Tag Archives: evolution

Bigger is Better

Population size impacts host-pathogen coevolution (2021) Papkou et al. 2021, Proc B, https://doi.org/10.1098/rspb.2021.2269

Image credit: Kbradnam, CC BY-SA 2.5, via Wikimedia Commons

The Crux

Host-pathogen interactions are maybe best characterized as a battle – a pathogen (a parasite that causes disease) doing what it can to maximize how much it can get from a given host organism, and a host doing what it can to defend itself from this endless attack. As a result, hosts and pathogens are locked in an endless evolutionary battle, whereby hosts evolve to better defend themselves and pathogens evolve to better attack the host. A key factor in this battle is population size, as this affects the evolutionary potential of a given population of organisms to respond to selection.

The larger a population of hosts, the more novel genetic variants there are, which are simply organisms with different genetic make-ups, which can be the result of mutations popping up or through combinations with other genetic variants within the population. The more variation there is, the more diverse the population is, and the more chance it has of carrying the genes that could help it respond to a new threat, like a pathogen.

This means that a larger host population is more likely to have a genetic variant that is able to defend itself from these pathogens. That variant will then be selected for and the host population will become more resistant to that pathogen over time. While a lot of theory has been dedicated to understanding these coevolutionary battles, actual experimental evidence is lacking. Today’s authors used a model system to conduct evolutionary experiments to test the effect of host population size on host-pathogen coevolution.

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The Fascinating Lives of Colonial Animals

A physonect siphonophore colony observed during an exploration of the Central Pacific Basin. (Image Credit: NOAA Office of Ocean Exploration and Research)

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The Species On The Globe Go Round And Round

Today we associate lions with Africa, but they used to be widespread around the northern hemisphere (Image Credit: MLbay, Pixabay licence, Image Cropped)

While I continuously hear my little one’s nursery rhyme about a certain stuff going round and round, I think, what else moves round and round in my field? Species! 

They move around as they are looking for a mate, food, to avoid cold weather, the list goes on. They occupy a reasonable range that can be handled by their bodily functions, and either stay in that range or move when the environment changes. A species’ historical movement is one of the most important aspects of its natural history.

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Better Means Faster

Species interactions have predictable impacts on diversification (2021) Zeng and Wiens, Ecology Letters. https://doi.org/10.1111/ele.13635

Image Credit: MacNeil Lyons/NPS, CC BY 2.0

The Crux

No organism on the planet lives in complete isolation from other organisms. Many organisms serve as a food source for others, and even apex predators have to compete for their food. Species interactions like predation, competition, and parasitism directly impact organisms in their daily lives, but there is also a possibility that these same species interactions have had an impact on much longer timescales. That is, species interactions may have had a direct effect on the diversity of life on our planet.

Species interactions have been previously shown to affect diversification rates (see Did You Know?), so the question that today’s authors asked was whether there is a general trend to the effects of species interactions on diversification rates? Specifically, do species interactions with negative fitness (such as being killed by a predator) impacts decrease diversification rates, and do species interactions with positive fitness (such as successfully parasitizing a host) impacts increase diversification rates?

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Changing With the Times

High parasite diversity accelerates host adaptation and diversification (2018) Betts et al., Science. https://doi:10.1126/science.aam9974

Image Credit: Dr. Graham Beards, CC BY-SA 3.0

The Crux

Host-parasite relationships are often thought of or depicted in a pairwise structure. That is, one host is attacked by one parasite, without an acknowledgement or consideration of how complex the relationship can be. For example, hosts are often attacked by more than one type of parasite, and the parasites themselves have to compete with one another for resources from the host. Because parasites are costly for a host, the hosts benefit from evolving resistance to the parasites. It follows that the more parasites a host is attacked by, the higher the benefit of evolving resistance, so we’d expect to see more resistance in hosts that are attacked more often. This should then result in differential evolutionary rates among hosts, which would then result in greater evolutionary divergence (see Did You Know?)

To test this idea, the authors of today’s study used a bacterium (Pseudomonas aeruginosa) and five lytic viral parasites (hereafter bacteriophages). These bacteriophages reproduce within host cells until they eventually cause the host to burst, killing the host (think of the chestburster in Alien, but a LOT of them). Because their reproduction results in the death of the host, lytic parasites impose a very strong selection pressure on hosts, making this a perfect host-parasite system to test the above prediction.

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A Short Review of Sexuality in the Natural World

The discovery of ‘lesbian’ seagulls in California in the 1970s shook outdated beliefs that homosexuality was unnatural. Since then, scientists have documented cases of homosexuality in hundreds more species (Image Credit: JanBirdie, Pixabay licence)

Darwin’s work on evolution, natural selection and “survival of the fittest” is probably the most well-known scientific hypothesis out there.

Survival of the fittest means that the “fittest” have the highest reproductive success – whether that is achieved by roaring the loudest, building the most beautiful nest, camouflaging the best, or performing the most impressive mating dance. Passing on their genes to the next generation is what makes an individual successful in this context.

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A Story About Mortality: The Evolution of Aging and Death

A flatworm (Pseudocerus liparus) crawling on a sponge – passing through a forest of hydroids and tunicates. (Image credit: Christa Rohrbach, CC BY-NC-SA 4.0)

Last week I posted an article about fascinating creatures that escape death almost completely, including the famous “immortal jellyfish” (link below). Yet while the jellyfish’s attitude to aging is awe-inspiring, its existence poses a more obvious, yet perplexing question: why do we age?

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A Story About Mortality: What Jellyfish Can Teach Us

The hydromedusa of Podocoryna borealis. (Image credit: Lara Beckmann, NorHydro, CC BY-SA 4.0)

Our existences are often centered around the hope that we will live a long and fulfilled life. At the same time, while we aim to grow old, many of us abhor the aging process, dreaming of remaining young and healthy for as long as possible. It explains why we are so fascinated by the concept of immortality. Think of vampire stories, constant quests for the fountain of youth, or even the newest anti-aging products in the drugstore next door. But apart from the few extra years we gain nowadays through modern medicine and improved life circumstances, many of us can’t extend our lives much further.

We share this fate with many other animals that go through the stages of birth, growth, reproduction and death. But despite that, we don’t need to rely on science-fiction to get a glimpse of everlasting life: some organisms on our planet don’t follow these stages and some cheat it altogether – escaping death almost completely.

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