Sexual Cannibalism in the Australian Redback Spider 1 2 Proximate Immediate behavior Proximate questions address the mechanisms that produce a behavior environmental stimuli genetic ID: 193679
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A Deadly PassionSexual Cannibalism in the Australian Redback Spider
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Proximate (Immediate) behaviorProximate questions address the mechanisms that produce a behavior:
environmental stimuli
genetic
and physiological
mechanisms
For example,
How does an animal carry out a particular behavior?Slide3
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Ultimate behaviorUltimate questions address the evolutionary significance of a behavior:
how a behavior increases the evolutionary fitness of the animal demonstrating it, helping it to survive and reproduce in its environment.
For example,
Why does the animal show this behavior?Slide4
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What is evolutionary fitness?Evolutionary fitness measures how well an organism can make viable genes and pass on fertile offspring to the next generation compared to others in the population. Slide5
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Adaptive behaviorAn adaptive behavior increases an individual’s evolutionary fitness relative to other individuals in the population.Slide6
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CQ#1: Red-crowned cranes breed in spring and early summer. Choose a proximate explanation:Breeding is most likely to be successful in spring and early summer.Increasing day length triggers the release of breeding hormones.
Ample food is available for chicks at this time.Slide7
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Breeding is most likely to be successful in spring and early summer.Hormonal changes in the spring trigger breeding behaviors.Breeding is triggered by the effect of increased day length on the birds’ photoreceptors.
CQ#2: Red-crowned cranes breed in spring and early summer. Choose an ultimate explanation:Slide8
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Sexual cannibalism In some species, one sex (usually the female) consumes the other during sexual reproduction.
Australian redback spiderPraying mantis
ScorpionSlide9
Deadly Mating
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Sexual cannibalism in Australian redback spidersUniversity of Toronto’s Maydianne Andrade has been studying Australian redback spiders for over a decade.Her goal: To explain sexual cannibalism in the Australian redback spider.Slide11
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Courtship in the Australian redback spiderThe male courts the much larger female for up to eight hours.
He strums on the strands of her web as he slowly approaches her.Slide12
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Courtship in the Australian redback spider The male has two specialized legs or palps, each of which is used to transfer sperm to the female. Slide13
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Mating of Australian redback spidersThe male mounts the female and inserts one of his palps into one of the female’s sperm receptacles.
The male moves into a “headstand.”
The male somersaults and dangles his abdomen in front of the female’s jaws. Slide14
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Mating of Australian redback spidersThe female begins to feed on the male, liquefying and slurping up the contents of his abdomen.
After the male is finished with his first palp, he disengages, performs a brief courtship, inserts his second palp, and somersaults again to dangle his abdomen in the female’s jaws.
The female finishes eating the male. Slide15
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redback somersault video15Slide16
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Mating of Australian redback spidersThe female produces an egg sac with 40-300 eggs.
Each egg is fertilized by a separate sperm.
If a female has mated with more than one male, a single egg sac can contain eggs fertilized by different males.Slide17
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Behavior of female redbacksMaydianne Andrade was interested in explaining the behavior of both females and males. Why do females cannibalize males during copulation?
First, we consider three hypotheses to explain the female’s behavior.Slide18
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Behavior of female redbacksHypothesis 1: Mistaken PreyFemales mistake males for prey.
How would one
test the
hypothesis?Slide19
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CQ#3: If the Mistaken Prey hypothesis is correct, what would you predict?
Females would sometimes attack males as soon as they enter her web.
65% of females would cannibalize their mates.
Females would only attack males when they somersault to dangle in front of her jaws. Slide20
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What does happen?Prediction: Females sometimes attack males as soon as they enter her web.
Results:
A female only eats a male after he somersaults to dangle in front of her jaws. In contrast, she often attacks prey as soon as they enter the web.
