From Plant Press, Vol. 17, No. 3, July 2014.
By Gary A. Krupnick
Baird Auditorium at the National Museum of Natural History provided the location for a full day of biogeography talks at the 12th Smithsonian Botanical Symposium, “Location, Location, Location...New Advances in the Science of Biogeography.” The speakers celebrated the past contributions of biogeography and provided a look toward future ones that bring a deeper understanding of the relationship between our planet and its biota. The invited speakers addressed why “location” matters with a wide range of modern studies and applications on the geography of life.
Held over two days, the Symposium kicked off on April 24, 2014, with a poster session at the Conservatory of the United States Botanic Garden. An international group of 24 presenters displayed their posters and spoke about their research ranging in topics from lichen biodiversity and algae phylogeny, to the evolution of sea slugs and the effects of climate change on plants.
The next day, the Symposium began with opening remarks by Warren L. Wagner, Chair of the Department of Botany. John Kress, the Interim Under Secretary for Science, also welcomed the participants and speakers to the Smithsonian Institution.
The presentation of the 2014 José Cuatrecasas Medal for Excellence in Tropical Botany took place as Laurence Dorr announced H. Peter Linder as this year’s recipient. Linder was recognized for his many accomplishments as an educator and scientist, including his contributions to the systematics, biogeography, and evolution of Restionaceae and Poaceae. Although Linder was unable to attend the Symposium, he sent a message stating how honored he was to receive such recognition: “Although I have little contact to the Andean Asteraceae, I know of the work of José Cuatrecasas. The list of previous recipients is also very impressive—a long list of people I have seen as role models, and whose work I have much appreciated. It is very nice to know that my work on Restionaceae and the danthonioid grasses is appreciated.”
Each invited speaker was introduced by the Symposium Convener, Vicki Funk. Susanne Renner, from the University of Munich, gave the first scientific presentation, “Historical Biogeography and Ecological Biogeography – Come Together Now.” Renner began her talk by noting the first instance of biogeography in the scientific literature. In 1820, Augustin P. de Candolle hinted at biological geography: because species become locally adapted, regional floras and faunas differ. De Candolle recognized that to understand biogeographic patterns, one needs to study both the speed of ecological adaptation and the differentiation of regional floras and faunas by speciation and extinction. The German geographer Friedrich Ratzel coined the word biogeography in 1891. Renner’s talk covered three areas of interest. She first spoke about regional hummingbird and plant communities to describe the speed of adaptation. To approach this topic, the first step is to develop a well-dated phylogeny of hummingbird and plants. Fossil evidence of wing shape suggests swifts are stem relatives of hummingbirds, and precursors of hummingbirds are found in European fossils that date back to 34-28 million years ago. Molecular evidence places the age of modern hummingbirds at 25-18 million years ago. Looking at bird-adapted plant clades, Renner found similar increases in lineages over time, as demonstrated by data of swordbills and passionflowers in the Andes, and hummingbirds and their plants in North America.
Renner then spoke about the worldwide endoparasites Apodanthaceae to describe the problems of relaxed clock models without “good” calibration fossils. Dating clade divergences help us understand the factors that lead to distribution patterns. For a holoparasitic angiosperm, the host age can be used as a calibration point. Renner explained that fossil calibrations estimate older ages of divergence than random local clocks, leading Renner to place more trust in the local clock estimates.
Renner’s third area of interest was applying the fossilized birth-death method to show slow diversification in royal ferns (Osmundaceae), a family of 11-21 extant species and 150 named fossil species. She explained that the traditional method of molecular clock dating includes forcing the oldest fossil record to a specific node in the tree while ignoring the other fossils. In the new fossilized birth-death method, the precise relationship of each fossil is irrelevant and all fossils are used in the tree. The four parameters of the new model are speciation rate, extinction rate, fossil recovery rate, and proportion of sampled extant species. The fossilized birth-death method can thus disentangle speciation and extinction.
Rachel Warnock, a postdoctoral fellow in the Department of Paleobiology at the Smithsonian Institution, presented the talk, “Testing the Molecular Clock using Simulated Trees, Fossils and Sequences.” The molecular clock establishes an evolutionary timeline by comparing the genes of living species. Warnock identified two caveats of the molecular clock: (1) the molecular clock does not tick at a constant rate; and (2) calibration of the clock relies on an incomplete fossil record. She pointed out that there is a lag time between the first observed fossil of a species and the true time of origin and divergence.
