Ch 12 Flashcards
Lifestyles of slime molds
spend most of their lives as single cells but undergo radical development to a slug (multlicellular)
cells in stalk act like somatic cells (responsible for growth)
spore cells act like germ cells (reproduction)
*some individuals sacrifice when moving toward food or away from predators
Cellular slime molds (social amoebas) served for what?
model system to study major transitions
Do all organisms tend to become larger and more complex through time?
Not a good statement because some parasites become less complex. Some haven’t changes in billion years (archaea and bacteria specifically)
Eusocial societies
example - bees
work with a division of labor and sterile workers
What is a common feature among processes that share major transitions
Individuals give up the ability to reproduce independently, and they join together to form a larger grouping that shares reproduction
-replicating models join together to form protocells
economies of scale
arise when groups can do things that individuals can not
ex. social insects that acquire large prey items
What is the advantage of individuals aggregating into higher-level grouping?
They can take advantage of economies of scale and efficiencies of specialization
What happens when aggregation and specialization facilitate changes in information technologies?
Organisms develop new and increasingly efficient ways to acquire, process, transmit, and store information
ex. change from RNA storage system
Why are major transitions difficult to explain by natural selection?
because advantages at individual level need to be indentified during the transition and when it’s complete
Why do higher-level individuals continue to exist?
Once higher level individuals get locked into their current biology, they can’t revert back to previous state
genetic imprinting
alleles are differentially expressed according to whether they are inherited from the mother or father
parthogenesis
reproduction without fertilization. it occurs when a female gamete develops new individuals with out being fertilized by a male gamete. so eggs are already laid fertilized
What would happen if parthenogenesis evolved?
Their offspring wouldn’t express any of the paternally derived genes
*common in plants, but not conifers since chloroplasts are transmitted thru pollen
Were pollen-derived transmission and imprinting evolve to prevent parthenogenesis?
No but once present they served this purpose
example of exaptation (when a trait was derived for a different purpose, but coopted for another function).
When did eukaryotic and prokaryotic cells arise?
Pcells orginated 3bya
Ecells originated 1-2bya
How many times has life came about?
Life as we know it originated once, but there were many previous dead ends where only one group of ancestor made it
What has suggested links with both Archaea and bacteria?
Work on enzymes, RNA, and ribosomes
Informational genes?
transcription and translation genes; are more closely related arhaeal genes.
Operational genes
metabolic processes, cell membrane function, AA production; are more closely related to bacterial genes
Whole genome analyses suggests what?
Fusion of an archaeal cell (probable eocyte) and bacterium probably involved some sort of endosymbiosis (symbiosis within a cell) where one cell engulfed the other but didn’t metabolize it
working hypothesis
a hypothesis that could be falsified or supported by future analysis
How did organelles come about?
Endosymbiotic theory (Margulis); chloroplasts and mitochondria evolved from a long term symbiotic relationship. Endosymbionts provided hosts with critical resources (energy & food) & hosts provide protection from dangers in environment. Relationship became so strong that obligate relationship evolved
What serves as evidence in support of the Endosymbiotic Theory?
Chloroplasts and mitochondria has its own distinct genome & circular chromz that resemble those found in bacteria. Also, phylogenetic analyses find chloroplast RNA is more closely related to cyanobacteria than other eukaryotes = suggests chloroplasts were once free living cyanobacteria.
What do mitochondrial genes most closely resemble?
Proteobacteria more than other eukaryotes
What is “promiscuous DNA” mean
200-600 insertions of mtDNA into human nuclear genome
What conclusion came from Huang experiment
Series of endosymbiotic mergers followed by endosymbiosis. This expt was the one about antibiotic resistance when exposed to kanamycin. If chromosome was in mt it won’t work because mt has its own genome; but when the gene migrated to the nucleus it works.
Apicoplast? how did it arise?
Organelle found only is Apicoplasta; contains pathogens such as plasmodium f. (agent of malaria)
Arose thru SECONDARY endosymbiosis event (engulfed twice=quadruple membrane); since it has two kingdoms it can be targeted specifically.
How can apicoplast be useful to treat malaria?
If target the similar pathways of euk’s, you can risk harming human host. Instead it targets apicoplast pathways because of prokz ancestry.
