July 24/2024

 

The Shocking Sex Lives of Electric Eels in Brazil

BY JAMES HALL

11/15/ 2023

atlasobscura.com

NONATO MENDES IGNORED THE LEECHES squirming underneath his T-shirt. With a deep breath, he plunged his gloved hand into the net that was piled on the deck of the boat, grabbing the electric eel behind its head. Skillfully keeping its writhing body away from him, he avoided the excruciating jolt—8 times stronger than a police-issued taser. It was his 96th capture that year, the last needed for his field research.

For more than 20 years, Mendes, a federal environmental agent at Brazil’s Instituto Chico Mendes & a Ph.D. student at the University of São Paulo, has unraveled the enigma of electric eels. Now, after a decade of analysis, he believes he’s cracked one of their biggest secrets: their spawning behavior & the environmental conditions that drive it.

Electric eels, immediately recognizable with their pudgy, scarred bodies, wide mouths, & beady eyes, are the apex aquatic predators of the Amazon. “People fear them even more than jaguars; you see a jaguar, but you don’t see these fish until you step on one in the river & get electrocuted,” Mendes says.

Native to the rivers of the Amazon basin & the Guianas, electric eels are not true eels; they actually belong to the knifefish family. The 3 species in the electric eel genus Electrophorus generate powerful shocks to catch prey & defend themselves—a trait that sparked Mendes’s curiosity from an early age.

Growing up in the northern Brazilian city of Macapá, where the Amazon River meets the Atlantic Ocean, Mendes, who has autism, became fixated on electricity—his father was an electrician—& later the natural world. During fishing trips, he discovered the electric eels that lurked in a local lagoon. They were the perfect fusion of his passions.

Over the years, Mendes has uncovered new details about the animals’ hunting techniques & other behavior. Yet their reproductive biology remained elusive. Electric eels are popular fish in aquariums & zoos, but breeding them in captivity has proven nearly impossible—figuring out how to do so would reduce captures of wild eels.

Conventional thinking was that electric eels spawned during the peak of the dry season, when breeding pairs occupied the isolated pools that formed as rivers receded. But no field study had confirmed this, leaving the timing of their breeding season an enigma. Mendes, intrigued, set out to solve the mystery.

In 2005, Mendes set up base on the Curiau River floodplain in his home state of Amapá for a year-long study on the Vari’s electric eel (Electrophorus varii), the most primitive electric eel species. He recruited local fishermen to help.

Luis Sousa, a longtime Curiau River fisherman who became one of the project’s field assistants, says the secret to finding the eels is no secret at all: “You find the fish it eats. So, we know where to look for them because these spots mean good fishing.”

Equipped with shrimp nets, cast nets, & hand lines, the team set out by boat every 2 months to capture enough specimens to gather data on size, weight, stomach contents, & gonad development, which signals whether the animals are ready to reproduce. Yet electric eels don’t take kindly to being caught. Thick rubber gloves offered some protection from electric shocks, but an occasional electrocution was just par for the course. “It’s agony,” says Mendes. “First, every muscle in your body contracts; then, you get intense pain. After, there’s numbness & exhaustion—you feel wiped out.”

Fieldwork had other hazards, too: Swarms of mosquitoes & legions of leeches feasted on the researchers’ blood & encounters with the highly venomous Fer-de-Lance viper were frequent. The team persevered, & even before the last eel was caught, Mendes noticed a pattern.

As the Amazon’s rainy season arrived & torrents of rain swelled the rivers, the team began to catch eels with gonads almost bursting with sperm or eggs. Later analysis of the data revealed a possible mating trigger—one particularly apt for an electric fish.

“My hypothesis is that it might be electrical conductivity in the water caused by the rain & atmospheric conditions, maybe even lightning, that drives electric eels to begin spawning,” says Mendes. But even armed with this data, it would take more than a decade of painstaking analysis before he published his discoveries in 2016.

“The rising water period triggers a lot of behaviors in South American fishes, & for fishes to be using that cue to synchronize breeding would make a lot of sense,“ says Mark Sabaj, an ichthyologist at the University of Drexel, who wasn’t involved in the research. Mendes’s reputation in the field adds credibility to the hypothesis. Notes Sabaj: “I would buy into it as his knowledge & personal experience of these fish far exceeds anyone else’s. He’s like the electric fish whisperer.”

