A hierarchy of different chromosome conformations plays a role in many biological systems. These conformations contribute to the regulation of gene expression, cellular development, chromosome transmission, and defects can lead to human disease. The highest functional level of this hierarchy is the partitioning of the genome into compartments of active and inactive chromatin domains (1’s -10’s Mb). These compartments are further partitioned into Topologically Associating Domains (TADs) that spatially cluster co-regulated genes (100’s kb – 1’s Mb). The final level that has been observed is long range loops formed between regulatory elements and promoters (10’s kb – 100’s Mb). At all of these levels, mechanisms that establish these conformations remain poorly understood. To gain new insights into processes that determine chromosome folding I used the mating type switching system in budding yeast to study the chromosome conformation at length scales analogous to looping interaction. I specifically examined the role in chromosome conformation in the mating type switching system. Budding yeast cells can have two sexes: MATa and MATα. The mating types are determined by allele-specific expression of the MAT locus on chromosome III. The MATa allele encodes for transcription factors responsible for the MATa mating type and the MATα allele encodes transcription factors responsible for the MATα mating type. Yeast cells can switch their mating type by a process that repairs a break at MAT using one of two silent loci, HML or HMR, as a donor to convert the allele at the MAT locus. When MATa cells switch they prefer to use HML, which contains the MATα allele, located at the end of the left arm. MATα cells prefer to use HMR, which contains the MATa allele, located on the end of the right arm of chromosome III. The sequences of the HM loci are not important for donor preference. Instead the cell chooses the donor on the left arm in MATa cells and chooses the donor on the right arm in MATα cells. This lack of sequence specificity has led to the hypothesis that the conformation of the chromosome may play a role in donor preference. I found that the conformation of chromosome III is, indeed, different between the two mating types. In MATa cells the chromosomes displays a more crumpled conformation in which the left arm of the chromosome interacts with a large region of the right arm which includes the centromere and the MAT locus. In MATα cells, on the other hand, the left arm of the chromosomes displays a more extend conformation. I found that the Recombination Enhancer (RE), which enhances recombination along the left arm of the chromosome in MATa cells, is responsible for these mating type-specific conformations. Deleting the RE affects the conformation of the chromosomes in both MATa and MATα cells. The left portion of the RE, which is essential for donor preference during the switching reaction in MATa cells, does not contribute to the conformation in MATa. This region does have a minor effect on the conformation in MATα cells. However, I found that the right portion of the RE is responsible for the conformation of chromosome III in both mating types prior to initiation of switching. This work demonstrates that chromosome conformation is determined by specific cis regulatory elements that drive cell-type specific chromosome conformation.

Doctor of Philosophy / Department of Psychological Sciences / Gary L. Brase / Operational Sex Ratio (OSR: the ratio of reproductively viable males to females in a given population) has been theorized and studied as a construct that may influence behaviors. The encoding of sex ratio was examined in order to determine whether the cognitive process underlying it is automatic or effortful. Further, the current work examines whether OSR or Adult Sex Ratio (ASR: the ratio of adult males to females) is encoded. The current work involved four experiments; two using frequency tracking methodology and two using summary statistic methodology. Experiment 1 found a strong correlation between OSR of conditions and estimates of sex ratio. Participants in Experiment 1 were uninformed on the purpose of the experiment, thus the strong correlations between actual and estimated sex ratio suggest a level of automaticity. Experiment 2 found a strong correlation between the ASR of conditions and estimates, suggesting that individuals do not encode OSR over ASR. Experiments 3.a. and 3.b. demonstrated automaticity in estimates of sex ratio from briefly presented sets of faces, for two different durations: 1000ms and 330ms, the later of which is widely accepted as the length of a single eye fixation. Overall this work demonstrated a human ability to recall proportion of sexes from arrays of serially presented individuals (Experiments 1 and 2), and that ASR is encoded when participants are presented with conditions including older adults. This work found the encoding of sex ratio to be highly automatic, particularly stemming from the results of Experiments 3.a. and 3.b. Conclusions from this work help to verify previous research on sex ratio’s effect on mating strategies through evidence supporting the automatic nature of encoding sex ratio. Further, the current work is a foundation for future research regarding sex ratio, and leads to several proposals for future endeavors.

