In basidiomycetous fungi, the viability of gametes is an important component of sexual
fitness and can have implications for speciation events. Prior estimates of basidiospore
germination are highly variable and the occurrence of reproduction between these lineages
suggests that reproductive isolation is incomplete. Genetic incompatibilities during
meiosis have been attributed to much of the offspring inviability. However, the influence
of environmental factors on basidiospore germination in Cryptococcus are not well
known. In this study, we used human opportunistic yeast pathogens, Cryptococcus neoformans
and Cryptococcus deneoformans, as models to investigate the potential effects
of selected genetic and environmental factors on basidiospore germination. We evaluated
basidiospore germination of six genetic crosses by pairing a total of five strains,
three intraspecific crosses and three interspecific crosses, between C. neoformans and
C. deneoformans. The offspring of genetic crosses were incubated under multiple media
and temperature treatments and scored for their germination ability. In general, spores
from intraspecific crosses had greater germination potential than those from interspecific
crosses. Growth under high temperatures was the most significant influence on basidiospore
germination on these crosses. Furthermore, there were notable interaction effects
between environmental factors and parental strains or strain pairs on basidiospore
germination. The interaction between the sex-specific genes and environmental pressures
impact reproductive barriers and blur species distinctions within the Cryptococcus
neoformans species complex. And so, reduced viability of hybrid offspring can have implications for Cryptococcus speciation, ecology, and pathogenesis as hybridization events
are an effective method of increasing pathogenicity, expanding species distributions and
increasing tolerance to novel environments or hosts. / Thesis / Master of Science (MSc) / In basidiomycetous fungi, the viability of gametes is an important component of sexual
fitness and can have implications for speciation events. The Cryptococcus neoformans
species complex are a group of opportunistic pathogens, for which hybridization can
be facilitated readily under laboratory conditions, creating offspring that are generally
completely inviable or have low germination potential. Antagonistic genetic interactions
are mostly responsible for offspring inviability, yet the impacts of environmental factors
is not known. Multiple genetic crosses between Cryptococcus strains were used as
a model to investigate species relationships by examining the impacts of genetic and
environmental factors on offspring germination potential.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20396 |
| Date | January 2016 |
| Creators | Forsythe, Adrian |
| Contributors | Xu, Jianping, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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