Category Archives: Nestmate Discrimination

This category includes research assessing the ability of the Comanche harvester ant (Pogonomyrmex comanche) to distinguish nestmates from non-nestmates.

The Spatial Ecology of the Comanche Harvester Ant

I have successfully presented my dissertation work and am currently finishing up the revisions for the final submission to the University of Texas at Arlington for the PhD degree. I expect the final dissertation to be available from the university library by July 2015.

The title of the dissertation is: The Spatial Ecology of the Comanche Harvester Ant, Pogonomyrmex comanche (Hymenoptera, Formicidae)

Dr. Esther Betran was the chair of my committee (UTA).

Other committee members were:

Dr. Jonathan Campbell (UTA)

Dr. Paul Chippindale (UTA)

Dr. Sophia Passy (UTA)

and Dr. Walter Tschinkel (FSU)

Here is the slide presentation and the notes which are numbered to correspond to the slides. I have included some of the corrections that came out of the discussion with my committee and otherwise have noted where there are other problems which I am addressing in the revision.

The slides:

and the notes:

Comanche Harvester Ants are Pansies!

As part of investigating nestmate discrimination, I decided to test if Comanche can distinguish other ant species. So I ran behavioral trials between the Comanche harvester ant (Pogonomyrmex comanche) and the Barbatus harvester ant (or harvester ants or big red ants, Pogonomyrmex barbatus) and: !

Comanche are pansies — mostly they did nothing, either in arenas with P. barbatus or when P. barbatus was introduced to their nest mound near the entrance. In fact, P. barbatus sometimes entered the nest seemingly without harm since they also returned to the external nest.

Out of 19 arena encounters, there were 4 with any aggression and only one of these had an extended grabbing encounter. Barbatus was always the aggressor.

Out of 14 on the nest encounters, 2 showed some aggression by Comanche, mostly a kind of harassment. Mostly, Barbatus just left the mound though twice barbatus entered the nest. Once Barbatus showed great difficulty maneuvering over the sandy mound.

All trials were recorded with a camcorder so I am still analyzing them.


Ant Antennae

I have been thinking about ant antennae for awhile now. First, I became very interested in antennae because there are so many different forms in insects and also in ants. The form of antennae is a key characteristic in ant identification — how are they attached, how long are they, how many segments, is there a club or not, and if there is a club how many segments make up the club?

While the morphology is important to identification, this variety certainly raises functional questions. What are these differences about physiologically? Why are they important and what do they mean behaviorally?

Recently I have been  raising more questions about antennal physiology and sensory perception because of my observations of interactions between individual Comanche harvester ants. I have been conducting nestmate discrimination tests between individual ants by introducing the ants in an arena and observing the ants’ behavior. While these interactions may vary, the antennae almost always have some role. Sometimes, it has been a brief touch or haphazard encounter but other times, the ants spend some seconds or longer facing each other and running their antennae over each other. This may or may not be accompanied by mandible gaping or gaster waging and the encounters may or may not develop. Mostly, the ants go their own way.

It is obvious that the antennae are more than chemosensory or smelling structures and this is well documented in many insects. Antennae may have sensory receptors for mechanical force, tactile stimuli, chemo-sensation, smell/taste, humidity, and air flow.  This multiplicity of perception is a challenge to understand and to place in the context of behavior: what information does an ant get and how does she respond?

Also, the elbow shape of ant antennae make the antennae particularly mobile, rather like our arms. Perhaps, the sensory structure can be thought of, loosely, like our hands and fingers — very sensitive. Although ants don’t use their antennae to manipulate their environment as we use our hands, these structures are key to how the ants interact with their environment. That they have an antenna on each side of the head gives a kind of stereo view of the world — whatever sense they are using. I find this rather fascinating to think about: the stereo world of the ants along all these perceptual lines.

I wonder what these means for the behaviors I am observing. How much are they detecting just being in proximity to one another, how much if they have a bare encounter, and why do some of them spend many seconds using their antennae on one another and others do not? What can they detect, what do they pay attention to, and why are there such differences in responses? Context matters but there is more to this than context.

For the Comanche ant, these questions seem particularly important because they do not use trunk trails and have poor recruitment to resources, etc. which means that pheromones may not be so key to their communication as it is in other ant species. They seem to be rather visual in their orientation for foraging. So what is their perceptual world?  I wonder.



