Early generation hybrids may drive range expansion of two invasive fishes DataSet

Introgressive hybridization between two invasive species has the potential to contribute to their invasion success and provide genetic resiliency to rapidly adapt to new environments. Additionally, differences in the behaviour of hybrids may lead to deleterious ecosystem effects that compound any negative impacts of the invading parental species. Invasive silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) exhibit introgressive hybridization which could influence their invasion ecology. In order to investigate the role hybrids may have in the invasion ecology of bigheaded carps, [CAA1] we examined the distribution, movements, and environmental cues for movement of two invasive fishes (bighead carp, silver carp) and their hybrids in the Illinois River (USA). Early generation hybrids (e.g., F1,F2, and first generation backcross individuals) composed a greater proportion of the population at the invasion front where abundances of bigheaded carp were low. A greater proportion of early hybrids passed through dams upstream towards the invasion front than did other hybrids and parental species. The movements and environmental cues for movement of late-generation backcrosses (more genetically similar to parental genotype) were not different from the parental species with which they shared the most alleles. Although the direction of the relationship between movement and environment was sometimes different for the parental species and associated advanced generation hybrids, these results indicate that management for parental species will also influence most hybrids. Although early generation hybrids are rare, our results indicate they may disperse towards low-density population zones (i.e., invasion fronts) or are produced at greater frequency in low density areas. These rare hybrids have the potential to produce a variety of unique genetic combinations which could result in more rapid adaptation of a non-native population to their invaded range potentially facilitating the establishment of invasive species

Incorporating metapopulation Dynamics to Inform Invasive Species Management: Evaluating Bighead and Silver Carp Control Strategies in the Illinois River

1. Invasive species management can benefit from predictive models that incorporate spatially explicit demographics and dispersal to guide resource allocation decisions. 2. We used invasive bigheaded carps (Hypophthalmichthys spp.) in the Illinois River, USA as a case study to create a spatially explicit model to evaluate the allocation of future management efforts. Specifically, we compared additional harvest (e.g. near the invasion front vs. source populations) and enhanced movement deterrents to meet the management goal of reducing abundance at the invasion front. 3. We found additional harvest in lower river pools (i.e. targeting source populations) more effectively limited population sizes upriver at the invasion front compared to allocating the same harvest levels near the invasion front. Likewise, decreasing passage (i.e. lock and dam structures) at the farthest, feasible downriver location limited invasion front population size more than placing movement deterrents farther upriver. 4. Synthesis and applications. Our work highlights the benefits of adopting a multipronged approach for invasive species management, combining suppression of source populations with disrupting movement between source and sink populations thereby producing compounding benefits for control. Our results also demonstrate the importance of considering metapopulation dynamics for invasive species control programs when achieving long-term management goals

Low-pass filtered broadband sound.

<p>Spectrogram (left) and power spectrum (right) of the unfiltered (top) broadband sound used by Vetter et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192561#pone.0192561.ref014" target="_blank">14</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192561#pone.0192561.ref015" target="_blank">15</a>] and Murchy et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192561#pone.0192561.ref010" target="_blank">10</a>] to deter bigheaded carp. Bottom spectrogram and power spectrum represent the same broadband sound with a 5 kHz low-pass filter applied using Audacity (version 2). Spectrograms were generated using MatLab (version 9.3) and power spectra were analyzed in Audacity.</p

Audiogram for bighead, silver, and common carp.

<p>Each data point represents the minimum sound pressure level (SPL; dB re 1 μPa SPL_rms) necessary to invoke an AEP response at each frequency examined (100 Hz– 5 kHz). Data are plotted as mean ± SD. Silver carp had the lowest thresholds of the species examined.</p

Example AEP traces recorded in response to high frequencies.

<p>Examples of AEPs (with FFT analysis) elicited at 3 kHz from a silver carp <b>(A)</b> and 5 kHz from a bighead carp <b>(B)</b>; upper traces were taken at sound pressure levels above the hearing threshold while the lower traces represent a baseline recorded at sound pressure levels below the hearing threshold.</p

Mean sound pressure and particle motion thresholds for each species at all frequencies examined.

<p>Letters indicate significant groups and * indicates significantly lower mean thresholds (ANOVA P < 0.05). BHC = bighead carp; SVC = silver carp; CC = common carp.</p

Example auditory evoked potentials (AEP) recorded from a bighead carp at 500 Hz.

<p>Averaged AEP traces <b>(A)</b> and FFT analysis <b>(B)</b> at six different sound pressure levels, including below the hearing threshold (86 dB re 1 μPa SPL_rms). FFT peaks are two times the stimulus frequency (1000 Hz). Hearing threshold was 89 dB re 1 μPa SPL_rms for this bighead carp.</p

Example auditory evoked potentials (AEPs) recorded from a silver carp at 500 Hz.

<p>Averaged AEP traces <b>(A)</b> and FFT analysis <b>(B)</b> at six different sound pressure levels, including below the hearing threshold (80 dB re 1 μPa SPL_rms). FFT peaks are two times the stimulus frequency (1000 Hz). Hearing threshold was 83 dB re 1 μPa SPL_rms for this silver carp.</p

Acoustic characterization of the experimental tank.

<p><b>A)</b> Acoustic impedance (ratio of sound pressure level to particle motion level) at three sound pressure levels (119, 130, and 145 dB 1 μPa SPL_rms) for all frequencies examined. There are no apparent resonances at any of the frequencies. <b>B)</b> Particle acceleration levels for each of the x, y, and z magnitude vectors at 130 dB re 1 μPa for all frequencies examined.</p

Particle acceleration thresholds (dB re 1 ms^-2) for the bighead, silver, and common carp.

<p>Each threshold was derived using a tri-axial accelerometer and are reported as the combined magnitude vector of the x, y, and z-axes Data are reported as mean (± SD).</p