AOBPreview originally published online on March 24, 2009
Annals of Botany 2009 103(8):1279-1289; doi:10.1093/aob/mcp068
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Inherited variability in multiple traits determines fitness in populations of an annual legume from contrasting latitudinal origins
Área de Biodiversidad y Conservación, Universidad Rey Juan Carlos. c/ Tulipán s/n, E-28933 Móstoles, Madrid, Spain
* For correspondence. E-mail ruben.milla{at}gmail.com
Received: 16 December 2008 Returned for revision: 30 January 2009 Accepted: 10 February 2009 Published electronically: 24 March 2009
Background and Aims: Variation in fitness depends on corresponding variation in multiple traits which have both genetically controlled and plastic components. These traits are subjected to varying degrees of local adaptation in specific populations and, consequently, are genetically controlled to different extents. In this study it is hypothesized that modulation of different traits would have contrasting relevance for the fitness of populations of diverse origins. Specifically, assuming that environmental pressures vary across a latitudinal gradient, it is suggested that inherited variation in traits differentially determines fitness in annual Lupinus angustifolius populations from contrasting latitudinal origins in western Spain.
Methods: Seeds of L. angustifolius from three contrasting origins were grown in a common garden. Traits related to more plastic vegetative growth and more genetically conserved phenology were measured, together with estimates of reproductive success. Fitness was estimated by the number of viable seeds per plant. Structural Equation Models were used to infer causal relationships among multiple traits and fitness, separating the direct and indirect effects of morphological, phenological and reproductive traits.
Key Results: Phenological, vegetative and reproductive traits accounted for most of the fitness variation. Fitness was highest in plants of southernmost origin, mainly due to earlier flowering. Fitness within each seed origin was controlled by variation in different traits. Southern origin plants that grew to a larger size achieved higher fitness. However, plant size in plants of northernmost origin was irrelevant, but early flowering promoted higher fitness. Variation in fruit and seed set had a greater effect on the fitness of plants of central origin than phenological and size variation.
Conclusions: It is concluded that modulation of a functional trait can be relevant to fitness in a given population (i.e. affecting intensity and direction), but irrelevant in other populations. This points to the need to consider integrated phenotypes when trying to unravel local adaptation effects over single traits.
Key words: Lupinus, Structural Equation Models, fitness, phenology, functional traits, reproductive success, SLA, seed size
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