Biology Reference
In-Depth Information
The alien newt
Triturus carnifex
has introgressed with native
T. cristatus
in both
Great Britain (Brede et al., 2000) and the Geneva Basin of Switzerland and France
(Arntzen and Thorpe, 1999). In the former case, evidence of introgression is still limited
to the introduction site. In the latter, the alien has largely replaced the native across the
landscape over a period of 30-40 generations, although it is not clear whether this is due
to introgression, competition, habitat degradation, or a combination of all three.
Hybridization threatens native bisexual and hybridogenic complexes of water
frogs (
Rana
spp.) in Europe.
Rana
kl.
grafi
is a hybridogenic lineage that occupies
northeastern Spain and southeastern France and originated from the hybridization
of
R. ridibunda
with either
R. perezi
or the hybridogenic
R
. kl.
esculenta
(Pagano
et al., 2001a, c). This lineage is maintained by the standard hybridogenic mecha-
nism of destruction of one parental genome prior to meiosis followed by back-
crossing to one or the other parental species to re-form either a new generation of
similar hybrids or reconstituted individuals of the parental species. Several of
these hybridogenic lineages (or kleptons, designated by “kl.”) occur across Europe,
involving a number of different parental species and their resultant hemiclonal
classes (Graf and Polls Pelaz, 1989; Günther, 1990; Pagano et al., 2001a; Arnold
and Ovenden, 2002). Alien
R. ridibunda
,
R. lessonae
, and
R
. kl.
esculenta
have
been recently introduced to Spain, are hybridizing with the native
R. perezi
, and
are introgressing foreign genes into the local complex of water frogs (Arano et al.,
1995). It is thought that this poses a threat to the bisexual
R. perezi
by boosting
heterozygosity values in local hybridogenic
R
. kl.
grafi
, which may then outcompete
R. perezi
. Similar fears attend the introduction of the alien
R
. kl.
esculenta
(Arano
et al., 1995). Although the feared displacement mechanism, strictly speaking, is
competition, the system could not be maintained without the successful introduction
of the alien genomes; hence, continued hybridization is key to the threat. Similarly,
in Switzerland, hybridization of alien
R. ridibunda
with native
R. lessonae
and
native
R
. kl.
esculenta
has led to creation of, respectively, additional numbers of
R. ridibunda
and new genotypes of
R
. kl.
esculenta
, which themselves are capable
of producing additional generations of
R. ridibunda
by backcrossing with the alien
frogs (Vorburger and Reyer, 2003). These new genomic combinations have con-
tributed to the rapid replacement of the two native water frogs by
R. ridibunda
during the past half century (Vorburger and Reyer, 2003). The standard mecha-
nism for maintaining hybridogenesis does not involve meiotic recombination,
although such does occasionally occur (Pagano and Schmeller, 1999). In southern
France, introduction of alien water frogs has also led to introgression of for-
eign genes into local water frog gene pools (Pagano and Schmeller, 1999; Pagano
et al., 2003) as well as creation of novel assemblages of water frog genomes that
were previously absent (Pagano et al., 2001c). The potential for similar genetic
pollution elsewhere in the ranges of these hybridogenic water frog complexes
is obvious.
As mentioned earlier,
Podarcis wagleriana
is native to Sicily and the satellite
Aegadian Islands and
P. raffonei
to the nearby Aeolian Islands (Capula, 1994a). On
some of these islands, the introduced
P. sicula
has been documented to hybridize
with the native - with
P. wagleriana
on Marettimo and with
P. raffonei
on Vulcano
