Botany

The monsoon tropics of northern Australia are home to many endemic species, including numerous spiny solanums (Solanum subgenus Leptostemonum). Solanum eburneum is an andromonoecious species restricted to clayey soils in the vicinity of the East Baines River, Northern Territory, with a range largely encompassed within Judbarra/Gregory National Park. For at least 30 years, regional botanists have recognized a subpopulation of S. eburneum as S. ‘bullita’ but no formal comparison between it and typical S. eburneum has been done. The current study represents the first rigorous morphological comparison between the two taxa using data garnered from seedlings through mature plants, including measurements of vegetative, floral, and fruiting characteristics. Using plants grown from wild-collected seeds, morphological analyses are combined with molecular phylogenetic comparisons, crossing experiments, and field observations to establish the distinctive nature of S. ‘bullita.’ The implications of recognizing the new taxon are explored, including potential effects on the conservation status of S. eburneum.

Spiny solanums of the fire-prone Australian monsoon tropics are often assumed to be “fire weeds,” with increased levels of recruitment associated with frequent bush fires. During fieldwork on the Kimberley Plateau, seeds of the endemic Solanum beaugleholei were collected from a habitat where an intense fire had recently burned. Seeds were removed from fruits exposed to three qualitative levels of burning: scorched, partially burned, and unburned. Fruits/seeds were then collected from an unburned S. beaugleholei population ca. 25 km away. In the lab, half of the seeds of each of the four “fire treatments” were soaked and treated with gibberellic acid, while the other half were soaked in water only. To understand the effect of the fire on the seeds, time to germination and rates of germination were recorded. Seeds collected from the unburned population and unburned seeds from the fire site showed the highest germination rates and shortest time to germination, allowing us to infer that fire has a negative effect on seed germination in S. beaugleholei. As a means to further confirm and clarify these findings, the seedlings were grown into mature greenhouse plants and hand pollinated to establish a new seed source for experiments replicating fire conditions ex situ. Seeds were given pre-sowing treatments exploring the potential roles of various ecological correlates of fire exposure in hastening or promoting seed germination and seedling growth. Understanding the effect of fire on S. beaugleholei may be useful in conservation efforts. Because fire appears to hinder seedling recruitment in S. beaugleholei, frequent incidences of fire (including prescribed burns) on the Kimberly Plateau could result in declines of this uncommon endemic species in certain habitats.

Little is known about the methods of seed dispersal employed by rock-specialist spiny solanums (Solanum subgenus Leptostemonum) in the monsoon tropics of northern Australia. Previous studies infer that endozoochory may play a role, but no specific animal taxa have been identified as effective seed dispersers. The elusive rock macropod species co-occurring with solanums are potential candidates, particularly species of Petrogale (rock wallabies) and Macropus (wallaroos). To assess the potential of these animals as seed dispersers, a study is underway to determine whether rock macropods might ingest Solanum fruits and pass seeds intact. Eight Solanum taxa endemic to northern Australia were grown from wild-collected seeds hand-pollinated at flowering maturity, and then used as sources of fruit. Ripened fruits will be presented to rock macropods in captivity to determine the following: a) Will rock macropods consume Solanum fruits, and which species?, and b) Do the seeds consumed with the fruits survive gut passage? Intact seeds were removed from scats and sown to test for germinability compared with uningested seeds. Determining whether co-occurring species of mammals participate in successful endozoochorous Solanum seed dispersal has implications for conservation efforts by highlighting the importance of plant-animal interactions among narrowly endemic species. Here we present preliminary data, including experiments on seed gut passage time and germination rates following ingestion by captive rodents as proxy subjects.

This presentation outlines the steps necessary to test primers specifically designed for Fluidigm digital PCR and Illumina MiSeq next generation sequencing for phylogenetic investigations. The primers validated for this study were designed from 12 transcriptomes from the One Thousand Plants Project (1KP) using MarkerMiner 1.0 (6 Solanum sp. (Solanceae) and 6 Draba sp. (Brassicaceae)). The primers chosen were used for phylogenetic inferences in the Australian monsoon tropical spiny solanum group (Solanaceae) and the North American Cordilleran species of Draba (Brassicaceae). Previous investigations of these taxa have recovered poor phylogenetic resolution with only a few commonly employed loci (e.g., ITS, trnL-trnF, matK-trnK), and additional loci are needed to confidently reconstruct their evolutionary histories. MarkerMiner 1.0 identified a large set of orthologous SCN genes and, from these, we selected 192 loci with intronic regions to validate. Three taxa from each phylogenetic study were used for validation. After primer pair validation, phylogenetically diverse taxa were amplified with these primers using Fluidigm and sequenced with MiSeq Illumina. Details of the primer design and validation steps will be presented here.