Mendes’s research revealed another surprise: Female electric eels prefer large mates, the bigger, the better, possibly because of the males’ outsized role in parental care. The larger the eel, the more powerful its electric discharge, giving big males an advantage when competing for & defending prime nesting spots, as well as protecting their young.

“Males guard the offspring for about 4 months until the moment they disperse, which is an amazing investment of time,” says Douglas Bastos, a researcher at the Instituto Nacional de Pesquisas da Amazônia (INPA) who has studied the behavior. “During this period, they are very attentive to their young, & hyperaggressive in defending them.”

Beyond potentially solving some scientific mysteries, the research could soon have some benefits for the eels themselves. Currently, all global demand for the animals is met by collecting wild specimens from the Peruvian Amazon. While this trade remains sustainable & electric eels are not endangered, Mendes believes his findings may one day eliminate the need for capturing them from the wild.

To test out whether his theory is correct, Mendes plans to try replicating the environmental conditions that trigger wild spawning in a captive setting. “I think we’ll achieve the first-ever breeding in captivity,” he says. “But it’s not just about the science. If it means wild electric eels can stay in the rivers, where they belong, I’ll be very happy.”

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July 17/2024

 

Why Are Snails & Slugs So Slow?

By John Tooker, Daniel Bliss, & Jared Adam 

1/2/2024

atlasobscura.com

WANDER THROUGH YOUR BACKYARD OR walk along a stream & it’s likely you’ll see a snail: small, squishy animals with shells on their backs. Snails are found in water, whether in salty oceans, rivers, or lakes. They’re also on land: in forests, grasslands, & even your garden.

As you explore your yard or woods, you can also encounter slugs, which are slow-moving animals related to snails. They look like them too, except that slugs lack shells. Not only can you find slugs crossing sidewalks or on plants at the park—some are in our oceans.

All told, an estimated 240,000 species of snails & slugs live all over the world. But no matter what continent they’re on, or what ocean they’re in, there’s one thing they all have in common: They move slowly.

Here’s an example of just how slow they are: The World Snail Racing Championships, held in the United Kingdom, pits the quickest snails against one another in a “foot” race. The fastest snail on record sped through the course at a blazing 0.006 miles per hour.

Or to look at it another way, if you were that slow, it would take about 3 minutes to get a bite of food from your plate to your mouth.

Why is it that snails & slugs are in no hurry? As researchers who specialize in the study of plants & animals, we’ve learned the answer is more complicated than you might think.

Snails & slugs are members of a large group of related animals known as mollusks, which also includes clams, oysters, squids, & octopuses. Within mollusks, there’s a smaller set of related animals called gastropods; this includes snails & slugs.

Because they live in such diverse places, different gastropods have evolved to consume almost every type of food. Some species are herbivores—they eat living plants. Some are detritivores—they feed on dead or decomposing plants. Others are carnivores or scavengers—they eat other animals.

The lack of speed of snails & slugs can be attributed to at least 3 factors: how they move, what they eat, & what eats them.

First, while some animals fly, jump, or slither, snails & slugs move using what biologists call the “ventral foot.” But the word “foot” here can be confusing. A snail or slug foot is nothing like a human foot. Instead, it’s a band of muscle that runs along the underside of their body & is covered in sticky mucus. When contracted, this muscle ripples, sending tiny waves from the animal’s tail to its head. These waves compress the mucus on the bottom of the foot into a slippery liquid, allowing the snail or slug to glide over the ground or climb plants.

It’s a unique way to move, & it forces snails & slugs to go slowly because their speed is limited by the number of foot contractions & the amount of mucus they can make. And snails & slugs don’t need to rush to find their food, anyway.

Many animals, particularly predators, must move fast to catch a meal; a cheetah needs to outrun a gazelle, for example. But most slugs & snails eat plants, decaying matter, or marine animals, like sponges, which are anchored in place. None move around much, so dinner’s not going anywhere—no rush.

Nor do snails & slugs need to be fast to avoid predators. They’ve evolved other ways to evade mice, birds, shrews, and other enemies. Typically, snails withdraw into their shells to hide until the predator passes.

Land slugs hide in plain sight. Most are shades of gray, tan, or brown and blend in well with their surroundings. Predators simply don’t notice them. They also have an additional layer of protection. Land slugs are covered with a sticky mucus, similar to the mucus that lubricates their movement. But this version is so gooey that it can gum up the mouths of predators and make it hard to chew. Not to mention that most predators probably wouldn’t find the slime very tasty.

