Experiments with genetically modified plants reveal new aspects on the biochemistry of flowers Animals “personally” bring their gametes together – seeking out exual partners, mating, fertilizing, and reproducing. Plants, however, are sessile organisms and require the help of a third party, the pollinator, which can be a bird, mouse or insect that transport pollen to receptive stigmas frequently over large distances. The colors and shapes of flowers as well as their volatile signals and nectar attract and reward the pollinators for their efforts. But not all flower visitors are pollinators, as many come only to steal nectar without transporting pollen or eat flower parts.

Flower visitor Selasphorus rufus (left); flower components nicotine (N), a repellent present in the nectar, and benzylacetone (BA), a volatile attractant released by petals (right). Both components optimize the plant’s production of outcrossed seeds. Pictures: Danny Kessler, MPI Chemical Ecology.

Scientists at the Max Planck Institute for Chemical Ecology, Jena, have discovered that the chemistry of floral scents and nectar enforces good pollinator behavior and allows plants to optimize their ability to exchange gametes with each other. In a paper published in the latest issue of SCIENCE (August 29, 2008), the scientists report the results from field experiments with genetically modified wild tobacco plants that show that particular components of the floral fragrance attracted pollinators, while bitter-tasting and poisonous components of floral nectar enforced modest drinking behavior. Apart from sugars, the floral nectar of tobacco also contains nicotine, which is bitter and used to deter nectar thieves or herbivores. But given the right timing and dose, nicotine in the nectar and the attractant, benzyl acetone, released at night as part of the floral scent, ensure that the visits of pollinators such as hummingbirds and hawk moths optimize the tobacco plant’s ability to exchange gametes and produce outcrossed seeds. Prior to these field tests, the researchers showed that the amount of nicotine in the floral nectar of wild tobacco influenced pollination by the tobacco hornworm Manduca sexta and two hummingbird species. To understand the floral biochemistry and plants’ ecological interactions with their mobile visitors, the researchers generated four different lines of genetically modified wild tobacco (Nicotiana attenuata). Apart from control plants that had received only a blind copy of the transgenic DNA fragment, transgenic lines were created (by means of RNA interference) that were unable to produce either nicotine or benzyl acetone; the latter has a sweet odor we know from cocoa beans and is similar to the smell of jasmine and strawberry. A fourth line of  transgenic plants could produce neither nicotine nor benzyl acetone. After a series of control experiments in the field showed that the genetic modifications per se did not influence growth, flower formation, nectar production, or the frequency of outcrossing, the scientists ran a series of three tests: First, measurements of floral nectar showed that its volume was only half the size in transgenic plants which were impaired in nicotine production, compared to control plants and the lines that could not produce benzyl acetone as an attractant. Conclusion: Floral visitors are principally attracted by the scent, and they drink more nectar if it doesn’t taste bitter.
Using video cameras, the researchers confirmed this result: Both attractant-deficient lines were rarely visited by hummingbirds (e.g. Archilochus alexandri) and white-lined sphinx moths (Hyles lineata). When visitors took nectar from flowers which contained a natural amount of deterring nicotine, they stayed for a short time only, while they enjoyed the nicotine-free nectar of corresponding transgenic lines. Consequently, these flowers were visited for longer periods, especially by hummingbirds. However, such observations do not prove that different visiting behaviors affect outcrossing and reproduction among plants. Therefore, two further analyses were performed, one focused on female fitness (production rate of seeds in the ovary), the other on male fitness (successful pollination of neighboring plants).
To determine female fitness, the flowers of the four transgenic plant lines were emasculated by removing the anthers. This enabled the researchers to measure only animal-mediated fertilization success rates, because self-pollination was prevented – a method utilized by plant breeders. It could be shown that only the control plants were normally crosspollinated by pollen of the surrounding wild-grown tobacco plants, whereas the transgenic nicotine- and benzyl acetone-deficient lines could only produce less than half of the seeds.The scientists measured the male fitness of the four transgenic lines by emasculating flowers of plants and subsequently
determining the origin of pollen which had fertilized their seeds with DNA probes. This paternity test allowed scientists to identify which of the transgenic plant lines were most successful at passing their pollen along to neighboring plants. Here it could also be shown that the control plants producing natural amounts of nicotine and benzyl acetone were the most potent ones; the big losers (almost five times less of cross-fertilized seeds) were the plants that produced neither nicotine nor benzyl acetone. Interestingly, during the growing season, the male fertilization success switched from the attractant (benzyl acetone)- deficient to the nicotine-deficient plants. In other words: The influence of nicotine in the nectar on successful pollinatormediated fertilization of tobacco plants decreased continuously, whereas the attractant became more and more important. These measurements were confirmed by video recordings which showed that early in the year, when hummingbirds visit tobacco, nicotine in the nectar causes them to drink less of the bitter nectar, and in turn visit other flowers, thus increasing pollen transfer. Later in the year, moths visit frequently, attracted by the odor of benzyl acetone. The bitter taste of the nectar doesn’t seem to bother them. The leader of the studies, Ian Baldwin, notes that just as the manufacturers of soft drinks protect their formulas and strive for constancy in order not to lose market share, altering their recipes only in response to the dictates of global sales, so plants evolve and incorporate ingredients into their nectar recipes in response to the dictates of their Darwinian fitness. “Nectar, which was thought to be nature’s soft drink, may not be so soft after all,” Baldwin says. Unlike animals, plants are sessile, and through chemistry, flowers can optimize visitors’ behavior.
The scientists also observed that nicotine in the nectar deters flower-eating insects which have a straightforward negative impact on reproduction. Odorant attractants lure not only pollinators but also herbivores. Tobacco plants seem to solve this dilemma by using nicotine as a deterrent.