Half-way through the first round of nestmate discrimination tests

Out of 400 trials for this first experiment with nestmate discrimination, done out of context, there have been 12 aggressive interactions so far — 3%. There are 300 trials left for this experiment.

This low level of aggression may indicate a low level of aggression in this species (also meaning that aggression is not a significant factor structuring the population) or that context matters (either the context of the interaction or the task of the individual ants). Further experiments will address these issues.

I will do a full scoring of the behaviors when this experiment is complete and the videos are coded. Right now I am only recording the level of aggression I observe while making the recordings.

Here is a video of an aggressive encounter between two Comanche harvester ants.

Update on Nestmate Discrimination

I included three different colonies located far enough away from the GL colonies to be considered different populations. These colonies are in the EP-1 and TI-1 sites of the Fort Worth Nature Center and in the Southwest Nature Preserve in Arlington, Texas. I tested the colonies against themselves and against one colony in the GL neighborhood and found no aggressive behavior in my observation.  I have not examined the video recording yet.

This is really a surprise — either context is super important or the Comanche harvester ant is more gregarious than most Pogonomyrmex ants. Context probably does matter and that will be the follow-up nestmate discrimination test.

Here are maps of the colonies I am currently using for these tests.

Locations of Comanche Harvester Ant Colonies used in the nestmate discrimination test. Fort Worth Nature Center, Fort Worth and the Southwest Nature Preserve, Arlington, Texas.

Locations of Comanche Harvester Ant Colonies used in the nestmate discrimination test. Fort Worth Nature Center, Fort Worth and the Southwest Nature Preserve, Arlington, Texas.

More on Nestmate Discrimination

Today, I ran 50 more trials including some with one colony from the EP-1 site and one from the TI-1 site — none of these trials showed any aggression in the original observation. Aggression may be seen in the video recording but I will not look at that for another week in part to avoid bias. I am a bit surprised that these interactions got no aggressive response. This week I will also do trials with the SWNP site. Need a map of these colonies to add to the neighborhood map.

Decided to change my ranking system for the response – -same behavioral responses but need a different order so that the numbers make some kind of sense (even though they are not a direct measure but are descriptive). So, the new order is:

-2 for antennal contact (sustained)

-1 for a brief bump or physical contact

0 for no physical interaction

1 for gaster pumping or mandible gabe

2 for grabbing a body part

3 for a tumble or fight — usually means attempt to sting (abdomen turned toward opponent)

Comanche harvester ants from two different colonies displaying aggression. The ant on top has the other ant in her mandibles.

Nestmate Discrimination Test Continues

In the FWNC, GL site, I video captured another 46 nestmate discrimination trials between colonies of the Comanche harvester ant, Pogonomyrmex comanche. Out of all, there were two very aggressive encounters. These were characterized by one ant grabbing the other in her mandibles. At some points, there were attempts to sting.

Comanche harvester ants from two different colonies displaying aggression.

Comanche harvester ants from two different colonies displaying aggression.

Comanche harvester ants from two different colonies displaying aggression. Note the abdomen curled towards the other ant -- this is an attempt to sting.

Comanche harvester ants from two different colonies displaying aggression. Note the abdomen curled towards the other ant — this is an attempt to sting.


Here is a map of the neighborhood —  the colonies I am testing for recognition, to see if they can be said to form a neighborhood:

Map of the Comanche harvester ant colonies used in the nestmate discrimination tests in the GL site at FWNC

Map of the Comanche harvester ant colonies used in the nestmate discrimination tests in the GL site at FWNC

Notes: In several encounters the ants wag or pump their gasters. This has been understood as an aggressive maneuver — preparation for stinging. However, I have seen one ant wag her gaster and it did not appear to be aggressive but perhaps more appeasing (subjective observation). In most cases, the wagging does have a menacing air. (Is there a way to clearly describe and measure a difference?) Wagging is sometimes done by one ant and sometimes by both. Attempts to sting may or may not follow such wagging.

I decided I should also test one of these neighborhood colonies with one from the EP-1 site, the TI-1 site, and the SWNP — this will further test the idea of dear enemy and distance. The Comanche ant, despite her species epithet, seems rather docile and easy going. I wonder if the populations are that similar in genetics and odor — perhaps there are noticeable differences with greater distances that may mark different populations…this brings into consideration the ideas of subpopulations and metapopulations.

I had been concerned that the new colony that emerged within this neighborhood had met its end since I had not seen them active for nearly a week. But today, they became active about 12:30  pm, about the time that the other colonies were quitting for the day — too hot for these girls to walk on the sand.

