ants/docs/FOOD-QUALITY.md

# food quality perception and evaluation in ants

reference doc for food quality mechanics in the simulation. all claims sourced
from published research. confidence levels noted where information is
extrapolated or less well-established.


## 1. sensory detection: what ants can taste

### sensory organs

ants detect food using gustatory (taste) sensilla distributed across multiple
body parts. the primary taste organs are:

- **foreleg tarsi** — contact chemoreceptors. in fire ants (Solenopsis invicta),
  the foreleg tarsi play a MORE important role in sucrose detection than the
  antennal flagellum. sensilla chaetica, trichoid II, and basiconica I/II all
  have a clear pore at their tip for chemoreception.
- **antennal flagellum** — both olfactory and gustatory sensilla. used for
  close-range assessment and during trophallaxis.
- **maxillary and labial palps** — mouthpart sensilla for evaluation during
  ingestion.
- **pharynx** — internal gustatory sensilla that evaluate food as it enters the
  crop.

**confidence: high** — well-established insect morphology, confirmed across
multiple ant species.

### gustatory receptor (GR) genes

the number of GR genes varies by species and correlates with dietary breadth:

| species                  | common name         | GR genes |
|--------------------------|---------------------|----------|
| Linepithema humile       | Argentine ant       | 96       |
| Apis mellifera           | honeybee            | 10       |
| Drosophila melanogaster  | fruit fly           | 68       |

ant GR genes fall into four clades: CO2 receptors, GR43a-like (internal
fructose/nutrient sensors), sugar receptors, and bitter receptors. generalist
species tend to have expanded bitter receptor families, presumably broadening
the range of plant secondary metabolites they can detect.

**confidence: high** — genomic data from sequenced ant genomes.

### sugars

**preference hierarchy**: sucrose > glucose >> fructose (in fire ants)

- fire ant workers strongly prefer sucrose and glucose but show only weak
  attraction to fructose.
- SinvGr43a is a fructose-responsive gustatory receptor in S. invicta, but it
  acts primarily as an INTERNAL nutrient sensor (linked to neuropeptide
  regulation and lipid metabolism) rather than a peripheral taste receptor.
- concentration matters: ants discriminate between sucrose concentrations.
  1.0 M sucrose elicits strong behavioral responses (trail-laying, feeding),
  while 0.01 M sucrose does not. in Lasius niger experiments, 0.2 M sucrose
  led to lower food acceptance than 1.0 M.
- threshold detection in related insects: ~10 mM for antennal sensilla,
  ~100 mM for tarsal sensilla (moth data — ant-specific thresholds likely
  similar order of magnitude but not precisely established).

**confidence: high** for preference hierarchy and concentration discrimination.
moderate for exact threshold values in ants specifically.

### amino acids and proteins

- ants discriminate essential amino acids (EAAs) from non-essential ones.
- when deficient in both carbs and EAAs and offered sucrose+EAA vs
  sucrose+non-EAA solutions, ants focused foraging on the EAA solution
  regardless of amino acid:carbohydrate ratio.
- S. invicta workers showed strong preference for leucine (an EAA) over other
  tested amino acids, with preference intensifying at higher concentrations.
- when choosing between high-protein foods, ants preferred free amino acids
  over whole proteins. no preference emerged with high-carb foods.

**confidence: high** — multiple controlled experiments across species.

### salts and minerals

- Solenopsis richteri workers prefer zinc, magnesium, and ammonium.
- sodium preference varies and shows a geographical gradient: ants farther from
  the ocean consume more sodium. non-predatory species consume more sodium than
  predatory species (predators get sodium from prey).
- salts and acids are attractive at low concentrations but aversive at high
  concentrations (inverted U response curve).

**confidence: high** — field and lab studies.

### toxins and deterrents

- quinine is aversive to Lasius niger.
- high concentrations of caffeine in sucrose reduced feeding in Oecophylla
  smaragdina (weaver ants).
- alkaloids reduced feeding in Ectatomma ruidum.
- leaf-cutter ants (Atta, Acromyrmex) avoid leaves containing anti-fungal
  terpenoids that would harm their cultivar fungus.

**confidence: high** — behavioral assays with known compounds.


## 2. nutritional assessment and post-ingestive feedback

### speed of assessment

ants can compensate for nutritional deficiencies in their colony in under 10
minutes. this is fast enough that it likely involves rapid nutrient sensing
rather than slow learning/feedback loops.

