Rapid evolution of seed dispersal in an urban environment

Rapid evolution of seed dispersal in an urban environment in the weed Crepis sancta

P.-O. Cheptou, O. Carrue, S. Rouifed, A. Cantarel

Abstract

Dispersal is a ubiquitous trait in living organisms. Evolutionary theory postulates that the loss or death of propagules during dispersal episodes (cost of dispersal) should select against dispersal. The cost of dispersal is expected to be a strong selective force in fragmented habitats. We analyzed patchy populations of the weed Crepis sancta occupying small patches on sidewalks, around trees planted within the city of Montpellier (South of France), to investigate the recent evolutionary consequences of the cost of dispersal. C. sancta produces both dispersing and nondispersing seeds. First, we showed that, in urban patches, dispersing seeds have a 55% lower chance of settling in their patch compared with nondispersing seeds and, thus, fall on a concrete matrix unsuitable for germination. Second, we showed that the proportion of nondispersing seeds in urban patches measured in a common environment is significantly higher than in surrounding, unfragmented populations. Third, by using a quantitative genetic model, we estimated that the pattern is consistent with short-term evolution that occurs over ≈5–12 generations of selection, which is generated by a high cost of dispersal in urban populations. This study shows that a high cost of dispersal after recent fragmentation causes rapid evolution toward lower dispersal. 

 Read the article on PNAS

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How plants manipulate the scatter-hoarding behaviour of seed-dispersing animals

From the abstract:
Some plants that are dispersed by scatter-hoarding animals appear to have evolved the ability to manipulate the behaviour of those animals to increase the likelihood that seeds and nuts will be stored and that a portion of those items will not be recovered.

Plants have achieved this in at least four ways:
1. By producing large, nutritious seeds and nuts that are attractive to animals and that stimulate hoarding behaviour.
2. By imposing handling costs that cause animals to hoard rather than to eat items immediately. These handling costs can take one of two forms: physical barriers (e.g. hard seed coats) that take time to remove and secondary chemicals (e.g. tannins) that impose metabolic costs.
3. By masting, where a population of plants synchronizes reproductive effort, producing large nut crops at intervals of several years. Mast crops not only satiate seed predators, but also increase the amount of seed dispersal because scatter-hoarding animals are not easily satiated during caching (causing animals to store more food than they can consume) but are satiated during cache recovery.
4. By producing seeds that do not emit strong odours so that buried seeds are less likely to be discovered.

These, and perhaps other, traits have increased the relative success of plant species with seeds dispersed by scatter-hoarding animals.

Read the full paper!

Swarming Behavior in Plant Roots

Marzena Ciszak 1,2, Diego Comparini 2, Barbara Mazzolai 3, Frantisek Baluska 4, F. Tito Arecchi 1,5, Tamás Vicsek 6, and Stefano Mancuso 2 from

(1) CNR-Istituto Nazionale di Ottica, Florence, Italy; (2) LINV-Department of Plant Soil & Environmental Science, University of Florence, Florence, Italy; (3) Center for Micro-BioRobotics, Istituto Italiano di Tecnologia, Pontedera (PI), Italy; (4) Institute of Cellular and Molecular Botany, University of Bonn, Bonn, Germany; (5) Department of Physics, University of Florence, Florence, Italy; (6) Department of Biological Physics, Eötvös Loránd University, Budapest, Hungary.

Abstract

Interactions between individuals that are guided by simple rules can generate swarming behavior. Swarming behavior has been observed in many groups of organisms, including humans, and recent research has revealed that plants also demonstrate social behavior based on mutual interaction with other individuals. However, this behavior has not previously been analyzed in the context of swarming. Here, we show that roots can be influenced by their neighbors to induce a tendency to align the directions of their growth. In the apparently noisy patterns formed by growing roots, episodic alignments are observed as the roots grow close to each other. These events are incompatible with the statistics of purely random growth. We present experimental results and a theoretical model that describes the growth of maize roots in terms of swarming.

PLoS ONE

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