In contrast, sea slugs are often easy to see because they are colorful. But these bright colors advertise to predators that they should stay away, because the slugs are protected with nasty-tasting poisons.

Snails and slugs, small as they are, are big contributors to the health of their ecosystems. By feeding on seeds and young plants, they can control which plants grow in an area. By eating decaying matter, they help recycle nutrients that growing plants can use. And despite their best efforts, snails and slugs do often become food for other animals.

So the next time you see a snail or slug hanging from a plant, dawdling in your yard or gliding across a concrete sidewalk, stop and observe. Remember its remarkable biology, the unique way it moves and looks, and the many ways it benefits the environment.

And then, let them be. These small animals help keep our world running.

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July 10/2024

 

5 animals with incredibly long lifespans

6/3/2020

by Fredy

quizzclub.com

Besides humans, what are some of the longest-living creatures on our planet?

#5 Pink cockatoos are one of the longest-living pets (40-60 yrs.)

These charismatic parrots make wonderful companions & surprise with their mental abilities. Cookie, the oldest recorded cockatoo in captivity, died in 2016 at the impressive age of 82.

#4 Being the largest living species of tortoise on Earth, the Galápagos giant tortoise is also one of the longest-living vertebrates (over 100 yrs.)

The oldest known individual died in 2006 at the estimated age of more than 170 years!

💡 Did you know?

- besides having incredibly long lifespans, living creatures can be biologically immortal;

- for example, the immortal jellyfish, native to tropic waters, is capable of extreme regeneration. When starving or injured, it can transform dead cells into healthy ones & regenerate its entire body;

- anyway, it's not impossible to kill them, so most often they end up being eaten by predators.

#3 A harpoon dating back to the 19th century was found in a bowhead whale's blubber in 2007 (over 200 yrs.)

Being the 5th-largest marine mammal, it's also claimed to be the longest-living mammal on Earth.

#2 Among all vertebrate species, the Greenland shark has the longest recorded lifespan (over 300 yrs.)

The oldest individual, born approximately between 1504 & 1744, was somewhere between 270 & 510 years old! These sharks, being among the largest extant shark species, grow very slowly & reach sexual maturity at the age of 150.

#1 Thanks to their slow life style, ocean quahogs can survive for centuries (over 500 yrs.)

The oldest individual of this mollusk species, aged 512, was collected in 2006. It became the oldest non-colonial animal ever discovered.

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July 3/2024

 

Crabs keep evolving to go from the sea to the land — & back again

By Carys Matthews 

livescience.com

11/15/2023

Crabs have evolved to migrate from the sea to land then back again multiple times over the last 100 million years, scientists have discovered. 

A new study, published Nov. 6 in the journal Systematic Biology, found that true crabs (Brachyura) — which consist of 7,600 species across 109 families — have evolved to migrate from marine to land habitats between 7 & 17 times. (True crabs are distinct from other crustaceans that have developed crab-like bodies).

They also found that on 2 or 3 occasions, crabs even went back to the sea from land. "It is 100% harder going from being on land to water," lead author Joanna Wolfe, a researcher in organismic & evolutionary biology at Harvard University, told Live Science. 

Most arthropods left the ocean just once during evolutionary shifts more than 300 million years ago, in a process known as terrestrialization. 

In the new study, researchers set out to discover how often & when true crabs left the marine environment for land. They compiled 3 new datasets for 333 species of true crabs from 88 families, including both marine & non-marine groups. 

Using the entire crab fossil record, the researchers applied 2 mapping pathways: one where the crab goes from a fully marine environment to land directly through intertidal zones such as beaches, & a second where the species migrates from fully marine to land indirectly, through estuaries, fresh water, riverbanks, coastal forests, & jungles.

Their findings enabled the team to classify each crab species into a gradient of terrestriality — or how suitable they are to life on land. Using methods originally developed to study how viruses like COVID-19 evolved, the researchers determined the timing of true crab evolution. 

Their findings  suggest that true crabs emerged about 45 million years earlier than previous estimates & could date back to the mid-Triassic period (251.9 million to 201.3 million years ago), making them as old as some of the earliest known dinosaurs.

They left the ocean between 7 & 17 times as a result of convergent evolution — when different organisms independently evolve similar traits. 

Most crabs, they found, are only able to survive in semi-terrestrial habitats, with land-based crabs found to be concentrated in one species-rich group of the family tree. "It is a common misconception that crabs are trying to evolve to live permanently on land. Most crab species still flourish in the ocean," Wolfe said. 

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