Does it pay to be parasitized?

Raven Edwards wrote this post as a project for Dr. Stacy Krueger-Hadfield’s Evolution course at the University of Alabama at Birmingham. She is a Master’s student in Dr. James McClintock’s lab where she is studying the growth of variegated sea urchins. Raven completed a B.S. in Biology at the University of Alabama at Birmingham.

Could you recognize a relative you’ve never met before? According to the recent study by Hervey et al. (2019), common eiders can!

Common eiders exhibit a behavior known as conspecific brood parasitism, in which some females will lay eggs in a nest belonging to another female. This act of cooperative breeding can actually benefit the host female by inclusive fitness gains under certain circumstances. In this paper, inclusive fitness is defined as the genetic contribution of the host to the next generation resulting from the parasitic egg; thus, there are only inclusive fitness gains if the host is closely related to its parasitizer. So, this begs the question, how do females known they are being parasitized by a relative?

The two working hypotheses behind this cooperative breeding are nest site fidelity and kin recognition. For nest fidelity, females must consistently nest in the area where they hatched year after year and only parasitize nearby nests. For kin recognition, females must be able to recognize relatives even if they have never met previously.

Using the feathers and hatch membranes left behind in nests, Hervey et al. (2019) genotyped two colonies of eiders in Manitoba, Canada, in 2016 and 2017 using microsatellites. Of the 205 nests studied, 104 were parasitized, with the relatedness between the parasitizer and the host female higher than that between neighboring nests. Females whose nests had failed the previous year would often re-nest 100 m or more away the following year. Overall, these results show that females show very little nest site fidelity.

Figure 2. Movement of nesting location by females found in both 2016 (dots) and 2017 (arrows). Modified from Figure 6A in Hervey et al., 2019.

Since common eiders don’t consistently nest in their hatching location, they must be capable of recognizing their relatives in some way. Hervey et al. assert that the most likely method of recognition in the common eider is through a combination of visual and olfactory cues. Research has been done regarding visual recognition of kin phenotypes, but little is known about olfactory recognition in birds as a whole. Regardless, this recognition is extremely important because host females will only receive fitness benefits when parasitized by a relative. Does it pay to be parasitized? In common eiders it definitely does, thanks to their ability to recognize relatives! 


Hervey, S. D., Barnas, A. F., Stechmann, T. J., Rockwell, R. F., Ellis-Felege, S. N., & Darby, B. J. (2019). Kin grouping is insufficient to explain the inclusive fitness gains of conspecific brood parasitism in the common eider. Molecular Ecology 28: 4825-4838.

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