Morphological Diversification under High Integration in a Hyper Diverse Mammal Clade

Brandon P Hedrick,Alexa Sadier,Stephen J Rossiter,Kalina T J Davies,V David Munteanu,Karen E Sears,Gregory L Mutumi,Elizabeth Dumont,Liliana M Dávalos

doi:10.1007/s10914-019-09472-x

Abstract

Diversification and adaptive radiations are tied to evolvability, which in turn is linked to morphological integration. Tightly integrated structures typically evolve in unison, whereas loosely integrated structures evolve separately. Highly integrated structures are therefore thought to constrain evolutionary change by limiting morphological disparity. Mounting evidence suggests that high integration may facilitate evolutionary change along a single trajectory. We used geometric morphometrics to compare cranial disparity and integration among phyllostomid bats—which exhibit the greatest dietary diversity of any mammalian family— and their sister taxa within the superfamily Noctilionoidea. Our results reveal that phyllostomids are more tightly integrated and have less disparity in cranial shape than their outgroups, despite exhibiting tenfold higher species richness and significantly increased rates of speciation. Phyllostomid cranial morphology appears to have diverged from that of other noctilionoids by evolving along a single axis of morphological variation that describes the relative length of the rostrum. We propose that phyllostomids were able to evolve to occupy a wide range of dietary niches by varying rostrum length, possibly along a line of least evolutionary resistance. This study provides a compelling empirical example of how increased integration can lead to adaptation, implying that both high and low integration can underlie diverse phenotypes in adaptive radiation.

Highlights

Adaptive radiations are characterized by the rapid diversification of species and divergence of new forms, often as a result of an evolutionary innovation (Simpson 1953; Schluter 2000; Yoder et al 2010)
We examined the relationship between phyllostomids and their outgroups using three methods prior to evaluating integration and disparity to determine whether or not phyllostomids and non-phyllostomid noctilionoids evolved along different trajectories
A number of studies have examined the relationship between morphological disparity, species richness, and the magnitude of integration with theoretical modeling (Klingenberg 2005; Marroig et al 2009; Goswami et al 2014; Randau and Goswami 2017; Felice et al 2018), the relationships among these factors have rarely been investigated with empirical data

Summary

Introduction

Adaptive radiations are characterized by the rapid diversification of species and divergence of new forms, often as a result of an evolutionary innovation (Simpson 1953; Schluter 2000; Yoder et al 2010). As lineages move into a variety of previously unoccupied niches, they can experience high rates of morphological change, increasing clade-wide morphological disparity and functional disparity. The term ‘evolvability’ refers to the potential for diversification and describes the Surface scans used in this manuscript will be archived on Morphosource. All other data are given in the manuscript and its supplementary material. University, Cambridge, MA 02138, USA 3 School of Natural Sciences, University of California–Merced, Merced, CA 95343, USA

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