Conflict within Families Flashcards
Conflict among males and females
The reproductive interests of males and females often differ - this conflict is a fundamental component of sexual selection, as covered in earlier modules. In later lectures, we will consider conflict between males and females over parental care and how the intensity of this conflict varies. Here, we will simply note how extreme this sexual conflict can become, resulting in infanticide.
e.g. langurs and lions - Males have a short tenure of groups of females, so they should attempt to father offspring as soon as possible. Therefore, males taking over a female group kill dependent offspring in order to bring females into oestrus sooner than if they waited for dependent offspring to become independent. In sex-role reversed species, females in a similar situation may be infanticidal, e.g. wattled jacana.
Conflict over reproduction in cooperative groups
Competition to maximise reproduction often results in conflict among co-breeding members of cooperative groups, despite that fact that group members are close relatives:
e.g. Egg-removal in acorn woodpeckers (Koenig et al. 1995. Animal Behaviour 50: 607-621) - Joint-nesting females are usually close relatives, nevertheless, females compete through the removal and destruction of eggs laid by co-breeders. This conflict is also evident in groups of joint-laying greater anis that are composed of non-relatives (Riehl 2011 Proceedings of the Royal Society B 278: 1728-1735.
Helpers may also seek reproductive opportunities within cooperative groups resulting in conflict with breeders:
e.g. Subordinate reproduction by meerkats (Clutton-Brock et al. 2010 American Naturalist 176: 664-673) - Similarly, the negative effect of subordinate reproduction on the fitness of dominants’ pups results in reproductive suppression by dominants of subordinate reproduction.
e.g. Worker policing in Hymenoptera – Haplodiploid sex determination results in unusual patterns of relatedness within colonies of Hymenoptera (see handouts/notes from APS209 to refresh your memories of how this works). Males develop from unfertilized eggs, and in many social insects, workers retain functional ovaries and can produce sons.
Workers should lay eggs to produce sons because: worker – son relatedness = 0.5
(assuming queen mates only once) worker – brother relatedness = 0.25
worker – nephew relatedness = 0.375
But, if queens mate many times, relatedness changes so: queen prefers sons (r = 0.5) to grandsons (r = 0.25)
workers prefer sons (r = 0.5) to brothers (r = 0.25)
workers prefer brothers (r = 0.25) to nephews (r = 0.125)
So, workers should prevent workers reproducing = WORKER POLICING (Ratnieks 1988 American Naturalist 132:217-236)
- worker policing in honeybees (Ratnieks & Visscher 1989 Nature 342: 796-797) – workers eat introduced eggs from other workers more than they eat introduced eggs from queens, so they can discriminate between eggs laid by workers and those laid by queens.
- intraspecific variation in worker policing in Dolichosvespula wasps (Foster & Ratnieks 2000 Nature 407: 692-693) – policing of egg-laying by workers is a facultative behaviour that depends on the mating frequency (hence relatedness of colony members). The same effect can be seen inter-specifically (Wenseleers & Ratnieks 2006 Nature 444: 50), a study that also shows that policing enforces altruism by reducing the benefit of independent reproduction.
e.g. Harassment in white-fronted bee-eaters (Emlen & Wrege 1992. Nature 356: 331-333) - Breeders harass close kin to induce breeding failure and hence to recruit helpers. Breeders gain more inclusive fitness if their kin help rather than breeding independently. For the recruited helpers, the pay-offs are similar if breeders are closely related to them.
The risk of inbreeding may also result in conflict between breeders and helpers:
e.g. Incest avoidance in acorn woodpeckers (Koenig et al. 1998. American Naturalist 151: 243-255) – In cooperative groups of kin, following the death of one parent, conflict is likely between a remaining parent and opposite-sex offspring over who reproduces within the group.
Resolution of this conflict depends on the sex of the protagonists, but it may incur substantial costs in terms of reproductive output (Koenig et al. 1999 Animal Behaviour 57: 1287-1293).
