Polyandry and tibial spur chewing in the
Carolina ground cricket,
Eunemobius carolinus
Piascik, EK. Judge, KA. Gwynne, DT. (Can J Zool) 2010
http://www.ojibway.ca/orthoptera.htm
Nuptial Gifts in Various Insects
•Male material donations transferred to the female during
or directly after copulation
Spermatophylax
Photo by Gwynne DT
Insect prey
http://farm1.static.flickr.com/62/175348691_7df74ddb73.jpg?v=0
Male body parts
http://www.livescience.com/imageoftheday/siod_050214.html
Do nuptial gifts provide direct benefits
or are they manipulative devices?
A. Males provide females
with direct benefits
B. Males manipulate
females
Increase in female fitness with
increased number of matings
Decrease in female fitness with
increased number of matings
Example:
Nutritional and hydration
benefits
Example:
Allohormones in male
secretions reduce female
receptivity to subsequent
matings
Sexual Conflict
• Occurs when the two sexes have conflicting optimal fitness
strategies
• Males mate multiply to increase fertilization success
• Females mate less to avoid costs
http://www.ijmphotography.co.uk/Images/Wildlife-And-Nature/Large/IJM_DamselMating.jpg
Polyandry and Sexual Conflict
• Females will mate with a variety of males,
exceeding the mating rate necessary to produce
all her offspring
Why are females mating with several males?
• Can nuptial gifts benefit the female and
overcome these costs?
Nutritious gifts
• Nuptial gifts may be providing the female with
nutrients
• Increase the fitness of the male’s own
offspring
• Increase the fitness of the female
The Coercion Hypothesis
• Gifts manipulate the female’s mating rate
Sakaluk et al. 2006
Material Benefits Hypothesis
• Resource-deprived females are predicted to:
•
mating rate
•
copulation duration
•
gift consumption
•
latency to copulate
Katydids increase their
refractory period
Simmons and Gwynne 1991
Seed beetles increase their
mating frequency
Ursprung et al. 2009
Nursery web spiders accept
more copulations
Prokop and Maxwell 2009
Fedorka and Mousseau 2002
Mays 1971
Female southern ground
crickets gain material
benefits from multiple
matings
Female striped ground
crickets copulate longer
when chewing on tibial
spurs
(Fedorka and Mousseau 2002)
(Bidochka and Snedden 1985)
Carolina ground cricket,
Eunemobius carolinus
Testing the
Material Benefits Hypothesis
• Manipulate the nutritional content in female diet
• Prediction: If females are nutritionally deprived,
then they will
1)
2)
3)
4)
increase their mating rate,
copulate sooner,
copulate longer and
chew longer
***This study would provide useful information on the
basic mating behaviour of E. Carolinus
Study animals
Female diet manipulation
•
Females were placed in one of two diet
treatments (upon adult eclosion) varying in
nutritional content
• Low-diet: 67% rabbit chow, 33% cellulose
• High-diet: 99% rabbit chow, 1% cellulose
Mating trials
Each female was given an opportunity to mate with
one male once a day for four consecutive days
90 minutes
Mating trials
Males
Day
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
H
H
H
H
H
H
H
H
L
L
L
L
L
L
L
L
2
H
H
H
H
L
L
L
L
H
H
H
H
L
L
L
L
3
H
H
L
L
H
H
L
L
H
H
L
L
H
H
L
L
4
H
L
H
L
H
L
H
L
H
L
H
L
H
L
H
L
Male A: H L H L
Male B: L L L H
Fecundity and lifespan
Ovipositor
Eggs
Fecundity and lifespan
• Total egg count
= total # eggs from gauze over lifetime
• Egg-laying rate
= total egg count / lifespan (days)
Survival was monitored daily
Food and water were replaced weekly
Trend for females on the low-quality diet
to copulate sooner than those on the highquality diet
No significant effects of diet treatment on
any of the mating variables
Females of this species may not receive
direct benefits from multiple matings
• Females fed a low-quality diet did not mate more
often or sooner than females fed a high-quality diet
• When they did mate, they did not copulate or feed for
longer
No difference in female mass before first
mating opportunity
p=0.361
Females fed low-quality diet lived
significantly longer
p=0.045
High-quality diet = solid line, n=22
Low-quality diet = broken line, n=21
Nutrient restriction was insufficient to
limit the material benefit
• The diet DID have an effect on the females
• Females fed on low quality diets lived longer which
indicates food stress because dietary restriction is
known to extend the lifespan of animals (Partridge et
al. 2005)
Correlations among mating behaviours
and male lifespan
Spur chewing may be costly to males
• Males may be taking longer breaks from mating as they
recoup lost energy reserve
• Sagebrush crickets are less likely to re-mate as a result of
female wing-feeding (Sakaluk et al. 2004)
• Future work could examine condition dependence of male
haemolymph gifts, also effects on male immune function
and life span
Males may be coercing females
• Male control over insemination
• Spermatophore attachment
• Chemicals in the ingested hemolymph that function as a
chemical signal to increase male fitness
• Field crickets exposed to courtship had shorter lifespans
(Bateman et al. 2006)
• BUT E. carolinus that mated are actually living longer and
laid more eggs than those that failed to mate.
Mating behaviour
• 1971: Mays described the mating behaviour of E.
carolinus based on 2 pairings
• Current study: describes mating encounters based on
70 complete mating sequences
• We now have a comprehensive description of
courtship and copulation of this previously undescribed gift-giving species
Older females were more likely to mate
than younger females
p=0.024
Diameter of data points is related to the number of
observations with that combination of values
Smallest=1
Largest=6
Further insight into the role of spur
chewing during mating in E. carolinus
• Effects on both female and male fitness
• Our results do suggest that spur chewing may be
costly for males
• Male mass loss correlated with both copulation and
spur chewing in this cricket species
• Further studies should examine the relationship of
both the gift size and the gift`s chemical composition
to female fitness
Acknowledgements
Dr. Darryl Gwynne
Dr. Kevin Judge
Dr. G.K. Morris
The Gwynne Lab:
Laura Robson
Kyla Ercit
http://www.pbase.com/tmurray74/image/89343329