Santa Cruz Island Reserve

26 May, 03 AM - 28 May, 10 AM

Title: A comparative evaluation of dispersal barriers using flightless weevils Trigonoscuta Project Location and Duration: I plan to collect weevils from sand dunes of Imperial and San Bernardino Co. California as well as dune locations on the Channel Islands of Southern California. The duration of field activity is one month in total. The remaining lab work will be completed in the following year and a half. Objectives: I propose to investigate island insularity using dune-restricted weevils. I will measure rates of migration between populations in continental and oceanic island settings. This will let me identify the ways in which the surrounding habitats act as barriers. Introduction: The use of islands as natural laboratories to study evolution dates back to at least the days of Wallace and Darwin. Island systems have been indispensable in understanding the processes generating biodiversity. Examples from the Galapagos, Caribbean and Hawaiian archipelagos demonstrate utility of islands for the study of adaptation, community assembly, and speciation (Gillespie 2004, Losos et al. 2003, Grant & Grant 2002). In addition to what one might traditionally consider islands, habitat islands are also of great interest to evolutionary biologists studying many of the same questions (Carstens & Knowles 2007, Vandergast et al. 2004, Masta 2000, Wake 1987). Unlike true oceanic islands, habitat islands are discrete patches of habitat surrounded by a contrasting habitat that acts as a barrier and is likely to change through time (Whittaker & Fernandez-Palacios 2006). Barriers between the different habitats may be more or less stringent for some taxa. This is a notable difference from water-bound islands, as the rules governing dispersal and vicariance may not be the same for oceanic and habitat islands. A study of habitat island system in the desert southwest of North America will elucidate the ways in which dispersal and vicariance operate in this unique island-like system. Study system: The weevil genus Trigonoscuta (Coleoptera: Curculionidae: Entiminae) has a distribution that covers Californian coastal dunes as well the dunes of the Mojave and Sonoran deserts. In addition, each one of the California Channel Islands has its own endemic species. Trigonoscuta is highly restricted to sand dunes, feeding on a variety of dune plants. All the members of this genus are entirely flightless. Larvae and adults bury themselves under the sand during the day and are surface active during the night. Currently there is no phylogeny for this group. Most Trigonoscuta are known from only one sand dune system and most species are allopatric (Pierce 1975). This suggests a link between the geologic history and the formation of these species. Pierce posthumously published the most recent revision in 1975. Some authors have questioned the validity of the species that he described (Anderson 2000). I am combining my study of molecular phylogenetic relationships with morphological work being done by Dr. Charles O?Brien. This approach will result in a more robust examination of the group than relying on either morphological or molecular analyses alone. Trigonoscuta are distributed in several different island settings, which allows for comparisons of insularity between dune systems. There are eight Channel Islands off the coast of California. The four Northern most islands are hypothesized not to have been connected to the California mainland within the last 18,000 years, but were interconnected to one another forming one large island (Schoenherr et al. 1999). The islands vary in size from small rocky islands a mile in area to large islands with an area of ~90 square miles. They are also varying distances from the mainland varying from 13 to 61 miles. These geographical differences allows for examining a variety of island effects on their inhabitants. Hypothesis: If desert sand dunes represent islands of habitats they will have similar levels of migration between populations. However if they should display levels of migration significantly above or below those seen in oceanic islands then we would conclude that barriers to migration are strongly dependent on the surrounding habitat. Methods: Phylogenetic analysis: In order to make appropriate comparisons of migration rates I will need to first find the relationships between the different populations. I propose to construct a phylogeny based on DNA sequence data from several independent nuclear loci as well as several mitochondrial loci, in addition to morphological characters. Sequence alignment will be preformed in MUSCLE and checked by eye (Edgar 2004). Tests for the models of molecular evolution will be done in MrModeltest using the AIC criterion for model selection. I will conduct a partitioned Bayesian phylogenetic analysis in MrBayes v. 3.1.2. (Hulsenbeck and Ronquist 2001). Population Genetics: In order to test hypotheses of migration between dune systems I will need to first gather some initial information from the sequence data to be used in further test. Haplotype Reconstruction; The identification of single nucleotide polymorphisms (SNPs) can be done in the program PolyPhred (Nickerson et al. 1997, Brumfield et al. 2003). Recombination is tested for using the four gamete test (Hudson and Kaplan 1985). This is accomplished in the program SITES (Hey and Wakeley 1997). After estimating the number of recombination