Pitcher plant port-a-potty for the tree shrew

A pitcher plant (courtesy of Wikimedia Commons)

Timeline, 2009: As humans, we are a bit limited in our imaginations. For example, we’d probably never consider climbing onto the edge of a toilet seat and licking the sides while…um…employing the toilet for standard uses. Perhaps one reason—among many obvious choices—is that we’re not tree shrews living in the wilds of Borneo in Southeast Asia.

If you’re now envisioning tree-dwelling rodents enjoying the civilized development of having their own toilet, you’re not too far off. Borneo is home to a number of unusual relationships between species, but none may be stranger than the one that has developed between the tree shrew and the pitcher plant. The pitcher plant is carnivorous, and as its name implies, has a pitcher-shaped structure that it uses to trap its food.

The many uses of the pitcher plant

Normally, a pitcher plant growing on the ground is the perfect trap for hapless animals drawn to its minimal nectar output. For some species, they’re not a death trap but a place to brood offspring—one frog uses the pitcher plant to lay its eggs, where trapped, digested insects may provide some nourishment. The insects fall in because the funnel-shaped pitcher part of the plant has a slippery lip that acts as a deadly superslide for any insect that alights on it. Unable to gain a foothold, the animal slides helplessly into the plant’s interior, landing in a pool of digestive enzymes or bacteria that slowly break it down.

What does a pitcher plant do with digested insect? It does what any organism, plant or otherwise, does with its food—it extracts nutrients from it. One primary nutrient that plants (and everything else) require is nitrogen. This element is part of life’s important building blocks for DNA and RNA and the amino acids that make up proteins. Thus, to grow and reproduce, organisms must acquire nitrogen from somewhere. Some plants form a partnership with bacteria to get their nitrogen. Pitcher plants digest insects for it.

Unless no insects are available. While ground-growing pitcher plants in Borneo can subsist on available ants and other crawly critters, some pitcher plants grow on vines and trees, where ants are largely unavailable. In addition, mountainous environments are not known for harboring lots of ants, so the pitcher plant needed a new plan for getting its nutrients.

Nectar for nitrogen

The plan, it seems, was selection for making more nectar, reducing the slippery factor, and behaving like both a toilet and a food source for an abundant animal in the Borneo mountains, the mountain tree shrew. Using video cameras, researchers based at a Borneo field station captured one of the most unusual mutually beneficial relationships in nature: the tree shrew, while enjoying the abundant nectar uniquely produced by these aerial pitcher plants, also poops into the pitcher plant mid-meal. The plant, perfectly shaped for the tree shrew to park its rear just so while it eats, takes up the feces and extracts nitrogen from it. In fact, these pitcher plants may derive up to 100 percent of their nitrogen from the tree shrew poop.

Researchers think that this friendly relationship must have been in the making for a very long time. The pitcher plant opening is perfectly shaped and oriented so that the nectar collects just at the lip and the shrew must orient while eating so that the funnel-like pitcher collects any poop that emerges. The plant also has developed sturdier and thicker structures that can support the weight of a dining/excreting tree shrew, which isn’t much at less than half a pound, but quite a bit for a plant to support.

As odd as this adaptation may seem, it’s not unique. Ground-dwelling pitcher plants have formed similar mutually beneficial relationships with insect larvae that help themselves to some of the insect pickings that fall in. These larvae excrete any leftovers, and the plant harvests nutrients from these excretions. Interestingly, the tree shrew itself dines on insects, so the pitcher plant is still indirectly deriving its nitrogen from insects even when it uses tree shrew poop. It’s just getting it from the tail end of a rodent intermediary instead.

