DOI: 10.25338/b81931
title: Wolbachia frequency data from: Why did the Wolbachia transinfection cross the road? Drift, deterministic dynamics and disease control

description: Maternally inherited Wolbachia transinfections are being
 introduced into natural mosquito populations to reduce the transmission of
 dengue, Zika and other arboviruses. Wolbachia-induced cytoplasmic
 incompatibility provides a frequency-dependent reproductive advantage to
 infected females that can spread transinfections within and among
 populations. However, because transinfections generally reduce host
 fitness, they tend to spread within populations only after their frequency
 exceeds a critical threshold. This produces bistability with stable
 equilibrium frequencies at both 0 and 1, analogous to the bistability
 produced by underdominance between alleles or karyotypes and by population
 dynamics under Allee effects. Here, we analyze how stochastic frequency
 variation produced by finite population size can facilitate the local
 spread of variants with bistable dynamics into areas where invasion is
 unexpected from deterministic models. Our exemplar is the establishment
 of wMel Wolbachia in the Aedes
 aegypti population of Pyramid Estates (PE), a small community in
 far north Queensland, Australia. In 2011, wMel was stably
 introduced into Gordonvale, separated from PE by barriers to Ae.
 aegypti dispersal. After nearly six years during
 which wMel was observed only at low frequencies in PE,
 corresponding to an apparent equilibrium between immigration and
 selection, wMel rose to fixation by 2018. Using analytic
 approximations and statistical analyses, we demonstrate that the observed
 fixation of wMel at PE is consistent with both stochastic
 transition past an unstable threshold frequency and deterministic
 transformation produced by steady immigration at a rate just above the
 threshold required for deterministic invasion. The indeterminacy results
 from a delicate balance of parameters needed to produce the delayed
 transition observed. Our analyses suggest that
 once Wolbachia transinfections are established locally
 through systematic introductions, stochastic “threshold crossing” is
 likely to only minimally enhance spatial spread, providing a local ratchet
 that slightly – but systematically – aids area-wide transformation of
 disease-vector populations in heterogeneous landscapes.
description: The methods are described in our text and in the references
 provided there, specifically Hoffmann et al. (2011, Nature
 476:454-457), Schmidt et al. (2017, PLoS Biol. 15:e2001894) and Ryan et
 al. (2019, Gates Open Research 3:1547).
description: The file "collection_data_2018-08-14.cvs" contains the
 raw data on the <em>Wolbachia</em> infection frequencies in
 <em>Aedes aegypti</em> sampled in Pyramid Estates and
 Gordonvale up to August 2018. The individual rows are the results from
 individual traps together with their geographical location.
 The file "PE(data_for_Figs2,4&5).csv" contains
 the pooled data that are plotted in Figure 2 (with x-axis in days) and
 analyzed in Figures 4 and 5 (with the data represented as estimates of
 infection frequencies over discrete generations). The “dates” for the
 individual pooled samples used in Fig. 2 are the weighted arithmetic means
 of the sampling times within each temporal pooling period, with weights
 corresponding to sample sizes.