Janz, N. | Search bioRxiv

bioRxiv2020

Altered parasitism of a butterfly assemblage associated with a range-expanding species

AimBiotic interactions are an important factor structuring ecological communities but data scarcity limits our understanding of the impact of their response to climate and land use changes on communities. We studied the impact of a change in species assemblage on biotic interactions in a community of closely-related butterflies. Specifically, we examined the impact of the recent range expansion of Araschnia levana on the resident species, with a particular focus on natural enemies, parasitoids, shared with other butterfly species in the assemblage. LocationSweden. Time periodTwo years (2017-2018). Major taxa studiedNettle-feeding butterflies (Aglais urticae, Aglais io, Araschnia levana, and Vanessa atalanta) and their parasitoids. MethodsWe assessed parasitism in 6777 butterfly larvae sampled in the field from 19 sites distributed along a 500 km latitudinal gradient, and every two weeks throughout species reproductive seasons. We identified the parasitoid complex of each butterfly species and their overlap, and analysed how parasitism rates were affected by species assemblage, variations in abundance, time, and the arrival of A. levana. ResultsParasitoids caused high mortality, with substantial overlap across the four host species. The composition of the host community influenced parasitism rates and this effect was specific to each species. In particular, the rate of parasitism in resident species was comparatively higher at sites where A. levana has been established for longer. Main conclusionsParasitoid pressure is a significant source of mortality in the nettle-feeding butterfly community studied. Variations in butterfly species assemblages are associated with substantial variations in rates of parasitism. This is likely to affect the population dynamics of their butterfly host species, and, potentially, the larger number of species with which they interact.

ecology↗

bioRxiv2019

Bayesian inference of ancestral host-parasite interactions under a phylogenetic model of host repertoire evolution

Intimate ecological interactions, such as those between parasites and their hosts, may persist over long time spans, coupling the evolutionary histories of the lineages involved. Most methods that reconstruct the coevolutionary history of such associations make the simplifying assumption that parasites have a single host. Many methods also focus on congruence between host and parasite phylogenies, using cospeciation as the null model. However, there is an increasing body of evidence suggesting that the host ranges of parasites are more complex: that host ranges often include more than one host and evolve via gains and losses of hosts rather than through cospeciation alone. Here, we develop a Bayesian approach for inferring coevolutionary history based on a model accommodating these complexities. Specifically, a parasite is assumed to have a host repertoire, which includes both potential hosts and one or more actual hosts. Over time, potential hosts can be added or lost, and potential hosts can develop into actual hosts or vice versa. Thus, host colonization is modeled as a two-step process, which may potentially be influenced by host relatedness or host traits. We first explore the statistical behavior of our model by simulating evolution of host-parasite interactions under a range of parameters. We then use our approach, implemented in the program RevBayes, to infer the coevolutionary history between 34 Nymphalini butterfly species and 25 angiosperm families.

evolutionary biology↗