DNA-based species detection capabilities using laser transmission spectroscopy.

Early detection of invasive species is critical for effective biocontrol to mitigate potential ecological and economic damage. Laser transmission spectroscopy (LTS) is a powerful solution offering real-time, DNA-based species detection in the field. LTS can measure the size, shape and number of nanoparticles in a solution and was used here to detect size shifts resulting from hybridization of the polymerase chain reaction product to nanoparticles functionalized with species-specific oligonucleotide probes or with the species-specific oligonucleotide probes alone. We carried out a series of DNA detection experiments using the invasive freshwater quagga mussel (Dreissena bugensis) to evaluate the capability of the LTS platform for invasive species detection. Specifically, we tested LTS sensitivity to (i) DNA concentrations of a single target species, (ii) the presence of a target species within a mixed sample of other closely related species, (iii) species-specific functionalized nanoparticles versus species-specific oligonucleotide probes alone, and (iv) amplified DNA fragments versus unamplified genomic DNA. We demonstrate that LTS is a highly sensitive technique for rapid target species detection, with detection limits in the picomolar range, capable of successful identification in multispecies samples containing target and non-target species DNA. These results indicate that the LTS DNA detection platform will be useful for field application of target species. Additionally, we find that LTS detection is effective with species-specific oligonucleotide tags alone or when they are attached to polystyrene nanobeads and with both amplified and unamplified DNA, indicating that the technique may also have versatility for broader applications.

Hybrid zone dynamics and species replacement between Orconectes crayfishes in a northern Wisconsin lake.

Hybrid zones that result in the genetic assimilation (replacement) of one species by another are underrepresented in the animal literature, most likely due to their transient nature. One such zone involves the rusty crayfish, Orconectes rusticus, and its congener O. propinquus. Orconectes rusticus was recently introduced into northern Wisconsin and Michigan lakes and streams, where it is hybridizing with and displacing resident O. propinquus. Here we report on a study investigating the dynamics of a hybrid zone between the two crayfish in Trout Lake, Wisconsin, where both the time (circa 1979) and location of the initial introduction are known. Our prediction was that hybridization should hasten the demise of O. propinquus because we expected that male O. rusticus (which are larger than congeners) would outcompete male O. propinquus for mates of both species. If hybrid progeny are unfit, then the result would be decreased reproductive output of O. propinquus females. However, we found a pattern of cytonuclear disequilibrium between allozymes and mtDNA suggesting that a majority (94.5%) of F1 hybrids resulted from matings between O. rusticus females and O. propinquus males. Also contrary to expectations, fecundity (O. rusticus and O. propinquus) and early hybrid survivorship did not differ significantly from nonhybrids. Moreover, adults of mixed ancestry were superior to both O. rusticus and O. propinquus in competition for a limiting food resource. Using a single-locus model, we estimated that hybridization increases the advance of O. rusticus genes in Trout Lake between 4.8% and 36.3% above that due to the previously documented ecological interactions. Consequently, whereas hybridization may be hastening the elimination of genetically pure O. propinquus, introgression is nevertheless slowing the loss of O. propinquus nuclear genes. Although our results suggest that O. rusticus and O. propinquus may not be true species under the biological concept, their ecological differences are of great conservation importance.

Ecological forecasts: an emerging imperative.

Planning and decision-making can be improved by access to reliable forecasts of ecosystem state, ecosystem services, and natural capital. Availability of new data sets, together with progress in computation and statistics, will increase our ability to forecast ecosystem change. An agenda that would lead toward a capacity to produce, evaluate, and communicate forecasts of critical ecosystem services requires a process that engages scientists and decision-makers. Interdisciplinary linkages are necessary because of the climate and societal controls on ecosystems, the feedbacks involving social change, and the decision-making relevance of forecasts.

Progress in invasion biology: predicting invaders.

Predicting which species are probable invaders has been a long-standing goal of ecologists, but only recently have quantitative methods been used to achieve such a goal. Although restricted to few taxa, these studies reveal clear relationships between the characteristics of releases and the species involved, and the successful establishment and spread of invaders. For example, the probability of bird establishment increases with the number of individuals released and the number of release events. Also, the probability of plant invasiveness increases if the species has a history of invasion and reproduces vegetatively. These promising quantitative approaches should be more widely applied to allow us to predict patterns of invading species more successfully.

Global biodiversity scenarios for the year 2100.

Scenarios of changes in biodiversity for the year 2100 can now be developed based on scenarios of changes in atmospheric carbon dioxide, climate, vegetation, and land use and the known sensitivity of biodiversity to these changes. This study identified a ranking of the importance of drivers of change, a ranking of the biomes with respect to expected changes, and the major sources of uncertainties. For terrestrial ecosystems, land-use change probably will have the largest effect, followed by climate change, nitrogen deposition, biotic exchange, and elevated carbon dioxide concentration. For freshwater ecosystems, biotic exchange is much more important. Mediterranean climate and grassland ecosystems likely will experience the greatest proportional change in biodiversity because of the substantial influence of all drivers of biodiversity change. Northern temperate ecosystems are estimated to experience the least biodiversity change because major land-use change has already occurred. Plausible changes in biodiversity in other biomes depend on interactions among the causes of biodiversity change. These interactions represent one of the largest uncertainties in projections of future biodiversity change.

Biological invasions: Lessons for ecology.

