Reproductive ecology of a parasitic plant differs by host species: vector interactions and the maintenance of host races
- 445 Downloads
Parasitic plants often attack multiple host species with unique defenses, physiology, and ecology. Reproductive phenology and vectors of parasitic plant genes (pollinators and dispersers) can contribute to or erode reproductive isolation of populations infecting different host species. We asked whether desert mistletoe, Phoradendron californicum (Santalaceae tribe Visceae syn. Viscaceae), differs ecologically across its dominant leguminous hosts in ways affecting reproductive isolation. Parasite flowering phenology on one host species (velvet mesquite, Prosopis velutina) differed significantly from that on four others, and phenology was not predicted by host species phenology or host individual. Comparing mistletoe populations on mesquite and another common host species (catclaw acacia, Senegalia greggii) for which genetically distinct host races are known, we tested for differences in interactions with vectors by quantifying pollinator visitation, reward production, pollen receipt, and fruit consumption. Mistletoes on mesquite produced more pollinator rewards per flower (1.86 times the nectar and 1.92 times the pollen) and received ~ 2 more pollen grains per flower than those on acacia. Mistletoes on the two host species interacted with distinct but overlapping pollinator communities, and pollinator taxa differed in visitation according to host species. Yet, mistletoes of neither host showed uniformly greater reproductive success. Fruit set (0.70) did not differ by host, and the rates of fruit ripening and removal differed in contrasting ways. Altogether, we estimate strong but asymmetric pre-zygotic isolating barriers between mistletoes on the two hosts. These host-associated differences in reproduction have implications for interactions with mutualist vectors and population genetic structure.
KeywordsPhenology Pollination Mistletoe Reproductive isolation Seed dispersal
We thank J. Knighton/Wisor, M. A. Iacuelli, A. L. Pond, E. May, and J. P. Berry for help with fieldwork and the Bronstein lab group for helpful comments. We acknowledge support from the following: a National Science Foundation (NSF) Doctoral Dissertation Improvement Grant to KMY and JLB (DEB-1601370), a Graduate Research Fellowship to KMY (DGE-1143953), a Ginny Saylor Research Grant from the Arizona Native Plants Society to KMY, and a University of Arizona Graduate Research and Project Grant to KMY.
Author contribution statement
KMY and JLB conceived the study. KMY conducted the field work and data analyses. KMY and JLB wrote the manuscript.
- Altizer SM, Thrall PH, Antonovics J (1998) Vector behavior and the transmission of anther-smut infection in Silene alba. Am Midl Nat 139:147–163. https://doi.org/10.1674/0003-0031(1998)139[0147:vbatto]2.0.co;2Google Scholar
- Burgess TL (1995) Desert grassland, mixed shrub savanna, shrub steppe, or semidesert scrub? The dilemma of coexisting growth forms. In: McClaran MP, Van Devender TR (eds) The desert grassland. Univ. of Arizona Press, USA, pp 31–64Google Scholar
- Craig TP, Horner JD, Itami JK (1997) Hybridization studies on the host races of Eurosta solidaginis: implications for sympatric speciation. Evol 51:1552–1560. https://doi.org/10.1111/j.1558-5646.1997.tb01478.x Google Scholar
- De Vega C, Berjano R, Arista M, Ortiz PL, Talavera S, Stuessy TF (2008) Genetic races associated with the genera and sections of host species in the holoparasitic plant Cytinus (Cytinaceae) in the Western Mediterranean basin. New Phytol 178:875–887. https://doi.org/10.1111/j.1469-8137.2008.02423.x CrossRefPubMedGoogle Scholar
- Gaddis KD (2014) The population biology of dispersal and gene flow in the desert shrub Acacia (Senegalia) greggii A. Gray in the Mojave National Preserve. In: Ph.D. thesis, University of California, Los Angeles, CAGoogle Scholar
- Kahle-Zuber D (2008) Biology and evolution of the European mistletoe (Viscum album). In: Ph.D thesis, ETH Zurich, Zurich, SwitzerlandGoogle Scholar
- Ladley JJ, Kelly D (1996) Dispersal, germination, and survival of New Zealand mistletoes (Loranthaceae): dependence on birds. NZ J Ecol 20:69–79Google Scholar
- Larson DL (1991) Ecology of desert mistletoe seed dispersal. In: Ph.D thesis, University of Illinois at Chicago, Chicago, ILGoogle Scholar
- Li J, Corajod J, Deyoung J (2010) Host preferences of beechdrops (Epifagus): evidence from chloroplast DNA sequence data. Mich Bot 49:79–84Google Scholar
- Mattsson M, Hood GR, Feder JL, Ruedas LA (2015) Rapid and repeatable shifts in life-history timing of Rhagoletis pomonella (Diptera: Tephritidae) following colonization of novel host plants in the Pacific Northwestern United States. Ecol Evol. https://doi.org/10.1002/ece3.1826 PubMedPubMedCentralGoogle Scholar
- Nickrent DL (2002) Mistletoe phylogenetics: Current relationships gained from analysis of DNA sequences. In: Proceedings of the Western International Forest Disease Work Conference, August 14–18, 2000. Waikoloa, Hawai’i, pp 48–57Google Scholar
- Nickrent DL (2011) Santalales (including mistletoes). Encyclopedia of Life Sciences. doi: https://doi.org/10.1002/9780470015902.a0003714.pub2 Google Scholar
- Overton JM (1997) Host specialization and partial reproductive isolation in desert mistletoe (Phoradendron californicum). Southwest Nat 42:201–209Google Scholar
- Restrepo C, Sargent S, Levey D, Watson D (2002) The role of vertebrates in the diversification of New World mistletoes. In: Galetti MGM (ed) Seed dispersal and frugivory: ecology, evolution and conservation, 6th edn. CABI Publishing, Wallingford, UK, pp 83–98Google Scholar
- USA National Phenology Network (2015) Plant phenology data for the United States, 2011-01 to 2015-07. In: USA-NPN, Tucson, Arizona, USAGoogle Scholar
- Walsberg GE (1977) Ecology and energetics of contrasting social systems in Phainopepla nitens (Aves: Ptilogonatidae). University of California Press, OaklandGoogle Scholar