### post-ingestive feedback mechanism

the term "post-ingestive feedback" refers to the process by which nutrients
interact with receptors on enteroendocrine cells in the gut after ingestion.
these cells secrete hormones that signal the brain and other tissues about
nutrient composition, food texture, and meal size.

mechanistic details (primarily from Drosophila, likely conserved in ants):
- Dh44 neurons are necessary and sufficient for post-ingestive nutrient sensing
- gut-to-brain signaling uses neuropeptide pathways
- the internal fructose sensor GR43a (mentioned above) is part of this system,
  linking circulating nutrient levels to feeding behavior and lipid metabolism

**confidence: moderate** — the gut-sensor mechanism is well-established in
Drosophila. the specific molecular pathways in ants are inferred by homology
rather than directly demonstrated. the behavioral outcomes (rapid compensation)
are directly measured in ants.

### learning and memory about food quality

- ants can learn which foods are nutritious vs empty calories. foraging
  motivation and food quality affect both route memory formation speed and the
  likelihood of returning to a food source.
- two parameters dominate quality assessment at a food site:
  1. **amount of food available** — initially dominates the decision to return
  2. **reliability of food encounter** — takes precedence after a few visits
- ants may learn the location of higher-quality food faster, with most ants
  eventually congregating at the best source.

**confidence: high** — direct behavioral experiments.


## 3. the geometric framework for nutrition

### core concept

the geometric framework (developed by Simpson & Raubenheimer) models nutrition
as a multi-dimensional space where each axis represents a nutrient. animals have
an "intake target" — an optimal point in this space — and regulate their feeding
to approach it.

### how it applies to ant colonies

- colonies have separate appetites for protein and carbohydrate, enabling them
  to compensate for changes in nutrient density and to select among
  nutritionally complementary foods.
- **workers need carbohydrates** (energy for foraging, maintenance).
- **larvae need protein** (growth, development).
- this creates a fundamental tension: the colony must collect both, but the
  ratio shifts with brood load.

### colony-level regulation

- in Monomorium pharaonis (pharaoh's ant), colonies defended a slightly
  carbohydrate-biased intake target.
- when confined to imbalanced protein:carbohydrate (P:C) diets, colonies used a
  "generalist equal-distance strategy": overharvesting BOTH protein and
  carbohydrate to reach the target ratio, rather than prioritizing one.
- ants regulate macronutrient intake at both individual and colony levels,
  maintaining their specific elemental body composition.

### what happens when the balance is off

- when carbohydrate-supplemented, fire ant colonies consumed less cricket and
  specifically avoided high-lipid ovaries.
- when amino-acid-supplemented, they consumed less male cricket (lower lipid,
  higher protein).
- this demonstrates independent regulation of at least protein, carbohydrate,
  and lipid.

**confidence: high** — the geometric framework is well-validated across multiple
ant species and other social insects.


## 4. food quality and recruitment behavior

### the pharaoh's ant baseline (Monomorium pharaonis)

- trail-marking ants deposited significantly more pheromone when returning from
  high-quality food (1.0 M sucrose) vs low-quality food (0.01 M sucrose).
- at low food quality, there was no significant difference in marking intensity
  between fed and unfed trail-marking ants — the quality signal disappeared.

### Lasius niger (black garden ant)

- deposits up to 22x more pheromone within 10 cm of a food source compared to
  near the nest.
- uses an all-or-nothing individual response to food quality (binary: mark or
  don't mark), which contrasts with Pharaoh's ant graded response.
- L. niger is proficient at visual-based orientation, so it's less reliant on
  pheromone trails than pharaoh's ants.
- the presence of existing pheromone trails does NOT influence an individual
  ant's subjective reward evaluation — they assess food quality independently.

### general principles across species

- the more rewarding a food source, the higher the pheromone concentration on
  the trail.
- some species use multiple pheromones: a long-lasting exploration pheromone
  (weak recruitment) and a shorter-lasting exploitation pheromone (strong
  recruitment). the exploitation pheromone is deposited preferentially for
  high-quality food.

### tandem running (Temnothorax spp.)

- tandem running is a one-to-one recruitment method where a leader guides a
  follower from nest to food.
- tandem running is favored when food sources are hard to find, differ in
  energetic value, and are long-lasting.
- colonies can adaptively allocate foragers across sources of different quality
  using tandem running.
- followers learn specific routes from leaders — 90% of tandem leaders guided
  followers along routes they had originally learned as followers themselves.
- gene expression: learning and memory genes are specifically upregulated in
  scouts and tandem-followers.