Conclusion:
The female does not mistake her mate for prey.Slide21
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Behavior of female redbacksHypothesis 2: Mate Rejection
Females eat males that are unsuitable as mates.How would one
test
this hypothesis
?Slide22
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Females would attack males only during copulation. Cannibalized males would be smaller and produce fewer offspring than non-cannibalized males. Cannibalized males would father twice as many offspring as non-cannibalized males.
CQ#4: If the
Mate Rejection
hypothesis is correct, what would you predict?Slide23
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What does happen?Prediction: Cannibalized males are smaller and produce fewer offspring than non-cannibalized males
Results:
Cannibalized males do not differ in size, mass, or condition from non-cannibalized males.
Cannibalized males father, on average, twice as many offspring as non-cannibalized males.
Conclusion:
Females do not cannibalize low-quality males who are unsuitable mates.Slide24
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Behavior of female redbacksHypothesis 3: Hungry LoverFemales eat their mates because they are hungry.
How would one
test
this hypothesis?Slide25
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CQ#5: If the Hungry Lover hypothesis is correct, what would you predict?Females would only eat males that somersault to dangle in front of their jaws.
Cannibalized males would be smaller and produce fewer offspring than non-cannibalized males.
Females would be more likely to cannibalize males if their diet has not been supplemented. Slide26
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What does happen?Prediction: Females are more likely to cannibalize males if their diet has not been supplemented.
Results:
29% of females that were given supplemental food were cannibalistic.
62% of females that fed naturally were cannibalistic.
Conclusion:
Females eat their mates because they are hungry. Slide27
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CQ#6: Choose a proximate explanation for female cannibalism:The female eats the male because he dangles his abdomen in front of her jaws.
The female can produce a larger egg sac if she eats the male.
The female gains nutrients by eating her mate. Slide28
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CQ#7: Choose an ultimate explanation for female cannabilism:
The female eats the male because he dangles his abdomen in front of her jaws.
The female gains nutrients from eating the male.
The female copulates longer while eating her mate. Slide29
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Behavior of male redbacksFemale redback spiders eat their mates because they are hungry.But why doesn’t the male try to escape? Is self-sacrifice an adaptive behavior for the male?
Maydianne Andrade tested two hypotheses to explain male behavior.Slide30
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Behavior of male redbacksHypothesis 1: Paternal InvestmentMales benefit by contributing nutrients (their own bodies!) to increase the number and size of their offspring.
To test the hypothesis:
Compare the size and mass of the egg sacs produced by females that have eaten their mates to those of females that have not eaten their mates.Slide31
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CQ#8: If the Paternal Investment hypothesis is correct, what would you predict?
Consuming the male would significantly increase the number and mass of eggs in the female’s egg sac.
The male’s food value would be low because his mass would be only 1-2% of the mass of the female.
Eggs in the same egg sac could be fertilized by more than one male. Slide32
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Behavior of male redbacksPrediction: C
onsuming the male will significantly increase the number and mass of eggs in the female’s egg sac.
Results:
Consuming the male does not increase the number or mass of eggs in the female’s egg sac.
This might be due to the small size of the male relative to the female and even relative to her egg sac!
Conclusion:
The male does not benefit from contributing nutrients to his offspring. Slide33
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Behavior of male redbacksHypothesis 2: Nuptial GiftMales benefit from self-sacrifice by increasing their fertilization success.
How would one test
this hypothesis
?Slide34
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CQ#9: If the Nuptial Gift hypothesis is right, what would you predict?
Non-cannibalized males would copulate longer than cannibalized males.Cannibalized males would father more offspring than non-cannibalized males.
65% of females would cannibalize their mates. Slide35
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Behavior of male redbacksPrediction: C
annibalized males father more offspring than non-cannibalized males.
Results:
Cannibalized males copulate for an average of 25 minutes, while non-cannibalized males copulate for an average of 11 minutes.
Cannibalized males father twice as many offspring, on average, as non-cannibalized males.
Conclusion:
Males double their fertilization success by sacrificing themselves to their mates! Slide36
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CQ#10: Choose a proximate explanation for male self-sacrifice:
The male’s somersault is triggered when he inserts a palp in the female’s sperm receptor.The male is providing nutrients to his offspring.
