Predictable convergent evolutionary traits in bioluminescent organs of squid

Since I’ve been busy with work and Uni recently and unsure when I will next have a post out, I thought I would put up my talk about a paper review I gave for part of my course today. I hope you enjoy it!

The paper I chose, Predicting transcriptome evolution in the convergent and complex bioluminescent organs of squid, is a paper that looks at whether we can predict how a convergent evolutionary trait is expressed by one organism, by looking at a similar structure in another.

Specifically, my paper looks at a bacterial photophore organ in the bioluminescent squid Euprymna scolopes and Uroteuthis edulis. The authors of this paper set out to show that these were convergent evolutionary traits, and that overall gene expression levels, referred to as transcriptomes, that give rise to the convergent traits, were similar in E. scolpes and U. edulis.

To show this, the authors used previously studied genome information for their squid and three mature females from each species. Each squid had several organs dissected and RNA extracted to make comparisons with, such as eyes, brains, and skin cells. Photophores and the ANG (accessory nidamental gland) was also looked at as it is another symbiotic organ and is believed might play a role in the development of non-bacterial photophores. Quantitative PCR was used to gather the sequences they were looking for on the desired loci.

The results showed that photophore transcriptomes were statistically more similar to each other than to any of the tissue samples that were sequenced, even when compared across species. Their results also showed that there was a high level of shared transcriptome signal between convergent structures, despite quite a lot overall gene expression divergence between the two species. The authors were also able to report there was very strong statistical evidence to show that the bacterial photophores for the two squid where indeed evolutionary convergent.

The authors then created a model to see if they could use the information they gathered from the sequencing of photophores in one species to identify the similar structure in the other squid species. They were able to accurately do this, and found that transcriptomes can give an organ such a strong identity signal that the authors were able to use there model to accurately predict organ identity, just from the gene expression level, even on phylogenetically non-homologous photophores.

In conclusion, I think this paper could affect how we look and interpret morphological and physiological adaptations in organisms. Do they arise through completely random mutations or are the more constrained in what structures they can give rise to due to these internal factors? Can these traits possibly be predicted and anticipated based on the current machinery that an organism possesses?

Not the most fun five minutes of my life!

Link to original paper

Tell me what you think!