Western North American Naturalist Volume 70 Number 3 Article 10 10-11-2010 Reproductive biology, hybridization, and flower visitors of rare Sclerocactus taxa in Utah's Uintah Basin Vincent J. Tepedino Utah State University, Logan, [email protected] Terry L. Griswold Utah State University, Logan, [email protected] William R. Bowlin Utah State University, Logan Follow this and additional works at: https://scholarsarchive.byu.edu/wnan Recommended Citation Tepedino, Vincent J.; Griswold, Terry L.; and Bowlin, William R. (2010) "Reproductive biology, hybridization, and flower visitors of rare Sclerocactus taxa in Utah's Uintah Basin," Western North American Naturalist: Vol. 70 : No. 3 , Article 10. Available at: https://scholarsarchive.byu.edu/wnan/vol70/iss3/10 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 70(3), © 2010, pp. 377–386 REPRODUCTIVE BIOLOGY, HYBRIDIZATION, AND FLOWER VISITORS OF RARE SCLEROCACTUS TAXA IN UTAH’S UINTAH BASIN Vincent J. Tepedino1,2, Terry L. Griswold1, and William R. Bowlin1,3 ABSTRACT.—We studied the mating system and flower visitors of 2 threatened species of Sclerocactus (Cactaceae) in the Uintah Basin of eastern Utah—an area undergoing rapid energy development. We found that both S. wetlandicus and S. brevispinus are predominantly outcrossed and are essentially self-incompatible. A third presumptive taxon (unde- scribed; here called S. wetlandicus-var1) is fully self-compatible but cannot produce seeds unless the flowers are visited by pollinators. We found tentative evidence for pollinator limitation of fruit set in S. brevispinus but not in the other taxa. Pollinators are largely species of native ground-nesting bees in the subfamily Halictinae. These bees are indiscrimi- nate collectors of pollen and nectar from Sclerocactus flowers and other plant species. The well-being of Sclerocactus populations requires that land managers ensure the preservation of halictid bee habitat, which includes both nesting sites and a diversity of floral resources. These bees are also undoubtedly the pollen vectors responsible for the produc- tion of hybrids in areas where S. wetlandicus and S. brevispinus meet. We experimentally confirmed that reciprocal crosses between S. wetlandicus and S. brevispinus are indistinguishable from each other or from pure crosses in fruits/flower, seeds/fruit and seed weights. We suggest that hybridization preceded energy development, that it attests to the ongoing process of evolution in the Sclerocactus group, and that it should not be suppressed by anthropogenic activity. Key words: Sclerocactus, pollination, breeding system, native bees, hybridization, conservation, Cactaceae. The Uintah Basin of eastern Utah is cur- complicate matters further, Welsh et al. (2008) rently undergoing considerable habitat modifi- refer to earlier treatments of Sclerocactus as cation due to energy development (oil and gas “amateurish and essentially worthless” and rec- drilling, with oil shale extraction a future pos- ognize only 3 species in Utah, compared to 7 by sibility; Federal Register 2007). Habitat modi- Heil and Porter (2003) and 6 by Hochstätter fication removes extant plants and prospective (2005). sites for recruits, posing both direct and indi- Of especial interest here are 3 closely rect problems for plants. Habitat destruction related taxa (Heil and Porter 2003): S. glaucus also lengthens the distance between popula- (K. Schumann) L.D. Benson, in western Colo - tions, thereby isolating them and lowering the rado and in eastern Utah; S. wetlandicus likelihood that they will maintain or increase Hochstätter; and S. brevispinus K.D. Heil & their genetic variation by crossing with plants J.M. Porter (called S. wetlandicus var. ilseae by from other populations. The nesting habitat of Hochstätter [2005]). This systematic treatment potential pollinators is also removed as are alter - by Heil and Porter (2003) is supported by re- nate sources of pollen and nectar which may cent studies of chloroplast DNA, AFLPs, and succor pollinators when their usual host plants morphology (Porter et al. 2007). In contrast, are scant or absent. Welsh et al. (2008) recognize glaucus and Among the taxa threatened by this energy de- ilseae as varieties of S. whipplei and subsume velopment are members of the genus Sclero- wetlandicus as a misnomer under glaucus. All cactus (Cactaceae), a group of barrel cacti entities are rare; indeed, they are listed to - restricted to western North America. The sys- gether as threatened under the Endangered tematics of this genus is somewhat unsettled. Species Act under their former designation, S. The most recent revisions (Heil and Porter 2003, glaucus. Hochstätter 2005) differ in the number of rec- The rarity of these taxa, coupled with the ognized species (15 and 10, respectively; Porter burgeoning energy development in their habi- et al. [2007] put the present number at 22). To tat calls for a better understanding of their 1Bee Biology and Systematics Laboratory, USDA–ARS, Department of Biology Utah State University, Logan, UT 84322-5310. 