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Smithsonian's annual science seminar

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STRI Science Symposium 2006
by Eric Jackson

The Smithsonian Tropical Research Institute (STRI) is a world-class scholarly institution set in academically underdeveloped Panama. To the extent that excellence is found in the bastions of mediocrity and worse that dominate Panama's higher education, STRI's influence is responsible for a share of it. The institute's English-language lectures and its bookstore provide opportunities for English-speaking lay people for whom TV and the English sections of Panama's bookstores afford insufficient intellectual stimulation for the good life. Although too few people in Panama recognize it, this US government institution, an outpost of American academia staffed by an international team of top researchers, is a good thing to have here.

Once a year STRI puts on a science symposium, which is open to the public but oriented toward its scientists and students, so that they may all get an idea of what one another are doing. This year's event was held on March 13 and 14, but this reporter got caught in a whirl of news events, production schedules and other events that has delayed publication of a summary of the 21 scientists' presentations until now.

Rick Condit --- condit@ctfs.si.edu

The symposium started at 8:30 in the morning and this reporter walked in a few minutes later to catch the first presentation, in which STRI staff scientist Rick Condit spoke of local species distribution in dispersal- and habitat-limited tree communities. Condit noted that "at the local scale, speciation (as well as invasion) is an important driving force." However, he said on a wider scale the situation is different, and noted that in general rare tree species have wide ranges.

Condit's long-term work here, a part of the Center for Tropical Forest Science (CTFS) project, involves the mapping of 50-hectare forest plots in which every stem 10 millimeters in diameter or greater is recorded. From these data, collected constantly over time, he has built mathematical models of forests and demonstrated the effects of soil moisture and other variables on their composition.

Maria Pia Miglietta --- migliettam@si.edu

From forests the symposium moved to marine biology, wherein Maria Pia Miglietta, a postdoctoral fellow from Duke, spoke on the ways that the life cycles of hydrozoa --- soft, colonial sea animals, coelenterates that are usually small but can be as large as the Portuguese man of war --- have evolved. These creatures tend to have complicated live cycles that include both sexual and asexual reproduction, with the dispersal of sperm and eggs at certain points in their lives, and the budding of polyps at others. Then there are extra complications like heterochromy, wherein the timing of development will vary; and paedomorphosis, in which adults keep the juvenile form. She has been studying related species in the waters off of Florida and off of Panama.

About half of the hydrozoa have lost their medusa, or planktonic, stage, Miglietti explained. But those who have not lost this part of the life cycle will add tentacles as they grow, a convenient feature for the biologist who wants to tell at a glance how old a particular specimen is.

It turns out, however, that in some species like the Turritopsis and the Podocoryna, the number of tentacles at maturity is declining. This, she believes, is an adaptation that selects for faster reproduction, which is triggered, it seems, by temperature conditions in the Podocoryna and light in the Turritopsis.

But why the change? Is this a long-term trend linked to heredity, or is it a response to changing conditions? That's the nature of Miglietti's research.

Andy Jones --- jonesf@si.edu

Next, Andy Jones got back to the forests. A University of George PhD in plant biology, Jones holds the prestigious Earl S. Tupper Post Doctoral Fellow in Tropical Biology and in that role he's looking for insights into a long-running debate about the relative importance of genetic drift and natural selection in the evolutionary process by researching the demography and spatial distribution of forest tree species. He worked the north woods of Michigan, looking at pines and oaks, and he's down here studying jacarandas.

In the course of charting the "spatial genetic structures" of forests, Jones has found that gene flow among trees is extensive, and that differentiation can be as close as 30 to 100 meters away.

(Like this reporter, Jones has his undergrad degrees from a Mid-American Conference school, in his case Miami University of Ohio, a BS in zoology and an MS in botany. His accomplishments, but not particularly this reporter's, indicate to all you high school kids worried about getting into prestigious universities that one need not start out in the rarified places that let mediocre kids of the rich and powerful in on legacy admissions to reach the top of one's chosen field. So calm down, pay less attention to the competition, concentrate on learning and work hard --- the rest of it ought to come in due course.)

