Niche Shifts, Hybridization, Polyploidy and Geographic Parthenogenesis in Western North American Hawthorns (Crataegus subg. Sanguineae, Rosaceae)

Timothy A Dickinson,Brigitte Xueqi Yan,Mehdi Zarrei,Shery Han

doi:10.3390/agronomy11112133

Timothy A Dickinson, Brigitte Xueqi Yan + Show 2 more

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https://doi.org/10.3390/agronomy11112133

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Abstract

We compare biogeographic and morphological parameters of two agamic complexes of western North American hawthorns so as to evaluate possible explanations of the differences in range between sexually reproducing taxa and their apomictic sister taxa. We have documented range, breeding system, morphology, leaf vascular architecture, and niche breadth in these hawthorns, for which phylogenetic relationships and ploidy levels are known. Species distribution data from herbarium specimens and online databases were analyzed in order to compare ranges and climate niches described by bioclimatic variables. Flow cytometry documented ploidy level and breeding system. Voucher specimens provided morphometric data that were analyzed using uni- and multivariate methods. Members of two black-fruited taxonomic sections of Crataegus subg. Sanguineae (sections Douglasianae, Salignae) have previously been identified as hybrids. They are presumptively self-fertile polyploids with pseudogamous gametophytic apomixis. Their morphologies, geographic ranges, and niche characteristics resemble those of their diploid, sexual parent or are intermediate between them and those of their other parent, one or both of two partially sympatric tetraploid apomicts in red-fruited C. subg. Americanae with much wider distributions. Comparing sections Douglasianae and Salignae suggests that geographic parthenogenesis (larger range sizes in apomicts, compared to sexually reproducing taxa) may have less to do with adaptation than it does with reproductive assurance in the pseudogamously apomictic and self-compatible hybrids. Greater climate niche breadth in allopolyploids compared to diploids similarly may be more due to parental traits than to effects of genome duplication per se.

Highlights

Introduction iationsHawthorns (Crataegus L.) belong to the Amygdaloideae Arn., the same subfamily of the Rosaceae as apricots, cherries, peaches, plums, and other commercially important Prunus species
Geographic parthenogenesis provides a useful lens through which to examine the interplay of morphology, ploidy level variation, breeding system variation, and ecological amplitude in some related, widespread North American hawthorn species
We suggest that our results will provide useful insights for understanding other Crataegus species groups in North America and elsewhere

Summary

Introduction

Hawthorns (Crataegus L.) belong to the Amygdaloideae Arn., the same subfamily of the Rosaceae as apricots, cherries, peaches, plums, and other commercially important Prunus species. Hawthorns have fleshy fruits that develop from hypanthial (inferior) ovaries and so belong to subtribe Malinae Reveal, as do apples, pears, and quinces. Like these commercially more important genera [1], hawthorns are cultivated (and gathered in the wild) for their fruit, notably in China (C. pinnatifida Bunge, C. scabrifolia (Franchet) Rehder), western Eurasia (C. azarolus L., C. germanica (L.) Kuntze), Mesoamerica &. Sessé ex DC), the Pacific Northwest of North America Douglasianae Rehder), and the Southeastern United States Other aspects of the cultural importance of hawthorns include the use of their thorniness and the density of their branching in building barriers (hedges) for defense

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