This dissertation is devoted to better understanding the role that fluids play in the selection of the shapes and functions of objects and creatures in nature. Toward that end, three specific examples are considered: stalactites, icicles, and species of colonial green algae known as Volvox. In the cases of stalactites and icicles, the object's growth is considered as a free-boundary problem. For stalactites, the coupling of thin-film fluid dynamics with calcium carbonate chemistry leads to a local, geometric growth law that is proportional to the thickness of the water layer covering the surface at any point. Application of this law to a uniformly translating shape allows a universal stalactite form to be derived; the comparison of this shape to images of actual stalactites supports the theory. In the case of icicles, the transport of the latent heat of fusion is coupled with the dynamics of both the thin-film of water encompassing the icicle and a thermally buoyant boundary layer in the immediately surrounding air. The uniformly translating shape solution is found to be parameter-free, and is, in fact, the same shape exhibited by stalactites. A comparison between this shape and icicle images validates the theory. The final example considers how advection of nutrients due to the stirring of water by the flagella of a Volvox colony leads to a metabolite uptake rate that is much greater than would occur by diffusion alone. Moreover, nutrient acquisition by pure diffusion would limit the size of Volvox species to a certain bottleneck radius at the point where diffusional uptake just meets metabolic demands, whereas advection increases the uptake in such a way as to avoid this problem entirely, thus enabling the evolution of the larger Volvox species.

A detailed limnological study of Clark's Borrow Pit Pond (SW* Sec. 30 T22N R9E, Delaware County, IN) was conducted from the spring of 1978 through the fall of 1979 to ascertain what factors regulate the abundance of Volvox aureus, a major phytoplanktor of the pond. This algal species often dominates the spring and sometimes fall phytoplankton blooms that occur annually, but disappears fran the plankton throughout the remainder of the year.Laboratory growth experiments suggest that the spring peak of V. aureus (105 colonies ml-l in 1978) is most likely induced by the high nutrient levels in the pond (total P = 4.6 µmoles ℓ-1; NO3 - N + NH3 - N = 11.8 Wholes 2-1) and warming temperatures. Competition from other algal species is reduced at this time by the presence of the zooplanktor Da hnia ambigua which effectively grazes all but the V. aureus colonies. Decreased nutrient levels in the summer months (total P = 1.0 µmoles Z-1 N03 - N + NH3 - N = 1.3 µmoles Z-1 ) restrict the abundance of V. aureus, and other algal species (notably blue-greens) dominate. Two of these species, Oscillatoria sp. and Microcystis sp., were shown to exhibit no allelopathic influences on the growth of V. aureus. However, experiments suggested a heat labile inhibitor or inhibitors of V. aureus may periodically affect its growth in the pond. Increasing nutrient levels in the fall sometimes induce a second V. aureus bloom, but this declines rapidly as the water temperature drops below 10° C. Consequently, the abundance of V. aureus in Clark's Pond is influenced mainly by abiotic factors (nutrient availability and water temperature) and only to a lesser degree by biotic factors (grazing and competition).

The fitness of any evolutionary unit can be understood in terms of its two basic components: fecundity and viability. The trade-offs between these fitness components drive the evolution of a variety of life-history traits in extant multicellular lineages. Here, I show evidence that the evolution of germ-soma separation and the emergence of individuality at a higher level during the unicellular-multicellular transition are also consequences of these trade-offs. The transition from unicellular to larger multicellular organisms has benefits, costs, and requirements. I argue that germ-soma separation evolved as a means to counteract the increasing costs and requirements of larger multicellular colonies. Volvocalean green algae are uniquely suited for studying this transition since they range from unicells to undifferentiated colonies, to multicellular individuals with complete germ-soma separation. In these flagellated organisms, the increase in cell specialization observed as colony size increases can be explained in terms of increased requirements for self-propulsion and to avoid sinking. The collective flagellar beating also serves to enhance molecular transport of nutrients and wastes. Standard hydrodynamic measurements and concepts are used to analyze motility (self-propulsion) and its consequences for different degrees of cell specialization in the Volvocales as colony size increases. This approach is used to calculate the physical hydrodynamic limits on motility to the spheroid colony design. To test the importance of collective flagellar beating on nutrient uptake, the effect of advective dynamics on the productivity of large colonies is quantified. I conclude first, that when colony size exceeds a threshold, a specialized and sterile soma must evolve, and the somatic to reproductive cell ratio must increase as colony size increases to keep colonies buoyant and motile. Second, larger colonies have higher motility capabilities with increased germ-soma specialization due to an enhancement of colony design. Third, advection has a significant effect on the productivity of large colonies. And fourth, there are clear trade-offs between investing in reproduction, increasing colony size (i.e. colony radius), and motility. This work shows that the evolution of cell specialization is the expected outcome of reducing the cost of reproduction in order to realize the benefits associated with increasing size.

