Why insects shoes homosexual behaviour? what is the advantage of this behaviour? What is the fate of this behaviour?

1. विकृ वि एिं प्रकृ वि
Vikriti Evam Prakriti
What seems unnatural is also natural
1

2. Spotted hyena
Bonobo American bison
Two male mallards Swans, Cygnus atratu
2
West African giraffe
Two male Bonin flying
foxes (Pteropus pselaphon)
Male big horn sheep
Bottlenose dolphins, killer whales, grey whales, and West Indian manatees, Japanese
macaques, mallards, penguins
SSS behaviour has been reported ~100 species of insects (Bagemihl, 1999)

3. ame ex exual
Behaviour in insects
3
Kishor Pujar
III Ph.D. Agricultural Entomology
PALB 9014
University of Agricultural Sciences Bangalore

4. Behaviour that is
usually performed at
some stage during
reproduction with a
member of the opposite
sex, but which is instead
aimed towards members
of the same sex.
Copulation
courtship mounting
Genital
contact
Introduction
4
SSS
or
Homosexual behaviour
“Darwinian paradox”
Compulsory
Produce offspring
Less energy investment
X
X
X
Why do they do that?
Does it cost ?
What is the fate of homosexuality?
It is impossible to maintain genes
which do not promote reproduction

5. 5
Characters Homosexuality Heterosexuality
Attraction towards Same sex Opposite sex
Courtship Yes Yes
Mounting Yes Yes
Reproductive organs
contact
Yes Yes
Fertilization No Yes
Why it is sexual behaviour ? Why not simple interaction?

6. 6
,,,,,,,,,
• Switzer et al.,2004
Mistaken identity/late sex recognition (80%)
• Cockroaches, flies, wasps, beetles (Iguchi, 1996)
By-product of heterosexual behaviour
• Flies, Wasps, butterflies (He, 2008)
Mating interruption
• Beetles (Levan et al., 2009)
Practice for heterosexual encounters
• Fruit fly, Dosphila melanogaster (Machiano et al..,2017)
Biased sex ratio
Encounters satellite male strategy
Prison effect
Indirect sperm translocation
Dumping of old sperm
Why it happens?

7. Mistaken identity/late sex recognition
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Individuals fails to recognize their mate
Lack of experience
Overlapping of the phenotypic character
Majority of the insects

8. 8
Male Female
Body
length
22.1 mm 19.4 mm
Pronotum
width
4.3 mm 3.7 mm
Pronotum
length
2.9 mm 2.6 mm
FW length 16.5 mm 13.4 mm
FW width 6.5 mm 3.3 mm
Jaiswara et al. (2020)
Same-sex sexual behavior in Xenogryllus marmoratus (Haan, 1844)
(Grylloidea: Gryllidae: Eneopterinae): Observation in the wild from YouTube
(Olivero and Robillard, 2017)
River bed in Hofu city, Japan, October 20, 2014
Male
Female
Pine cricket, Xenogryllus marmoratus

9. 9

10. 10
Acceptance threshold theory can explain occurrence of homosexual behavior
Engel et al. (2014)
If the discriminating male has a high-acceptance threshold and is very
restrictive, it will risk rejecting many females, while if it has a low-acceptance
threshold and is very permissive, it will accept males as mating partners.
-Reeve (1989)
How can an insects become a gender blind?????
Strategy of permissiveness
High-
acceptance
threshold
Selective
If the phenotypic cues
of the both sexes are
overlapping
It will reject
females
Costs more
in deprived
female
condition
Low
acceptance threshold
More permisive
Risk of rejecting
females will be
reduced
Chance of mating
with males

11. Three
females
One
female
Alone One male
Three
males
11
Nicrophorus vespilloides
(Silphidae: Coleoptera)
Collected from deciduous forest in Freiburg, Germany
Plastic containers filled with moist
peat
After eclosion Males were kept in 5
different densities
20 days
treatment
60 days
treatment
Female deprived condition
Institute of Experimental Ecology and Conservation Genomics,
University of Ulm, Ulm, Germany

12. 12
Wald-x2
4,36 =3.45, p =0.49
3 ♀
1 ♀
Alone 1 ♀ 3 ♀
Wald-x2
1,131=4.46, (p=0.035),
3 ♂ 1 ♂ Alone
3 ♂ 1 ♂
 Males in female-deprived situations engaged significantly more often in SSB than males
kept with females
 In female deprived condition searching time increases and males become more permissive
 Males maintained with one or three females did not engage in SSB at all
 Males kept in complete isolation showed the highest occurrence of SSB (80.0%)
Prison Effect
N=36
N=86

