Adam Porter Associate Professor
Education Ph.D. 1989, University of California - Davis Specialties Genetics & Ecology of Species Boundaries I am a population geneticist interested in how evolution works at the population, subspecies and species levels. My subjects of study are often butterflies. I combine a breadth of approaches that include field ecology, laboratory experiments, molecular population genetics, statistical theory, computer simulation and mathematical modeling. The field and laboratory experiments tell us about the ecological processes that create selection and adaptation to local conditions, and about the movements of different genotypes from place to place. The laboratory genetics tells us about the ability of genes to spread among populations, and about the genetic contribution to the phenotype. The statistical theory allows us to test hypotheses, and put both numerical values and estimates of error onto the processes we are interested in. The mathematical modeling and computer simulation allow us to figure out what processes are likely to be most important to measure in the first place, and computer simulation allows us to test the logic of these ideas when the explanations get particularly complex. My research program deals with evolutionary genetics in four major ways: Introgression and species boundaries: Species under the biological species concept are often defined as being unable to share genes. In practice, this is a very difficult thing to measure and we usually rely on morphological and behavioral traits (and a liberal dose of opinion) to distinguish species. I study genetic patterns at the boundary between species in an effort to measure of the rate at which genes are exchanged across such a boundary. If negligible, it indicates that the species are evolving independently and are 'good species' under the biological species concept's definition. If the rate is not negligible, then then the species are not evolving independently, and adaptations can readily spread between them. Such species will need to be treated together when managing their evolution and when making inferences about how their traits have evolved. An especially interesting corollary of this work is that 'diagnostic' traits used by systematists to recognize species can sometimes be adaptations to local ecological conditions. These can be maintained by natural selection even under the homogenizing influence of gene flow, and much of the remainder of the genome may be shared. Species boundaries may be studied from two ecological contexts. The first is when geographic ranges of the species are adjacent, whereupon hybridization is spatially limited and occurs in hybrid zones. Examples of studies on this situation include Porter et al. (1997), Porter (1997), and Porter & Geiger (1995, 1988). Mark Scriber and I are currently working on this problem in the tiger swallowtail butterfly hybrid zone between Papilio glaucus and Papilio canadensis, where a consicerable proportion of the diagnostic traits are linked to the X and Y chromosomes. The second is when species are sympatric, whereupon hybridization occurs throughout the geographic range. Examples of this include Porter & Ribi (1994) and Ribi & Porter (1995). I am currently doing theoretical work on this problem, using F-statistics to measure rates of introgression and gene flow in an extension of the work in Porter (1990) and Porter & Geiger (1995, 1988). My student, Baiqing Wang, and I are applying this to the study of introgression between two sympatric Colias butterflies, Colias eurytheme and Colias philodice, that are economic pests of forage legume crops, particularly alfalfa and clover. Their hybridization indicates that adaptations conferring advantages to these crop habitats may readily spread between the species, and indicates they should perhaps be treated ecologically as a single species by pest management protocols. We are genearating high-resolution AFLP maps of the genome to study this interesting problem in the detail it deserves. The management of insecticide resistance: Colorado potato beetles are major pests of potato and eggplant crops worldwide, in no small part because they have evolved resistance to most of the pesticides that have been used against them. Mitch Baker, Dave Ferro, Andrei Alyokhin and I are applying mathematical models of non-equilibrium evolutionary dynamics to study evolutionary shifts in resistance that we induce experimentally in natural Colorado potato beetle populations. From these shifts, we are estimating the rate that resistance spreads and the costs to being a resistant insect in a field that has not been treated with insecticide. Our goal is to figure out the set of field conditions that will be least conducive to the spread of resistance in the potato beetle population. We can then manage against the spread of insecticide resistance by planting crops in a way that mimics these conditions. And, the methods we are inventing forthis study will be applicable to the control of resistance in a variety of pest species. While we don't expect to be able to fully stop the evolution and spread of resistance, slowing its spread will ultimately reduce the amount of pesticide in the environment and save a lot of money along the way. Speciation and the evolution of regulatory genetic pathways: Hybrids between species often die or are infertile, and it has been known since the late 1930s