Dominance, reproductive behaviours and female mate choice in sterilised versus non-sterilised invasive male crayfish

© 2020, The Author(s). Many methods of controlling invasive crayfishes have limited success because they fail to target all life stages of the population, notably by capturing only large adults that can result in increased juvenile recruitment by removing intraspecific predation. An alternative approach uses the sterile male release technique that involves the mass release of sterile males into the environment, which then mate with fertile females, resulting in unfertilised eggs and, ultimately, reduced juvenile recruitment. This does, however, rely on the sterilised males exhibiting behaviours similar to non-sterilised (entire) males and remaining attractive to females during mate choice. Post-copulatory male guarding behaviour and female promiscuity might also be affected by male sterilisation. To test for the presence of normal reproductive behaviours in sterilised male American signal crayfish Pacifastacus leniusculus, a two-stage experiment examined how sterilisation affects female mate choice and promiscuity, male hierarchical status (relative dominance) and post-copulation guarding. Sterilised males showed similar reproductive behaviours to entire males and remained as attractive to females, with no differences in relative dominance. Post-copulation, guarding behaviours were also unaffected. Females did not display promiscuous behaviour and this was unaffected by whether males were entire or sterilised. The results demonstrated that sterilised males were equally as capable as entire males of achieving dominance and winning mates. In combination, these findings suggest that male sterilisation could be an effective control technique to help reduce juvenile recruitment in wild P. leniusculus populations by reducing reproductive success

Using eDNA to detect the distribution and density of invasive crayfish in the Honghe-Hani rice terrace World Heritage site

The Honghe-Hani landscape in China is a UNESCO World Natural Heritage site due to the beauty of its thousands of rice terraces, but these structures are in danger from the invasive crayfish Procambarus clarkii. Crayfish dig nest holes, which collapse terrace walls and destroy rice production. Under the current control strategy, farmers self-report crayfish and are issued pesticide, but this strategy is not expected to eradicate the crayfish nor to prevent their spread since farmers are not able to detect small numbers of crayfish. Thus, we tested whether environmental DNA (eDNA) from paddy-water samples could provide a sensitive detection method. In an aquarium experiment, Real-time Quantitative polymerase chain reaction (qPCR) successfully detected crayfish, even at a simulated density of one crayfish per average-sized paddy (with one false negative). In a field test, we tested eDNA and bottle traps against direct counts of crayfish. eDNA successfully detected crayfish in all 25 paddies where crayfish were observed and in none of the 7 paddies where crayfish were absent. Bottle-trapping was successful in only 68% of the crayfish-present paddies. eDNA concentrations also correlated positively with crayfish counts. In sum, these results suggest that single samples of eDNA are able to detect small crayfish populations, but not perfectly. Thus, we conclude that a program of repeated eDNA sampling is now feasible and likely reliable for measuring crayfish geographic range and for detecting new invasion fronts in the Honghe Hani landscape, which would inform regional control efforts and help to prevent the further spread of this invasive crayfish

Predicting predatory impact of juvenile invasive lionfish (Pterois volitans) on a crustacean prey using functional response analysis: effects of temperature, habitat complexity and light regimes

The ecological implications of biotic interactions, such as predator-prey relationships, are often context-dependent. Comparative functional responses analysis can be used under different abiotic contexts to improve understanding and prediction of the ecological impact of invasive species. Pterois volitans (Lionfish) [Linnaeus 1758] is an established invasive species in the Caribbean and Gulf of Mexico, with a more recent invasion into the Mediterranean. Lionfish are generalist predators that impact a wide range of commercial and non-commercial species. Functional response analysis was employed to quantify interaction strength between lionfish and a generic prey species, the shrimp (Paleomonetes varians) [Leach 1814], under the contexts of differing temperature, habitat complexity and light wavelength. Lionfish have prey population destabilising Type II functional responses under all contexts examined. Significantly more prey were consumed at 26 °C than at 22 °C. Habitat complexity did not significantly alter the functional response parameters. Significantly more prey were consumed under white light and blue light than under red light. Attack rate was significantly higher under white light than under blue or red light. Light wavelength did not significantly change handling times. The impacts on prey populations through feeding rates may increase with concomitant temperature increase. As attack rates are very high at low habitat complexity this may elucidate the cause of high impact upon degraded reef ecosystems with low-density prey populations, although there was little protection conferred through habitat complexity. Only red light (i.e. dark) afforded any reduction in predation pressure. Management initiatives should account for these environmental factors when planning mitigation and prevention strategies

Supporting Datasets for Life History Responses to Temperature and Seasonality Mediate Ectotherm Consumer-Resource Dynamics Under Climate Warming

