Mutualists construct the ecological conditions that trigger the transition from parasitism

The evolution of mutualism between hosts and initially parasitic symbionts represents a major transition in evolution. Although vertical transmission of symbionts during host reproduction and partner control both favour the stability of mutualism, these mechanisms require specifically evolved features that may be absent during the transition. Therefore, the first steps of the transition from parasitism to mutualism are not fully understood. Spatial structure might be the key to this transition. We explore this hypothesis using a spatially explicit agent-based model. We demonstrate that, starting from a parasitic system with global dispersal, the coevolution between mutualistic effort and local dispersal of hosts and symbionts leads to a stable coexistence between parasites and mutualists. The local dispersal evolution mimics vertical transmission and triggers the formation of mutualistic clusters, counteracting the individual selection level of parasites that maintain global dispersal. However, the transition also requires competition between hosts in order to occur. Indeed, the transition occurs when mutualistic symbionts increase the density of hosts, which strengthens competition between hosts and disfavours parasitic host/symbiont pairs: mutualists create ecological conditions that allow their own spread. Therefore, the transition to mutualism may come from an eco-evolutionary feedback loop involving spatially structured population dynamics.

Letters: Complex response of beta diversity to dispersal in meta-community models

Dispersal is one of the most important drivers of community assembly. The conventional belief that dispersal leads to biotic homogenization (lower beta diversity) has been recently challenged by an experiment conducted in nectar microbes (Vannette & Fukami, 2017), showing that dispersal could lead to community divergence. In this paper, I re-examined the relationship between beta diversity and local dispersal in a range of theoretical models: from the classic island biogeography model and meta-population model to a meta-community model that incorporates biotic interactions. I find that the emergence of hump-shaped beta diversity-dispersal relationship is closely related to local dispersal (rather than global dispersal), non-neutrality and biotic interactions. The results reveal rich metacommunity dynamics in relation to dispersal types and biotic interactions which might be overlooked in previous theoretical and empirical studies. The findings call for more realistic experimental manipulations on dispersals in future community assembly studies.

Weed diversity is driven by complex interplay between multi-scale dispersal and local filtering

Arable weeds are key organisms for biodiversity maintenance and ecosystem service provision in agroecosystems. Disentangling the drivers of weed diversity is critical to counteract the global decline of farmland biodiversity. Even if distinct scale-dependent processes were alternatively proposed, no general framework unifying the multi-scale drivers of weed dynamics has yet emerged. Here, we investigate the joint effects of field- and landscape-scale processes on weed assemblages in 444 arable fields. First, field margins sheltered greater weed diversity than field core, evidencing their role as biodiversity refugia. Second, community similarity between field core and margin decreased with the distance to margin, highlighting a major role of local dispersal. Third, weed diversity at field margins increased with organic field cover in the landscape, pointing out massive regional dispersal. Fourth, while both local and landscape dispersal explained up to 41% of field core weed diversity, crop type strongly modulated their strength, depicting an intense filtering effect by agricultural management. This study sheds new light on the complex multi-scale interactions shaping weed diversity, field margins playing a key role by strengthening regional dispersal and sustaining local dispersal. Land-sharing strategies improving habitat heterogeneity both locally and regionally should largely promote agroecosystem multifunctionality and sustainability.

Baseline Flight Potential of Euschistus servus (Hemiptera: Pentatomidae) and Its Implications on Local Dispersal

The brown stink bug, Euschistus servus (Say), is a damaging pest of multiple crops in the southeastern United States. In addition to crops, both the weedy field borders and wooded areas of a typical farmscape in this region harbor E. servus host plants, many of which are temporally and spatially limiting in availability or nutritional suitability. Therefore, local dispersal is required so that individuals efficiently track and utilize host resources. This research sought to establish the baseline flight capacity of adult E. servus across the season in relation to body weight, sex, and plant host use with a flight mill system. Across this 2-yr study, among the individuals with a flight response in the flight mill, 90.1% of individuals flew in a range of >0–1 km, with an individual maximum flight distance of 15.9 km. In 2017, mean total distance flown varied across the season. Except for the individuals collected from corn in 2019, during both 2017 and 2019, the highest numerical mean flight potential occurred soon after overwintering emergence and a relatively low flight potential occurred during the cropping season. Individuals collected from wheat, corn, and early season weeds lost a higher proportion of body weight after flight than did individuals from soybean and late season weeds. The baseline dispersal potential information generated from this study can be extrapolated to the farmscape level aiming to develop, plan, and implement E. servus management programs.

Tardigrades in the Canopy: Associations with Tree Vole Nests in Southwest Oregon

Tardigrades live in many ecosystems, but local dispersal mechanisms and the influence of ecological gradients on tardigrade communities are not fully understood. Here we examine tardigrade communities in nests of the red tree vole (Arborimus longicaudus True), an arboreal mammal occupying the canopy of coniferous forests in western Oregon and northwestern California. We found 12 species of tardigrades from resin ducts sampled from 43 nests along a transect that spanned the east-west range of the tree vole in southern Oregon. Tardigrade occurrence was more likely in larger trees and species numbers were significantly higher in areas that received more precipitation. At sites where they occurred, tardigrades were more abundant in tree vole nests at greater heights within the forest canopy. Of the 12 species of tardigrades that were found, seven have not been previously reported in Oregon. Our results suggest that tardigrades in forest canopies in the Pacific Northwest are impacted by regional precipitation gradients as well as local environmental variables, and that nest building by small mammals may facilitate dispersal of tardigrades within the forest canopy.