Escape from floral herbivory by early flowering in Arabidopsis halleri subsp. gemmifera

Abstract

Natural selection on flowering phenology has been studied primarily in terms of plant-pollinator interactions and effects of abiotic conditions. Little is known, however, about geographic variation in other biotic factors such as herbivores and its consequence for differential selection on flowering phenology among populations. Here, we examine selection by floral herbivores on the flowering phenology of Arabidopsis halleri subsp. gemmifera using two adjacent populations with contrasting herbivory regimes. Intensive floral herbivory by the leaf beetle Phaedon brassicae occurs in one population, while the beetle is absent in another population. We tested the hypothesis that the two populations experience differential selection on flowering time that is attributable to the presence or absence of floral herbivory. A two-year field study showed that early flowering was favoured in the population under intensive floral herbivory, whereas selection for early flowering was not found in one year in the population where floral herbivory was absent. Selection for early flowering disappeared when the abundance of floral herbivores was artificially decreased in a field experiment. Thus, the heterogeneous distribution of P. brassicae was a major agent for differential selection on flowering time. However, flowering time did not differ between the two populations when plants were grown in the laboratory. The lack of genetic differentiation in flowering time may be explained by ongoing gene flow or recent invasion of P. brassicae. This study illustrates that the role of floral herbivory in shaping geographic variation in selection on flowering phenology may be more important than previously thought.

Coexistence of Trichome Variation in a Natural Plant Population: A Combined Study Using Ecological and Candidate Gene Approaches

“…gemmifera at the study site, the most influential herbivore was the crucifer-specialist leaf beetle Phaedon brassicae (Figure 1D). Both adults and larvae of this species fed on leaves and young inflorescences, and larvae were much more abundant than adults in the flowering season [40]. Other herbivorous insects, such as a specialist butterfly, Pieris napi , were much less abundant than P. brassicae , and their effects on the plants were negligible at the study site (see below).…”

Associational effects against a leaf beetle mediate a minority advantage in defense and growth between hairy and glabrous plants

“…In this field site of our previous study, we found that leaf damage on hairy plants decreased as the frequency of neighboring glabrous plants within a 1-m patch scale increased (Sato et al 2014). Although it remains unknown how important biomass production is in the lifetime fitness of A. halleri in the field, the growth before flowering could be a major component of fitness because the fecundity of hairy plants depends on their size before flowering (Kawagoe and Kudoh 2010). In the indoor cultivation described in the present study, the biomass in the growth stage was also positively correlated with flower production.…”

Taxonomy and systematics are key to biological information: Arabidopsis, Eutrema (Thellungiella), Noccaea and Schrenkiella (Brassicaceae) as examples

“…Numerous ecological studies are of course also available focusing on herbivory (Kawagoe and Kudoh, 2010), flowering time (Shimizu et al, 2011) or reproduction (Llaurens et al, 2008), for example.…”