Not much is known about the mechanisms affecting the genetic composition of populations of different species. To investi­gate one of these potential mechanisms, mating behaviour, the fruit fly Drosophila melanogaster, was chosen as an experimen­tal animal. To quantify mating behaviour in easily measurable parameters, it was subdivided into several distinct components; mating activity, mating time, mating competition ability and male mating capacity. As behavioural components to a great extent are influenced by environmental conditions all experiments were performed under controlled temperature and humidity. All components of mating behaviour were estimated by introducing females and males into mating chambers. Mating behaviour seems to be one of the major factors affect­ing the genetic composition of Drosophila melanogaster popula­tions. The experiments performed showed that differences in mating properties led to a substantial sexual selection among the genotypes. This selection was of a stabilizing type with regard to characters associated to bristle number and Y chromo­somal chromatin. This selection situation seems to warrant the retention of intermediate phenotypes in a population and will therefore contribute to the genetic variation present. Differences in mating properties were also shown to be able to maintain a balanced polymorphism for allozyme variants in populations. This maintenance was obtained through different forms of balancing selection as heterozygous superiority in sexual activity and balancing selection between female and male genotypes. Heterozygous superiority or overdominance in fitness always leads to balanced polymorphism through segre­gation of individuals with lowered fitness. The balancing selection between the female and male genotypes is best looked upon as a form of marginal overdominance, conferring the aver­aged highest fitness to the heterozygous genotype, thereby maintaining the polymorphism of the population. / <p>Härtill 5 uppsatser</p> / digitalisering@umu

Divergence in the face of gene flow is perhaps the most wildly disputed subject among researchers through time. The debate is an old one and we find its origin as far back as the era of Darwin. The theories dealing with sympatric and parapatric speciation, its processes and ecological conditions, are numerous and the empirical data supporting the ideas is constantly growing. However, the reach of a consensus almost seem as distant as ever. Two fundamental prerequisites can be identified for the evolution of divergence with gene flow, the act of disruptive selection, and the development of assortative mating. A set of models in which speciation with gene flow seem particularly likely is when a shift occurs in host preference in phytophagous insects and mating takes place on the host. In the work behind this thesis, the role of assortative mating in the initial stages of sympatric and parapatric speciation has been studied, as has the interaction between assortative mating and inbreeding and how it effects speciation in small sympatric populations, an aspect not much attended to earlier in the literature. My results show that assortative mating based on resource preference, can evolve rapidly upon secondary contact, and even in parapatric populations with a migration rate of 8% (13-15 individuals) per generation. However for assortative mating to be maintained selection against hybrids is needed. My results also suggests that small inbred populations have a hard time coping with strong assortative mating an as a consequence tend to relax their mating preferences to avoid inbreeding depression. Based on these results, I advocate for the importance of considering not only assortative mating in itself, but also the joint effects of assortative mating and inbreeding when dealing with theories of speciation with gene flow.

This thesis expands our understanding of the role of several different mating behaviours in the process of forming and maintaining human mating pair-bonds. Chapter 2 investigated within-sex mating strategies and found that their distribution reflects the presence of two phenotypes, one favouring the pursuit of short-term mating and one the establishment of mating pair-bonds, each driven by prenatal testosterone exposure. Chapter 3 investigated the possible functional role of kissing in mating relationships, and found that it was utilised divergently by individuals pursuing different mating strategies, with those interested in short-term mating utilising it to assess the suitability of potential mates at initial relationship stages, and those interested in long-term mating using it to mediate pair-bond attachments. Chapter 4 examined female attitudes towards kissing across the menstrual cycle and found that attitudes varied with cycle phase, mediated by fluctuations in the hormone progesterone. This chapter also investigated the effects of kissing-related information on mate assessment and found that such information influenced mate desirability, even in the presence of typically dominant visual cues. Lastly, Chapter 5 investigated the cognitive effects of established pair-bonds, finding that individuals ‘in love’ with a mating partner show improved empathising abilities, particularly males when it comes to assessing negative emotional states in others. Using an evolutionary framework, each chapter of this thesis contributes novel insights to our understanding of these diverse behaviours. These results suggest that that future research must take into account within-sex phenotypic differences in order to truly understand human mating strategy decisions, and that different mating strategy phenotypes might adaptively utilise the same courtship behaviours in divergent ways. Furthermore, these results also suggest that pair-bonding in humans may be a relatively recent phenomenon, and that the formation of such pair-bonds can have adaptive cognitive effects for males within such bonded relationships.

