Constantine Alexander's blog

Less is more for reef-building corals

Inflexibility of coral host leads to higher resistance to environmental stresses

		This shows Pocillopora coral and fish in Moorea, French Polynesian, the study site for the National Science Foundation's Moorea Coral Reef Long-Term Ecological Research. Credit: Hollie Putnam, University of Hawaii - SOEST

Researchers at the University of Hawaii – Manoa (UHM) School of Ocean and Earth Science and Technology (SOEST) made a discovery that challenges a major theory in the field of coral reef ecology. The general assumption has been that the more flexible corals are, regarding which species of single celled algae (Symbiodinium) they host in coral tissues, the greater ability corals will have to survive environmental stress. In their paper published August 29, 2012, however, scientists at the Hawaii Institute of Marine Biology (HIMB) at SOEST and colleagues documented that the more flexible corals are, the more sensitive to environment disturbances they are.

"This is exactly the opposite of what we expected," said Hollie Putnam, PhD candidate at UHM and lead author of the study. This finding was surprising, as it is thought corals exploit the ability to host a variety of Symbiodinium to adapt to climate change. "Our findings suggest more is not always better," she continued.

"The relationship of coral species to their algal symbionts is fundamental to their biology," says David Garrison, program director in the National Science Foundation (NSF)'s Division of Ocean Sciences, which funded the research. "This study gives us a new understanding of how corals are likely to respond to the stresses of environmental change."

Reef corals are the sum of an animal (host), and single celled algae that live inside the corals' tissues (also called 'endosymbionts'). This is a mutually beneficial arrangement – the coral provide protection and keep the algae in shallow, sunlit seas; and the algae produce large amounts of energy through photosynthesis, which coral use to survive and build their skeletons. The stability of this symbiosis is critical to the survival of corals and if they lose their endosymbionts they bleach and often die. Corals can host different types of endosymbionts, which affects their response to stress.

Putnam and other scientists from Dr. Ruth Gates' laboratory at HIMB took tiny tissue samples from 34 species of coral in Moorea, French Polynesia. By analyzing the DNA from the endosymbionts in these samples, they were able identify the types of Symbiodinium. This revealed that some corals host a single Symbiodinium type that is the same in all individuals of that coral species, and that others host many types that vary among individuals within a coral species.

"The corals we sampled spanned a range of environmental sensitivities from resistant to susceptible, and we were able to link, for the first time, patterns in environmental performance of corals to the number and variety of symbionts they host," reported Putnam. These patterns show that corals hosting diverse Symbiodinium communities, those that are flexible with respect to endosymbionts (termed 'generalists'), are environmentally sensitive. In contrast, environmentally resistant corals were those that associate with one or few specific types of Symbiodinium (termed 'specifists').

"Coral reefs are economically and ecologically important, providing a home for a high diversity of organisms necessary for food supplies, recreation, and tourism in many countries. The better we understand how corals respond to stress, the more capable we will be to forecast and manage future reefs communities," said senior author Professor Ruth Gates. Coral reefs can undergo mass mortality due to high temperatures, and ocean acidification is threatening the capacity for skeletal growth. These global stressors are superimposed on the local threats of pollution, coastal development and overfishing, together threatening the persistence of corals as a functional ecosystem in the future.

In the future, the Gates Lab will examine what causes the differences in success between corals that are flexible and inflexible in their Symbiodinium associations and compare the symbiotic flexibility in corals and reefs across much larger areas – in locations such as Hawaii, Moorea, Taiwan and American Samoa. This further understanding will allow better predictions of the future of reefs under further ocean warming and acidification.

The research was conducted at NSF's Moorea Coral Reef Long-Term Ecological Research (LTER) site, one of 26 such NSF sites around the globe in ecosystems from coral reefs to freshwater lakes, and from forests to grasslands.

Contact: Marcie Grabowski
mworkman@hawaii.edu
808-956-3151
University of Hawaii ‑ SOEST

 

 

 

Why are there so many species of beetles and so few crocodiles?

