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Madi Stuhlreyer's Topic Choice: The Evolution of Parental Care in Penguins

Allport, Susan. A Natural History of Parenting: From Emperor Penguins to Reluctant Ewes, a Naturalist Looks at Parenting in the Animal World and Ours. New York: Harmony, 1997. Print. This source analyzes the evolution of parenting, but touches specifically on those evolutionary changes within the emperor penguin genus. Allport discusses why some species require more development post-partum, while others are born with all instincts intact. This will help develop not only the evolutionary aspect of my topic, but also how and why penguins have a distinctive parenting style.

Clutton-Brock, T. H. The Evolution of Parental Care. Princeton, NJ: Princeton UP, 1991. Print. One of the chapters of this source specifically targets the topic of trade-offs when it comes to parental care. It discusses how the feeding of young can be a detriment to parents' health and overall survival success. This can easily relate to penguins and their paternal care behaviors. The energy cost of caring for their young for so long after hatching greatly exceeds the energy needed for reproduction or gestation. But Clutton-Brock goes on to comment on how evolution has crafted the breeding season to reduce the energetic costs of parental care. For example, penguins reproduce after developing a large fat supply so that they will have more energy in a time when feeding is not readily available to them.

Davis, Lloyd Spencer, and Martin Renner. Penguins. New Haven: Yale UP, 2003. Print. As this source may not heavily comment on the evolution of the parental care of penguins, it does give a general natural history of penguins. This background is essential to understanding their basic behaviors. Additionally, it will also aid in analyzing their more complex mating and parental mechanisms.

Kendeigh, S. Charles. Parental Care and Its Evolution in Birds. Urbana: U of Illinois, 1952. Print. This source not only discusses at length multiple types of birds and their individual behaviors, but also goes into extreme detail about their parental care. This will be helpful in analyzing and comparing the behaviors of penguins to those of different types of birds. Charles discusses the mating and rearing habits of numerous types of birds in his book, but initially depicts more general behavior of birds when it comes to nesting and paternal vs. maternal care across genera.

Polito, Michael J., and Wayne Z. Trivelpiece. "Transition to Independence and Evidence of Extended Parental Care in the Gentoo Penguin (Pygoscelis Papua)." Marine Biology (2008): n. pag. WorldCat@OSU. Web. Sept. 2014. This study used radio telemetry to study the habits and behaviors of Gentoo penguin chicks. They found that these penguins had an extended duration of parental care compared to other Pygoscelis species. It was found that their fledging period, the time between a chick’s first trip to sea and its absolute independence from the group, was longer than other penguins of the same genus. They hypothesized that this was because it allowed chicks to better develop their foraging skills before becoming completely independent from their parents. This study will assist in bringing primary evidence of a behavioral change within a population, which may cause an evolutionary change over time.

Changes Made to Parental Investment Page

Sexual Selection

At the end of the article's second paragraph, sexual selection is discussed and explained in detail - mentioning that in humans, there is competition among the males and selection among females because of females higher parental investment and goes on to explain that a female will chose a mate with the highest fitness and good genes- but sexual selection is not mentioned by name. Stuhlreyer.7 (talk) 13:25, 1 October 2014 (UTC)

How Evolution Ties In

The evolutionary changes of parental investment among species need to be discussed. Although the changes of offspring are discussed, as well as sexual selection, a specific evolutionary force, evolution should be mentioned and discussed in detail. Stuhlreyer.7 (talk) 12:50, 1 October 2014 (UTC)

Changes Made to Paternal Care Page

The Evolution of Paternal Care

Examples of different species should be added to the section on the evolution of paternal care. Please expand upon the evolutionary changes that have occurred among sex-specific patterns. Additionally, what are these patterns and in what species can we find them? Stuhlreyer.7 (talk) 13:00, 1 October 2014 (UTC)

Addition to Paternal Care Page

A study discovered an extended duration of paternal care in the Gentoo penguin, when compared to other Pygoscelis species. It was found that their fledging period, the time between a chick’s first trip to sea and its absolute independence from the group, was longer than other penguins of the same genus. They hypothesized that this was because it allowed chicks to better develop their foraging skills before becoming completely independent from their parents. By doing so, a chick may have a higher chance of survival and increase the population’s overall fitness. [40]

