Moving on from the KLI but staying close...

KLI Fellow Nicole Grunstra will leave the KLI after nearly 2.5 years to take up a postdoctoral research position at the University of Vienna, as part of the FWF-funded project “Evolvability of inner and middle ears in birds and mammals.”

While at the KLI, Nicole, an evolutionary anthropologist, focused her research on the evolutionary aspects of the human “childbirth dilemma”. Human childbirth is comparatively difficult and risky, in large part due to a tight fit between the bony birth canal and the fetus. Nicole’s research aimed to better understand what functional and evolutionary constraints act on the human pelvis to help explain this tight fetopelvic fit. She collaborated with researchers at the University of Vienna and approached this question by morphological and modeling quantitative approaches on humans and other mammals. You can read about her past work here, here, and here.

Nicole will continue her comparative morphological research when she officially re-joins the team of Dr. Philipp Mitteroecker in early 2022 to work on the evolvability of the vertebrate ear. The “Univie” team is comprised of several “core” project members and includes several other collaborators on the project, including KLI alumna Lumila Menéndez and former KLI Visiting Fellow Frank Zachos from the Natural History Museum Vienna.

Specifically, the team will study and contrast the evolvability of the middle and inner ear in mammals and birds. Both groups are considered evolutionarily “successful” vertebrate lineages, but while birds comprise the more diverse clade in terms of recognized species, mammals are much more disparate morphologically, behaviorally and ecologically. In many mammalian lineages, an increase in the heterogeneity and regionalization of meristic structures (e.g., teeth and vertebrae) has led to a diversification in dietary strategies and gaits through morphological adaptation and ecological specialization. Underlying such diversification processes are changes in the developmental system that also determine the variational properties of the phenotype, including integration and modularity of its parts. Such variational properties are key components of evolvability, or the capacity for adaptive evolution.

The middle and inner ear perform key functions of hearing, balance, and gaze stabilization, and are thus vital for hunting, communication, positional behavior and other key survival strategies. The transformation of the primary jaw joint into three middle ear ossicles is one of the hallmark transitions in mammalian evolution, which has increased the genetic, regulatory, and developmental complexity of the mammalian ear. This increase in independent genetic-developmental factors may, in turn, have increased the evolutionary degrees of freedom for independent adaptations of the different functional ear parts. Therefore, the team posits that mammalian ear morphology shows a higher degree of evolvability compared to birds, and that this increased capacity for adaptive evolution has been a key contributor to the evolutionary success of mammals as a predominantly nocturnal radiation reliant on hearing, as well as to their further adaptive diversification into the wealth of ecological niches that they occupy today. They will test these hypotheses by studying within-species patterns of integration and modularity in both mammals and birds, and comparing these patterns to macroevolutionary patterns of variation in both groups as well as studying functional morphological associations between ear morphology and auditory and locomotor traits.

Read more about the “ear evolvability hypothesis” in Evolutionary Biology in 2020.

by Nicole Grunstra