Variation in brain anatomy in frogs and its possible bearing on their locomotor ecology

Abstract

Despite the long-standing interest in the evolution of the brain, relatively little is known about variation in brain anatomy in frogs. Yet, frogs are ecologically diverse and, as such, variation in brain anatomy linked to differences in lifestyle or locomotor behavior can be expected. Here we present a comparative morphological study focusing on the macro- and micro-anatomy of the six regions of the brain and its choroid plexus: the olfactory bulbs, the telencephalon, the diencephalon, the mesencephalon, the rhombencephalon, and the cerebellum. We also report on the comparative anatomy of the plexus brachialis responsible for the innervation of the forelimbs. It is commonly thought that amphibians have a simplified brain organization, associated with their supposedly limited behavioral complexity and reduced motor skills. We compare frogs with different ecologies that also use their limbs in different contexts and for other functions. Our results show that brain morphology is more complex and more variable than typically assumed. Moreover, variation in brain morphology among species appears related to locomotor behavior as suggested by our quantitative analyses. Thus we propose that brain morphology may be related to the locomotor mode, at least in the frogs included in our analysis.

A gyroscopic advantage: phylogenetic patterns of compensatory movements in frogs

“…We presumed a close relationship between head compensatory movements and the type of habitat and/or locomotion. A large body of empirical work shows that the habitat and locomotion type is closely linked to morphology and/or performance (Jorgensen and Reilly, 2013;Gomes et al, 2009;Manzano et al, 2017;Moen et al, 2013;Robovská-Havelková et al, 2014;Knight, 2018;Hill et al, 2018). However, our results did not support this hypothesis.…”

“…Several anatomical (diplasiocoelous vertebrae, organization of pectoral and pelvic girdle) and behavioral (tongueprotraction mechanism) characteristics were examined but are shared with other groups of frogs. A previous study on the brain morphology of frogs revealed the relationship between locomotion/ ecology and size of the cerebellum and diencephalon (Manzano et al, 2017). Thus, a comparative neuroanatomical survey examining the endorgans and associated innervation of the inner ear responsible for compensatory movements can be promising for rationale of the uncovered pattern.…”

“…The prevailing uniformity and morphological specializations are associated with, and likely evolved as, an adaptation for saltatory locomotion (Havelková et al, 2007;Prǐkryl et al, 2009;Jenkins and Shubin, 1998;Reilly and Jorgensen, 2011; but see Herrel et al, 2016). Despite this morphological specialization, numerous studies on anuran morphology, ecology and performance have corroborated the relationship between the habitat type, locomotion mode and morphology (Zug, 1978;Reilly and Jorgensen, 2011;Moen et al, 2013;Robovská-Havelková et al, 2014;Reilly et al, 2015Reilly et al, , 2016Manzano et al, 2017). Such relationships are associated with ecological morphology (ecomorphology), which is a comparative discipline focused on the interaction of morphological and ecological diversity among organisms both in the present and over evolutionary time (Motta and Kotrschal, 1992).…”

Relationship between myological variables and different take‐off and landing behaviours in frogs

“…This categorization (Table ) follows Grizante, Navas, Garland, and Kohlsdorf () and Soliz et al (), who also searched for a way to incorporate more subtlety in the ecological settings of the taxa studied. For example, landing behaviour of Scinax fuscovarius is recorded as hand hit and digit hit following descriptions of movements implied in jumping (Manzano, Herrel, Fabre, & Abdala, ) (Figure ). Our field observations indicate that, occasionally, this species also exhibits belly hit.…”

“…Values of each category were inferred considering the recorded frequency of each behaviour. Likewise, climber‐walker species, as Phyllomedusa sauvagii , walk across narrow substrates using their arms, they use their digits to grip the branches while climbing, but they are also able to jump in order to escape predators and in that case, they land with their body (Manzano et al, ). Thus, we assigned them 0.6 for digit hit and 0.4 for belly hit.…”