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4. GENETIC DIVERSITY...
their species boundaries are not distinct at present (Loos 1993b; Charmet and Balfourier
1994), they tend to connect this phenomena with changes in the pattern of agriculture. More
generally, Bennett et al (2002) hypothesised that due to the sowing beyond their natural
species distribution, they come into contact. The hybridisation in these new environments
is increasing and leading to unification of both species into a single entity. This opinion postulating
a kind of “reverse evolution” although debatable in interpretation, has raised for the
first time an important general point: L. multiflorum and L. perenne are undergoing further
dynamic changes.
The DNA transposon, Tpo1 and the retrotransposon Lolcopia1 seem to be the most
important drivers of these changes. The copy number of Tpo1 reflects a slow, but significant
increase in L. multiflorum in comparison with L. perenne, especially evident when wild
ecotypes are compared. Dramatic evidence for genome increase in the former species also
emerged from Lolcopia1. About 40% more copies of this retrotransposon have been observed
in L. multiflorum, suggesting that Lolcopia1 is active in this species. Although it would
be necessary to make comparisons to the other members of the genus and its closest relatives
to assess the contribution of these transposons to genome evolution of Lolium, it has
become clear thatL. multiflorum represent a more recent lineage.
Hence, the phylogenetic history and future of L. multiflorum and L. perenne can be demonstrated
as follow. Considering high band sharing and the lack of differences in Lolcopia2
alongside with data from the other markers used in the present studies L. multiflorum and
L. perenne should be regarded as “species complex’’ at the very early stage of divergence.
L. perenne might represent the more ancient lineage judging from Tpo1 and Lolcopia1. This
opinion is in agreement with old concepts suggesting that ancestral forms of Lolium resembled
the present L. perenne (Thomas 1981; Bulińska-Radomska and Lester 1988). Based
on the known Lolium history and the data from transposon analysis, it can be postulated that
ancestral “species complex”, similar to L. perenne, colonized Europe before the last glaciation
event in the Quaternary (Balfourier et al. 2000). As discussed earlier it survived the last
Ice Age in refugia distributed not only in Near East and the three southern peninsulas of
Europe (Balkan, Italian and Iberian), which were free of ice sheets, but also in more northern
regions. Indeed, there are at least 35 localities from central and eastern Europe proposed
to be the full-glacial refugia (Willis and Niklas 2004). The presumably more diffuse distribution
of species complex during the cold stage than previously thought entailed that some
populations were not sufficiently isolated for diversification to have occurred. This history
is recorded by Lolcopia2 and several other markers that do not diversify L. multiflorum and
L. perenne. Moreover, as cpDNA analyses have shown, the Tatra ecotype might be a relict
from those remote times. In recent years, much has been learnt about the role of multiple
glacial-interglacial cycles in the Quaternary period in biota evolution. Until recently, it has
been believed that the predominant response of species to habitat fragmentation was extinction
with speciation taking place in isolated populations and then re-colonisation into north
and east after the last glaciation. This scenario has been also proposed for Lolium perenne
(Balfourier et al. 1998; 2000). Nevertheless, it has become far clear that responses of plant
species to the Quaternary Ice Age were complex. Although some species became extinct,
others survived the full-glacial periods including many tree species (Willis and Niklas 2004).
So did Lolium. Having in mind the Tpo1 and Lolcopia1 evidences, it is reasonable to specu-