PHYLOGENETIC AFFINITIES AMONG SIDA SPECIES AND ALLIED GENERA (MALVACEAE: MALVEAE), AND EXAMINATION OF SIDA FALLAX WITHIN THE HAWAIIAN ISLANDS AND THROUGHOUT THE PACIFIC

Date
2022
Authors
Pejhanmehr, Mersedeh
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Morden, Clifford W.
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Botany
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Abstract
Malveae has the greatest generic and species diversity of the three tribes of subfamily Malvoideae (Malvaceae) with approximately 70 genera and 1040 species. Within Malveae, Sida is one of the largest genera with over 100 species of mostly herbs and small shrubs with world-wide distribution. The generic circumscription of Sida is problematic. Previous genetic analysis with a limited representation of species and genera and one gene region internal transcribed spacer (ITS) indicated that Sida is polyphyletic with a core group of species forming a distinct clade, but many species more closely associated with other genera and clades. In addition, section classification of Sida is problematic and many of these sections are not monophyletic. A study was conducted to investigate these objectives: first characterize the relationships among Sida species; second, determine their relationship to other Malveae genera; third, examine how these associations compare to the section classification; and fourth, investigate the biogeography of species within Sida. To do this, phylogenetic analyses of an extensive sampling of Sida species and most Malveae genera based on nuclear (ITS) and chloroplast DNA (psbA–trnH, rpl16, ndhF and matK) markers were carried out. Sequences were compared using Bayesian phylogenetic analyses. The nuclear and plastid phylogenies indicated that Sida as currently recognized is polyphyletic. The main Sida clade is monophyletic and represents the true “Sida” and is sister to the monotypic genus Fryxellia. The main Sida clade consists of at least 66 species including the type species, S. rhombifolia. Evidence indicates that Sida is largely of central and south American origins which is the center of diversity of the genus. There are at least 18 species currently classified as Sida that were not within the main Sida clade and should be revaluated. The previously identified section alliances are not consistent with the phylogeny and are in need of reevaluation based on morphological and phylogenetic grounds. Sida fallax Walp. (`ilima) (Malveae; Malvoideae; Malvaceae) is native to the Pacific area and is extensively distributed throughout this region. It is noteworthy that Sida fallax is the most widespread and variable taxon of Malvaceae in Hawaiian Islands and it occurs with diverse morphological forms and in different habitats from Hawaii Island to Midway Atoll. There are two extreme ecological forms of S. fallax with many intermediate morphological types between them in the Hawaiian Islands. A low elevation ecotype that is a sprawling, or prostrate shrubs with densely pubescent leaves that occurs along beaches and in dry, coastal shrublands. Sida fallax from other Pacific locations exhibit this form only. In contrast, the mountain ecotype is an erect shrub up to 2 m tall with glabrous leaves that is found in upland communities and mesic forest sites. The range of morphological and ecological diversity in Sida fallax suggest that this species requires further biosystematics investigation. Phylogenetic and population studies were carried out on S. fallax. The purpose of the phylogenetic study was two-fold. The first objective was to explore the genetic diversity among S. fallax populations throughout its native range in the Pacific region. The diversity in habitat and its wide distribution throughout the Pacific regions calls into question whether S. fallax is a single species or potentially multiple cryptic species. The second objective was to investigate the origin of S. fallax. To do this, populations of Sida fallax throughout Hawaiian Islands and different parts of Pacific region were collected. Bayesian phylogenetic analyses based on nuclear [(ITS) and external transcribed spacer (ETS)] and chloroplast regions (psbA–trnH) were carried out. The nuclear and plastid phylogenies of this study clearly demonstrated that Sida fallax is a single species throughout the Pacific region and the different forms of Hawaiian S. fallax are not genetically distinct at the sequence level. Although the pattern of dispersal of S. fallax is not clear, it is evident that an American origin is most likely. The population study objective was to investigate the genetic variation within and among populations from the various habitats and geographic locations throughout the Hawaiian range of S. fallax. To do this, populations were collected from six of the main Hawaiian Islands (Kauaʻi, Oʻahu, Maui, Molokaʻi, Lānaʻi, and Hawaiʻi) and Nihoa in the Northwestern Hawaiian Islands. DNA samples of 124 samples from 26 populations were selected for Multiplexed ISSR genotyping by sequencing (MIG-seq) to detect single nucleotide polymorphisms (SNP). Genetic differences among individuals and populations from across the range of habitat and locations of S. fallax in the Hawaiian Islands were evaluated using PCO analyses. The relationship of FST with the geographical distance between the populations was assessed using Mantel test. The Mantel test identified a significant positive correlation between genetic and geographic distances among S. fallax populations. Three main island groupings were evident in PCO graphs: 1) Oʻahu, Kauaʻi and Nihoa; 2) Maui, Molokaʻi, and Lānaʻi (collectively referred to as Maui Nui); 3) Hawaiʻi Island. Populations from each island grouping intersect at the center of the graph, the zone of intersection (ZOI), suggesting gene flow still exists among them. There was a trend of coastal/beach populations occurring more predominantly near the ZOI, and the mountain/inland or most isolated populations being more away from the ZOI. Overall, populations on a single island were more closely related to each other and to populations on islands within their respective groups than they were to populations on other islands. Because long-distance seed dispersal via ocean currents is more probable for beach ecotype populations, the beach ecotype populations of all islands showed somewhat closer relationships to each other than to mountain ecotype populations and provided some continuity among all the island groups. The overall genetic relationships among islands were to a large extent predictive based on island position within the chain, and, to a lesser extent, within island topography.
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Systematic biology, Hawaiian Islands, Malvaceae, Malveae, Phylogeny, Population genetics, Sida
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170 pages
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