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Mini Symposium
- 1. Offspring sex varies with maternal investment ability: empirical demonstration based on cross- fostering Authors: Kylie A. Robert, Lisa E. Schwanz and Harriet R. Mills Presented By: Jennifer Driskell
- 2. Background-Tammar Wallabies What do they look like? What do they eat? Grass and leaves Where do they live? How long do they live? ~ 14 years
- 3. Reproduction Newborn Joey Close-up of newborn 70 Days Old 150 Days Old 200 Days Old
- 4. Reproduction Continued After about a 28 day gestation, a single Joey will be born The Joey will climb into the pouch and attach its mouth to a teat to continue developing If the mother becomes pregnant while a Joey is in the pouch, the embryo’s development will pause until the Joey leaves the pouch
- 5. The Aims of the Study Examine whether offspring sex is correlated with maternal investment ability (likelihood of weaning an offspring) To test the assumption that maternal investment has a greater influence on the fitness of sons than of daughters (survival of offspring)
- 6. The Bigger Picture To determine if maternal investment plays a role in the sex-ratio of populations Cost of Maternal Care: -Time -Energy -Immunity -Increased predation risk Benefits of Maternal Care: -Increased survival of young
- 7. Materials and Methods 32 adult female tammar wallabies were captured in Tutanning Nature Reserve, Western Australia All were carrying a single young (13 daughters, 19 sons) less than 100 days old Females were: Weighed Measured (foot length mm) Ear tagged
- 8. Materials and Methods Cont. Young were: Treatment Groups: Weighed (Birthed/Fostered) Sexed (visually) Group 1: Female/Female Micro-chipped Group 2: Female/Male Assigned to 1 of 5 Group 3: Male/Female treatment groups Group 4: Male/Male Re-attached to teats Group 5: Own offspring after brief removal from Measured teat Offspring survival and body size at weaning (~300 days) and ~1 year of age
- 9. Results No difference in maternal mass or maternal condition index at end of study or at weaning Weaning success was 61.5% for all cross-fostered offspring and 50% for sham offspring Cross-fostering did not reduce weaning success Mass of surviving offspring at weaning was not influenced by the sex of offspring originally produced, foster sex, or their interactions
- 10. Results Continued Graph A indicates that a mother that originally birthed a son had a significantly greater probability of weaning her pouch young irrespective of its sex than a mother that birthed a daughter Graph B indicates that although weaning success of male offspring was more strongly influenced than that of a female offspring based upon the sex of the originally produced offspring, the cross-foster nor foster sex were significant predictors of weaning success
- 11. Discussion This study provides evidence that female tammar wallabies with greater investment ability give birth to more sons. This study failed to provide evidence that the fitness of sons depended on maternal investment more than the fitness of daughters. Small sample size Offspring success based off of captivity
- 12. Back to the Bigger Picture Natural Selection vs. Population Balance Natural Selection selects for the most “fit” In this case, the most fit would be the mother capable of providing a greater maternal investment ability That mother produces more sons Thus natural selection inadvertently would be selecting for more male wallabies This can be a huge problem: Our guest lecturer stated that in hunting if you kill all but 1 buck he could still fertilize all of the females However if there was only one female she would only produce so many offspring In the case of the wallabies they would most likely be males This was one of the first studies that looked at sex-allocation so it will be interesting to see where the research goes from here!
- 13. QUESTIONS?
- 14. References Article: • Robert, Kylie A., Lisa E. Schwanz, and Harriet R. Mills. "Offspring sex varies with maternal investment ability: empirical demonstration based on cross-fostering." Biology Letters 618 Nov. (2009): 242-45. Web. 3 Apr. 2012. Images: • http://gallery.photo.net/photo/6529679-md.jpg • http://classes.ansci.illinois.edu/ansc438/lactation/marsupials. html • http://ih3.redbubble.net/image.6437941.9531/flat,550x550,0 75,f.jpg • http://www.iayork.com/Images/2009/7-22- 09/TammerWallaby.jpg
Notes de l'éditeur
- What do they look like?-18 inches from head to base of tail-Mostly grayish brownWhere do they live?-Southern and Southwestern Coastal Australia-Some of the nearby islandsWhat do they eat?-Herbivorous-Spend their night’s feeding-Can drink sea water when fresh water is limited
- Reproduction-After about a 28 day gestation, a single Joey will be born-The Joey will climb into the pouch and attach its mouth to a teat to continue developing-If the mother becomes pregnant while a Joey is in the pouch, the embryo’s development will pause until the Joey leaves the pouch
- Maternal Condition Index- calculated as the residuals from a regression between maternal mass and pes length.
- GRAPH A-a mother that originally birthed a son had a significantly greater probability of weaning her pouch young irrespective of its sex than a mother that birthed a daughter. -this indicates that mothers with greater investment ability were more likely to produce sons.GRAPH B-although weaning success of male offspring was more strongly influenced than that of a female offspring based upon the sex of the originally produced offspring, the cross-fostering nor foster sex were significant predictors of weaning successHigher weaning success for mothers that birthed sons occurred in both male and female foster young, thus it is clearly attributed to maternal investment during lactation
- The role of maternal investment ability was not reflected in relationships between maternal mass or condition and offspring sex. Maternal condition at fertilization may be more closely linked to offspring sex than the measures at cross-fostering.Survival to weaning in sons appeared to be more strongly influenced than in daughters by maternal investment ability; however this effect was not significant.
- Natural Selection selects for the most “fit” -In this case the most fit would be the mother capable of providing a greater maternal investment ability-That mother produces more sons -Thus natural selection inadvertently would be selecting for more male wallabiesThis can be a huge problem:-Guest lecturer stated that in hunting if you kill at but 1 buck he could still fertilize all of the females-However if there was only one female she would only produce so many offspring and they would likely be malesThis was one of the first studies that studied sex-allocation so it will be interesting to see where the research goes from here.