Global climate change is altering patterns of biodiversity by changing when and where species live. Species that hybridize with a related species at their geographic range boundary could be affected in new ways by climate change. Several outcomes are possible: the geographic range of both species could shift congruently with little change in hybridization, individual traits that are shared across the hybrid zone could shift while other traits remain stable, hybridization could fall apart as the species move independently, or there could be little change in hybridization patterns and species boundaries. The investigators will explore the effect of changing climatic conditions on hybridization patterns using two species of swallowtail butterfly. The zone of contact between these two species was studied in the past and the investigators will compare the historical data to modern samples. They will use a variety of genetic traits to make this comparison. In addition, experiments with hybrid crosses will test how individuals perform under winter warming, summer heat stress, and extreme winter cold, factors that have changed in the recent past.
This project is likely to become an example of how climate modifies patterns of genetic diversity. In conjunction with this project, the investigators will develop management recommendations for the conservation of species affected by climate change. Furthermore, students working on this project will participate in MSU's 'Bug House', a program that uses insects to introduce K-8 grade students to scientific concepts. Finally, all of the graduate students and postdocs working on this project will collaborate on a wiki that facilitates cross-institutional research.
Geographically extensive studies of a thermally-correlated hybrid zone between Papilio glaucus and P. canadensis (Eastern and Canadian Tiger Swallowtail butterflies) were made across the mid-west and New England states. These two species exhibit many important physiological, behavioral, and genetic differences, including larval host use and diapause induction (Mercader et al. 2009; Scriber 2010; Scriber and Sonke 2011; Scriber et al. 2012; Scriber and Lehnert 2012; Lehnert et al. 2012; Aardema and Scriber 2013; Scriber et al. 2014). We have recently documented increased movement of many, but not all species-diagnostic traits beyond the geographically historical hybrid zone (Scriber 2011). Patterns of hybridization may be quickly changing and that the species boundaries are becoming less defined by congruent patterns (geographic concordance) of species-specific diagnostic characters. These changes correlate (and may be directly caused by) regional climate warming in North America (Scriber 2010; Scriber et al 2014). Why some diagnostic traits should be moving, but not others, is not thoroughly understood, nor is it entirely clear what factors contribute to the maintenance of hybrid genotypes. Hybridization with genetic introgression between the two species has apparently generated a delayed post-diapause emergence of chromosomally-recombinant adults from the over-wintering pupae (Ording et al. 2010; Scriber 2011). This delayed emergence of hybrids results in immediate temporal reproductive isolation from both parental species, and may be the major driving force behind the hybrid speciation process that created the Mountain Swallowtail (P. appalachiensis) inside the hybrid zone (Ording et al. 2010; Scriber et al. 2011; Kunte et al. 2011). This hybrid speciation is not due to polyploidy (as in many plants), but due to homoploid chromosomal recombination (especially in the sex chromosomes). This group of tiger swallowtail butterflies represents one of the very first examples ever documented of "hybrid speciation" in animals (Scriber and Ording 2005; Scriber et al 2008; Kunte et al. 2011). Since our discovery, several additional cases have also been found to be likely. The general significance and implications of our research findings extends to conservation ecology as well as evolutionary theory. We have shown the hybridization is not an "evolutionary dead end", but may actually generate new genotypes and even new species. The use of hybrids and hybrid zones may become more important for genetic rescue of species in the face of rapid and extensive environmental changes such as climate change. Their value for may reside in the capacity they provide for enhanced genetic variation and the resultant capability they may contribute for rapid adaptations to abrupt and serious environmental disturbances (Aardema et al. 2011; Scriber 2014). References from our project: Mercader, RJ, M. Aardema, and JM Scriber. 2009. Hybridization leads to host use divergence in a polyphagous butterfly sibling species pair. Oecologia 158: 651-662. Ording, G.J., Mercader, R.J., Aardema, M.L. and Scriber, J.M. (2010). Allochronic isolation and incipient hybrid speciation in tiger swallowtail butterflies. Oecologia, 162, 523-531. Scriber, J.M. (2010) INVITED REVIEW: Integrating ancient patterns and current dynamics of insect-plant interactions: taxonomic and geographic latitude in herbivore specialization. Insect Science, 17: 471-507. Scriber, J.M. (2011) INVITED REVIEW: Impacts of climate warming on hybrid zone movement; Geographically diffuse and biologically porous "species borders" Insect Science, 18: 121-159. Aardema, M.L., Scriber, J.M. and Hellmann, J.J. 2011. Considering local adaptation in issues of Lepidopteran conservation- a review and recommendations. American Midland Naturalist. 165: 294-303. Scriber, J.M. and Sonke, B. 2011. Effects of diurnal temperature range on adult size and emergence times from diapausing pupae in Papilio glaucus and P. canadensis. Insect Science (special issue on the "Response of Insects to Global Change"). 18 (3): 435-442. Kunte K, Shea C, Aardema ML, Scriber JM, Junger TE, Gilbert LE and Kronforst MR, Sex chromosome mosaicism and hybrid speciation among tiger swallowtail butterflies. PLoS Genetics 7(9): e1002274. doi:10.1371/journal.pgen.1002274. (2011). Lehnert, M.S., Scriber J.M., Gerard P.D. and Emmel T.C., 2012. The "converse of Bergmann’s Rule" in tiger swallowtail butterflies; Boundaries of species and subspecies wing traits are independent of thermal and host-plant induction. American Entomologist, 58 (3): 156-165. Lehnert M. and Scriber JM, 2012. Salicaceae detoxification abilities in Florida swallowtail butterflies (Papilio glaucus maynardi Gauthier): Novel ability or Pleistocene holdover? Insect Science 19: 337-335. DOI: 10.1111/j.1744-7917.2011.01459.x Scriber, J.M.; Maher, E.; Aardema, M.L. 2012. Differential effects of short term winter thermal stress on diapausing tiger swallowtail butterflies (Papilio spp.). Insect Science. 19, 277–285. Aardema, M.L. and Scriber, J. M. 2013. No evidence the male mate choice contributes to maintenance of a shared, sex-limited trait in mimetic and non-mimetic female tiger swallowtail butterflies, Papilio glaucus. Evolutionary Biology 40: 108-116. DOI 10.1007/s11692-012-9190-7. Scriber, JM, Eliot, B, Maher, E., McGuire, M, Niblack, M. 2014. Adaptations to "Thermal Time" Constraints in Papilio: Latitudinal and Local Size Clines Differ in Response to Regional Climate Change. Open Access Insects, 5, 199-226; doi:10.3390/insects5010199. Scriber, J.M. 2014. Review: Climate-driven reshuffling of species and genes; potential conservation roles for species translocations and recombinant hybrid genotypes. Open Access Insects, 5, 1–61.
