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7. ROLE OF QTLs IN THE EARLY EVOLUTION...
7.4.2. QTLs involved in the evolution of L. multiflorum and L. perenne
A glance at teosinte, a grass that grows robustly in uncultivated areas of Mexico has
to evoke astonishment. Although maize is a descendant of teosinte, the seeds and plants
look much different. The teosinte plant produces several tillers, whereas maize has one main
stem. Teosinte stalks each bear several ears, but they are much smaller than those of maize.
Nevertheless, thousands of years of mutations and human selection catalyzed the evolution
of teosinte from a wild grass into modern corn. Despite of these differences teosinte and
maize are a single species. The differences between maize and teosinte are governed by
a few major genes, a few blocs of multiple linked genes plus a larger number of small effect
loci. They are scattered throughout the genome. For example, a QTL on the first chromosome
causes the ears of corn to be big and to grow on a few short branches. A gene on the
second chromosome causes more rows of kernels to grow, yielding more food per corn plant
(Doebley 2004). The striking example of maize demonstrates how QTL mapping can open
“a door” into searches for the “footprints” of domestication and evolution.
A glance at L. multiflorum and L. perenne, grasses that grow predominantly in Europe
in cultivated and semi-natural areas has to evoke astonishment as well. Although they are
classified by botanists as distinct taxa, they are nearly unrecognizable, they possess the
same gene pool, similar genomes (Chapter 3-6), karyotypes (Naylor 1960) and they are fully
interfertile. The broad genetic analyses presented in the proceding chapters have demonstrated
that the paradox of L. multiflorum and L. perenne could best be explained by regarding
them, similarly to teosinte and maize as a single species. This raises next questions. Can
one demonstrate that discrete shifts in morphology results from intraspecific variation How
many genes are involved in minor differences between them What are these genes What
is the influence of human activity (breeding) on their diversification The current pioneering
studies on QTLs potentially involved in morphological differences between L. multiflorum and
L. perenne confirm little genomic diversification of these species but also seem to demonstrate
that they begin to evolve and it can be expected that they will follow in teosinte and
maize or many other domesticated species footsteps. All the more there are old conceptions
that perennial forage grasses are not domesticated with the single exception...L. multiflorum.
It was developed by unconscious selection prior to the twelfth century in the Lombardy and
Piedmont plains of Italy (Beddows 1953). The domestication of Italian ryegrass likely was associated
with the domestication of livestock for agriculture. Ryegrass used to exist in “hybrid
swarms” with perennial and Italian phenotypes as opposite extremes of a continuum. Hay
harvesting, and reseeding with shattered seeds, resulted in the selection of tall, sparsetillered,
semi-annual phenotype that has since been elevated to species status (Casler and
Duncan 2002). This theory is in perfect agreement with the results from the previous chapters
suggesting that L. multiflorum is younger than L. perenne and stems from the “complex species”.
This means that in a case of L. multiflorum and L. perenne we are witnessing the same
sort of processes which have entailed the diversification of teosinte and maize for a few thousand
years. At this point one can ask: Why are they not so different Since they have only
hundreds of years to evolve whereas maize and teosinte - thousands. Thereby, the previous
questions should be transformed. What are the genes and how many of them are involved in
the domestication of L. multiflorum And the answer is - a lot of genes.