Citation for article: Kessler, D., K. Gase, I. T. Baldwin 2008. Field experiments with transformed plants reveal the sense of floral scents. SCIENCE, August 29, 2008

The thawing of permafrost in northern latitudes, which greatly increases microbial decomposition of carbon compounds in soil, will dominate other effects of warming in the region and could become a major force promoting the release of carbon dioxide and thus further warming, according to a new assessment in the September 2008 issue of BioScience. The study, by Edward A. G. Schuur of the University of Florida and an international team of coauthors, more than doubles previous estimates of the amount of carbon stored in the permafrost: the new figure is equivalent to twice the total amount of atmospheric carbon dioxide. The authors conclude that releases of the gas from melting permafrost could amount to roughly half those resulting from global land-use change during this century.

Schuur and his colleagues refine earlier assessments by considering complex processes that mix soil from different depths during melting and freezing of permafrost, which occur to some degree every year. They judge that over millennia, soil processes have buried and frozen over a trillion metric tons of organic compounds in the world’s vast permafrost regions. The relatively rapid warming now under way is bringing the organic material back into the ecosystem, in part by turning over soil. Some effects of permafrost thawing can be seen in Alaska and Siberia as dramatic subsidence features called thermokarsts.

Schuur and his colleagues acknowledge many difficulties in estimating carbon dioxide emissions from permafrost regions, which hold more carbon in the Arctic and boreal regions of the Northern Hemisphere than in the Southern Hemisphere. Data are limited, and emissions are influenced by the amount of surface water, topography, wildfires, snow cover, and other factors. Thawing, although believed to be critical, is hard to model accurately.

Some warming-related trends in Arctic regions, such as the encroachment of trees into tundra, may cause absorption of carbon dioxide and thus partly counter the effects of thawing permafrost. But Schuur and colleagues’ new assessment indicates that thawing is likely to dominate known countervailing trends.

Although most people imagine wolves chasing deer and other hoofed animals, new research suggests that, when they can, wolves actually prefer fishing to hunting. The study, published today in the open access journal BMC Ecology, shows that when salmon is available, wolves will reduce deer hunting activity and instead focus on seafood.

Chris Darimont from the University of Victoria and the Raincoast Conservation Foundation, Canada, led a team of researchers who studied the feeding habits of wolves in a remote 3,300 km2 area of British Columbia. As Darimont describes, “Over the course of four years, we identified prey remains in wolf droppings and carried out chemical analysis of shed wolf hair in order to determine what the wolves like to eat at various times of year”.

For most of the year, the wolves tend to eat deer, as one would expect. During the autumn, however, salmon becomes available and the wolves shift their culinary preferences. According to the authors, “One might expect that wolves would move onto salmon only if their mainstay deer were in short supply. Our data show that this is not the case, salmon availability clearly outperformed deer availability in predicting wolves’ use of salmon.”

This work gives researchers as much insight into salmon ecology as wolf ecology. Darimont’s mentor and co-author Thomas Reimchen, also of the University of Victoria, admits, “Salmon continue to surprise us, showing us new ways in which their oceanic migrations eventually permeate entire terrestrial ecosystems. In terms of providing food and nutrients to a whole food web, we like to think of them as North America’s answer to the Serengeti’s wildebeest.”

The authors explain that the wolves’ taste for fishy fare is likely based on safety, nutrition and energetics. Darimont said, “Selecting benign prey such as salmon makes sense from a safety point of view. While hunting deer, wolves commonly incur serious and often fatal injuries. In addition to safety benefits we determined that salmon also provides enhanced nutrition in terms of fat and energy”.

