RESEARCH THEMES

One long-standing question in evolutionary biology is: how do new morphological innovations arise? Integrative advances in palaeontology, genomics, development and evolution have unveiled general principles behind evolutionary novelties. However, we are far from understanding the mechanisms by which novelties emerge from ancestral genomic and developmental programs and then diversify in new ecological contexts. To solve this problem, we use the dramatic morphological and ecological diversity of bat teeth as a model system to study the origin and diversification of a major mammalian innovation, the tooth classes. Using morphological, genomic, developmental and modelling approaches on multiple species of bats from various ecological contexts, our goal is to understand the origin of mammalian tooth classes and establish a predictive model to study their evolution.

This work is currently funded by an ERC - CoG and previous research was funded by an NSF - IOS grant in collaboration with K. Sears (UCLA), S. Santana (UW) and P. François (U. de Montréal).

Relevant work linked to this research:

Sadier, A., Anthwal, N., Krause, A.L. et al. Bat teeth illuminate the diversification of mammalian tooth classes. Nat Commun14, 4687 (2023). https://doi.org/10.1038/s41467-023-40158-4 

Grossnickle, D. M., Sadier, A., Patterson, E., Cortés-Viruet, N. N., Jiménez-Rivera, S. M., Sears, K. E., & Santana, S. E. (2024). The hierarchical radiation of phyllostomid bats as revealed by adaptive molar morphology. Current Biology. https://doi.org/10.1016/j.cub.2024.02.027

Bats have evolved specialized sensory systems to forage, hunt and orientate themselves, sometimes in complete darkness. Like many other traits, sensory systems like vision and echolocation have diversified following the colonization of various dietary niches. In the lab, we study the evolution of vision and echolocation using intergative approaches during development. We showed that color vision is mosaic in Noctilionoid bats, UV vision being lost multiple time independently. We also showed that the development of the bat cochlea constraint the development of other sensory systems.

Relevant work linked to this research:

Anthwal, N., Hall, R. P., de la Rosa Hernandez, F. A., Koger, M., Yohe, L. R., Hedrick, B. P., Davies, K. T. J., Mutumi, G. L., Roseman, C. C., Dumont, E. R., Davalos, L. M., Rossiter, S. J., Sadier*, A. (co-last), & Sears*, K. E. (2023). Cochlea development shapes bat sensory system evolution. The Anatomical Record, 1–12. https://doi.org/10.1002/ar.25353

Sadier*, A., Davies*, K.T., Yohe, L.R., Yun, K., Donat, P., Hedrick, B.P., Dumont, E.R., Davalos, L.M., Rossiter, S.J., and Sears, K.E. (2018). Multifactorial processes underlie parallel opsin loss in neotropical bats. Elife 7. https://elifesciences.org/articles/37412

Developmental evolution rarely involve the emergence of new genes but rather by the modification of existing networks and pathways. To study this, we focused on the Edar gene that plays an important role in tooth - and more largely ectodermal appendages - morphogenesis. Combining developmental experiments and fine mathematical modeling in wild-type and mutant mice, we revealed that, contrarily to what was previously thought, a newly formed tooth organizing center can actively impair or erase a previously formed one. This precise dynamic likely reflects the evolutionary history of mice, who lost premolars while maintaining their embryonic organizing centers and uncovers how patterning can be used by evolution to produce variation. More broadly, we showed that overwriting or correcting previously established patterns during development might be more common than anticipated, simply due to the fact that developmental programs are modified by incrementation during evolution.

Relevant work linked to this research:

Sadier, A., Twarogowska, M., Steklikova, K., Hayden, L., Lambert, A., Schneider, P., Laudet, V., Hovorakova, M., Calvez, V., and Pantalacci, S. (2019). Modeling Edar expression reveals the hidden dynamics of tooth signaling center patterning. PLoS Biol 17, e3000064 https://doi.org/10.1371/journal.pbio.3000064

The EDA pathway has been implicated in the evolution of ectodermal appendages, with examples of mutation at the regulatory and protein coding levels. During my PhD, I investigated the isoforms of one gene of this pathway, EDARADD, that could potentially lead to morphological variation. We showed that the two isoforms of this pathway modulate the downstream activity of the pathway and that one is frequently lost in mammals. This work was one of the first example to highlight the importance of gain/loss of isoforms in modifying the activity of developmental pathways and highlighted a new implication of the EDA pathway in morphological evolution.

Relevant work linked to this research:

Sadier, A., Lambert, E., Chevret, P., Decimo, D., Semon, M., Tohme, M., Ruggiero, F., Ohlmann, T., Pantalacci, S., and Laudet, V. (2015). Tinkering signaling pathways by gain and loss of protein isoforms: the case of the EDA pathway regulator EDARADD. BMC Evol Biol 15, 129. https://doi.org/10.1186/s12862-015-0395-0

Sadier, A., Viriot, L., Pantalacci, S., and Laudet, V. (2014). The ectodysplasin pathway: from diseases to adaptations. Trends Genet 30, 24–31. https://doi.org/10.1016/j.tig.2013.08.006