Jessica Stapley --- stapleyj@si.edu

Australian National University PhD Jessica Stapley, in Panama as a STRI postdoctoral fellow, stayed in the general area of forest species, but switched the subject from trees to reptiles and the methodology from census taking to experimentation. Her talk was on sexual selection among the Norops limifrons rainforest lizards.

It's a male thing --- the guys have a dewlap, a skin flap on their neck, which they show off to attract a mate. Some of these will sport a white dewlap, and others an orange one.

So is it a speciation thing? These lizards can mate and reproduce regardless of their white or orange heritage. But Stapley is getting beyond that, with experiments about the sorts of dewlaps that turn different sorts of females on. Do whites prefer whites, and oranges oranges, driving the two types into different evolutionary directions? And what about the preferences of lizards descended from white and orange liaisons?

(No doubt in the racially obsessed United States, someone advocating one social theory about race or another may at some point want to seize upon Stapley's work to "prove" some point. It seems that her work so far indicates that lizard guys with white dewlaps tend to be a bit more attractive to the ladies of either or mixed persuasion, but apparently not to the point that and orange guy can't find a mate.)

Dr. Stapley's website via South Africa's University of Witswatersrand has some very good photos of another species, the Augrabies flat lizard of Australia, whose competitive male behavior she has studied.

D. Ross Robertson --- drr@stri.org

For the last lecture of the first morning's session, STRI staff scientist Ross Robertson went back to the sea, and immersed himself in the subject of how many species of shorefishes there may be in the Eastern Tropical Pacific.

But really, it wasn't a matter of bandying numbers about, but of reviewing the scientific literature about the description of new species, doing statistical analyses that take different habitats into account, figuring in the natural histories of species that are hemmed into the Pacific coast of the Americas by a large stretch of open deep ocean from the shallows of the Central Pacific and by the continental land mass from Caribbean and Atlantic waters. It's an estimate that has to account for upwellings, deep areas, places that have more or less rain and certain islands that scientists haven't much studied. It involve inquiries of taxonomists about how long it takes them to identify unknown species. Like almost all of the rest of biology, it's a subject bound to be affected by the DNA revolution.

The pelagic and multi-habitat fish species are mostly known, Roberston noted. However, the University of Queensland-educated ichthyologist discovery of new reef and soft bottom species continues and shows no sign of leveling off.

Most fish species off of the west coast of the tropical Americas, he said, are endemic to the region, and this is especially true with fish that inhabit deep reefs.

"It's going to take decades" to know approximately how many fish species we have living in the Eastern Tropical Pacific, Robertson concluded.

Fernando Santos-Granero --- santosf@si.edu

Because STRI has the world-famous Barro Colorado Island laboratory and several marine biology labs, the institute's scientific staff, fellows and students are overwhelmingly dominated by biologists. However, when English industrialist John Smithson left his bequest to the US government way back when, the stipulated purpose was that it be used to further the advancement of knowledge, and with that purpose in mind Congress established the Smithsonian Institution. One of the many fields of knowledge that the Smithsonian advances is anthropology, and at this year's science seminar Fernando Santos-Granero represented that field in a lecture on native forms of slavery and servitude in the contact-time tropical Americas.

You don't get too many more controversial topics than this one, especially in the United States, which has never fully recovered from the multiple traumas resulting from the importation of African slaves and the creation of the peculiar institution of chattel slavery. Santos-Granero, who got his undergrad education at the Pontificia Universidad Catolica del Peru and his PhD at the London School of Economics, began his lecture by citing the academic objections to his work.

