Advancing Our Understanding of Cognition by Including Amphibians and Reptiles in Comparative Cognition Research
Abstract
Comparative cognition provides distinct, multidisciplinary perspectives on cognition. However, the taxonomic scope remains narrow. Including amphibians, reptiles, and invertebrates is crucial. Ectothermic animals present intriguing models because of their ecological and physiological traits. Investigating their cognitive adaptations can illuminate cognition’s evolution. This presents challenges, including limited prior knowledge, methodologies, and expertise. Despite barriers, researchers have discovered cognitive sophistication in reptiles and amphibians, elucidating shared cognitive principles and unique adaptations.
Comparative cognition’s position at the intersection of fields including psychology, biology, and neuroscience, as well as many others, enables it to offer a unique window into cognitive capacities across organisms (e.g., Beran et al., 2014). While maintaining its historical roots in attempting to understand and explain the human mind and capabilities through comparisons with nonhuman animal minds and capabilities, the field has evolved to also appreciate the intricacies of cognition beyond the human form in their own right through transformative technologies and doubling down on interdisciplinary approaches. Although the field has arguably always been somewhat interdisciplinary by nature, this stronger focus holds the promise of a more comprehensive future understanding of various species’ distinctive cognitive abilities, the threads of cognition common across species, and the neural mechanisms that underlie them.
Despite great advances and evolving technologies, the taxonomic scope of the field remains relatively narrow. Gaining a full understanding of cognition will be possible only by expanding the taxonomic scope of our research beyond the traditional lines of work on humans, rodents, other mammals, and birds. More specifically, few researchers have strayed outside the box to investigate the cognitive abilities of amphibians or reptiles systematically or even further to invertebrates (e.g., Beran et al., 2014; Burghardt, 2013; Shettleworth, 2010; Sotelo et al, 2015). Although limited pockets of exceptions exist, most comparative cognition research remains concentrated within a few species (e.g., Beran et al., 2014). This focus may be because of the lingering view that these creatures’ behaviors are largely instinctual (e.g., Maier & Schneirla, 1935) or the many barriers and challenges posed by investigating an understudied species. Fortunately, today’s researchers are more often recognizing that we must be more inclusive of oft-ignored species such as reptiles and amphibians in our efforts to better understand the cognitive abilities of humans and nonhuman animals (e.g., Matsubara et al., 2017).
Ectothermic animals, including reptiles and amphibians, make for particularly interesting models of study. For example, endothermic and ectothermic animals may face different pressures (e.g., energy requirements, activity patterns, thermoregulation) within the same environment, which could potentially underlie differential cognitive capabilities. Ectothermic animals’ reliance on external heat sources often leads to lowered metabolic energy requirements (e.g., Hochachka & Somero, 2002). Thus, endothermic animals inhabiting the same environment may need to obtain more food to meet their daily energy demands, leading to differential cognitive capabilities.
As another example, although certain members of both endothermic and ectothermic classifications need to conserve energy during unfavorable environmental conditions such as harsh temperatures or lowered food availability, they may do so in diverse ways. Processes such as brumation, hibernation, and aestivation differ substantially between ectothermic and endothermic animals. For instance, hibernating endothermic animals move from hibernation to sleep throughout the hibernation period, and ectothermic animals depend on their surroundings and remain torpid until the environmental temperature increases (e.g., Healy & Jones, 2002). Such differences could potentially relate to differential memory processes and capabilities across these states. Amphibians also generally progress through various stages of metamorphosis (e.g., DeFranco et al., 1991). Exploring capabilities through these phases could enable us to understand how metamorphosis impacts cognition. As a last example, endothermic animals’ ability to generate metabolic heat could lead to differential cognitive and behavioral flexibility relative to ectothermic animals. Thus, these groups represent a diverse array of species with potentially unique cognitive adaptations because of their ectothermic nature. These adaptations could provide valuable insights into the evolution of cognitive capabilities. Greater understanding of the similarity and differences among endothermic and ectothermic animals would enable us to track more clearly the evolution of cognitive abilities.
However, exploring the cognitive capabilities of outside-the-norm species can pose barriers and unique challenges relative to work with more commonly used organisms. Underrepresentation in and of itself is both an opportunity and a barrier; although numerous questions remain to be researched, less existing knowledge is available to guide and direct researchers. There are also fewer established methodologies, guidelines on housing, husbandry, and enrichment, as well as fewer experts on cognition to whom we can direct questions about these underrepresented species when compared with species that are used more often. Moreover, the diversity within the reptile and amphibian taxa with respect to ecological niche, behavior, and likely cognitive adaptations can make it challenging to generalize across species. Low public awareness and popularity also impacts funding availability for such research.
