Urbanization alters plastic responses in the common dandelion Taraxacum officinale

Abstract

Urban environments expose species to contrasting selection pressures relative to rural areas due to altered microclimatic conditions, habitat fragmentation, and changes in species interactions. To improve our understanding on how urbanization impacts selection through biotic interactions, we assessed differences in plant defense and tolerance, dispersal, and flowering phenology of a common plant species (Taraxacum officinale) along an urbanization gradient and their reaction norms in response to a biotic stressor (i.e., herbivory). We raised plants from 45 lines collected along an urbanization gradient under common garden conditions and assessed the impact of herbivory on plant growth (i.e., aboveground biomass), dispersal capacity (i.e., seed morphology), and plant phenology (i.e., early seed production) by exposing half of our plants to two events of herbivory (i.e., grazing by locusts). Independent from their genetic background, all plants consistently increased their resistance to herbivores by which the second exposure to locusts resulted in lower levels of damage suffered. Herbivory had consistent effects on seed pappus length, with seeds showing a longer pappus (and, hence, increased dispersal capacities) regardless of urbanization level. Aboveground plant biomass was neither affected by urbanization nor herbivore presence. In contrast to consistent responses in plant defenses and pappus length, plant fitness did vary between lines. Urban lines had a reduced early seed production following herbivory while rural and suburban lines did not show any plastic response. Our results show that herbivory affects plant phenotypes but more importantly that differences in herbivory reaction norms exist between urban and rural populations. K E Y W O R D S biomass, evolved reaction norms, herbivory, seed morphology, Taraxacum officinale, urbanization 1 | INTRODUC TI ON One of the most prominent anthropogenic changes is the rapid expansion of urbanized areas, a type of ecosystem that vastly differs from natural ones in terms of environmental conditions and landscape structure. Urban environments are characterized by higher temperatures (urban heat island) and increased levels of light, sound, and chemical pollution. Furthermore, green spaces are rare, more enclosed | 4083 PISMAN et Al.

Some like it hot: adaptation to the urban heat island in common dandelion

“…The characteristics of cities that are most impactful on vegetation are increased temperatures, impervious surface cover, habitat fragmentation, changes in herbivore communities, and light, air and soil pollution. Habitat fragmentation was found to alter dispersal characteristics in urban plants of holy hawksbeard (Crepis sancta) 38 and urban-rural adaptation to changes in herbivory pressure has been demonstrated in white clover (Trifolium repens) 39 as well as dandelions 40 . More generally speaking, the combined pressures of the urban environment (pan-urban effects) have led to phenological adaptation in common ragweed (Ambrosia artemisiifolia) 41 and changes in life-history traits in Arabidopsis thaliana 27 .…”

Dandelion (Taraxacum officinale) has Successfully Adapted to Grow in Suburban Environments

“…Urbanization facilitates environmental and evolutionary change (Santangelo et al 2022). Urban environments subject plants to unique selection pressures due to changes in microclimatic conditions, habitat fragmentation, and altered interactions with different plant species (Pisman et al 2020). Urbanization is known to reduce plant diversity richness and can also impact plant growth and physiology (Hou et al 2023;Gregg et al 2003).…”

Dandelion Has Successfully Adapted to Grow in Suburban Environments

“…The genus Taraxacum was described by Wiggers (1746Wiggers ( -1811, and the current classification was established by Georg Heinrich Weber in 1780 (Britton and Brown, 1970). T. officinale is a ruderal species that are the first to colonize disturbed lands (Pisman et al 2020).…”

“…Rapid expansion of urban areas creates a type of ecosystem that differs from natural areas in terms of environmental conditions and landscape structure. Urban environments expose plants contrasting selection pressures compared to rural environments due to changes in microclimatic conditions, habitat fragmentation, and altered interaction with different species of plants (Pisman et al 2020). Urbanization is known to decrease plant diversity richness (Hou et al 2023); it can also alter the plant growth and physiology (Gregg et al 2003).…”