How to be winner in the game of evolution

January 13, 2017, University of Arizona
A simplified evolutionary tree of six representative animal phyla, illustrating differences in body form, habitat, and species numbers among them. Credit: T. Jezkova/Shutterstock/Aaron Ambos/J. Wiens

A new study by University of Arizona biologists helps explain why different groups of animals differ dramatically in their number of species, and how this is related to differences in their body forms and ways of life.

For millennia, humans have marveled at the seemingly boundless variety and diversity of animals inhabiting the Earth. So far, biologists have described and catalogued about 1.5 million animal , a number that many think might be eclipsed by the number of species still awaiting discovery.

All are divided among roughly 30 phyla, but these phyla differ dramatically in how many species they contain, from a single species to more than 1.2 million in the case of insects and their kin. Animals have incredible variation in their body shapes and ways of life, including the plant-like, immobile marine sponges that lack heads, eyes, limbs and complex organs, parasitic worms that live inside other organisms (e.g. nematodes, platyhelminths), and phyla with eyes, skeletons, limbs and complex organs that dominate the land in terms of species numbers (arthropods) and body size (chordates).

Amidst this dazzling array of life forms, one question has remained as elusive as it is obvious: why is it that some groups on the evolutionary tree of animals have branched into a dizzying thicket of species while others split into a mere handful and called it a day?

From the beginnings of their discipline, biologists have tried to find and understand the patterns underlying species diversity. In other words, what is the recipe that allows a phylum to diversify into many species, or, in the words of evolutionary biologists, to be "successful?" A fundamental but unresolved problem is whether the basic biology of these phyla is related to their species numbers. For example, does having a head, limbs, and eyes allow some groups to be more successful and thus have greater species numbers?

In the new study, Tereza Jezkova and John Wiens, both in the University of Arizona's Department of Ecology and Evolutionary Biology, have helped resolve this problem. They assembled a database of 18 traits, including traits related to anatomy, reproduction, and ecology. They then tested how each trait was related to the number of species in each phylum, and to how quickly species in each phylum multiplied over time (diversification). The results are published in the journal American Naturalist.

Jezkova and Wiens found that just three traits explained most variation in diversification and species numbers among phyla: the most successful phyla have a skeleton (either internal or external), live on land (instead of in the ocean), and parasitize other organisms. Other traits, including those that might seem more dramatic, had surprisingly little impact on diversification and species numbers: evolutionary accomplishments such as having a head, limbs, and complex organ systems for circulation and digestion don't seem to be primary accessories in the evolutionary "dress for success."

"Parasitism isn't correlated with any of the other traits, so it seems to have a strong effect on its own," said Wiens.

He explained that when a host species splits into two species, it takes its parasite population(s) with it.

This colorful chocolate chip sea star, along with sea cucumbers and sea urchins belongs to the Echinoderms, the only phylum with a body plan of five-fold symmetry. Credit: Ethan Daniels/Shutterstock
"You can have a number of parasite species living inside the same host," he said, "for example, there could be ten species of nematodes in one host species, and if that host species splits into two, there are 20 species of nematodes. So that really multiplies the diversity."

The researchers used a statistical method called multiple regression analysis to tease out whether a trait such as parasitic lifestyle is a likely driver of species diversification.

"We tested all these unique traits individually," Wiens explained, "for example, having a head, having eyes, where the species in a phylum tend to live, whether they reproduce sexually or asexually, whether they undergo metamorphosis or not; and from that we picked six traits that each had a strong effect on their own. We then fed those six traits into a multiple regression model. And then we asked, 'what combination of traits explains the most variation without including any unnecessary variables?'—and from that we could reduce it down to three key variables."

The authors point out that the analysis does not make any assumptions about the fossil record, which is not a true reflection of past biodiversity as it does not reveal most soft-bodied animals or traits like a parasitic lifestyle.

"We wanted to know what explains the pattern of diversity in the species we see today," said Wiens. "Who are the winners, and who are the losers?"

Marine biodiversity is in jeopardy from human activities such as acidification from carbon emissions, posing an existential threat to many marine animals, Wiens said.

"Many unique products of animal evolution live only in the oceans and could easily be lost, so groups that have survived for hundreds of millions of years could disappear in our lifetime, which is terrible. Many of the animals phyla that are losers in terms of present-day tend to be in the ocean, and because of human activity, they may go completely extinct."

The study also suggests that man-made extinction may wage a heavy toll on Earth's biodiversity due to the effect of secondary extinctions, Wiens explained.

"When a species goes extinct, all its associated species that live in it or on it, are likely to go extinct as well."