Because of the lack of standardized and preexisting tests and (sometimes) limited knowledge regarding the sensory capacities in the literature for such species, researchers must often make efforts to understand their species’ ecological niche and the challenges their species face in their natural environments before constructing informative experiments. Researchers may feel ill-prepared to do so because of their graduate school training, often with one species, or be unable to tolerate the likely delay in publication to resolve these issues within their planned career trajectory. Because many traditional comparative cognitive paradigms used in research were developed for mammals and birds, they may not always be suitable for reptiles or amphibians. They may require an environment with a different humidity level or satiate more quickly to reward, for example. Researchers often must either adapt or create new experimental paradigms tailored to the specific characteristics and behaviors of such species. However, this situation is not completely unlike the challenges faced by researchers who endeavor to draw from developmental paradigms with humans for use with species such as nonhuman primates or dogs. In the same way that comparative cognition researchers adapted paradigms from human developmental research with young children for work with nonhuman primates, dogs, and rodents, it is likely that researchers working with amphibians and reptiles will similarly innovate, given enough time and resources.
When researchers have surmounted these barriers to work with amphibians and reptiles, they have often found a greater degree of cognitive sophistication than first supposed (e.g., Matsubara et al., 2017). For example, Wilkinson and colleagues (2010) found that red-footed tortoises (Geochelone carbonaria) could remember locations and find their way in environments. Further, red-backed salamanders (Plethodon cinereus) selected larger quantities in a forced-choice discrimination task (Uller et al., 2003), and Oriental fire-bellied toads (Bombina orientalis) showed evidence of quantity discriminations (Stancher et al., 2015). Studies also revealed that tiger salamanders (Ambystoma tigrinum) and fire salamanders (Salamandra salamandra) remember information across brumation (e.g., Kundey et al., 2018; Wilkinson et al., 2017). Other work suggests that leopard geckos (Eublepharis macularius) and tiger salamanders recognize changes in objects’ identities and locations (e.g., Kundey & Phillips, 2021). Still other researchers have found preliminary evidence that tokay geckos (Gekko gecko) can differentiate themselves from other geckos using skin and fecal chemicals (e.g., Szabo & Ringler, 2023).
This sampling of work to date is only the beginning in terms of interesting directions to explore. Much remains to be learned in areas such as navigation, problem solving, learning and memory processes, and social cognition. With respect to navigation, do amphibians or reptiles have a sense of place or create cognitive maps, and how do these capabilities compare with other species (e.g., Krochmal & Roth, 2023)? What are the limits of their problem-solving capabilities? How and to what extent do they adapt when faced with novel challenges? How might chemoreception contribute to cognitive processing? Work with amphibians and reptiles also holds promise for applications outside of understanding the cognitive abilities of species within these taxa. For example, understanding the cognitive abilities of amphibians and reptiles could impact efforts for their conservation, particularly in light of environmental challenges and habitat loss. Cognitive skills could influence their survival and adaptive abilities in changing environments. Researchers are also increasingly moving toward cross-taxonomic comparisons to examine similarities and differences among amphibians, reptiles, birds, and mammals. Such work could help to elucidate the evolutionary history of particular cognitive traits in these taxa and their relationship to those of other animals.
Despite my own forays into comparative cognition work with salamanders and reptiles, my work thus far with them has involved “less complicated” tasks, such as simple navigational paradigms or memory tasks. Thus, I remain guilty of ignoring these species in my other line of research exploring organisms’ learning of patterned sequences. Historically, most studies of pattern learning have included humans, rats, or mice (e.g., Kundey & Rowan, 2009). When researchers have included other species, the species are typically either other mammals or birds. For several years I have worked with leopard geckos and tiger salamanders, but that work has existed in a separate track from my pattern learning work. In reflecting on why this is, I have considered many of the barriers discussed previously. For example, our serial pattern learning work with rats or mice often involves hundreds of trails per day. In my work with salamanders and reptiles, obtaining 10 successful trials a day is often ambitious. Overcoming the challenges associated with this work would benefit our understanding within this sub-area as well in areas such as tracing the evolutionary history of pattern learning abilities and would potentially lead to the development of paradigms that are more efficient for data collection.
Overall, increased work with understudied species holds promise to unlock deeper understanding and appreciation of these creatures’ capabilities, enriching our understanding of the cognitive tapestry woven through the animal kingdom.
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