Nematode may trick birds with berry-bellied ants

Comparison of normal worker ants (top) and ants infected with a nematode. When the ant Cephalotes atratus is infected with a parasitic nematode, its normally black abdomen turns red, resembling the many red berries in the tropical forest canopy. According to researchers, this is a strategy concocted by nematodes to entice birds to eat the normally unpalatable ant and spread the parasite in their droppings. (Credit: Steve Yanoviak/University of Arkansas)

Timeline, 2008: Host-parasite relationships can be some of the most interesting studies in biology. In some cases, a parasite requires more than one host to complete its life cycle, undergoing early development in one host, adult existence in another host, and egg-laying in still another. There’s the hairworm that turns grasshoppers into zombies as part of its life cycle, and the toxoplasma parasite, which may alter the behavior of humans and animals alike. Often, the infection ends with the host engaging in life-threatening behaviors that lead the parasite to the next step in the cycle.

A recent discovery of a most unusual host-parasite relationship, however, results in changes not only in host behavior but also in host appearance. The infected host, an ant living in the forest canopy in Panama and Peru, actually takes on the look of a luscious, ripe fruit.

Berry-butted ants

Researchers had traveled to the Peruvian forest on a quest to learn more about the airborne acrobatics of these ants, Cephalotes atratus. This ant is a true entomological artist, adjusting itself in midair if knocked from its perch. Re-orienting its body, it can glide back to the tree trunk, grabbing on and climbing to where it belongs, avoiding the dangers of the forest floor.

As the investigators monitored the colony, they became aware of some odd-looking members of the group. These ants had large red abdomens that shimmered and glowed and looked for all the world like one of the tropical berries dotting the forest around them. Curious about these odd ants, the scientists took some to the lab for further investigation. Ant researchers are an obsessive breed, and they had even placed a bet over whether or not these berry-bellied ants were a new species.

A belly full of another species’ eggs

When they sliced open one of the bellies under a microscope, what they found surprised them. Inside, a female nematode had packed the ant’s abdomen full of her eggs. The bright red belly was an incubator and, the researchers surmised, a way station on the nematode’s route to the next step in its life cycle. This was the same old C. atratus with a brand new look.

Tropical birds would normally ignore these ants, which are black, bitter, and well defended with a tough, crunchy armor. But any tropical bird would go for a bright, red, beautiful berry just waiting to be plucked. The scientists found that in addition to triggering changes to make the ant belly look like a berry, the nematode also, in the time-honored manner of parasites, altered its host’s behavior: the berry-bellied ants, perched on their trees, would hold their burgeoning abdomens aloft, a typical sign of alarm in ants. A bird would easily be tricked into thinking that the bug was a berry. One quick snap, and that belly full of nematode eggs would be inside the belly of a bird.

Poop: A life cycle completed

And then the eggs would exit the bird the usual way, ending up in the bird’s feces. The ants enter the picture again, this time collecting the feces and their contents as food for their colony’s larvae. The eggs hatch in the larvae and the new nematodes make their way to the ant belly to start the cycle anew.

The nematode itself is a new find, a new species dubbed Myrmeconema neotropicum. And it seems that earlier discoverers of the berry-bellied ants also thought they had a new species on their hands: the researchers turned up a few previous berry-bellied specimens in museums and other collections labeled with new species names. No one had thought that the difference in appearance might be the result of a parasitic infection: this relationship is the first known example of a parasite causing its host to mimic a fruit.

Birds remain the missing link

There is one hitch to the newly discovered nematode-ant-bird association: the researchers never actually saw a tropical bird snap up a juicy, fruit-mimicking ant. They report seeing different species of birds scan the bushes where such ants sheltered, but there were never any witnessed ant consumptions. Thus, this inferred piece of the puzzle—the involvement of birds and their droppings in the life cycle of this nematode—remains to be proven.

Going to Hawaii? Watch out for the flesh-eating caterpillars

Flesh-eating caterpillars lurk in Hawaii’s rainforests

Islands can produce some of the strangest evolutionary novelties on the planet. Island-living elephants shrink to tiny sizes, while tortoises grow gigantic. The fate of species on islands is its own specialized study because the only way species can arrive on an island is over the water. Scientists, in the study of island biogeography, focus on how plants, animals, and microbiota end up on the islands where they occur.