13. 13
The phenomenon that the incidence of SSB increases under the absence
of mating opportunity
Prison Effect
Males were kept in absence of females for 60 days
It is a consequence of a discrimination
strategy or mistaken identity
This theory was not supported by researchers
Phenotypic cues are
not the ultimate cause
for the selection of
mate

14. 14
No difference between social conditions Wald-x2
4,36 =0:50, p<0.97 The males’ social environment affected the occurrence of
matings (GLM, Wald-x2
4,87 =21.84,P<0.001.
Males kept with three females copulated less often with a female than males kept in isolation or
with a male
When more females were offered male becomes choosy and multiple mating cause exhaustion
Inference Insects doesn’t lose the discriminating ability but follow permissive strategy

15. Why did the male 1 pine cricket produced spermatophore?
As the spermataphore is costly
Do all insects make such mistake during SSSB
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16. 16
Testing multiple hypotheses for the maintenance of male homosexual copulatory behaviour
in flour beetles
Sexing of pupae
Dark incubator
@290 C & 70%
RH
Adults kept in flour
either in group or
individual (@ 2gm
flour/beetle)
Mating observations
at 29–320C in plastic
arenas with filter
paper to provide
traction.
Two T. castaneum
Genetic strains differing
in adult body colour:
a wild-type strain (+ ⁄ +)
Chicago black (b ⁄ b)
Indirect sperm
translocation
Body colour phenotype
of adult progeny to
distinguish between
progeny sired by either
black or wild-type males.
♀ Isolated to oviposit
Adult progeny phenotype
♀ Isolated to oviposit
Adult progeny phenotype
Levan et al. (2009)
n = 86 pairs
172 matings
Red flour beetle Tribolium castaneum
(Coleoptera: Tenebrionidae)
Control: 65 matings b/b or ++ with b/b

17. In six of 86 pairs (7%), females produced progeny with body colour phenotypes indicating
that they were sired indirectly by their mate’s previous homosexual partner
In case of Chicago black male and female combination, wild type of progenies produced
None of the 65 control matings produced any unexpected progeny
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Mounting male is releasing a spermatophore from its extended genitalia Spermatophore deposited on a mounted
male after release by the mounting male
Inference Insect use SSS as tool for indirect sperm translocation

18. 18
Why it has to use the other male to transfer the spermatophore as
himself is capable of doing it?
Sperm dumping
SSS is a strategic process
not an
unintentional behaviour
Discarding the aged sperm of poor performance (low
motility, fertilizing ability and sperm competitive ability)
• Ex: Red flour beetles and most of the crickets, (Reinhardt
And Siva-Jothy, 2005)
Younger sperms are more preferred by females
• Income breeders whose gamete production is fuelled by
adult nutrient input and adults mate repeatedly during their
1- to 2-year adult lifespan (7 mating in 15 mins)
It occurs in males who can’t down regualte sperm
production (Ex: Red flour beetles )
• Down regulation is necessary if female population is less
High sperm production : Selective advantage if more
females were there

19. 19
Genes Function Reference
fruitless Associated with courtship Hall, 1994; Yamamoto et al., 1996
dissatisfaction Associated with courtship Finley et al., 1997
prospero Associated with courtship Balakireva et al., 1998
quick-to-court Associated with courtship Gaines et al., 2000
traF Associated with courtship
Ferveur et al., 1995; O’Dell et al.,
1995
mini-white transgene
(mw)
Associated with courtship
Zhang and Odenwald, 1995;
Hing and Carlson, 1996
What is the consequence?
For or against?
Any physiological evidences?
Gene mutation can induce SSSB

20. • Bed bugs – Traumatic insemination (TI)
• Bloated individuals are the target (irrespective of sex)
• TI causes the scars in female paragenitalia
• Females produce alarm pheromone to warn and to be released
• Same strategy by males during SSSB
• Scars indicates the homosexual character in bedbugs
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Homosexual interactions in bed bugs: alarm pheromones as male recognition signals
Cimex lectularius
(Ryne, 2009)

