Invasiveness of an introduced species: the role of hybridization and ecological constraints

Abstract

Introduced species are confronted with new environments to which they need to adapt. However, the ecological success of an introduced species is generally difficult to predict, especially when hybridizations may be involved in the invasion success. In western Europe, the lake frog Pelophylax ridibundus appears to be particularly successful. A reason for this species' success might be the presence of the invader's genetic material prior to the introduction in the form of a hybrid between P. ridibundus and a second indigenous water frog species. These hybrids reproduce by hybridogenesis, only transmitting the ridibundus genome to gametes and backcrossing with the indigenous species (i.e. P. lessonae). This reproductive system allows the hybrid to be independent from P. ridibundus, and allows the ridibundus genome to be more widely spread than the species itself. Matings among hybrids produce newly formed P. ridibundus offspring (N), if the genomes are compatible. Therefore, we hypothesize that hybridogenesis increases the invasiveness of P. ridibundus (1) by enhancing propagule pressure through N individuals, and/or (2) by increasing adaptation of invaders to the native water frogs' habitat through hybrid-derived ridibundus genomes that are locally adapted. We find support for the first hypothesis because a notable fraction of N tadpoles is viable. However, in our seminatural experiments they did not outperform ridibundus tadpoles in the native water frogs' habitat, nor did they differ physiologically. This does not support the second hypothesis and highlights ecological constraints on the invasion. However, we cannot rule out that these constraints may fall with ongoing selection, making a replacement of indigenous species highly probable in the future.

Multi-event models reveal the absence of interaction between an invasive frog and a native endangered amphibian

“…To our knowledge, our study is the first to assess the potential impact of colonization by alien PR on native amphibians in western Europe that are not phylogenetically closely related ranids of PR (Luquet et al 2011). The results indicate that native BV and invasive PR rarely cohabit on the riverbanks of the mountain rivers in the study area.…”

“…Furthermore, previous studies have shown that PR occupies larger habitats, such as dead arms, gravel pits and lakes (Pagano et al 2001;Van Buskirk 2003), as well as small water bodies such as ponds in gravel beds (Joly and Morand 1994;Morand and Joly 1995). PR tadpoles require high dissolved oxygen rates, which are provided by strong river influence (Luquet et al 2011). In addition, PR often occurs in permanent water bodies with a high density of predator fishes (Van Buskirk 2003).…”

“…Furthermore, previous studies have shown that PR is a ubiquitous amphibian, breeding in a wide variety of flowing and stagnant waters such as rivers, brooks, dead arms, reservoirs and lakes (Pagano et al 2001;Van Buskirk 2003), as well as smaller bodies of water, such as ponds in gravel beds (Joly and Morand 1994;Morand and Joly 1995). As a consequence, this invasion has had an impact on closely related Ranid taxa, observed in the form of competition at the larval stage (Luquet et al 2011) and also in genetic introgression (Holsbeek and Jooris 2010;Hotz and Uzzell 1983;Hotz et al 1985;Plötner et al 2008;Ragghianti et al 2007). However, the consequences of this colonization on other amphibian native species have not been previously investigated.…”

Incorporating evolutionary processes into population viability models

“…Inbreeding (Vander Wal et al ), outbreeding (Frankham et al ), hybridization (Luquet et al ), selection, and adaptation (Hohenlohe et al ) are central influences on evolutionary processes affecting population persistence (Table ). Early researchers used effective population size ( N e ) to assess genetic population viability and evolutionary potential (Frankel & Soulé ; Reed et al ; Nunney & Elam ).…”

Modelling interspecific hybridization with genome exclusion to identify conservation actions: the case of native and invasive Pelophylax waterfrogs

“…To this aim, we adapted and implemented a model of interspecific hybridization without genetic introgression that we have recently developed (Quilodr an et al 2014). The case study of biological invasion reinforced by nonintrogressive hybridization that we investigated here is the colonization of Western Europe by the waterfrog Pelophylax ridibundus coming either from Central or Southern Europe (Holsbeek and Jooris 2010), apparently mediated by human activities (Luquet et al 2011). In France and Switzerland, this waterfrog was introduced during the 20th century for frog legs consumption and for scientific purposes.…”