LAZY ANT

Aesop’s Fables
NIKITA NEGI UAS, GKVK, BANGALORE23-03-2020 1

Hardworking
Active

Seminar-I

Lazy Ants
Nikita Negi
PALB 8141
Sr. M.Sc.

(Herbers, 1981)
57-86%
75%
70%
Reported spending >50% of their time in resting
Blackbird
Humming bird
60%
Howler monkey
Lion
(Wolf et al., 1975)
(Schellar, 1972)
Birds
Mammals
(Wolf et al., 1975)

50% of worker appear to be inactive at any one time
High level of inactivity
common in social insects
Honeybees
(Moore et al., 1998)
Bumble bee
(Jandt et al., 2012)
Termites
(Maistrello and Sbrenna, 1999)
Ants
Dornhaus, 2008

Ecologically
successful
group
Constitute
80%
biomass
Dominate
most
terrestrial
habitats
Surprising?????

“Laziness” in social insects
Inactivity in social animals is further
complicated by social behaviors, such as
division of labour and specialization
Survival of an individual is dependent
upon the amount of work done by
others in the group
Division of labour

What could be the reason for
being lazy / inactive ?????
• Consequence of laboratory artifact
• Influence of circadian rhythm

Inactivity
Most of the reports on high levels of inactivity in social insects came from
observations of workers in laboratory conditions
Inactivity
(Gadagkar and Joshi,1984; Cole, 1985; Moore, 2001)

Does colony level inactivity occurs in the field at same level
compared to those observed in the laboratory?
Lab Artifact?

Methods
• Colonies of Temnothorax rugatulus ants were collected in the Santa
Catalina Mountains, Arizona, USA.
• Total 11 colonies were collected.
• 7 colonies – field
Mean and median colony sizes were 42 and 34 workers
• 4 colonies- laboratory
Mean and median colony sizes were 40.75 and 42 workers
Charbonneau et al. 2014

Semi artificial nest simulating natural nest Filming apparatus in the field
• Each colony was filmed
3 x 5min (2 days)
• Behavioural state of each ant
was recorded
Lab
Charbonneau et al., 2014

Activity category Observable task
Nest building
Brood care
Self grooming
Grooming other
Trophallaxis
Eating
Moving but not active
Stationary and not active
ACTIVE
Undifferentiated
InactiveNIKITA NEGI UAS, GKVK, BANGALORE23-03-2020 15

There was no significant differences in inactivity in ant colony between
field and lab observations
76.9% of average time
in laboratory
76.3% in field
condition

Simplest explanation
• Physiological need for rest
Klein et al., 2010
Is it so??
All workers should have consistent and comparable levels of inactivity
Who is going to do the intensive work like brood care??

Shift work/circadian
influence
• Day duty
• Night duty

Methods
• 5 colonies of T. rugatulus ants were collected
Artificial nest
8 a.m
12 p.m
4 p.m
8 p.m
12 a.m
4 a.m
3 consecutive days
Charbonneau and Dornhaus, 2015
5 minute HD
videos,
every 4 hours,
over 24 hours
Individual marking allows workers to be
tracked across multiple time points and days

Influence of Inter-individual interaction on inactivity
There is a difference in the inactivity level between the colonies that
means inactivity is influenced by inter-individual interaction
Frequency distribution of individual inactivity for each colony measured across 3 days and 6 time
points
Worker differ significantly in their level of inactivity

Do workers differ in circadian rhythm, employing shift work?
• Positive correlation between day & night inactivity
It’s an individual effect rather than a group effectSome workers were consistently inactive and some were consistently active

“Inactivity”- specialized task
 Specialized task-
foraging, building and
brood care
 Intra-worker variation is
lower than inter- worker
variation
 Time spent on these task
is highy consistent
Generalized task
 Eating
 Grooming

Possible reasons for inactivity
a) Lab artifact hypothesis
b) Shift work hypothesis
c) Immaturity hypothesis
d) Senescence hypothesis
e) Reproduction hypothesis
f) Communication hypothesis
g) Repletism hypothesis
h) Pace of life hypothesis
i) Reserve worker hypothesis
Age and inactivity

Model system used to answer this questions
The ant: Temnothorax rugatulus
Worker ant
Queen ant

Recording ant behavior
AntsWater
Sample unit: 5 minute HD videos
Food “Stone” wall

Lazy ants chill out while other workers toil

Parameters
•Mean walking speed
• Body size
•Position near the centre
•Degree of centrality: Interaction network
• Corpulence =
max gaster width
head to thorax length

Age and Inactivity Hypothesis
Young workers
may be inactive
Senescing worker
may be inactive
Developing physiology Degrading physiology
Inexperience Decrease locomotion
More vulnerable Decreased immune

Age and Inactivity hypothesis
Charbonneau et al. 2017
 Inactive worker walk slowly
 Have smaller spatial fidelity zone
 More corpulent
 Less connected in interaction network

Worker reproduction
Hiding from queen? Selfish? Worker Policing?
 They are selfishly resting
 Avoiding the risky task
 Laying the male eggs

Reproductive hypothesis
Reproductive potential
 Presence of oocyte
 Length of ovariole
Laying trophic egg

Trophic eggs
Perry And Roitberg, 2006

Repletism hypothesis
Myrmecocystussp
Proformicasp
Pernolepis sp Holldobler and Wilson, 1990
Extreme traits:
Repletes size > nestmates
Reduce mobility
Acting as a food stores?

Repletism hypothesis
Reduce mobility

Communication hypothesis
Should hold central position in colony interaction

Communication hypothesis
Inactive are least central in the colony interaction network
Charbonneau et al. 2017NIKITA NEGI UAS, GKVK, BANGALORE23-03-2020 36

Pace-of-life hypothesis
Inactivity is negatively correlated with walking speed
Inactives were the slowest task group Charbonneau et al. 2017
Pace of life predicts
that
• Larger body
• Slow Metabolic
rate
• Decrease activity

Predicted (P) and observed (O) outcomes of behavioral,
physiological & morphological measures of inactive
workers compared with their nest-mates

Why nature has to support such
lazy workers which apparently do
nothing ?

Reserve labour force
20 colonies are collected from Santa Catalina mountains, USA
allowed to emigrate to artificial nests
20% most actives workers removed (5 colonies)
20% most inactive removed (9 colonies)
20% randomly selected worker (6 colonies)
colonies were filmed 3 days before removal
1 week post removal
2 week post removal Charbonneau et al., 2017NIKITA NEGI UAS, GKVK, BANGALORE23-03-2020 40

Compensation
No
Replacement

Negative correlation between activity of inactive & active
workers
Hasegawa et al. 2016
Inactive workers process more task when active workers rest
Inactives replaces actives

Significant negative correlation between tasks processesd by active and
inactive worker
Task replacement is actually happening in colony
Hasegawa et al. 2016

Sustainability of colony Variable- colony with inactives
Invariable-without inactives
• Efficiency of variable system is lower
than invariable system
• Number of task processed is also small
• Inactives- workers with high threshold,
do not process task at lower stimulus
• Persistence of colony = no. of
task performed
• Low/no tasks processed =
extinction
• Persistence is low in invariable
system
Hasegawa et al. 2016NIKITA NEGI UAS, GKVK, BANGALORE23-03-2020 44

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Editor's Notes