Scholarly literature tends to talk of indigenous people taking war captives, which it distinguishes from slavery. "Slavery," by most of these academic definitions, is a colonial thing. The arguments against any allegation of slavery in the Americas before the Europeans came include that those taken for involuntary servitude were assimilated into the societies for which they labored; that their existence didn't change the nature of the owners' economy; that they were well treated; that they were not legal property or "chattels" as one would say in the legalese of the Common Law system; and that condition was not hereditary.

Santos-Granero allowed that the word "slave" might be misleading to those who define the term according to the institutions that white people established in the Americas --- more than one system, as anyone who cares to ponder the historical differences between US and Panamanian racism will understand if she or he does so in light of any informed and dispassionate inquiry --- but nevertheless he maintained that at the time of the Conquest slavery was "a widespread native institution." He demonstrated this by reference to six indigenous cultures that he studied, one in Florida, four in South America and one in the Antilles.

He found various systems of servitude that were unlike the plantation slavery of US history, but similar in a number of ways to the slavery of pre-colonial Africa.

In enslaving indigenous societies of the Americas, there tended to be a set of cultural notions about "self" and "other" and about the nature and purposes of war. In many cases tribes would mount large-scale expeditions aimed at capturing large numbers of "others," particularly women and children to become servants of the conquering group. (At other times, subjugated tribes weren't incorporated into the winning society as slaves, but obliged to pay tribute to the victors.)

In the tropical American capturing societies that Santos-Granero studied, five to 19 percent of the population were slaves. This compares to three to 26 percent in slave-owning societies in North America's Pacific Northwest and five to 20 percent among the aboriginal natives of that continent's Great Plains.

Somewhat like the Catholic conceptions of slavery that were imposed in Latin America, but very different than the Protestant institution of chattel slavery, indigenous slavery tended to have as its professed aim the conversion of subhuman enemies into "people," and later into kinfolk. It was an assimilation process with "equal doses of force, persuasion, coercion and seduction," Santos-Granero said.

Moreover, while if one views economics as a quantitative study of "things" and limits the latter to some narrow Western concepts, it may be possible to claim that indigenous American slavery lacked an economic purpose as existed in the ante-bellum US South, but for the capturing societies that Santos-Granero studied "life force" was, economically philosophically, the scarcest of all economic resources, finite and in constant circulation. The enslavement of others was part of "a competition to accumulate as much life force as possible." So, he also noted, were some other indigenous practices like cannibalism and head-shrinking, which were considered by those participating in them to be other ways to appropriate life force.

Hubert Herz

The seminar got back to rainforest biology with Hubert Herz's talk on host-plant selection by leaf-cutting ants and the influence of the fungal mutualist.

Those of you readers who have much experience with gardening in Panama will know what leaf-cutter ants can do --- they'll strip your succulent sprouting pumpkin hill in an instant, defoliate a shrub overnight and take the product of your hard labor down trails they cut through the grass and down into the ground. They don't actually eat the vegetation they strip, but instead use it for substrate and fertilizer for their underground fungus gardens. It's the fungi they grow that sustain them.

They are worse in a forest setting than in your garden --- "50 to 80 percent of the flora in the foraging area are used... not only leaves, but also flowers and fruit," Herz pointed out. But as STRI scientist Allen Herre and others have pointed out, much of the space of an object that you would identify as a plant will typically be taken up by fungi living in some relationship with that organism. Thus it would be intuitive that for fungus farmers collecting fungus-infected greenery to put on their crops, the properties of the things they collect would be important.

Thus Herz, a visiting scientist from the University of Würzburg in Germany, is looking into whether fungus is involved in the ants' plant selections, what cues do the insects look for to make such decisions, and how ants recognize plants to begin with. He's doing this experimentally, by injecting substances into leaves without changing their integrity or appearance, putting the leaves along foraging trails and thus testing the ants' preferences among treated and untreated leaves.

As in, injecting the leaves with a fungicide that the ants can't detect. On the first day, they harvested the treated leaves as well as the untreated ones, but on the second day they left the treated leaves alone. The delay in rejecting the leaves that harm their crops meant that the information that the leaves were bad must have come from the way their fungi reacted to them.

