Allozyme variation and genetic relationships among species in the Carex willdenowii complex (Cyperaceae)

Abstract

A taxonomic study by Naczi, Reznicek, and Ford (American Journal of Botany, 85, 434-447, 1998) has determined that three species (Carex willdenowii, C. basiantha, and C. superata) can be recognized within the C. willdenowii complex. To determine the amount of genetic divergence within and between these species, allozyme analyses were conducted on 14 populations distributed from Pennsylvania to eastern Texas. Seventeen loci were surveyed, 13 of which were polymorphic, with all populations being polymorphic at one or more loci. Interspecific genetic identities ranged from 0.560 (C. willdenowii and C. basiantha) to 0.807 (C. basiantha and C. superata). Alleles for the isozymes Aat-1, Dia-1, Idh-2, Mdh-2, Per-1, Pgm-1, and Pgm-2 served to distinguish C. willdenowii from C. basiantha and C. superata. Carex basiantha and C. superata were recognized by alleles of Mdh-2, Pgm-1, and Tpi-2. The genetic identities of populations within species were high and exceeded 0.957. A caespitose growth habit and perigynia in close proximity to the staminate flowers suggest adaptations for selfing and therefore low levels of heterozygosity. Paradoxically, the values for expected heterozygosities (Hexp) were always lower than those obtained by direct count (Hobs): F values were highly negative, indicating heterozygous excess. Disassortative mating and selection are discussed as possible mechanisms for maintaining heterozygous excess within populations.

High Levels of Gene Flow and Heterozygote Excess Characterize Rhizoctonia solani AG-1 IA (Thanatephorus cucumeris) from Texas

“…Overdominant selection favoring heterozygotes (Mitton, 1989), associative overdominance (Nei, 1987), and negative assortative mating (e.g., self-incompatibility in plants; Hartl and Clark, 1989) are common textbook explanations for observed heterozygote excess and are generally used to explain heterozygote excess in natural populations (e.g., Ford et al, 1998;Doligez and Joly, 1997). For our data, overdominance (heterozygote advantage) can be ruled out, as it is highly unlikely that all seven RFLP loci were not neutral.…”

Genetic variation and population structure ofCarex breviculmis (Cyperaceae) in Korea

“…43, No. 3, 2000 Huh and Huh, 1998Ford et al, 1998Ford et al, 1998Ford et al, 1998Vellend and Waterway, 1999 Current study this value is higher than average for species with a reproduction mode that is sexual and asexual (43.8%) and for long-lived herbaceous perennials (39.6%), it is similar to that for temperature-zone species (48.5%; Hamrick and Godt, 1989). In addition, among the northern rhizomatous Carex species (Table 4), C. breviculmis had the highest HT value.…”

“…First, the breeding system of a species is an important determinant of variability at both the species and population levels. Typical of the species, flowers of C. breviculrnis are monoecious and highly reduced (Lee, 1997;Ford et al, 1998), apparently making it a species that is primarily wind-pollinated. Predominantly outcrossing species maintain higher levels of intrapopulation genetic variation than do predominantly inbreeding species (Gottlieb, 1981;Brown, 1989).…”

“…This low level of genetic differ-entiation also suggests that gene flow among the population is high (Nm = 3.69). Ford et al (1998) reported that seed dispersal in the Carex section contributed more to gene flow than did pollen dispersal, namely because (1) perigynia possess eliosome-like bodies; (2) plants are frequently found on slopes; and (3) morphological adaptations, such as perigynia with long beaks, could favor long-distance dispersal by small mammals .…”

Allozyme Variation and Population Structure of Carex okamotoi (Cyperaceae), a Korean Endemic Species

“…In these areas perigynia may fall downslope and could be carried some distance by snow or water. Morphological adaptations, such as perigynia with long serrated beaks, could favor long-distance by small mammals [5,6].…”