A female deep-sea anglerfish (Melanocetus johnsonii) with fang-like teeth and bioluminescent lure to attract unlucky prey. All anglerfish of this and many other related species are female, sparking a long search for the males. They were eventually found,
The extreme life of the sea
The Strangest Family Lives:
ACROSS SPECIES, MALES WILL endure great trials to find mates. They’ll hurl themselves into combat, develop elaborate ritualised displays, or pay absurd prices for drinks at bars. But nobody gives up more for sex than the anglerfish males of the deep ocean.
These animals give a new dedication to the phrase “mating for life”.
Deep-sea bottom-dwelling anglerfish are among the sea’s most hideous animals. Wrinkled black skin stretches over feeble muscles. Beady black eyes stare above a hatchet-like jaw, protruding tongue, and glittering needle teeth.
The typical anglerfish sports a long jointed stalk (the esca) atop its head: a dorsal fin modified into a lure, waggled on command to simulate a floating morsel of food.
Most deep-sea anglers store symbiotic bacteria in their lures, letting the fleshy knobs shine like beacons in the black. The fish hangs inert in the water column, waiting to strike with incredible speed. Touching the lure triggers the angler’s bite reflex – insurance against a sloppy mistake, for it cannot afford to miss a meal in the starved ocean depths.
Neither must it be picky; its jaw and stomach are extremely elastic, capable of devouring animals twice its size.
For a century, marine biologists considered anglerfish rarities, seen dead on beaches or found in deep trawling nets. From those few samples, they noted two curious things: every specimen was female, and most adults carried odd fleshy parasites attached to their bodies.
These weren’t remarkable findings for such a rare and mysterious fish. But in 1925, British ichthyologist Charles Regan took it on himself to thoroughly dissect an anglerfish parasite.
He was shocked: it was an anglerfish male! Adult males never really existed to be found. They lived only as blind parasitic dwarves, attached permanently to much larger females.
It’s an extreme example of sexual dimorphism: inherent physical differences between sexes.
Female anglers are vicious and successful hunters, able to devour most organisms they encounter. The great abyss holds little to threaten them.
A male is the polar opposite, tiny and helpless. His undeveloped digestive tract means that even if he caught prey, he couldn’t eat it.
BETWEEN PREDATION and starvation, he isn’t long for the world. But he has one thing going for him: some of the most sophisticated sensory organs in the deep ocean. Olfactory glands for some anglerfish, enormous light-gathering eyes for others – whatever the species, the male’s senses are finely tuned to detect females.
He’s in a desperate race against time: find a mate and attach, or die. He soldiers on through cold black water guided only by hunger, instinct, and smell. When a female finally comes
into view – a grotesque monster dozens of times his size – our hero acts immediately. He bites her, latching on with every ounce of strength in his feeble jaws.
This union releases an insidious enzyme in his own body, which will both save and end his life. His lips and mouth dissolve as he chews, liquefying and binding him to the female’s flesh until the pair are utterly fused. He can never leave her.
This cheery scene is just the first stage of mating. In the following days and weeks, the parasitic male’s circulatory system merges with his host’s. Her blood delivers nutrients, pumped through a shared lattice of new vessels and capillaries to sustain him for as long as she lives.
His old form diminishes with time. Fins aren’t needed, nor his amazing eyes – nor, at last, his brain and internal organs. They dissolve until only one system remains: the testes.
The female has little to do with this process, barely noticing his paltry calorie consumption and, on occasion, chemically inducing him to release sperm.
He doesn’t even get the consolation of monogamy! Numerous males will attach themselves to a female over her life, all suffering the same gruesome fate for a chance at reproduction.
A male angler begins his life as a tiny, pathetic dwarf in a darkened netherworld. If he is very lucky, he may end it as a pair of disembodied gonads.
HEAT-RESISTANT CORALS OF OFU
ON THE ISLAND OF OFU in American Samoa, the sun rises at about 6am on the day before Christmas. It’s a bright summer day in the southern hemisphere.