The research also warns that this already vestigial predator-prey relationship – one that once spread from California to Alaska – might not be around forever. Darimont cautions, “There are multiple threats to salmon systems, including overexploitation by fisheries and the destruction of spawning habitats, as well as diseases from exotic salmon aquaculture that collectively have led to coast-wide declines of up to 90% over the last century”.

Darimont, C. T., P. C. Paquet and T. E. Reimchen. 2008. Spawning salmon disrupt trophic coupling between wolves and ungulate prey in coastal British Columbia.  BMC Ecology

Shedding some genetically induced excess baggage may have helped a tiny fish thrive in freshwater and outsize its marine ancestors, according to a UBC study published today in Science Express.

Measuring three to 10 centimetres long, stickleback fish originated in the ocean but began populating freshwater lakes and streams following the last ice age. Over the past 20,000 years – a relatively short time span in evolutionary terms – freshwater sticklebacks have lost their bony lateral plates, or “armour,” in these new environments.

Lateral plate morphs in marine stickleback. Complete morph (top), partial morph (middle), and low morph (bottom). These fish were stained to highlight bones. Courtesy of Rowan Barrett, UBC

“Scientists have identified a mutant form of a gene, or allele, that prohibits the growth of armour,” says UBC Zoology PhD candidate Rowan Barrett. Found in fewer than one per cent of marine sticklebacks, this allele is very common in freshwater populations.

Barrett and co-authors UBC post-doctoral fellow Sean Rogers and Prof. Dolph Schluter set out to investigate whether the armour gene may have helped sticklebacks “invade” freshwater environments. They relocated 200 marine sticklebacks with the rare armour reduction allele to freshwater experimental ponds.

“By documenting the physical traits and genetic makeup of the offspring produced by these marine sticklebacks in freshwater, we were able to track how natural selection operates on this gene,” says Rogers.

“We found a significant increase in the frequency of this allele in their offspring, evidence that natural selection favours reduced armour in freshwater,” says Barrett.

Barrett and Rogers also found that offspring carrying the allele are significantly larger in size. “It leads us to believe that the genetic expression is also tied to increased growth rate,” says Barrett.

“If the fish aren’t expending resources growing bones – which may be significantly more difficult in freshwater due to its lack of ions – they can devote more energy to increasing biomass,” says Barrett. “This in turn allows them to breed earlier and improves over-winter survival rate.”

Celebrating its 150th anniversary this week, Darwin’s first publication of his natural selection theory proposed that challenging environments would lead to a struggle for existence, or “survival of the fittest.” Since then, scientists have advanced the theory by contributing an understanding of how genes affect evolution.

“This study provides further evidence for Darwin’s theory of natural selection by showing that environmental conditions can directly impact genes controlling physical traits that affect the survival of species,” says Barrett.

A 75-million-year-old fossil of a pregnant turtle and a nest of fossilized eggs that were discovered in the badlands of southeastern Alberta by scientists and staff from the University of Calgary and the Royal Tyrrell Museum of Palaeontology are yielding new ideas on the evolution of egg-laying and reproduction in turtles and tortoises.

It is the first time the fossil of a pregnant turtle has been found and the description of this discovery was published today in the British journal Biology Letters.

The mother carrying the eggs was found in 1999 by Tyrrell staff while the nest of eggs was discovered in 2005 by U of C scientist Darla Zelenitsky, the lead author of the article and an expert on fossil nest sites, and her field assistant. Both were found about 85 km south of Medicine Hat in the Manyberries area.

“Although it is relatively rare to find the eggs and babies of extinct animals, it is even rarer to find them inside the body of the mother,” says Darla Zelenitsky, who was also involved in the first discovery of a dinosaur with eggs inside its body.

It was almost by accident that scientists realized that the fossil turtle was pregnant.

“The turtle specimen was partly broken when it was first discovered. It is this fortuitous break that revealed that the fossil was a mother,” says François Therrien, a co-investigator of the study and curator of dinosaur palaeoecology at the Royal Tyrrell Museum.

The remains of at least five crushed eggs were visible within the body of the fossil female and a CT scan exposed more eggs hidden under its shell. The turtle, estimated to be about 40 cm long, could have produced around 20 eggs. The nest, which was laid by a different female, contained 26 eggs, each approximately 4 cm in diameter.

Both specimens belong to an extinct turtle called Adocus, a large river turtle that lived with the dinosaurs and resembles today’s slider and cooter turtles.