What happens after they arrive is apparently anybody’s guess. Islands are unusual because they can lack the stiff competition of mainland ecosystems. Common factors in our daily lives, like ants, can be completely lacking. Because so many pieces of an ecological puzzle are missing on an island, niches remain open for the organisms that do arrive and get a foothold. Animals and plants end up doing things on islands that their kindred are not known to do anywhere else in the world. A recently discovered example is a caterpillar that has broken all the rules of caterpillardom. It eats meat. It hunts its prey. It uses its silk as a weapon. It deliberately camouflages itself with non-caterpillar components. And it’s a brutal killer.

Like a wolf that dives for clams

This particular capterpillar and its four just-discovered relatives reside on one of the most isolated island chains in the world, the Hawaiian archipelago. These islands are well known for evolutionary novelties, and these new species of the genus Hyposmocoma are no different. Well, actually, they’re very different. One scientist has said that discovering the behavior of these larval moths is like discovering a wolf species that dives for clams.

This caterpillar, a tiny, brutal, sneaky killer, creeps up on its prey, an unsuspecting snail resting on a leaf in the Hawaiian rainforest. The caterpillar itself is bound in silk, and it proceeds to spend almost a half hour anchoring the hapless snail to the leaf with more silk. The silk, made of gelatinous proteins, pins the snail by its shell as tightly as a spider wraps its threads around prey.

Once the caterpillar has immobilized its target, preventing the snail from escaping through a fall off of the leaf, the nascent moth emerges from its own silk casing. The snail retreats into its shell, and the caterpillar follows, beginning to feed on the trapped snail, starting with the head. It literally eats the snail alive.

This behavior is extraordinarily unusual for a caterpillar, the juvenile form of moths and butterflies. The vast majority of caterpillar species are vegetarian; of the 150,000 known species, only 200 have been identified as flesh eaters and predators. These few do not use their silks to trap their food, and they don’t eat snails, which are mollusks, targeting instead soft-bodied insects.

Caterpillar divers and adaptive radiation

But the genus Hyposmocoma is known for its diversity. Some of its members dive underwater for food. The interesting thing about the snail-eating caterpillars is that they seem to have radiated through almost all of the Hawaiian islands. The first species was identified on Maui, but since its discovery, researchers have found species on most of the other islands. Evolutionary biologists are intrigued by the many novel aspects of this caterpillar’s life history because it is so unusual for this many unique factors—novel food source, novel hunting technique, novel eating technique—to have evolved in the same species.

Wearing the spoils of capture as camouflage

One other unique thing about this caterpillar’s approach to dinner is its use of decoration. Once the mollusk-eating caterpillar has spent the day dining on escargot, it will attach the snail’s empty shell to its silken casing, along with bits of lichen and other materials, in an apparent attempt to camouflage itself.

With clones like these, who needs anemones?

Finding Nemo makes marine biologists of us all

I once lived a block away from a beach in Northern California, and when my sons and I wandered the sands at low tide, we often saw sea anemones attached to the rocks, closed up and looking much like rocks themselves, waiting for the water to return. My sons, fans of Finding Nemo, still find these animals intriguing because of their association with a cartoon clownfish, but as it turns out, these brainless organisms have a few lessons to teach the grownups about the art of war.

Attack of the clones

Anemones, which look like plants that open and close with the rise and fall of the tides, are really animals from the phylum Cnidaria, which makes them close relatives of corals and jellyfish. Although they do provide a home for clownfish in a mutualistic relationship, where both the clownfish and the anemone benefit from the association, anemones are predators. They consist primarily of their stinging tentacles and a central mouth that allows them to eat fish, mussels, plankton, and marine worms.

Although anemones seem to be adhered permanently to rocks, they can, in fact, move around. Anemones have a “foot” that they use to attach to objects, but they also can be free-swimming, which comes in handy in the art of sea anemone warfare. (To see them in action, click on video, above.)