Univ., Diss.--Regensburg, 1998.

Die Entdeckung der Kanalrhodopsine (ChRs) C1 und C2 aus der Grünalge Chlamydomonas reinhartii vor 10 Jahren brachte die neue Proteinfamilie der lichtgesteuerten Ionenkanäle hervor. Diese 7-Transmembranproteine verwenden all-trans Retinal, um Licht einer bestimmten Wellenlänge zu absorbieren. Bei Lichtabsorption isomerisiert das Retinal und das Protein öffnet daraufhin seine Pore, die es Ionen wie H+, Na+ und Ca2+ erlaubt, abhängig von ihrem elektrochemischen Gradienten, die Membran zu passieren. Insbesondere in der Neurophysiologie findet seit kurzem das C2 eine breite Anwendung, da seine Expression in Nervenzellen es erlaubt, mittels kurzer Lichtpulse die elektrische Aktivität dieser Zellen zu kontrollieren. In dieser Arbeit wurden zum ersten Mal die beiden neuen ChRs V1 und V2 aus der mehrzelligen Grünalge Volvox carteri elektrophysiologisch charakterisiert. Hierbei zeigte sich, dass V2, ähnlich wie C2, im blauen Spektralbereich absorbiert und auch, dass sich die kinetischen Eigenschaften stark ähneln. Dagegen besitzt V1 eine um 70 nm längerwellig verschobene Absorption auf 535 nm bei einer ~ 10 x langsameren Abklingkinetik als C2. Durch die schlechte Membranintegration von V1 in eukaryotischen Zellen ist der Photostrom gering und die Anwendungen in Neuronen stark eingeschränkt. Um die Membranintegration zu verbessern, wurden einzelne Helices von V1 gegen die entsprechenden Helices der anderen ChRs ausgetauscht. Hierbei wurde eine Chimäre C1V1-25, die aus den ersten 2 Helices von C1 und den restlichen 5 Helices von V1 besteht, entwickelt. Die Chimäre besitzt weiterhin eine rotverschobene Absorption bei 539 nm, einen 4 x höheren Photostrom als V1 und der doppelt so hoch ist wie der von C2. / The discovery of the channelrhodopsins (ChRs), C1 and C2 from the green alga Chlamydomonas reinhardtii 10 years ago, created the new protein family of light-gated ion channels. Those 7-Transmembranproteins are utilizing all-trans retinal to absorb light at specific wavelength. Upon light absorption the retinal isomerizes which leads to opening of a protein pore allowing ions such as H+, Na+ and Ca2+ to pass the membrane depending on their electrochemical gradient. In the last years C2 attracted a lot of attention in neuroscience since its expression in neurons allows to control their electrical properties with short light pulses. This work presents the electrophysiological characterization of two new ChRs V1 and V2 from the multicellular agla Volvox carteri for the first time . V2 absorbs light in the blue visible range like C2 and almost identical kinetic properties. In contrast, V1 exhibit a 70 nm redshifted absorption towards 535 nm and a ~ 10 x slower off-kinetic than C2. Since V1 displays only weak membrane targeting the resulting overall small photocurrent in eukaryotic cells significantly hampered its application in neuronal cells. To improve membrane targeting and to retain redshifted absorbance helices from V1 were exchanged with the corresponding helices from the other ChRs. A chimera called C1V1-25, which consists out of the first 2 helices from C1 and the last 5 helices from V1 showed a absorbance maximum at 539 nm and exhibit a 4 times higher photocurrent even beeing 2 times higher then the one of C2.

Univ., Diss.--Regensburg, 2000.