A Novel Technique to Control Invasive Species – Trojan Y

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In this project, USGS scientists are developing a new genetic technique – Trojan Y – to help eradicate invasive species. Although the methodology has been well-developed in theory, this is the first test of its practical application.

Research staff conducting Trojan Y genotype experiments
Research staff conducting Trojan Y genotype experiments

The Science Issue and Relevance: The establishment of invasive species has become more problematic in modern times, as humans have accelerated the intentional and accidental spread of species across their natural dispersal barriers. Once introduced and established, invasive species are notoriously difficult to extirpate. For freshwater fishes, available management techniques include physical removal, dewatering, and ichthyocide (poison); however, these procedures are effort-intensive, expensive, and can harm native fauna. Research on novel techniques to control and eradicate invasive species is desperately needed. In this project, we are developing a new genetic technique – Trojan Y – to eradicate invasive species. Although the methodology has been well-developed in theory, this is the first test of its practical application.

Methodology for Addressing the Issue: The technique involves augmenting wild populations with individuals that are phenotypically sex-reversed from the expected genotype (i.e., carriers of Trojan sex chromosomes). For example, in species with XY sex-determination systems, the addition of YY females should cause a disproportionate influx of Y chromosomes into subsequent generations, biasing the sex ratio towards males.  If enough carriers of Trojan Y chromosomes are introduced, the population should eventually go extinct as females become fewer and fewer. In our study we are using two candidate species: 1) African jewelfish, an invasive cichlid species that is widespread throughout south Florida, but whose genetics are unknown, and 2) the guppy, which has better-known genetics and a short time to maturity. Although it is not invasive in Florida, guppy is easier and faster to work with than the jewlfish and may serve as a proof-of-concept species.

A molecular marker is needed to identify individual sex chromosomes
A molecular marker is needed to identify individual sex chromosomes

Advantages of the Trojan Y chromosome strategy include:

  • It is species-specific (unlike poison or dewatering)
  • It is safer than genetic modification, because no genetically engineered genes are being transferred to subsequent generations.
  • It is reversible. If the influx of Trojan Y fish into the environment is stopped (before the population is extinct) the effect will be stopped in a few generations.
  • It is flexible. The strength of the effect is based on the proportion of treated individuals added. So it can be used for anything from mild control to complete eradication.
  • Does not require massive population influxes, as with sterile male techniques.

Future Steps: We are currently working on developing YY female African jewelfish and guppies in the laboratory and documenting genetic markers for the identification of individuals (e.g., to discriminate amongst fish that are phenotypically similar but genetically distinct). Once in hand, we will assess Trojan Y fish’s behavior, reproductive parameters and other life-history characters to evaluate underlying assumptions of the Trojan Y model. Eventually we plan to conduct small-scale field experiments in mesocosms or experimental ponds to assess the efficacy of the Trojan Y model. The same Trojan Y technology may also be possible with other invasive species (e.g., other fishes, applesnails, crayfish).

Common guppy found in Florida
Common guppy found in Florida