Researchers found that Charles Darwin’s famous finches defy what has long been considered a key to evolutionary success: genetic diversity. The study of the finches of the Galapagos Islands could change the way conservation biologists think about species with naturally fragmented populations to understand their potential for extinction: here.
Venus flytrap ‘teeth’ form a ‘horrid prison’ for medium-sized prey
March 26, 2019
In “Testing Darwin‘s Hypothesis about the Wonderful Venus Flytrap: Marginal Spikes Form a ‘Horrid Prison’ for Moderate-Sized Insect Prey”, Alexander L. Davis investigates the importance of marginal spikes, the “teeth” lining the outer edge of the plant’s snap traps, in successfully capturing prey. He found that Venus flytraps experience a 90 percent decrease in moderate-sized cricket prey capture success when marginal spikes are removed. This effect disappears, however, for larger prey, suggesting that the spikes may provide a foothold for large prey to escape.
The study combined field observations, laboratory experiments and semi-natural experiments, and was the first to test the adaptive benefit of marginal spikes, one of Darwin’s original hypotheses about the Venus flytrap. “We provide the first direct test of how prey capture performance is affected by the presence of marginal spikes, trichomes that provide a novel function in Venus flytraps by forming what Darwin described as a ‘horrid prison'”, Davis writes.
Botanical carnivory is a novel feeding strategy that has arisen at least nine different times in evolutionary history of plants. Pitfall traps evolved independently at least six times and sticky traps five. The snap traps characteristic of the Venus flytrap, however, have most likely evolved only once in the ancestral lineage. Darwin was the first to document evidence for carnivory in flytraps, and proposed that the cage-like structure enhances prey capture success.
For the laboratory portion, Davis and his coauthors assembled “prey capture arenas”, wherein 34 Venus flytraps were set up in planters with “on ramps” for crickets. The number of individual traps open and closed, along with whether or not the closed traps contained prey, were recorded initially, after three days, and again after a week. Davis then removed the marginal spikes from half of the plants. He allowed a week of recovery so the traps could reopen, and conducted a second trial. Cricket mass, the length of the plants’ traps, and the prey capture success rate of the traps on each plant were recorded and analyzed using logistic regression models.
Davis and coauthors then moved to a semi-natural experiment in the North Carolina Botanical Garden. Davis placed 22 plants in the North Carolina Botanical Garden, with half of the traps on each plant with intact marginal spikes and the other half with the spikes removed. Plants were kept on the group in a forested, open area of the gardens, and with ramps that allowed terrestrial arthropod access for a period of 4 weeks. For all prey catches, trap length, as well as prey mass and — digestion permitting — prey type, were recorded. Results were calculated using a generalized linear mixed effects model, then combined with results from the laboratory experiments using Fisher’s method.
Davis found that marginal spikes are adaptive for prey capture of small and medium-sized insects, but not larger insects. In the controlled laboratory prey capture trials, 16.5% of trap closures resulted in successful prey capture, whereas only 5.8% of trap closures were successful when marginal spikes were removed. Similarly, plants in the botanical garden had a prey capture success rate of 13.3% with marginal spikes intact and 9.2% with spikes removed.
The benefits of the marginal spikes were most dramatic for medium-size traps, which experienced the most rapid decline in capture rate for medium-size prey and gained the most from having the marginal spikes intact. Surprisingly, this effect disappeared for larger prey, which Davis speculated could be due to larger insects using the spikes as leverage for prying themselves free.
These findings offer clues for explaining the evolution of one of the most unique plant traits. “Characterizing the role of adaptive traits aids our understanding of selective forces underlying the diversity of trap types and the rarity of snap traps, offering insights into the origins of one of the most wonderful evolutionary innovations among all plants,” Davis writes.
The Roots of a Theory: How Plant Specimens Led a Young Darwin to Discovery
Plant specimens may seem an unlikely starting point for Darwin’s theory of evolution by natural selection – but, as Professor John Parker investigates in this podcast, the Cambridge botanist John Stevens Henslow proved a crucial mentor for the young naturalist. Find out how Darwin shipped his collections from the Beagle voyage back to Cambridge, and how these almost 200 year-old specimens can today give us a snapshot of long-extinct botanical life.
Researchers have genetically transformed the Common Primrose (Primula vulgaris) for the first time in a development that could shed light on one of the plant world’s most renowned reproductive systems.
The complicated sex life of Primula was a subject that fascinated Charles Darwin and generations of geneticists that followed because it’s one of the best examples of heteromorphic flower development.
