Researchers uncover insights into the evolution of color patterns in frogs and toads

Hexbyte Glen Cove

The images are all Ptychadena robeensis, taken by Sandra Goutte, PhD, a research associate at the Evolutionary Genomics Lab at NYUAD. Credit: NYU Abu Dhabi

A team of researchers from NYU Abu Dhabi (NYUAD) has discovered new insights into the evolution of color patterns in frogs and toads—collectively known as anurans. Animal color patterns can help them camouflage with their surroundings and avoid detection from preys or predators. Many anurans have a light stripe along their back, which, when observed from above, creates the optical illusion that the animal is split in two halves and confuses visually-oriented predators. Although this color pattern is widespread in frogs around the world, little is known regarding its evolution or genetic origin.

In their paper published in the journal Molecular Biology and Evolution, the researchers of the Evolutionary Genomics Lab at NYUAD completed a broad-scale , which included over 2,700 species of anurans, to further the understanding of the evolutionary history of the vertebral stripe. They found that the vertebral stripe has evolved hundreds of times and is selected for in terrestrial habitats where visual predators coming directly from above—such as mammals or birds—are more prevalent. In contrast, the pattern was lost significantly more often in arboreal lineages—those living in trees—than in other habitats. While beneficial to frogs living on the ground, this color pattern may thus be disadvantageous to frogs living in trees.

To understand the genetic basis of the pattern, the researchers focused on the Ethiopian grass species Ptychadena robeensis, which is polymorphic—meaning that it presents the vertebral stripe trait in multiple forms—wide, thin or absent. They found that the gene ASIP is linked to the stripe pattern in that species. This genetic variation affects the level of expression of ASIP in the different morphs, a higher expression leading to a wide stripe and a lower expression leading to a thin stripe.

They also compared the genes of closely-related species of frogs and found that, while they present the same stripe patterns, they do not share the found in P. robeensis. This led the researchers to the conclusion that the stripe alleles found in P. robeensis evolved recently. The researchers further conclude that the vertebral stripe evolves rapidly in anurans, which may allow species to adapt to environmental changes or variable conditions.

This study is the first large-scale study of the adaptive value of the anuran vertebral stripe, whose evolutionary history has, until now, not been well understood. This study also establishes a link between the ASIP gene and a color pattern in anurans for the first time. ASIP is a well-studied gene in mammals, known to be linked to melanin production and color variation. The fact that it is linked to color patterns in frogs opens new research avenues on anuran color patterns and comparative studies across vertebrates.

“Our findings establish that the vertebral in frogs and toads holds a great potential in the field of evolutionary biology as it represents a clear example of repeated evolution. Studying this in other species can thus help us understand to which extent evolution predictably employs the same molecular paths when identical phenotypes evolve under similar selection pressures,” said Sandra Goutte, Ph.D., a research associate at the Evolutionary Genomics Lab at NYUAD. “The identification of ASIP’s role in the coloration of anurans by our team can also guide future across vertebrates.”

More information:
Sandra Goutte et al, Genomic Analyses Reveal Association of ASIP with a Recurrently evolving Adaptive Color Pattern in Frogs, Molecular Biology and Evolution (2022). DOI: 10.1093/molbev/msac235

Researchers uncover insights into the evolution of color patterns in frogs and toads (2022, November 17)
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The ocean in a cup: Environmental DNA successfully captures marine biodiversity

Hexbyte Glen Cove

Dolphins in the Port of L.A. eDNA can help researchers identify the breadth of animal life in the oceans through the shed DNA found in as little as a cup of seawater. Credit: Zachary Gold

Measuring marine biodiversity with “environmental DNA”—an application of gene sequencing to environmental biology—should permit rapid assessment of changes in marine life. That makes environmental DNA (eDNA) a critical tool for managing our response to climate change. But eDNA only works well if key implementation steps are followed, according to a new study of the Los Angeles and Long Beach area published in the journal PeerJ.

“What do we need to know to use eDNA in the coastal ocean, and can we make it work well in an important urban setting? Those are the questions that motivated us to launch this study,” said Regina Wetzer, Curator and Director of the Marine Biodiversity Center at the Natural History Museum of Los Angeles County (NHM).

Answering those questions involved contributions from a natural history museum, multiple academic institutions, environmental consultants, and government agencies—highlighting the challenges involved in using eDNA, but also the widespread interest in its use.

eDNA uses genetic sequencing of samples from the environment (in this case, ocean water) to inventory biodiversity. “There are genes that differ enough between species that they can be used as identification markers. Every organism sheds DNA by dropping skin cells or other materials, so we can take a cup of seawater, sequence the DNA in it, and use that to inventory organisms in the area,” said Zack Gold, lead author of the study.

The neighboring Port of Los Angeles and Port of Long Beach form one of the largest port complexes in the world and are a site of intense environmental interest. That made it an interesting site to test eDNA’s ability to act as an effective tool for biodiversity assessment.

NHM’s Dean Pentcheff recovering a seawater sample for eDNA. Credit: Janie Chen

This study paired eDNA sampling and conventional ship-based trawl net sampling at seven sites in the port complex. At each site, researchers collected multiple eDNA samples, each about one liter of seawater, just before the trawl net was towed through the same area. That permitted a comparison between eDNA and traditional biodiversity assessment techniques: eDNA detected nearly all of the 17 species of fish found in the trawls, but also detected an additional 55 native fish species. Detecting those additional species through conventional sampling requires many more sampling trips and a very high expense.

“We were happy to see eDNA validated alongside ‘conventional’ sampling, but we were really excited to see the extra information that came from the eDNA,” said Dean Pentcheff, researcher and program manager of the Diversity Initiative for the Southern California Ocean (DISCO) at NHM. But getting that extra information depended on having a complete genetic reference library for all the fish in the area—a in an eDNA sample can only be resolved to a species if there is a reference sequence on file for that species. All the fish in the eDNA samples in this study were resolved only after the researchers added the last few fish references to the sequence library.

The eDNA samples from different locations in the ports yielded different species inventories at a statistically significant level. That answered an important question: Can eDNA measure variability across an area as small as the port complex, or does seawater mix so thoroughly that local differences are completely blurred? This study demonstrated that eDNA in this ocean environment can expose differences between places as close as a few hundred meters apart.

Reccovering sampling trawl net at night. eDNA proved more accurate and would be less expensive than more traditional sampling. Credit: Wood Environment and Infrastructure, Inc.

Based on this pilot project, the authors assembled a set of recommendations for managers considering eDNA as a tool for biodiversity assessments. The recommendations cover careful selection of the identifying genes and specific advice on how to clean up the from eDNA samples before searching for sequence matches. Because of the successful species resolution that resulted from building a full sequence reference library, a key recommendation is to create regional reference databases.

“These samples of the environment are like time capsules that we’ll be able to exploit in the future,” said Adam Wall, Crustacea Collections Manager at NHM. That sentiment prompted another of the group’s recommendations: Archive eDNA samples and sequence data for long-term use. As sequencing technology improves, additional information could come from the samples. As genetic data analysis techniques improve and genetic reference libraries are expanded, the sequence data can be analyzed again to get additional results beyond the fish inventories published in this study.

More information:
Zachary Gold et al, A manager’s guide to using eDNA metabarcoding in marine ecosystems, PeerJ (2022). DOI: 10.7717/peerj.14071

Journal information:

The ocean in a cup: Environmental DNA successfully captures marine biodiversity (2022, November 16)
retrieved 17 November 2022

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