Importance of Assessing Population Genetic Structure before Eradication of Invasive Species: Examples from Insular Norway Rat Populations

Abstract

Determining the inter-island migration abilities of pest species and delimiting eradication units enable more viable long-term eradication campaigns because recurrent colonization from neighboring islands is avoided. We examined the genetic structure of the invasive Norway rat (Rattus norvegicus) to identify gene flow between islands and delimit population units at different geographical scales. We investigated variation in eight microsatellite loci in rat populations from 18 islands, representing five archipelagos off the Brittany coast (France). Although most of the islands are isolated from each other, short genetic distances, weak F ST values between close islands, and a high level of cross-assignment showed that individuals collected on different islands could represent a single population unit. A Bayesian clustering method also supported the existence of high levels of gene flow between some neighboring islands. Thus, the statement "one island equals one population" can be false when inter-island distances are less than a few hundred meters. Genetic studies enable the definition of island clusters among which migration may occur that should be considered eradication units. To avoid reinvasion and to minimize ecological and economic costs, rats on all islands in an eradication unit should be eradicated simultaneously. We suggest that the genetic monitoring we performed here can be applied for management of any pest.Resumen: La determinación de las capacidades de migración interinsular de especies plaga y la delimitación de unidades de erradicación hace posible que las campañas de erradicación sean más viables a largo plazo porque se evita la recolonización recurrente desde islas vecinas. Examinamos la estructura genética de la rata Rattus norvegicus para identificar el flujo de genes entre islas y delimitar unidades poblacionales en diferentes escalas geográficas. Investigamos la variación en ochos loci microsatélites en poblaciones de ratas de 18 islas, representando a cinco archipiélagos de la costa de Bretaña (Francia). Aunque la mayoría de las islas están aisladas unas de otras, las distancias genéticas cortas, los valores F ST débiles entre islas cercanas y un alto nivel de asignación cruzada mostraron que los individuos recolectados en islas diferentes pudieran representar a una sola unidad poblacional. Un método de agrupamiento Bayesiano también sostuvo la existencia de altos niveles de flujo génico entre algunas islas cercanas. Por lo tanto, la afirmación de que "una isla equivale a una población" puede ser falsa cuando las distancias interinsulares son menores a unos cuantos cientos de metros. Los estudios genéticos permiten la definición de grupos insulares, entre los que puede ocurrir migración, y que Genetic Tools and Eradication StrategiesAbdelkrim et al.deben ser considerados como unidades de erradicación. Para evitar la reinvasión y para minimizar costos ecológicos y económicos, se debería erradicar simultáneamente a las ratas de todas las islas en una unidad de erradicación. Sugerimos que el ...

Using population genetic tools to develop a control strategy for feral cats (Felis catus) in Hawai'i

“…Generally, F ST values below 0.05 suggest high levels of gene flow and population connectivity (Thulin et al 2006). Therefore, we conclude that the three populations were not founded independently, there was rapid colonisation from initial founders owing to high growth rates, and ongoing gene flow has occurred (Abdelkrim et al 2005;Pontier et al 2005). Apparently, feral cats in Hawai'i have not differentiated markedly from their initial founders (Pontier et al 2005).…”

“…Successful management of invasive species requires identifying a target population of manageable size that has a low recolonisation risk (Robertson and Gemmell 2004). Attempts to control only a fraction of the population or a sink population could result in rapid recolonisation (Robertson and Gemmell 2004;Abdelkrim et al 2005). Identifying routes of potential migration is difficult using direct observations, but vital for controlling invasive species (Robertson and Gemmell 2004;Abdelkrim et al 2005;Rollins et al 2006).…”

“…Identifying routes of potential migration is difficult using direct observations, but vital for controlling invasive species (Robertson and Gemmell 2004;Abdelkrim et al 2005;Rollins et al 2006). Population genetics can provide valuable information about the demographic status and dynamics of invasive species and may provide an alternative approach for developing control strategies (Robertson and Gemmell 2004;Abdelkrim et al 2005;Pontier et al 2005). …”

“…Only recently have these tools been applied in invasive species management (Robertson and Gemmell 2004;Abdelkrim et al 2005;Rollins et al 2006). Invasive species are the main cause of species extinctions in island ecosystems (Courchamp et al 1999) and the second main cause of biodiversity loss after habitat destruction (Vitousek et al 1997).…”

Towards modelling persistence of woodland birds: the role of genetics

“…Perhaps the most straightforward of these is identifying patterns of spatial population structure, important for maintaining populations, and for focussing pest control and eradication (Abdelkrim et al 2005;. Some recent in-depth reviews of spatial genetic approaches include Manel et al (2003), Holderegger and Wagner (2008), Storfer et al (2007) and Guillot et al (2009).…”