Biologyhttp://hdl.handle.net/10211.3/1410722024-03-28T17:53:49Z2024-03-28T17:53:49ZNatural chimerism in the invasive colonial ascidian Didemnum vexillumWeinberg, Rachel Bethhttp://hdl.handle.net/10211.3/2141412020-11-08T11:00:32Z2019-01-01T00:00:00ZNatural chimerism in the invasive colonial ascidian Didemnum vexillum
Weinberg, Rachel Beth
Colonial, asexually reproducing organisms are typically treated as genetically homogenous entities composed of clonal units. However, processes such as fusion and somatic mutation may lead to the integration of multiple genetic lines in a single physiologically continuous organism. This state, known as chimerism, has been documented in a broad range of sessile modular taxa, including plants, fungi, slime molds, and colonial metazoans such as ascidians. In the invasive colonial ascidian Didemnum vexillum, naturally occurring chimerism has been documented from the presence of more than two alleles at microsatellite loci, however factors such as homozygosity and spatial separation of genets within a colony may mask chimerism using this detection method alone. In order to more accurately quantify the prevalence of chimerism in introduced D. vexillum populations, zooids were dissected from 35 colonies and individually genotyped. Both spatial and molecular masking of chimerism was found in a proportion of the chimeric colonies, indicating that the sampling strategy applied here has the potential to identify chimerism in D. vexillum colonies that appear monogeneic from single tissue samples. In Umpqua, Oregon, 70% of the colonies sampled were chimeric, which is the highest prevalence of chimerism reported in any D. vexillum population studied to date. In Half Moon Bay, 30% of the samples were chimeric, which is similar to the rates of chimerism previously estimated in this population using single tissue samples. The significant differences in chimerism between the two populations were not associated with significant differences in genetic diversity or inbreeding, as measured by expected and observed heterozygosity. Relatedness was significantly higher among genets within chimeric colonies than across genets in the population as a whole, providing evidence from two natural populations that chimerism in D. vexillum is genetically mediated. These results show that there may be extreme variation in chimerism prevalence across populations, providing a basis for future studies to investigate the causes of this variation and its potential role in facilitating the successful establishment of non-native species.
2019-01-01T00:00:00ZPhylogeography of Leptasterias species relative to an estuarine outflow in the Pacific NorthwestPerez, Jeyna Kimhttp://hdl.handle.net/10211.3/2141262020-11-07T11:00:10Z2019-01-01T00:00:00ZPhylogeography of Leptasterias species relative to an estuarine outflow in the Pacific Northwest
Perez, Jeyna Kim
Comparing the phylogeography of sympatric species complexes can provide evidence of
shared responses to historic events. Leptasterias is a genus of brooding, low-dispersing
sea stars comprising several cryptic species complexes found from California to Alaska.
Assessing their response to environmental events may elucidate processes underlying
their diversity. Prior phylogenetic work around the San Francisco Bay, California
suggests an outflow-associated pattern of Leptasterias clade distributions. For
comparison, we examined Leptasterias phylogeography in the San Juan Islands (SJI),
Washington to assess the potential effects of low-salinity outflow from the Fraser River.
Mitochondrial cytochrome oxidase 1 (COI) barcoding (n=268) confirmed three sympatric
cryptic clades of Leptasterias in the SJI discussed in Foltz 2008: L. aequalis A (I. pusilla
complex), L. aequalis B (L. aequalis complex), and L. hexactis C (L. hexactis complex).
Fine-scale sampling in the SJI showed an association between Leptasterias spp. COI
clade frequency distribution and habitat exposure to waves and estuarine outflow.
Selective forces from stressors such as low-salinity plumes or wave exposure could be
maintaining the clade distributions seen in this island archipelago. In California, clades
within the L. pusilla complex dominated bay-proximal sites more frequently exposed to
low-salinity plumes out of the San Francisco Bay. Similarly in the SJI, the L. pusilla
complex dominated sites more frequently exposed to low-salinity plumes from the Fraser
River, while L. aequalis and L. hexactis dominated more wave-exposed, marine sites.
