Genetic variation underlying local adaptation of diapause induction along a cline in a butterfly

Abstract

Diapause is a life history strategy allowing individuals to arrest development until favourable conditions return, and it is commonly induced by shortened day length that is latitude specific for local populations. Although understanding the evolutionary dynamics of a threshold trait like diapause induction provides insights into the adaptive process and adaptive potential of populations, the genetic mechanism of variation in photoperiodic induction of diapause is not well understood. Here, we investigate genetic variation underlying latitudinal variation in diapause induction and the selection dynamics acting upon it. Using a genomewide scan for divergent regions between two populations of the butterfly Pararge aegeria that differ strongly in their induction thresholds, we identified and investigated the patterns of variation in those regions. We then tested the association of these regions with diapause induction using between-population crosses, finding significant SNP associations in four genes present in two chromosomal regions, one with the gene period, and the other with the genes kinesin, carnitine O-acetyltransferase and timeless. Patterns of allele frequencies in these two regions in population samples along a latitudinal cline suggest strong selection against heterozygotes at two genes within these loci (period, timeless). Evidence for additional loci modifying the diapause decision was found in patterns of allelic change in relation to induction thresholds over the cline, as well as in backcross analyses. Taken together, population-specific adaptations of diapause induction appear to be due to a combination of alleles of larger and smaller effect size, consistent with an exponential distribution of effect sizes involved in local adaption.

Intra-Species Differences in Population Size shape Life History and Genome Evolution

“…Outliers were identified as non-overlapping windows of 50 kb within the 0.5% of lowest and highest genetic differentiation per comparison. To reduce the number of false-positive results, the outlier threshold was chosen at 0.5% highest and lowest percentile of each pairwise genetic differentiation 74, 75 . To find candidate genes within windows of highest differentiation, a total of three selection criteria were used.…”

Genomic basis of circannual rhythm in the european corn borer moth

“…Recent studies in two other insects show that per alleles are associated with polymorphism in the timing of 253 autumnal initiation of diapause (critical photoperiod for entrance) (68,69). Genetic changes at per may 254 therefore provide the capacity to adjust diapause transition times across two different seasons, enabling 255 insects to synchronize with both the end and beginning of winter.…”

The genetic architecture underlying diapause termination in a planktonic crustacean

“…For instance, the circadian clock gene timeless was found to be in control of diapause incidence (Sandrelli et al, ) and allele frequencies of timeless alleles differentially affecting diapause induction behaviour were shown to covary over latitude (Tauber et al, ) in Drosophila . This pattern, a functional role of one or several circadian clock genes in the control of diapause induction and associated cline in allele frequencies for these genes in natural populations is recurrently observed, e.g., for the parasitic wasp Nasonia vitripennis ( period, cycle and cryptochrome ; Paolucci, Salis, Vermeulen, Beukeboom, & Zande, ) or more recently for the speckled wood butterfly ( period & timeless ; Pruisscher, Nylin, Gotthard, & Wheat, ). However, Emerson, Dake, Bradshaw, and Holzapfel () found that the photoperiodic seasonal clock in control of diapause can evolve independently from the circadian clock.…”