Linkage map of the peppered moth, Biston betularia (Lepidoptera, Geometridae): a model of industrial melanism

Abstract

We have constructed a linkage map for the peppered moth (Biston betularia), the classical ecological genetics model of industrial melanism, aimed both at localizing the network of loci controlling melanism and making inferences about chromosome dynamics. The linkage map, which is based primarily on amplified fragment length polymorphisms (AFLPs) and genes, consists of 31 linkage groups (LGs; consistent with the karyotype). Comparison with the evolutionarily distant Bombyx mori suggests that the gene content of chromosomes is highly conserved. Gene order is conserved on the autosomes, but noticeably less so on the Z chromosome, as confirmed by physical mapping using bacterial artificial chromosome fluorescence in situ hybridization (BAC-FISH). Synteny mapping identified three pairs of B. betularia LGs (11/29, 23/30 and 24/31) as being orthologous to three B. mori chromosomes (11, 23 and 24, respectively). A similar finding in an outgroup moth (Plutella xylostella) indicates that the B. mori karyotype (n ¼ 28) is a phylogenetically derived state resulting from three chromosome fusions. As with other Lepidoptera, the B. betularia W chromosome consists largely of repetitive sequence, but exceptionally we found a W homolog of a Z-linked gene (laminin A), possibly resulting from ectopic recombination between the sex chromosomes. The B. betularia linkage map, featuring the network of known melanization genes, serves as a resource for melanism research in Lepidoptera. Moreover, its close resemblance to the ancestral lepidopteran karyotype (n ¼ 31) makes it a useful reference point for reconstructing chromosome dynamic events and ancestral genome architectures. Our study highlights the unusual evolutionary stability of lepidopteran autosomes; in contrast, higher rates of intrachromosomal rearrangements support a special role of the Z chromosome in adaptive evolution and speciation.

A FISH-based chromosome map for the European corn borer yields insights into ancient chromosomal fusions in the silkworm

“…The gene order on each chromosome was well conserved between O. nubilalis and B. mori with few exceptions (Figure 1). We designated the same chromosome numbers, 1-31 excluding 11 and 30, as those of orthologous chromosomes in previously characterized species of n = 31 karyotype (Baxter et al, 2011;Sahara et al, 2013;Van't Hof et al, 2013).…”

“…As we first described syntenic gene order on four pairs of chromosomes between the silkworm, Bombyx mori, and a butterfly, Heliconius melpomene (Yasukochi et al, 2006), a number of reports have demonstrated extensive shared synteny between B. mori and other species based on genetic linkage studies (Pringle et al, 2007;Beldade et al, 2009;Baxter et al, 2011;Van't Hof et al, 2013) and chromosomal fluorescence in situ hybridization (FISH) analysis Yoshido et al, 2011;Sahara et al, 2013).…”

“…Reports using distantly related species having 31 chromosomes consistently show that chromosomes 11, 23 and 24 of B. mori (n = 28) were generated by ancestral chromosomal fusion events (Baxter et al, 2011;Sahara et al, 2013;Van't Hof et al, 2013). Genome sequencing with high resolution assignments to chromosomes enabled more direct and precise comparison between species (International Silkworm Genome Consortium 2008; Heliconius Genome Consortium, 2012; Ahola et al, 2014).…”

Neo-sex chromosomes and adaptive potential in tortricid pests

“…1 A-E and 2). Although genome organization of the nontineoid Ditrysia (21) was shown to be highly conserved (22)(23)(24), our results revealed that a neo-Z chromosome formed following fusion between chromosomes corresponding to the linkage groups Z and 15 of the Bombyx mori reference genome, henceforth referred to as F(Z;15), thus supporting an earlier anecdotal prediction (15). Sex-linkage of the Acetylcholinesterase 1 (Ace-1) and Notch orthologs of the B. mori chromosome 15 genes in two other tortricid pests (Fig.…”

Karyotypes versus Genomes: The Nymphalid Butterflies <b><i>Melitaea cinxia, Danaus plexippus</i></b>, and <b><i>D. chrysippus</i></b>

“…As probes, we selected B. mori protein sequences which had formerly been used by Sahara et al [2013] and Van't Hof et al [2013] for demonstrating conserved synteny of chromosomes from Helicoverpa armigera and Biston betularia , respectively, with chromosomes of B. mori . Coverage of genes from all but one autosome was about the same in female and male libraries, the female/male ratio equalling ∼ 1.0.…”