No description available.

Thesis advisor: David Burgess / The contractile ring is pictured, analyzed, and even named under the basic assumption that the geometry of the structure begins and ends circularly and the ring is a single homogenous structure acting uniformly. However, under physiological conditions cell-to-cell adhesions force cells and therefore initial contractile rings into highly irregular and noncircular shapes. To investigate this basic assumption of contractile ring geometry, contractile ring shape of dividing sea urchin embryos was analyzed under three conditions: in seawater where cell-to-cell adhesion is strong, calcium free seawater where cell-to-cell adhesion is minimized, and in microfabricated chambers to artificially manipulate the initial contractile ring shape. We found that contractile ring geometry evolves over time to become circular even when it begins as an irregular shape due to cell-to-cell adhesions or artificial manipulation. By analyzing velocities of specific regions of the contractile ring, it became apparent that there is always a pattern of rounding regions of lowest circularity before overall ring contraction. This pattern suggests that the contractile ring is capable of producing varying forces in a coordinated manner. Therefore the contractile ring can not only be noncircular, but can also possess regions with different molecular and biophysical properties. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

Thesis advisor: David R. Burgess / Establishment and maintenance of cell polarity has become an increasingly interesting biological question in a diversity of cell types and has been found to play a role in a variety of biological functions. Previously, it was thought that the echinoderm embryo remained relatively unpolarized until the first asymmetric division at the 16 cell stage of development. However, there is mounting evidence to suggest that polarity is established much earlier. I analyzed roles of the cell polarity regulators, the PAR complex proteins, and how their disruption in early development affects later developmental milestones such as blastula formation. I found that PAR6 along with aPKC and CDC42 localize to the apical cortex (free surface) as early as the 2 cell stage of development and this localization is retained through the gastrula stage. Interestingly, PAR1 also colocalizes with these apical markers through the gastrula stage, despite the formation of a polarized epithelium and a series of asymmetric divisions. Additionally, PAR1 was found to be in complex with aPKC, but not PAR6, during these developmental stages. PAR6, aPKC, and CDC42 are anchored in the cortex by assembled myosin; however, a clear role for myosin assembly in PAR1 localization could not be determined. Furthermore, myosin assembly was found to be necessary to maintain proper PAR6 localization through subsequent cleavage divisions. Interference with myosin assembly prevented the embryos from reaching the blastula stage, while transient disruptions of either actin or microtubules did not have this effect. Similarly, inhibition of aPKC activity during early cleavage stages impeded blastula formation; however, aPKC is not involved in the regulation of the first asymmetric division at the 16 cell stage in sea urchin embryos. These observations suggest that disruptions of the polarity complex in the early embryo can have a significant impact on the ability of the embryo to reach later critical stages in development. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

This study used an energy budget approach to record changes in the biology of the Antarctic sea urchin Sterechinus neumayeri in relation to environmental seasonality (i. e changes in chlorophyll standing stock and seawater temperature) over an unbroken two year period. Chlorophyll standing stock showed a brief but intense bloom each austral summer which contrasted with prolonged winter minima. Benthic chlorophyll standing stock, as recorded from sediment cores showed a similar cycle. Seawater temperature varied between -1.8°C and +1.2°C. Feeding activity was highly seasonal and closely correlated to chlorophyll standing stock. Feeding ceased during the austral winter of 1997 and 1998 for 6 and 4 months respectively. Metabolism, as measured by oxygen consumption and also ammonia excretion showed strong seasonality, with relatively brief 3 to 4 month periods of elevated activity in the austral summer contrasting with prolonged winter dormancy. Laboratory studies indicated that only 10-15% of the 3 fold seasonal rise in metabolism was caused directly by temperature (Q10=2.5) and that 80- 85% was related to increased physiological activity associated with feeding. Growth rate was measured over one year and was very slow. Comparison with other studies indicated that echinoid growth rate is strongly dependent on food availability, but that maximal growth rate is limited by seawater temperature, or by a co-varying factor. S. neumayeri is an annual spawner and histology was used to describe both the vitellogenic cycle and also to calculate reproductive output. Comparison with other published studies worldwide indicated that reproductive output is highly dependent on food availability, and that maximal reproductive output is not limited by temperature. Although the overall P: B ratio was low, the ratio of reproductive production to total production was higher than expected. These results indicated that due to the low metabolic rate only 12-16% of total body energy levels were used to endure the prolonged non-feeding polar winter. The overall annual growth efficiency was greater than for warmer water species, due to the larger relative contribution to reproductive output.

Thesis (M.S.) in Zoology--University of Maine, 2002. / Includes vita. Includes bibliographical references (leaves 97-110).

No description available.

No description available.

Sea urchins are an ecologically important species that can drastically alter marine communities due to their consumption and destruction of macroalgal beds (e.g. kelp forests). These beds form highly productive ecosystems that provide shelter and nursery habitat for many benthic and pelagic species. When their populations explode, due to a lack of predators and/or various environmental conditions, sea urchins can overgraze and decimate macroalgal beds. This creates areas called sea urchin barrens, which is a problem seen around the world. Sea urchin aquaculture is a method to remove these over-populated sea urchins from the environment, feed them either a prepared or macroalgal diet for approximately 12-weeks to produce a marketable roe product in a process termed roe or gonad enhancement. Two feeding trials were conducted on two species of sea urchins that are native to the waters off Vancouver Island, British Columbia, Canada: the green (Strongylocentrotus droebachiensis) and red (Mesocentrotus franciscanus) sea urchin. There were nine treatments per feeding trial, where three diets (two prepared diets; V10.1.9 and V10.1.10, and one natural bull kelp (Nereocystis luetkeana) diet and three different temperatures (8, 12, and 16oC; which are temperatures commonly found in the waters around Vancouver Island) were examined to assess the feasibility of a sea urchin gonad enhancement operation with these species and diets. Overall, green sea urchins fed V10.1.9 at 8 and 12°C produced the highest gonad yields (mean ± SE: 29.4 ± 1.1% and 29.4 ± 1.5%, respectively) while V10.1.9 at 12°C also had the highest gonad yield increase per week (mean ± SE: 2.2 ± 0.2%) and the lowest FCR-G (mean ± SE: 1.0E-2 ± 9.0E-4 feed g gonad increase g-1). Green sea urchins fed V10.1.10 at 12°C, however, produced the most preferred gonad taste, gonad yields still above market minimum (mean ± SE: 25.6 ± 1.5%), and the third lowest FCR (mean ± SE: 1.5E-2 ± 1.9E-3 feed g gonad increase g-1), while urchins fed V10.1.10 at 16°C had the best colour (mean degree of colour difference ± SE: 6.0 ± 0.9). Therefore, it can be suggested that optimal conditions moving forward for green sea urchins would be feeding V10.1.10 at 12°C. For red sea urchins, those fed V10.1.10 produced the highest gonad yields at 12°C (mean ± SE: 12.7 ± 1.5%) and the best colour at 16°C (mean degree of colour difference ± SE: 30.3 ± 3.1), while red sea urchins fed V10.1.9 at 16°C produced the second highest gonad yields (mean ± SE: 11.0 ± 0.4%), the lowest FCR-G (1.9E-3 ± 2.8E-4 feed g gonad increase g-1), the most preferred gonad taste, and a low degree of colour difference (mean ± SE: 32.3 ± 2.1). Therefore, it can be suggested that optimal conditions moving forward for red sea urchins would be feeding V10.1.9 at 16°C. / Graduate

Thesis (M.M.S.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 76-80.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2002. / Restricted until October 2003. Bibliography: leaves 114-129.