407 lines
15 KiB
Markdown
407 lines
15 KiB
Markdown
# Ant Pheromone Biology
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Reference doc on ant pheromone types, chemistry, triggers, and environmental
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factors. Organized for simulation design — what matters for modeling, what
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the real biology says, and where the data is thin.
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## Pheromone types
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### Trail pheromones
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Guide nestmates to food, new nest sites, or other resources. Encode distance
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and quality information through concentration gradients.
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Gland sources vary by subfamily:
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- Poison gland (most Myrmicinae — stinging ants)
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- Dufour's gland (most Formicinae — non-venomous ants)
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- Pygidial gland, sternal glands, hindgut (various)
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Known compounds by species:
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species compound gland
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Atta texana, A. cephalotes methyl 4-methylpyrrole-2-carboxylate poison
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Atta sexdens rubropilosa 3-ethyl-2,5-dimethylpyrazine poison
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Tetramorium caespitum 70:30 2,5-dimethylpyrazine + EDMP poison
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Tetramorium meridionale indole (major) + 4 pyrazines poison
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Monomorium pharaonis (E,E)-faranal poison
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Myrmica spp. EDMP + homofarnesenes poison + Dufour's
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Solenopsis invicta various poison
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Volatility is a feature — trails evaporate in minutes to hours, so paths to
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depleted food naturally fade. The evaporation rate is effectively the colony's
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spatial memory duration.
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### Alarm pheromones
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Fast-acting signals that trigger either panic (flee) or aggression (attack)
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depending on species, colony size, and context.
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Triggers:
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- Physical disturbance of nest or individual
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- Predator detection (olfactory, visual, or tactile)
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- Crushing/injury of nestmates (damaged ants release alarm compounds)
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- Intrusion by non-nestmates
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Known compounds:
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compound species gland
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4-methyl-3-heptanone Atta, Pogonomyrmex, Ooceraea mandibular
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formic acid Formica, Camponotus poison
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n-undecane Camponotus, many Formicinae Dufour's
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2-heptanone Iridomyrmex pruinosus mandibular
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3-octanol Acromyrmex echinatior mandibular
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3-octanone Acromyrmex octospinosus mandibular
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(S)-(-)-citronellal Platythyrea punctata mandibular
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(S)-(-)-actinidine Platythyrea punctata mandibular
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Behavioral response sequence: stop movement -> swing antennae -> alerted
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posture -> species-specific response (flee or attack). Larger species and
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larger colonies tend toward aggression; smaller species tend toward evacuation.
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#### Carpenter ant alarm system (formic acid + n-undecane)
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Two-component blend from two different glands:
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- Formic acid (poison gland) -> avoidance behavior, move away from source
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- n-Undecane (Dufour's gland) -> attraction toward source, approach to attack
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Each component alone produces a distinct response. Together they create the
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full alarm sequence: alert, then approach and aggress. Formic acid also
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modulates nestmate recognition — puts ants into a heightened discriminatory
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state where they're more likely to attack non-nestmates.
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Processed in ~5 specific "alarm-sensitive" glomeruli clustered in the
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dorsalmost part of the antennal lobe, relayed to the lateral horn.
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#### What triggers alarm? Plants? Predators?
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No strong evidence for specific plants that trigger false alarm responses,
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though some alarm compounds (citronellal) are also found in plant oils, so
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cross-reactivity is plausible. Some alarm compounds (citral, 2-heptanone,
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4-methyl-3-heptanone) have antifungal properties, suggesting a dual role in
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pathogen defense — the alarm system may have originally evolved as an
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antimicrobial response.
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Main natural triggers are physical: nest disturbance, predator contact, and
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injured nestmates releasing their contents. The "danger zone" concept maps
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best to areas where nestmates have been injured or where persistent threats
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exist, not to specific environmental chemicals.
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### Repellent / negative pheromone
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Deposited at trail junctions leading to unrewarding branches. Prevents the
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colony from getting stuck on depleted food. Key details from Pharaoh's ant
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studies:
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- Lasts ~2x longer than attractive trail pheromone (~78 min vs ~33 min)
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- Ants encountering it U-turn or zigzag
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- Deposited specifically at bifurcation points, not along entire failed paths
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Source: Nature 438, 442 (2005)
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### Queen pheromones
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Complex, multifunctional. Known effects:
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- Attract workers for queen attendance
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- Promote brood care
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- Induce nestmate discrimination
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- Inhibit larval sexual development (through worker behaviors)
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- Suppress reproduction in other queens and workers
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- Induce worker policing of reproductive workers
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- Mediate queen acceptance/rejection in polygyne colonies
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Chemistry is poorly characterized compared to trail/alarm pheromones. Involves
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cuticular hydrocarbons and at least one dedicated odorant receptor (HsOr263 in
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Harpegnathos saltator). Difficult to isolate because the signal may be a
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complex blend rather than a single compound.
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### Necrophoresis / death pheromones
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Trigger corpse removal for nest hygiene. Dual-signal system:
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1. Loss of "life signals": living ants produce dolichodial and iridomyrmecin
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on their cuticle. These disappear within ~60 minutes of death. Their absence
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is the initial trigger.