Additions Made to "Parental Investment" Page

https://en.wikipedia.org/wiki/Parental_investment

Added: Penguins are a prime example of a species that drastically sacrifices their own health and well-being in exchange for the survival of their offspring and the overall fitness of the population. This altruistic behavior, one that does not necessarily benefit the individual, but the population as a whole, can be seen in the King Penguin. Although some animals do exhibit altruistic behaviors towards individuals that are not of direct relation, many of these behaviors appear mostly in parent-offspring relationships. While breeding, males remain in a fasting-period at the breeding site for five weeks, waiting for the female to return for her own incubation shift. However, during this time period, males may decide to abandon their egg if the female is delayed in her return to the breeding grounds. This is an interesting case, as it shows that these penguins initially show a trade-off of their own health, in hopes of increasing the survivorship of their egg, but there comes a point where the male penguin’s costs become too high in comparison to the gain of a successful breeding season. In a study, Olof Olsson investigated the correlation between how many experiences in breeding an individual has and the duration an individual will wait until abandoning his egg. He proposed that the more experienced the individual, the better that individual will be at replenishing his exhausted body reserves, allowing him to remain at the egg for a longer period of time. The males’ sacrifice of their body weight and possible survivorship, in order to increase their offspring’s chance of survival is a trade-off between current reproductive success and the parents’ future survival. This trade-off makes sense with other examples of kin-based altruism and is a clear example of the use of altruism in an attempt to increase overall fitness of a population at the expense of the individual’s fitness.

Final Copy of Paper

Parental investment among species is widely variable. Some animals play significant roles in the survival of their offspring, while others invest little to no time in ensuring their offspring’s health. There are multitudes of species of penguins, but the evolution of parental care and investment is similar in many ways throughout the genus. Across species, there is a pattern of altruistic behavior to increase the overall survivorship of the offspring or population as a whole, which in turn increases population fitness. Mating behaviors do not necessarily impact the success of the offspring, as offspring do not exist prior to mating, but species have still evolved to select for the highest gain, with lowest cost behaviors even if these behaviors do not necessarily benefit them directly. In order to increase their chance of successful breeding, penguins of the species Aptenodytes patagonicus and Aptenodytes forsteri, King and Emperor Penguins respectively, have an adaptive behavior when it comes to choosing a mate. These species of penguins have the longest breeding cycles of all the penguin species and because of this, they optimize their chances of successful breeding by having a “high divorce rate” (Bried et al. 1999). Keeping the same mate through consecutive breeding cycles has a negative impact on their chance of successfully producing offspring. In order to survive and carry on their genes, scientists believe that these particular species of penguins have adapted lower retention rates of mates because monogamy is simply too costly (Olsson 1998). This adaptive behavior directly correlates to the penguins’ overall mating success and therefore the success of future offspring.

Similarly, many penguins have a comparable mating pattern where one mate leaves the colony for an extended period of time, while the other parent remains behind to care for the egg. In order to locate one another, penguins implore the use of calling techniques. In this behavior, it is difficult for offspring to locate their parents and for mates to locate their partners after an extended separation due to high ambient noise of the environment. However, a study showed that King Penguin chicks are able to identify their parents and mates only respond to their partner’s calls, despite the multiple background noises (waves, wind, beaks and wings flapping), which can be louder than 70dB (Jouventin et al. 1999). This ability to detect mates, offspring and parents within a population is a function of parental care that may have adapted in the King Penguin due to the breeding behaviors of that species and evolved to increase breeding success and overall fitness. Researchers used King Penguins in this study because of their non-nesting mating behaviors. Other species use their nests as landmarks, making it easier to find offspring and mates in a densely populated area. However, it is possible that this species adapted increased coding and decoding ability in order to make up for their inability to find one another using landmarks. In an attempt to increase the chance of passing on an individual’s genes, some animals exhibit altruistic behavior. This is a behavior that not necessarily benefits the individual, but the population as a whole. Penguins are included in this group. Although some animals do exhibit altruistic behaviors towards individuals that are not of direct relation, many of these behaviors appear mostly in parent-offspring relationships. King penguins developed certain parental altruistic behaviors in an attempt to increase offspring survival and overall fitness of the population, while decreasing their own health and individual fitness. While breeding, males remain in a fasting-period at the breeding site for five weeks, waiting for the female to return for her own incubation shift. However, during this time period, males may decide to abandon their egg if the female is delayed in her return to the breeding grounds. This is an interesting case, as it shows that these penguins initially show a trade-off of their own health, in hopes of increasing the survivorship of their egg, but there comes a point where the male penguin’s costs become too high in comparison to the gain of a successful breeding season. In a study, Olsson investigates the correlation between how many experiences in breeding an individual has and the duration an individual will wait until abandoning his egg. He proposes that the more experienced the individual, the better that individual will be at replenishing his exhausted body reserves, allowing him to remain at the egg for a longer period of time. The males’ sacrifice of their body weight and possible survivorship, in order to increase their offspring’s chance of survival is a trade-off between current reproductive success and the parents’ future survival (Olsson 1997). This trade-off makes sense with other examples of kin-based altruism and is a clear example of the use of altruism in an attempt to increase overall fitness of a population at the expense of the individual’s fitness.