Warnock explained that the fossil record can be used to obtain accurate constraints on divergence times, but these will invariably be imprecise. She pointed out that the accuracy of molecular clock estimates is determined by the effective, rather than the specified priors. The most reliable and informative results will be obtained with accurate and precise constraints. She said that molecular data cannot be used to mitigate the imprecision associated with fossil calibrations, so priors must be improved. Improving divergence time estimation requires considering preservation and sampling biases. She ended with suggesting that the integration of molecular and paleontological data is essential for telling evolutionary time.
Ben Winger, a doctoral student from the University of Chicago and the Field Museum, presented “Resolving the Geographic History of Neotropical Bird Migration: An Extension of the DEC Model.” With collaborator Rick Ree of the Field Museum, Winger has been developing a method to reconstruct the historical biogeography of migrating birds, specifically to understand where a lineage arose and how it came to be found where it is today. Migratory species are a complicated evolutionary problem because they exist in two or more different geographic ranges at different times of the year.
The dilemma is summarized by two theories. The “Temperate Home” theory suggests that a northern population shifts towards the tropics to avoid a harsh winter. The “Out of the Tropics” theory suggests that a tropical population shifts northward to escape competition for resources in the crowded tropics, and exploit a seasonal flush of resources in the temperate zone. Existing historical biogeographic models are not well suited for understanding the evolution of migration because we cannot consider the breeding range and the wintering range simultaneously.
During his talk Winger introduced an approach to answering this dilemma by using migratory songbirds as a case study. The Emberizoidea or New World nine-primaried oscines is a lineage of about 750 bird species and composed of five major groups – all New World sparrows, warblers, cardinals and buntings, blackbirds and orioles, and tanagers. Ree developed the Dispersal-Extinction-Cladogensis (DEC) model for inferring historical biogeography. Presenting a series of presence absence matrices, transition matrices, and geographic pathways, Winger concluded that the out of the tropics theories that invoke a shift of the breeding range out of the tropics are poorly supported, and that the evolution of Neotropical migration in Emberizoids is consistent with the temperate home theories.
Jonathan Price, the University of Hawaii at Hilo, brought things down to a smaller scale with his talk, “Answering Big Questions with Small Landmasses: Evolutionary Biogeography from Atlantic and Pacific Archipelagos.” Price explained that island systems compared to continental systems can be rather simple (definable temporal and spatial constraints, relatively few species derived from original colonists), but can also be quite complex (wide array of climatic habitats, complex ecological interactions), making for an interesting study system in biogeography.
Price found similar species-area relationships and similar distributions of lineages in his comparison of the Marquesas, Societies, and Hawaii archipelagoes. Most lineages have only one species per archipelago, while a few lineages are very diverse. Those lineages that do not speciate in one archipelago do not speciate elsewhere, while those that speciate greatly in one archipelago do so in others. The species radiations are also much larger in larger archipelagoes.
Price spoke about the location where island colonists originate. For the Hawaiian archipelago, most colonists came from the Indo-Pacific. Three-quarters of Hawaiian colonists were from tropical regions, while one-third were from temperate. Many lineages also colonized other Pacific Islands after evolving in Hawaii. He also explained that major climatic adaptations are highly conserved, suggesting Hawaiian taxa are in habitats related to their area of origin: low elevation taxa have a tropical origin, while high elevation taxa are from temperate regions. He concluded that diversification is moderated by both physical constraints and ecological opportunity, but mostly in key lineages.
Brian Bowen, the Hawaii Institute of Marine Biology, switched things up with a marine focus during his talk, “Origins of Tropical Marine Biodiversity.” Bowen explained that the primary marine biodiversity hotspot is the Coral Triangle located between the Philippines, Indonesia, and New Guinea. Three hypotheses explain the existence of this hotspot: (1) intense competition forges new species with high fitness that radiate out (“center of speciation”); (2) speciation occurs at outer archipelagoes under ecological release and accumulate in the center of the range (“center of accumulation”); and (3) distinct Indian and Pacific faunas overlap at the border between both oceans (“center of overlap”).
Bowen continued to explain that populations do not have to be physically isolated to diverge and speciate. For example, sexual selection on the basis of vocal cues has promoted reproductive isolation among sympatric sister species of the Caribbean and East Pacific reef fishes called grunts (genus Haemulon).
