Aggregates in which cells are separated by their

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aggregates in which cells are separated by their membranes The feeding stage of the life cycle consists of solitary cells that function individually, but when food is depleted, the cells form an aggregate that functions as a unit Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity A common cellular slime mold on forest floors
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The life cycle of cellular slime mold ( Dictyostelium )
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Some Dicty cells are “obligate cheaters,” and never form the stalk... linked to a single gene mutation in cell surface protein may gain a reproductive advantage obligate are rare or absent in wild Noncheaters preferentially aggregate with other noncheaters Primitive form of cooperative behavior
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Dictyostelium has primitive farming symbiosis: About 1/3 of wild Dictyostelium engage in husbandry Stop feeding early and incorporate bacteria into fruiting bodies Carry bacteria during spore dispersal to seed a new crop Advantageous at some new sites, disadvantageous at other Farming Dictyostelium will reassociate with bacteria – persistent interaction Social behavior because benefits of farming go to established kin groups
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Fungi Fungi are diverse and widespread Essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients
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Fungi are heterotrophs that feed by absorption Despite their diversity, fungi share key traits, most importantly the way in which they derive nutrition Fungi are heterotrophs but do not ingest their food They secrete exoenzymes that break down complex molecules, and then they absorb the smaller compounds The versatility of these enzymes contributes to fungi’s ecological success
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Fungi exhibit diverse lifestyles: Decomposers (a.k.a. saprobes ) these are everywhere – common on the forest floor Parasites (~30% of fungi are parasitic) absorb nutrients from a living host responsible for ~80% of plant diseases Mutualistic symbionts root tip fungi and plants – help in nutrient scavenging and receive carbon from the plant (more on this later...)
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The two most common body structures are multicellular filaments and single cells (yeasts ) The morphology of multicellular fungi enhances their ability to absorb nutrients
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