21. 21
• Cimex lectularius Fed with blood meal 7 days prior to
experiment
• The optimal feeding frequency is every 7–10 day
Experimental insects
• Mounting behaviour in this study consisted of the combined
behaviours of mounting and probing with the male paramere.
Mating and Mounting Behaviour
• The 2–3-week-old virgin males (focal) were placed dorsally in
a petri dish with tissue paper
Male–Male Interactions
• All the females were blood fed before the experiments &
introduced to a virgin male, which performed the mounting
behaviour.
• The chemicals were delivered by a continuous manual puffing
when the male mounted the female
Male–Female Interactions
(1) Operated (treatment) applied nail polish to the
two large metathoracic glands between the first
and second pair of legs
(2) Sham operated (control)
Prior to the experiment male bed bugs allowed the
feed on blood meal after drying of nail polish
(1) Male + Female (control group)
(2) Male + Female with hexane stimulus (solvent control)
(3) Male + Female with male extract stimulus (treatment)

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Male Mating Scars
One-week-
old males
• Marked with
correction fluid
(Tip-ex)
• Randomly
divided into
two groups,
each with 10
males
Group 1
(Control)
• 10 males
individually
kept in 3 ml
jars + a piece
of filter paper
Group
2(Treatment)
• 10 males kept
Individually in
30 ml jars +
filter paper +
four additional
males.
Feed
• Blood meal on
every 7-10
days till death
Observations
• Piercing
Scars

23. 23
Blocked Control Blocked Control Control
Blocked
Duration per mounting event in male–male interactions
(N=12); (N=11);
No. of mountings was low in treatment (blocked)
Total time of all mountings and time per mount in blocked was high (100 S and 40
S respectively
Alarm pheromone is the terminating signal for homosexual in bed bugs

24. 24
(Control) (Treatment)
Male–female mounting interactions Male Mating Scars
The arrows point to the most obvious melanized tissue from
damage of the cuticle
F+M
N=19
F+M+H
N=13
F+M+ME
N=21
Male extracts inhibited the mounting by males <50
Control and Solvent control showed no significant difference
(250 & 200 respectively)
Alarm pheromone is terminating signal in heterosexual behaviour also
Homosexual behaviour is
not in favour

25. 25
Danaus plexippus
Paragenitalia and traumatic insemination in Coridromius spp. Tatarnic et al.2006
Female Male
(Caballero-Mendieta and Cordero, 2012)
(Dunkle, 1991)
Heterosexual
behaviour also
not safe
But Necessary

26. 26
Homosexual behaviour and its longevity cost in females and males of the seed beetle
Acanthoscelides obtectus
Stojkovic et al. (2010)
Acanthoscelides obtectus
Coleoptera:Chrysomelidae: Bruchinae)
Base population of 5000 beetles Obtained from laboratory population
established in 1986
Research location: Belgrade, Serbia, South East Europe
The B population was maintained at large size in large bottles with
approximately 5000 common bean seeds for an approximately 40-day
interval
Dark incubator at 30 0C and 70% relative humidity
Base
population
M & F together
In 10 petridish
100 bean seeds
at 10th day
100 individuals/ petri dish + No
bean seeds. M & F allowed to
mate from emergence till death
M & F together
In 10 vials
Early lines
48 h old
Late lines
(10 days
old)
50 indiviuals/ petri dish +
50 bean seeds
Females were
allowed to lay egg for
48 hr after emergence

27. 27
Longevity assays
The longevities of eight different groups of females and males were therefore established
within the B population and the E and L lines:
Virgin females
housed alone (V)
Females from
heterosexual
pairings (He)
Males from
heterosexual
pairings (He)
virgin males
housed alone (V)
Pairs of virgin
males from the
E and L selection
treatments (Ho2)
E/L
population
Virgin Female
pairs(Ho1)
E/L
population
Virgin male
pairs(Ho1)
Pairs of virgin
females from the
E and L selection
treatments (Ho2)
Each of the groups consisted of 100 individuals

28. 28
Longevity
assays
Female
Male

29. • Longevity was high in individuals which are Virgin and shows
Homosexuality
• Homosexuality and being virgin has no significant difference
• Heterosexuality resulted in reduction in longevity
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Reason: Heterosexuality forces to invest more energy in egg production
Energy conserved in individuals which are virgin and shows
high homosexuality
Inference: Homosexuality results in more longevity
Survival and reproduction is the fundamental
concept of all living organisms
But

30. Conclusion
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• No evolutionary causes
• Instant response of the organism
• Insects make best of it
• Nature has accepted this un-natural process
But not by us………………

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32. In 1265.78 million 2.5 million were
homosexual in 2012 =0.22%
In 1391.99 million 41.77 million are
homosexual in 2021= 3%
Indian Scenario
9% = bisexual,
1% =pansexual and
2% =asexual.
Totally, 17% identify as not heterosexual 32

33. Thank You
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