In the rocky intertidal, organisms frequently experience a wide range of daily body temperatures depending on the stage of the tide and the time of day. In the intertidal, the thermal adaption of a species and its ability to invade a new region may be closely linked. In this research, the physiological effects of thermal stress in both low tide and high tide conditions are compared between Mytilus galloprovincialis, a worldwide mussel invader, and M. trossulus, a sibling species. In a seawater tank, mussels were exposed to one of three aerial temperature treatments (20, 25, 30 degrees C) in a cycle with one of two water temperatures (18, 12 degrees C). In 18 degrees C water, there was no effect of the aerial treatments on growth or survival in either species. In contrast, in 12 degrees C water, aerial exposure affected the survival and growth of both species. Growth and survival rates of M. galloprovincialis were higher in all conditions than the rates of M. trossulus, especially in the 18 degrees C water experiments and in the aerial exposure treatments of the winter 12 degrees C water experiment. M. galloprovincialis appears to be warm-adapted with regard to both low tide and high tide thermal stress. These results when paired with previous research suggest that as climates shift due to global warming, the temperatures favorable to M. galloprovincialis will become more common.

To understand the mechanisms of invasions it is necessary to explore how thermal environments affect the distribution of both native and invasive species. We examined patterns of species distribution at several scales to determine how thermal selection affects the distribution of native (Mytilus trossulus) and invading (M. galloprovincialis) mussels inhabiting marine rocky intertidal and subtidal habitats. Previous work on these species has focused on the role of water temperature in setting distribution patterns, neglecting the role of aerial exposure at low tide. We therefore examined patterns of abundance in shaded and sun-exposed intertidal habitats and in intertidal versus subtidal habitats at sites within the San Francisco Bay over 3 yr. At half (2/4) of the sites the abundance of the native mussel was significantly higher in shaded intertidal habitats compared to warmer, sun-exposed intertidal habitats, where the invasive mussels were more abundant. Additionally, when comparisons were made between paired subtidal and intertidal sites, native mussel abundance was higher in subtidal habitats. In general, however, there was an unexplained and steady decrease in M. trossulus abundance at all sites. Field transplant experiments showed that the native mussel had lower survivorship than the invading species in all habitats examined (subtidal, shaded, and sunexposed intertidal). Overall survivorship was lowest for both species in the sun-exposed intertidal treatments. This study shows that physiological stress associated with aerial exposure is likely to contribute to the local and geographic distribution of these mussel species. Moreover, our results suggest that processes that operate over larger geographic scales may be experimentally detectable over much smaller scales.

No abstract

SummaryAlthough gap junction plaque assembly has been extensively studied, mechanisms involved in plaque disassembly are not well understood. Disassembly involves an internalization process in which annular gap junction vesicles are formed. These vesicles undergo fission, but the molecular machinery needed for these fissions has not been described. The mechanoenzyme dynamin has been previously demonstrated to play a role in gap junction plaque internalization. To investigate the role of dynamin in annular gap junction vesicle fission, immunocytochemical, time-lapse and transmission electron microscopy were used to analyze SW-13 adrenocortical cells in culture. Dynamin was demonstrated to colocalize with gap junction plaques and vesicles. Dynamin inhibition, by siRNA knockdown or treatment with the dynamin GTPase inhibitor dynasore, increased the number and size of gap junction 'buds' suspended from the gap junction plaques. Buds, in control populations, were frequently released to form annular gap junction vesicles. In dynamin-inhibited populations, the buds were larger and infrequently released and thus fewer annular gap junction vesicles were formed. In addition, the number of annular gap junction vesicle fissions per hour was reduced in the dynamin-inhibited populations. We believe this to be the first report addressing the details of annular gap junction vesicle fissions and demonstrating a role of dynamin in this process. This information is crucial for elucidating the relationship between gap junctions, membrane regulation and cell behavior.

No abstract