Background: It is thought that all animals age: they show an increased probability of death at greater ages. However, the lifespans of many animals vary widely. What is it that determines whether or not an animal lives for one year or one hundred years? One of the key drivers is thought to be how likely you are to be killed by something else. Those animals that that are unlikely to be eaten, whether that is because they are very large (elephants), well armoured (tortoises) or poisonous (poison dart frogs), tend to evolve lower rates of ageing. After all, if you are going to live for a long time anyway, you might as well make the most of it. On the other hand, if you live precariously from day to day then there isn’t much point in investing later in life because you probably won’t get that far.
What we did: We compared lifespans of amphibians and snakes that either had a chemical defense (in amphibians) or venom (in snakes) with those that did not have those traits. We showed that (accounting for their evolutionary history) poisonous amphibians had a significantly longer lifespan than non-poisonous amphibians, but there was no difference in venomous and non-venomous snakes.
Importance: This study has two major implications. The first is that it is vital to incorporate evolutionary history into these sorts of analyses. We had built our study on the findings of an earlier piece of work (which did not account for evolutionary history) that suggested that the snakes also showed a longer lifespan when they were venomous, but our results refute that earlier finding. Second, our findings offer yet more evidence for an offensive role for the origins of snake venom, which has been suggested in other recent studies.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Species with a chemical defense, but not chemical offense, live longer”, was published in the Journal of Evolutionary Biology in 2013. You can find this paper at the publisher or for free at Figshare.
Image credit: Ephraimstochter, http://bit.ly/1xHxpks, Public Domain.
Background: Ageing is thought to be one of the most widespread biological phenomenon, though it has often been said that insects do not live long enough to experience it. Experiments with insects in laboratories under ideal conditions have shown that ageing does occur, but there are very few studies that have demonstrated this in the wild.
What we did: We used two extensive datasets of sightings of the azure damselfly, Coenagrion puella, to look for an effect of “demographic senescence”. What this means is that the chance of an animal dying on any given day increases as it gets older. Hundreds of animals were marked and followed for their whole lives over two summers. The damselflies live for, on average, 7 days after marking and that follows a period of around 10-12 days of maturation. What we showed was that, even over so short a lifespan, there was a detectable signal of age-related mortality. We also demonstrated that there were a number of other variables, principally weather and parasites, that also influence the chance of a damselfly dying.
Importance: Ours was only the second study that comprehensively demonstrated ageing in a wild insect population.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Empirical evidence of senescence in adult damselflies (Odonata: Zygoptera)”, was published in the Journal of Animal Ecology in 2010. You can find this paper online at the publisher, or on Figshare.
Image credit: Tim, CC BY-NC-SA 2.0, http://bit.ly/1vvSVWl
Background: When this paper was published, we had already demonstrated that ageing (an increase in the probability of dying in older individuals) was present in one species of damselfly. This was a surprise, as many biologists speculated that short-lived animals like damselflies did not live long enough in the wild to experience ageing. However, anybody who has worked with insects in the field knows that they exhibit clear signs of ageing like the tattered wings of the dragonfly shown above. Having shown that at least one species of damselfly age, it was still unclear as to whether this was the exception or the rule.
What we did: We expanded our analysis from a single species to consider all the species for which there was published data on age-related mortality which we could use to detect ageing. We found that this phenomenon was present in the vast majority of studies in which we were able to test for it. Furthermore, we were able to show that it was more apparent in territorial species where males face greater stress in having to defend their territories to obtain mates.
Importance: This study conclusively demonstrated that ageing is commonplace in dragonflies and damselflies, where once it had been proposed that no wild insect populations exhibited ageing at all. We also show a hallmark of the evolution of territoriality in the lifespans of dragonflies and damselflies.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “A comparative analysis of senescence in adult damselflies and dragonflies”, was published in the Journal of Evolutionary Biology in 2011. You can find this paper online at the publisher, or on Figshare.
Image credit: steews4, CC BY-ND 2.0, http://bit.ly/1rrAEeW