New production by Salty Wave

Salty Wave has been busy producing a series of Video Explainers for the Institute of Molecular Bioscience at the University of Queensland, Australia. 

Take a look at The Science of Acute Pain to understand how pain is felt and experienced by many people.

The sounds cavefish make

Scientists have discovered one of the ways cavefish have adapted to subterranean living is by using sound differently to surface fish morphs.

“Astyanax mexicanus is the only vertebrate where extant cave-dwelling and surface-dwelling morphotypes still exist within the same species” says Dr Sylvie Retaux, a neuroscientist from the Paris-Saclay Institute of Neuroscience, France, who is fascinated by sonic cavefish. 

A cavefish recorded in the Pachon cave, located in the North of the Sierra de El Abra, North-East Mexico.
(Photo © Sylvie Rétaux)

25,000 years ago, the ancestors of A. mexicanus were swept away from their river habitat into the caves of North-Eastern Mexico by flood waters. Trapped in the caves and isolated from the surface, the cavefish gradually lost their eyes and pigment as a consequence, but kept their hearing, a finding reported by Arthur Popper in the 1970’s.

Retaux led the research study “Evolution of acoustic communication in blind cavefish” published by Nature Communications to determine whether this loss of sight was compensated by other senses. “We wanted to test whether acoustic communication would exist and would have evolved with their adaptation to darkness” said Retaux. 

The research team ventured to six of the thirty caves that host Astyanax mexicanus troglomorphic cavefish populations in San Luis Potosi and Tamaulipas, North-Eastern Mexico (Molino, Pachón, Los Sabinos, Tinaja, Chica, and Subterráneo); and a well in the village of Praxedis Guerrero, inhabited by the surface morphs. 

Reaching the cavefish proved to be no ordinary task, and an adventure in the making. The team traversed through mud, contended with the dark, and wore masks to protect against histoplasmosis, a disease of the lungs caused by fungus, all while carrying heavy backpacks full of electronic equipment. The researchers also had to contend with a sheer 68-metre vertical rock face to reach the Molino study site. But once inside the caves, the acoustic environment was very calm says Retaux. “It is a kind of dream for bio-acousticians. Almost no sonic pollution down there.”

Pool number 1 in the Los Sabinos cave, located in the middle of the Sierra de El Abra.
(Photo © Jean-Louis Lacaille-Muzquiz)

Both Astyanax morphs are known to produce the same repertoire of 6 sounds: clicks, serial clicks, sharp clicks, clocs, serial clocs and rumblings; and the anatomical structures used to make these noises are conserved between the morphs. “They scrape their teeth, use a series of small bones (the Weber apparatus), drum on the swim bladder or they can produce hydrodynamic waves with their fins” Retaux says.

The team discovered a sound made by wild cavefish when compared to surface morphs represented a different behaviour. The sharp click by surface morphs is visually triggered in the presence of rivals and is used to establish and maintain hierarchy. However, when cavefish produced the same sound it was in response to detecting food odours while foraging. 

Unlike the surface morphs, cavefish don’t display schooling behaviour and are non-aggressive. “It is unclear whether they ‘call’ other individuals to come and share food when they find some, but it is a possibility. In any case, communication about finding food is crucial for cavefish, much more beneficial than spending energy in aggressive behaviours” Retaux explains. “Drastic environmental changes can induce significant evolution or shifts in behaviours and probably, in the brain, the neural circuits that govern these behaviours” she says.

Even though morphological, physiological and behavioural changes occurred in cavefish, studies report Astyanax morphs breed with one another when flood waters wash surface morphs into the cave system. “A really interesting hypothesis is that one of the sounds of their repertoire, which again, is shared by the two forms, is used during courtship. In this case, a prediction is that the use and meaning of this particular sound has not changed, contrary to the sharp click that has evolved from an aggressive signal to a feeding signal” says Retaux.   

Both Astyanax morphs are the perfect model for researchers to reconstruct the evolutionary paths each morphotype has taken since their common ancestors were separated. The lateral line in cavefish is enhanced, an adaptation which has increased their sensitivity and response to living in confined zones with no light. “It is a sense that we humans do not have but that fishes and amphibians do have, which allows them to detect differences in the water pressure around them.”  

The only audible sounds in the caves, are water dripping or bats chirping and Retaux plans a return trip to record the acoustic environment. She wants to answer the ironic question Arthur Popper asked when he first discovered cavefish have exceptional hearing: what are cavefish listening to?

Thank you to Dr. Sylvie Retaux for permission to publish her field trip photos.

Adventures with Blue Whales and Blue Waters

My book review - Adventures with Blue Whales and Blue Waters - featuring The Secret Life of Whales by marine biologist, Micheline Jenner; and The Oceans, A Deep History by paleoceanographer, Eelco Rohling - was published by Cosmos Magazine Winter 79 Edition.

I recommend both books, which are very different stories, but written by scientists who share a great respect and love of the ocean and its wildlife. Fantastic stories.

Episode 3 - Noisemakers Series by Salty Wave Blue

Welcome to the podcast series – Noisemakers – presented by Salty Wave Blue. This episode features my interview with Dr. Sebastian Thomas (March 2017) from the University of Melbourne, who discusses why mangrove forests are considered the major players of blue carbon, amazing sounds from the noisemakers of the wild, quizzes to solve and some fascinating tales to follow from the rainforest to the reef.

Stock Media provided by Pond 5 and Monsoon Enterprises.

This podcast is dedicated to my dog, Scruffy, who loved mangrove forest walks.

Episode 3

Viral Vectors for Change

Viruses have dominated the microscopic world of the oceans for billions of years and researchers find it difficult to track and isolate their activities because they are invisible to the naked eye.

