Abstract
Sex allocation theory assumes that offspring sex (son vs. daughter) has consequences for maternal fitness. The most compelling experiment to test this theory would involve manipulating offspring sex and measuring the fitness consequences of having the “wrong” sex. Unfortunately, the logistical challenges of such an experiment limit its application. In tammar wallabies (Macropus eugenii), previous evidence suggests that mothers in good body condition are more likely to produce sons compared to mothers in poor condition, in support of the Trivers-Willard Hypothesis (TW) of condition-dependent sex allocation. More recently, we have found in our population of tammar wallabies that females with seemingly poor access to resources (based on condition loss over the dry summer) are more likely to produce sons, consistent with predictions from the Local Resource Competition (LRC) hypothesis, which proposes that production of sons or daughters is driven by the level of potential competition between mothers and philopatric daughters. We conducted a cross-fostering experiment in free-ranging tammar wallabies to disassociate the effects of rearing and birthing offspring of each sex. This allowed us to test the prediction of the LRC hypothesis that rearing daughters reduces the future direct fitness of mothers post-weaning and the prediction of the TW hypothesis that rearing sons requires more energy during lactation. Overall, we found limited costs to the mother of rearing the “wrong” sex, with switching of offspring sex only reducing the likelihood of a mother having a pouch young the following year. Thus, we found some support for both hypotheses in that rearing an unexpected son or an unexpected daughter both lead to reduced future maternal fitness. The study suggests that there may be context-specific costs associated with rearing the “wrong” sex.
Highlights
Does the production of a daughter versus a son influence maternal fitness? Offspring sex could be extremely important for maternal fitness, and empirical tests across living organisms have provided compelling confirmation of many hypotheses [1,2]
Mothers may indirectly benefit from producing the philopatric sex if they can bequeath the benefit of a high quality habitat or high social rank (Local Resource Inheritance, LRI, or Rank Inheritance; [5,9,10,11,12,13]), and may directly benefit if philopatric offspring increase the future reproductive success of the mother through cooperation (Local Resource Enhancement, LRE; [14,15,16,17,18])
Mothers may benefit from producing an offspring of the dispersive sex if philopatric offspring would cause competition for access to limited local resources with the mother or with siblings (Local Resource Competition, LRC; [10,18,19,20,21,22,23])
Summary
Does the production of a daughter versus a son influence maternal fitness? Offspring sex could be extremely important for maternal fitness, and empirical tests across living organisms have provided compelling confirmation of many hypotheses [1,2]. Assuming offspring provisioning influences reproductive success more strongly in sons than in daughters, mothers of greater condition are predicted to produce more sons than those of poor condition (Trivers-Willard Hypothesis, TW; [4,5,6,7]). Different provisioning rates for sons and daughters may have direct fitness consequences for mothers if sons ‘cost’ more to rear and diminish maternal body reserves for future reproduction [5,8]( this is not strictly true if mothers invest according to their optimal levels regardless of the offspring sex). The TW and Local Resource (LRI/C) hypotheses of sex allocation may operate simultaneously in a given population if individual mothers differ in their ability to provision offspring or in their access to resources post-weaning [22,23,24]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.