How did the evolution of multicellularity come about
Transition occurred multiple times in many taxa. NOT necc. an obligate condition. But the cell may have joined together and disbanded like the slime molds.
How does the slug orient itself in its environment when composed of previously independent cells?
Dependent on cAMP (cyclic adenosine monphosphate) *orients in direction from which cAMP was emitted. Then the cells make proteins that allow them to stick together
cAMP-signaling system
Provides info. about benefits of multicellularity in addition to how slug moves. & allows slug to orient to environmental cues like light and temp or ammonia & O2 gradients
*slug can sense and respond to these cues that individual cells cannot
Slugs produce slime “sheath” that protects itself from nematodes. This is completely absent from individual cells. What is this an example of?
Example of ECONOMY OF SCALE; Surface to area ratio makes a slug sheath much less expensive to produce than individual sheaths
Benefit of multicellularity in slugs versus single cell amoeba stage
allowed to move faster than cellular stage; slugs move more efficiently and benefit from economy of scale
What occurs when slug reaches soil surface?
Fruiting bodies form stalks made from non reproductive cells and spores (reproductive cells)
Spores dispersing by contact with invertebrates serves as an example of what? (2)
Economy of scale and Selective advantage
Which slug cells get to become spores?
Slug cells that become spores are usually those that have the GREATEST NUMBER OF RESOURCES.
Most of cells in fruiting bodies are genetically highly related = form of GENETIC ALTRUISM
define individuals
integrated and indivisible wholes that can reproduce and pass on to their offspring heritable variations
Is the slug an individual?
Groups of slime mold cells are not individuals as they’re capable of reproduction at a different stage of development
Critical component of the transfer of fitness from lower to higher levels of organization involves what two parts?
The differentiation of cell lines to those specialized in reproduction (germ cells) and specialized in maintenance and growth of the organism (somatic cells=soma)
What can natural selection act on (during the slim mold transition)
Can act on transitions from one level of individuality to another
What is special about the volvocine algae?
Type of green algae that evolved from unicellular ancestors ~230mya. Very recent evolution of multicellularity in multiple lineages. Exceptional variation found in group
Somatic cells are smaller and the reproductive cells are larger
What is another important features of the volvacine algae?
each somatic cell has two flagella- long hairlike projections for motion
however the germ cells lack this since they’re specialized for reproduction.
How is a cell fate determined?
Depends on expression of gene regA. If expressed, it suppresses a number of nuclear genes that code for chloroplast proteins. Also, slows down cell growth (preventing cell div.). Lastly, cells stay small and produce flagella, becoming soma cells
What happens if regA is not expressed?
Cells photosynthesize and grow LARGE, it also won’t produce flagella = forming germ cells
regA evolution?
Traces back to unicellular volvocine ancestor of modern-day unicellular volvocine species. (in the C. reinhardtii the flagellated cells first grow in size and then absorbs its flagellum and produces daughter cells).
regA-like gene is expressed as function of environmental cues. Why is this important?
Over evo-time the regA gene was co-opted into regulating cell differentiation into germ and soma cells in multicell. organisms like C. carteri
What are benefits of group living?
- foraging, safety from predators
- *requires sociality
- coordination and commination between individuals
define Group
Set of conspecific individuals who affect each other’s fitness
there are various degrees of group living
How is the majority of time spent in an organism?
foraging for food and some type of anti-predatory behavior
What is foraging in groups an example of? What organism serves as a direct example?
Economies of scale ; bluegill sunfish - their foraging success per fish often increases as a function of group size (but this is actually “passive” benefit of group foraging)
Which organism is the most remarkable case of group-level foraging?
Honeybees; when worker finds a new food source, it performs a waggle dance on a vertical honeycomb within the hive. the dance conveys info about the food source.
the “many eyes” hypothesis states:
More “eyes” in a group searching for predators the less chance there is for a predator to remain unnoticed. Applies to any sensory modalities.
What is larger group attracts predators?
group size maximized at intermediate group sizes.
What is an anti-predatory behavior in schooling species of fish?
Schools produce hydrodynamic effect allowing for faster movement than swimming alone = increases escape from predz.
Flash explosions (in fish)
individuals in a school swim off in all directions which confuses predz facilitating escape.
What are the costs of living in a group
other members are competitors for food resources and transmission of parasites (ectoparasites that cling on the outside of host and can easily move from one to another)
