The 3-5 year cyclical fluctuations in populations of many vole and lemming species have perplexed ecologists for many years. Numerous hypotheses have been proposed to explain microtine rodent cycles, including various aspects of social behavior. Microtine rodents commonly form kin groups composed of related females. Charnov and Finerty (1980) proposed that the formation and breakup of kin groups could, in part, explain the rates of population increase and decline associated with cycles. My experiment sought to determine if kin groups provided population-level benefits in gray-tailed voles, Microtus canicaudus. I compared unmanipulated populations with populations in which kin-structuring was experimentally disrupted to determine if kin groups affected population growth rates and size, reproduction, pregnancy and lactation rates, and recruitment, movement and survival of juveniles. I monitored demography and reproductive behavior in eight 0.2 ha experimental enclosures during a summer breeding season. I found no differences in demographic or female reproductive parameters between control and treatment enclosures, with the exception of a delayed time to first pregnancy for females introduced into the treatment enclosures. In addition, I found no differences in the time to sexual maturation or dispersal movements of juvenile males between control and treatment enclosures. I conclude that disrupting the formation of kin groups does not adversely affect demographic or reproductive parameters at the population-level in gray-tailed voles, and suggest that the contribution of kin groups to social behaviors that may affect population regulation is probably quite small. / Graduation date: 1998

Numerous laboratory studies with at least 12 species of rodents have reported that exposure of females to strange males results in pregnancy disruption or infanticide. The proximate causes and ultimate benefits of these behaviors have been proposed from an evolutionary perspective. To determine if exposure to strange males or females caused pregnancy disruption and (or) infanticide in a resident gray-tailed vole (Microtus canicaudus) population, pregnancy rate and juvenile recruitment were monitored in populations of 12 female and 12 male voles following introduction of unfamiliar adults. These experiments were conducted in 12 0.2 ha enclosures using three treatments and a control. Every 10 days 12 males, six males, or six females were removed and replaced in the three treatments, respectively, or the populations were left unmanipulated in the control (3 replicates/treatment). The time to first parturition, time between parturitions, number of juveniles recruited/parturition, and percent of births followed by lactation did not vary among the controls and three treatments. The only observable effects of treatment were a slight non-significant delay in time to first birth in the 12-male treatment and a slightly significant difference in the number of pregnancies per female. These results do not support previous laboratory studies indicating that exposure to strangers causes pregnancy disruption and (or) infanticide at high rates. Therefore, in field conditions, little evidence was found indicating that female gray-tailed voles' reproductive fitness declines after exposure to strangers. I propose that results from laboratory studies on behavioral aspects of mammals should be validated with field data prior to being extrapolated to natural populations and applied to evolutionary paradigms. / Graduation date: 1997

Thesis (M. S.)--Texas A&M University, 2005. / "Major Subject: Physiology of Reproduction" Title from author supplied metadata (automated record created on Feb. 23, 2007.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Physiology of Reproduction" Title from author supplied metadata (automated record created on Feb. 23, 2007.) Vita. Abstract. Includes bibliographical references.

Apomixis holds vast potential for improving agriculture worldwide. It would make plant breeding faster, allow for fixation of hybrid genotypes, and help genetically isolate transgenic crops. However, efforts to introduce apomixis into agriculturally important crops, through either plant breeding or molecular genetics, have failed to produce any new apomictic varieties. This could possibly be remedied if researchers better understood the genetics of apomixis, including the underlying genes, their regulation, and the cellular pathways they control. My work increased our knowledge of these processes by using a mixture of novel methods and underutilized resources. In this study I pursued a two-pronged approach that involved both traditional and reverse molecular genetic techniques. I analyzed the Semigamy mutation from Pima Cotton (Gossypium barbadense), which produces large numbers of haploid and chimeric offspring. Although interesting and potentially useful, little is known about this gene, its expression, regulation, and localization, or the cellular processes in which it is involved. This knowledge advanced our understanding of both this part of apomixis and plant reproduction in general. I was able to determine that the Semigamy mutation is recessive to the wild-type and is incompletely expressed even in the homozygous state. Second, I attempted to recreate the various steps of apomixis in the model species Arabidopsis thaliana using the host of tools made available by its fully sequenced genome. Mutants in various organisms, including microbes, plants, and animals, have phenotypes resembling various components of apomixis, and the sequences of most of the genes involved are available in public databases. I identified homologous Arabidopsis genes by comparing these sequences against the entire Arabidopsis genome. Mutants carrying altered versions of these genes were then studied and characterized using various techniques to see if they had any effect on plant reproduction. This method had not been used to study apomixis before this study and revealed several new reproductive Arabidopsis mutations, specifically those in genes homologous to the S. cerevisiae ste12 and rec8 genes. These results will advance the study of apomixis and potentially enable researchers to one day apply it to agriculturally important crop species.