The eggs of Adocus are extremely thick and hard, whereas those of most modern turtles are either thinner or soft-shelled. The thick eggshell may have evolved to protect the eggs from desiccation in dry environments or to protect them from voracious predators during the time of the dinosaurs.

Zelenitsky says the pregnant turtle specimen and the nest shed light on the evolution of reproductive traits of modern turtles, specifically those traits related to their eggs and nests.

“Based on these fossils, we have determined that the ancestor of living hidden-necked turtles, which are most of today’s turtles and tortoises, laid a large number of eggs and had hard, rigid shells,” says Therrien.

This appears to be Hottentotta trilineatus (Peters, 1861), Family Buthidae with a litter of young. At least some members of this genus are parthenogenic, but in this species males are known. It inhabits South Africa, Botswana, R. D. Congo, Djibouti, Ethiopia, Kenya, Mozambique, possibly Namibia, Somalia, Tanzania, Uganda, Zambia, and Zimbabwe. Some members of the genus have medically significant venom, and this species, about 50 mm long, is fast moving and aggressive. JCM Natural History Photography, Copyright John C. Murphy.

A new genetic study by the University of Hawaii, the Wildlife Conservation Society, and others have found that there are two species of goliath grouper instead of one.

Above: A new genetic study by the University of Hawaii, the Wildlife Conservation Society, and others has found that there are two species of goliath grouper instead of one. Photo Credit: Rachel Graham/Wildlife Conservation Society.

Researchers from the University of Hawaii, the Wildlife Conservation Society, Smithsonian Tropical Research Institute, National Marine Fisheries Service and Projecto Meros do Brazil discovered a new species of fish—a grouper that reaches more than six feet in length and can weigh nearly 1,000 pounds. This newly discovered species can be found roaming the tropical reefs of the Eastern Pacific Ocean.

Was the massive fish hiding among the corals and sea grass to evade marine biologists? No, it was just a case of mistaken identity, as explained in a recent genetic study in the journal Endangered Species Research.

It turns out that goliath in the Atlantic—which inhabit the tropical waters of the Americas and western Africa—are not the same groupers that swim in Pacific waters, even though they look identical.

“For more than a century, ichthyologists have thought that Pacific and Atlantic goliath grouper were the same species, and the argument was settled before the widespread use of genetic techniques. The genetic data were the key to our finding: two species, one on each side of the isthmus.,” said Dr. Matthew Craig of the Hawaii Institute of Marine Biology, lead author of the study.

Because the two populations of grouper are identical in body form and markings, they were both considered part of the same species: Epinephelus itajara. About three-and-a-half million years ago—before the Caribbean and the Pacific became separated by present-day Panama—they were the same species.

Since that time, the two populations have evolved into genetically distinct populations. While testing the hypothesis that Pacific and West Atlantic grouper were the same species, the research team found significant differences in the DNA from both populations. The differences indicate that the two populations have effectively evolved into two separate species after being separated from one another by Central America. The new Pacific species is now classified as Epinephelus quinquefasciatus. E. itajara is currently listed as critically endangered to extinction in the World Conservation Union’s Red List of Endangered Species of Fauna and Flora. Due to its scarcity, E. quinquefasciatus may also be considered critically endangered.

“In light of our new findings, the Pacific goliath grouper should be treated with separate management and conservation strategies,” said WCS researcher Dr. Rachel Graham, a co-author on the study and convener of the first International Symposium on Goliath grouper which provided the impetus for this highly collaborative study.

The oldest gecko may be Hoburogecko suchanovi Alifanov, 1992, which lived in Mongolia about 100 million years ago. However, it is known from skull fragments and its exact identity has been questioned. Yanatarogecko [Bauer et al. 2004 Journal of Zoology (2005), 265: 327-332] was described on the basis of a specimen trapped in amber in the Baltic area of Russia. It had sub-digital scansors on the toes similar to those of modern climbing geckos suggesting the complex adhesive system originated 20–30 million years earlier than had a previously discovered fossil gecko. Now, Arnold and Poinar have described a second gecko from amber dated at 97-110 million years old from the Lower Cretaceous of Myanmar. The remains are a lower limb and foot, and a partial tail. It appears to be the oldest unequivocal fossil gecko, predating Hoburogecko by 43–56 million years. The Myanmar specimen has the foot proportions and adhesive mechanism (pads on the toes with transverse lamellae) found in modern geckos. Thus, suggesting that modern day geckos had already evolved 100 million years ago. The specimen is tiny, even when compared with hatchlings of the smallest living geckos. However, the high numbers of lamellae on its toe pads suggest it is from a species with relatively large adult body size. The full citation of this paper is: Arnold, E. N. and G. Poinar. 2008. A 100 million year old gecko with sophisticated adhesive toe pads, preserved in amber from Myanmar. Zootaxa 1847:62-68.