  We surveyed populations of the damselfly E. annexum, and their prey zooplankton, to characterize seasonal changes in population abundances and biomass. We sampled three ponds of Lux Arbor Reserve, southwestern Michigan, USA, twice per month from May 2016 to November 2016, and again from April to May 2017. We recorded surface water temperatures at hourly intervals using HOBO pendant temperature loggers (UA-001-64, Onset Corporation, Bourne, MA, USA). We collected E. annexum at three locations within each pond by sweeping a D-frame aquatic dip net (500 mm mesh, Wildco Wildlife Supply Co., Yulee, FL, USA) through macrophyte beds along a 1-m transect parallel to shore at depths of 0.25-0.75 m. We sampled zooplankton using vertical zooplankton net tows (153 mm mesh, 20.32 cm diameter opening, Wildco Wildlife Supply Co.) at water depths of 0.25 to 1.0 m and froze samples for estimation of biomass. We monitored adult emergence of E. annexum from May to June 2017 using floating insect emergence traps. We collected and counted all damselflies every other day and identified males to species.  We identified E. annexum under a dissecting microscope (Stemi 508, Zeiss, USA) using published and online taxonomic guides. We tracked growth in body size of E. annexum by measuring the head capsule width of the first 20 individuals in each sample with an ocular micrometer (± 0.1 mm) and drying and weighing (± 0.01 mg) at least ten individuals of each probable instar. We estimated zooplankton biomass by sorting individuals of the Orders Diptera, Cladocera, Copepoda, and Rotifera from each sample under a dissecting microscope, drying them for 24 hours at 60°C, and weighing them (± 0.01 mg). We then calculated zooplankton biomass per liter sampled as: (dry weight)/(volume filtered by the plankton net). We estimated the volume filtered as: pi * net radius2 * sample depth * filtering efficiency, assuming filtering efficiency of 0.5. The datasets presented here represent unprocessed data with measurements from three ponds, including hourly temperature, damselfy counts and head capsule widths, and zooplankton weights from biweekly pond sampling. These data also include counts of emerging adult damselflies. The included R script ("Insect_abundances_1_30_23.R") processes these data files to characterize seasonal changes in damselfly body sizes, abundances, zooplankton biomass, abundances of emerging adult damselflies, and pond temperature seasonality. The R script produces Figure S1, and the estimates of K, Smin, Smax, Tav, Tamp, and the phase shift of the temperature function for Table S1, of the manuscript supplementary materials.  </p

Trophic tangles through time? Opposing direct and indirect effects of an invasive omnivore on stream ecosystem processes.

Omnivores can impact ecosystems via opposing direct or indirect effects. For example, omnivores that feed on herbivores and plants could either increase plant biomass due to the removal of herbivores or decrease plant biomass due to direct consumption. Thus, empirical quantification of the relative importance of direct and indirect impacts of omnivores is needed, especially the impacts of invasive omnivores. Here we investigated how an invasive omnivore (signal crayfish, Pacifastacus leniusculus) impacts stream ecosystems. First, we performed a large-scale experiment to examine the short-term (three month) direct and indirect impacts of crayfish on a stream food web. Second, we performed a comparative study of un-invaded areas and areas invaded 90 years ago to examine whether patterns from the experiment scaled up to longer time frames. In the experiment, crayfish increased leaf litter breakdown rate, decreased the abundance and biomass of other benthic invertebrates, and increased algal production. Thus, crayfish controlled detritus via direct consumption and likely drove a trophic cascade through predation on grazers. Consistent with the experiment, the comparative study also found that benthic invertebrate biomass decreased with crayfish. However, contrary to the experiment, crayfish presence was not significantly associated with higher leaf litter breakdown in the comparative study. We posit that during invasion, generalist crayfish replace the more specialized native detritivores (caddisflies), thereby leading to little long-term change in net detrital breakdown. A feeding experiment revealed that these native detritivores and the crayfish were both effective consumers of detritus. Thus, the impacts of omnivores represent a temporally-shifting interplay between direct and indirect effects that can control basal resources

Invertebrate communities and the comparative study of crayfish.

<p>Each point represents the average for a study pool. (a) Invertebrate biomass (average biomass for coarse mesh leaf litter bags) as a function of crayfish density. Shown is the best fit exponential decay relationship (invertebrate biomass = 42.7 * exp (crayfish * −3.2)). (b). Average individual invertebrate mass as a function of crayfish density. White symbols with the solid line are caddisflies (Tricoptera), corresponding to the left y-axis and gray symbols with the dashed line correspond to stoneflies (Plecoptera), corresponding to the right y-axis. If pools did not contain any individuals, these points are not shown.</p

Results from the experimental manipulation of crayfish densities.

<p>Each point represents a study pool. Total non-crayfish benthic invertebrate abundance corresponds to open white symbols and gray confidence interval while total non-crayfish biomass corresponds to the gray symbols and darker gray confidence intervals. Benthic invertebrates were negatively associated with crayfish for both non-crayfish benthic invertebrate numerical density (log (invertebrates m⁻²) = −0.087 * crayfish +3.38, <i>R²</i> = 0.59, <i>P</i><0.001) and biomass density (log (invertebrates m⁻²) = −0.046 * crayfish +2.82; <i>R²</i> = 0.33, <i>P</i> = 0.02). The solid lines denote these best fit linear model and the polygons indicate 95% confidence intervals. Note data are log-transformed.</p

Ecosystem processes in the comparative study.

<p>Each point represents a different study pool. (a). Rate of algal accrual on elevated tiles. The gray polygon denotes the 95% confidence interval. (b). Rate of breakdown of leaves. Also shown in this panel in the open polygon and dashed line is the prediction interval and predicted line from the 2008 experimental relationship between leaf litter breakdown rate and crayfish.</p