Anthropogenic introduction of species is homogenizing the earth's biota. Consequences of introductions are sometimes great, and are directly related to global climate change, biodiversity AND release of genetically engineered organisms. Progress in invasion studies hinges on the following research trends: realization that species' ranges are naturally dynamic; recognition that colonist species and target communities cannot be studied independently, but that species-community interactions determine invasion success; increasingly quantitative tests of how species and habitat characteristics relate to invasibility and impact; recognition from paleobiological, experimental and modeling studies that history, chance and determinism together shape community invasibility.

Periphytic food and predatory crayfish: relative roles in determining snail distribution.

In the laboratory and field, we examined how periphyton (food of snails) and predatory crayfish influenced snail distribution in Trout Lake, a permanent, northern Wisconsin lake. Laboratory experiments (with no crayfish) tested the importance of periphyton biomass in determining snail preference among rocks, and among rock, sand, and macrophyte substrates. Among rocks with four different amounts of periphyton, periphyton biomass and the number of Lymnaea emarginata, Physa spp., and Amnicola spp. were positively related. A similar, but non-significant, trend occurred for Helisoma anceps. A field experiment at a site in Trout Lake where predation risk was low confirmed the preference by snails for periphyton covered rocks; more snails colonized rocks with periphyton than rocks without. When given a choice of rock, sand, and macrophytes in the laboratory, L. emarginata preferred high periphyton biomass and rock. Laboratory and field results contrasted with the distribution of snails in Trout Lake; no snails occurred in areas with abundant periphyton-covered rocks, but snails were abundant nearby on scattered rocks with little periphyton. However, where snails were absent, crayfish were abundant (14.5 crayfish-trap-1-day-1), and where snails were abundant, crayfish were rare (3.2 crayfish-trap-1-day-1), suggesting that crayfish predation reduced snails. The hypothesis that the negative association between snail and periphyton biomass resulted from snail grazing was supported by the results of a field snail enclosure-exclosure experiment (1 m2 cages; n=3). All experiments and observations therefore suggest that: 1) crayfish predation is more important than a preference for high periphyton biomass in determining snail distribution in Trout Lake; 2) periphyton biomass is negtively related to snail grazing; and 3) crayfish had a positive indirect effect on periphyton by preying on grazing snails.

Regulation of Lake Primary Productivity by Food Web Structure.

We performed whole-lake manipulations of fish populations to test the hypothesis that higher trophic levels regulate zooplankton and phytoplankton community structure, biomass, and primary productivity. The study involved three lakes and spanned 2 yr. Results demonstrated hierarchical control of primary production by abiotic factors and a trophic cascade involving fish predation. In Paul Lake, the reference lake, productivity varied from year to year, illustrating the effects of climatic factors and the natural dynamics of unmanipulated food web interactions. In Tuesday Lake, piscivore addition and planktivore reduction caused an increase in zooplankton biomass, a compositional shift from a copepod/rotifer assemblage to a cladoceran assemblage, a reduction in algal biomass, and a continuous reduction in primary productivity. In Peter Lake, piscivore reduction and planktivore addition decreased zooplanktivory, because potential planktivores remained in littoral refugia to escape from remaining piscivores. Both zooplankton biomass and the dominance of large cladocerans increased. Algal biomass and primary production increased because of increased concentrations of gelatinous colonial green algae. Food web effects and abiotic factors were equally potent regulators of primary production in these experiments. Some of the unexplained variance in primary productivity of the world's lakes may be attributed to variability in fish populations and its effects on lower trophic levels.

Habitat disturbance and the stability of freshwater gastropod populations.

The interaction of population stability and habitat permanence has a major influence on the microdistribution of freshwater snails. For two years (February 1980-January 1982), we monitored the abundance of macrophytes and the abundance and size structure of four species of macrophyte-associated freshwater snails in an English pond. Previous work (Lodge, in press) showed that two species, the pulmonate Lymnaea peregra (Mull.) and the prosobranch Valvata piscinalis (Mull.), were associated with cubmersed macrophytes, while two other species, the pulnonate Planorbis vortex (Linn.), and the prosobranch Bithynia tentaculata (Linn.), were associated with emergent macrophytes. A dramatic decline of submersed macrophytes provided a test of the hypotheses that the population stability of Lymnaea and Valvata was 1) high, and 2) an important cause of the association of those two species with submersed macrophytes.When the submersed macrophytes declined in August 1980, >99% of the Lymnaea and about 35% of the Valvata population died. The populations of Planorbis and Bithynia were not reduced. In 1980, Lymnaea and Valvata had simple annual life cycles, but with the regrowth of submersed macrophytes in spring 1981, the Lymnaea and Valvata populations responded with early, high, and repeated reproduction with some overlap of generations. In both years, Planorbis had an annual semelparous life cycle, while Bithynia lived up to 3 years and bred iteroparously.Following the terminology of Connell and Sousa (1983), Lymnaea exhibited low resistance to habitat disturbance but high adjustment following the disturbance. Valvata showed higher resistance than Lymnaea, and also high adjustment. Although the population stability of Planorbis and Bithynia could not be rigorously evaluated, published accounts of those species' life cycles suggest that stability, specially the adjustment component, was low. We suggest that the population stability of the four species is a major determinant of the association of Lymnaea and Valvata with the impermanent macrophyte habitat and that of Planorbis and Bithynia with the permanent macrophyte habitat.