Budding yeast are capable of existing in both a haploid and diploid state. Haploid cells have two mating types, MATa and MAT&alpha;. When cells from the two mating types come in contact they signal using reciprocal pheromones and pheromone receptors, starting a regulated pheromone response that includes transcription of pheromone-response genes, polarization in the direction of highest pheromone concentration, and cell cycle arrest. Once cells have chosen a mating partner, they must fuse their cell walls, plasma membranes, and nuclei to form a single diploid cell.

Gibberella zeae (anamorph Fusarium graminearum) is a homothallic ascomycete pathogen that is responsible for causing Fusarium head blight (FHB) of wheat and small grains. In addition to causing a reduction in yield, harvested grain is frequently contaminated with trichothecene mycotoxins that are harmful for human and animal health. Use of wheat varieties with resistance to FHB is an important strategy to lower its impact. In order to produce varieties with durable resistance, we must understand the origin and degree of genetic diversity present in the pathogen population. In my research, I focused my efforts on an investigation of the role of mating and sexual development in the generation of genotypic and phenotypic variability in G. zeae. The goal of one part of my work was to develop new genetic markers that can be used to monitor out-crossing and genetic diversity in the population. I also optimized gene deletion protocols for G. zeae so that I could produce mutant and control strains to address my research hypothesis that MAT genes play a direct role in pathogenicity. Application of novel repetitive RFLP probes to a group of G. zeae isolates originating from and near Kentucky revealed a surprisingly high degree of diversity in these local populations. Diversity between locations was greater than that within locations, suggesting the relative importance of local inoculum sources. The probes were also useful as genetic markers for segregation analysis. I crossed two genetically closely related, and commonly used, laboratory strains of G. zeae and found that this resulted in transgressive segregation for both aggressiveness and toxigenicity. I showed that the very high and very low levels of aggressiveness and toxigenicity in transgressive segregants are heritable. I also showed that selfing produced a higher degree of diversity in these traits among the progeny than was observed among conidial progeny. This suggests the presence of epigenetic factors that impact pathogenicity. Sexual behavior in G. zeae is under the control of MATing type genes. I deleted the complete MAT1 locus, and the MAT1-1-1, and MAT1-2-1 genes separately. Deletion of each of the targeted sequences produced the expected shifts in fertility phenotype. The mat1KO strains became asexual, while mat1-1-1KO and mat1-2-1KO strains shifted to obligate heterothallism. Deletion of the MAT1-1-1 and MAT1-2-1 genes had a negative effect on aggressiveness and mycotoxin production in planta, but deletion of the complete MAT1 locus had no effect. The set of mutant and ectopic control strains that I generated will be a useful asset that will be made available to the research community.

This study investigates the reproductive strategies of the pill-box crab, Halicarcinus cookii on the Kaikoura Peninsula, New Zealand. Various aspects essential to understanding reproductive strategies were examined including growth, population dynamics, reproductive biology and mating behaviour. H. cookii exhibits obvious sexual dimorphism such that females develop wide abdomens forming brood chambers, and males tend to grow larger than females and have larger chelipeds in relation to body size. H. cookii allocates energy into growth and reproduction in separate phases of its life cycle where growth ceases as reproductive maturity begins due to a terminal/pubertal moult. Despite the presence of ovigerous females throughout the 15 month sampling period, the population was highly seasonal, with peaks in recruitment and growth occurring primarily during the winter months and peaks in numbers of mature individuals during the summer months. Reproductive output increased with body size in H. cookii, as larger females produced more eggs and larger males transferred more sperm than their smaller counterparts. Ovaries matured prior to the terminal/pubertal moult (anecdysis) and, in multiparous females, in synchrony with brood development, allowing females to produce broods in quick succession, maximising their reproductive output in their short life span (approximately 12-18 months, 6 months as an adult). Incubation duration of broods decreased as seawater temperature increased, suggesting that temperature is the primary cause of the seasonal population cycling. Sperm storage allowed females to produce at least 4 fertilised broods without re-mating. Some sperm mixing in the spermathecae appeared to occur and the ventral-type structure implies last male sperm precedence. Males therefore preferentially mated with females closest to laying a new brood and guarded them longer than other females to ensure their paternity. Guarding duration varied according to the sex ratio allowing males to maximise their reproductive output.

