Biological Inspiration: Ants By Adam Feldman

“Encounter Patterns” in Ant Colonies Ants communicate through the use of pheromones perceived through their antennae Ants communicate through the use of pheromones perceived through their antennae For example, determines if another is a nestmate For example, determines if another is a nestmate Study antennal contact between workers Study antennal contact between workers ‘Antennal contact’ refers to brief contact between the antennae of two ants ‘Antennal contact’ refers to brief contact between the antennae of two ants

Experiment 1 Is a pattern of antennal contact a characteristic of the behavior of an ant colony? Is a pattern of antennal contact a characteristic of the behavior of an ant colony? Examine 3 species of ants: Myrmica rubra, Solenopsis invicta (the fire ant), and Lasius fuliginosus Examine 3 species of ants: Myrmica rubra, Solenopsis invicta (the fire ant), and Lasius fuliginosus How does each species vary antennal contact behavior in response to the presence of food? How does each species vary antennal contact behavior in response to the presence of food?

Experiment 2 Does antennal contact help determine ant density? Does antennal contact help determine ant density? How does antennal contact rate vary as ant density varies? How does antennal contact rate vary as ant density varies? ‘Contact rate’ defined as the number of contacts per ant, per unit time ‘Contact rate’ defined as the number of contacts per ant, per unit time Only L. fuliginosus workers used in the remainder of the experiments Only L. fuliginosus workers used in the remainder of the experiments

Experiment 3 How is the rate of antennal contacts affected by the change of ant density? How is the rate of antennal contacts affected by the change of ant density? How does behavior change with the introduction of ants which are non-nestmates? How does behavior change with the introduction of ants which are non-nestmates? Contact Rate Contact Rate Speed of movement Speed of movement

Differences in Contact Rate by Species (Method) Each colony lives in an isolated environment Each colony lives in an isolated environment 12x23cm plastic arena with Fluon walls 12x23cm plastic arena with Fluon walls Divided into four regions – food, nest, two empty Divided into four regions – food, nest, two empty Colonies consist only of worker ants – no queen or brood (except S. invicta which contain both) Colonies consist only of worker ants – no queen or brood (except S. invicta which contain both) Experiments do not begin until the colony has been in its arena for at least a week Experiments do not begin until the colony has been in its arena for at least a week

Differences in Contact Rate by Species (Results) Contact rates highest in L. fuliginosus Contact rates highest in L. fuliginosus Largest of the three species Largest of the three species M. rubra increased contact between returning foragers and preceding ant trail formation M. rubra increased contact between returning foragers and preceding ant trail formation Antennal contact is involved in forager recruitment Antennal contact is involved in forager recruitment S. invicta increased contact where food is found S. invicta increased contact where food is found Foragers recruited from nearby ants Foragers recruited from nearby ants Contrasts with bee behavior Contrasts with bee behavior

Attraction to Edges (Method) Ants displayed a tendency to gather at the arena edges Ants displayed a tendency to gather at the arena edges Attraction to arena edges Attraction to arena edges Movement to edges designed to facilitate higher local density Movement to edges designed to facilitate higher local density Experiment in arena without edges Experiment in arena without edges Create arena on the surface of a sphere Create arena on the surface of a sphere Two attempts correspond to size of smallest square arenas Two attempts correspond to size of smallest square arenas

Attraction to Edges (Results) Ants displayed an attraction to arena edges Ants displayed an attraction to arena edges As ant density decreased, clustering increased, especially at the arena edges As ant density decreased, clustering increased, especially at the arena edges As arena size increased quadratically, edge size only increased linearly As arena size increased quadratically, edge size only increased linearly By staying at the edges, ants could maintain local density By staying at the edges, ants could maintain local density Aggregation in edgeless arena Aggregation in edgeless arena Indicates that maintaining density is the reason for clustering, not affinity for the edges Indicates that maintaining density is the reason for clustering, not affinity for the edges

Tendency to Aggregate (Methods) Suppose ants’ tendency to aggregate (cluster) related to desire to control contact rate Suppose ants’ tendency to aggregate (cluster) related to desire to control contact rate Ants must be able to see (or otherwise sense) each other before deciding to initiate a contact Ants must be able to see (or otherwise sense) each other before deciding to initiate a contact Measure the average scanning distance of an ant Measure the average scanning distance of an ant From what distance can one ant detect the presence of another From what distance can one ant detect the presence of another

Tendency to Aggregate (Results) Appears that ants can detect one another at distances up to 1.2cm Appears that ants can detect one another at distances up to 1.2cm Ants closer than this turned towards each other much more than statistically likely Ants closer than this turned towards each other much more than statistically likely Ants farther than this behaved as though no other ant was present Ants farther than this behaved as though no other ant was present Ants can indeed control contact rate by choosing in advance whether or not to approach another ant Ants can indeed control contact rate by choosing in advance whether or not to approach another ant

Contact Rate vs. Density (Methods) Changes of ant density Changes of ant density Three ant groups – 100, 200, and 450 workers each Three ant groups – 100, 200, and 450 workers each Four square arenas – 25cm, 50cm, 75cm, and 100cm Four square arenas – 25cm, 50cm, 75cm, and 100cm Each arena divided into 6.25x6.25cm grid squares Each arena divided into 6.25x6.25cm grid squares The contact rate in each grid square was determined, so Local Contact Rate could be studied separately from Overall Contact Rate The contact rate in each grid square was determined, so Local Contact Rate could be studied separately from Overall Contact Rate

