Hexbyte Glen Cove New research helps explain diversity of life and paradox of sex thumbnail

Hexbyte Glen Cove New research helps explain diversity of life and paradox of sex

Hexbyte Glen Cove

Credit: Pixabay/CC0 Public Domain

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 study, published in the Proceedings of the Royal Society B, tested whether and might help explain this mysterious pattern.

“We wanted to understand the diversity of life,” said paper co-author John Wiens, a professor in the University of Arizona Department of Ecology and Evolutionary Biology. “Why are most living things , plants and fungi?”

Wiens worked with a visiting scientist in his lab, Lian Chen from Nanjing Forestry University in China. They estimated rates of proliferation in 17 major groups that spanned all , 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.

The researchers 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.

Wiens and Chen also found that the rapid proliferation of sexual species may help explain the “paradox of sex,” or 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 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 that showed it is probably at least twice as important for explaining these patterns of diversity as sexual reproduction,” Wiens said.

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 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.”

More information:
Lian Chen et al, Multicellularity and sex helped shape the Tree of Life, Proceedings of the Royal Society B: Biological Sciences (2021). DOI: 10.1098/rspb.2021.1265

New research helps explain diversity of life and paradox of sex (2021, July 29)

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Hexbyte Glen Cove Republican and Democratic voters agree on one thing—the need for generous COVID-19 relief thumbnail

Hexbyte Glen Cove Republican and Democratic voters agree on one thing—the need for generous COVID-19 relief

Hexbyte Glen Cove

Bright Line Watch asked experts to rate the severity of the threats posed to democracy. More than 90 percent of the polled experts viewed the items that scored highest across the (ab)normality-and-importance dimensions as either a “moderate,” “serious,” or “grave” threat. Credit: Bright Line Watch

Both Democrats and Republicans overwhelmingly favor politicians who support generous COVID-19 relief spending, yet remain deeply polarized over the legitimacy of the 2020 presidential election results and former President Donald Trump’s second impeachment. Meanwhile, political experts find that the former president’s actions and those taken by congressional supporters in the aftermath of the election represent serious departures from American democratic norms.

Those are among the most recent findings of Bright Line Watch, the political science research project cofounded by Gretchen Helmke, a professor of political science at the University of Rochester, and her colleagues at the University of Chicago and Dartmouth College. The watchdog group started regular surveys about the health of US democracy in February 2017.

Read Bright Line Watch’s latest (February 2021) survey, “American democracy at the start of the Biden presidency.”

The team found strong bipartisan support for a new COVID-19 relief package, with Republican voters favoring a hypothetical candidate who supports a $500 billion pandemic appropriation over one who opposes it by 11 points, independents by 12 points, and Democrats by 18 points.

COVID relief has proven to be extremely popular with supporters of both parties, says Bright Line Watch cofounder Brendan Nyhan, a professor of government at Dartmouth College. “We’ve seen Democrats and Republicans in Congress at times compete to provide more generous offers of aid and assistance. The public seems to largely agree that the government should provide more help given the economic circumstances Americans currently face.”

Meanwhile, the legitimacy of the election result remains a polarizing issue: while 42 percent of Republican public policymakers expressed confidence in the integrity of the election results at the national level, only 22 percent of Republicans in the public sample felt the same way. To Helmke, the public’s continued partisan view of the election is troubling.

“In a democracy people basically have to trust that the rules are fair and that if their party or their team loses, the stakes of that loss won’t be intolerable, that in the future they’ll be able to contest an election again, and that they’ll have a chance of winning. That keeps everyone committed to democracy and to playing by the rules,” Helmke says. “Once you break that faith—that elections actually determine who the winner is—people’s allegiance to democracy wanes.”

While the latest survey provides a snapshot of the state of democracy in the early days of the new Biden administration, it’s also a look in the rearview mirror. The Bright Line Watch team found that loyalties and antipathy toward the former president—whose Senate impeachment trial began immediately after the surveys were conducted—continue to shape the views of citizens and government officials alike.

As a result, the “country still lives in the shadow of the Trump legacy,” the team writes.

As they had done throughout the project, the group fielded two parallel surveys—one to political experts and one to a representative sample of the US population—between January 28 and February 8.

Among the key findings in the survey of the public:

  • Partisan differences in confidence in the 2020 election and on legal and political accountability for former President Trump are profound. Democrats trust the election, support disqualifying Trump from holding future office, and believe he should face criminal prosecution. Republicans distrust the election results and favor moving on without consequences for Trump. Independents are split.
  • While there is cross-party consensus on government spending on pandemic relief, stark polarization over the certification of the presidential election and impeachment continues, with Republicans punishing Republican candidates for crossing the party line on either issue.

Among the key findings in the survey of political experts:

  • The experts overwhelmingly favor a set of reform proposals to expand voting participation, tighten campaign finance regulation, and modify how electoral districts are configured and votes are cast. They also favor abolishing the Senate filibuster and imposing term limits on Supreme Court justices. The only reform the experts reject is compulsory voting.
  • Experts rate the January 6 insurrection and President Trump’s pressure on state-level officials to overturn the election as among the most abnormal and important events of the Trump presidency. They overwhelmingly regard these events and the votes by a majority of Republican lawmakers in Congress not to certify the presidential results as grave or serious threats to American democracy.

Thinking of secession?

The specter of secession entered into the group’s battery of questions after legislators at the local and state level started mentioning it publicly. For the first time Bright Line Watch asked its public sample about the prospect of breaking up the United States into more than one country—a genuinely radical proposition, the team acknowledges.

“Until recently, we would have regarded it as too marginal to include in a survey. But state legislators in Mississippi and Texas and state GOP leaders in Texas and Wyoming have openly advocated secession in recent months, prompting us to design two survey items to gauge perceptions of this idea,” they write.

Notably, when presented with a proposal for their region to secede from the United States, almost one in three Americans polled (29 percent) is willing to entertain the prospect. Republicans (33 percent) support secession more than Democrats (21 percent); but Democrats are more amenable to secession than Republicans in areas where they tend to hold power.

Yet, the researchers caution against reading too much into that data: the results reflect initial reactions by respondents about an issue that they are very unlikely to have considered carefully, the team cautions.


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