Pre-invasion history and demography shape the genetic variation in the insecticide resistance-related acetylcholinesterase 2 gene in the invasive Colorado potato beetle

Abstract

BackgroundInvasive pest species offers a unique opportunity to study the effects of genetic architecture, demography and selection on patterns of genetic variability. Invasive Colorado potato beetle (Leptinotarsa decemlineata) populations have experienced a rapid range expansion and intense selection by insecticides. By comparing native and invasive beetle populations, we studied the origins of organophosphate (OP) resistance-associated mutations in the acetylcholinesterase 2 (AChE2) gene, and the role of selection and demography on its genetic variability.ResultsAnalysis of three Mexican, two US and five European populations yielded a total of 49 haplotypes. Contrary to the expectations all genetic variability was associated with a point mutation linked to insecticide resistance (S291G), this mutation was found in 100% of Mexican, 95% of US and 71% of European beetle sequences analysed. Only two susceptible haplotypes, genetically very differentiated, were found, one in US and one in Europe. The genetic variability at the AChE2 gene was compared with two other genes not directly affected by insecticide selection, diapause protein 1 and juvenile hormone esterase. All three genes showed reduction in genetic variability indicative of a population bottleneck associated with the invasion.ConclusionsStochastic effects during invasion explain most of the observed patterns of genetic variability at the three genes investigated. The high frequency of the S291G mutation in the AChE2 gene among native populations suggests this mutation is the ancestral state and thus, either a pre-adaptation of the beetle for OP resistance or the AChE2 is not the major gene conferring OP resistance. The long historical association with host plant alkaloids together with recombination may have contributed to the high genetic variation at this locus. The genetic diversity in the AChE2 locus of the European beetles, in turn, strongly reflects founder effects followed by rapid invasion. Our results suggest that despite the long history of insecticide use in this species, demographic events together with pre-invasion history have been strongly influential in shaping the genetic diversity of the AChE2 gene in the invasive beetle populations.

Role of dispersal in resistance evolution and spread

“…The frequencies of an organophospate resistance allele in L. decemlineata show a surprising spatial distribution. The allele is fixed in ancestral Mexican populations, is at high frequency (0.95) in US populations, and is variable, but lower on average, in Europe [33]. This suggests that the species may have been preadapted to organophosphates but lost resistance alleles during bottlenecks upon introduction to Europe.…”

Assessing Sexual Dicromatism: The Importance of Proper Parameterization in Tetrachromatic Visual Models

“…Fortunately, determination of a species’ eye type does not require microspectrophotometry, as opsin gene sequences can be used to estimate sensitivity [33]. Even though not all SWS1 opsin gene sequence variations have been compared to measured photopigment sensitivities, the peak absorbance of short-wavelength photoreceptor can usually be estimated [28, 33]. This method is relatively rapid, inexpensive, and could easily be implemented in any molecular laboratory [33].…”

“…Initial comparative analyses assumed a strong association between visual systems and phylogeny [25–27], but recent studies have shown that this is not always the case. Changes between ultraviolet sensitive (UVS) and violet sensitive (VS) eye types have occurred several times in some Orders (e.g., Passeriformes and Charadriiformes: [28]), and both UVS and VS eye types can be present within the same family (e.g., Maluridae: [29]). Furthermore, the very basic organizations of visual systems can differ among and within Orders.…”

Multiple strong postmating and intrinsic postzygotic reproductive barriers isolate florally diverse species of Jaltomata (Solanaceae)

“…Notably, this floral variation – including novel variation in petal and nectar color, overall size, and shape of floral organs (Figure 1), appears to have arisen within the last 5 MY (Sarkinen et al 2013), likely in response to pollinator preferences (e.g. Fenster et al 2004; and see Discussion).…”