Studying Personality Variation in Invertebrates: Why Bother?
In this article, Simona Kralj-Fiser and Wiebke Schuett review literature relating to the personality of a range of invertebrate species, and find that there are numerous fruitful avenues for further study and validation of personality variation in invertebrates. By comparing a range of research, the authors honed in on a group of personality traits (including life histories, social and sexual behaviors, complete metamorphosis, male emasculation during copulation, asexual reproduction, eusociality, and parasitism) that have been identified and could be studied further to better understand how invertebrates exhibit different personalities, and how those traits might change over time.
When it comes to animal rights and advocacy, invertebrate species are often difficult to advocate for. They are so vastly different from humans and other animals – even animals such as chickens and fish that are not mammalian – that they are often thought of as not being able to experience pain or to have any personalities whatsoever. With their paper published in a 2014 issue of Animal Behaviour, Simona Kralj-Fiser and Wiebke Schuett present findings that challenge this perception. Their introduction sums up the prevailing wisdom succinctly: “the lack of data on invertebrate personality might be due to a traditional belief that invertebrates are just ‘minirobots’, which stereotypically respond to stimuli and thus should exhibit few or no individual differences in behaviour.” Analyzing hundreds of articles and narrowing down to 47 peer-reviewed papers that consider different aspects of personality in different invertebrate species, they find that “most personality studies on invertebrates have been conducted in the Arthropoda (mainly Insecta, but also Crustacea and Chelicerata); the remaining studies investigated Cnidaria and Mollusca. Taken together, even such an increased number of invertebrate studies in a personality context is almost negligible given the size of the taxa.” In other words, the field of potential study in this area is vast and practically untapped.
Looking at the studies together, they find that there are numerous avenues for additional research that could illuminate the complexity of invertebrate personalities, and how it varies across species and individuals. Kralj-Fiser and Wiebke Schuett underline these possibilities in specific detail: “invertebrates exhibit a range of aspects in their life histories, social and sexual behaviours that are extremely rare or absent in vertebrates, but that offer new avenues for personality research. Examples are complete metamorphosis from larval to adult stage, asexual reproduction and peculiar sexual behaviours (e.g. sexual cannibalism, male emasculation during copulation), eusociality and parasitism.” Of this range, the aspect of “life histories” seems to stand out as an interesting avenue, which they say “has both advantages and disadvantages for personality research.” Part of the challenge lies in the vast changes that many invertebrates go through during their lives. “Particularly salient for personality development may be a shift from a juvenile to an adult stage that often involves significant changes in hormonal profiles and morphology,” the authors note. “These changes are specifically dramatic in animals that undergo a metamorphosis and change their lifestyle and environment.” As a path of exploration of personality traits, this seems like a particularly exciting possibility that would allow advocates to better tell the stories of invertebrates.
The authors note that their findings are tentative and based on a small amount of data, which calls for much wider research to be carried out. “Despite increasing effort made to understand how past selective forces have driven the evolution of personality differences,” they say, “it is still impossible to employ a comparative approach, which would require data from a diversity of invertebrates (alongside vertebrates).” As more data is gathered and put together, a clearer picture will emerge, though of course, animal advocates would hope that this pursuit can be accomplished without using invertebrates in invasive, captive research projects.
Original Abstract:
Research on animal personality variation has been burgeoning in the last 20 years but surprisingly few studies have investigated personalities in invertebrate species although they make up 98% of all animal species. Such lack of invertebrate studies might be due to a traditional belief that invertebrates are just ‘minirobots’. Lately, studies highlighting personality differences in a range of invertebrate species have challenged this idea. However, the number of invertebrate species investigated still contrasts markedly with the effort that has been made studying vertebrates, which represent only a single subphylum. We describe how investigating proximate, evolutionary and ecological correlates of personality variation in invertebrates may broaden our understanding of personality variation in general. In our opinion, personality studies on invertebrates are much needed, because invertebrates exhibit a range of aspects in their life histories, social and sexual behaviours that are extremely rare or absent in most studied vertebrates, but that offer new avenues for personality research. Examples are complete metamorphosis, male emasculation during copulation, asexual reproduction, eusociality and parasitism. Further invertebrate personality studies could enable a comparative approach to unravel how past selective forces have driven the evolution of personality differences. Finally, we point out the advantages of studying personality variation in many invertebrate species, such as easier access to relevant data on proximate and ultimate factors, arising from easy maintenance, fast life cycles and short generation times.