Colonies #6 and #8 never  became active.

I think I need to include further characterization of the use of the antennae in these interactions — duration, number of bouts, total time spent in this behavior.

Two Comanche harvester ant foragers use prolonged antennal contact.

First set of raw data for nestmate discrimination test 1

NMD Test 1:  Review of Videos

(Two Comanche harvester ants use antennal contact in a nestmate discrimination test, shown above)

At this point, I have gotten a complete set of interactions for one focal colony. I summarize the methods below and then give the raw data. Analysis is forth coming.

I used a simple interaction test as an initial test of nestmate discrimination out of context.

I asked the question: does the Comanche harvester ant behave differently, with more aggression, to non-nestmates than to nestmates, irrespective of context?

Methods: I arbitrarily chose a focal colony and then located the 10 closest colonies. I also included an additional colony  located far enough away to be outside of the foraging range. (outside of the ‘neighborhood’).  I used these 12 different colonies in pairs to test the Comanche harvester ants’ nestmate discrimination behavior.  GIS coordinates were recorded for each colony.

I ran individual interaction trials as follows: I collected an ant  from the nest area from each of two colonies and placed each ant in her own plastic cup. I transported the cups to a nearby area for the trial and placed them on a table. I gave the ants 2 minutes to relax, then introduced one ant into the cup of the other. I did not record the ant identities (This information was not important to the question of recognition.). I made observations and took notes during a 3 minute interaction period. I also recorded the ant interaction with a Canon Vixia HF M400 camcorder for 3 minutes. Each pairing with different individual ants was repeated 5 times, including the focal colony with itself. I ran the trials randomly. I gave the interactions an identification code in the field. After the trial, I released the ants into the area. I used clean cups for each trial. I later cleaned and dried the used cups before re-use.

Video Review Methods:  I used the video recording to check for observational bias in the original observation, to make accurate counts of the frequency of non-physical displays (gaster pumping and mandible gape), physical encounters, and type of physical encounter (bumping/non-specific touch; antennal touching; grabbing a body part (prolonged contact); ‘fight’ (prolonged contact, attempt to sting). I coded the videos to avoid bias when viewing. I recorded the frequencies of behavior with additional descriptive notes. I used the first minute of interaction for this test since prolonged containment might be an additional influence on response.  I used the remainder of the recording for observation of details of ant behavior and movement.

The Raw Data for the first Focal Colony Interactions (#0)

Here is the video from which the still at the top of the page was made.

Nestmate Discrimination Field Test 1

Introduction: Ants are thought to discriminate nestmates from non-nestmates based on a colony specific odor in the cuticle. They use their antennae to detect the odor — if the other ant is a nestmate the physical contact is friendly but if the other ant is not a nestmate, there may be aggressive displays or physical contact. My preliminary work suggested that the Comanche harvester ant has such differences in behavior and may further distinguish colonies that are close from those which are located farther away (the dear enemy idea). I am testing this ability in the field through several different tests — staged encounters between ants.

Today I began one of the tests by introducing two ants into a small plastic cup and observing their behavior for 3 minutes.  I recorded what I observed but I also videoed it.  The video allows me to check my original observation for bias and to catch subtleties of behavior I may have missed. I don’t have the completed data yet — this test is in process — so no results per se.

Methods: I arbitrarily choose a focal colony and then find the 10 closest nests to this colony. I stage introductions of the focal colony with itself (control) and the focal colony with each of the other 10 colonies. I record the distance from the focal colony to the 10 neighbors and get a GIS location for each colony.  I have 5 interactions for each pair.  These interactions are not conducted in any particular order.

Each ant is collected in a separate plastic cup and cups are not reused (until thoroughly washed and dried). The ants have 2 minutes in their cups to relax. I set a timer for 3 minutes, set the video on one of the ants in her cup and introduce the other. When the timer rings, I record my observation based on a ranking of behaviors observed. I view the video later and check the original ranking, subtle behaviors, and for bias.  The encounters and videos have separate identification numbers which are linked to the colonies and their information. I also record any other observations as notes for each encounter.

The ranking of behavior I am using is:

0: no reaction

1: antennal contact; physical encounter

2: mandible gape; gaster movement

3: grab antenna, leg, petiole

4: prolonged physical contact

5: injury

Here are two videos of these events:

Non-aggressive encounter between the focal colony and a neighboring colony

Aggressive encounter between the focal colony and a neighboring colony