The conservation paradox of an introduced population of a threatened species: spadefoot toads in the coastal dunes of the Netherlands

Abstract

Species that are threatened in their native range may actually prosper as introduced populations. To investigate how such introduced populations were established involves determining from where within the natural range the founder individuals originated. This can be accomplished through mtDNA barcoding. The common spadefoot toad (Pelobates fuscus) naturally occurs in the south and east of the Netherlands and has shown a rapid decline. Yet, a flourishing introduced population was recently discovered in the coastal dunes in the west of the country. We use mtDNA barcoding to determine the provenance of the introduced population. We sampled both native and introduced populations from the Netherlands and compared our sequences to haplotypes from across the entire distribution range. The mtDNA haplotypes found in the introduced population are distinct from those naturally occurring in the Netherlands and point towards an origin in the Pannonian Basin, on the boundary between Central and Southeastern Europe. Paradoxically, the thriving P. fuscus population in the Dutch coastal dunes should be considered a conservation risk to local biodiversity, even though within the native range in the Netherlands the species is severely threatened. Our study illustrates the complicated conservation questions associated with species that are both native and invasive.

Piecing the barcoding puzzle of Palearctic water frogs (Pelophylax) sheds light on amphibian biogeography and global invasions

“…In addition, many introduced populations are protected by national decree because they belong to species that supposedly occur naturally in other parts of the same country (e.g., P. ridibundus in France). Such a “conservation paradox” (sensu Koster et al., 2023) does not only safeguards invasive species, it also prevents conservation biologists from studying invasions by making it more difficult to obtain research permits.…”

“…Amphibian translocations are increasingly reported worldwide (in link to the pet trade, as pest control, garden ornaments, or as food, medicine or research resources), generating a high socioeconomic cost when introduced species become a threat to autochthonous wildlife (Measey et al, 2020;Soto et al, 2022). Establishing the identity and origin of non-native amphibians is instrumental to inform wildlife managers and conservation scientists (Dubey, Lavanchy, et al, 2019;Koster et al, 2023;Kuijt et al, 2023), but it first requires a priori knowledge of their native diversity, which is rarely trivial (Robbemont et al, 2023). For example, infamous global invaders such as the cane toad (Rhinella marina), the clawed frog (Xenopus laevis) or the Asian common toad (Duttaphrynus melanostictus) all belong to species complexes composed of multiple lineages in their home range (Furman et al, 2015;Rivera et al, 2022;Wogan et al, 2016).…”

Acknowledging more biodiversity without more species

“…Moreover, when evolutionary units elude legislation, they may cause conservation paradoxes ( 16 ). For example, invasive intraspecific lineages are legally protected in countries where native lineages of the same taxon also occur, since both have the same name and conservation status ( 17 ).…”

“…Subspecies are increasingly represented in national red lists ( 89 , 90 ), although they are exceptions, especially in Asia (e.g., China, Vietnam, Thailand). Characterizing the intraspecific variation of endangered species into consistent taxonomic units is the premise of successful recovery plans ( 91 , 92 ) as it contributes to evidence-based policy decisions, e.g., when codifying translocation actions, fighting illegal trafficking ( 93 ), and managing biological invasions ( 17 ). The description of new phylogeographic subspecies can also breathe life into the conservation of otherwise neglected declining populations, for instance by bringing forward the uniqueness of regional biodiversity in an intelligible way ( 75 ).…”

Extreme genetic depletion upon postglacial colonization hampers determining the provenance of introduced palmate newt populations

“…Therefore, the accuracy with which mtDNA barcoding can pinpoint the provenance of invasive species strongly depends on the source locality of the introduced population. As a consequence, their origin can be determined with high spatial resolution in some cases (Dubey et al, 2019;Dufresnes et al, 2019a;Koster et al, 2023;Kuijt et al, 2023;Robbemont et al, 2023), but remains imprecise in others (de Brouwer et al, 2023;Vliegenthart et al, 2023).…”