Rivulus marmoratus (Cyprinodont; Aplochelidae) is the only vertebrate known to reproduce by obligate internal self-fertilization. Selfing is the ultimate form of inbreeding and leads to virtual homozygosity in approximately ten generations, so that this mode of reproduction is effectively clonal. Populations of this species consist of arrays of homozygous clones, with high clonal diversity and low representation of each clone. Males occur at low frequency (<1%) in most populations, with a few notable exceptions. Females have never been recorded.High frequencies of males have been reported on two occasions; high numbers of males were reported on the island of Curacao in the 1970's, and males comprised up to 24% of the populations sampled on several Belize Cays during 1990-91. Hermaphrodites collected from one island, Twin Cays, proved to be heterozygous at mini-satellite loci when progeny tested and DNA fingerprinted. This was evidence that recent outcrossing had occurred.Earlier experiments with Floridian clonal lines had suggested that sex in this species was thermolabile; incubation of embryos at low temperatures (19° C)) produced up to 100% males. It was suggested that this might be part of an environmental sex determination (ESD) system in this species.If the induction of males is indeed part of and ESD in this species, then it may be that the temperature at which males are induced in a particular clone will be related to the temperature regime that clone encounters in nature. Therefore, it was hypothesized that the temperature at which males are induced would be related to the geographic origin of each clone, so that clones from the cooler extremes of the range would produce males at a lower threshold temperature than clones from the more equatorial center of the range. This study used laboratory reared descendants of clones from Vero Beach, Florida, Rio de Janiero, Brazil (the extreme north and south of the range), and from several Belize barrier islands and the Belize mainland (near the center of the range) in an effort to detect differences in the production of males between clonal lines based on their geographic origin. Eggs were collected from these hermaphrodites and incubated at 26° C)C, 22.5° C), or 19 ° C), representing normal, and below average temperatures for this species. These embryos were hatched and reared to sexual maturity at which time their sex was evaluated.Incubation at 26° C) resulted in 2-17% males, incubation at 22.5° C) resulted in 6-53% males, and incubation at 19° C) resulted in 47-74% males. However, the variation in male induction between clonal lines did not correspond to a geographic hypothesis.Also, significant numbers of deformed individuals were noted, particularly among individuals incubated at the lower two temperatures. Incubation at 26° C) resulted in 0-24% deformed, incubation at 22.5° C) resulted in 6-66% deformed, and incubation at 19° C) resulted in 36-87% deformed. It is clear that development at these lower temperatures is difficult for this species, and it may be that low temperature developmental stress is not a general challenge to this species. / Master of Science

The dissertation consists of a series of experiments conducted to study developmental stability of various genetic stocks at different stages in the life cycle. The primary measures of stability were type and degree of asymmetry of bilateral traits and heterosis. Higher relative asymmetry (RA), which was defined as (|L-R| / [(L+R)/2]) x 100, was observed in lines of White Leghorns selected 23 generations for high or low antibody response to sheep red blood cells than in their F1 crosses. The bilateral traits were 39-day shank length and length and weight of the first primary wing feather. Shank length was again measured on day 49 while body, heart, shank, and lung weights and ceca lengths were obtained on day 56. Heterosis was positive for organ sizes and negative for degree of RA. Shank length and diameter, weight and length of the first primary wing feather, and distance between the junction of maxilla and mandibles and auditory canal (face length) were used to classify bilateral types and measure RA in six genetic stocks. The stocks were the S23 generation of White Leghorn lines selected for high or low antibody response to SRBC, sublines where selection had been relaxed for eight generations, and reciprocal crosses of the selected lines. Differences were found among all stocks for the traits measured. Rankings among traits for RA in descending order were face length, shank diameter, feather weight, and shank and feather lengths. The RA of shank and feather lengths did not differ from each other. The mean RA of the five traits was higher for the two selected lines than the crosses between them. The RAs of the two lines where selection had been relaxed was similar to that of selected lines. In a line of White Rocks selected 39 generations for low eight-week body weight, bilateral traits measured were shank length and diameter, face length, and weight and length of the first primary wing feather of females at 240 days of age. The RAs of individuals that had not commenced egg production by 245 days of age were similar to those that had entered lay. In both cases, these RAs were higher than those of a subline in which selection had been relaxed for four generations. Broiler sire lines had higher RA than dam lines for lung weight at hatch. Heterosis of RAs suggested superior homeostasis in F1 crosses than in the sire lines. Based on populations studied, it may be concluded that RAs were trait specific with the RA of shank length being lower (0 < RA < 2%) than lung weight which was 10% or higher regardless of genetic background. The types of bilateral asymmetry exhibited although less consistent, still had consistency such that feather weight and ceca weight exhibited antisymmetry across different stocks. Length and width of shank and weight of lung, were generally of fluctuating asymmetry. Heart:lung ratios differed among genetic stocks. In White Leghorns, lungs from late embryonic development to 25 days after hatch were heavier in a line which had heavier juvenile body weight than in one with lower juvenile body weight. In commercial broilers, heart:lung ratios at hatch were lower and thus inferior in parental lines than in their F1 crosses. / Ph. D.

