Kin recognition plays multiple roles across the animal kingdom. From an

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1 Sample paper critique #1 Kin recognition plays multiple roles across the animal kingdom. From an evolutionary point of view, one might expect kin recognition to be particularly important in the recognition of offspring; an!"#$!%&s genes might be better propagated if it pays preferential attention to the well-being of its own offspring. Ebensperger et al. address '(#)*#))+,*#"*'(,#-*.!.,-*/0!1'!'#"2*3,$!%,)*45*65'*4#)1-#$#"!',*7,'8,,"*9(,#-*:8"* Young and Unrelated Pups in the Communally Breeding Rodent, Octodon degus;< i Female degus often deliver their litters with other females and nurse unrelated offspring. As the authors note, there is a tension between the evolutionary benefits of nepotism and the benefits of communal nursing, such as the adoption of degu pups by other degus after the death of the parent. Previous research shows that degu dams can indeed differentiate their own offspring from others. With this in mind, the researchers set out to determine how the tension is resolved: whether dams show a preference for their own offspring or not. To accomplish this, the authors placed pairs of unrelated, pregnant females in experimental cages. Food intake to the mothers was restricted in order to increase the cost of lactation after giving birth, the idea being to increase the pressure on the dam to choose carefully to which pup she attended. The main experiment was simple. Each cage was divided by a plastic barrier that the dams could cross and that pups could not. Two pups, one related to the experimental female and one unrelated, were placed on the far side of the barrier from the nest. The behavior of the mother was then recorded, with attention to interactions between the dam and each pup, as well as how long it took the

2 mother to take the first pup back to the nest and which pup was retrieved first. Some dams were exposed to two pups of different ages in order to potentially aid her in distinguishing her offspring from the unrelated pup. Additionally, some dams were tested during early lactation (low energetic cost) while others were tested during intermediate lactation (high cost). Thus, in total the experimenters created four experimental conditions. Overall, the authors found that dams showed no preference for their own offspring over unrelated pups, whether in their interactions or in the order of pup retrieval. Even dams exposed to pups clearly of different ages did not discriminate in favor of their offspring. The authors did find that dams in the intermediate phase of lactation interacted more with pups, though again, this did not depend on their relatedness. The authors draw two possible conclusions from their data: either the evolutionary advantage of nepotism does not outweigh the cost, or the mothers are unable to effectively identify their own pups. They then offer five possible explanations for why these conclusions might be the case. First, discrimination in favor of related pups might lead to errors that would be evolutionarily costly, or second, discrimination might be energetically costly for the female. Paternal genes expressed in the pup or mother immediately after pup birth might also suppress recognition of offspring. Fourth, mothers may not be able to recognize their own pups in the presence of other pups. Finally, evolution may not have had time to select for discriminating mothers, implying that communal nesting is a recent phenomenon. The authors also explain their positive

3 results, concluding that females in the intermediate stage of lactation spend more time with pups likely as a result of a heightened maternal state. The problem of kin recognition is certainly worth investigating, especially in how it relates to treatment of offspring. The issue extends beyond rodents and is especially recognized in brood parasites such as the cuckoo. However, the wider applicability of the experiment presented in this paper is uncertain. Here, the authors present data showing that female degus do not discriminate against unrelated pups, but this is not by any means general. The authors even note in their introduction that some rodent species are not capable of recognizing kin, rendering the tension between discrimination and nondiscrimination moot in those species. Knowing that the results can only be conclusively applied to O. degus, an obscure Chilean rodent, makes the experiment lose some of its luster. That does not make it irrelevant, however. Now that the authors have established that degus do not discriminate, they are able to propose further experiments to determine the ultimate causation for non-discrimination in degus. The results of these future experiments could be very informative in understanding the evolution of communal breeding and allonursing, and could perhaps be generalized. The methods chosen for this preliminary experiment were sound, though not entirely convincing. The experimenters monitored time spent by the dam with each experimental pup, as well as the number of interactions, order of retrieval, etc. However, they did not measure the frequency of nursing, noting that the chaos of the nest made quantification impossible. Because the experimenters focused on lactation as way of assessing cost to the mother, it is unfortunate that the purpose of lactation, nursing, could not be directly measured, though the authors do note that nursing of unrelated pups did

4 occur. Additionally, one aspect of the experimental design was unclear: the role of the non-participating dam in the experiment. As mentioned above, pregnant degus were placed in pairs into the experimental cages, yet in the paper no mention is made of interactions between multiple females and the experimental pups, or whether both females played a role in retrieving the pups. It is certainly possible that the presence of another dam affects the discriminatory behavior of the focal dam. In light of this, failing to clarify the role of multiple dams seems a glaring omission. It is in cases like these that a figure or diagram of the experimental design would be helpful, particularly one that illustrates both the physical set-up of the experiment in addition to the different experimental conditions. The data that the authors did collect was in general presented well and concisely, with all the relevant statistical information. The three figures were also clear in what they represented, complete with appropriate labeling. However, there was one notable discrepancy between the text s description of the data and the representation in a figure. The authors state explicitly in the text that the order of pup retrieval did not depend on pup age difference or time of lactation. Yet for one condition, in which the females were in early lactation and pups were of different age, the bar in the figure corresponding to retrieving own-pup first is clearly much higher than the bar representing retrieving the unrelated pup first. The lack of error bars in the figure makes this discrepancy particularly confusing. If the reader accepts the methods used by the authors, then their conclusions are sound. Because there were no significant differences between dam behavior toward related and unrelated pups, it is clear that female degus, despite paying a cost in body

5 mass in order to lactate, do not treat their offspring preferentially. This must result from either an inability to discriminate or a lack of incentive to do so, the two conclusions well articulated by authors and explained above. That dams spend more time with pups in general during intermediate lactation is also well explained by the aforementioned maternal state. The discussion of possible causes for non-discrimination is excellent and complete, offering numerous possible hypotheses to test in the future. Further experiments will hold great interest for the ethology community and will hopefully demonstrate the value of the groundwork done in this experiment. i Ebensperger, L.A., Hurtado, M.J., & Valdivia, I. Lactating females do not discriminate between their own young and unrelated pups in the communally breeding rodent, Octodon degus. Ethology 112, (2006).