### response to environmental change

- ants strongly upregulate pheromone deposition immediately after experiencing
  an environmental change (e.g., food source moves or changes quality).
- VULNERABILITY: pheromone-based positive feedback can trap colonies at local
  optima. if a poor feeder is established first, the pheromone trail can
  outcompete incipient trails to a better source added later. this is a known
  failure mode of stigmergic systems.

**confidence: high** — extensive experimental literature across species.


## 5. food source evaluation and decision-making

### comparing multiple food sources

- ants integrate food quality with foraging cost (distance, danger).
- the marginal value theorem (MVT) predicts: leave a food patch when the
  current rate of energy gain drops to the average expected rate for the habitat.
- in practice: ants stay longer at patches that are farther apart or when
  current patches are poor (both increase travel-cost-to-benefit ratio).

### distance vs quality tradeoff

- closer low-quality food vs farther high-quality food: ants can get trapped at
  the closer source due to pheromone positive feedback (see vulnerability above).
- learning speed differences help: ants learn routes to higher-quality food
  faster, which can partially overcome the distance disadvantage.
- small differences in learning speed for different food qualities can drive
  efficient collective foraging at the colony level.

### memory and reassessment

- ants DO remember food source locations and quality.
- assessment updates over multiple visits — initial visits weight "amount of
  food" heavily, later visits weight "reliability" more.
- private information (individual memory) can sometimes trap colonies at local
  optima, independent of pheromone effects.
- ants do NOT appear to actively correct erroneous pheromone trails — trails
  decay naturally rather than being "erased."

**confidence: high** for behavioral patterns. the MVT application to ants is
well-supported theoretically but ants don't perfectly optimize — they use
heuristics that approximate MVT predictions.


## 6. trophallaxis and food quality communication

### what gets transferred

trophallactic fluid in Camponotus floridanus contains far more than just food:

- **nutrients** — sugars, amino acids, lipids
- **proteins** — both digestion-related and non-digestion-related. many are
  regulators of growth, development, and behavioral maturation.
- **juvenile hormone III (JH)** — a key developmental regulator. when workers'
  food was supplemented with JH, larvae they reared via trophallaxis were TWICE
  as likely to complete metamorphosis and became larger workers.
- **JH esterase paralogs** — enzymes that break down JH, providing a
  regulatory counterbalance.
- **cuticular hydrocarbons (CHCs)** — nestmate recognition cues.
- **small RNAs (microRNAs)** — potential gene expression regulators.

### quality information transfer

- food receivers perceive the odor of food delivered by the donor and associate
  it with the food reward.
- through individual experience, workers evaluate the characteristic information
  of food and assess its quality.
- social information can OVERRIDE individual assessment: carpenter ants
  receiving social instructions will consume food they would otherwise reject,
  even toxic food, despite noxious effects. social instruction overrides
  individual evaluation.

### the crop as a social stomach

- the crop (foregut) stores liquids separately from the midgut.
- food intended for sharing is kept available for trophallaxis without being
  fully digested.
- this allows ants to act as mobile food storage and distribution units.

**confidence: high** — proteomic and molecular analysis of trophallactic fluid
is well-established, particularly in Camponotus floridanus.


## 7. species-specific food quality concerns

### fire ants (Solenopsis invicta)

- omnivorous, regulate protein/carb/lipid independently.
- prefer sucrose and leucine, with preference intensifying at higher
  concentrations.
- prefer single-component solutions over multi-component mixtures.
- larvae display independent appetites for solid protein, amino acid solution,
  and sucrose solution.
- when infected with SINV-1 virus: reduced foraging, declined lipid intake,
  shifted preference toward carbohydrate-rich foods.

### leaf-cutter ants (Atta, Acromyrmex)

food quality is evaluated at TWO levels: for the ant AND for the fungal
cultivar.

- **leaf selection criteria**: plant chemistry, nutrient content, tenderness,
  vein thickness, trichome density, endophyte load.
- prefer young leaves with soft cuticles, fewer defenses, higher nutritional
  value.
- **fungal feedback**: ants detect chemical signals from the fungus. if a leaf
  type is toxic to the fungus, the colony stops collecting it. this is a
  learned colony-level response.
- fungus gardens preferentially break down simpler, more digestible substrates
  first.
- the fungus produces specific enzyme profiles in response to different plant
  substrates (different protein expression for different leaves).
- foraged material (fruits, flowers, leaves) is combined to maximize cultivar
  performance — a multidimensional nutritional optimization.
- trace mineral management: concentrations of toxic trace minerals (Cu, Mn, Zn)
  in foraged leaves peak near the macronutrient intake target, suggesting
  active regulation of micronutrient toxicity.