Heteromorphy (or heterostyly) is a phenomenon in which plants exhibit two or three distinct forms of flowers based on the position of the male and female sex organs. Now, some of the secrets that eluded Darwin could be revealed following the biotechnological success announced by researchers from the John Innes Centre, the University of East Anglia (UEA) and the Earlham Institute.
The technology known as Agrobacterium-mediated plant transformation involves using soil bacteria to insert or modify genes in a plant genome. Genetic transformation is a valuable tool that allows researchers to study gene function and genetically controlled characteristics in organisms.
It is a research method routinely used on model organisms such as Nicotiana benthamiana and Arabidopsis thaliana to understand the molecular workings of plants. However, these species cannot be used to study heteromorphy because their flowers are all homomorphic which means they are able to self-fertilise.
“Now we have a transformation system we can use gene editing tools such as CRISPR-Cas9 to work out exactly what the gene function is that controls heteromorphy in the Primula family,” says Sadiye Hayta, of the John Innes Centre.
“Longer term, there may be implications for commercial crops. If we understand the roles of these different genes we could take them over to a commercial crop and use it in a hybrid system,” she adds.
Until now attempts to transform Primula have been unsuccessful because the plant has proved resistant to laboratory regeneration of whole plants from tissue culture.
The flowering plant is one of the best-known examples of heteromorphic flower development. This reproductive system enthralled not only Darwin but many leading geneticists from the early 1900s including William Bateson, the first director of the John Innes Centre and colleagues JBS Haldane, Cyril Darlington and Dorothea de Winton.
Darwin, in a landmark paper of 1862, worked out the functional significance of the different anatomical formations: they made the plants self-incompatible. This is Nature’s way of promoting cross-pollination to maintain genetic variation in the population, driving natural selection.
Fundamental research into heteromorphy has continued. In a research paper in 2016 a John Innes Centre — University of East Anglia team led by Professor Philip Gilmartin identified the S-Locus supergene that controls heteromorphy as described by Darwin.
Armed with this fundamental knowledge and a the newly announced transformation system, scientists can delve deeper into the mysteries of heteromorphy.
Co-author Mark Smedley, of the John Innes Centre says: “It is not every day you get to work on a paper that references Darwin. This is a fundamental story that scientists have been trying to unravel for 200 years.”
Professor Philip Gilmartin of the UEA whose laboratory started out on this scientific mission more than 20 years ago, said: “The development of a Primula transformation system is an important component of our lab’s long-term study to identify and characterise the genes that control development of the two forms of Primula flower studied by Charles Darwin.”
It’s a piece of research that would have excited Darwin. Towards the end of his illustrious career the author of On the Origin of Species remarked:
“I do not think anything in my scientific life has given me so much satisfaction as making out the meaning of the structure of these plants.”
Smithsonian Books, $19.95
Charles Darwin famously derived his theory of evolution from observations he made of species and their geographic distributions during his five-year voyage around the world on the H.M.S. Beagle. But in the introduction of On the Origin of Species, the naturalist also cites another influence: the thousands of fossils that he collected on that trip. Darwin’s Fossils is paleobiologist Adrian Lister’s account of that little-appreciated foundation of evolutionary theory.
While sailors on board the Beagle charted the coastal waters of South America (the actual purpose of the expedition), Darwin explored the shore and rambled inland on excursions that sometimes lasted weeks. The fossils he unearthed — some relatively fresh, others millions of years old — have tremendous significance in the history of science, Lister contends.
Many of the species Darwin discovered in the fossils were previously unknown to science, including several giant ground sloths, compact car–sized relatives of armadillos called glyptodonts (SN Online: 2/22/16) and ancient kin of horses and elephants. Because many of those animals were apparently extinct — but just as apparently related to species still living in the region — Darwin concluded the fossils were strong evidence for the “transmutation”, or evolution, of species. This evidence was all the more convincing to him, Lister suggests, because he had unearthed the fossils himself. He saw firsthand the fossils’ geologic context, which enabled him to more easily infer how species had changed through time.
Copiously illustrated and suitable for general readers as well as the science savvy, Darwin’s Fossils is a quick, easy read that provides a fascinating overview of the naturalist’s wide-ranging fieldwork during the Beagle voyage. His insights from fossils went beyond just biological evolution. Darwin’s studies of coral reefs (the mineralized parts of which are, after all, huge fossils) encircling islands in the Pacific and Indian oceans led him to theorize correctly how such reefs form. And his observations of strata containing marine fossils thousands of meters up into the Andes led to an improved understanding of how geologic forces sculpt the world.
