The relative importance of sexual reproduction versus clonal spread in an aridland bunchgrass

Abstract

Festuca idahoensis (Idaho fescue) is a perennial caespitose grass, common in semi-arid rangelands of the Intermountain West. To determine how individuals are recruited into a population, we studied two long-term monitoring plots that were established in 1937 at the Northern Great Basin Experimental Range in southeastern Oregon. The plots measured 3.05x3.05 m, and were located approximately 30 m apart. One plot was ungrazed, the other was subject to moderate levels of cattle grazing. The number of F. idahoensis plants in both plots increased ten-fold between 1937 and 1996, but whether this was due primarily to reproduction by seed or clonal fragmentation was unknown. In 1996, we mapped and sampled 160 plants of F. idahoensis. We used dominant inter-simple sequence repeat (ISSR) markers and codominant allozyme markers in order to identify genetic individuals and measure genetic diversity. Both plots were characterized by high levels of genetic and clonal diversity. When information from ISSRs, allozymes and sample location were combined, 126 genets were recognized, each consisting of one to four samples (ramets). By measuring the diameter of clones surrounding plants that were present in 1937, we estimated that clonal spread occurred at a rate of approximately 3.7 cm per decade, and thus was of secondary importance in the maintenance and increase of F. idahoensis stands. Sexual reproduction, rather than clonal fragmentation, accounted for most of the recruitment of new plants into these plots. The grazed plot had fewer ramets, genotypes, and clones than the ungrazed plot, but the ramets were significantly larger. Levels of genetic diversity did not differ in the grazed and ungrazed plots, but there was some evidence for a small, but significant level of genetic differentiation between the two. The results also indicate that F. idahoensis has the potential to be a long-lived species with some individuals persisting in excess of 60 years. This study demonstrates how long-term monitoring can be supplemented by genetic analysis to obtain detailed information on the population dynamics of plants. In the case of this community dominant species, this provides essential information for understanding succession and developing management and restoration strategies.

Long-Term Grazing Effects on Genetic Variation in Idaho Fescue

“…Hack) either exposed to grazing by cattle, grazing by a native rodent, or protected from grazers by an exclosure for 20 years. In their study of sexual and clonal recruitment in Idaho fescue from a different Northem Great Basin Experimental Range pasture than ours,Liston et al (2003) also failed to detect any difference in genetic diversity at ISSR loci between plants sampled from inside and outside a grazing exclosure.Our negative result does not guarantee that grazing has had no affect on Idaho fescue during the 64 years the cattle exclosure has been in place at the Northern Great Basin Experimental Range. Other researchers have noted differences for Idaho fescue at NGBER between grazed and ungrazed sites.…”

“…For expected heterozygosity, we used the unbiased estimator described by Lynch and Milligan (1994) for dominant markers, including adherence to their recommendation of excluding all loci for which the null allele frequency was less than 3/N. Although Idaho fescue is a tetraploid, Liston et al (2003) observed disomic inheritance for allozyme loci in their study of Idaho fescue at NGBER. To calculate the allele frequencies necessary for estimating He, we assumed both disomic inheritance and that our samples were in Hardy-Weinberg equilibrium.…”

“…Proponemos que, en este sitio, tanto los mecanismos que deben estar presentes para causar cambios en la variaci6n genetica neutral del "Idaho fescue" no son afectados por el apacentamiento del ganado o que cualquiera de los efectos del apacentamiento en la variacion genetica neutral son superados por el flujo genetico entre las muestras apacentadas y no apacentadas. co-evolve with large ungulates making them less grazing tolerant (Mack and Thompson 1982 Liston et al 2003). When grazing affects ecological features of plants such as population size and gene flow, this should in tum influence genetic variation measured at selectively neutral markers.…”

Recruiting mechanisms of Cylindropuntia leptocaulis (Cactaceae) in the Southern Chihuahuan Desert

“…It has been proposed that ramet establishment is more efficient than genet establishment for the recruitment of new individuals of succulent species in arid environments (Arizaga and Ezcurra, 2002;Clark-Tapia et al, 2005;Liston et al, 2003). Furthermore, some authors (Allen et al, 1991;Mandujano et al, 1998Mandujano et al, , 2007 have observed that several Opuntia species in the Chihuahuan Desert undergo clonal propagation in highly stressful sites, such as intercanopy space, without the need for nurse plants.…”

Reproductive Systems

“…Similar dates have been estimated for other clonal grasses (de Witte and St€ ocklin 2010). A more recent study with molecular markers suggested a minimum age for a plant of Festuca idahoensis as at least 60 years (Liston et al 2003).…”