### harvester ants (Pogonomyrmex spp.)

- seed specialists. selection based on multiple factors:
  - caloric reward (energy density)
  - seed size (prefer 3-30 mg in P. rugosus)
  - protein and energy content (P. salinus preferentially selects
    Lepidium papilliferum seeds for their higher protein/energy content)
  - handling time and travel cost
- individual foraging choices are labile — converge on the most energetically
  profitable species over time.
- colony dietary history influences individual seed preferences.

### honeypot ants (Myrmecocystus spp.)

- specialized repletes (living storage vessels) store liquid carbohydrates.
- foragers collect sweet exudates from cynipid galls and regurgitate to repletes
  via trophallaxis.
- replete honey composition: primarily glucose and fructose, ~67g sugar per
  100g, pH 3.85.
- the crop keeps food separated from the midgut so it remains available for
  redistribution without being digested.
- when food is scarce, the process reverses: repletes regurgitate stored sugar
  to feed the colony.

### Temnothorax spp. (acorn/rock ants)

- use tandem running rather than mass recruitment.
- stored excess food is sufficient for reducing protein foraging — colonies with
  food reserves are less responsive to protein opportunities.
- small colonies respond more strongly to larval demand signals than large ones.

**confidence: high for fire ants and leaf-cutters** (extensively studied).
moderate for harvester ants (good behavioral data, less molecular detail).
moderate for honeypot ants (descriptive natural history is solid, mechanistic
data is thinner).


## 8. larval nutritional signaling

### the demand chain

nutritional information flows through a hierarchical demand chain:

    larvae → nurses → foragers → environment

1. **larvae signal hunger** via non-volatile contact pheromones and begging
   behaviors (physical solicitation).
2. **nurses respond** by soliciting food from foragers or from stored reserves.
3. **foragers adjust** foraging effort and target macronutrient composition based
   on upstream demand.

### larval pheromone effects (dose-dependent)

- workers in colonies WITH larvae increase foraging activity compared to
  broodless colonies.
- workers suppress ovarian activation in the presence of larvae (progressive
  effect — stronger in smaller colonies).
- the response is dose-dependent: more larvae = stronger foraging drive +
  stronger ovarian suppression.

### specificity of demand

- the chain is nutrient-specific. ants can match foraging to deficiencies in
  single amino acids, suggesting the demand signal carries information about
  WHAT is needed, not just "feed me."
- workers shift foraging toward protein-rich sources when larval demand is high
  (more brood = more protein foraging).
- in Temnothorax longispinosus, stored excess food alone is sufficient to reduce
  protein foraging — the colony tracks its reserves.

### information propagation in large colonies

- in small colonies, direct larva-worker contact may suffice.
- in larger colonies, larval pheromones may propagate through the trophallaxis
  network: transferred from nurse to forager via oral fluid exchange, carrying
  the chemical signal deeper into the nest.
- this is less well-characterized mechanistically than the direct-contact
  pathway.

**confidence: high** for the existence and behavioral effects of the demand
chain. moderate for the specific molecular identity of larval hunger pheromones.
the propagation mechanism in large colonies is plausible but not definitively
demonstrated.


## simulation implications

key parameters to model for food quality in the simulation:

1. **food quality value (0-255, already allocated in world.R bits 6-13)**
   - maps to sugar concentration / caloric density
   - affects pheromone deposition intensity (graded or binary per species model)
   - affects recruitment strength

2. **colony nutritional state**
   - protein vs carbohydrate balance (two-axis model from geometric framework)
   - brood load shifts target toward protein
   - deficit in either axis biases forager preferences

3. **individual forager memory**
   - food source location + quality rating
   - updates over visits (amount → reliability weighting shift)
   - learning speed proportional to food quality

4. **trophallaxis network effects**
   - quality information propagates through social feeding
   - social information can override individual assessment
   - larval demand propagates upstream through nurses to foragers

5. **pheromone trail modulation**
   - trail intensity proportional to food quality (above some threshold)
   - dual-pheromone option: exploration (weak, long-lived) vs exploitation
     (strong, short-lived)
   - trap risk: established trails to poor sources resist switching

6. **distance-quality tradeoff**
   - not a simple linear comparison — pheromone feedback creates path dependence
   - closer poor food can dominate farther good food due to positive feedback
   - learning speed differences partially compensate


## sources

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