Leaf-cutter ants are specialized eusocial animals, and not everyone in the nest works directly with the fungus crops. But when "naive" ants that don't know about the fungicide-laced leaves are put into the nest, they thereafter also reject treated foliage. What is learned from the fungus gardens is thus passed on to the previously clueless, and the ants begin to clear the tainted leaves from their trails.

So what cue does the garden give off to tell the ants that a certain kind of leaf is bad? It's probably not in the form of volatile chemicals, Herz opined. He hasn't found any information transfer among the worker ants that gather leaves. He's going to look at electrical signals that the ants' antennae may pick up from the fungi. With further experiments, he will attempt to find out about the cues that the ants use to distinguish the good leaves from the tainted ones, and there he expects that volatile chemicals may indeed play a role.

Jeremy Niven

At STRI, you have many scientists who are among the top authorities in their fields working at high levels of specialized sophistication. But then, when blazing new trails in the search for knowledge the tight boxes into which established knowledge is sorted can sometimes be less than helpful. It's one reason why they have the Tuesday afternoon science lecture series and the annual science seminar --- people in the STRI community find it helpful to look outside their specialties to keep their minds limber and sometimes to get new ideas for their own work.

As one STRI scientist, marine biologist Helena Fortunato, who's Portuguese, once explained to this reporter, people come to this community of scholars from different educational traditions. In the European tradition, she noted, everything is very specialized. (That norm, by the way, is largely copied by Panamanian academia, at least in the jealous defense of specialized intellectual turf if not in standards of excellence.) The American educational style, by contrast, is more likely to be generalist. And the British, who ran an empire with civil servants who received general educations and famously muddled through? When it comes to educational culture, "the British aren't really Europeans," Fortunato opined.

And maybe to demonstrate that, Cambridge University's Jeremy Niven strayed from the main focus of most of his work --- but not all that far --- to talk about some experiments he did about the role of visual information in controlling insect limb movements. (Niven holds a postdoctoral fellowship in evolutionary neurobiology, part of a new program researching evolutionary neurobiology and behavior associated with brain miniaturization that's directed by STRI staff scientist William T. Wcislo and funded by donations from Frank Levinson and the Peninsula Community Foundation.)

We all know that "the self-awareness of where you are" normally depends heavily upon vision, but anyone who has lived with a blind person will also recognize that not all spatial sense used to move about depends on information gathered from eyesight, and those who know both those who were blind from birth and those who lost their vision later in life will know that there tend to be gradations in the adaptation of other senses to compensate.

Such human knowledge doesn't particularly apply to insects. "Virtually nothing is known about vision and movement in insects," Niven pointed out. But now he has discovered a few things.

"When you are a bush cricket, you have a choice of doing many things," Niven explained. And you may have to rely on your repertoire of other things to do if somebody like Niven paints over one of your eyes and tests how well you walk over a ladder.

He found that painting over an eye led to more missed steps by a cricket with the leg on the side of the blinded eye. But it seems that the crickets will change their lead legs to the sighted side, then follow with their blind side legs. It also seems that the crickets use their antennae to sense their way around their world and with their vision impaired they probably do so more than they would otherwise.

Nélida Gomez

STRI's Barro Colorado lab has been the fount of many a scholarly article about jungle figs and the wasps that pollinate them and the bats who disperse their seeds. It's not just that said locale provides these organisms in great abundance and diversity, but also that there are many a specialized relationship between certain fig species and certain animal species who depend on each other to the exclusion of relatives on one side or another, and thus these are useful in theoretical work based upon the study of the co-evolution of symbionts.

However, evolution is not the only reason that gets STRI scientists into the strangler figs, ficus bushes, banyan trees and their relatives to study the interactions between these various figs and the animals that play important roles in their life cycles. There are also biochemical minutiae, which may have implications for diverse other fields of inquiry, to be discovered here.

