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Octopus bimaculoides: Temperament and Behavior<< Cephalopod Articles | By
During my research on molluscan behavior at Portland State University in Portland, OR, I applied for and was granted student aid money from the Hawaiian Malacological Society.
First of all, what do we know about octopus behavior? Surprisingly little work has been done quantifying the nature of octopuses, actually. There is, of course, a surplus of anecdotal evidence surrounding the behavioral capabilities of these creatures, but in the scientific literature the number of studies actually documenting such feats is small. That is not to say that these studies do not document an amazing complexity of behavior for these organisms, this is hardly the case. What studies have done is contribute pieces of the how of behavior in this group, as well as speculating on the why of these same acts. The overall picture that we are gaining from our continued studies is that octopuses possess a startling array and complexity of behaviors, and that these behaviors are indicators of a very different life from other marine organisms.
The particular aspect of octopus behavior that fascinated me as I began to study at Portland State was that within the scientific literature, cephalopod researchers have noted consistent variability in individual octopus responses for over 30 years. What I mean by this is that these researchers have been noticing that their study organisms act very differently from one another, in ways that are stable within individuals but consistently different from one another. Essentially, these researchers provided the first notes of the individuality of octopuses, an aspect of behavior normally accorded for primates and other vertebrates. In 1993, two researchers set about to define how octopuses differ from one another, on an individual basis. What Jennifer
Temperament was chosen as the model that best represented these early individual differences in behavior. In humans, temperamental traits are behavioral styles that an individual is born with, are influenced by and influence the environment, and result in the adult personality. A discrete response to a stimulus is not a temperamental trait, rather, a combination of certain responses that an individual shows consistently over time define the behavioral style of a particular individual, and it is these styles that represent expressions of temperament. Temperament dimensions, therefore, can be used to define how very young individuals differ.
Why would researchers be interested in temperament? Over the past few years behaviorists have shown increased interest in the study of individual differences in their subject organisms, as the importance of these traits have been documented. Temperament traits have major heritable components, based in the physiology of the organism, and it is these heritable components that allow these traits to act as evolutionarily selectable material, much like any physical trait. Temperamental traits, or stable individual differences, provide a basis for the development of behavior in a group of animals across evolutionary time through furnishing material for selection.
The study of temperament also allows us to make inferences about the behavioral substrate an individual is born with, and how levels of this substrate differ among individuals. How then do individual O. bimaculoides differ? Do they display behaviors that can be considered individual temperament?The answer is yes. At three weeks of age I was able to identify at least four dimensions of temperament, termed Active Engagement, Arousal/Readiness, Aggression, and Avoidance/Disinterest. These dimensional names represent trait continuums along which young octopuses can be ordered relative to one another. Furthermore, the data indicated that related octopuses were more similar along these dimensions at three weeks of age than ones that were unrelated. While this makes sense intuitively, in behavioral research simple relationships such as "genes make traits" do not exist, and it is extremely difficult to pinpoint the biological basis for behaviors. Showing that this relationship exists for these traits in octopuses is a first step towards learning about the evolution of these behaviors. Furthermore, scientists that study individual differences have hypothesized these heritable components in the expression of temperamental traits, but very few studies across differing taxa have been able to demonstrate this relationship.
What were the particular octopuses like in my study? One brood of octopuses, for example, scored in the median range for Active Engagement, with high Arousal/Readiness scores, high Aggression scores, and high Avoidance/Disinterest scores. This group of octopuses was extremely Reactive, Aroused, and Aggressive, but were not particularly Active or Interested in seeking out contexts in which to be reactive in. This was in contrast to another group of octopuses, who were highly Actively Engaged, not at all Aroused or Ready, highly Aggressive, and not very Avoidant or Disinterested. This second brood at a very early age was particularly Active in Engaging with their environment, acting Aggressively, choosing to act towards or approach stimulus as opposed to assessing situations from afar, or Avoiding them altogether. How each of these strategies might be evolutionarily stable strategies for these organisms was the subject of much of my thesis work.
My study was also longitudinal in nature, and tested these individuals on their four dimensions of temperament throughout the first five months of life. For my master's thesis only the first 9 weeks have been analyzed. Longitudinal results show that from week 3 to week 6 there are major changes in an octopus's approach to its environment, while they become less Actively Engaged, less Aggressive, and more highly Aroused and Ready. Weeks 6 to 9 are a period of more stability, when major changes are not observed along any of the temperament dimensions. I have hypothesized that the major changes observed from week 3 to week 6 represent two major life history changes. The first is the change in the dispersal behaviors of these organisms, and is marked by the significant decrease in Active Engagement and Aggressive behaviors. The second, indicated by these two dimensional changes along with a significant increase in Arousal/Readiness tendencies, I hypothesized is a transition from a life controlled by innately programmed behaviors to one of greater plasticity of response, with arousal mechanisms providing the basis for behaviors expressed in choice mediated contexts. No studies have been performed on O. bimaculoides in the wild with regards to this development;unfortunately with the octopuses what we have are mostly laboratory studies from which we are able to derive information. But by hypothesizing how these dimensions might be important in the early life of these organisms, both at week 3 and across the first nine weeks of life, documenting temperamental trait development allows hypothesis to be made towards an ecological view of the bases for behavior in these marine invertebrates.
Octopuses provide an excellent behavioral model for these types of studies, and also a relatively little known one from the standpoint of the development of behavior. In addition to this, working with this marine mollusc allows us to assess these types of traits in an organism that is so different from the vertebrates in its approach to its environment and its life, and yet probably no less intelligent in its endeavors to do so. I hope that I am fortunate enough to continue my work with cephalopods. I plan to study them for many years to come, and I hope to continue working with organizations such as the HMS in order to do so.
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