Sea anemone warfare could well be characterized as an attack of the clones. These animals reproduce by a process called lateral fission, in which new anemones grow by mitosis from an existing anemone, although they can engage in sexual reproduction when necessary. But when a colony of anemones is engaged in a battle, it consists entirely of genetically identical clones.

Yet even though they are identical, these clones, like the genetically identical cells in your liver and your heart, have different jobs to do in anemone warfare. Scientists have known that anemones can be aggressive with one another, tossing around stinging cells as their weapons of choice in battle. But observing groups of anemones in their natural environment is almost impossible because the creatures only fight at high tide, masked by the waves.

To solve this problem, a group of California researchers took a rock with two clone tribes of anemones on it into the lab and created their own, controlled high and low tides. What they saw astonished them. The clones, although identical, appeared to have different jobs and assorted themselves in different positions depending on their role in the colony.

Battle arms, or “acrorhagi”

The warring groups had a clearly marked demilitarized zone on the rock, a border region that researchers say can be maintained for long periods in the wild. When the tide is high, though, one group of clones will send out scouts, anemones that venture into the border area in an apparent bid to expand the territory for the colony. When the opposition colony senses the presence of the scouts, its warriors go into action, puffing up large specialized battle arms called acrorhagi, tripling their body length, and firing off salvos of stinging cells at the adventuresome scouts. Even warriors as far as four rows back get into the action, rearing up the toss cells and defend their territory.

In the midst of this battle, the reproductive clones hunker down in the center of the colony, protected and able to produce more clones. Clones differentiate into warriors or scouts or reproducers based on environmental signals interacting with their genes; every clonal group has a different response to these signals and arranges its armies in different permutations.

Poor Stumpy

Warriors very rarely win a battle, and typically, the anemones maintained their territories rather than achieving any major expansions. The scouts appear to run the greatest risk; one hapless scout from the lab studies, whom the researchers nicknamed Stumpy, was so aggressive in its explorations that when it returned to its home colony, it was attacked by its own clones. Researchers speculated that it bore far too many foreign stinging cells sustained in the attacks, thus resulting in a case of mistaken identity for poor Stumpy.

How Bumpy the Jelly eats without tentacles

Robot explores the deep sea

The deep dark layers of the sea—where sunlight doesn’t penetrate and oxygen levels drop as precipitously as the ocean shelves—may be home to some of the last great mysteries of our planet. New discoveries lie hidden in the depths, but it takes a robot to assist us in uncovering them.

The Monterey Bay Aquarium Research Institute in California has such a robot, Ventana, a deep-diving submarine robot that can roam the dark parts of the ocean where humans cannot go. In 1990, Ventana came across an unusual jelly(fish) in the mesopelagic zone, between 500 and 1800 feet down, where sunlight does not penetrate, but oxygen levels remain relatively high. This jelly was weird among its brethren. It had four fleshy arms that trailed behind its softball-sized gelatinous body (or bell), but no tentacles. Wart-like bumps covered its arms and bell, and as it moved through the water trailing its arms, it looked like a slow-moving meteor or translucent blue shooting star.

An elusive, warty marine invertebrate

Marine scientists at the aquarium were intrigued, but they felt they needed to find out more before introducing the jelly to the world. Over the next 13 years, they had only seven sightings of the animal, five in Monterey Bay, and two sightings 3000 miles away in the Gulf of California. It was the latter two, in 1993, that surprised them, because it demonstrated that the new jelly was not just a local creature endemic to Monterey Bay, but might have a wider distribution.

They captured at least one of the jellies, anxious to find out more about its habits. They placed their captive in a tank with small shrimp and pieces of squid and watched. The bits of squid and hapless shrimp collided with the bumps on the jelly’s bell and stuck there. Over time, the prey moved slowly down the bell, was transferred to one of the “arms,” and then slowly moved up the arm and into the mouth. The “arms” appeared to serve as lip-like extensions for prey, much as pseudopodia serve as prey-capturing extensions for some cells, like macrophages.

