Collaborative Research: The role of multifunctionality in the evolution of cranial morphological diversity in bats

University Of Utah, Salt Lake City UT

Investigators

Abstract

From insect wings to bird beaks, most anatomical structures carry out more than one function. How anatomical structures have evolved to accomplish more than one function is a long-standing, important question in the field of organismal biology. This project addresses this question by examining the skull and how its different functions – such as sensing, breathing, and feeding– interact and in so doing may have shaped the diversity of skull morphology over evolutionary time. To study this topic, this project focuses on bats, the second most species-rich Order of mammals, because this group offers extraordinary diversity in number of species, a wide range of skull shapes and sizes, and novel skull functions such as echolocation. To understand how the interaction among skull functions helped generate bat skull diversity, the researchers will first measure and map the diversity of internal and external skull morphology across bats. The researchers will then use computational models and physiological data to predict and compare how well differently shaped skulls perform during feeding, respiration, and olfaction, identifying what parts of the skull affect these functions and how. Finally, the researchers will reconstruct how functionally relevant skull features have evolved in the context of competing functions. The project will generate massive datasets of skull internal and external morphology (3D models, histological series), enable training of undergraduate and graduate students, and support the development of a museum exhibit projected to reach thousands of visitors across two cities. Quantitative information revealing the performance relationships and tradeoffs among cranial functions is scarce, which hinders a full understanding of the factors shaping cranial morphological diversity in vertebrates. This proposal outlines a highly integrative research framework that will explicitly link morphological and performance diversity across the multiple functions of a key vertebrate structure, the cranium, thereby increasing the understanding of which and how intrinsic and extrinsic factors contributed to its morphological evolution. This project’s central hypothesis is that the morphological diversity of the cranium of bats is the result of structural, mechanical, and physiological interactions among its functions, including tradeoffs and facilitation. The project will particularly focus on examining the rostrum (snout), because its morphological and functional variation underlies most of the cranial diversity across bat species, and conserved and derived cranial functions interface within its limited space. The team will use an integrative and cross-disciplinary approach to complete three aims and test predictions derived from the main hypothesis. In Aim 1, the team will use micro-Computed Tomography (micro-CT) to image bat skulls and geometric morphometric analyses of internal and external cranial features to identify the major traits that underlie cranial morphological diversity across bats. In Aim 2, the team will use models of natural and altered morphologies of selected bat species to conduct measurements, calculations, and computational modeling with validation to (1) translate variation in cranial morphology into performance outputs for several functions relevant to bat ecology (feeding, respiration, olfaction, vision and echolocation), and (2) identify performance relationships and tradeoffs among functions. In Aim 3, the team will use phylogenetic comparative analyses to identify patterns of evolution in functionally-relevant cranial traits, and examine the effect of tradeoffs on morphological diversity. The project will generate predictive (finite element, computational fluid dynamic) models that will be experimentally validated, which will greatly advance the field of biomechanics and serve as the basis for future studies aimed at measuring in vivo performance. By coupling descriptive and experimental approaches within a phylogenetic framework, the project will be the first to explicitly address the role of multifunctionality in the morphological diversification of the cranium across a whole mammalian Order. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.