Environmental effects on molecular and phenotypic variation in populations of Eruca sativa across a steep climatic gradient

Abstract

In Israel Eruca sativa has a geographically narrow distribution across a steep climatic gradient that ranges from mesic Mediterranean to hot desert environments. These conditions offer an opportunity to study the influence of the environment on intraspecific genetic variation. For this, we combined an analysis of neutral genetic markers with a phenotypic evaluation in common-garden experiments, and environmental characterization of populations that included climatic and edaphic parameters, as well as geographic distribution. A Bayesian clustering of individuals from nine representative populations based on amplified fragment length polymorphism (AFLP) divided the populations into a southern and a northern geographic cluster, with one admixed population at the geographic border between them. Linear mixed models, with cluster added as a grouping factor, revealed no clear effects of environment or geography on genetic distances, but this may be due to a strong association of geography and environment with genetic clusters. However, environmental factors accounted for part of the phenotypic variation observed in the common-garden experiments. In addition, candidate loci for selection were identified by association with environmental parameters and by two outlier methods. One locus, identified by all three methods, also showed an association with trichome density and herbivore damage, in net-house and field experiments, respectively. Accordingly, we propose that because trichomes are directly linked to defense against both herbivores and excess radiation, they could potentially be related to adaptive variation in these populations. These results demonstrate the value of combining environmental and phenotypic data with a detailed genetic survey when studying adaptation in plant populations.

Adaptional evolution of trichome in Caragana korshinskii to natural drought stress on the Loess Plateau, China

“…2013; Westberg et al. 2013). In this study, the C. korshinskii trichome was observed to be larger and denser due to the plant's necessity for slowed transpiration rate, and, as such, contributed effectively to enhancing the plant's drought resistance (Fig.…”

“…Plants lose most water due to transpiration, the rate of which is affected considerably by diffusion resistance (Lange et al 1971;Pangle et al 2015). The trichome is a specialized structure of leaf epidermal cells that covers the plant's surface and serves to enhance its diffuse resistance to transpiration (Fu et al 2013;Westberg et al 2013). In this study, the C. korshinskii trichome was observed to be larger and denser due to the plant's necessity for slowed transpiration rate, and, as such, contributed effectively to enhancing the plant's drought resistance (Fig.…”

Intraspecific variation in defense against a generalist lepidopteran herbivore in populations of Eruca sativa (Mill.)

“…2012; Westberg et al. 2013). Phenotypic evaluation in common‐garden experiments has shown that populations from the southern arid environments differ from those in the northern, more favorable mesic Mediterranean habitats in several phenological and morphological traits, including trichome density and herbivory damage (Westberg et al.…”

“…Interestingly, the strong statistical association found between AFLP (amplified fragment length polymorphism) outlier loci and trichome density measured in an insect‐free environment was replaced with an association of these loci to the level of herbivore damage in a common‐garden field experiment (Westberg et al. 2013). Accordingly, we hypothesized that populations of E. sativa from arid (desert) and Mediterranean (Med) habitats differ in their induced defense response to herbivory.…”

“…1), growing in nature mostly around the Mediterranean basin. Information that we have gathered in the last few years on wild populations of E. sativa indicates genetic differences between populations originating from the steep climatic gradient in Israel (Barazani et al 2012;Westberg et al 2013). Phenotypic evaluation in common-garden experiments has shown that populations from the southern arid environments differ from those in the northern, more favorable mesic Mediterranean habitats in several phenological and morphological traits, including trichome density and herbivory damage (Westberg et al 2013).…”