Answer may be 'adaptive zones' that limit species number, life scientists report

		The relationships between age and species richness in major groups reveals that in almost every major group, age and diversity are not strongly correlated, life scientists report. Credit: Amisha Gadani/UCLA ecology and evolutionary biology

There are more than 400,000 species of beetles and only two species of the tuatara, a reptile cousin of snakes and lizards that lives in New Zealand. Crocodiles and alligators, while nearly 250 million years old, have diversified into only 23 species. Why evolution has produced "winners" — including mammals and many species of birds and fish — and "losers" is a major question in evolutionary biology.

Scientists have often posited that because some animal and plant lineages are much older than others, they have had more time to produce new species (the dearth of crocodiles notwithstanding). This idea — that time is an important predictor of species number — underlies many theoretical models used by biologists. However, it fails to explain species numbers across all multi-cellular life on the planet, a team of life scientists reports Aug. 28 in the online journal PLoS Biology, a publication of the Public Library of Science.

"We found no evidence of that," said Michael Alfaro, a UCLA associate professor of ecology and evolutionary biology and senior author of the new study. "When we look across the tree of life, the age of the group tells us almost nothing about how many species we would expect to find. In most groups, it tells us nothing."

Another idea, that some groups are innately better or worse at producing species, similarly fails to explain differences in species number among all of the major living lineages of plants and animals, the life scientists found.

"We know that some groups, like flowering plants or cichlid fishes, have been exceptionally good at producing species during certain periods of their evolutionary history," Alfaro said. "However, when we look at the ages of all of the major groups of plants and animals, these differences in speciation rate are not sufficient to explain the differences in species number that exist in extant groups."

Alfaro and his colleagues studied 1,397 major groups of multi-cellular eukaryotes — including animals, plants and fungi — that account for 1.2 million species. Working as "evolutionary detectives," they were able to see whether the groups that split the earliest tended to have the most species. They assigned a "species richness score" to these 1,397 groups, using novel statistical and computational methods they developed.

If age does not explain species diversity, an alternative idea is that a lineage will produce species up until the point that it fills an "adaptive zone" that allows a maximum number of species, Alfaro said. In other words, a lineage of bats, whales or penguins has a maximum capacity that is determined by habitat requirements and competitors.

When an adaptive zone is first colonized, the growth of new species will be rapid, up until that limit has been reached. Once a zone is full, this speciation rate will level off. New species will not emerge until one of two events occurs: First, an existing species may go extinct, in which case it may be replaced. Second, a species within the adaptive zone may evolve a new trait — sharp teeth, wings, chemical defenses or camouflage, for example — that confers a significant ecological advantage and takes it into a new adaptive zone, creating opportunities for new species to emerge, Alfaro said.

"Adaptive zones are an old idea in evolutionary biology, but there is little understanding of whether speciation rates or adaptive zones are more important in explaining species richness across the tree of life," Alfaro said. "If adaptive zones control biodiversity at the broadest scales, then the rate of species growth will be a good explanation of species richness only right after a lineage has entered into a new adaptive zone. Once the adaptive zone has filled up, then, no matter how much time goes by, the number of species will not change much."

Thus, these adaptive zones, which Alfaro also calls "ecological limits," serve to restrict the number of new species that can emerge.

"Most of the groups that we studied have hit their limits," he said. "Ecological limits can explain the data we see. What's really driving things is how many times lineages evolve new innovations that move them into new adaptive zones.

"The ultimate goal in our field is to have a reconstruction of the entire evolutionary history of all species on the planet," Alfaro added. "Here we provide a piece of the puzzle. Our study sheds light on the causal factors of biodiversity across the tree of life."

Daniel Rabosky, an assistant professor of ecology and evolutionary biology at the University of Michigan–Ann Arbor is the lead author of the study, and Graham Slater, a National Science Foundation–funded UCLA postdoctoral scholar in ecology and evolutionary biology, is a co-author.

The research is funded by the National Science Foundation and by the University of California's Miller Institute for Basic Research in Science.

In a 2009 study published in Proceedings of the National Academy of Sciences, Alfaro and his colleagues reported that mammals and many species of birds and fish are among evolution's "winners," while crocodiles, alligators and a reptile cousin of snakes and lizards known as the tuatara are among the "losers." That study also showed that new species emerge nearly as often as they die off.

UCLA is California's largest university, with an enrollment of nearly 38,000 undergraduate and graduate students. The UCLA College of Letters and Science and the university's 11 professional schools feature renowned faculty and offer 337 degree programs and majors. UCLA is a national and international leader in the breadth and quality of its academic, research, health care, cultural, continuing education and athletic programs. Six alumni and five faculty have been awarded the Nobel Prize.

