Mutating Morphologies and Moth Memories

I got back from a short ski trip on Thursday to find the usual log jam in my Outlook inbox, mostly caused by journal tables of contents. I try to keep up with the literature in my current and two past fields, so you can imagine the mass of bold font facing me upon my return. A large pile of papers relating to my actual job awaits my attention tomorrow, but first, here’s some short, sweet and fun science from last week’s journals.

A Retrotransposon-Mediated Gene Duplication Underlies Morphological Variation of Tomato Fruit , by Han Xiao and colleagues from Ohio State University, the Ohio Agricultural Research and Development Center, Michigan State University, and the College of Wooster, made the cover of Science. This is an extremely rare occurrence in transposable element research, so I salute you, fellow TE geeks! Cite my damn papers next time, ‘kay?

(Yes, that’s right, I included a picture of the cover of Science on a Nature Network blog. Hope I don’t get in any trouble).
Xiao’s paper relates to a previous post on this blog in which I discussed the ability of transposable elements to drive host evolution via gene duplications and rearrangements. In this new case, a long terminal repeat (LTR) retrotransposon inserted into the sun locus of a cultivated tomato variety, and mediated the creation of an almost exactly duplicated mutated locus on a different chromosome.
The sun locus was previously found to be associated with fruit shape, with the mutated strain bearing a much more elongated fruit than its wild ancestor. Examination of the locus pinpointed the LTR insertion to the intron of a putative defensin gene named DELF1. The LTR mediated a downregulation of DELF1 and a concomitant upregulation of the nearby IQD12 gene. Some clever genetic tinkering subsequently showed that tomato fruit shape depends on the level of IQD12 expression. This identification of IQD12 as the gene responsible for the phenotypic variation associated with the sun locus prompted its renaming as SUN.
I love this kind of molecular detective work. Especially when it highlights the importance of TEs in genome evolution. I’m currently running a poll on my other blog , and most respondents who found me through Google did so while trying to find TE-related fodder for their arguments with creationists. I hope this new example of phenotypic variation caused by TE insertion is useful to these brave souls!
The second paper is completely outside my area of expertise, but I just thought it was really cool. Retention of Memory through Metamorphosis: Can a
Moth Remember What It Learned As a Caterpillar? , by Douglas Blackiston and colleagues from Georgetown University, is open access in PLoS One.
Metamorphosis is an alien and fascinating process for us boring mammals who stay much the same shape throughout our whole lives. As the authors say, “…it is hard to believe that a cryptic caterpillar chewing on a leaf, or a maggot wriggling in decaying flesh, is in fact the same animal as the colorful butterfly or noisy blowfly emerging from the transitional pupal stage”. (What unexpectedly eloquent language in a scientific paper! I salute you, caterpillar geeks! You don’t need to cite my damn papers). But do the neurons responsible for memory survive the extensive remodelling that goes on within the pupa? Previous studies were inconclusive and suggested that some apparent memories may actually be the result of similar environmental stimuli encountered by the larval and adult animal.
The authors conditioned tobacco hornworm larvae to associate the smell of ethyl acetate (EA) with a small electric shock. After 8 rounds of shocks, most caterpillars understandably avoided EA in subsequent choice experiments. A similar proportion of adult moths that had been shocked as larvae also avoided EA, suggesting that the caterpillars’ conditioning had survived metamorphosis. EA aversion was not associated with exposure to the chemical alone, without electric shocks, at either the larval or pupal stage.
The survival of these conditioned responses depended on the time of exposure to the conditioning regime; caterpillars exposed at an earlier stage did not retain their aversion to EA. The authors speculate that memory survival may correlate with survival of different parts of the mushroom bodies, “paired structures in the larval and adult insect brain that receive input from the antennal lobes”.
The exact implications of this study are not yet known, and much molecular and cellular detective work will be needed to dissect the mechanisms of memory retention. Watch this space – as long as I manage to spot the relevant research in the disaster zone that is my inbox.