Influence of multiple factors on plant local adaptation: soil type and folivore effects in <Emphasis Type="Italic">Ruellia nudiflora</Emphasis> (Acanthaceae)

Different environmental factors can have contrasting effects on the extent of plant local adaptation (LA). Here we evaluate the influence of folivory and soil type on LA in Ruellia nudiflora by performing reciprocal transplants at two sites in Yucatan (Mexico) while controlling for soil source and folivory level. Soil samples were collected at each site and half of the plants of each source at each site were grown with one soil source and half with the other. After transplanting, we reduced folivory by using an insecticide applied to half of the plants of each population source grown on each soil at each site. This resulted in a fully-crossed design with site, population source, soil source and folivory as main effects. We evaluated LA by means of a significant site × origin interaction showing a home-site advantage of native plants. Additionally, to test for an effect of soil source and folivores on LA, we estimated the three-way interactions of site × origin × soil source and site × origin × folivory. We recorded fruit number and survival throughout an 8-month period. For survival, we found evidence of home-site advantage at one site, while for fecundity we found no evidence of LA and at one site even observed evidence of lower fecundity for local relative to foreign plants. Importantly, folivory had no influence on the degree of home-site advantage for either response variable, while soil source influenced the degree of home-site advantage in fecundity at one site (suggesting some degree of specialization to soil characteristics in R. nudiflora). Our results emphasize the need for simultaneously evaluating multiple factors of influence in tests of LA.