The [great] cormorant is a large water bird with black plumage. It has a wingspan of about 100 centimeters. From the Ussuri River region of Siberia and the northern-east region of China they fly to spend about five months in Kinmen; they do not embark on their return journey to the breeding grounds until April the following year.
The cormorant is equipped with webbed feet, a strong bill, easily wet-able feathers and a special flexible pouch on its throat, making the bird an efficient catcher of fish. Highly gregarious, the cormorants like to feed and roost in large numbers. They also fly in line formations. Every year the entertaining antics and sheer number of these birds attract many visitors, both domestic and abroad, to Kinmen.
Great cormorants reveal overlooked secondary dispersal of plants and invertebrates by piscivorous waterbirds
Casper H. A. van Leeuwen, Ádám Lovas-Kiss, Maria Ovegård, Andy J. Green
4 October 2017
In wetland ecosystems, birds and fish are important dispersal vectors for plants and invertebrates, but the consequences of their interactions as vectors are unknown. Darwin suggested that piscivorous birds carry out secondary dispersal of seeds and invertebrates via predation on fish.
We tested this hypothesis in the great cormorant (Phalacrocorax carbo L.). Cormorants regurgitate pellets daily, which we collected at seven European locations and examined for intact propagules. One-third of pellets contained at least one intact plant seed, with seeds from 16 families covering a broad range of freshwater, marine and terrestrial habitats.
Of 21 plant species, only two have an endozoochory dispersal syndrome, compared with five for water and eight for unassisted dispersal syndromes. One-fifth of the pellets contained at least one intact propagule of aquatic invertebrates from seven taxa. Secondary dispersal by piscivorous birds may be vital to maintain connectivity in meta-populations and between river catchments, and in the movement of plants and invertebrates in response to climate change. Secondary dispersal pathways associated with complex food webs must be studied in detail if we are to understand species movements in a changing world.
All photos on this blog post, of slides shown during the lecture, are cell phone photos. The slide the photo of which is on top of this blog post describes carnivorous plants as ‘living flypaper‘.
In his book on carnivorous plants, Darwin also included pictures of plant details as seen through a microscope.
Like this enlarged picture of a sundew leaf.
In a letter to botanist Hooker, Darwin wrote that sundew (Drosera) ‘leaves are first rate chemists’.
Darwin acknowledged that carnivorous plants should make people question the rigid hierarchical separation between plants and animals, which, as we saw, Linnaeus and others had advocated. In a letter to Charles Lyell, he wrote: ‘By Jove I sometimes think Drosera is a disguised animal!’
And Nepenthes pitcher plants. Frenchman Étienne de Flacourt had described Nepenthes pitcher plants for the first time in 1658. He thought the pitchers were flowers. Georg Everhard Rumphius (1627-1702), a German Dutch East India Company employee staying on Ambon island corrected that, noting the pitchers were leaves. In fact, carnivorous plants’ flowers are often at a distance from their prey catching leaves, to prevent the plants from eating their own pollinating insects.
Rumphius did not know yet the insectivorous function of the pitchers. He did note that a small crustacean species lived in them, staying alive. This was forgotten: in 1987 two zoologists claimed they had discovered that crustacean’s lifestyle for the first time. In 2004, Rumphius’ earlier description was rediscovered.
In 1874 Hooker, advised to do so by Darwin, did experiments with Nepenthes plants, establishing they were carnivorous; just in time for Darwin’s 1875 Insectivorous plants book.
Darwin’s United States correspondent Mary Treat wrote:
From all appearance the terrible Sarracenia was eating its victim alive. And yet, perhaps, I should not say ‘terrible,’ for the plant seems to supply its victims with a Lethe-like draught before devouring them.
The Lethe, in ancient Greek mythology, was a river in the underworld making those who drank from it forget everything.
All photos on this blog post, mainly of slides shown during the lecture, are cell phone photos.
Today, Darwin’s best known book is On the Origin of Species. However, Peeters said, during Darwin’s life his best sold book was his 1875 Insectivorous plants.
Before Darwin, people either thought carnivorous plants did not exist; or they looked at them with fascination often mixed with exaggeration of how big carnivorous plants’ prey was.
In 1768, for the first time live Venus flytrap plants were brought from North America to England. In a 1770 book, John Ellis described them. He named the genus Dionaea, a Greek name for the goddess of beauty Aphrodite (Venus in Latin).
However, Linnaeus did not believe that carnivorous plants existed.
In support of that view, Linnaeus quoted the Bible, Genesis 1:30:
And to every beast of the earth, and to every fowl of the air, and to every thing that creepeth upon the earth, wherein there is life, I have given every green herb for meat: and it was so.
