Development of Spots on Buterfly Wings

A really cool new study:

DailyScience: How Butterflies Got Their Spots: A 'Supergene' Controls Wing Pattern Diversity:

To explore the genetic backgrounds of each of these species, the authors crossed different races of each species and genotyped the offspring in order to identify genes responsible for the color patterns. Thus, they were able to map the color pattern controlling loci in each species: N, Yb, and Sb for H. melpomene; Cr for H. erato; and P for H. numata. Using molecular markers within the pattern encoding genic regions, the authors then found that the loci controlling color pattern variation for each species lie within the same genomic equivalent locations.

This "supergene" region therefore seems to be responsible for producing wing pattern diversity in Heliconius butterflies. Such a locus plays what researchers call a "jack-of-all-trades flexibility" rather than a constraining role. Under natural selection, this region presumably functions as a "developmental switching mechanism" by responding to a wide range of mimetic pressures to produce radially divergent, locally adapted wing patterns.

PLoS-Biology Synopsis: Jack-of-All-Trades "Supergene" Controls Butterfly Wing Pattern Diversity:

Using molecular markers developed in the region of the pattern genes, they found that the three loci controlling color pattern variation for each species inhabit the same genomic location. Indeed, the elements controlling white and yellow pattern variation in H. melpomene (N, Yb, and Sb) and H. erato (Cr) are tightly linked to genetic markers that occupy the same position in both species. Similarly, the locus P, which controls whole-wing variation in H. numata, is also linked to the same series of markers.

These results, Joron et al. conclude, suggest that a single conserved locus is responsible for producing wing pattern diversity in Heliconius butterflies. Rather than a constraining role, this locus provides what the researchers call a "jack-of-all-trades flexibility." It presumably functions as a "developmental switching mechanism" for natural selection, they explain, by responding to a wide range of mimetic pressures to produce radically divergent, locally adapted wing patterns. Now researchers can begin to identify and determine the modus operandi of the genes at the center of what has been called a "developmental hotspot" to better understand how they drive the adaptive evolution of mimetic color pattern shifts.

The PDF of the paper is here.