Habitat variation, mutualism and predation shape the spatio‐temporal dynamics of tansy aphids

Abstract

1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants.2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small-scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered.3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within-field dispersal determined the spatio-temporal distribution of aphid colonies.4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation.5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio-temporal dynamics of tansy aphids, particularly in a small-scale field site.

Effect of plant chemical variation and mutualistic ants on the local population genetic structure of an aphid herbivore

“…The specialised aphid M. fuscoviride is obligatorily anttended (Flatt & Weisser, 2000), often by the black garden ant, Lasius niger L., or the common red ant Myrmica rubra L., and has a myriad of natural enemies including parasitoid wasps and generalist predators (Senft et al, 2017). Tansy plants grow in patches of genetically identical shoots (in our field, there were 18 ± 8.7 shoots per plant (mean ± SE)).…”

“…In addition to variation in the VOCs, we showed-through untargeted metabolomic profiling of the leaves-that all plants of certain metabotypes (clusters of plants with similar metabolomic profiles) were colonised by aphids at the peak of the season (even on "less preferred" volatile chemotypes) (Clancy et al, 2018). The two common mutualistic ant species in this system also responded to plant chemical variation (Clancy et al, 2016), and the presence of ants increased colonisation success and benefited the population growth of M. fuscoviride aphids (Flatt & Weisser, 2000;Senft, Weisser, & Zytynska, 2017). Interestingly, there was no association between plant volatile chemotype and metabotype, leading to a unique system where we can disentangle effects of these two aspects of chemical diversity (Clancy et al, 2018).…”

“…Further, L. niger also exhibited preferences across plant metabotypes, with ants observed on 78% of plants from metabotype B (Figure 2). Myrmica rubra ants showed some variation across chemotypes and metabotypes but this was not statistically significant (Figure 2), potentially through confounding effects of competitive exclusion by L. niger (Senft et al, 2017). Myrmica rubra ants showed some variation across chemotypes and metabotypes but this was not statistically significant (Figure 2), potentially through confounding effects of competitive exclusion by L. niger (Senft et al, 2017).…”

“…Hence, while aphid genotypes might actively choose a host based on the volatile profile, the probability of successfully colonising a plant and persisting on the plant across the season is increased on certain "optimal" metabotypes where population growth rates are increased; higher population sizes were also found to reduce the chance of local extinction through predation in this system (Senft et al, 2017).…”

“…) of which 172 were visited each week in 2014 and four times in 2015;importantly, only 87 of them were colonised by aphids across both seasons leading to a heterogeneous distribution of aphids(Senft et al, 2017).…”