Many moth species overwinter in the larval stage of their life cycle. They often enter a phase known as diapause (suspended development), and many have evolved additional mechanisms for survival in cold winters. Typically they produce cryoprotective substances such as glycerol in their bodies but some may also synthesise anti-freeze proteins (AFPs); remarkably these can bind to ice crystals, inhibiting their growth. The Spruce Budworm Choristoneura fumiferana, a destructive pest of conifers in Canada and NW USA that overwinters as a tiny caterpillar (second instar) on host tree branches, is known to produce AFPs as well as wrapping itself up in a silken 'hibernaculum' for diapause. In a recent publication* the location and sequence of the genes specifying these AFPs was found. Similar genes were then found in other north American Choristoneura species but not in a few other tortrix species for which genome data are available (including the codling moth Cydia pomonella, common in the UK, which overwinters as a 5th instar larva but in a loose cocoon spun under tree bark or in leaf litter). However, similar genes were found in the genome of the Bramble Shoot Moth Notocelia uddmanniana. This strikingly-marked species is also common in the UK, and in a nice correlation to the Canadian story it overwinters similarly as a tiny caterpillar in a hibernaculum on the stems of blackberries, raspberries and loganberries (therefore perhaps more exposed than C. pomonella). This study raises some interesting questions about the evolutionary relationships of these species and the origins of AFPs.
Notocelia
uddmanniana
*The Spruce Budworm Genome: Reconstructing the Evolutionary History of Antifreeze Proteins. Catherine Béliveau et al. 2022 Genome Biol. Evol. https://doi.org/10.1093/gbe/evac087.
John Thacker, Harwell VC22
Thank you John for letting us know about this interesting research. I have an amateur interest in genetics/genomics and managed to follow the gist of the paper. What I found particularly interesting is the puzzle over how N. uddmanniana has similar genes for antifreeze proteins to C. fumiferana, even though they aren't very closely related (divergence about 50-75 million years ago).
ReplyDeleteI suspect that as the DNA of more species is sequenced, genes for AFPs will be found in other species which over-winter as young larvae in exposed locations. There is probably some kind of cost of producing AFPs, but there is a benefit in coming out of diapause near to the food source rather than having to climb back to it having spent the winter in a more-sheltered location but further away from the food.
Very pertinent comments, Tim. One explanation for the puzzle you highlight is that 'convergent evolution' has occurred (i.e., independent development of similar gene products in species that have already diverged, in response to a major stimulus) In this case I suppose the stimulus (selective pressure) could have been the onset of the last ice age - but, as you say, as more moth genomes are sequenced the story may change.
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