Mathieu Joron

Abstract: The coexistence of discrete morphs that differ in multiple traits is common within natural populations of many taxa. Such morphs are often associated with chromosomal inversions, presumably because the recombination suppressing effects of inversions help maintain alternate adaptive combinations of alleles across the multiple loci affecting these traits. However, inversions can also harbour selected mutations at their breakpoints, leading to their rise in frequency in addition to (or independent from) their role in recombination suppression. In this review, we first describe the different ways that breakpoints can create mutations. We then critically examine the evidence for the breakpoint-mutation and recombination suppression hypotheses for explaining the existence of discrete morphs associated with chromosomal inversions. We find that the evidence that inversions are favoured due to recombination suppression is often indirect. The evidence that breakpoints harbour mutations that are adaptive is also largely indirect, with the characterization of inversion breakpoints at the sequence level being incomplete in most systems. Direct tests of the role of suppressed recombination and breakpoint mutations in inversion evolution are thus needed. Finally, we emphasize how the two hypotheses of recombination suppression and breakpoint mutation can act in conjunction, with implications for understanding the emergence of supergenes and their evolutionary dynamics. We conclude by discussing how breakpoint characterization could improve our understanding of complex, discrete phenotypic forms in nature.

TL;DR: A substantially improved assembly of the Heliconius melpomene genome is presented, developed using novel methods that should be applicable to improving other genome assemblies produced using short read sequencing.

TL;DR: Protection against predators induced by chemical defences of 13 lepidopteran species belonging to six mimicry complexes is compared, finding that prey with a two- to three-fold difference in toxin content generated similar avoidance learning indices.

TL;DR: Mullerian and Batesian color patterns are often determined by relatively few pattern-regulating loci with major effects as discussed by the authors, which can be explained by the shape of a "number-dependent" selection function first modeled by Fritz Muller in 1879.

TL;DR: The factors maintaining multiple mimetic morphs in the butterfly Heliconius numata are studied to suggest that many complex polymorphisms, instead of representing adaptations to the existence of alternative ecological optima, could be maintained primarily because chromosomal rearrangements are prone to carrying recessive harmful mutations.