Nélida Gomez, a Panamanian chemical ecologist and academic programs coordinators at STRI, has been looking at the chemical cues --- we may think of them as smells and tastes, but if we detected volatile substances with antennae rather than the sensory organs we possess we well might call these cues something else --- that various figs emit for the benefit of wasps that pollinate them and bats that eat them and so spread their seeds. She looked at nine types of figs at the age when they are receptive to pollination by insects and seven kinds of figs when they are mature and ready to eat.

Gomez, who got her undergraduate education at the University of Panama and her acquaintance with STRI through a fellowship that had her working in this country's mangrove swamps, en route to a master's degree at a US university and a doctorate in Germany, used gas chromotography to study two series of volatile chemicals put off by figs, the monoterpenes and the sesquiterpenes. The volatile chemicals coming from the same fruits will, as one might guess if one considers the difference between ripe and unripe fruit, be different in their mature stages than from when they are younger. Having gathered information from this biochemical inquiry, she observed which bats and insects were attracted to which fruits, in order to answer a series of questions.

It turns out that similar wasp species are not attracted to similar blends of chemicals. That would suggest that the different fruit preferences of their young form part of the distinctions among closely related wasps that make them different species.

However, similar ripe fruit tend to have similar chemical blends and to attract similar bat species. More notable than the specific chemical attractions, the size of the fruit seem to have more to do with which kinds of bats prefer which kinds of figs: the larger bats like bigger fruits, while smaller bats like smaller ones.

Elisabeth K.V. Kalko --- kalkoe@si.edu

The next speaker, STRI staff scientist Elisabeth Kalko, kept on the subject of bats, talking on the community composition and functional diversity of bats. "How little we know," she remarked, but pointed out that one thing that is known is that on Barro Colorado Island 74 bat species have been identified. A few are dominant, fruitivores are very abundant, and there are plenty of rare species. The PhD from Germany's University of Tübingen, currently affiliated with the University of Ulm, thinks that the island is probably home to more than the 74 species found so far.

The cliché "blind as a bat" is partially founded in reality --- most of the Chiroptera can in fact see, but nevertheless make their way around the dark places they inhabit not by sight but by echolocation, that is, guiding themselves from the echoes of their chirps. This form of navigation, Kalko pointed out, makes it possible to track certain rare bat species acoustically. She also noted that with the advance of research we now know that bat chirps serve more functions than was previously thought.

We also now have infrared photography, which in addition to fecal samples makes it possible to know what predatory bats eat. "They eat more than we thought," Kalko noted.

Her research has delved into the different foraging strategies of similar bat species. Despite the differences, the ones that disperse seeds tend to fly away with their food to feeding roosts, of which they tend to have several and which tent to be randomly spaced. Their defecation of seeds is what spreads various plant species around the forest.

A relatively large island it may be, but Barro Colorado is nevertheless a forest fragment and for the most part a secondary forest at that. Thus Kalko pointed out that what she has been studying is about bats' foraging in forest fragments, which may be different from the way things are done in the much rarer large uninterrupted forests.

Benjamin Turner --- turnerbl@si.edu

STRI staff scientist Ben Turner was the first speaker on the second day of the annual science seminar. A soil specialist, Turner was educated at the University of Sheffield and the University of London in the UK and has studied the chemistry of soils in the Falkland Islands (or Malvinas, for those of the Argentine persuasion), the Florida Everglades and Panama. He's interested not only in which plant nutrients are found in tropical soils, but also in their availability to plants and how that affects above-ground ecologies and the diversity of species.

"Phosphorus regulates ecosystems," Turner stated at the outset of his presentation. "The older a system gets, the more important phosphorus is."

Organic phosphorus is abundant in soil and plant litter, but the phosphorus that's taken up by a plant's roots inorganic. Often this usable phosphorus comes from the breakdown of organic compounds. But the concentration of phosphorus in the environment, in turn, drives the presence of the microbes that break down these compounds.