Explore further: Land animals proliferate faster than aquatic counterparts

More information: Tereza Jezkova et al. What Explains Patterns of Diversification and Richness among Animal Phyla?, The American Naturalist (2017). DOI: 10.1086/690194

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Bart_A
2 / 5 (8) Jan 13, 2017
We should remember that the taxonomy classification is quite arbitrary, and not a science in and of itself. As we find out more and more about the building blocks of chromosomes and genes of these various species, we see extremely complex relationships that aren't as simple as claimed. Species within a supposed single genus can have for example huge variations in number of chromosomes, something we would think would have better correlation if in face such species "evolved" over millions of years.

humy
4.4 / 5 (7) Jan 14, 2017
Species within a supposed single genus can have for example huge variations in number of chromosomes, something we would think would have better correlation if in face such species "evolved" over millions of years.


Err any given change in number of chromosomes normally requires just ONE mutation (either chromosomes copied or deletion), NOT many over millions of years. So millions of years are not required for a change in the number of chromosomes event and there wouldn't necessarily be a good correlation between how many chromosomes two species have and how closely they are related. + what is the source of information that the two are generally not at all correlated? Please show a link showing this.
Nick Gotts
4.5 / 5 (8) Jan 15, 2017
We should remember that creationists are always likely to spout some ignorant and/or dishonest nonsense in response to any article about evolution.
FredJose
1 / 5 (7) Jan 16, 2017
We should remember that creationists are always likely to spout some ignorant and/or dishonest nonsense in response to any article about evolution.

Strangely, it's the very act of saying ANYTHING in favor of a mythical, completely unscientific and irrational "evolution" that is perpetrating the greatest spread of lies the world currently knows. Darwinian evolution is nothing but a pack of lies - as is becoming clearer each day the more we know about the genetic make-up of biological life..

There is just no way that a purely materialistic chemical or physical process can generate the required information to build increasingly complex SYSTEMS from lower order organisms. You cannot get the abstract knowledge from naturalistic causes. Coding and decoding plus reparation requires external intelligence. Nothing else will do.
antialias_physorg
5 / 5 (8) Jan 16, 2017
Strangely, it's the very act of saying ANYTHING in favor of a mythical, completely unscientific and irrational "evolution"

How is it unscientific when you can observe it in the wild, in the fossil record and also in the lab? What more do you want?

It's really hard to call something a lie when the evidence is available for you every time you open your eyes. That pretty much classifies as " spouting some ignorant and/or dishonest nonsense", wouldn't you agree?


There is just no way that a purely materialistic chemical or physical process can generate the required information to build increasingly complex SYSTEMS

And yet something as simple as water and cold can create supremely complex snowflakes.
What was your argument again?

Remember: just because you're too dumb to understand something doesn't mean it ain't so.
Guy_Underbridge
5 / 5 (3) Jan 16, 2017
Say what you will, but if I read the creation tale in Genesis, then Origin of the Species, I get a different opinion of which I would classify as "mythical, completely unscientific and irrational", Freddo...
TheGhostofOtto1923
5 / 5 (3) Jan 16, 2017
It's really hard to call something a lie when the evidence is available
Naw it's the easiest thing in the world. It requires no thought only emotion. Faith allows the world to be what you want it to be without having to understand and accept what it actually is. Or what's worse, having to accept that you don't know what it is.

IOW religionists are lazy, immature, fear mongering bigots. They have to be in order to garner the love and admiration of Father Xmas. It says so in the books dontcha know.

"The God of the Old Testament is arguably the most unpleasant character in all fiction: jealous and proud of it; a petty, unjust, unforgiving control-freak; a vindictive, bloodthirsty ethnic cleanser; a misogynistic, homophobic, racist, infanticidal, genocidal, filicidal, pestilential, megalomaniacal, sadomasochistic, capriciously malevolent bully." - Dawkins
TheGhostofOtto1923
5 / 5 (1) Jan 16, 2017
There is just no way that a purely materialistic chemical or physical process can generate the required information to build increasingly complex SYSTEMS from lower order organisms. You cannot get the abstract knowledge from naturalistic causes
-And it always AMAZES me how they think they can just declare something and expect that it be true. God did this of course when he just declared that the universe exist, and poof! there it was.

But that want-have compulsion of the infant crying for its mama to deliver is what generated the concept of an omnipotent, omniscient god who delivers on command in the first place.

Any faithers present at creation though would have been impatient that it took 6_whole_days.
434a
5 / 5 (3) Jan 16, 2017
Darwinian evolution is nothing but a pack of lies etc


So you're saying that a being that is capable of engineering millions of species is not capable of creating a self perpetuating process that delivers these millions of species by the simple expedient of starting with a few naturally occurring chemicals and a lot of time. No, this designer is impatient, he - it's always a he isn't it - needs it all to happen in one day...because he's got better things to be doing than waiting around. Of course once he's created the millions of species that's it, no more new ones. After all, there is no mechanism for new ones to...evolve...because he couldn't work out how to make that happen. No! Straight in there with the eyeballs and the gametes, sod this waiting around malarkey. I mean, everyone's looking forward to armageddon and the rapture, wouldn't have wanted to wait billions of years for all this to turn up, complete waste of effort...no live fast die young that's the motto..

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