Entry Five

A small taste of what I will probably have to do a lot of in my coming career. The first draft of this paper was not pretty and about an almost completely different topic. I actually found that I had fun researching this new topic. I never thought I would find birds interesting. The next entry will be another installment of Spero for all you avid readers out there. Psh...yeah

Bringing the Family Together: A look at Conspecific Brood Parasitism and Relatedness

Conspecific brood parasitism(CBP) is a custom practiced by many avian species. In this form of brood parasitism, a female will lay her eggs in the nest of a female of the same species and often in the nest of a host related to her. Extensive research has been done concerning this habit and it’s effect on the fitness of the species that practice it. CPB is often described as a “game” in that often, the parasitic individual will find that she has in turn been the victim of parasitism. All this in the name of increasing reproductive success. CBP has a more important role in the evolution of nest size than was previously believed (Lyon, 1998). In some cases, this practice has a positive effect on fitness (Andersson, 2001). The success and evolution of conspecific brood parasitism is closely related to the kinship of the host and parasite. It is also important to realize that CBP my not be a form of parasitism at all, but cooperation between related individuals (Dickinson, 2007).

CBP is most commonly found practiced in the order Anseriformes due to the nature of their precocial young and the decreased cost of parenting (Dugger, 2001). There are many costs to be taken into account when looking into parasitic species. Most of the time the addition of eggs to a nest has a negative effect on the success of the host female. In these precocial species this is not always true. Several species have shown that an increase in nest size has no negative effect on offspring survival and in some cases has actually aided it (Lopez, 2002). If a female is able to incubate more eggs with a somewhat minimal cost to her own health, then increased clutch size increases the chances for survival. Predators may take one or two eggs, but there are still 2-3 more that survive. In some species the host will strategically place the parasite eggs on the outside of the nest so that they are more easily accessed by predators. The parasite eggs act as a kind of buffer, keeping the hosts own eggs safe. This is a cost to the parasite and a risk that it takes in laying its eggs in another nest.

Because many water-fowl return to the place of their birth to nest, many of the individuals in the nesting site may be related. Relatedness is an important factor when considering CBP in these species. Host females are more likely to accept young from a parasitic individual closely related to them. An intricate cost-benefit analysis between the host parasite must be followed for there to be any positive effect on either ones fitness (Lyon, 1998). While a host female appears able to support parasitic young, a related parasite would do better to lay her eggs in that nest. That way there is a better chance for both to benefit. The host has that added padding of young that are not her own to soften the blow if she were to lose one. The parasite benefits if all the young are successfully reared. This cooperation of related individuals is what makes CBP a beneficial practice. There is a potential for increased fitness for both parasite and host. This is observed more in precocial species not only because the need for parental care decreases after hatching but because offspring competition also decreases. This increases the probability that a host will be able to take on more eggs than just her own.

Another important factor in evaluating this kin-based parasitic relationship is the individuals ability to detect a relation. This ability decreases as the distance between the relatedness increases. If a parasite will gain no benefit from laying an egg in the nest of a relative if that relative is not going to recognize the egg as kin. A parasite will suffer a direct cost if she lays her egg in the nest of a relative and the relative is unable to recognize the egg. The host will more than likely eject the egg even if there is some amount of gain received from accepting it (Lopez, 2002).

In evaluating conspecific brood parasitism and its relationship to kin-based cooperation, the word “parasitism” seems to be somewhat false. For the parasitic individual to gain the most benefit, there should be cooperation from both sides. In typical parasitism, one individual gains a benefit at the cost of the host. In many cases, whether eggs were intentionally kept by the host or not, the host gains at least some benefit to fitness in indirect ways. Evidence supporting the benefits of CBP is not altogether convincing. In some species there is no cost suffered or benefit gained. The individuals accept the parasitic eggs and their success does not increase or decrease (Dugger, 2001). Further research may support the idea that CBP is in fact be a twisted for of symbiosis with the two individuals working only for their own benefit but helping the other in their attempts at success.

Research and References

Andersson, Malte and Peter Waldeck. 2007. Host-parasite kinship in a female-philopatric bird population: evidence from relatedness trend analysis. Molecular Ecology 16.13. 2797-2806.

Andersson, Malte. 2001. Relatedness and the Evolution of Conspecific Brood Parasitism. American Naturalist 158.6. 599-615.

Dickinson, Janis L. 2007. Decoding dumping ducks. Molecular Ecology 16.13. 2621-2612.

Dugger, Bruce and Peter Blums. 2001. Effect of Conspecific Brood Parasitism on Host Fitness for Tufted Duck and Common Pochard. Auk 118.3. 717-727.

Lopez-Sepulcre, Andres and Hanna Kokko. 2002. The Role of Kin Recognition in the Evolution of Conspecific Brood Parasitism. Animal Behavior 64.2. 215-223.

Lyon, B.E., W.M. Hochachka and J.M. Eadie. 2002. Paternity-Parasitism Trade-Offs: A Model and Tedt of Host-Parasite Cooperation in an Avian Conspecific Brood Parasite. Evolution 56.6. 1253-1266.

Lyon, B.E. 1998. Optimal Clutch Size and Conspecific Brood Parasitism. Nature 392.6674. 380-383.