Experimental evolution of insect resistance to two pesticide classes reveals mechanistic diversity and context-dependent fitness costs

Abstract

Does rapid adaptation to stressors evolve through similar underlying mechanisms among diverse populations, or are there many roads to a similar phenotype? The experimental evolution of pesticide resistance in insects provides a powerful model to study the diverse evolutionary signatures of adaptation and their associated costs. Here, we selected for resistance to two pesticides (organophosphates and pyrethroids) in six field-derived populations of the red flour beetle (Tribolium castaneum). After several generations of selection, we performed transcriptomic analyses and measured survival, development, and fecundity in the presence and absence of pesticides to detect fitness costs of resistance evolution. All pesticide-selected populations exhibited significantly improved survival after pesticide exposure without substantial fitness costs, compared to control populations. Populations that evolved to resist organophosphates had distinct gene expression in the presence and absence of organophosphates, supporting different detoxification mechanisms and cuticular modifications among populations. In contrast, pyrethroid resistant populations demonstrated common differential expression of cytochrome P450 transcripts. Furthermore, some populations evolved similar mechanisms against both pesticides while others showed little overlap in their evolved responses, suggesting variation in potential cross-resistance phenotypes. Overall, between populations, we observed both parallel and divergent patterns in gene expression associated with acquired pesticide resistance, without ubiquitous fitness costs.

Interactions between evolved pesticide resistance and pesticide exposure influence immunity against pathogens

“…1A-B, compare OP Reg:PTx and Pyr Reg:PTx; Suppl. Table 3; Birnbaum et al, 2021). Interestingly, there was a positive significant interaction between OP and Bt treatment (OP PTx:BtTx) indicating that larvae dually exposed to OP and Btt had improved survival compared to larvae exposed to OP only (Fig.…”

“…Insects, including T. castaneum , can rapidly evolve resistance to pesticides through mechanisms that enhance metabolic detoxification and cuticular modifications (Rösner et al, 2020). Here, populations selected for pesticide resistance evolved it within 6-8 generations (Birnbaum et al, 2021), demonstrating increased survival and faster development after pesticide exposure compared to control-selected populations. Differential gene expression between pesticide- and control- selection regimes suggested that OP resistance is associated with constitutive changes in cuticle gene expression while Pyr resistance is associated with oxidoreductase activity, heme binding, and cuticular modifications, consistent with previous studies in OP and Pyr resistant insects (Carvalho et al, 2013; Tandonnet et al, 2020; Zimmer et al, 2017).…”

“…Initial exposure doses were calculated as one tenth the manufacturer’s recommended dose (OP [Malathion 50% EC, Southern Ag]- 0.103 mg/ml; Pyr [Demon WP, 40% cypermethrin, Syngenta]- 0.0251 mg/ml). We approximated LC50 pesticide concentrations for ancestral populations using dose response curves (Birnbaum et al, 2021), and adjusted these after the second generation (LC50: 5.14 mg/ml OP and 0.188 mg/ml Pyr). To create pesticide exposure diets, we combined 0.15 g/ml standard diet with 10 ml of pesticide solutions diluted in DI water (Milutinović et al, 2013).…”

“…We transferred individuals to new pesticide exposure containers every four weeks. After six generations of selection, we tested for increased pesticide resistance in F2 larvae (reared for two generations without selection to avoid parental effects) from the pesticide-regime (here, used interchangeably with evolution-regime) populations and found these populations had significantly increased survival against pesticides compared to control-regime populations (Birnbaum et al, 2021). Meanwhile, we continued selection in all populations for another two generations (to generation 8).…”

Assessing the predictability of fungicide resistance evolution through in vitro selection

“…However, experimental evolution can still prove useful, by allowing the selection of resistance to be studied at even greater speed (Palmer and Kishony 2013). The rapid evolution of resistance under experimental conditions can be used to predict resistance before it occurs in the field or clinic (Lloyd et al 2020), or to test a range of different selective scenarios (Hegreness et al 2008;Birnbaum et al 2021), informing resistance risk assessments and management strategies.…”