Abstract
During the last two centuries, the North American common ragweed (Ambrosia artemisiifolia L.) invaded a large part of the globe. Local adaptation of this species was revealed by a common garden experiment, demonstrating that the distribution of the species in Europe could extend considerably to the North. Our study compares two populations of common ragweed (one from the native range and one from the invaded range) that differ in flowering time in the wild: the invasive population flowers earlier than the native population under non-inductive long-day photoperiods. Experiments conducted in controlled environments established that the two populations differ in their flowering time even under inductive short-day photoperiods, suggesting a change in autonomous flowering control. Genetic analysis revealed that early flowering is dominantly inherited and accompanied by the increased expression of the floral activator AaFTL1 and decreased expression of the floral repressor AaFTL2. Early flowering is also accompanied by reduced reproductive output, which is evolutionarily disadvantageous under long vegetation periods. In contrast, under short vegetation periods, only early-flowering plants can produce any viable seeds, making the higher seed set of late-flowering plants irrelevant. Thus, earlier flowering appears to be a specific adaptation to the higher latitudes of northern Europe.
Highlights
Common ragweed (Ambrosia artemisiifolia L.) is an annual invasive plant with a negative impact on the economy due to its role as an agricultural weed (Weaver, 2001; Essl et al, 2015) and as a source of allergenic wind-dispersed pollen grains (Arbes et al, 2005)
Under short vegetation periods, only early-flowering plants can produce any viable seeds, making the higher seed set of late-flowering plants irrelevant
A previous study (Scalone et al, 2016) reported that an invasive A. artemisiifolia population flowered earlier than a native population, when both were grown in the same experimental garden with naturally changing photoperiod
Summary
Common ragweed (Ambrosia artemisiifolia L.) is an annual invasive plant with a negative impact on the economy due to its role as an agricultural weed (Weaver, 2001; Essl et al, 2015) and as a source of allergenic wind-dispersed pollen grains (Arbes et al, 2005). The first sign of flowering is a pale green bud at the shoot apex, forming the main inflorescence (see Supplementary Fig. S1 at JXB online for a scheme of reproductive development of A. artemisiifolia and images of the plant). This inflorescence grows to become a leafless raceme with dozens of staminate (male) flower heads (Essl et al, 2015). Pistillate (female) flowers develop at the axils Fertilized female flowers develop a fruit that mostly consists of a single seed (Essl et al, 2015)
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