Title: Evaluating the role of evolutionary history in determining susceptibility to extinction: the two largest Mascarene landsnail radiations
Principal Supervisor: Ben Warren
UMR 7205 Institut de Systématique, Evolution, Biodiversité, Paris
Co-supervisors: Vincent Florens (University of Mauritius) and Dominique Strasberg (Université de la Réunion)
Summary of the project:
Why are some species threatened with extinction, while others are at comparatively little risk? It is clear that a species’ decline in population size to extinction is dependent not only on its exposure to environmental change, but also its susceptibility to such change. Evolutionary history is expected to play a major role in determining such susceptibility, but the processes by which this comes about are poorly understood. Gaps in our knowledge include both the role of common parameters in the evolutionary history of all groups (e.g. time in geographic isolation, rates of diversification), and the role of key evolutionary transitions concerning a lineage’s morphology, ecology and distribution.
Understanding such evolutionary factors involved in biodiversity decline is critical for our future. Although the fossil record has been used to document multiple extinction events in deep time, our ability to draw inferences relevant to living species under threat is limited by multiple factors, including an understanding of their relative exposure to environmental change. Similarly, although there exist many living clades of high diversity that appear to be vulnerable to contemporary environmental changes, we are usually missing data on a large proportion of extinct species, especially those that disappeared before scientific collecting began. Islands of the Mascarene archipelago, Indian Ocean, are unusual among sizable and biologically diverse landmasses worldwide, in that they had no human population until European arrival 400 years ago. As a consequence, the impact of recent human activity has been unusually severe (even among oceanic archipelagos), with the extinction of 50-60% of the archipelago’s native vertebrate fauna. On both the local and global scales, invertebrate clades are far more diverse than vertebrate counterparts, and have likely lost more species through extinction. However, for most such clades there exist little or no data on extinct species. An important exception is the Mascarene landsnails, for which there exist extensive collections (at the MNHN, and in Mauritius) covering 101 extinct species, in the form of subfossil shells. Furthermore, the entire (living and historically extinct) malacofauna has received thorough species-level taxonomic treatment, with substantial data on geographic distributions (Griffiths & Florens 2006).
The student will benefit from extensive sampling and data from the two largest landsnail radiations of the archipelago (Streptaxidae, and Omphalotropis, Assimineidae) and collaboration between the MNHN (Warren), the Universities of Mauritius and La Réunion (Florens & Strasberg), and relevant conservation organisations (National Parks of Réunion and Mauritius). Both radiations include many extinct and threatened species. Of the 44 described Mascarene Streptaxidae morphospecies, ~12 are extinct, 13 are IUCN Threatened, and one is IUCN Near Threatened. Similarly, of the 23 described Mascarene Omphalotropis morphospecies, ~ 9 are extinct, and one is IUCN Threatened. Genetic sampling of living species is ~94% complete for Streptaxidae, and 100% complete for Omphalotropis. Furthermore, molecular datasets are extensive for both the Streptaxid (~60% of sequences obtained for Actin & 16S, 100% for COI) and Omphalotropis radiations (~ 100% for COI, 70% 16S, 7% LSU).
Completing molecular datasets for living forms (using the MNHN’s laboratory platform), and scoring morphological characters for both living and extinct forms (benefitting from Florens as the taxonomic and morphological expert, and extensive collections at the MNHN) will allow phylogenies to be constructed that include both living and extinct forms. In addition to phylogenetic reconstruction (e.g. using RAxML, MrBayes), tools for ancestral state reconstruction (e.g. phytools, Mesquite) and for identifying shifts in diversification rate (e.g. RPANDA, BiSSE) will be used to address the following questions:
– Are extinct and threatened species phylogenetically clustered?
– Are there key evolutionary changes (in morphology or ecology) or geographic shifts that have rendered particular clades susceptible to extinction?
– Is susceptibility to extinction associated with time in geographic isolation, or with changes in speciation rate?
The availability of two sympatric radiations in a common volcanic island setting allows us to largely control for differences in exposure to environmental change (unlike radiations of widely-dispersed allopatric species), and furthermore to distinguish general findings from any clade-specific results.
In addition to important empirical findings from the unique dataset, there is much potential for a student interested in modelling to either benefit from Warren’s ongoing collaboration with Isaac Overcast (formerly at Ecole Normale Supérieure, Paris), or develop similar collaborations, to integrate their findings of time in situ for extinct, threatened and non-threatened species into a modelling framework that tests alternative eco-evolutionary scenarios of species turnover.
Proven competences (e.g. internship M2) in molecular phylogenetics (phylogenetic reconstruction, dating, biogeographic & ancestral state reconstruction), and/or in morphometrics (experience of evaluating and scoring morphological traits), and in submitting written reports. Interest in coding/modelling would be a bonus (not critical). Strong interest in the study set up and questions is important.
Written applications should be submitted using the following website (due to open March 28):
Applications can be written in French or English and should include:
– Application form, including Letter of motivation
– Copy of Masters diploma
– Relevé des notes M1 and 1st semester of M2 (or all of M2, for candidates having completed their M2).
– Reference letter from your Masters supervisor.
Following the procedure of the ED 227 (detailed in the link above), short-listed candidates will first be interviewed by the supervisors (either at the MNHN or by video). A single selected candidate will then be auditioned by the ED 227 (most probably by video) between the 4th and 6th of July 2022.
We welcome applications from graduates of any university worldwide. However, some knowledge of the French system would be ideal.
Griffiths, O. L, and F. B. FLORENS. 2006. A Field Guide to the Non-marine Molluscs of the Mascarene Islands (Mauritius, Rodrigues and Réunion) and the Northern Dependencies of Mauritius. Bioculture Press, Mauritius.
WARREN, B. H., Hagen, O., Gerber, F., Thébaud, C., Paradis, E. and E. Conti. 2018. Evaluating alternative explanations for an association of extinction risk and evolutionary uniqueness in multiple insular lineages. Evolution 72 (10): 2005-2024.
WARREN, B. H., D. Simberloff, R. E. Ricklefs, R. Aguilee, F. L. Condamine, D. Gravel, H. Morlon, N. Mouquet, J. Rosindell, J. Casquet, E. Conti, J. Cornuault, J. M. Fernandez-Palacios, T. Hengl, S. J. Norder, K. F. Rijsdijk, I. Sanmartin, D. STRASBERG, K. A. Triantis, L. M. Valente, R. J. Whittaker, R. G. Gillespie, B. C. Emerson, and C. Thebaud. 2015. Islands as model systems in ecology and evolution: prospects fifty years after MacArthur-Wilson. Ecology Letters 18:200-217