Importance of Feedback loops in social organization, types of feedback loop structures, redundancy and robustness.
Proximate mechanisms of today define ultimate questions for tomorrow.
Focus on theoretical issues focused on social insects as reference model and also how to use these issues experimentally in that context.
Insect societies can be seen as nonlinear dynamical systems. And this perspective opens up new ways to approach experimental set ups and also interpret results.
Hypothesis there is amplification — design experiment to detect, quantify,
There is very important information in the details of the exact structure of the feedback loop mechanisms.
Proximate and ultimate
We need to look at and understand proximate first — since ultimate is speculative.
Robustness of mechanisms with variation from below.
Take social insect as reference model.
Self-organizing sex ratios.
Food availability with sex ratio. Population wide sex ratio.
What are mechanisms that regulate sex ratio? Must be distributed regulation mechanism.
Positive feedback is a mechanism for realizing self-organization — not equivalent conceptually, but empirically often occur.
Versus template.
Foraging, aggregation, building. There is no natural situation, coupling between self-organization and self-organization. In natural condition,
To understand how different feedback structures generate different types of patterns.
Stress question of dynamics: organization of society is by dynamics: way that you organize experiment and measure: if take snapshot data collection and get results that are not statistically significant which are amplified over time by repeated feedings or nonfeeding of related larvae.
Plus amplification by if give a bit more food to related larvae and then have system where if larvae a little larger more likely to get fed more etc.
Example of amplification, which a statistical assessment would miss. Experimentally, need to design experiment to give opportunity to detect such amplification feed back loops.
Can been even more opportunity for feedback .
May have statistically significant difference which might think mean something biologically concerning colony phenotype which do not
Why — there may be systemic neutralization of the variation.
Subpoint: there are structural features of feedback loops that generation this
There are ways in which interaction occurs that neutralizes variation
(problems with detecting amplifications) Measurement errors in the laboratory can also be responsible for predictions that are far from what is observed.
Redundancy and robustness to internal changes.
How to take the dynamical features seriously.
A positive feedback loops
Negative feedback
How to
Amplification
Positive feedback
In social insects prevalent
Where there is differentiation (different states — like foragers and nurses) as output there is reason to believe it is result of a positive feedback loop
Stabilizaton of differentiation may require negative feedback loop.
Very often have mixture of selforganization and template influence on differentiation. E.g. genetic variation predisposes an indivdual to be in one of the variant states, but the interaction mechanisms are what drives the realized differentiation.
Strength of loop is significant: if have a positive feedback loop, but may be too weak w.r.t. another feedback loop so it has no actual effect. Even if can identify positive loops — what may be explaining phenomenon may be something else operating that is stronger. Example: recruitment: give qualitiative description of bees recruitment and ants -= dance vs. trail, don’t see big difference. Due to the specific forms of amplification in each cases, results is completely different.
Bees — equal sources distribute equally
Ants — equal sources usually have skewed distribution
This is quantitative difference and not qualitative difference.
Link between individual behavior and collective response.
Observe collective level. Open way to first set of experiments to identify for well defined conditions, identify t he mechanisms. Then see if it is reproducible. Open new way to make prediction for new conditions to determine how for example if increase population size, or distribution of food or shelter, then see what happens.
Often such models don’t work under new conditions because have not captured the complexity of the indiviedyual or parameter exactly. But if make measurement error then on basis of small variations having large effects downstream.
In description need to mention that basic behavior can be changed by the structure of community
Bottom up is to Start with individual behaviors — then derive global effects
But reverse occurs, since when new global effects open up new selection opportunities that can then change behaviors of individuals — can take this step-wise.
This process is general and not specific to social insect study.
Negative feedback of Zach — social structure in honeybee evolution. Nursing and foraging — latter is risky, so do less of this. Feedback loop to minimize risk and hence to minimize foraging, then turn off vitelligen apparatus.
Idea: redundancy — need to talk about it.
Redundancy concept comes from engineering. To have different devices doing same thing can lower probability of system failure. Two or three mechanisms or processes can perform same function and give you functional robustness.
Different types of redundancy
redundancy can be a systemic property. Suppose 3 processes perform same function — It would selected for in an environment of high probability of failure and need to respond to perturbations.
If each of 3 types have possibility o f breaking down, then have selection pressure for all of them to come under one control. Then change from 3 ways to fail to one. Get regulatory redundancy is then removed by selection.
Whether redundancy is adaptive or maladaptive depends on selection environment and selective pressures.
Totipotency is a special form of redundancy. Developmental process. Capacity of moving from one state to another — can also be interpreted as having pathways from one attractor to another.
Size of individual worker is highly variable (not like size of cell). With limited resources better to make 10 tiny ants than 2 big ants. Relative costs of loss is involved in size. If see total weight of colony, could distribute total biomass in different ways (tiny or large), you have more redundancy with 10 tiny ones than 2 big ones in terms of individual loss. Small number of large workers, ponerine ants, bumble bees, but having different number of workers changes the types and kinds of interactions. if have fewer, larger individuals do they need to be more plastic?
If size variation and redundancy relationship hold, expect small social insect colonies to not have obligate soldiers. Double statistical correlation — small societies are weakly polymorphic where Workers are involved in defense. If follow growth of society in its lifetime. Then When society is small has no soldier, when it gets big enough can afford to have soldiers. amplification mechanism of when colony larger, can feed some larvae more and they be larger individuals and become solider. (there is also a negative feedback of pheromone control to stabilize the growth of larger size larvae)
Regulation or stabilization in dynamical process requires the coupling of positive feedback and negative feedback. Standard pattern. Way of Establishing and maintaining group features. Here again the details of the mechanisms matter. Different specific feedback mechanisms can push system into different stable attractors.
Why polygyny? 2 jobs. One: can help with faster growth of society, larger number of workers more quickly. Two: 2 queens can have complementarities as a source of diversity. Where diversity gives possibility of better response with amplification. Plasticity.
Proximate mechanisms of today define the setting for the ultimate questions of tomorrow.
One way — is modifies the set of variants over which selection can operate.
Canalizing pathways means some of the structures upstream determine possibilities downstream in development also affects how likely it is for selection to modify those features.
Example: how to feed larvae. Strategy providing all food at onece (cap it) vs sequential feeding. These early behavioral choices constrain later behavioral opportunities. And ultimate questions about adaptation are affected by these differences.
Look at social spider colony — looks similar to social insects, collective capture, synchronization, but no eusociality. How explain this? Might look for canalization.
Experimentation can mimic contexts of evolutionary history. By isolating individuals out of social groups and explore the mechanisms.
Reduce or increase artificially the size of colony to see what happens. Can use this to try to understand different types of interaction. Try to analyze behavior of solitary species, manipulate them to see what they do and behavior of social. Can identify the mechanisms that are modified or conserved and this Could help to answer how easy it was to move from solitary to social.