Contact: Stuart Wolpert
swolpert@support.ucla.edu
310-206-0511
University of California - Los Angeles

 

 

Male snails babysit for other dads

		Males of the whelk Solenoptera macrospira provide all parental care, carrying egg capsules on their back -- even though most of the offspring are not theirs. Male, left; female on the right. Credit: Peter Marko

Pity the male of the marine whelk, Solenosteira macrospira. He does all the work of raising the young, from egg-laying to hatching — even though few of the baby snails are his own.

The surprising new finding by researchers at the University of California, Davis, puts S. macrospira in a small club of reproductive outliers characterized by male-only child care. Throw in extensive promiscuity and sibling cannibalism, and the species has one of the most extreme life histories in the animal kingdom.

The family secrets of the snail, which lives in tidal mudflats off Baja California, are reported online in a study in the journal Ecology Letters.

In the study, UC Davis researchers report that, on average, only one in four of the hundreds of eggs that a male S. macrospira carries around on his back belong to him. Some carry the offspring of as many as 25 other males.

Such extreme cases provide the raw material on which natural selection can work and shed light on more "mainstream" species, said study author Rick Grosberg, a professor of evolution and ecology at UC Davis.

"It opens our eyes to viewing other kinds of behavior not as weird or harmful but as normal," he said.

The snails were first described in an amateur shell-collectors newsletter, The Festivus, in 1973. Grosberg started studying the animals in 1994, when he brought some back from a collecting trip and realized that only male snails had egg capsules on their shells.

When the snails mate, the female glues capsules containing hundreds of eggs each to the male's shell.

The male's shell likely acts as a substitute rock, since the snails' habitat offers few surfaces on which to glue eggs, said co-author Stephanie Kamel, a postdoctoral researcher in Grosberg's lab.

Moving in and out with the tide on dad's (or stepdad's) back also protects the egg capsules from the extremes of heat and drying they might face if left on a stationary rock.

A male's shell may become covered in dozens of capsules, each containing up to 250 eggs. As the eggs hatch, a process that takes about a month, some of the baby snails devour the rest of their littermates. Typically only a handful of hatchlings survives the fratricide to emerge from a capsule and crawl away.

Kamel carried out DNA analysis of brood capsules to determine the eggs' parentage. On average, she found that the male snails had sired just 24 percent of the offspring on their backs. Many had sired far less.

"The promiscuity in the female snails is extraordinary," Kamel said, noting that some females mate with as many as a dozen different males.

Why do they do it? Typically in the animal kingdom, females invest more resources in an egg than a male does in a sperm, so mothers have a stronger interest in providing parental care. Males may mate with multiple partners to increase their chances of siring offspring, but typically make less investment in caring for those young. When dads do get involved, it's nearly always because they are assured that all or most of the offspring are their own. Male sea horses, for example, carry developing young in a pouch — but all are their own genetic offspring.

One explanation could be that caring for the kids just doesn't cost the male snails much. But by tethering individual snails to a post sunk in the sand, Grosberg was able to follow them over time and show that the capsules do impose a significant burden, reflected in weight loss.

It may be that carrying the egg capsules simply represents the best of limited options for the males, Grosberg said, since it's impossible for them to mate without the female attaching an egg capsule to their backs.

Or carrying egg capsules may be a way for a male to show a female that he's good parent material.

"If he wants to get any action, he has to pay the price," Grosberg said.

Grosberg is fascinated by the conflicts that occur between parents, between siblings, and between parents and offspring as they each try to get resources and maximize their success in breeding. You can see these conflicts and rivalries all the way from simple animals to humans, he notes.

"Everything that intrigues me about family life happens in these snails," he said.

At the same time, no animal has gone as far as humans in evolving increasing cooperation between relatives, tribes and larger and larger (and less closely related) groups over time.

"We're good at seeing other forms of reward," Grosberg said.

The work was funded by the National Science Foundation.

