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

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.

Genome Size, Cytotype Diversity and Reproductive Mode Variation of Cotoneaster integerrimus (Rosaceae) from the Balkans

“…The question remains as to why C. integerrimus diploids are so rare. Geographic distribution of C. integerrimus diploids in our sample confirmed a restricted and smaller geographic range relative to asexual tetraploids, which is a common pattern in different agamic groups [47][48][49][50]. These areas inhabited with diploids are considered as relict habitats in glacial refugia during the Pleistocene climate changes [10,51].…”

Apomictic Mountain Whitebeam (Sorbus austriaca, Rosaceae) Comprises Several Genetically and Morphologically Divergent Lineages

“…In this way, apomictic genotypes promote range expansions to remote areas, where they can function as pioneer colonisers of new habitats [ 15 ]. The fleshy fruits of Sorbus , such as those of other Malinae (e.g., Crataegus ), are adapted to dispersal by vertebrates, mainly birds, often over relatively long distances [ 16 , 88 ].…”

“…Apomicts show a better adaptive capacity and greater colonisation ability by often occupying extreme ecological niches or disturbed habitats. Furthermore, they may have larger distribution ranges than their sexual relatives, a phenomenon known as ‘geographical parthenogenesis’ [ 9 , 13 , 14 , 15 , 16 ]. While some apomictic species have broad ranges, there are numerous examples of apomict species with narrow ranges, such as Rubus L. [ 17 ], Sorbus L. [ 18 , 19 ], or Taraxacum F.H.…”