Evolution of Family Life & Brood Parasitism

Gina looking for coot nests
Parental control through favoritism and aggression

Raising a family is challenging. Conflicts of interest arise between parents, who seek to optimize family size each breeding season, and offspring, who seek to maximize the amount of care they receive (to a point). How parents manage their investment in the face of these conflicts has been a focus in life history theory.

American coots (Fulica americana) have a decidedly active — and aggressive — strategy of parental intervention.  My research shows that coots use a mixed strategy for controlling brood size: they use both brood reduction and parental control, but at different points in the parental care stage. After an initial period of high mortality for late-hatching chicks (brood reduction), Parental behaviors such as parental aggression, brood division and favoritism act as mechanisms for parental control that allow adults to optimally invest in their offspring (Shizuka & Lyon 2013). In the process, parents create a “favoritism hierarchy”, that is distinct from the competitive hierarchy created by hatching asynchrony. Changes in parental care strategies across time might be common, but it requires intensive observations throughout the parental care period (both in the nest & outside the nest), which is tractable in subprecocial birds like coots, but may be more difficult in altricial birds.


Learning, recognition and coevolution between brood parasites and hosts

Family life in coots is complicated by another factor–they are facultative conspecific brood parasites, meaning that neighbors opportunistically lay eggs in each other’s nest. This is a challenge similar to those faced by hosts of more famous brood parasites like cowbirds and cuckoos: hosts gain no fitness by raising foreign offspring to which they are not related. However, American coots have an ability to do what most birds seem unable to do: recognize and reject brood parasitic chicks (Shizuka and Lyon 2010). More shockingly, they do this despite the fact that parasitism occurs within species, and thus parasitic chicks look much like their own. Through a series of cross-fostering experiments we showed that coot have a reliable learning rule: learn the attributes of the first-hatched chicks in a brood as a template for discriminating between the later-hatched chicks. This works in coots because parasitic chicks rarely hatch on the first day. Moreover, they manipulate incubation patterns to ensure that suspected parasite eggs hatch later than expected (Shizuka & Lyon 2011). Put together, our study shows that when the risk of learning errors can be mitigated, chick recognition can evolve — confirming a key prediction made by the ‘cost of misimprinting’ model (Lotem 1993).

This work has led me to further ponder the ubiquitous role of learning mechanisms in ecological and evolutionary processes. Equally important is the ecology of information in which organisms evolve, which ultimately influences the evolution of learning. I seek to combine field experiments and theory to further understand learning processes in the contexts of host-parasite coevolution, speciation and family dynamics.

This work was funded in part by an NSF Doctoral Dissertation Improvement Grant (NSF: please bring this program back!!)

Photo: Bruce Lyon


Media coverage of this work:

Nature — Quirks and Quarks (CBC Radio) — Science News — Science Daily — Vancouver Sun