Book collections and possum selection

Variety is the spice of life. That is certainly true of my life. I’ve always been drawn to variation. I can see it in my youth. I enjoyed comics in general but I preferred Warlord and 2000AD with their multiple series in each issue compared to those comics centred around a particular hero. When I did read superhero comics I much preferred the Justice League and the Legion of Superheroes (with various heroes working together) over their solo stories. Batman and Flash working on their own were boring. Batman and Flash working together was intriguing. Variation leads to interactions, that’s what makes life interesting.

I loved Narnia, the Dark is Rising and the Lord of the Rings with their multiple characters and viewpoints, none of which were the main hero. They were teams of people working together, each with their own strengths and weaknesses. Frodo gets nowhere without Sam and Aragorn. Will needs Bran and the the Drew siblings. Lucy, Eustace, Jill, Shasta, and Digory all work with Aslan in one story or anther. I can contrast that to the Earthsea series or anything by Alan Garner, all masterfully written, unforgettable stories and characters, but essentially one hero in each story. I liked those books but they did not draw me back the same way as those others did.

I tend to collect things. I have many (many) books of all sorts, many board games, many fantasy-related figures (that I also paint). I like the vibrancy and complexity. It would take a season of one of those ‘de-clutter shows’ to sort me out. But why would I want to do that? I can appreciate a minimalist look but it comes across to me as sterile and ready to be added to by other bits ‘n pieces.

A small corner of my home: books, games, figures in abundance. Image from Adrian Paterson.

My research is also about variation. In the last couple years I have worked with my postgrads and colleagues on spiders, weevils, leopards, marbled cats, possums, red panda, elephants, fur seals, tahr, black-fronted terns, blackbirds and thrushes, ferns, and various plant species. I have used different types of research; conservation biology, phylogenetics and taxonomy, molecular ecology, behavioural ecology, GIS, fire ecology, comparative analyses, and wildlife monitoring.

While I enjoy how these multiple ideas and organisms bounce around creating new ways of addressing a question, there is always the thought that this is at the expense of depth of knowledge. Jack of all trades, master of none… Still, Jack can be the person that links and holds different masters together, interpreting, clarifying, stimulating.

So variation is a great thing. Without variation nothing changes. We would be stuck doing the same old things, always.

Evolution is powered by variation, mostly through natural selection. There is no evolutionary change if there is no variation to select from. Usually, in genetic approaches to biological questions, we are measuring how much variation there is in a local population. Among other things, this tells us about the potential for the population to change over future generations, the flexibility to respond to crises or opportunities.

One species that we think about a lot here in New Zealand is the possum. The Australian brush-tailed possum (Trichosurus vulpecula) is usually seen as our number one pest species. It impacts our economy and it impacts our biodiversity. We have spent many decades trying to control the spread and density of possum populations. We have become very good at using traps and toxins to reduce these populations, at least temporarily, to nearly zero.

Nearly zero. To an evolutionary biologist that sounds a little alarming. We automatically wonder about those individuals that survive. Is it just luck that allows them to survive – right place at the right time? Or do they have some traits that allowed them to survive better? If it is the latter then we would expect selection to pass on these traits to recovering populations and eventually there would be populations of individuals that are tricky to kill using traps and toxins.

Double trouble: possums have been a major target for control in New Zealand for decades. Image from Adrian Paterson.

What kind of traits would help possums to survive? Traps are generally pretty effective in killing anything that interacts with them. This is where variation comes in. What if there were individuals that we were generally more cautious and didn’t interact with new devices that they found in the forest? Toxins rely on ingesting a lethal amount. What if there were individuals that had metabolisms that were better at dealing with these toxins?

In either case we would have selection favouring individuals that could survive the control measures. A larger problem would be if they could pass these traits on.

Arsalan Emami-Khoyi, as part of work done during his PhD at Lincoln University, has just published some work in Genes that begins to answer this question. Arsalan worked with his supervisors, Adrian Paterson and James Ross, and his post doc mentor, Peter Teske, to identify the transcriptome diversity from brushtail possum liver and brain cerebral cortex cells.

Transcriptomes tell us which genes are switched on and off in these different tissues. If there is any potential for selection to be occurring in a possum’s response to toxins, then we would expect to see variation in the genes that are working in the cells that deal primarily with toxins – the liver or hepatic cells.

Likewise, curiosity, or boldness, is a behavioural function that occurs in the brain. If there is any potential for selection to be occurring in a possum’s response to novel objects in the environment, then we would expect to see variation in the genes that are working in the cells that deal primarily with behaviour – cells in the cerebral cortex.

Possums tend to be very curious about objects in their environment. Image from Adrian Paterson.

Arsalan collected brain and liver tissues samples from different possums and identified their transcriptomes. He found that possums did indeed have high levels of variation in the genes that are concerned with dealing with toxins (in liver cells) and behavioural complexity (in cerebral cortex cells). Although the sample size was too small to be conclusive, these were results are consistent with the idea that possum DNA is under selection from the environment.

This only occurs because of variation. If there were no differences between individuals in their DNA from liver and cerebral cortex cells then there would be no selection. Given that there is variation, then there is scope for those few individuals that survive to do so because of possessing certain traits. Because they are genetic traits they will be passed onto the survivors’ descendents.

Variation opens up many paths into the future, whether this is choosing the next book to read, or board game to play, or whether possums will get better at avoiding traps and toxins. The original quote “A jack of all trades is a master of none” originally ended with “but often times better than a master of one”. I think that is a much better way of looking at the world.

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