughout Indiana vs. 13 sites in Central Florida (∼215 and ∼95 frost days/yr respectively) and tested these in feeding assays with three crayfishes using dried, ground, and reconstituted plant material, we found a significant effect of latitude for only one of three species of herbivore. Overall, our results suggest a preference for high‐latitude plants, but the strength of this relationship varied considerably across small scales of latitude that differed considerably in numbers of frost‐free days. The difference in results suggests that large changes in frost frequency over small spatial scales may affect selection for plant defenses, that local variance in herbivory overrode differential selection at geographic scales, or that these possibilities interact when durations of cold weather periodically exclude herbivores from shallower habitats, producing heterogeneous selection for defenses at small spatial scales.