Modelling bioenergetic and population-level impacts of invasive bigheaded carps (Hypophthalmichthys spp.) on native paddlefish (Polyodon spathula) in backwaters of the lower Mississippi River

1. While invasions of large rivers by exotic fish species are well documented, assessing actual or potential impacts on native species is a challenge. Rapid assessments may be possible through the application of a combination of bioenergetic and population dynamic models.
2. Paddlefish (Polyodon spathula) is a native species in the central USA with a history of population decline due to waterway development and overharvesting for roe. It is not known whether paddlefish are impacted by resource competition from invasive bigheaded carp populations, including silver (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), which have expanded dramatically in the Mississippi River.
3. We used bioenergetic models to project the potential impact of invasive silver and bighead carp on zooplankton density and paddlefish somatic growth in backwater habitat. Bioenergetic outputs were translated to impacts on fecundity, becoming inputs for 50-year metapopulation simulations of backwater habitat connected to the main-stem Mississippi River by episodic flood events.
4. Competition with carp reduced growth and increased the risk of population decline for paddlefish. Impacts increased disproportionately with increased carp abundance and were further exacerbated in scenarios with increased diet overlap or decreased zooplankton abundance.
5. We also analysed paddlefish condition data collected at sites near the lower Mississippi River with varying histories of carp invasion. These data give credence to the bioenergetic model output; paddlefish had reduced body condition at sites with long-established, high-density carp populations.
6. We conclude that invasive bigheaded carps have great potential to reduce paddlefish growth, fecundity, and abundance. The pairing of bioenergetics and population models is likely to be broadly useful in assessing the risks posed by other invasive species.

     

A modified microassay for human macrophage activation: I. Activation by antigen-stimulated lymphocytes and correlation with delayed hypersensitivity

The degree of activation of glass-adherent human blood monocyte-macrophages cultured with autologous lymphocytes was assessed by measurement of [¹⁴C]glucosamine uptake. In the absence of streptokinase-streptodornase (SK-SD) or purified protein derivative of tuberculin (PPD) minimal incorporation of the labeled compound occurred. Enhanced glucosamine uptake in the presence of antigen was positively correlated with cell donor-delayed skin hypersensitivity (PPD) and in vitro lymphoproliferative response (PPD, SK-SD). Increasing antigen or mononuclear cell concentrations resulted in increasing macrophage glucosamine uptake. Lymphoblasts, cell clumping, and macrophages with prominent pseudopodia were seen on stained monolayers of stimulated cells. Radioautography of such monolayers showed that the radiolabel was present only in mononuclear phagocytes. Adherent cell protein also generally increased in stimulated monolayers but did not account for the enhanced glucosamine uptake. Measurement of radioactive glucosamine incorporation into human macrophages is a useful tool to assess their degree of activation by lymphocytes stimulated by specific antigen.