Bidirectional selection on threshold size for flowering in Cynoglossum officinale (hound's-tongue)

Abstract

Previous studies have demonstrated that many facultative biennials show variation in threshold size for flowering. In order to quantify the genetic variation for this character, we performed a two-way artificial selection experiment on threshold size in Cynoglossum officinale. The parental generation, established from seed from a natural population, showed large variation in threshold sizes (2.6-13.4 g). After one generation of selection for low threshold sizes all plants in the F1 flowered at sizes below 3.2 g. In the high selection line none of the F1 plants under 3.6 g flowered, and there were very large nonflowering plants (up to 17.2 g). By interpreting the logistic regression of flowering probability on plant size as a cumulative frequency distribution of threshold sizes, we could derive the frequency distributions of threshold sizes in each generation. These were used to estimate the narrow-sense heritabiities by the standard procedure for artificial selection on a quantitative character. This gave 'heritabilities' of 0.35 and 0.32 for the high and low selection lines, respectively. A previously constructed optimization model, applied to the population in our study area, predicted strong selection against low threshold sizes, but a fairly equal fitness for threshold sizes around and above the optimum. This flat fitness profile may explain why the natural population of Cynoglossum officinale harbours extensive genetic variation for this character.

Evolution of flowering strategies inOenothera glazioviana: an integral projection model approach

“…This means that a wide range of combinations of b 0 and b s provide a similar description of the data, and so have approximately equal tness. This provides a potential mechanism allowing the maintenance of genetic diversity, and indeed selection experiments have shown that natural populations harbour extensive genetic variation for threshold sizes of owering (Wesselingh & de Jong 1995;Wesselingh & Klinkhamer 1996). Rose et al (2002) draw the same conclusion from the tness landscape of the monocarpic thistle Carlina vulgaris, which is remarkably similar to that calculated here for Oenothera.…”

“…However, the tted parameters of a logistic regression can be interpreted in terms of an underlying, unobserved distribution of threshold sizes for reproduction. Assume there is some distribution of threshold sizes for owering, f T within a population, then for a particular size, x, if 50% ower, this implies that 50% of the population have a threshold less than x (Wesselingh & de Jong 1995). In this way we may interpret the tted logistic curve as a cumulative distribution function, calculating ¶ p f (x)/ ¶ x, using equation (2.6), we obtain…”

Demographic and Evolutionary Impacts of Native and Invasive Insect Herbivores on Cirsium Canescens

“…The population could still be flowering at a suboptimal small size if some lack of genetic variation prevented adaptation to the new conditions. However, several studies have demonstrated that natural populations harbor extensive genetic variation for threshold flowering size (Wesselingh and de Jong 1995, Wesselingh and Klinkhamer 1996, reviewed in Metcalf et al 2003. Consequently, we hypothesize that an important aspect of the selective environment remains to be incorporated into our models.…”

Why age and size at maturity have changed in Pacific salmon

“…To understand genetic changes in the PMRN, knowledge of the heritability of the threshold size at maturity is critical (cf. Wesselingh & de Jong 1995, Wesselingh & (Morita et al 2005). Data include 3 cohorts, the 1989 to 1991 brood years, and pooled sexes.…”