The jelly’s feeding mechanism was unusual, as were its choices in prey size. The animal probably dines on some of the many other jellies that inhabit its zone, and it appears to favor prey a little larger—at ¾ to two inches—than the average jelly prefers.

It’s a triple! A brand new subfamily, genus, and species!

Given these unusual characteristics, the scientists who made the discovery designated this jelly—which they had heretofore called “Bumpy” in honor of its appearance—a new subfamily, genus, and species. They assigned it the subfamily, Stellamedusidae, and gave it the species name Stellamedusa ventana. “Stella” derives from “star” because of the jelly’s shooting-star-like appearance as it moves through the water; “medusa” is a common name for jellies; and “ventana” comes from the robot submarine without which the researchers would never have made their discovery. This additional subfamily brings the total number of jelly subfamilies to eight and is quite a find; lions and housecats belong to the same family, but are in different subfamilies, so S. ventana is as distantly related to other jellies as the “king of the jungle” is to Kitty.

Patience: They waited 13 years to report this

Although the jelly is unusual among other jellies in lacking tentacles, the researchers who identified it and published a paper on their discovery in the Journal of the Marine Biological Association of the United Kingdom, say that several deep-sea species have evolved in a similar way, using “arms” instead of tentacles. The researchers waited 13 years to report their find because they wanted to uncover more information about S. ventana, but the creature still remains an enigma. In spite of its potentially wide distribution, it apparently has never turned up in fishermen’s nets and, with only seven sightings in 13 years, remains elusive.

Ahem. La-la-la-laaaaaa…squeak

It’s true. They can sing

Male mice can sing. They aren’t exactly sitting underneath an open window on a moonlit night, guitar in hand, crooning an evening serenade to their lady love, but apparently, they do sing for the ladies.

Very few mammals sing. In fact, until the mouse discovery, we and whales were the only verified members of the mammalian choir. Scientists knew that mice vocalize; for example, mice that are surprised or in pain can emit sounds that humans can easily hear, under 30 kHz. Newborn mice can make sounds that their mothers recognize, summoning the dams to make them warm or return them to the nest. And male mice make ultrasonic sounds, above 30 kHz, that the human ear cannot hear. Usually, males make these sounds in response to the smell of an available female.

Birds, mice, whales, people

Because humans and whales make pretty large research animals and ethical issues prevent studies with either, research into how language is learned and how the brain transmits messages about language has relied on birdsong. You may not have thought about it much, but the song a bird sings is really a song, containing repeated melody lines or syllables, and the bird can repeat it given the necessary stimulus. But birds also must learn their songs, and the birds they’re trying to attract must be able to understand them. Because of this requirement for learning, birdsong has been the model for how mammals acquire and learn language.

Birds may be catching a break now, thanks to a recent breakthrough in mouse song. Researchers examined the vocalizations of 45 male mice by placing the mice in a recording chamber. The scientists then inserted through a tube a cotton swab soaked in enough female mouse urine to convince the male to burst into song. After recording the mouse’s vocalization, the researchers manipulated the recordings to so that humans could hear them and then analyzed them using software.

Gus-Gus, is that you?

What they report is that the mice appear to be singing actual songs that contain syllables—very rapidly produced syllables at about 10 per second. In addition, the songs had phrases that the animals would repeat. The mice all seemed to have their own individual songs, and almost all 45 mice sang in response to the urine stimulus.

That mice sing at all was discovered by accident, but the finding that they do sing what appear to be genuine songs opens up a multitude of research possibilities. Among directly related questions to address, scientists must examine how females respond to these calls and whether or not different experiences in fetal development affect the song or success of the song. In addition, scientists must try to demonstrate that the songs are truly learned if the mouse is to be used as a mammalian model for mammalian communication, replacing birdsong.

