Recent inner ear specialization for high-speed hunting in cheetahs

Abstract

The cheetah, Acinonyx jubatus, is the fastest living land mammal. Because of its specialized hunting strategy, this species evolved a series of specialized morphological and functional body features to increase its exceptional predatory performance during high-speed hunting. Using high-resolution X-ray computed micro-tomography (μCT), we provide the first analyses of the size and shape of the vestibular system of the inner ear in cats, an organ essential for maintaining body balance and adapting head posture and gaze direction during movement in most vertebrates. We demonstrate that the vestibular system of modern cheetahs is extremely different in shape and proportions relative to other cats analysed (12 modern and two fossil felid species), including a closely-related fossil cheetah species. These distinctive attributes (i.e., one of the greatest volumes of the vestibular system, dorsal extension of the anterior and posterior semicircular canals) correlate with a greater afferent sensitivity of the inner ear to head motions, facilitating postural and visual stability during high-speed prey pursuit and capture. These features are not present in the fossil cheetah A. pardinensis, that went extinct about 126,000 years ago, demonstrating that the unique and highly specialized inner ear of the sole living species of cheetah likely evolved extremely recently, possibly later than the middle Pleistocene.

Comparative neocortical neuromorphology in felids: African lion, African leopard, and cheetah

“…To achieve this, cheetahs exhibit a modified morphology compared to other felids, having elongated hind legs and spine, an aerodynamic skull, semiretractable claws, and enhanced metabolic and adrenal systems (Hudson et al, 2010(Hudson et al, , 2011Russell & Bryant, 2001). Further, the cheetah's specialized vestibular system is larger than that of other felids, allowing it to maintain postural stability and balance during prey pursuits (Grohé, Lee, & Flynn, 2018). The cheetah has evolved to prioritize acceleration and agility over the pouncing behavior characteristic of Panthera (Kleiman & Eisenberg, 1973).…”

The bony labyrinth of toothed whales reflects both phylogeny and habitat preferences

“…Early development of the inner ear largely before birth may partly explain its strong link to phylogeny 16 – 18 . In addition, intraspecific variability of this structure is lower than the inter-genera disparity giving solid grounds to its use in systematics and phylogeny 19 – 21 . While molecular data help us understand the relationships of living taxa, the search for pertinent morphological characters is critical to our understanding of the origin and divergence of clades.…”

The ecological signal on the shape of the lacertid vestibular system: simple versus complex microhabitats

“…Previous studies have related vestibular system enlargement and SC elongation to higher sensitivity and differences in lifestyle. For instance, Grohé et al (2018) found that the vestibular systems of cheetahs (Acinonyx jubatus) differ strongly in shape and proportions (larger vestibular systems, longer SCs, ASC less extended anteriorly, PSC and LSC extended dorsally) from those of other cat species (including a closely related extinct cheetah species). They consider this to be an adaptation to the species' specialized high-speed hunting strategy.…”

“…Considering the above, and bearing in mind the anatomical complexity of the vestibular system, clearly not only the size of the semicircular canals, but also their shape can influence the system's sensitivity and response time to head motion. The shape of the vestibular system has been studied in several taxa, both extant and extinct, and was often linked to microhabitat structure, locomotor style (terrestrial vs. arboreal, swimming vs. walking, bipedal vs. quadrupedal) and phylogeny (Spoor et al, 2002;Maddin & Sherratt, 2014;Billet et al, 2015;Pfaff et al, 2015;Grohé et al, 2016;Mennecart et al, 2017;Dickson et al, 2017;Le Maitre et al, 2017;Loza et al, 2017;Palci et al, 2017;Boyle & Herel, 2018;Grohé et al, 2018). It is generally suggested by previous studies that species which are more agile and more sensitive to motion possess longer and relatively circular canals.…”