It tends to work into a downward cycle, with phosphorus content declining with a soil's age, a trend that does not exist with another key plant nutrient, nitrogen.

Organic carbon in the soil is also of interest to Turner, and very likely applicable to the analysis of how greenhouse gases may or may not affect global climate. "Even small changes in soil carbon could have important feedback effects on atmospheric carbon dioxide," he pointed out.

Bettina Engelbrecht

Dr. Engelbrecht, a long-term visiting research from Germany's University of Kaiserslautern, talked about plant species diversity and distribution across different tropical rainfall gradients. She started out by noting that diversity goes up with rainfall, but more specifically the determining factor isn't so much the amount of precipitation in the rainy season but the length of the dry season.

One thing that makes Panama a good place for her studies is that because of the Panama Canal the ACP has more than a century of rainfall data, going back to the beginning of the American canal project and even earlier with the measurements taken by the French in their failed bid to build a waterway here.

So why is the relationship between rainfall and the dry season's length on the one hand and species diversity the way it is? Engelbrecht mentioned four hypotheses that various people have advanced:

1.      That the abundance of pests increases with rainfall, and predation falls heaviest on the dominant species and thus makes room for others;

2.      That the rain washes away nutrients, which affects trees' growth rate and capacity for excluding competitors and thus leaves space for other species;

3.      That increased moisture encourages shade-tolerant --- almost by definition non-dominant --- trees; and

4.      That with increased moisture, more species of trees are able to tolerate drought.

She found that the data from Panama don't support the first hypothesis, although those from the Western Ghats in India might. The second idea, she said, does not really explain the effect --- after all, competitive exclusion works within the same species too. For the third hypothesis she found "no relation whatsoever" with the facts found in the forest.

It's the last hypothesis, that the increased moisture in the soil that's left over from dry season allows more species to survive the dry season, that Engelbrecht thinks is most likely.

Marife D. Corre

The next speaker was Marife D. Corre, a visiting soil specialist from the University of Goettingen, who spoke on the impact of elevated nitrogen input on a tropical forest.

A lot of our air pollution is composed of nitrogen compounds --- N₂O is a greenhouse gas and NO is the source of acid rain. Over the last 100 years the levels of these man-made forms of nitrogen in the atmosphere has increased. These levels are different in highland and lowland areas, so Corre is studying a plot in Gigante, a lowland forest, and Fortuna, a wooded area in the Chiriqui highlands. She's looking for the processes by which the forests react to different nitrogen contents in the environment.

Mark Seid

Dr. Seid, a postdoctoral fellow in the same new program as Jeremy Niven, is a zoologist from the University of Zurich in Switzerland. He's studying the neurological biochemistry of ants that change the roles the play in the colonies they inhabit, in particular the relationship between biogenic amines and the size of an ant's repertoire.

Not all ant species demonstrate "temporal polyethism," or the moving from one role to another over a lifetime, and within a given nest of a species that does, not all ants change their roles. The mysteries of why these things are so may hold molecular keys to new findings in the field of caste theory.

(This kind of work is about social insects, but can be prone to being seized upon by people with different theories about human society. If the propensity to change jobs --- only a part of temporal polyethism --- can be attributed to the presence of absence of a certain chemical in the body, for example, might not employers want to test job applicants for this? We are a long way from being able to do test for a chemical that indicates that specific human trait, so it seems, but genetic or biochemical testing by potential employers for other conditions is already such a present threat that a number of jurisdictions have prohibited or regulated it by law.)

Corey Tarwater

The next presentation got into ornithology. Corey Tarwater is studying parental care among antshrikes on Barro Colorado Island and at another STRI site, the Limbo forest plot. Her presentation on this occasion, cited not only her own work but the findings of a team of biologists conducting a long-term study of the ecology of lowland forest birds along the Pipeline Road.

