Survival of all-female fish species points to its DNA

February 13, 2018

The very rare animals that reproduce asexually — only about one in a thousand of all vertebrate species — are thought to be at an extreme fitness and ecological disadvantage compared with their sexual counterparts, who always reshuffle their DNA to make each offspring genetically unique.

But that theory doesn’t hold true for the Amazon molly, an all-female fish species that scientists have now traced back its evolutionary history to show that is has thrived for millennia in the fresh waters along the Mexico-Texas border (and, more recently, in aquariums everywhere). Ever since the Amazon molly was the first asexual vertebrate discovered in 1932, scientists have wondered how this came to be. Now, new clues are being uncovered with the completion of its genome. Download Full Image

To better understand how this fish’s reproduction deviates from the norm, an international team of scientists has sequenced the first Amazon molly genome.

“This study caps an intensive collaborative study, marking the first glimpse of the genomic features of an asexual vertebrate, and setting up a platform for future molecular, cellular and developmental work in this interesting species,” said Michael Lynch, who directs the Biodesign Institute's Center for Mechanisms of Evolution at Arizona State University.

Their findings suggest that the molly’s asexual reproduction is unusual not because the animals are at a disadvantage but because the fish has a hardy genetic makeup that is extremely rare in nature and that keeps the animals healthy.

“It appears the stars aligned for this species,” said first author Wesley C. Warren, assistant director of comparative genomics at McDonnell Genome Institute at Washington University School of Medicine in St. Louis. “The fish’s original genome had to be perfectly aligned and all of the elements compatible to allow an asexual reproducer to survive in good health for so long. That kind of combination is rare — kind of like Fred Astaire and Ginger Rogers — that sort of combo doesn’t come around very often.”

The findings are published Feb. 12 in the journal Nature Ecology & Evolution.

A fish tale

Ever since the Amazon molly was the first asexual vertebrate discovered in 1932, scientists have wondered how this came to be.

One of the theories that spell out why asexual reproduction should stand in the way of a species’ fitness and success is the idea that if no new DNA is introduced during reproduction, then harmful gene mutations can accumulate over successive generations, leading to eventual extinction. Another hypothesis states that because asexual reproduction limits genetic diversity within a species, the animals eventually become unable to adapt to changes in the environment.

“The expectation is that these asexual organisms are at a genetic disadvantage,” said Warren, also an assistant professor of genetics. “In reality, the Amazon molly is doing quite well.”

The researchers found that the Amazon mollies resulted from a sexual-reproduction event involving two different species of fish, when an Atlantic molly (P. mexicana) first mated with a Sailfin molly 100,000 to 200,000 years ago.

Since then, the Amazon molly has been a hybrid that has remarkably remained frozen in evolutionary — yet still thriving.

“That’s about 500,000 generations if you calculate it out to the present day,” Warren said. “The expectation is that many harmful mutations would accumulate in that time, but that’s not what we found.”

The Amazon molly reproduces by “mating” with a male fish of a related species. But the male’s DNA is not incorporated into the offspring. Instead, mating with the male fish triggers the replication of the entire maternal genome. In essence, mollies clone themselves. They don’t lay eggs but instead give birth to large broods of live offspring.

Send in the clones

Scientists have long theorized that clones, by failing to purge harmful mutations, should lead to genomic decay, and eventual extinction over generations.

The scientists found no widespread signs of genomic decay.

This was the case even when they examined genes involved in organs the molly would not have needed for eons, such as making sperm or male development. Remarkably, these genes remain intact and the molly genetically diverse.

So while the Amazon molly has thrived over eons, it remains resistant to giving away its genomic secrets — for now.

Though it’s still unclear why the Amazon molly’s genome remains so healthy and free of harmful mutations after so many generations of asexual reproduction, the researchers believe the answer will soon be found in the animal’s genome.

“It may be that the Amazon molly has the best of both worlds,” said research colleague Manfred Schartl at the University of Wurzburg in Germany. “It seems to have some advantages that we see in species that reproduce sexually and other advantages normally seen in species that produce offspring non-sexually."

Whatever the reasons, the researchers said the Amazon molly is an exception to ideas about the evolutionary disadvantages of asexual reproduction.

“The success of this species appears to be a random event,” Warren said. “That’s very rare in nature because the combination has to be perfect for species like the molly to thrive over so many generations.”

Written by Joe Caspermeyer, Arizona State University, and Jim Dryden, Washington University in St. Louis

Joe Caspermeyer

Manager (natural sciences), Media Relations & Strategic Communications


A road map for climate-change policy

ASU's Morrison Prize awarded to authors navigating rocky terrain of partisan politics

February 13, 2018

Even with widespread agreement that the world’s climate is rapidly changing, the United States has struggled to combat the issue, hindered by divisive partisanship. Is there an effective path forward for a nation so torn ideologically?

Hari M. Osofsky and Jacqueline Peel believe there is. And they have been awarded this year’s Morrison Prize for their academic article, “Energy Partisanship,” which not only outlines the critical importance of bridging and circumventing the partisan divide, but also provides guidance for doing so. Morrison Prize co-winners Jacqueline Peel, associate dean of the master's program at the University of Melbourne Law School in Melbourne, Australia, and Hari M. Osofsky, dean of Penn State Law and the Penn State School of International Affairs. Download Full Image

The Morrison Prize, established in 2015, is administered through the program on law and sustainability at the Sandra Day O’Connor College of Law at Arizona State University. The annual contest awards a $10,000 prize to the author of the most impactful sustainability-related legal academic article published in North America during the previous year. The prize is named after its funder, Richard N. Morrison, who is also a co-founder of the Morrison Institute for Public Policy at ASU.