OK, that’s cute, but why is it relevant?

If the mouse song is learned, the animal will become an important model for these studies. Because mice have been used for decades in genetics studies, there are hundreds of different varieties of mice with genes knocked out or knocked in, and researchers can make their own special strains to assess the effects of a particular gene on song structure or production. We may be able to use this model to identify genes directly involved in learning and communication in mammals.

Identifying these genes could lead to investigations of how developmental processes and differences result in differential learning abilities. For example, people who are autistic exhibit altered communication skills. A stronger understanding of the genetics of mammalian communication may help us to unravel the underpinnings of this aspect of autism and other communication disorders.

These findings also lead to another question that remains to be addressed: Are there other animals that sing a secret song that our ears can’t hear?

Termite toots causing global warming?

Termites to blame for global warming?

I was, um, in the bathroom at the Denver Zoo listening to the info feed the nice woman with the colonial accent was providing for folks using the facilities. The facts are all about poop and related activities, which I suppose is appropriate to the moment at hand. To add to the excretory atmosphere, the stall doors bear representations of animal hindquarters. Just letting you know that in case you ever want to stare at a close-up view of a baboon’s rear while you’re micturating. At any rate, as I was washing my hands, I heard a little tidbit about termites and greenhouse gases. The pleasant voice informed me that termites contribute a good percentage of the world’s greenhouse gases to the atmosphere, in the form of methane. Tooty little buggers, they must be.

It’s true. More methane than cows

Like most animals that survive on cellulose-based diets, termites have friendly micro-organisms that help them break down normally undigestible macromolecules. In the process, the micro-organisms produce a lot of methane gas. That gas, whether it’s in a cow or a termite, has to go somewhere, and that somewhere is out. Contrary to what some people may think, and according to the pleasant voice at the Denver Zoo, termites expel more of this stuff than cows do.

Should we blame the bacteria instead?

Actually, the helpful gut micro-organisms in termites are not all bacteria. Some are protozoans, depending on the termite species. But they’d be nothing without their hosts, so I guess we can just go ahead and blame them both. And I blame the Denver Zoo and their scatalogically oriented bathroom experience for the existence of this particular blog post.

Should we kill all the termites?

Well, that’s a terrible idea for any number of reasons, but as it turns out, it’s also not gonna help. One of the primary poisons used to knock of the wood-chewing insects happens also to be a “powerful greenhouse gas.” In addition, termites serve as a model for efficient harvesting of energy from biofuels, pulling about 90% from what they take in, compared to humanity’s sadly low success rates. So, yes, they eat our houses and expel about 15% of the methane in the atmosphere, but…they’re still better than we are at efficiently extracting energy from what they take in.

The mysterious reproductive life of the giant panda

Photo credit: Mehgan Murphy, Smithsonian’s National Zoo

National Zoo’s giant panda had pseudopregnancy

National Zoo officials announced today that Mei Xiang (link has Panda Cam!), who had been monitored for several months for pregnancy, was not pregnant after all. Instead, she was experiencing a common feature of panda endocrinology, the pseudopregnancy.

Panda pseudopregnancy a common event

How could officials not be sure for months about whether or not the pregnancy was real? Panda pseudopregnancy so perfectly mimics an actual pregnancy that even hormone levels follow those of a real gestation. Staff had been monitoring her by ultrasound and blood testing, and even though ultrasound had yet to show a viable fetus, whether the pregnancy was real or pseudo was not confirmed until the hormones wrote the final chapter.

Pseudopregnancy hormones like pregnancy hormones

Late this month, Mei Xiang showed a drop in progesterone hormone. When hormone levels hit baseline in a possibly pregnant panda, one of two things can happen: a birth, or confirmation of pseudopregnancy. The progesterone decline set the clock on a 24-hour watch to see if Mei Xiang would bear a cub. She didn’t.

Ovulation once a year!