This study suggests that estuarine sources may influence spatial genetic variation among
Leptasterias populations. This combined regional comparison o f the distribution o f
cryptic Leptasterias lineages relative to large sources o f estuarine outflow confirms some
effect o f low-salinity plumes and wave exposure. Spatial and temporal patterns seen
related to estuarine features in California poses concern for Leptasterias populations in
the SJI, and further regional work in the context o f local habitat is needed to expand upon
these findings.
2019-01-01T00:00:00ZVariation in reproductive strategies of Embiotocids : a comparative approachIzumiyama, Michael S.http://hdl.handle.net/10211.3/2139722020-01-22T23:54:10Z2019-01-01T00:00:00ZVariation in reproductive strategies of Embiotocids : a comparative approach
Izumiyama, Michael S.
Reproductive strategies of marine fishes are diverse, surfperches (Embiotocidae)
represent a unique family of viviparous fishes that exhibit internal fertilization, gestation
to the sub-adult stage, and live-birth. Maternal investment is extremely high in
surfperches, which invokes the expectation that broodsize is limited, and females should
be selective and choose few mates, yet polyandry occurs in all six species examined to
date. Surfperches are found in the northern Pacific in temperate waters with the majority
of species residing along the coast o f the eastern Pacific. Our study characterized the
reproductive life history of calico surfperch (Amphisticus koelzi) which is the only
species o f surfperch missing from previous literature, as well as assigned paternity with
the utilization of RADseq. All calico surfperch broods examined were sired by multiple
fathers, and the number of fathers ranged from four to eight. Additionally, we compared the reproductive strategy of Western Pacific
surfperches (including calico surfperches) to an Eastern Pacific species of surfperch
Ditrema temminchii by assigning paternity. We discovered that the prevalence o f multiple
paternity in Eastern Pacific surfperches ranges from 92-100%, however, the prevalence
of multiple paternity is noticeably reduced in D. temminckii with only 60% of broods
being sired by multiple fathers. In addition, the total number o f sires per brood is lower
compared to the Eastern Pacific surfperches, suggesting a different mating strategy. The average number o f sires was 1.86 per brood, and paternity was skewed, indicating the
majority o f paternity was allocated to a single male. The number of fathers is an accurate
approximation for the number of mates in D. temminckii, which was examined by
genotyping spermatozoa within the uterine sacs o f females (sperm donors) and sires
within broods (paternal contributors). The contrast in the frequency of multiple paternity
in D. temminckii with eastern Pacific surfperches suggests variation in the mating
strategy that may be associated with a stronger female choice on males.
2019-01-01T00:00:00ZPreliminary monograph of Marasmius from Sao Tome and PrincipeGrace, Christopher Leehttp://hdl.handle.net/10211.3/2139052020-04-15T10:00:14Z2019-01-01T00:00:00ZPreliminary monograph of Marasmius from Sao Tome and Principe
Grace, Christopher Lee
This treatise serves as a preliminary monograph and phylogenetic treatment of
Marasmius from the African island nation of Sao Tome and Principe (ST&P), based on
data generated from 30 specimens collected in 2008. Twenty-one species are described,
five of which represent species new to science (Marasmius albisubiculosus, M.
elaeocephaliformis, M. laranja, M. segregatus, M. leptocephalus), and all represent new
distribution records for ST&P. Species are delimited based on comprehensive
morphological characters and DNA sequence data. Prior to the collection of these
specimens, only one Marasmius species had been documented from these islands.
Phylogenetic hypotheses generated from analyses of DNA sequences of the Internal
Transcribed Spacer regions (ITS1+5.8S+ITS2) are proposed to explore the evolutionary
relationships amongst ST&P Marasmius and global Marasmius diversity. A dichotomous
key to aid in identification, illustrations of pertinent micromorphological features, color
photographs of basidiomes, comprehensive descriptions and commentaries are provided.
2019-01-01T00:00:00Z