Graduation date: 1991

Apomixis holds vast potential for improving agriculture worldwide. It would make plant breeding faster, allow for fixation of hybrid genotypes, and help genetically isolate transgenic crops. However, efforts to introduce apomixis into agriculturally important crops, through either plant breeding or molecular genetics, have failed to produce any new apomictic varieties. This could possibly be remedied if researchers better understood the genetics of apomixis, including the underlying genes, their regulation, and the cellular pathways they control. My work increased our knowledge of these processes by using a mixture of novel methods and underutilized resources. In this study I pursued a two-pronged approach that involved both traditional and reverse molecular genetic techniques. I analyzed the Semigamy mutation from Pima Cotton (Gossypium barbadense), which produces large numbers of haploid and chimeric offspring. Although interesting and potentially useful, little is known about this gene, its expression, regulation, and localization, or the cellular processes in which it is involved. This knowledge advanced our understanding of both this part of apomixis and plant reproduction in general. I was able to determine that the Semigamy mutation is recessive to the wild-type and is incompletely expressed even in the homozygous state. Second, I attempted to recreate the various steps of apomixis in the model species Arabidopsis thaliana using the host of tools made available by its fully sequenced genome. Mutants in various organisms, including microbes, plants, and animals, have phenotypes resembling various components of apomixis, and the sequences of most of the genes involved are available in public databases. I identified homologous Arabidopsis genes by comparing these sequences against the entire Arabidopsis genome. Mutants carrying altered versions of these genes were then studied and characterized using various techniques to see if they had any effect on plant reproduction. This method had not been used to study apomixis before this study and revealed several new reproductive Arabidopsis mutations, specifically those in genes homologous to the S. cerevisiae ste12 and rec8 genes. These results will advance the study of apomixis and potentially enable researchers to one day apply it to agriculturally important crop species.

Reproductive, maternal, and weight traits were analyzed for Angus (A), Brahman (B), and Hereford (H) straightbred cows; F1 and F2 BA and BH cows; and 3/8 B 5/8 A first (Bn) and second (Bn2) generation cows in Central Texas. Heterosis was estimated for calf crop born (CCB), calf crop weaned (CCW), and cow weight at palpation (PW) by linear contrasts within cow breed groups. F1 BA cows expressed heterosis (P<0.01) for CCB (0.10) and CCW (0.11), while F2 BA cows expressed negative heterosis (P<0.10) for CCB (-0.06) and CCW (-0.07). F1 BH cows expressed heterosis (P<0.001) for CCB (0.15) and CCW (0.16), and F2 BH cows retained F1 heterosis (P<0.001) for CCB (0.13) and CCW (0.15). Bn2 cows expressed heterosis (P<0.01) for CCB (0.14), but Bn cows did not express heterosis (P>0.10) for CCB or CCW. Only the F1 BA (22.9 kg) and F2 BH (42.1 kg) groups expressed heterosis (P<0.10) for PW. Bn2 cows (-65.7 kg) expressed negative heterosis (P<0.01) for PW. Heterosis for calf survival (CS), birth weight (BW), and weaning weight (WW) was estimated by linear contrasts within calf breed groups for B- and H-influenced calves. F1 BH (0.11) and F2 BH (0.14) calves expressed heterosis (P<0.01) for CS. None of the groups expressed heterosis (P>0.10) for BW, but B-sired F1 BH calves were 5.5 kg heavier (P<0.01) than H-sired F1 calves at birth. F1 BH (22.4 kg) and F2 BH (26.2 kg) calves expressed heterosis (P<0.001) for WW, and H-sired F1 BH calves were 20.7 kg heavier (P<0.10) than B-sired F1 calves at weaning.

The sexual reproduction of four gorgonian corals, Ellisella robusta, Subergorgia suberosa, Subergorgia mollis and Bebryce indica at Wanlitong, a non-upwelling area, and Talauko, an upwelling area, in south Taiwan were compared in order to understand their reproductive strategies. Four species were gonochoric. E. robusta, S. suberosa and S. mollis were broadcasting spawners with annual reproductive cycle. The reproductive mode of B. indica was not certain and it may reproduce several times within one year. The mean diameter of mature oocytes of E. robusta, S. suberosa, S. mollis and B. indica was 360, 322, 461, and 312 £gm, respectively. Their fecundity was 3.2, 1.4, 1.1, and 2.0 oocytes/polyp, respectively. Corals with longer oogenesis duration produce larger mature oocytes. The three broadcasting species spawned in September, October and November after the seasonal disturbances. It may be advantageous for the survival of their offspring. The reproductive traits of E. robusta, S. suberosa, and B. indica were similar between Wanlitong and Talauko populations. It suggests that reproductive traits of theses species may be not influenced by upwelling.

Thesis (Ph. D.)--Texas A & M University, 2003. / "Major Subject: Physiology of Reproduction." Title from author supplied metadata (automated record created on Apr. 30, 2004.). Vita. Abstract. Includes bibliographical references.