A major challenge in plant ecology is in understanding how species strategies mediate interactions between the environment and fitness. Variation in niche strategies that affect phenological, physiological, and reproductive traits will allow species to partition resources differently in space and time, allowing for coexistence of many species and strategies within a community. How species differentially respond to variable environments will ultimately influence their population dynamics and geographic distribution. This dissertation approaches this topic from two perspectives: (a) examining the interaction between biogeography and variable demographic strategies in desert annual plants, and (b) examining the costs and benefits of contrasting reproductive strategies in co-occurring selfing and outcrossing desert annuals. Firstly, I tested the abundant center model to determine the role of range position on plant population dynamics. I examined how the geographic and climatic position of 13 desert annuals found at a common location, the Desert Laboratory at Tumamoc Hill in Tucson, Arizona, related to their demography over a 25-year time span. I found that species for which the Desert Laboratory was close to the center of their geographic range have less variable long-term survival and fecundity compared to species for which the Desert Laboratory was further from the center of their range. Secondly, I studied how related species with contrasting mating systems respond to variable environments to affect plant performance. In a three-year field study I investigated how inter-annual variation in plant reproductive phenology affects synchrony with pollinators and herbivores. Since selfing species are guaranteed to reproduce in the absence of pollinators, seasonal and annual variation in phenology resulted in less variable plant reproductive success compared to outcrossing species. Greater variation in reproduction in outcrossing species resulted from asynchrony in some years between plants and pollinators. In a greenhouse study examining the interaction between mating system and drought, I found that the physiological functioning and survival of outcrossing species was more strongly negatively affected by drought conditions, suggesting that selfing species have an advantage in more arid environments. These studies demonstrate how plant reproductive and physiological strategies can play a critical role in influencing fitness, population dynamics and geographic distribution.

Over the last 40 years North American grassland bird populations have declined more than any other bird guild. This trend is especially evident in Vermont, where species experiencing precipitous declines include the Savannah Sparrow (Passerculus sandwichensis) and Bobolink (Dolichonyx oryzivorus). These declines are linked to habitat loss due to reforestation and suburbanization as well as the intensification of grassland management. Modern grassland management includes earlier first-haying dates (late-May) and shorter intervals between haying events (35 days). These management practices have severe repercussions for songbird populations because 1) early-haying results in complete nest failure (99% Savannah Sparrow and 100% Bobolink nests), 2) the interval between the first and second haying is too short for birds to renest, and 3) intensively managed fields comprise a significant portion of the total available habitat (as much as 40%). In 2002-2006, I examined how hayfield and pasture management affected grassland songbird ecological and evolutionary behavior in the agricultural landscape of the Champlain Valley, Vermont and New York. I studied songbirds in four grassland management types: early-hayed fields harvested in late-May or early-June and again in mid-July; middle-hayed fields harvested in late-June or early-July; late-hayed fields harvested after 1 August; rotationally-grazed pastures, a matrix of small paddocks where cows are moved after the grass in a paddock is eaten to a low point. I addressed the following objectives: 1. Determined the annual productivity, survival, and recruitment of Bobolinks and Savannah Sparrows in the four treatment types. 2. Identified the effects of early-haying on the social and genetic mating systems of Savannah Sparrows. 3. Conducted a population viability analysis for Bobolinks and Savannah Sparrows nesting in the Champlain Valley, assessing sensitivities of life-history parameters and identifying effective management alternatives. This study provides information on how agricultural management affects the ecology, evolution, and viability of grassland birds. It will help inform landowners, managers, and law-makers about management practices and habitat requirements needed to sustain populations.