But science has finally caught up with these tiny vectors of change, says Marine researcher, Dr Karen Weynburg, a Synthetic Biology Fellow at the CSIRO and University of Queensland.

“For some people, it's just not on their radar that viruses are so central to everything in life” Weynburg says.

Stock media provided by Ryhor Bruyeu / Pond5

In the paper: Marine prasinoviruses and their tiny plankton hosts: a review, research led by Weynburg reported viruses co-evolved with their hosts and are immersed in a constant battle of survival to outwit and outplay for control.

“Recently there's been a discovery that probably what happened was that all life was RNA” Weynburg says. This research has shown viruses existed before cells and were the precursors of life. Viruses switched from RNA to DNA to avoid their genomes being attacked and removed by the host cell.

Viruses are not regarded by science as a real organism because they cannot reproduce or metabolise without a host cell. Traditionally, they are classified according to the host they infect, be it an animal, a plant or prokaryotic bacteria.

“The jury's still out on whether viruses are living or not, because they don't fulfill all the requirements of a living organism, but they have a sort of key if you like, the way they outwit hosts, they're clever players in the oceans of the world” says Weynburg.

“In terms of the marine environment, in one teaspoon of sea water you're going to have as many as ten million viruses, but those viruses will again, not just be abundant, they'll be hugely diverse, because they're affecting so many different hosts."

Sea turtle swimming in a coral reef habitat. Stock media provided by Charlie Blacker / Pond5

What Weynburg finds intriguing about viruses is they can be vectors for disease or work as part of an organisms’ immune system. A good example is when the activity of coral specific viral communities control the threat of bacterial pathogens, suggesting bacterial and viral communities have co-evolved with their coral hosts.

“I don't think it's a straight forward black and white situation where they're all good, they're all bad. It’s quite complicated and there's a lot of dynamics and interactions going on” Weynburg says.

“Viruses have to be very specific, very intimate with their host and therefore they've fine-tuned a strategy over millions of years."

Coral reef growing in Komodo National Park in the waters of Indonesia. Stock media provided by Ethan D / Pond5

Innovative technology is assisting researchers like Weynburg to understand just who and what viruses are and their interaction with the environment.

“People are beginning to realise they're playing a really crucial role and we have to start including them in future marine models and what's actually happening in the oceans in terms of biological dynamics.”

Microscopic marine cyanobacteria drove the oxygenation of Earth 2.5 billion years ago and they continue to generate 50 percent of atmospheric oxygen and primary production in the oceans. Every week viruses spearhead a massive turnover of microbes in the world’s oceans by initiating a new generation.

“If you took all the viruses out of the ocean today, there would be no life in it tomorrow” Weynburg says.

“Everything would grind to a halt because viruses keep the system ticking over. They keep the whole energetics and dynamics in the oceans going.”

Wave crashes on the ocean surface. Stock media provided by Quincy Dein / Pond5

With climate change a reality, Weynburg says, it is hard to predict how viruses will survive exposure to higher levels of UV and warmer ocean temperatures.

“We need more biological modelers to come in and really start plugging the data that we generate into models of what might happen in terms of climate change. We really don't have the answer yet” Weynburg says.

In her research paper, Weynburg refers to how a virus’ selective behaviour during infection is geared toward protecting its survival in the environment, for example, holding onto heat shock proteins to survive heat stress.

“Virus’ only keep the bits of DNA that work for them” Weynburg says. “They don't carry junk DNA like we do in our genomes. So, if they hold onto something like a heat-shock protein, it's going to be playing an important role in their infection."

Weynburg says viruses free up energy and nutrients for growing new cells by infecting and releasing the contents wrapped up in microscopic cells of marine microbes at the end of their lifetime.

These viruses also vicariously influence cloud formation by controlling blooms of cocolithophores in the sea and contribute to the recycling of iron crucial to biological processes in nutrient poor oceans.

“The blooms of the cocolithophores that you can see from space are huge and end up causing these cloud formations. The end of the blooms are actually only caused by two or three different strains of virus, which is quite fascinating” says Weynberg.

Cloud formation is stimulated by the activity of blooms of coccolithophores in the oceans, visible from space. Stock media provided by Nikolai Sorokin / Pond5

Management of climate is just one part of the viral power play. Since the mid 1970’s there has been an enormous leap in our understanding of marine virology. Weynburg’s research currently aims to mimic how viruses capture DNA segments to create whole genomes or existing genes.

“I'm sure down the line, viruses will have a myriad of roles that we can exploit if we think cleverly about it and we understand the system well enough” says Weynburg.

Scientists working in an experimental laboratory. Stock media provided by Yuralaits Edhar / Pond5

Questions about the ethics of applying these synthetic biology tools are already being considered by researchers long before “the horse has bolted” says Weynburg. The synthesised genomes can be targeted to treat disease and delivered by viral infection.

“Some people have already used virus captures to deliver proteins that will target cancer cells” she says. “If you think that you could use a virus to deliver something that would specifically attack a rogue cell, that is really exciting. We're on that brink of discovery now. It's real cutting edge technology”.

Report by Gabrielle Ahern


My interview with Dr Karen Weynburg will feature in an upcoming podcast episode of the SaltyWaveBlue NOISEMAKERS series published via Sound Cloud and iTunes, so stay tuned.

The paper - 'Marine prasinoviruses and their tiny plankton hosts: a review' is published by the journal - Viruses.

Images of marine microbes and more ecology themed boards are available on the SaltyWave Pinterest site: https://www.pinterest.com.au/saltywave/