2E-mail: [email protected] 3Present address: 2380 East 11000 North, Richmond UT 84333. 377 378 WESTERN NORTH AMERICAN NATURALIST [Volume 70 TABLE 1. Results of mating system experiments on 3 Sclerocactus taxa. Treatments: X = xenogamy, G = geitonogamy, A = autogamy, C = open-pollinated control, N = number of plants with flowers receiving treatments, F = number of fruits set, Ns = Number of fruits used to obtain seed number and weight. S/F = mean seeds per fruit, SW = average seed weight (g), SE = standard error. Within each taxa, differing letters for F, S/F, and S/W indicate significant differ- ences (P < 0.01; χ2 and Kruskal-Wallis tests, respectively). –3 –4 Taxon Treatment n F S/F SE SW 10 SE 10 Ns S. wetlandicus 1990 X 18 15 a 33.9 a 4.4 — — 15 G 18 4 b 17.0 a,b 7.5 — — 4 A 36 4 b 8.3 b 3.2 — — 4 C 19 12 a 28.1 a 5.5 — — 11 S. wetlandicus 2008 X 12 11 a 35.5 a 3.2 3.7 a 2.7 11 A 13 0 b — — — — 0 C 9 9 a 27.4 a 4.0 5.1 b 2.5 9 S. wetlandicus – var 1 2008 X 10 7 a 26.0 a,b 5.0 3.2 a 2.7 7 G 9 8 a 10.9 b 4.5 3.3 a 3.3 7 A 11 1 b — — — — 0 C 10 7 a 34.1 a 5.4 3.8 a 1.7 7 S. brevispinus 2008 X 19 19 a 22.8 a 2.1 4.9 a 2.7 19 G 18 5 c 5.0 b 1.7 5.2 a 1.7 5 A 18 0 c — — — — 0 C 19 13 b 21.7 a 2.8 4.7 a 1.2 13 S. brevispinus Ɋ × S. wetlandicus ɉ 2008 5 4 26.5 8.2 4.9 2.5 4 S. wetlandicus Ɋ × S. brevispinus ɉ 2008 14 14 37.5 4.4 3.4 2.3 13 reproduction and systematics. The majority of Porter 2003, Lambert et al. 2006, Reyes-Aguero flowering plants, including cacti (Grant and et al. 2006). Grant 1979), depend on animals, especially Here we describe the breeding systems of insects, to effect seed production by carrying S. brevispinus and S. wetlandicus, identify the pollen to receptive stigmas (Axelrod 1960, Rick- common insect visitors to the flowers, and report lefs and Renner 1994). Currently, no information results of preliminary reciprocal hybridization exists on the breeding system or compatibility experiments. For each taxon, we ask the follow- traits of any Sclerocactus species (contra Boyle ing questions: (1) Is seed production dependent 1997, which is in error). Information on poten- on pollinator visitation to the flowers? (2) Can tial pollinators is also absent. ovules be fertilized by self-pollen (i.e., are the Experimental evidence on the cross-com- taxa self-compatible)? (3) Is there any evidence patibility of these Sclerocactus taxa is especially that seed production is limited by insufficient important because of the implications for con- pollinators? (4) What are the common flower servation (Rieseberg 1991, Ellstrand and Elam visitors and are they shared by both taxa? (5) 1993, Rhymer and Simberloff 1996). Heil and Are the taxa capable of hybridization, and if Porter (2003) reported that S. brevispinus hy - so, is hybridization symmetrical? Such informa- bridizes freely with S. wetlandicus along “a well- tion should help guide policies for the effec- documented cline.” If hybridization can occur, tive conservation of these taxa. as it does for many other taxa in the Cactaceae Finally, we also apply questions 1–4 to a (Griffith 2003), then an additional threat appears: presumptive third taxon of Sclerocactus cur- the genetic integrity of S. brevispinus is at risk rently under study in the Uintah Basin, which of being compromised through swamping by we provisionally call “wetlandicus-var1.” This the more widespread S. wetlandicus (Heil and isolated population occurs over several square 2010] POLLINATION OF RARE UINTAH BASIN SCLEROCACTUS 379 miles to the northeast of S. wetlandicus sensu serve as a natural pollination control. Mature stricto. It can be separated from other S. wet- fruits were collected and filled seeds were landicus by its consistently greater width-to- counted; shriveled, misshapen seeds were re - height ratio, flattened apex, and increased corded but were excluded from the subsequent tendency to form multiple heads. In these char - analysis. After seeds air-dried for several months, acteristics (and others), it resembles S. brev - weight of total seeds per fruit was determined ispinus more than typical S.