events per locus, independently sorting fragments will be used in further analysis. Measuring Migration; The information from the process above will be used to estimate population genetic parameters using the model of Isolation with Migration IM (Hey and Nielson, 2004). This model will estimate population parameters between two populations. The parameters measured are the divergence time (t) the migration rates between the two populations (m1 & m2) and the effective population size of the two populations in question and the ancestral population. Anticipated Results: It is likely that there will be similar rates of migration and divergence times between the Northern Channel Islands and desert sand dunes. Historically these island systems have experienced similar conditions where the barriers separating them have been lowered. For example the conditions in the Pleistocene were cooler, possible allowing dispersal between desert dunes. At the same time the Northern Channel Islands were connected possible allowing for migration between dunes. However we may also find that certain dunes have experience little if any migration and reflect rates similar to islands that have never had a land bridge between them. For instance there are many dune-endemic species of insects in desert dunes. Hardy and Andrews (1976) found that the sand dunes of Southern California contain 42.6% dune restricted species of Coleoptera. Many of the other animals and plants that inhabit dunes are also highly restricted to them. With this high degree of restriction it appears that sand dunes are an island-like environment. Conclusion: Gaining an understanding of levels of isolation will help in having a broader understanding of speciation. In addition we will have a metric by which we can evaluate the degree to which habitats act as islands. This will give us a better appreciation how insular dunes systems are. This information could change the way in which people view these isolated habitats. Bringing with it a gained appreciation for dunes as islands and a rethinking of their priority for conservation efforts. Anderson, R.S. 2002. Chapter 125. Nemonychidae. pp. 692-694 In Arnett, R.H. Jr., Thomas, M.C. and Skelley, P. (eds.) American Beetles Volume 2. CRC Press.
 Brumfield, R. T., P. Beerli, D. A. Nickerson, and S. V. Edwards. 2003. The utility of single nucleotide polymorphisms in inferences of population history. Trends Ecol. Evol. 18:249-256. Carstens B. C. and Knowles L.L. 2007. Shifting distributions and speciation: species divergence during rapid climate change. Molecular Ecology 16: 619-627 Edgar, R.C. 2004 MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Research, 2004, Vol. 32, No. 5 1792-1797. Gillespie R. 2004. Community Assembly Through Adaptive Radiation in Hawaiian Spiders. Science 303:356-359 Grant P. R. and Grant B. R. 2002. Unpredictable evolution in a 30-year study of Darwin's finches. Science. 296: 707-711 Hardy, A. R., and F. G. Andrews. 1976. A final report to the office of endangered species on contract 14-16-0008-966. California Department of Food and Agriculture, Insect Taxonomy Laboratory, Sacramento, CA. Hey, J., and J. Wakeley. 1997. A coalescent estimator of the population recombination rate. Genetics 145:833-846. Hey, J., and R. Nielsen. 2004. Multilocus methods for estimating population sizes, migration rates and divergence time, with applications to the divergence of Drosophila pseudoobscura and D. persimilis. Genetics 167:747?760. Huelsenbeck, J. P. and Ronquist, F. 2001 MRBAYES: Bayesian inference of phylogenetic trees. Bioinformatics 17: 754-755. Losos, J. B.?, M. Leal?, R. E. Glor?, K. de Queiroz?, P. E. Hertz?, L. Rodr?guez Schettino?, A. Chamizo Lara?, T. R. Jackman?, and A. Larson. 2003. Niche lability in the evolution of a Caribbean lizard community. Nature 424:542-545 Masta S. E. 2000. Phylogeography of the jumping spider Habronattus pugillis (Araneae: Salticidae): Recent vicariance of sky island populations? Evolution 54(5): 1699-1711 Nickerson, D. A., V. O. Tobe, and S. L. Taylor. 1997. PolyPhred: Automating the detection and genotyping of single nucleotide substitutions using fluorescence-based resequencing. Nucleic Acids Res. 25:2745-2751. Schoenherr, A.A., Feldmeth, C.R., and Emerson M.J. 1999 Natural History of the Islands of California. University of California Press Van Dam A. and Van Dam M. 2008. Impact of off road vehicle use on Scarabaeidae species in the Algodones Sand Dunes, Annals of the American Entomological Society. Ann. Entomol. Soc. Am. 101(2): 411-417 Vandergast, A.G., R.G. Gillespie and G.K. Roderick. 2004. Influences of volcanic activity on the population genetic structure of Hawaiian Tetragnatha spiders: fragmentation, rapid population growth and the potential for accelerated evolution. Molecular Ecology 13:1729-1743 Wake, D. B. 1987. Adaptive radiation of salamanders in Middle American cloud forests. Ann. Missouri Bot. Gard. 74:242-264. Whittaker, R. J. & Ferna?ndez-Palacios, J. M. 2006 Island biogeography: ecology, evolution, and conservation, 2nd edn. Oxford, UK: Oxford University Press.

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Under Project # 20022 | Research

A comparative evaluation of dispersal barriers using flightless weevils Trigonoscuta

graduate_student - University of California, Berkeley

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Matthew Van Dam May 26 - 28, 2009 (3 days)

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