Messaggioda Stefano_A » gio giu 21, 2007 9:49 am
Tratto da “Environmentally caused dwarfism or a valid species - Is Testudo weissingeri Bour, 1996 a distinct evolutionary lineage? New evidence from mitochondrial and nuclear genomic markers”.
Di Uwe Fritz, Pavel Kiroký, Hajigholi Kami, Michael Wink.
Pubblicato su Molecular Phylogenetics and Evolution 37 (2005) 389–401.
Our mtDNA and nuclear fingerprinting data do not
support the distinctiveness of Testudo weissingeri. While
we found all traditionally recognized Testudo species
and some subspecies or geographic populations clearly
distinct in both data sets, neither the mtDNA data nor
nuclear fingerprinting revealed any significant differences
between T. marginata and T. weissingeri.
Our mtDNA findings are in line with the results of van der
Kuyl et al. (2002). These authors sequenced the slowly
evolving 12S rRNA gene of two T. marginata and two
T. weissingeri and found no differences. We used the
faster-evolving cytochrome b gene and greater sample
sizes for T. marginata (nD25) and T. weissingeri (nD7),
and found no distinction between the species.
Ed ancora…
Testudo weissingeri differs from T. marginata mainly
by its smaller size and some color-pattern characteristics.
The shell length in T. weissingeri is normally below
21.5 cm, while T. marginata usually exceeds 26.0 cm
(Bour, 1996). The dwarfism of T. weissingeri and related
allometric differences discriminate it morphologically by
multivariate methods from large-sized T. marginata
(Perälä, 2002b). However, small tortoises and individuals
colored like T. weissingeri also occur throughout the
range of T. marginata (Artner, 1996; U. Fritz unpubl.
observation).
(…)
Also, other characters originally thought to be diagnostic for
T. weissingeri, like the presence of thigh tubercles, are
common in T. marginata (Artner, 1996; Perälä, 2002d).
It is well known that many animal species show
reduced body sizes in an environment with limited
resources (e.g., Emys orbicularis: Fritz, 2003; Homo sapiens:
Shea and Bailey, 1996). Another example of this
phenomenon is the widespread island dwarfism (e.g.,
Jianu and Weishampel, 1999; Palombo, 2001; Sondaar,
1977; Vartanyan et al., 1993), currently attracting considerable
public interest with the newly described dwarfed Homo
Xoresiensis (Brown et al., 2004). Likewise,
Bringsøe et al. (2001) suggested that the small size of
T. weissingeri is a response to suboptimal habitat. Testudo
weissingeri occupies the hottest, driest and poorest
region within the range of T. marginata where it replaces
the latter species. Taking the environmental pressure and
the lack of differentiation in the mitochondrial and
nuclear genome into account, we conclude that Testudo
weissingeri Bour, 1996 is not a distinct evolutionary lineage
and relegate it to the synonymy of Testudo marginata.