Diversity of life and the 'paradox of sex'

Date:
July 29, 2021
Source:
University of Arizona
Summary:
New research finds that sexual reproduction and multicellularity
drive diversity among different species.



FULL STORY ========================================================================== There are huge differences in species numbers among the major branches
of the tree of life. Some groups of organisms have many species, while
others have few. For example, animals, plants and fungi each have over
100,000 known species, but most others -- such as many algal and bacterial groups -- have 10,000 or less.


==========================================================================
A new University of Arizona-led study, published in the Proceedings of the Royal Society B, tested whether sexual reproduction and multicellularity
might help explain this mysterious pattern.

"We wanted to understand the diversity of life," said paper co-author
John Wiens, a professor in the Department of Ecology and Evolutionary
Biology. "Why are most living things animals, plants and fungi?"
To address this, Wiens worked with a visiting scientist in his lab,
Lian Chen from Nanjing Forestry University in China. They estimated
rates of species proliferation in 17 major groups that spanned all
living organisms, including bacteria, protists, fungi, plants and
animals. The hard part was to estimate how many species in each group
were multicellular versus unicellular and how many reproduced sexually
versus asexually. For five years, Chen sifted through more than 1,100 scientific papers and characterized the reproductive modes and cellularity
of more than 1.5 million species.

They found that both multicellularity and sexual reproduction helped
explain the rapid proliferation of animal, plant and fungal species. The
rapid proliferation of these three groups explains why they now include
more than 90% of Earth's known species.

The duo also found that the rapid proliferation of sexual species may
help explain the "paradox of sex." The paradox is why so many species
reproduce sexually, despite the disadvantages of sexual reproduction.



==========================================================================
"For sexual species, only half the individuals are directly producing offspring. In an asexual species, every individual is directly producing offspring," Wiens said. "Sexual reproduction is not as efficient. Another disadvantage of sexual reproduction is that you do need two individuals
to make something happen, and those two individuals have to be the right
sexes. Asexual species, on the other hand, only need one individual
to reproduce." Chen and Wiens found a straightforward answer to the
paradox of sex. The reason why there are so many sexual species is
because sexual species actually proliferate more rapidly than asexual
species. This had not been shown across all of life before.

They also found that another explanation for the large number of sexual
species is that sexual reproduction and multicellularity are strongly associated across the tree of life, and that multicellularity helps
drive the large number of sexual species.

"Multicellularity is actually more important than sexual production. We
did a statistical analysis that showed it is probably at least twice
as important for explaining these patterns of diversity as sexual reproduction," Wiens said.

And while this study alone can't pinpoint exactly why multicellularity
is so important, researchers have previously suggested that it has to
do with the variety of cell types within a multicellular organism.



==========================================================================
"If you're a single cell, there's not much variety there," Wiens
said. "But multicellularity allows for different tissues or cell types and allows for diversity. But how exactly it leads to more rapid proliferation
will need more study." Chen and Wiens also tested how their conclusions
might change if most living species on Earth were species of bacteria
that are still unknown to science.

"Most bacteria are unicellular and asexual. But because bacteria are
much older than plants, animals and fungi, they have not proliferated
as rapidly, even if there are billions of bacterial species," Wiens
said. "Therefore, multicellularity and sexual reproduction still explain
the rapid proliferation of animals, plants and fungi." Future work will
be needed to understand how multicellularity and sexual reproduction
drive biodiversity. Wiens is also interested in how some groups are both multicellular and reproduce sexually yet don't proliferate rapidly.

"We have some ideas," he said. "One example is rhodophytes, the red algae.

These are mostly marine, and we know from animals
that marine groups don't seem to proliferate as rapidly." ========================================================================== Story Source: Materials provided by University_of_Arizona. Original
written by Mikayla Mace Kelley. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Lian Chen, John J. Wiens. Multicellularity and sex helped shape
the Tree
of Life. Proceedings of the Royal Society B: Biological Sciences,
2021; 288 (1955): 20211265 DOI: 10.1098/rspb.2021.1265 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210729122105.htm

--- up 11 weeks, 6 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)