Safe from the ocean swells behind a wall of coral, a lagoon sparkles in the sun-rise like liquid cobalt. At dawn, the water temperature is already 29°C: a coral nirvana.
By noon, fueled by the summer sun and stilled by low tide, the lagoon reaches 35°C. The corals simmer for more than three hours at temperatures well past their normal tolerance.
It’s long past dusk when finally they cool below 32°C. Santa Claus is well on his way across the Pacific.
The corals of the Ofu lagoon should be dead from their daily bake, and yet they thrive. When their heat endurance was estimated in experimental hot-water tanks, Ofu corals were among the toughest ever tested.
New research shows that the hot-water pulses of the daily tides have sparked them to develop heat resistance. Twenty-four-hour exposure to 35°C heat would have killed them all long ago, but three-hour stretches are bearable.
In the classic film The Princess Bride, the hero has trained himself to resist poison in a similar way: gradual exposure, day by day, until once-lethal doses grow laughable.
Taking a page from human biomedical research, coral researchers measured how individual coral colonies use their genes during stress. Three days of heating activates a battery of 250 different stress genes in the typical coral. In the Ofu lagoon, the corals keep about 60 of these “heat genes” operating at high capacity all the time.
Some of these corals seem to be born with these guardian genes turned on, but others turn them on only when moved by scientists to the reef ’s hottest region. Some never activate the crucial genes; these colonies simply die.
THE CUMULATIVE RESULT is a small band of survivors thriving in a small back-reef lagoon a quarter-mile across, growing in the intense sun and heat.
Though they are the Pacific’s toughest-known corals, human interference still pressures them.
Overfishing leads to choking algae growth, a landfill leaks heavy metals into the lagoon, and some on the island look to improve commerce by extending their tiny airstrip directly out over the reef, right where these corals live.
Luckily, these reefs are partly protected and deeply appreciated by the local villages, which are caught between their conservationist impulses and the realities of economic development.
We still have time to figure out the survival secrets of the mighty coral polyp, to help the villages of Ofu protect their reefs, and to see whether their coral’s survival skills can be duplicated.
The Strangest Family Lives:
LEO TOLSTOY ONCE WROTE that happy families are all alike, but “every unhappy family is unhappy in its own way.”
This might hold true for human families, but in the sea it disintegrates like soft bread.
Beneath the waves, even happy families hold nothing in common. What works for one may not work for another. The ocean’s most exotic inhabitants don’t share our common ancestry, or our highly specialized sex organs, or even our concept of gender.
Nature cares for the ends of reproduction, not the means.
Is it better to live fast, reproduce quickly, and then die, like the octopus Or would you rather live a long time, investing ever more in every egg as you age Steve Berkeley of the Long Marine Lab in Santa Cruz, California, has exhaustively charted the life-cycles of many fish.
A kelp forest species called the black rockfish (Sebastes melanops) starts producing eggs at five years old. Even at that tender age, they’re laying 45,000 eggs at a time.
But unlike octopuses, these fish enjoy many annual breeding seasons. At 10 years of age, they’ve grown to 16in and may produce 60,000 eggs.
Some closely related rockfish live up to a century, growing all the while and manufacturing more eggs with each passing season.
For these fish, long life and future reproduction is the strategy. This differs wildly from the octopus plan.
All this shows that there is no single answer to whether long life or fast reproduction is better. Well, there is a single answer but the answer is: “It depends.”
It depends on whether growing a body that can last 100 years is likely to pay off (in numbers of offspring) in the long run – or whether a cheaper, more disposable body lets you funnel more food energy immediately into reproduction early in life.
THERE IS NO CORRECT ANSWER to this conundrum - it depends on how quickly an individual is likely to die from predator attack, starvation, bad weather, or other lethal events. High rates of death make it less valuable to invest in a robust body. But of course, a robust body makes the death rate drop.