The African Treefrog, Leptopelis vermiculatus (Boulenger, 1909). It is also known as the Amani Forest Treefrog or Big-eyed Treefrog. It inhabits closed canopy rainforests above 900 m in the East and West Usambara, Nguu, Udzungwa, Mahenge, and Poroto Mountains, as well as Mount Rungwe in Tanzania. This individual was in the pet trade. JCM Natural History Photography.

Scientists at the Smithsonian Institution have discovered a new species of bird in Gabon, Africa, that was, until now, unknown to the scientific community. Their findings were published in the international science journal Zootaxa, Aug. 15.

ON THE LEFT. A male specimen of the newly-discovered olive-backed forest robin is carefully examined in the hand of Brian Schmidt, the Smithsonian ornithologist who discovered the species. Photo Credit Brian Schmidt. On THE RIGHT. Although less vibrant than the male olive-backed forest robin, this female still exhibits a bright orange and yellow throat and distinctive white dot in front of each eye. Photo Credit Carlton Ward.

The newly found olive-backed forest robin (Stiphrornis pyrrholaemus) was named by the scientists for its distinctive olive back and rump. Adult birds measure 4.5 inches in length and average 18 grams in weight. Males exhibit a fiery orange throat and breast, yellow belly, olive back and black feathers on the head. Females are similar, but less vibrant. Both sexes have a distinctive white dot on their face in front of each eye.

The bird was first observed by Smithsonian scientists in 2001 during a field expedition of the National Zoo’s Monitoring and Assessment of Biodiversity Program in southwest Gabon. It was initially thought, however, to be an immature individual of an already-recognized species. Brian Schmidt, a research ornithologist at the Smithsonian’s National Museum of Natural History and a member of the MAB program’s team, returned to Washington, D.C., from Gabon in 2003 with several specimens to enter into the museum’s bird collection. When he compared them with other forest robins of the genus Stiphrornis in the collection, Schmidt immediately noticed differences in color and plumage, and realized the newly collected birds might be unique.

“I suspected something when I found the first bird in Gabon since it didn’t exactly match any of the species descriptions in the field guides,” Schmidt said. “Once I was able to compare them side by side to other specimens in our collections it was clear that these birds were special. You, of course, have to be cautious, but I was still very excited at the prospect of possibly having found a new species of bird.”

To ensure that the specimens Schmidt collected were a new species, geneticists at the Smithsonian’s National Zoo compared the DNA of the new specimens to that of the four known forest robin species. The results clearly showed that these birds were in fact a separate and distinct species.

Discovering an unknown mammal or bird species is far from a common event. Before the 20th century, the rate of discoveries was great—several hundred new species were being described each decade. Since then, however, the pace has slowed and new species of vertebrates are generally only found in isolated areas.

Now officially recognized, the olive-backed forest robin brings Gabon’s number of known bird species to 753. Other than its existence, however, little is known to science about this newcomer.

There is some knowledge about the species’ habitat choice since all of the birds seen and heard in the wild were found in dense forest undergrowth. Other facts such as specific diet, mating and nesting habits, and the species’ complete habitat range are all things that still need research.

“This discovery is very exciting for us,” said Alfonso Alonso, who directs the Biodiversity Program in Gabon. The opportunity to study areas the tropics of Gabon allows scientists to learn about the organisms that live there and in turn develop plans to protect them in the future. “Finding the olive-backed forest robin strongly underscores the importance of our research. This helps us show the conservation importance of the area.”

The MAB program is part of the Center for Conservation Education and Sustainability at the National Zoo. This particular study in the program is being conducted in the Gamba Complex of Protected Areas, a coastal region in southwestern Gabon containing the Loango and Moukalaba-Doudou National Parks with a restricted-access industrial corridor between them.

Scientists in the program are assessing the species diversity of the region, conducting applied research on the impact of management and development and providing biodiversity education programs locally to guide the regional conservation strategy. The program has partnered with the Gabonese government and Shell Gabon to integrate biodiversity conservation into energy development. The partnership has produced the first in-depth study of rainforest biodiversity in this area of Central Africa, provided relevant scientific advancements on the effects of development on biodiversity and identified conservation strategies for the long-term management of the area.

“Although finding an unknown species like the olive-backed forest robin was not the goal of the MAB project,” Schmidt said, “it is definitely a reminder that the world still holds surprises for us.”