So, Linnaeus interpreted the Bible as saying that animals eat plants, not the other way round.
In this, Linnaeus was in a tradition, as pictured in this 17th century book, of seeing reality as a hierarchical ladder. God on top, humans below God. On the lower end, stones, etc. Plants one step below animals, forever unable to catch up with them.
Linnaeus made tremendous contributions to systematic biology, still relevant today. However, comparable to earlier naturalists like Scheuchzer, he was still what would now be called a ‘creationist‘. He opposed the idea of evolution, in his own eighteenth century advocated in rudimentary form by Buffon, and later elaborated by Darwin, including as an explanation for the origin of carnivorous plants, as we shall see.
Hungry Venus flytraps snap shut on a host of unfortunate flies. But, despite its name, flies aren’t the flytrap’s only meal. As long as its prey is roughly the right size and touches two of its hairs within twenty seconds, the plant will dine on any insect or spider that comes its way. Glands in the lobes then secrete enzymes that break the dinner down into a digestible soup. Ten days later, the trap pops open to reveal nothing but a dried out husk.
Thanks to Darwin and others, we now know more about the European carnivorous plant sundew than centuries ago.
Sundew has liquid droplets on it. Many other plants have dew droplets on them early in the morning. These evaporate as the sunshine gets stronger. In sundew, they don’t evaporate. People thought the sundew droplets were a peculiar kind of dew resistant to warmth; hence the plant’s name ‘sundew’.
In the late eighteenth century, Erasmus Darwin, the grandfather of Charles Darwin, said the sundew droplets were not dew. He correctly thought they had to do with insects. He did not know yet they had to do with eating these insects though.
Erasmus Darwin’s grandson Charles experimented with carnivorous plants. In 1875, the results of these experiments were published in his Insectivorous plants. Why did plants become carnivorous? Because they grew in soils with few nutrients, Charles Darwin pointed out. They needed other sources of nutrients. In the course of evolution, carnivorous plants developed mechanisms to lure, catch and digest arthropod prey.
Like this specialized sundew leaf from Darwin’s book.
Peeters pointed out there are three kinds of carnivorous plants’ traps. Traps snapping tight, glue traps and pitcher traps.
The sequel of this will come on this blog. So, stay tuned!
‘Darwin’s Backyard’ chronicles naturalist’s homespun experiments. Breeding pigeons, growing orchids and other hands-on work provided evidence for the theory of evolution. By Sid Perkins, 10:00am, August 24, 2017.
Tracing the evolution of Charles Darwin’s thoughts about evolution is becoming an increasingly accessible project, thanks to a growing cache of publicly available digitized Darwin manuscripts on the Museum’s site.
As of today—the 155th anniversary of the publication of Charles Darwin’s On the Origin of Species—the Museum’s Darwin Manuscripts Project has made available 12,000 high-resolution and color images of manuscript pages, drawings, book abstracts, and other writings, complete with transcriptions that decipher the famous naturalist’s handwriting. By June 2015, the Museum will host more than 30,000 digitized documents written by Darwin between 1835 and 1882.
“These notebooks, marginalia, portfolios, and abstracts were the basis for eight of Darwin’s books, beyond the Origin, that set down, enlarged, and defended the theory of evolution by natural selection,” said Darwin Manuscripts Project Director David Kohn. “In these writings, you can see Darwin as a thinker, a keen-eyed collector, an inspired observer, and a determined experimenter.”
The Darwin Manuscripts Project has been publishing Darwin’s writings since 2007, but the publication and interpretation of the entire corpus will make it possible for visitors to trace the gradual gestation and long maturation of Darwin’s theory of evolution by natural selection. The project involves a close collaboration with Cambridge University Library, which holds Darwin‘s archives, and the Darwin Correspondence Project. Content is being simultaneously published by the Cambridge Digital Library.
The 12,000 documents accessible on the site now cover the 25-year period in which Darwin became convinced of evolution; discovered natural selection; developed explanations of adaptation, speciation, and a branching tree of life; and wrote the Origin.
“Darwin’s work in creating the Origin of Species encompassed much more than just setting pen to paper and writing the epochal book,” Kohn said. “The Origin was the mature fruit of a prolonged process of scientific exploration and creativity that began toward the end of his Beagle voyage, which first kindled Darwin’s interest in evolution, and that continued to expand in range and deepen in conceptual rigor through numerous well-marked stages.”
The remainder of the manuscripts, which will be available in June 2015, will pick up in the year the Origin was published—1859—and will include the full record of Darwin’s massive experimental research program to substantiate the power of natural selection until his death in 1882.