There are, however, more examples of penguins adapting behaviors to increase the overall fitness of their population. Olsson again studies the unique breeding patterns of the king penguin, where he investigates the frequency and timing of breeding attempts in a certain population as well as how the quality of parenting affects the breeding success. Many birds time their breeding cycles with periods of high availability of food. This adaptive trait is key to increasing their offspring’s chance of survival and a clear example of natural selection in these species. King penguins that chose to mate earlier in the breeding season were more successful in mating behaviors. In the following season, these birds breed later, unlike unsuccessful pairs who would then follow their failed attempt with an earlier attempt. This change in behavior has evolved to increase successful mating as 93% of the birds bred early after a year of this cycling (Van Heezik 1994). This exemplifies that the penguins recognize the possibility of successful breeding and the species adapted to be overall more successful in mating strategies.

However, Olsson found that parental quality more strongly influences the outcome of breeding attempts compared to laying date (Olsson 1996). The successfulness of a chick reaching independence is not dependent on the parent’s sex. Olsson studies the differences in parental care from a female and compares this to the care from a male, and finds no significant differences in parental investment. From his findings, it is possible to conclude that evolution has made it so the gender of the caregiver will play no significant role in the offspring’s survival and therefore increase the population’s fitness. If it is insignificant if a male or female raises the offspring, more eggs will reach adulthood and carry on the strong genes that allow for this ability.

Researchers also discovered that population size is a cause for success or failure in some species of penguins. Tenaza discusses the species, the Adélie Penguin, Pygoscelis Adeliae, and their attempts at mating in larger colonies versus smaller ones. Smaller colonies had less offspring than larger colonies. Darling’s hypothesis explains this phenomenon; larger colonies expose higher levels of social interaction to their young, which leads to a shorter, more synchronous breeding season. This in turn decreases the chicks’ susceptibility to predation (Tenaza 1971). The phenomenon suggests an adaptive behavior that could increase population fitness, causing natural selection to select against chicks born into smaller colonies. Researchers propose theories that contradict Darling’s hypothesis and argue against the “Darling Effect”. A suggested alternative is that smaller colonies are often new colonies, established by young birds, causing there to be low nesting success among the population. The bottleneck effect may cause this pattern and establish an initial lower overall fitness of the population.

All of the previous examples discuss a change in the parents’ mating behavior or parental investment that could increase their offspring’s chance of survival. However, in a study conducted by Michael Polito and Wayne Trivelpiece on the Gentoo penguin, Pygoscelis papua, the change in parental investment actually cause a change in offspring behavior. This change in offspring behavior could then potentially increase their fitness, but the study only discusses how the parental investment causes a change in the offspring’s behavior. In the Gentoo penguin, there is an interesting behavior change to the fledging period, the time between a chick’s first trip to sea and its absolute independence from the group. In this population, after the chicks were exposed to an extended duration of parental care, the fledging period was longer than other penguins of the same genus (Polito et al. 2008). Due to this longer fledging period, the chicks are able to better develop their foraging skills before becoming completely independent from the group.

Nature then selects for this additional parental care and therefore increases the chicks’ chances of survival, but additionally it increases the fitness of this population. In conclusion, there are multiple methods that penguins implore to increase the overall fitness of their populations. Some behaviors directly affect their offspring’s survivorship, while other may indirectly affect them through the penguins’ different mating techniques. All of these species share the same goal of increasing the survival of their offspring and propagating their genes through multiple generations. Therefore, the parental care of penguins has evolved to increase the likelihood of achieving that goal.

References

Bried, J., F. Jiguet, P. Jouventin. 1999. Why do Aptenodytes penguins have high divorce rates?. The Auk, 116: 504-512.

Jouventin, P., T. Aubin, T. Lengagne. 1999. Finding a parent in a king penguin colony: the acoustic system of individual recognition. Animal Behavior, 57: 1175-1183.

Polito, M., W. Trivelpiece. 2008. Transition to Independence and Evidence of Extended Parental Care in the Gentoo Penguin (Pygoscelis Papua). Marine Biology, 154: 231-240.

Olsson, O. 1996. Seasonal effects of timing and reproduction in the king penguin: a unique breeding cycle. Journal of Avian Biology, 27: 7-14.

Olsson, O. 1997. Clutch abandonment: a state-dependent decision in king penguins. Journal of Avian Biology, 28: 264-267.

Olsson, O. 1998. Divorce in King Penguins: Asynchrony, Expensive Fat Storing and Ideal Free Mate Choice. Oikos, 83: 574-581.

Tenaza, R. 1971. Behavior and nesting success relative to nest location in Adélie penguins (Pygoscelis adeliae). The Condor, 73: 81-92.

Van Heezik, Y. M., P. J. Seddon, J. Cooper, and A. L. Plös. 1994. Interrelationships between breeding frequency, timing and outcome in King Penguins Aptenodytes patagonicus: Are King Penguins biennial breeders? Ibis, 136: 279-284.