Contact: Andy Fell
ahfell@ucdavis.edu
530-752-4533
University of California - Davis

 

 

The raccoon spreads dangerous diseases as it invades Europe

		The raccoon spreads dangerous diseases as it invades Europe. Credit: F.J. García

Furry, agile, intelligent and voracious: the raccoon is far from being a cuddly toy, which is what many people believe when they get one as a pet. It is more like an invader that escapes and is able to adapt and survive in new habitats. According to a study, its expansion across Spain and Europe is bringing infectious and parasitic diseases like rabies. This puts the health of native species and people at risk.

Originating in North America, the raccoon (Procyon lotor) is an invasive species that has established itself in Europe due to hunting and the fur trade along with its acquisition as a pet. In Spain, its presence in the wild is already commonplace in Madrid and Guadalajara and is sporadic in other regions such as the island of Mallorca. Its presence is however far from welcomed.

"Due to its rapid expansion and the long list of illnesses that it may carry, it poses a health risk that we must bear in mind," as outlined to SINC Beatriz Beltrán-Beck, the lead author of the study published in the 'European Journal of Wildlife Research' and researcher at the Research Institute of Hunting Resources (IREC, joint centre of the University of Castilla-La Mancha, the CSIC, and Castilla-La Mancha Council).

Bearing in mind that its population density could exceed 100 raccoons per km2, the success of the expansion of this small opportunistic carnivore is down to its ability to quickly adapt to different surroundings and omnivorous food habitats, its high reproductive potential and the absence of natural predators.

However, as Beltrán-Beck points out, "the impact that their expansion and invasion could have on the environment and the health of native species and humans is unknown." The researcher adds that the increase in population numbers and expansion to other countries and/or urban environments could increase the transmission of dangerous parasites and illnesses to domestic animals and humans.

The guest that nobody wants in their home

The research team gathered all types of information on the infectious and parasitic diseases that raccoons can transmit. The aim was to assess the propagation risk of infections along with possible control methods. But, according to the author, "there is little data in Europe on this species".

Rabies and a very pathogenic parasite to man (Baylisascaris procyonis), which was found in Germany, are some of the most significant illnesses found in the raccoon. But, along with bacterial illnesses, these are added to the West Nile virus which affects human, birds, horses and sheep.

Although in Western Europe rabies have been eliminated thanks to the oral vaccination for foxes (Vulpes vulpes), there is still concern that the raccoon could complicate the situation in some areas of Eastern Europe that are still home to rabies. In recent years 142 cases of rabies in raccoons have been identified, above all in Ukraine, Estonia, Germany and Lithuania.

This small American carnivore has been confirmed to be the host of the nematode worm Baylisascaris procyonis, which is responsible for Larva migrans, an illness caused by larval migration and parasite persistence under the skin, in the brain and in other organs. In the past this disease could only be found in America but is now emerging and on the rise in Europe.

"The infected raccoons can scatter millions of nematode B. procyonis eggs, which cause significant environmental contamination," warn the scientists. In the USA, between 68% and 82% of mammals have this parasite. Prevalence is also high in Germany although in Japan, for example, the parasite was not detected in any of the 1,688 raccoons captured for the purposes of other studies.

According to Beltrán-Beck, "more epidemiological studies are necessary on the current health situation and the implementation of measures that limit the possible impact of invading raccoons."

An unpleasant "pet"

Given its exotic origin and its rapid expansion since the 1970's, the raccoon is considered an invasive species in Europe. However, the majority of European countries, like Spain, do not control the trade of this animal, which is introduced onto the market as a pet.

"The case of Spain is a good example. The origin of its expansion is probably due to it escaping from the home where it was kept as a pet and due to the owners releasing it into the countryside when it reaches adulthood and becomes aggressive," adds the researcher.

According to the researcher, "this is mainly the case because there is a complete lack of knowledge of the biology, ecology, distribution and population density of the raccoon in Europe."

References:

• Beltrán-Beck B, García FJ, Gortázar C, (2012) "Raccoons in Europe: disease hazards due to the establishment of an invasive species", European Journal of Wildlife Research 58, pp 5
• García JT, García FJ, Alda F, González JL, Aramburu MJ, Cortés Y, Prieto B, Pliego B, Pérez M, Herrera J, García-Román L, (2012) "Recent invasion and status of the raccoon (Procyon lotor) in Spain", Biological Invasions, DOI 10.1007/s10530-011-0157-x

Contact: SINC
info@agenciasinc.es
34-914-251-820
FECYT - Spanish Foundation for Science and Technology