Does it drop enough to pay for the extra costs in body construction Because this answer might vary for different kinds of bodies—fish versus squid, for example - the best evolutionary strategy also might vary.
The rules of the game are still the same: each species bets on either long lives or short, tailoring its strategy to the hand it’s dealt.
Although this huge variation in how marine species live their lives is wholly understandable in terms of normal evolutionary science, marine mothers do more than a few things that continue to confound evolutionary biologists.
In the black rockfish studied by Steve Berkeley, older mothers give every egg an extra gift – a tiny oil droplet that the larvae use as an energy supply to grow faster and be more likely to survive.
The droplet is like a trust fund that helps a larva through a very tough part of a fish’s life, when perhaps fewer than 1 in 10,000 will survive.
According to other fish biologists, the problem with this set of results, and other examples where bigger females produce bigger eggs, is that it just shouldn’t happen.
It’s not that larger mothers shouldn’t make nice eggs and give their larvae oil-droplet gifts. It’s that smaller mothers should do the same.
If a certain-size egg is best for a large mother to make, it should also be best for a small mother to make.
Now, maybe small mothers cannot afford such gifts to all their larvae—but in that case, theory says that they should make fewer larvae and go ahead and give them those same gifts. But fish like the black rockfish apparently do not read much theory. In this case, the ways of mothers remain something of a mystery.
What about some of the other strangest family lives Can they be reconciled with our understanding of evolution’s relentless pressure for reproductive success
Sex change is one of the most interesting questions: some species that change sex start off male and change to female. Some do the reverse. Some flip back and forth, or are both sexes simultaneously.
One of the interesting ways to think about this is to consider the level of parental investment in each offspring.
For many marine species, eggs are cast out into the ocean to fend for themselves—no parental care is provided. The investment in an offspring is entirely accounted for by the food energy packed into it, like sending the kid off with one packed lunch for the rest of their lives.
And the vast majority of that investment is made by mothers, not fathers, because eggs are expensive to make, and sperm are cheap.
A small female can make only a few eggs, but a small male can produce many sperm to fertilize many eggs. So, for a species that reproduces early, at a small size, and then continues to grow, it can be best to be a male first – fertilising lots of eggs – and then, as he grows, to become a female able to make lots of eggs. Clownfish play precisely this game, and so do some limpets and shrimp.
Why do the reverse strategies exist: starting out as small females and then turning into larger males
Caribbean blueheaded wrasses follow this strategy, and so do California sheepheads and many groupers. The answer is often territoriality: males are successful when they hold territories and socially dominate other males.
Bigger males do this better than smaller males can, so being a small female turning into a bigger male is more successful than the reverse.
Blueheaded wrasses, for example, start out as yellow-striped females in a harem dominated by a large, territorial male.
If the previous male is removed (by a predator or an inquisitive biologist), the largest female turns into a male, starting the very next day.
Once the transformation begins, she starts acting like a male in a day, and starts making sperm within the week. Thereafter, he spawns every day with his harem, sometimes running out of sperm by late afternoon.
Why can’t big females hold territories and attract smaller males They probably can, and do in some species.
The point is not that one particular strategy is best. It is that different strategies can work well and appear to be beneficial in different settings.
Figuring out what those settings are has allowed biologists to put some of the wide variety of reproductive life in perspective. But it would be a mistake to think that we know all about the sea’s oddest families, or why they persist where they do.
This article is excerpted from The Extreme Life of the Sea by Stephen R Palumbi and Anthony R Palumbi, © 2014 by Princeton University Press, and reprinted by permission.
Stephen R Palumbi is Professor of Biology and Director of the Hopkins Marine Station at Stanford University, California, and Anthony R Palumbi is a science writer and novelist.
Their 226-page hardback book (ISBN 9780691149561) was reviewed in DIVER‘s June edition (Older, Deeper, Faster, Stranger) and costs £19.95.