Trojan Y Invasive Species Control - Sex Marker Identification

Science Center Objects

To control or possibly eliminate non-native species without harm to native fauna, a genetic technique using sex-reversed females with two Y chromosomes (Trojan Y) is being developed to reduce the breeding success of the species, ultimately resulting in population decline or loss.

African Jewelfish (Hemichromis letourneuxi)
African Jewelfish (Hemichromis letourneuxi)

The Science Issue and Relevance: Established populations of invasive species are difficult to eradicate. Removal of non-native freshwater fish species has relied upon physical removal, dewatering and ichthyocides (poison), which require intense effort, high costs and negatively affect the ecosystem. To control or possibly eliminate non-native species without harm to native fauna, a genetic technique using sex-reversed females with two Y chromosomes (Trojan Y) is being developed to reduce the breeding success of the species, ultimately resulting in population decline or loss.

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 the Trojan Y sex chromosome). 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. We are working with 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. The African Jewelfish (Hemichromis letourneuxi) is a non-native fish established in south Florida and is known to be aggressive and potentially harmful to native fauna. 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

Finding genetic markers: To implement this technology, Dr. Pam Schofield is developing females with YY sex-chromosome complements using aquaculture techniques, including gonadal hormones and selective breeding. A molecular marker is needed to identify individual sex chromosomes (e.g., to discriminate amongst fish that are phenotypically similar but genetically distinct). 

To identify sex-specific genetic markers, a number of new genetic markers are being tested (RAPDs, microsatellites, sex-linked gene sequences, RAD-seq and SNPs). Once identified, sex-determining markers will then be tested on wild and sex-reversed fish to assess their precision and accuracy.

Advantages of the Trojan Y chromosome strategy include:

  • It is does not harm non-native species or the ecosystem.
  • No genetically engineered genes are transferred into the next generation.
  • 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: Once genetic identification is possible, the Trojan Y method will be tested in small-scale field experiments in mesocosms or experimental ponds. Further studies such as behavior, breeding, interspecies interactions, and field trials are planned. The same Trojan Y technology may also be possible with other invasive species (e.g., other fishes, applesnails, crayfish).