"Bird work has been going on here by University of Illinois people for 30 years," Tarwater noted. Survival rate is a big theme, but getting a good handle on the probability of a bird being captured --- to see if it has a band from a previous capture, for example --- is a big difficulty in this work. "It skews your results terribly," she noted, adding that this is why some of the studies have gone on for 30 years.

While most tropical birds have two chicks at a time, Tarwater found that the Western Slaty Antshrike may have one or three. She determined that there is no more predation of larger broods, nor does it seem to be any problem for parents to feed three young instead of two. The survival problem comes, she said, after fledging. It is then when the survival rate among birds from smaller clutches is better.

One interesting sidelight to Tarwater's talk was about this species' division of household labor. In the 60 to 80 days when the young stay with the parents, both the male and female adults care for the chicks. The division of labor is that the parents divide the brood, with the males caring for the bigger ones and the females looking after the smaller ones.

Harilaos A. Lessios --- Lessiosh@si.edu

Dr. Lessios, a STRI staff scientist who did his undergraduate studies at Harvard and got his master's degree and PhD at Yale, is a marine biologist with research interests in evolutionary issues and the ecology of coral reefs. On this occasion his talk on the genetic connections of fish across the Eastern Pacific Barrier complemented the previous presentation of Ross Robertson.

The Eastern Pacific Barrier is a 5,000-kilometer stretch of deep ocean that separates the shallows of the Eastern Pacific from those of the Central Pacific. Charles Darwin noticed it back in 1872. Fish species on one side tend to be quite distinct from those on the other.

"But there are exceptions," Lessios noted, transpacific species that account for some 15 percent of the Eastern Pacific fish species.

Using estimated mutation rates, Lessios estimates that the last massive migrations of fish species across the Eastern Pacific Barrier were about 30,000 years ago, with the big exchanges coming about $5.5 million years before our time. But some fish make it across in small numbers. The probability of gene flow is limited not so much by the probability of crossing, but by the number of potential mates in the areas at the end of the migration, he added.

Using DNA analysis, Lessios has been looking at the nature of these relationships by studying 20 species found on both sides of the barrier.

In 16 of these species there has been recent gene flow, most of it going east to west. Gene flow, Lessios noted, is usually in the opposite direction from the invasion of a species from another environment. Why? "I haven't a clue," Lessios admitted.

William G. Eberhard --- archisepsis@biologia.ucr.ac.cr

Bill Eberhard, a STRI staff scientist who also teaches biology at the University of Costa Rica, began the second day's afternoon session by turning the seminar to the subject of communication between copulating spiders. "Male-female cooperation and conflict over female responses that could affect male paternity are played out during copulation," he said.

It seems that males who fail to please the promiscuous Physocyclus globosus females are substantially less likely to have their sperm used to fertilize eggs. The females let the males know what pleases and displeases them, and the conversations tend to go both ways.

So if the Panamanian schools take the Attorney General's advice and improve and expand their sex education, might this spider research be relevant? Maybe so. "Copulatory dialogues may be a very general phenomenon," Eberhard surmised.

Kaoru Kitijima

Next up was University of Florida botanist Kaoru Kitijima, who discussed the ecological implications of fast growth for woody plants.

"Fast growth is inherently incompatible with high survival," she concluded. She based that on observations that there is a negative relationship between the lifespans of leaves and photosynthesis, and a negative relationship between fast growth and survival among seedlings.

Why is that? Dr. Kitijima thinks that it's a matter of slower-growing seedlings investing a lot more of their energy and resources into defensive measures and storage capabilities --- things like more fiber and greater hardness to resist things that would eat them, and greater carbohydrate storage capacity and more extensive root systems for droughts and other times.

Sunshine A. Van Bael --- vanbaels@si.edu

Van Bael, a STRI long-term research fellow and PhD from the University of Illinois, does a lot of her research in Bocas del Toro and is interested in a wide range of ecological issues. On this occasion she spoke of interactions among endophytic fungi --- those that live within plants --- and beetles.

