DISSERTATION RESEARCH: Polyploidy and Reproductive Isolation in the North American Creosote Bush (Larrea tridentata, Zygophyllaceae)

许多植物既有二倍体个体（拥有两组染色体），也有多倍体个体（拥有四组或更多染色体）。相关的二倍体和多倍体植物很少被命名为不同的物种，部分原因是它们在自然界中杂交的可能性不确定。木馏油灌木是北美温暖沙漠的主要灌木，具有二倍体和多倍体两种种群。pi将评估这些种群杂交的能力。杂木油灌木非常适合这类研究，因为二倍体和多倍体种群在许多不同的地方接触，从而允许重复研究杂交水平。pi将使用实地研究和分子实验室技术来评估以下可能对杂交的影响：a)二倍体和多倍体在不同环境中发生的趋势，b)二倍体和多倍体在一年中的不同时间繁殖的趋势，以及c)自然发生的三倍体和五倍体杂种的繁殖成功率。将计算这些繁殖障碍的倍增效应。如果杂交的障碍很强，二倍体和多倍体可以成为不同的物种。如果有强有力的证据表明二倍体和多倍体种群不能杂交，那么许多同时具有二倍体和多倍体的其他物种将需要重新评估；这些结果可能会导致一个结论，即温带地区的植物物种多样性远比目前认为的要大。本科生将在现场和实验室参与拟议研究的所有部分。pi希望给予两名本科生在参与研究的基础上完成高级论文的机会。

Many plant species have both diploid individuals (possessing two sets of chromosomes) and polyploid individuals (possessing four or more sets). Related diploid and polyploid plants are rarely named as different species, in part due to uncertainty about their potential for interbreeding in nature. Creosote bush, a dominant shrub of North American warm deserts, has both diploid and polyploid populations. The PIs will evaluate the ability of these populations to interbreed. Creosote bushes are excellent for such studies because the diploid and polyploid populations come in contact at many different locations, thus allowing replicated studies of the level of interbreeding. The PIs will use field studies and molecular laboratory techniques to evaluate the following possible influences on interbreeding: a) the tendency of diploids and polyploids to occur in different environments, b) the tendency of diploids and polyploids to reproduce at different times of the year, and c) the reproductive success of naturally-occurring triploid and pentaploid hybrids. The multiplicative effects of these reproductive barriers will be calculated. If the barriers to interbreeding are strong, a case can be made for diploids and polyploids being distinct species.If there is strong evidence that diploid and polyploid populations are unable to interbreed, the many other species that have both diploids and polyploids will need to be re-evaluated; these results could potentially lead to a conclusion that plant species diversity in temperate regions is far greater than currently believed. Undergraduates will be involved in all parts of the proposed research in the field and laboratory. The PIs expect to give two undergraduates the opportunity to complete senior theses based on their involvement in the research.