Ecomorphological correlates of inner and middle ear anatomy within phyllostomid bats

Abstract

Echolocation is the primary sense used by most bats to navigate their environment. However, the influence of echolocating behaviors upon the morphology of the auditory apparatus remains largely uninvestigated. While it is known that middle ear ossicle size scales positively with body mass across mammals, and that peak call frequency scales negatively with body mass among bats, there are still large gaps in our understanding of the degree to which allometry or ecology influences the morphology of the chiropteran auditory apparatus. To investigate this, we used μCT datasets to quantify three morphological components of the inner and middle ear: ossicle size, ossicle shape, and cochlear spirality. These data were collected across 27 phyllostomid species, spanning a broad range of body sizes, habitats, and dietary categories, and the relationships between these variables and ear morphology were assessed using a comparative phylogenetic approach. Ossicle size consistently scaled with strong negative allometry relative to body mass. Cochlear spirality was significantly (p = .025) associated with wing aspect ratio (a proxy for habitat use) but was not associated with body mass. From a morphological perspective, the malleus and incus exhibited some variation in kind with diet and call frequency, while stapes morphology is more closely tied to body size. Future work will assess these relationships within other chiropteran lineages, and investigate potential morphological differences in the middle and inner ear of echolocating‐vs‐non‐echolocating taxa.

Ecological correlates of three‐dimensional muscle architecture within the dietarily diverse Strepsirrhini

“…Certainly, as shown by Charles et al (Figure 6b therein), increasing fascicle count reduces the standard deviation about the mean and, assuming similar accuracy of methods, increasing precision would also be desirable. However, as our own work on algorithmic reconstructions has previously shown (e.g., see Dickinson et al, 2018; Dickinson et al, 2023; Ratkiewicz et al, 2023), algorithmically reconstructed fascicles tend to yield greater errors on a per‐fascicle basis than their manually segmented counterparts. Indeed, in many instances, these results can yield larger numbers of fascicles than are conceivably contained within a muscle—an artifact stemming either from double‐counting of individual structures or from falsely identifying non‐fascicular structures as valid objects of interest.…”

“…Subsequently, individual fascicles from each muscle were segmented, with an average of 10–15 representative fascicles analyzed from throughout each muscle portion (Figures 2–4; Video 1). While algorithmic efforts to resolve muscle fascicles (e.g., see Kupczik et al, 2015; Dickinson Stark, & Kupczik, 2018; Ratkiewicz et al, 2023; Dickinson et al, 2023) typically measure higher numbers of fascicles (>100 per muscle), the automatic nature of this fascicle generation inherently increases the risk of error. Instead, we measure a comparable number of fascicles to gross dissection, sacrificing quantity for confidence in quality; further, reducing the number of fascicles makes it visually much more straightforward to visually identify individual fascicles and ascertain overarching trends relating to either the orientation or lengths of fascicles.…”

Ecomorphology and sensory biology of bats

“…Across mammals, smaller species tend to have a greater sensitivity to high frequency sounds, and bats, as expected from their relatively small size, are in keeping with this trend (Heffner, 2004; Heffner et al, 2003). In this issue, Dickinson et al (2023) investigate osteological features of the inner and middle ear of phyllostomid bats based on micro computed tomographic scan data. Their findings show ear ossicles have a strong negative allometric relationship to body size; this may be reflective of a general trend for sensory structures, which do not relate to body size in the same way musculoskeletal structures do (see further discussion in Eiting et al, 2023 and Smith & Bhatnagar, 2004).…”