Fungi live within the leaves of many plants without causing any harm, and in many cases conferring definite benefits, Van Bael noted. In grasses which tend to be born infected, fungi can give the plants drought resistance heavy metal tolerance or other protections.

In woody plant, fungus infections tend to be acquired after birth. Which benefits they may or may not confer on their host plants is the subject of a series of experiments that Van Bael is conducting. In the lab she has Cassidinae host plants, some of whose leaves are inoculated with fungi, others not. Then she puts leaf-eating tortoise beetle larvae from the same brood, some on the infected leaves and some on the foliage without the fungi. This particular fungus does not appear to matter to the larvae.

However, when it comes to adults, Van Bael notes, there is a preference to eat things that are infected with rare endophytic fungi. But are they rare precisely because they are tasty to insects? Those questions will be among the subjects of her ongoing experiments.

Mark Torchin --- torchinm@si.edu

STRI staff scientist Mark Torchin, who got his doctorate at the University of California - Santa Barbara, is a marine ecologist with a particular interest in parasite-host interactions and how they affect nature's balances. At the seminar he spoke of his work with Japanese mud snails and trematodes, parasitic flatworms that infect the snails and castrate them.

Japanese mud snails came to North America about a century ago, possibly with introduced oyster cultures. With the snails came a particular Japanese variety of trematode. There are mud snail species, and trematodes that infest them, indigenous to the Americas.

It turns out that in the waters off the Pacific Coast of North America where mud snails are abundant, trematodes are not so common. Given what the flukes tend to do to the crustaceans, that shouldn't be a huge surprise.

Meanwhile in the seas off of Japan, the presence of trematodes tends to drive mud snails into deeper waters and increase the latters' growth rate.

So what does that have to do with Panama? Well, it seems that we have plenty of mud snail species here, and also a variety of trematodes. That diversity is a job-creator for scientists like Torchin.

Carlos Jaramillo --- jaramilloc@si.edu

STRI staff scientist Carlos Jaramillo ended this year's seminar on a paleobotanical note. He studies plant fossils, including fossil pollens found in the soil, to track the diversity of life in the tropical Americas over geologic time. On that time scale, our planet has heated and cooled a number of times and thus some insights can be gathered about what effects we might expect if the global warming trend turns out to be as profound and prolonged as a lot of scientists predict.

(The causes of global warming are another question, as are the motives of those who are in denial, either on the broader question of whether climate change is in fact underway or on the more narrow issue of to what extent human activity is driving the process.)

The role that oil companies play in the greenhouse gases debate may in some instances put them odds with scientists, but in other respect these corporations hire a lot of scientists and have collected much data of interest to independent researchers like Jaramillo. The cores that they have drilled are invaluable for purposes other than the search for petroleum. The coal companies also open seams in the earth from which researchers like Jaramillo can extract much useful information. Thus, using techniques and sometimes data developed by energy companies, and looking at samples mainly taken from Venezuela and Colombia, Jaramillo has been building a database about plant diversity in the tropical Americas.

He finds that with global warming, diversity goes up in the tropics, while during ice ages tropical diversity goes down. Whether this is due to changes in the extinction rates or changes in the origination of new species --- or combinations of the two --- requires further research.

It seems to Jaramillo that the expansion and contraction of the tropics with climate changes would have something to do with the trends he sees. And then, for South America in particular, he says he can't ignore the possibilities that the rise of the Andes has a lot to do with the things he has found.

And then, regardless of the size of the tropical areas themselves, what if it's the area of the tropical forest in particular that drives plant diversity? That's clearly shrinking, due to human activity.

It's intuitive, but also supported by the geological record that Jaramillo studies: "Diversification takes more time, but extinction is really fast." Be advised.

Also in this section:
Panama Canal expansion would go through archaeological sites
Smithsonian's annual science seminar