Hybridization via long-distance pollen dispersal explains the occurrence of endemic () across the Southern Rockies

Ross A. McCauley, Shilah Allen, Meredith Breeden, Melanie Weber-Sauer Fort Lewis College, Department of Biology, Durango, Colorado, USA

Introduction In 2011 a new species of Ipomopsis, I. ramosa Schneider & Bregar was described from two adjacent small canyons at the western end of the San Juan Mountains in southwestern Colorado (Schnieder & Bregar, 2011). The species is one of three rare and highly restricted species of Ipomopsis at the southern end of the Rocky Mountains. These include I. sancti- spiritus Wilken & Fletcher occurring along 3 miles of a single canyon at the southern end of Ipomopsis polyantha the Sangre de Cristo range in north-central New Mexico (USFWS, 2002; Wilken & Photo © USFWS Fletcher,1988) and I. polyantha (Rydberg) V. Grant occurring on degraded shale soils within a range of approximately 6.5 square miles around the town of Pagosa Springs in southwestern Colorado (USFWS, 2011). All three species share an affinity with the widespread I. aggregata (Pursh) V. Grant and occur sympatrically with it although no indication of hybridization has ever been noted. All three species are ranked as G1 (Critically Imperiled) and both I. sancti-spiritus and I. polyantha are federally listed as endangered Ipomopsis ramosa species.

As part of work to further our knowledge of the evolutionary history of the newly described I. Ipomopsis aggregata Photo © Al Schneider ramosa we investigated its phylogenetic position within the genus. When combined with Ipomopsis sancti-spiritus newly discovered field observations on the pollination biology of I. ramosa we have Photo © Robert Sivinski discovered a plausible explanation for the occurrence of these three rare Ipomopsis species.

Materials & Methods Results & Discussion

I. ramosa field observations Field plots were established in early spring 2014 in an area with high I. ramosa density and pollinator visitation was determined by direct observation of at various times of day during the extent of the flowering period from May through August. Only insects were observed visiting the and were collected for later identification.

Potential for cross-pollination between I. ramosa and sympatric I. aggregata was assessed using florescent dye powder as a pollen analogue.

Laboratory studies DNA from I. ramosa and sympatric I. aggregata was extracted and amplified for both the nrITS and the chloroplast trnL-trnF regions.

Phylogenetic relationships were evaluated using sequence data from Porter et al. (2010) with trees constructed using parsimony in Mesquite ver. 3.02.

a) Literature Cited

Collins, C. 1995. The natural history and reproductive biology of the Pagosa , Ipomopsis polyantha (Rydberg) V. Grant var. polyantha (Polemoniaceae). M.A. Thesis. California State University, Fullerton. Figure 1. nr ITS consensus tree Figure 2. trnL-trnF consensus tree Grant, V. and K. A. Grant. 1965. pollination in the family. Columbia University Press, New York. Paige, K. N. and T. G. Whitham. 1985. Individual and population shifts in flower color by scarlet gilia: a mechanism for pollinator tracking. Phylogenetic placement of the three endemic Ipomopsis differed between nuclear and chloroplast data with ITS showing Science 227: 315-317. Porter, J. M., L. A. Johnson and D. Wilken. 2010. Phylogenetic systematics of Ipomopsis (Polemoniaceeae): Relationships and divergence a well-supported clustering of the three species. Chloroplast data showed differing sister groups with both I. polyantha and I. times estimated from chloroplast and nuclear DNA sequences. Systematic Botany 35: 181-200. sancti-spritus showing an affinity to I. multiflora (Nutt.) V.E. Grant. Ipomopsis ramosa was most closely related to sympatric Schnieder, A. and J. Bregar. 2011. Ipomopsis ramosa (Polemoniaceae), a new species for southwestern Colorado. Phytoneuron 45:1-11. U.S. Fish and Wildlife Service. 2002. Holy Ghost Ipomopsis (Ipomopsis sancti-spiritus) Recovery Plan. U.S. Fish and Wildlife Service, I. aggregata. Albuquerque, New Mexico. U.S. Fish and Wildlife Service. 2011. Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Ipomopsis Pollination studies of I. ramosa identified two main pollinators: the migratory Western Tiger polyantha (Pagosa Skyrocket) and Threatened Status for Penstemon debilis (Parachute Beardtongue) and Phacelia submutica (DeBeque Phacelia). Federal Register 76: 45054-45075. Swallowtail (Papilio rutulus) which visits early in the season and the Hummingbird Moth (Hyles Wilken, D. H. and R. Fletcher. 1988. Ipomopsis sancti-spiritus (Polemoniaceae), a new species from northern New Mexico. Brittonia 40: 48- lineata) later in the season. Minimal cross-pollination was observed between I. ramosa and 51. sympatric I. aggregata likely prevented by differing floral morphology. Wolf, P. G., P. S. Soltis, and D. E. Soltis. 1991. Genetic relationships and patterns of allozymic divergence in the Ipomopsis aggregata complex and related species (Polemoniaceae). American Journal of Botany 78: 515-526. The genetic patterns of relationship, small range sizes, and potential for pollinator service by a wide ranging insect species point to long-distance pollen dispersal leading to rare hybridization events giving rise to morphologically distinct and geographically isolated hybrid-derived taxa. Papilio rutulus visiting I. Acknowledgements ramosa We propose a common mechanism of recent hybridization leading to isolated neoendemics for the evolution of the We would like to thank the Fort Lewis College Undergraduate Student Research, Scholarly and Creative Activities Southern Rockies narrow-endemic Ipomopsis. Previous studies have proposed a relictual origin (Collins, 1995 – for I. grant program and the San Juan/Four Corners Native Society for providing funding for this project. M.B. polyantha) or recent origin via hybridization (Wolf et al., 1991 – for I. sancti-spiritus). Hybridization we feel is the most would like to thank the Botanical Society of America for additional support through the Undergraduate Student plausible mechanism. Ipomopsis is well-known for its ability to hybridize and the I. aggregata complex can exhibit large Research Award program. We would also like to thank the Dolores Ranger District of the San Juan National Forest for granting permission for the establishment of a research site for I. ramosa under permit number floral variation among closely related species (Grant & Grant, 1965) and even floral color variation in response to pollinator DOL271. preference within individual populations (Paige & Whithan, 1985).