Au cours du développement, les cellules acquièrent progressivement leur identité en établissant des profils transcriptionnels spécifiques qui seront maintenus à travers les divisions cellulaires successives par des mécanismes dits épigénétiques. En dépit de nombreuses sources de variations de l’environnement, génétiques ou aléatoires, les organismes vivants présentent des phénotypes très stéréotypés. Cela suggère l’existence de processus de régulation assurant l’homéostasie du développement. Chez la drosophile, la protéine Cycline G jouerait un rôle dans la stabilité du développement, processus qui tamponne les variations aléatoires du développement. De plus, cette cycline est un régulateur trancriptionnel et interagit avec deux Enhancers de Trithorax et Polycomb (ETP) : ASX et Corto, impliqués dans l’activation et la répression de nombreux gènes. L’analyse du= transcriptome des disques imaginaux d’ailes de larves de drosophile qui surpexpriment CycG nous a permis d’identifier ses cibles transcriptionnelles. Nous avons montré que le domaine d’interaction avec les ETP (ASX et Corto) de Cycline G pourrait être impliqué dans la stabilité du développement. Nos résultats suggèrent qu’une interaction fonctionnelle entre Cycline G et deux complexes Polycomb répresseurs (PR-DUB et PRC1), contrôlerait l’expression de gènes importants pour la stabilité du développement. Par ailleurs, l’interaction fonctionnelle entre des facteurs d’épissage et Cycline G serait également impliquée dans la stabilité du développement. Nos résultats suggèrent que la dérégulation de CycG induirait une augmentation du bruit transcriptionnel, ayant des répercussions sur la stabilité du développement. / During development, cells progressively acquire their identity by establishing specific transcriptional profiles that will be maintained throughout successive cell divisions by epigenetic mechanisms. Despite numerous sources of developmental variability - whether environmental, genetic or stochastic, living organisms exhibit uncannily stereotyped phenotypes, suggesting the existence of regulation processes tending to developmental homeostasis. In Drosophila, Cyclin G could participate in developmental stability, which buffers stochastic developmental variation. Moreover, this cyclin is a transcriptional regulator and interacts with two Enhancers of Trithorax and Polycomb (ETP): ASX and Corto, both involved in transcriptional gene silencing and activation. By studying the transcriptome of Drosophila imaginal wing discs overexpressing Cyclin G, we have identified its transcriptional targets. We determined that the ETP-interacting domain of Cyclin G (which binds ASX and Corto) may be involved in developmental stability. Our results show that a functional interaction between Cyclin G and two Polycomb group complexes involved in transcriptional gene silencing (PR-DUB and PRC1), may control the expression of genes required for developmental stability. Additionally, Cycling G might participate indevelopmental stability through functional interactions with splicing factors. Altogether, our results suggest that Cyclin G deregulation may induce an increase in transcriptional noise, resulting in heightened developmental variation.

Over the last 100 years sexual selection has advanced into a vast field of theoretical and empirical research. While Darwin’s idea of female preference being an integral mechanism of sexual selection is no longer debated, our understanding of female preference is still very limited. For example, we know little about the genetic variation in female preference, and the costs of preference over and above the costs of mating with particular male phenotypes. Additionally, while costs of mate choice are well documented, the benefits of mate choice and their implications are still debated. For example, controversy exists over the inevitability of good gene benefits and their capability to promote adaptive sexual selection. Furthermore, the adaptiveness of sexual selection itself is debated. Our understanding of the traits involved in mate choice is also far from complete. Here I investigated aspects of sexual selection in Drosophila simulans, employing a range of behavioural approaches along with artificial selection and environmental manipulations. The findings presented here indicate that female preference can evolve when directly selected on, and that preference itself is not particularly costly. There was also no conclusive evidence for the good genes benefits of mate choice in D. simulans. These benefits are considered crucial in promoting the adaptiveness of sexual selection, and although we found sexual selection to be adaptive under some test conditions it was not adaptive in other conditions. Our investigations into traits involved in mate choice established sex-specific genetic variation in cuticular hydrocarbons and the genetic architecture of this trait was found to sex-specific evolution of cuticular hydrocarbons under natural and sexual selection. Additionally, we found that a secondary sexual character, the sex combs was positively allometric – just like most signalling and weapon traits, and there was no association between trait fluctuating asymmetry and trait size. These findings collectively indicate that sexual selection in D. simulans is consistent with classical models of this process.