Contact Rate vs. Density (Results) Overall Contact Rate Overall Contact Rate If contacts were purely random (collisions), overall contact rate would increase linearly with density If contacts were purely random (collisions), overall contact rate would increase linearly with density While contact rate did increase with density at very low densities, it leveled off as density further increased While contact rate did increase with density at very low densities, it leveled off as density further increased Thus, statistically, overall contact rate could not be determined by random collisions Thus, statistically, overall contact rate could not be determined by random collisions

Contact Rate vs. Density (Results) Local Contact Rate Local Contact Rate Did not increase with density Did not increase with density Even at the local scale (one grid square), contact rate did not follow a model of random behavior Even at the local scale (one grid square), contact rate did not follow a model of random behavior Clearly, local contact rate is determined by design of the colony, not through any random element Clearly, local contact rate is determined by design of the colony, not through any random element

Contact Rate vs. Density (Results) Comparing Overall & Local Contact Rates Comparing Overall & Local Contact Rates Both locally and globally, ants control contact rate by preventing or encouraging contacts with nearby ants depending on density Both locally and globally, ants control contact rate by preventing or encouraging contacts with nearby ants depending on density Contact rate easier to regulate on flat surface than sphere Contact rate easier to regulate on flat surface than sphere Aggregating along an edge provides “protection” against too many contacts Aggregating along an edge provides “protection” against too many contacts Edgeless arenas create two dimensional clusters Edgeless arenas create two dimensional clusters

New Ant Encounters: Contact Rate (Methods) Start with a host group and add new ants Start with a host group and add new ants Host group 35 or 75 ants from colony A Host group 35 or 75 ants from colony A Add 15 ants from either colony A or colony B Add 15 ants from either colony A or colony B Observe contacts of host group prior to addition of new ants and for 10 minutes after Observe contacts of host group prior to addition of new ants and for 10 minutes after Observe contacts of new ants from moment of addition until 10 minutes have passed Observe contacts of new ants from moment of addition until 10 minutes have passed Examine immediate (1-3 minutes after addition) and lasting (5-10 minutes) changes in behavior Examine immediate (1-3 minutes after addition) and lasting (5-10 minutes) changes in behavior

Contact Rate: New Ant Encounters (Results) Response of host ants depend on rate of contact with added ants Response of host ants depend on rate of contact with added ants Contact rate increased if higher proportion of new ants encountered Contact rate increased if higher proportion of new ants encountered Experiments with 35 host ants showed more impact than experiments with 75 host ants, as did experiments with non-nestmates (colony B) Experiments with 35 host ants showed more impact than experiments with 75 host ants, as did experiments with non-nestmates (colony B) New ants not avoided New ants not avoided Behavior returns to normal within 5 minutes Behavior returns to normal within 5 minutes

New Ant Encounters: Speed (Methods) Increases in speed of movement may be the cause for any increased contact rate upon adding new ants Increases in speed of movement may be the cause for any increased contact rate upon adding new ants New ant experiments are re-examined (via videotape), with attention paid to ant speed New ant experiments are re-examined (via videotape), with attention paid to ant speed

Speed: New Ant Encounters (Results) New ants moved much faster than host ants, especially if they were non-nestmates New ants moved much faster than host ants, especially if they were non-nestmates However, speed changes did NOT account for changes in contact rate However, speed changes did NOT account for changes in contact rate Even undisturbed ants varied their speed greatly from minute to minute Even undisturbed ants varied their speed greatly from minute to minute Highest speed resulted from experiment involving 75 host ants and 15 non-nestmates Highest speed resulted from experiment involving 75 host ants and 15 non-nestmates Not the same experiment as the highest contact rate Not the same experiment as the highest contact rate

Conclusion Different species of ants will display different patterns of antennal contact Different species of ants will display different patterns of antennal contact Corresponds to other species-specific differences Corresponds to other species-specific differences S. invicta (colonizing species) increase contacts if food is found while L. fuliginosus (stable, old colonies) do not S. invicta (colonizing species) increase contacts if food is found while L. fuliginosus (stable, old colonies) do not Contact rate must be important Contact rate must be important Ants attempt to regulate it Ants attempt to regulate it One way, by detecting each other from up to 1.2cm away One way, by detecting each other from up to 1.2cm away

Conclusion Ants regulate contact rate to keep it fairly constant, despite density changes Ants regulate contact rate to keep it fairly constant, despite density changes Maintaining contact rate plays a role in colony organization by causing aggregations to result Maintaining contact rate plays a role in colony organization by causing aggregations to result Information transmitted by a contact can affect colony decision making Information transmitted by a contact can affect colony decision making Ant can change behavior based on who is encountered (forager vs. nest maintainer) Ant can change behavior based on who is encountered (forager vs. nest maintainer) Follows bee model (forager vs. nectar storer) Follows bee model (forager vs. nectar storer)

Conclusion Ant behavior is dictated by the proportion (not the number) of non-nestmates encountered Ant behavior is dictated by the proportion (not the number) of non-nestmates encountered Contact rate increases up to three fold upon introduction of non-nestmates Contact rate increases up to three fold upon introduction of non-nestmates Increase only lasts for several minutes Increase only lasts for several minutes Speed could account for this increase Speed could account for this increase Findings indicate it is not the only relevant mechanism Findings indicate it is not the only relevant mechanism Ants cause this increase by choosing how many nearby ants to approach Ants cause this increase by choosing how many nearby ants to approach Motivation: Quickly judge danger (lost vs. attack) Motivation: Quickly judge danger (lost vs. attack)

Conclusion Limitations Limitations Specialized domain Specialized domain Authors repeatedly stress that laboratory nature could alter results from real world values Authors repeatedly stress that laboratory nature could alter results from real world values Lack of queen & brood, trying to escape arena, etc Lack of queen & brood, trying to escape arena, etc Admitted imperfect counting techniques Admitted imperfect counting techniques