Sunday, March 6, 2016

Adoption in California Sea Lions


Ever since I swam with a sea lion in Key Largo, FL, I have been interested in learning more about these amazing creatures. They are highly intelligent, can be trained to do tricks in captivity for entertainment, and have even been trained to assist the U.S. navy with their in water needs.

One study on the California sea lion populations was used to provide evidence of adoption by adult female sea lions. This adoption behavior by the females is called alloparental behavior. Pups were captured at two different locations, San Jorge and Los Islotes Islands, where their measurements were recorded, DNA was taken in the form of toe clippings, and they received haircuts and flipper tags for identification. These pups ranged from 4 days to 8 weeks old, and when an adult female was seen nursing one of the tagged pups, a biopsy was performed on her to identify the amount of similarity between the genetic analyses of the female-pup pair. If there were more than one mismatch of the 14 loci being examined, it was determined that the female-pup pair was non-filial, meaning the pup was not the offspring of the female, indicating adoption. In situations where only one mismatch was observed, the pair was concluded as filial due to the fact that there could have been an error in the genotyping of the tissue samples. To reduce these errors, the PCR procedures were repeated for each sample. Additionally, the researchers looked at the effect the adoption of sea lion pups has on population viability, and they modeled different scenarios of how different factors of pup adoption could affect population growth.

A total of 15 female-pup pairs out of the 160 pairs sampled from both locations were identified as relationships that had been formed as the result of adoptions. One case that was not included in these recorded female-pup pairs because it was not randomly sampled was that of a female who was observed calling her pup with no response for three days. The next two months, the same female was observed nursing a tagged pup. The genetic relatedness of the random female-pup pairs, the non-filial pairs, and the filial pairs were calculated for both location and were recorded in the graph below.


 The results of the genetic analyses show that the filial pairs of both locations had a mean r-value of approximately .5, while the r-value of the random and non-filial pairs had means of roughly zero and did not significantly differ between each other. The error bars of the filial groups did not overlap with the random and non-filial groups, indicating that there was a distinct difference between the genetic relatedness of the two. This shows that there was little error in the identification of the filial female-pup pairs.

The adoption of the abandoned pups by adult females increases the population viability by reducing the mortality rates of the pups. Also, as long as their are no reproductive costs to the female, the growth of the population will increase because she may still produce her own offspring as well, increasing the population size. As the results from this experiment are rather broad when determining different effects of alloparenting on the population, this is an aspect that needs to be explored further in future experiments.

This research was important as it was the first form of evidence for adoption in California sea lions, and it can be used to expand upon the subject further. The methods used in this article allowed for an informative data analysis regarding genetics and behavior, and I would like to participate in research similar to this in my career by uncovering different behavioral characteristics of marine mammals.    

Reference:

First Evidence for Adoption in California Sea Lions

3 comments:

  1. Did the researchers measure reduced mortality among adopted pups, or is this just assumed?

    I would think that adopting pups would decrease the reproductive output of the females as they would be investing energy in feeding these pups. What do the authors think the evolutionary benefits to the female would be? How might this behavior have been molded by natural selection?

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  2. The researchers assumed that if the pups had not been adopted, they would die. Also, in the calculations they made for the population viability, the researchers assumes that a female who adopted a pup would not reproduce the next year, leading to a reduction in fecundity. So, yes there would be a decrease in reproductive output. What I meant to say was that if there were no costs as far as the female being able to reproduce in the future, the population would still be allowed to grow. They also assumed this in their calculations. The researchers did not state their thoughts on the evolutionary benefits to the female, but I believe that this behavior may have been molded y natural selection to simply allow for the survival of the species. When sea lion numbers were declining, perhaps the behavioral adaptation of alloparenting occured.

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  3. The researchers assumed that if the pups had not been adopted, they would die. Also, in the calculations they made for the population viability, the researchers assumes that a female who adopted a pup would not reproduce the next year, leading to a reduction in fecundity. So, yes there would be a decrease in reproductive output. What I meant to say was that if there were no costs as far as the female being able to reproduce in the future, the population would still be allowed to grow. They also assumed this in their calculations. The researchers did not state their thoughts on the evolutionary benefits to the female, but I believe that this behavior may have been molded y natural selection to simply allow for the survival of the species. When sea lion numbers were declining, perhaps the behavioral adaptation of alloparenting occured.

    ReplyDelete