Clinal differentiation during invasion: Senecio inaequidens (Asteraceae) along altitudinal gradients in Europe

Abstract

Abstract:The dynamics of plant population differentiation may be integral in predicting aspects of introduced species invasion. In the present study, we tested the hypothesis that European populations of Senecio inaequidens (Asteraceae), an invasive species with South African origins, differentiated during migration from two independent introduction sites into divergent altitudinal and climatic zones. We carried out 2 years of common garden experiments with eight populations sampled from Belgian and ten populations from French altitudinal transects. The Belgian transect followed a temperature and precipitation gradient. A temperature and summer drought gradient characterized the French transect. We evaluated differentiation and clinal variation in plants germinated from field-collected seed using the following traits: days to germination, days to flowering, height at maturity, final plant height and aboveground bio-mass. Results showed that S. inaequidens populations differentiated in growth traits during invasion. During the 1st year of sampling, the results indicated clinal variation for growth traits along both the Belgium and French altitudinal transects. Data from the 2nd year of study demonstrated that with increasing altitude, a reduction in three growth traits, including plant height at maturity, final plant height and aboveground biomass, was detected along the French transect, but no longer along the Belgian one. Phenological traits did not exhibit a clear clinal variation along altitudinal transects. The possible evolutionary causes for the observed differentiation are discussed.

The roles of genetic drift and natural selection in quantitative trait divergence along an altitudinal gradient in Arabidopsis thaliana

“…Similar trends have been reported as genetically based trait divergence within species, even when plants are sampled from regional altitudinal gradients where gene flow between populations can be high 1 (Monty and Mahy, 2009). For example, plant height or size and specific leaf area often decrease, whereas seed size often increases with altitude of origin within species when plants are grown in a common environment (Monty and Mahy, 2009;Montesinos-Navarro et al, 2011). The underlying mechanisms generating these high-altitude morphologies are still unclear, however, Körner (1999) proposed that small size at high altitude may allow plants to benefit from higher temperatures closer to the soil and thicker leaves may allow higher photosynthetic activity.…”

“…High-altitude species typically have a smaller stature and thicker leaves than low altitude species (Körner, 2003(Körner, , 2007. Similar trends have been reported as genetically based trait divergence within species, even when plants are sampled from regional altitudinal gradients where gene flow between populations can be high 1 (Monty and Mahy, 2009). For example, plant height or size and specific leaf area often decrease, whereas seed size often increases with altitude of origin within species when plants are grown in a common environment (Monty and Mahy, 2009;Montesinos-Navarro et al, 2011).…”

“…The reduced rosette leaf number with higher altitudes in our study is likely associated with above ground biomass accumulation during vegetative growth as neither rosette diameter after 3 weeks nor leaf area decreased with altitude. Smaller stature or size of plants growing at high altitude is one of the most conspicuous altitudinal pattern across species (Körner, 1999(Körner, , 2003 and has also been detected within other species, for example, in Senecio inaequidens (Monty and Mahy, 2009) and in Festuca eskia (Gonzalo-Turpin and Hazard, 2009). The physiological mechanism giving rise to this pattern is, however, unclear, although different hypotheses have been proposed, for example, that small plants benefit from the warmer temperatures close to the soil in cold conditions at high altitude (Körner, 1999).…”

“…Local adaptation often leads to the formation of clinal or ecotypic variation that can evolve over surprisingly short distances (e.g., Brady et al, 2005). Clinal variation can establish fast, repeatedly and with ongoing gene flow, as has for example been shown for cyanogenesis clines in white clover (Kooyers and Olsen, 2012) and for climateassociated morphological clines in invasive plants (Monty and Mahy, 2009). Understanding local adaptation requires the identification of genetically based traits under divergent selection.…”

Phenotypic divergence of the common toad (Bufo bufo) along an altitudinal gradient: evidence for local adaptation

“…We performed correlations between population pairwise Q ST s (larval life-history traits), F ST s (microsatellite markers), geographic distance and difference in altitude to estimate the relative importance of divergent selection and neutral genetic processes in phenotypic divergence. The difference in altitude between pairwise populations was considered a substitute for a score of environmental variables changing with altitude, most notably season length and temperature (for example, Monty and Mahy, 2009;Scheepens et al, 2010). First, we predicted strong phenotypic divergence among altitudinal regions and particularly faster developmental and growth rates corresponding with increasing altitude (countergradient pattern hypothesis).…”