Giant pandas ovulate only once a year. Regardless of whether conception occurs, the female panda will appear pregnant, behave as though she is pregnant, and register the hormone patterns of pregnancy. If conception does not occur in that one annual opportunity, a female panda will almost always enter into a pseudopregnant state. Mei Xiang has done that five times. She’s also experienced a genuine pregnancy, bearing a cub in 2005 that now lives in China as part of a panda breeding program.

Panda soon to be back for public viewing

Mei Xiang has been sequestered during her pseudopregnancy, but her habitat at the zoo will now open again for public viewing. During her pseudopregnancy, her behaviors included reduced activity and appetite. These are now both expected to increase.

For your consideration

Pandas have some unusual life history strategies, including being food specialists and often accidentally suffocating their offspring. And, it appears that many ovulations result in pseudopregnancy. What might be an explanation for why pandas are so prone to entering a pseudopregnant state if conception does not occur? Could the behaviors that accompany the pseudopregnancy have anything to do with it?

In pandas, the hormones of a pseudopregnancy are similar to those of a real pregnancy. What pathways underlie the female’s production of these hormones of pseudopregnancy?

Women can also experience pseudopregnancy, sometimes referred to as “hysterical pregnancy.” It can even involve abdominal distention and in some cases, hormonal changes. What are some of the physiological underpinnings of a pseudopregnancy in women?

Finally, dogs and mice are also known for having pseudopregnancies. Do you think the pressures that result in these pseudopregnancies are similar to those that result in a false pregnancy in the panda? Why or why not?

Can rain make buffalos have boys?

African buffalo shift sex ratios with rain

African buffalos (Syncerus caffer) have more males during the rainy season in Kruger National Park, and it’s not just a random accident of fate. Researchers have found that specific sequences on the Y chromosome are correlated with seasonal differences in birth sex ratios in the buffalo population.

X sperm vs. Y sperm

Does that mean that rain somehow makes buffalos have more boys? Not directly. Instead, it may come down to a DNA-level battle royale involving the Y chromosome. Sometimes, sperm carrying the Y win the race to the egg, while at other times, X-carrying sperm are the victors. These times correlate with higher frequencies of certain sequences, or haplotypes, of the Y chromosome occurring in the population, with one sequence being much more common during the rainy season, when more males are born.

Selfish genes gone rogue

The investigation suggested the existence of a suppressor of Y chromosome success acting during the dry season, when females birthed more females, and a distorter in favor of Y chromosome success in the rainy season, when more males are born. The distorter may shift meiosis in favor of the Y-carrying sperm or disrupt survival of X-carrying sperm. Interestingly, distorters are not considered to act for the benefit of the individual carrying them and are considered “selfish genes.” Suppressors…well…suppress the distorters. The authors refer to these apparent Y chromosome suppressor/distorter regions as sex-ratio, or SR,  genes.

Dry season not a good sperm season

They also noted that during the dry season, buffalo didn’t make as much sperm, and the sperm they did make weren’t as frequently normal looking or very good swimmers. They hypothesize that semen quality may interact with the decreased availability of food in the dry season, leading to drop in Y haplotypes associated with a male-biased sex ratio. The investigative team, whose lead author, Pim van Hooft, is based at Wageningen University in The Netherlands, also suggested that the SR genes may be present in other species, adding a new dimension to the increasingly complex mechanisms of sex ratios in mammals.

For your consideration

1. Sex determination in vertebrates happens in a number of different ways. Some mechanisms don’t involve sex chromosomes at all but instead rely on environmental cues. Find an example of a species that uses environmental cues to determine sex. How can an environmental trigger be similar to a chromosomal trigger as a sex determinant? How do they differ?

2. Many species have life history strategies that involve adjusting sex ratios. What are possible explanations can you find to explain how adjusting sex ratio might benefit a species? How might it be a potentially dangerous gamble?

3. Distorters in general appear to be doing their host individual no favors. Given that fact, what is one explanation for the existence and persistence of suppressors of distorters?

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