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2. Gain of "death signals": oleic acid and linoleic acid accumulate as the
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corpse decomposes. These are the classical necrophoresis triggers.
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Timing: only 15% of freshly killed corpses get removed. Rises to 80% for
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corpses 1-6 days post-mortem as fatty acids accumulate. The colony doesn't
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panic-clean — it waits for chemical confirmation.
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### Propaganda pheromones
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Used by slave-making (dulotic) ants during raids. Polyergus queens enter
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Formica host nests, kill the resident queen, acquire her chemical profile,
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and release substances from an enlarged Dufour's gland that reduce worker
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aggression. Raiding workers release:
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- Manipulative alarm signals (cause panic, disorganized defense)
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- Chemical weapons (directly repellent)
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- Appeasement substances (reduce aggression toward the raider)
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Stolen brood are chemically imprinted after eclosion, causing them to identify
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the slave-maker colony as home.
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### Cuticular hydrocarbons (CHCs) — colony recognition
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Not classical volatile pheromones but contact chemicals on the cuticle. Each
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colony has a distinctive CHC profile — a blend of dozens of hydrocarbons that
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workers learn and use to distinguish nestmates from non-nestmates. Non-nestmates
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are attacked. The postpharyngeal gland stores and distributes CHCs, homogenizing
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the colony odor through trophallaxis (food sharing).
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### Recruitment pheromones
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Functionally distinct from trail pheromones in some species. In Leptogenys
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diminuta, two gland sources serve different roles:
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- Poison gland secretions: orientation cues (where to go)
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- Pygidial gland secretions: recruitment stimulus (leave the nest and follow)
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This separation means "follow this path" and "come help" are independent
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signals that can be modulated separately.
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### Brood pheromones
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Signals from eggs, larvae, and pupae that attract worker care. Help workers
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assess developmental stage and nutritional needs. Part of the demand chain
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that links larval nutritional needs -> nurse behavior -> forager food
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preferences. Less well-characterized than adult pheromones.
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### Sex / mating pheromones
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Released by virgin queens (gynes) to attract males during nuptial flights.
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Less studied than other types. Identified in Polyergus breviceps.
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## Food quality
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### What "quality" means to ants
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Primarily macronutrient content — the protein-to-carbohydrate (P:C) ratio.
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Different colony members need different things:
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- Workers need carbohydrates (energy for foraging, maintenance)
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- Larvae and queens need protein (growth, egg production)
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- Foragers collect for the colony's current needs, relayed through a demand
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chain: larvae -> nurses -> foragers
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Sugar concentration is the primary quality axis for foraging workers. In the
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key Pharaoh's ant study, 1.0 M sucrose = "high quality" and 0.01 M sucrose =
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"low quality."
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Species-specific sugar preferences exist — carpenter ants (Camponotus modoc)
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and European fire ants (Myrmica rubra) show selective preferences for specific
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mono-, di-, and trisaccharides. Not all sugars are equal.
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### How ants assess quality
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Two mechanisms:
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1. Contact chemoreception — tasting with mouthparts and antennae
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2. Post-ingestive feedback — evaluating nutritional content after consumption
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Colony-level nutritional regulation follows a "geometric framework" model:
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colonies actively balance P:C intake, shifting forager preferences based on
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current deficits. A protein-starved colony will recruit more aggressively
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to protein sources.
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### How quality modulates pheromone deposition
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The Pharaoh's ant study (Jackson, Holcombe & Ratnieks 2004/2007):
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- Trail marking occurs at ~40% frequency among both fed and unfed foragers
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- High quality food (1.0 M sucrose) -> significantly more high-intensity
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continuous marking
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- Low quality food (0.01 M sucrose) -> no significant difference in marking
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intensity between fed and unfed ants
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- This is a graded individual response — ants modulate marking intensity,
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not all-or-nothing
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Contrast with Lasius niger, where trail strength modulation IS all-or-nothing
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at the individual level — an ant either marks or doesn't, based on quality.
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The difference: Pharaoh's ants live in dark enclosed spaces and rely heavily
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on pheromone trails, so they must always produce some trail. L. niger can use
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visual orientation and afford to skip trail-laying entirely for poor food.
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Ants also adjust deposition based on environmental uncertainty — they modulate
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trail marking in response to changing conditions and their error probability
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(Czaczkes et al. 2015).
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### Simulation relevance
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For the sim, food quality maps to a 0-255 value stored in cell metadata bits.
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When an ant picks up food, it reads the quality and stores it as cargoQuality.
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The deposition multiplier would scale pheromone output — high quality food
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gets stronger trails, attracting more ants. The colony naturally converges on
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the best source first, then shifts when it depletes.
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"Different types of food" is less important than "different concentrations."
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Real ants care about sugar molarity and protein content, not food identity.
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For the sim, a single quality scalar captures the essential dynamics.
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## Pheromone detection
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### Olfactory receptor genes
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Ants have 300-500 odorant receptor (Or) genes — 4-5x more than most insects
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(Drosophila has ~60). This expansion predates complex sociality but facilitated
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it. A specialized 9-exon Or gene subfamily detects cuticular hydrocarbons and
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candidate pheromones.
