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Polyandry and tibial spur chewing in the Carolina ground cricket, Eunemobius carolinus Piascik, EK. Judge, KA. Gwynne,

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Presentation on theme: "Polyandry and tibial spur chewing in the Carolina ground cricket, Eunemobius carolinus Piascik, EK. Judge, KA. Gwynne,"— Presentation transcript:

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2 Polyandry and tibial spur chewing in the Carolina ground cricket, Eunemobius carolinus Piascik, EK. Judge, KA. Gwynne, DT. (Can J Zool) 2010

3 Nuptial Gifts in Various Insects Spermatophylax Male body parts Insect prey Male material donations transferred to the female during or directly after copulation Photo by Gwynne DT

4 Do nuptial gifts provide direct benefits or are they manipulative devices? A. Males provide females with direct benefits Increase 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

5 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

6 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?

7 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

8 The Coercion Hypothesis Gifts manipulate the female’s mating rate Sakaluk et al. 2006

9 Material Benefits Hypothesis Resource-deprived females are predicted to: mating rate copulation duration gift consumption latency to copulate

10 Katydids increase their refractory period Simmons and Gwynne 1991

11 Seed beetles increase their mating frequency Ursprung et al. 2009

12 Nursery web spiders accept more copulations Prokop and Maxwell 2009

13 Fedorka and Mousseau 2002

14 Mays 1971

15 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)

16 Carolina ground cricket, Eunemobius carolinus

17 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

18 Study animals

19 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

20 Mating trials Each female was given an opportunity to mate with one male once a day for four consecutive days 90 minutes

21 Mating trials Males Day HHHHHHHHLLLLLLLL 2HHHHLLLLHHHHLLLL 3HHLLHHLLHHLLHHLL 4HLHLHLHLHLHLHLHL Male A: H L H L Male B: L L L H

22 Fecundity and lifespan Ovipositor Eggs

23 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

24 Trend for females on the low-quality diet to copulate sooner than those on the high- quality diet

25 No significant effects of diet treatment on any of the mating variables

26 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

27 No difference in female mass before first mating opportunity p=0.361

28 Females fed low-quality diet lived significantly longer High-quality diet = solid line, n=22 Low-quality diet = broken line, n=21 p=0.045

29 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)

30 Correlations among mating behaviours and male lifespan

31 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

32 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.

33 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

34 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

35 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

36 Acknowledgements Dr. Darryl Gwynne Dr. Kevin Judge Dr. G.K. Morris The Gwynne Lab: Laura Robson Kyla Ercit


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