A male that is cannibalized fathers twice as many offspring. Slide37
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CQ#11: Choose an ultimate explanation for male self-sacrifice:The male increases the length of copulation by sacrificing himself.
The male’s self-sacrifice is an innate, genetically programmed behavior.
The male is providing nutrients to his hungry mate. Slide38
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Is self-sacrifice adaptive for the male?Benefit:Doubled reproductive success
Cost:Near certain death
Benefit:
Live longer
Cost:
Lower reproductive success, with almost 0% chance of finding a new mate
Self-sacrifice
Escape
Evolutionary fitnessSlide39
Slide Credits
Slide 1, Slide 8—Center, and Slide 27 Description: Female and male Australian redback spiders. Author: A.C. Mason Source: Andrade Lab webpage. Link: http://www.utsc.utoronto.ca/~mandrade/
Permissions: Used with permission of copyright holder, Maydianne Andrade.
Slide 6 and Slide 7
Description: Red-crowned cranes.
Author: Frank J. Gualtieri Jr.
Source: Wikimedia Commons.
Link: http://commons.wikimedia.org/wiki/File:Tsuru1260.jpg
Permissions: Released by author to the public domain.
Slide 8—Left
Description: Photo of paying mantis.
Author: Jon Brierley
Source: University of Guelph, Arboretum
Link: http://www.uoguelph.ca/arboretum/PhotoGall/PhotoRecent6.htm
Permissions: Used with permission of copyright holder, Jon Brierley.Slide40
Slide 8—Right
Description: Photograph of scorpion (Centruroides suffusus). Author: Drini (Pedro Sánchez) Source: Wikimedia Commons Link: http://commons.wikimedia.org/wiki/File:Centruroides_vittatus.jpg Permissions: Licensed under the Creative Commons Attribution ShareAlike 3.0 License.
Slide 9—Right
Description: Maydianne Andrade and redback spider web.
Author: Ken Jones
Source: Ontario Innovation Trust
Link: http://www.oit.on.ca/Pages/SStories21-40/StoryUTorontoAndrade.html
Permissions: Used with permission of copyright holder, Maydianne Andrade.
Slide 10 and Slide 36
Description: Female and male redback spiders.
Author: Ken Jones
Source: University of New South Wales, Faculty of Science, News.
Link: http://www.science.unsw.edu.au/news/spider-love-little-guys-get-lots-more/
Permissions: Used with permission of copyright holder, Maydianne Andrade.
Slide 11 and Slide 35
Description: Male redback spider’s pedipalps.
Source: Andrade Lab webpage.
Link: http://www.utsc.utoronto.ca/~mandrade/index_files/Reproductive_biology.htm
Permissions: Used with permission of copyright holder, Maydianne Andrade.Slide41
Slide 12
Description: Drawing of male’s somersault during copulation. Source: Forster LM. 1992. The Stereotyped Behavior of Sexual Cannibalism in Latrodectus hasselti Thorell (Araneae, Theridiidae), the Australian Redback Spider. Australian Journal of Zoology. 40(1): 1–11. Copyright CSIRO 1992. Published by CSIRO PUBLISHING, Collingwood Victoria, Australia. http://www.publish.csiro.au/nid/90/paper/ZO9920001.htm Permissions: Used with permission of CSIRO Publishing.
Slide 14 Description: Video of male’s somersault during copulation.
Author: Ken Jones
Source: Andrade Lab webpage.
Link: http://www.utsc.utoronto.ca/~mandrade/index_files/Page332.htm
Permissions: Used with permission of copyright holder, Maydianne Andrade.
Slide 15 and Slide 26
Description: Female redback spider with egg sac.
Source: Pulse of the Planet
Link: http://pulseplanet.com/monthlyfeature/featurestories.php?id=20
Permissions: Used with permission of copyright holder, Maydianne Andrade.