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### Antennal lobe glomeruli
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Each Or gene roughly corresponds to one glomerulus in the antennal lobe.
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species glomeruli count
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Apterostigma cf. mayri ~630
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Camponotus (carpenter) ~430-460
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Apis mellifera (honeybee) ~163
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Drosophila melanogaster ~43
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Workers have more glomeruli than males, reflecting greater need for chemical
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discrimination. Worker and queen antennal lobes differ in composition and
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Or expression.
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## Environmental effects on pheromones
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### Temperature
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High temperatures accelerate degradation. Above ~40C, workers cannot
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discriminate previously-marked substrate. Above ~30C, foraging activity drops
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partly because trails decay too quickly to be useful.
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Different compounds have different thermal stability: in Tapinoma nigerrimum,
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most gaster secretions vanished at 25C, but iridodials persisted up to 55C.
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Aphaenogaster senilis secretions resisted elevated temperatures better.
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Pheromone persistence = f(temperature, time since deposition). Both interact —
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higher temperature accelerates decay at all time points.
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### Humidity
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Higher humidity slows evaporation of polar pheromone components. Specific
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experimental data is sparser than for temperature. The effect is real but
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less dramatic than temperature in most contexts.
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### Substrate surface
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Porous surfaces absorb pheromone and release it slowly (longer persistence).
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Smooth impermeable surfaces allow faster evaporation (shorter persistence).
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Direct experimental data on ants is thin — the Pharaoh's ant study
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(~9 min on plastic, ~3 min on paper) is one of the few quantitative
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comparisons. The physics is well understood but species-specific measurements
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are rare.
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### Volatility as design feature
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Trail pheromone volatility provides automatic negative feedback — trails to
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depleted food fade without any active erasure. The evaporation rate sets the
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colony's spatial memory duration. Too fast = no useful trails. Too slow =
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colony gets stuck on depleted paths. Evolution tuned this balance per species
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and habitat.
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## Colony-level dynamics
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### Colony size effects
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Larger colonies have higher collective response thresholds. The relationship
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is driven by social feedback — short-range excitatory and long-range
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inhibitory interactions. In army ants, increasing colony size causes a
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qualitative behavioral shift: organized search patterns in small colonies
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give way to spontaneous mass raids in large ones.
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Per-capita interaction rate is roughly scale-invariant — connectivity scales
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hypometrically with colony size.
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### Colony state modulates pheromone dynamics
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- Protein-starved colonies shift forager preferences toward protein, changing
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trail deposition patterns (more intense marking to protein sources)
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- Carbohydrate-rich diets increase social immunity
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- Weakly volatile "aggregation" pheromones mark the nest site as a constant
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baseline signal anchoring the colony spatially
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### "Colony mood"
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Not a scientific term, but maps onto real dynamics:
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- Alarm state propagates as more individuals detect alarm compounds and
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release their own (positive feedback cascade)
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- Foraging motivation modulated by colony nutritional state — hungry colonies
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produce stronger recruitment signals
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- The exploration/exploitation balance shifts with colony experience and
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environmental conditions
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## Sources
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Pharaoh's ant pheromone modulation
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Jackson, Holcombe & Ratnieks 2004/2007
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ScienceDirect S0003347207002278
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Negative pheromone
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Nature 438, 442 (2005)
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Alarm pheromone processing (carpenter ants)
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PMC2912167
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Alarm pheromone in clonal raider ant
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PMC9941220
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Formic acid + nestmate recognition
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J Exp Biol 224(20) jeb242784
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Necrophoresis dual signals
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PNAS 0901270106
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Corpse chemical changes
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J Chem Ecol 10.1007/s10886-013-0365-1
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Slave-maker chemical warfare
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PLOS ONE 10.1371/journal.pone.0147498
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Queen pheromone properties
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Behav Ecol Sociobiol 10.1007/s00265-023-03378-8
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Trail pheromone review
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Morgan 2009, Physiological Entomology
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10.1111/j.1365-3032.2008.00658.x
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Trail pheromone compound list
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Natural Product Communications 10.1177/1934578X1400900813
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Odorant receptors in social insects
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Nature Communications 10.1038/s41467-017-00099-1
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Pheromone-sensitive glomeruli
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Proc R Soc B 10.1098/rspb.2006.3565
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Olfactory system review
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PMC8002415
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Ant olfactory receptor expansion
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Vanderbilt (2012)
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Temperature effects on trail following
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J Chem Ecol 10.1007/s10886-012-0130-x
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Colony interaction scaling
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Frontiers in Ecology and Evolution 10.3389/fevo.2022.993627
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Collective sensory threshold
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PNAS 10.1073/pnas.2123076119
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Ant nutritional ecology
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ScienceDirect S221457451400090X
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Nutrient regulation
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Myrmecological News (Csata & Dussutour 2019)
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Exocrine glands of ants
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Chemoecology 10.1007/BF01256548
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Sugar preferences
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PMC8371376
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Pheromone deposition under uncertainty
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Czaczkes et al. 2015, PMC4590477
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