that this is caused by pairs of genes in the two species that interact in incompatible ways. Most evolutionary theory deals with genes on an individual basis and not as much attention is paid to the interactoins among different genes. but, in real organisms, it is virtually impossible to think of a gene that does not interact with other genes, either directly or through the interactions among their gene products. This is especially true of genes that regulate one another such as during the development from egg through the embryo to the adult. Norman Johnson and I have been modeling phenotypes that are constructed using gene interactions alone, and looking at the evolutionary consequences. One major consequence is that gene interactions evolving in separate, replicate populations lead directly to the disruption of hybrid phenotypes (Jonhson & Porter 2000) -- essentially, they lead to speciation. We've shown that this can occur, though less frequently, even when there are very high rates of gene flow between the evolving populations (Porter & Johnson 2002). Since most 'real' phenotypes are generated through regulatory genetic interactions, we argue that microevolutionary changes of gene regulatory systems are likely to be at the heart of adaptation and speciation (Johnson & Porter 2001). Conservation genetics: Species with small, spatially separated populations, especially those of concern to conservation biologists, are exposed to evolutionary conditions that have not been well studied by evolutionary biologists. I have been using computer simulation and mathematical modeling to address the evolution of such populations. One interesting case (Porter, 1999) occurs during habitat loss when individuals can flee and become established in sites that remain. These refugees carry their genes and cause two effects. First, genetic variation within sites increases and populations are more able to adapt to ecological changes and survive the effects of inbreeding. Second, genetic variation among sites decreases due to this homogenizing effect. This Conservation of butterflies: As butterfly biologist, I am especially concerned about the loss of rare species or locally adapted populations. To manage for the survival of such populations, we need to know those critical aspects of their natural history and ecology that cause their populations to be so limited. My student, Makiri Sei, is working out these problems in the Maritime Ringlet butterfly, Coenonympha tullia nipisiquit, confined to a few intertidal salt marshes in eastern maritime Canada. The young caterpillars live best in protected intertidal regions that entirely flood with seawater at high tide (Sei & Porter 2002). Care to join the lab? I think that some of the problems that have been especially difficult to solve in entomology and evolutionary biology will eventually fall when we can study them simultaneously from more than one research perspective (whether field work, lab experiments, molecular genetic analyses, computer simulation, or statistical and mathematical modeling). I am interested in advising graduate students who share this viewpoint and want to make a career out of tackling and solving some of these truly interesting problems. Selected Publications Porter, A.H. 2003. A test for deviation from island-model population structure. Molecular Ecology 12:903-916. Sei, M., & A. H. Porter. 2003. Microhabitat-specific early larval survival of the maritime ringlet (Coenonympha tullia nipisiquit, Nymphalidae, Lepidoptera). Animal Conservation 6:55-61. Porter, A. H., & N. A. Johnson. 2002. Speciation despite gene flow when developmental pathways evolve. Evolution 56:2103-2111. Johnson, N. A. & A. H. Porter. 2001. Toward a new synthesis: Population genetics and evolutionary developmental biology. Genetica 112-113: 45-58. Johnson, N. A. & A. H. Porter. 2000. Rapid speciation via parallel, directional selection on regulatory genetic pathways. Journal of Theoretical Biology 205: 527-542. Porter, A. H. 1999. Refugees from lost habitat and reorganization of genetic population structure. Conservation Biology 13: 850-859. Porter, A.H., & J. C. Mueller. 1998. Partial genetic isolation between Phyciodes tharos and P. cocyta (Nymphalidae). Journal of the Lepidopterists' Society 52: 182-205. Porter, A. H., R. Wenger, H. J. Geiger, A. Scholl, & A. M. Shapiro. 1997. The Pontia daplidice-edusa hybrid zone in northwestern Italy. Evolution 52: 1561-1573. Porter, A. H. 1997. The Pieris napi/bryoniae hybrid zone at Pont de Nant, Switzerland: broad overlap in the range of suitable host plants. Ecological Entomology 22: 189-196. Porter, A. H. & H. J. Geiger. 1995. Limitations to the inference of gene flow at regional geographic scales - an example from the Pieris napi group (Lepidoptera: Pieridae) in Europe. Biological Journal of the Linnean Society 54: 329-348. Ribi, G. & A. Porter. 1995. Mating between two hybridizing species, Viviparus ater and V. contectus (Mollusca: Prosobranchia). Animal Behaviour 49: 1389-1398. Porter, A. H., & G. Ribi. 1994. Population genetics of Viviparus (Mollusca: Prosobranchia): homogeneity of V. ater and apparent introgression into V. contectus. Heredity 73: 170-176. Porter, A. H. 1990. Testing nominal species boundaries using gene flow statistics: the taxonomy of two hybridizing admiral butterflies (Limenitis; Nymphalidae). Systematic Zoology 39: 131-148.
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