This piece reports on research suggesting that carotenoids don't merely contribute to the bright pigments that play a role in sexual selection in some birds, but also play a role in colour perception, and have other nutritional benefits. One of the researchers describes the emerging view as follows:
Now this doesn't sound like a common currency in the full sense that I'm interested in it, but presumably the claim made is still relevant: the net benefit (nutritional and narcissistic) of carotenoids is suppose to be a component of the fitness value, which in turn is one of the things that many behavioural ecologists take to determine a common currency that it is part of the job of scientists to describe. So some parts of a full 'currency for fitness' might map onto the factors described here.
"We are proposing a positive fitness feedback loop for these 'self-loving molecules,' given how high carotenoid accumulation can improve one's state and one's interest in selecting carotenoid richness in mates and food. This provides a window into how major sexual selection models, such as sensory biases and assortative mating, may be explained by a common, nutritional and narcissistic currency".
This is a cool notice of some recent work on cellular energy metabolism, and in particular conversion of electron to proton currents. I don't know enough molecular biology to give much of a gloss of the content, but it's a lively and interesting read. It also refers to Adenosine triphosphate (ATP) as "the single energy currency of the cell".
This might seem like an irrelevant use of the same term ('currency') but there's reason not to rush to this conclusion. But as I noted elsewhere on this blog, "Since any behavior has some energy cost (or gain), and any allocation of metabolic resources has an opportunity cost (in actions rendered unavailable, or made possible) it’s plausible to think that in a highly aggregated way, ATP represents an important overall budgetary bottom line."
You can get the actual article on the Nature website here (possibly behind a paywall): Crystal structure of the entire respiratory complex I.