Karyology and hydridization in the Carex flava complex in Switzerland

Abstract

The karyology of Carex flava aggregate in Switzerland was investigated. Fertility was measured and crossings were done. The microsporogenesis is described. In Switzerland, the C. flava group consists of C. flava var. flava (n = 30, 31), C. flava var. alpina (n = 30, 31), C. lepidocarpa (n = 34), C. demissa (n = 34, 35), and C. serotina (n = 34, 35, 36). The three species with high chromosome numbers often grow together with C. flava. Accordingly, F1‐hybrids with this parental species are frequent. Their meiosis and fertility are profoundly disturbed. With artificial hybrids, disturbances decrease as the differences in chromosome numbers of the parents decrease. Backcrossings with the parents over many generations lead to forms identical in morphology and fertility to the pure species, which are called stabilized cryptic backcrosses. The extensive genetic and karyotype‐variability within populations, particularly of C. flava, might be due to this introgression. In other parts of Europe (e.g. Britain) hybrids with C. flava as one parent are rare. As a consequence, introgression plays a little role and karyotypes are stable. Karyotype evolution in C. flava group is quite different from karyotype evolution in other Carex species. This is due to differences in life history tactics.

The Evolution of Chromosome Arrangements in Carex (Cyperaceae)

“…Heilborn also hypothesized that the direction of evolutionary change in the genus has been from lower to higher chromosome numbers (Heilborn, 1924: 188), and subsequent researchers (Davies, 1956;Hoshino, 1981;Schmid, 1982;Luceño & Castroviejo, 1993) have assumed this hypothesis to be true. Heilborn's hypothesis implies that ancestral character state reconstructions should recover lower numbers at the deepest nodes of a phylogeny.…”

“…Agmatoploidy contrasts with strict or quantitative aneuploidy, which refers to chromosome number changes due to duplication of single chromosomes; polyploidy, which refers to duplications of whole sets of chromosomes; and dysploidy, which is a general term for chromosome number changes by any mechanism that involve only a subset of an organism's chromosomes (Löve et al, 1957). Heilborn (1924: 210) held that although chromosome fission probably played a role in the origins of Carex, more recent chromosome number increases in the genus must be a consequence of chromosome duplications (also see Tanaka, 1949;Schmid, 1982). Tanaka (1949: 23) reported that in 44 plants from 21 different species, the pattern "(n-2) II+1III+1I" is predominant, which he suggested was evidence of quantitative aneuploidy (either one duplication and one deletion or two duplications).…”

“…Quantitative aneuploidy has been suggested as an important mode of evolution in the Carex flava L. complex (Schmid, 1982) based primarily on the fact that trivalents in the C. flava complex as studied in Switzerland are typically isomorphic. Carex brevior (Dewey) Mackenzie ex Lunell (n=24, 26, 28, 30, 32, 34) presents stronger evidence for quantitative aneuploidy.…”

Chromosome Evolution in Cyperales

“…Carex is the largest and most diverse group of organisms exhibiting holocentric chromosomes and agmatoploid evo- lution (Reznicek 1990) with polymorphisms between closely related species, as well as within species (Faulkner 1972;Schmid 1982;Whitkus 1991;Hoshino and Okamura 1994;Hoshino and Onimatsu 1994). Monoecy in the genus allows for artificial crosses to be made with relative ease, and plants are easily cloned.…”

“…Furthermore, hybrids between plants with different numbers of chromosomes reveal one large chromosome pairing with two small chromosomes (Wahl 1940;Tanaka 1949;Håkansson 1954;Davies 1955;Faulkner 1972;Schmid 1982;Cayouette andMorisset 1985, 1986;Hoshino et al 1993Hoshino et al , 1994Hoshino and Okamura 1994). Complicating the picture in hybrids from natural populations is the presence of various univalent and multivalent formations suggesting chromosomal structural rearrangements are involved (Tanaka 1949;Faulkner 1973;Schmid 1982;Cayouette and Morissett 1986;Hoshino and Waterway 1994).…”