He then provided examples of phylogeographic support for all three hypotheses that explain biodiversity hotspots. The evolution of West Pacific wrasses (Halichoeres) supports the hypothesis of speciation within a center of origin. The center of accumulation hypothesis is supported by the evolution of four derived species within the wrasse genus Thalassoma. Center of overlap is supported by the Indian Ocean lineage and the Pacific Ocean lineage of the peacock grouper. Whereas Hawaii was once thought as an evolutionary dead end for marine species, Bowen provided evidence that indicates Hawaii is both a recipient and a source of marine biodiversity.
Continuing on the global perspective theme of biogeography, Erica M. Goss from the University of Florida spoke about the spread of pathogens in the talk, “Untangling the Origin and Global Movement of Notorious Phytophthora Plant Pathogens.” Using population genetic data, Goss explained, it is possible to reconstruct global migration patterns of plant pathogens, which are moving at an unprecedented rate due to global trade.
Goss spoke about Phytophthora ramorum, a pathogen which was introduced into the western United States three independent times, once from Europe and twice from unknown sources. She provided a lengthy discussion about the migratory patterns of the potato late blight, P. infestans, a pathogen of Solanum species. In the 1840s, it migrated from South American to Europe. In the early 1900s, there were multiple migrations between the Americas and Europe. The divergence times of the multiple lineages can be traced using mtDNA genomes taken from herbarium samples.
Goss explained that a coalescent genealogy of the RAS locus indicates that the center of origin of P. infestans is the Andes Mountains; yet a multi-locus study shows support for a Mexico center of origin. She further explained that hybridization and introgression most likely play a role in the evolution of the pathogen resulting in either global diversification of the genus or the Andes acting as a sink for new species. Emerging pathogens are being discovered in both agricultural crops and in the wild.
Goss concluded with three working hypotheses for Phytophthora evolution: (1) allopatric speciation with historically dispersed limited soil and aquatic types; (2) sympatric speciation by aerial host-specific clades; and (3) speciation by micro-environment with clades showing a mixture of morphological characters.
The final talk of the day addressed how global climate change may impact biogeography of the future. Mauricio Diazgranados from the Department of Botany at Smithsonian’s National Museum of Natural History spoke on “Biogeography and Climate Change in the Andes.” After an introduction about the significance of the biodiversity of the Andes, Diazgranados gave an overview of global climate change. Current projections show that the temperatures in the tropical Andes will increase, while the northern Andes will experience increased precipitation and the southern Andes decreased precipitation. The effect on the paramos will be an upslope migration of the biological communities.
Diazgranados outlined five possible species responses to climate change: range shift, adaptation to altered habitat, expansion of habitat, contraction of habitat, and extinction/extirpation. Using the Espeletiinae (Compositae) as a case study, he spoke about how the distribution of these high-elevation plant species will be impacted by climate change. His species distribution modeling shows that of the 133 species examined, by the year 2080, 17 will experience extinction and 24 will have severe contraction in their range.
Diazgranados discussed limitations that impact these modeling scenarios. The first is the limited knowledge of species diversity: over 48 percent of Espeletiinae species are represented by fewer than 10 collections. He explained the difficulty in modeling with fewer than 10 collections. Secondly, the problem of scale affects how accurate species are modeled to habitat type. Another limitation is the accuracy of predictors: with over 6,000 reliable climate measuring stations worldwide, only 129 are in the Andes, leading to a deficiency of information.
Next he spoke about the uncertainty in future climate predictions where species responses differ between the climate change models. Narrowly distributed species pose another dilemma: 20 percent of Espeletiinae species have total areas of less than 4 km2. The sixth limitation Diazgranados presented was an issue of computing: the complete run of the 23 global climate change models on the 133 Espeletiinae species over 8 decades takes 1.9 terabytes of data with approximately 2 million files and over 24,000 maps. The final limitation discussed was measuring the various possible species responses to climate change.
Diazgranados concluded his talk with four take home messages: we need (1) much higher resolution of predictors; (2) more accurate information about soils and ecosystems; (3) better computing facilities; and (4) stronger efforts for geographers, geologists, climatologists, and soil scientists to work together.
Next year’s 13th Smithsonian Botanical Symposium will take place on Monday, June 1, 2015. It will be part of a larger five-day conference, “Next Generation Pteridology: An International Conference on Lycophyte and Fern Research.” The Smithsonian Botanical Symposium will open the conference as a one-day public event, followed by three days of focused scientific talks and workshops for pteridologists and other researchers. Field trips and garden tours will round out the conference. Be sure to check the symposium website for updates.