Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils

Abstract

Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre-adapted to serpentine soils.

Evolutionary ecology along invasion fronts of the annual grass Aegilops triuncialis

“…Although transgenerational plasticity effects cannot be ruled out completely, the fact that edge source maternal plants produced consistently larger seeds across all planting conditions argues for a least some genetic contribution to this phenotypic variation in seed size. The likelihood that phenotypic differences between serpentine and non-serpentine populations of A. triuncialis have some genetic basis is also supported by previous common garden glasshouse experiments (Lyons et al 2010;Meimberg et al 2010). These glasshouse studies found significant variation between serpentine and non-serpentine populations in a number of phenological and morphological traits.…”

Genetic lineages of the invasive Aegilops triuncialis differ in competitive response to neighboring grassland species

“…Meimberg et al (2010) sampled invasive populations throughout California and identified three lineages (East, West and South) with the East and West lineages occupying much larger areas than the South (Meimberg et al 2010). To minimize maternal effects, we used offspring from a common garden experiment (Espeland and Rice 2012), which included 11 populations (8 East and 3 West, defined as populations 102, 103, 105, 106, 107, 115, 117, 119, 122, 124 and 125 in Meimberg et al 2010).…”

“…To minimize maternal effects, we used offspring from a common garden experiment (Espeland and Rice 2012), which included 11 populations (8 East and 3 West, defined as populations 102, 103, 105, 106, 107, 115, 117, 119, 122, 124 and 125 in Meimberg et al 2010). Populations sampled in Meimberg et al (2010) lacked within population variation, and nearby populations were usually of the same lineage. ''West'' populations were found in the western part of northern California, specifically Mendocino, Colusa, Napa, Solano, and Yolo Counties.…”

“…If multiple introductions of invaders result in genetic variation in the introduced range, multiple genotype by environment interactions can lead to selection for different suites of traits and thus different competitive abilities among invasive populations. In fact, invasive lineages of exotic species can differ in important reproductive and phenotypic traits (Meimberg et al 2010). However, most work to date has been based on the assumption that competitive effect or response is invariant within a species (Bennett et al 2013;Mariotte et al 2012) or that differences are between native and introduced populations of an invasive species Kumschick et al 2013).…”

“…Meimberg et al (2010) showed that all of twenty sampled invasive populations identified with one of three lineages that differ in their range sizes as well as in reproductive traits. Populations within a lineage were found to be inbred, exhibiting no genetic variation within a lineage, and therefore act as replicates for a lineage.…”