This study employs ddRADtag with double digestion followed by HiSeq Illumina sequencing, to compare genetic variation within and among regionally sympatric populations in two separate study systems: Australian Solanum spp (Solanaceae). and North American Cordillera Draba oligosperma (Brassicaceae). The six spiny Australian species are: S. asymmetriphyllum, S. clarkiae, S. cowiei, S. dioicum-Tanami, S. echinatum, and S. sejunctum. For this Solanum study 21 populations and approximately 400 individuals were analyzed. For Draba oligosperma, 29 populations of 20 individuals per population were included. Detailed information about the a priori choosing the pair of restriction enzymes and the further laboratory steps to prepare the ddRADtag libraries will be presented. Various levels of multiplexing individuals were tested for sequencing depth.

The present study investigates Draba oligosperma Hook., few-seeded draba, an octaploid species with an unusual distribution from alpine Alaska to Arizona, and Wyoming to California. We are examining the role of apomixis in the speciation of polyploids. Preliminary results indicate that D. oligosperma may be an allopolyploid due to taxa placement in previous ITS/trnL-F phylogentics of the genus. Preliminary flow cytometric seed screen and greenhouse data also show it is an apomictic species. We aim to infer whether this species arose via allopolyploid formation and whether such an event has happened once or multiple times creating different lineages. We also explore the possibility of the occurrence of occasional sexuality in its distribution. We are using the population genomic method of ddRADtag to investigate this system. Twenty-nine populations from its entire distribution and 10 to 15 individuals per population were included in the dataset. In conjunction an improved phylogenetic study of North American Draba sp. that is underway. We will attempt to identify the parents of D. oligosperma.

Draba oligosperma Hook. (Brassicaceae) has a unique distribution pattern and an unusual mode of apomixis. Preliminary data from one population showed this species to be apomictic, but historical herbarium sheets containing pollen suggests it is sexual in parts of its distribution. To determine if the species is apomictic throughout its distribution, seed collections from California, Nevada, Utah, Idaho, Montana, Wyoming, and the Yukon were made during 2012, 2013, and 2014 field seasons. A total of 29 populations were sampled with ~30 individuals per population. For the seed screen, we have analyzed approximately 50% of the samples (~4350 seeds). Using high throughput flow cytometric seed screening (FCSS), we determined the stability of apomictic reproduction for this species. The unique and large distribution of this species will allow for the role of apomixis in speciation to be better understood.

Relationships among the spiny solanums of Australia have defied phylogenetic resolution for some time, especially the dioecious and andromonoecious taxa of the northern subarid tropics. Previous work using the ITS and trnK/matK gene regions helped define a number of clades, but left much to be desired relative to both the relationships among those clades and among the closely-allied species within them. For this study we analyzed data generated from ca. 50 Solanum species from Australia, the rest of the Old World, and the New World in an attempt to clarify relationships among the Australian taxa and to further explore the phylogeny of Old World spiny solanums. Phylogenetic inference was made from select unknown intronic regions mined from six transcriptomes from the 1000 Plants (1KP) project. 173 intronic regions were mined from the transcriptomes using MarkerMiner 1.0, and primer pairs for these regions were designed with the Primer3 plugin in Geneious. Seventeen of these primer pairs were validated and used for phylogenetic inference. The results shed new light on the origin of functional dioecy in Australian Solanum, clarify relationships among a number of rare and unusual species, aid in the recognition of new species, offer insight into recent speciation events, and inform efforts to develop conservation strategies for a number of species endemic to northern Australia’s Sandstone Country.

As obligate outcrossers, populations of dioecious plants might be more likely to avoid the perils of inbreeding than populations of self-fertilizing species. One way to test this hypothesis would be to compare representative populations in sympatry. The ca. 15 functionally dioecious species of Solanum in northern Australia represent a useful model for examining the potential genetic benefits of dioecy because a) Populations are often small and isolated from other conspecific populations, b) Populations are sympatric with hermaphroditic and andromonoecious (and potentially self-fertilizing) congeners, and c) Dioecy appears to be a recently-derived condition evidenced by retention of vestigial and/or non-functional reproductive organs. The present study employs ddRADtag with double digestion followed by Illumina sequencing to compare genetic variation within and among regionally sympatric populations of five Solanum species across three breeding systems: three dioecious species, a hermaphroditic species, and an andromonoecious species. Twenty populations and approximately 400 total individuals were analyzed. Where dioecious species are shown to have high intra- and meta-population genetic variability relative to self-fertilizing species, dioecy may represent an effective mechanism for avoiding inbreeding and maintaining genetic diversity. In contrast, where dioecious species show reduced genetic variability, low-density population structure and isolation of populations may be limiting gene migration, thus negating some of the potential benefits of the dioecious habit. This latter possibility has implications for conservation of functionally dioecious solanums in Australia, many of which are narrowly endemic and/or uncommon.