“We’re both honored and humbled to have our work recognized with this year’s Morrison Prize, especially given the remarkable scholarship honored with this award in past years,” Osofsky said. “Arizona State University helps to advance sustainability in needed ways by providing this opportunity for those writing in the field."

Osofsky, who co-authored the article as a professor at the University of Minnesota Law School, now serves as the dean of Penn State Law and the Penn State School of International Affairs. Peel is associate dean of the Masters program at the University of Melbourne Law School in Melbourne, Australia. And she says the political challenges hindering climate policy are not unique to the U.S.

“Partisanship is not just a challenge for energy and climate policy in the United States but more broadly for Western democracies, including my own,” Peel said. “Our article suggests that strategies of energy pragmatism are the best answers to energy partisanship.”

Bypassing the partisan roadblocks

“Energy Partisanship,” which was published in the Emory Law Journal, details how vitriol in American politics has impeded progress on climate policy. While Republicans, for example, allege Democrats are waging a “war on coal,” Democrats denounce Republicans as belonging to a “flat-Earth society.” Politicians play to their base, using sound bites and name-calling — and even the occasional stunt.

The article recounts how in 2015, Sen. James Inhofe, R-Okla., signed off on legislation that declared “climate change is real and not a hoax.” The landmark bipartisan measure had only one dissenting vote. Still, Inhofe later stated, “The hoax is that there are some people that are so arrogant to think that they are so powerful that they can change climate. Man can’t change climate.”

A few weeks later, in an attempt to illustrate his point, Inhofe threw a large snowball on the Senate floor, and made a statement directed at then-President Barack Obama: “You know what this is? It’s a snowball … just from outside here, so it’s very, very cold out. Very unseasonal. So, Mr. President, catch this.”

The reaction to Inhofe’s snowball throw was predictably partisan, viewed as either a salient point well made or a ridiculous act of showmanship that proved nothing.

Could Inhofe have swayed his opponents with a stronger scientific argument? Perhaps not. As the paper states, “an emerging body of psychological research indicates that these differences cannot be overcome simply by presenting politicians and the public with more and better scientific data; strongly divided partisan views are difficult to shift and not responsive to change in the face of expert opinion.”

Opinions are difficult, if not impossible, to change on climate change. And those partisan disagreements, as the paper points out, “constrain possibilities not only for U.S. legislative efforts but also for international ones.”

So what can be done?

Drawing on case studies and empirical data, Osofsky and Peel have identified specific strategies for overcoming partisanship and making greater progress in the area of energy sustainability. Specifically, they suggest looking beyond the legislative branch of the federal government, where consensus seems especially elusive. Among the suggestions:

  • seeking smaller-scale changes through state or local governments
  • bypassing legislatures through litigation or executive authority
  • creating incentives for the private sector to address energy issues
  • placing a stronger focus on topics within the climate-change discussion where greater consensus may be possible, such as economic development and disaster resilience

“At this moment of political polarization, we hope that our work on energy partisanship can assist efforts to encourage greater bipartisan collaboration and constructive dialogue across difference in energy and climate-change law and policy,” Osofsky said. “The Morrison Prize provides important support for our efforts to do so.”

About the Morrison Prize

Professor Troy Rule, director of the Law and Sustainability Program at ASU Law, says sustainability efforts are focused heavily on science and technology, which is important. But political challenges are often overlooked.

“Tens of billions of dollars are expended every year on hard science research aimed at promoting environmental sustainability,” Rule said. “This hard science research is producing powerful technological breakthroughs, some of which could dramatically improve environmental sustainability on this planet. Unfortunately, relatively few research dollars or scholarly efforts are devoted to overcoming the legal and policy obstacles that are impeding humanity’s adoption of these technologies.”

The Morrison Prize is intended to help close that gap.

“Humankind increasingly needs innovative legal constructs and policies capable of supporting and facilitating its growing array of sustainability-oriented technologies,” Rule said. “By encouraging and recognizing impactful sustainability-related legal academic research, the Morrison Prize seeks to help drive the legal and policy innovation that’s critical to the advancement of the sustainability movement.” 

Each year, law professors from around the world who have recently published articles in North American legal academic journals are eligible to enter the contest. All entries undergo independent review and scoring by a diverse group of full-time law professors who teach in environmental sustainability-related areas at various North American law schools. The scores from these judges are aggregated to determine the prize winner.

Osofsky and Peel, the third winners of the Morrison Prize, will be honored in person May 11 in Phoenix at the fourth annual Sustainability Conference of American Legal Educators.

“This award is particularly meaningful to us because it’s based on impact,” Osofsky said. “As legal scholars, it’s always our hope that our work will make a positive impact in academia and beyond, and to be recognized for doing so is very rewarding.”

In 2017, Vanderbilt University professors Michael P. Vandenbergh and Jonathan Gilligan won the prize for "Beyond Gridlock." The article underscored the difficulties of effecting change through government and highlighted the underutilized potential to reduce greenhouse-gas emissions through the private sector.

In 2016, Dave Owen, a professor at University of California, Hastings College of Law, and Colin Aspe, a freshwater conservation adviser at the Nature Conservancy, were the inaugural winners of the Morrison Prize. Their article, “Trading Dams,” described creative new policy approaches for better balancing hydroelectric energy generation and environmental protection on the nation’s river system.

Executive Director, Marketing and Communications, Sandra Day O’Connor College of Law