Polyploidy and habitat differentiation in Dactylis glomerata L. from Galicia (Spain)

Abstract

The microdistribution of diploid and tetraploid plants of Dactylis glomerata L. was examined and related to their immediate environment in several sites in central Galicia, where morphologically indistinguishable individuals of both ploidies grow in sympatry. The two related cytotypes differed in habitat preference. Diploids were mainly confined to the low-density forest-floor habitat in woodlands of mostly ancient origin, whereas tetraploids were widespread in varied habitats but clearly predominant in open areas, particularly in disturbed anthropic sites. The in situ comparison of plant performance showed that where plants of each ploidy were more common they produced more tillers, panicles and seeds. This habitat preference closely reflected differences in life-history characteristics. The tetraploids had an early and short flowering time almost always completed before the aestival drought, whereas the diploids began to flower several weeks later and flowered throughout the drought. Comparisons along artificial gradients of soil water availability and light transmittance indicated that the cytotypes had distinct physiological requirements which probably originated in metabolic and more general genetic differentiation and could be directly attributable to ploidy. Habitat differentiation increases the species' colonizing ability. It also amplifies divergence in reproductive strategy between diploids and tetraploids, which reduces ineffective crossing between cytotypes and thereby permits them to coexist in sympatry. The effect of hybridization at the polyploid level on the differentiation between cytotypes was assessed from the recent introduction of a foreign tetraploid entity into the study area. Hybridization between the two distinct tetraploids was found to increase habitat differentiation between the diploids and the tetraploids, but the major part of this differentiation is probably attributable to ploidy itself.

Allozyme polymorphism in diploid and polyploid populations of Galium

“…A comparable situation has been very well documented by enzyme analyses for Dactylis glomerata-2x and -4x populations in the northwestern Iberian Peninsula (Lumaret et a!., 1987;Lumaret and Barrientos, 1990) or for Tolmiea menziesii-2x and -4x in western North America (Soltis and Riesenberg, 1986). The role of polyploidy thus is to contribute to both stability and change in evolution (Ehrendorfer, 1980(Ehrendorfer, , 1988.…”

Population biology of intraspecific polyploidy in grasses

“…Lumaret et al (1987) demonstrate the power of cytotypic variation (Fig. 7.lA), in the sense that one evolutionary unit (Daetylis glomerata sensu lato) occupies three microhabitats.…”

“…Dactylis glomerata L., cocksfoot, orchard grass, is a rhizomatous grass naturally distributed throughout Europe to northern Africa and Asia that has been widely introduced elsewhere in the world (Miintzing, 1937;Myers, 1941;Stebbins & Zohary, 1959;Zohary & Nur, 1959;Borrill, 1961Borrill, , 1978Parker & Borrill, 1968;Lumaret et al, 1987;Lumaret, 1988b;Bretagnolle & Thompson, 1996). Diploid, tetraploid, and hexaploid plants and populations are known.…”

“…Nielsen (1944) found five ploidy levels within a single population of Panicum virgatum, and populations with three cytotypes were common (McMillan & Weiler, 1959). Lumaret et al (1987) mapped Dactylis glomerata plants with a plot of 10 X 80 m that had a local diploid and tetraploid cytotype and an agronomically introduced tetraploid cytotype and the tetraploid hybrids of the two tetraploid races (Fig. 7.1A).…”

“…In Dactylis glomerata there is sufficient data to suggest that patterns are deterministic not random (Stebbins & Zohary, 1959;Lumaret et al, 1987;Roy & Lumaret, 1987;Bretagnolle & Thompson, 1996), while for Andropogon gerardii, the lack of match between patterns at different scales (Keeler et al, 1987;Keeler, 1990Keeler, , 1992 could reasonably result from stochastic effects.…”