Polyandry and tibial spur chewing in the

Carolina ground cricket, Eunemobius carolinus

http://www.ojibway.ca/orthoptera.htm

Piascik, EK. Judge, KA. Gwynne, DT. (Can J Zool) 2010

Nuptial Gifts in Various Insects

Spermatophylax Male body partsInsect prey

•Male material donations transferred to the female during or directly after copulation

http://www.livescience.com/imageoftheday/siod_050214.htmlPhoto by Gwynne DT

http://farm1.static.flickr.com/62/175348691_7df74ddb73.jpg?v=0

Do nuptial gifts provide direct benefits or are they

manipulative devices?

A. Males provide females with direct

benefitsIncrease in female fitness with increased number of matings

Example:Nutritional and hydration benefits

B. Males manipulate females

Decrease in female fitness with increased number of matings

Example:Allohormones in male secretions reduce female receptivity to subsequent matings

• Occurs when the two sexes have conflicting optimal fitness strategies

• Males mate multiply to increase fertilization success

• Females mate less to avoid costs

Sexual Conflict

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

(Fedorka and Mousseau 2002)

Female striped ground crickets copulate longer when chewing on tibial spurs

(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) increase their mating rate,2) copulate sooner,3) copulate longer and 4) 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 dailyFood and water were replaced weekly

Trend for females on the low-quality diet to copulate sooner

than those on the high-quality 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

High-quality diet = solid line, n=22Low-quality diet = broken line, n=21

p=0.045

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 un-described gift-giving species

Older females were more likely to mate than younger females

Diameter of data points is related to the number of observations with that combination of values

Smallest=1 Largest=6

p=0.024

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 GwynneDr. Kevin Judge

Dr. G.K. Morris

The Gwynne Lab:Laura Robson

Kyla Ercit

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