Lecture 2 Biology 1002 Objectives 1)Examine an example of a heterotrophic protist, Amoeba, that use pseudopodia for movement and feeding. 2)Examine the plasmodial slime molds (Myxogastrida) and their relation between their biology and their ecology.

Three groups of protists use pseudopodia, cellular extensions, to move and often to feed. –Most species are heterotrophs that actively hunt bacteria, other protists, and detritus. –Other species are symbiotic, including some human parasites. –Little is known of their phylogenetic relationships to other protists and they themselves are distinct eukaryotic lineages. A diversity of protists use pseudopodia for movement and feeding Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Rhizopoda are all unicellular and use pseudopodia to move and to feed. Pseudopodium emerge from anywhere in the cell surface. –To move, an amoeba extends a pseudopod, anchors its tip, and then streams more cytoplasm into the pseudopodium. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig Amoeba sp.

Amoeboid movement is driven by changes in microtubules and microfilaments in the cytoskeleton. Pseudopodia activity is not random but in fact directed toward food. In some species pseudopodia extend out through openings in a protein shell around the organism. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Amoebas inhabit freshwater and marine environments and maybe also abundant in soils Most species are free-living heterotrophs. Some are important parasites. –These include Entamoeba histolytica which causes amoeboid dysentery in humans. These organisms spread via contaminated drinking water, food, and eating utensils. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The plasmodial slime molds (Myxogastrida) are brightly pigmented, heterotrophic organisms. The feeding stage is an amoeboid mass, the plasmodium, that may be several centimeters in diameter. The plasmodium is not multicellular, but a single mass of cytoplasm with multiple nuclei. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

The diploid nuclei undergo synchronous mitotic divisions, perhaps thousands at a time. Within the cytoplasm, cytoplasmic streaming distributes nutrients and oxygen throughout the plasmodium. The plasmodium phagocytises food particles from moist soil, leaf mulch, or rotting logs. If the habitat begins to dry or if food levels drop, the plasmodium differentiates into stages that lead to sexual reproduction. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The cellular slime molds (Dictyostelida) straddle the line between individuality and multicellularity. The feeding stage consists of solitary cells. When food is scarce, the cells form an aggregate (“slug”) that functions as a unit. Each cell retains its identity in the aggregate. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig

The dominant stage in a cellular slime mold is the haploid stage. Aggregates of amoebas form fruiting bodies that produce spores in asexual reproduction. Most cellular slime molds lack flagellated stages. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Slime molds and water molds maybe thought to resemble fungi, but they are not closely related. Any resemble is analogous not homologous. What does this mean?