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Small Sahelo-Saharan mammals evolution : case study of rodents of the genus Gerbillus

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Presented during the 17h Annual Sahelo-Saharan Interest Group Meeting organized by the NGO Sahara Conservation Fund in Senegal, from 4 to 6 May 2017. The Sahara Conservation Fund (SCF) gathers every year about a hundred people who are interested in the field of Sahelo-Saharan species conservation.

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Small Sahelo-Saharan mammals evolution : case study of rodents of the genus Gerbillus

  1. 1. 17th Annual Sahelo-Saharan Interest Group Meeting 2 days of talks on biodiversity conservation in the Sahara and in the Sahel Small Sahelo-Saharan mammals evolution : case study of rodents of the genus Gerbillus Arame NDIAYE et al. , Researcher– Institut de Recherche pour le Développement May 4 – 6, 2017
  2. 2. Importance of evolutionary biology in understanding small Saharo-Sahelian mammals evolution: case study of rodents of the genus Gerbillus (Rodentia: Muridae) Laurent GRANJON, Gauthier DOBIGNY, Pascale CHEVRET & Arame NDIAYE
  3. 3. Considered as one of the most speciose genus within rodents, with no less than fifty recognized species. Order Rodentia sub-Order Myomorpha Family Muridae sub-Family Gerbillinae Genus Gerbillus & Dipodillus (sensu Musser & Carleton 2005) Genus Gerbillus (incl. Dipodillus)
  4. 4. Diagnostic criteria Bulky and voluminous eyes Soft coat with back / belly line (white) LTC < LQ Plantar soles +/- hairy (intermediary) Bare foot soles Hairy plantar soles Hair tail with terminal brush +/- supplied
  5. 5. Terrestrial and nocturnal, mainly granivorous, they live in burrows comprising galleries found in sandy to more indurated substrates, or (rarely) in holes of rocky habitats Elements of ecology Include species that are potentially harmful to - dry crops (G. nigeriae) or market gardens (G. campestris) - or potentially reservoirs of pathogens that are transmissible to humans or livestock
  6. 6. The genus Gerbillus is widespread in arid to semiarid Africa and Asia via the Arabian Peninsula 6 42 4 6 asian species with only 1 endemic* 42 african species with 27 endemics* 4 afro-asian species Distribution * Only known from a given locality or limited region
  7. 7. Several attempted inventories of such species Lay (1983): 62 species (all in Gerbillus) Ellerman (1941): 77 species (42 Gerbillus - 35 Dipodillus) Musser and Carleton (2005): 51 species (38 Gerbillus - 13 Dipodillus) Two, or even 3 distinct genera (Dipodillus, Gerbillus ss and Monodia) vs 1 alone (Gerbillus) Characters used: - Body / Cranial Measurements - Size / shape of the tympanic bullae Hairiness of plantar soles Dental morphology (especially upper 1 molar) Shape of the mandible Different divisions of the genus proposed Gerbillus, Dipodillus Hendecapleura and Petteromys proposed as subgenera of Gerbillus or Dipodillus Taxonomy
  8. 8. Difficulty in accounting for real biodiversity in this genus Use of other methods such as molecular and cytogenetic tools Integrative Taxonomy Identification of species based essentially on morphological analysis G. henleyi But very conservative morphology… G. pyramidum Taxonomy Case of sibling species Under estimate of biodiversity Case of polymorphic species Overestimating diversity + Difficulty in finding diagnostic characters of subsets representing real evolutionary units
  9. 9. Molecular phylogeny of significant species sampling (N = 21): Usuals methods like DNA extraction (Qiagen), PCR of cytochrome B (1140bp) and IRBP (1272 bp) and Sanger sequencing 89 samples from 71 localities and 16 countries (+ outgroups) Ndiaye et al. (2016)
  10. 10. Mains molecular phylogeny results cyt b IRBP Clade A= Hendecapleura Clade C = Gerbillus Clade D = Monodia Clade B = Dipodillus Clade D = Monodia
  11. 11. subgenus Hendecapleura subgenus Dipodillus subgenus Gerbillus subgenus Monodia Combined analyse (cytb + IRBP) with taxonomic hypotheses G. poecilops, G. henleyi, G. nanus, G. amoenus G. rupicola, G. campestris G. dasyurus, G. simoni G. nancillus G. cheesmani, G. gerbillus G. andersoni, G. nigeriae, G. pyramidum, G. floweri, G. latastei, G. hesperinus, G. hoogstraali, G. occiduus, G. tarabuli, Gerbillus sp.1 & Gerbillus sp2 Outgroup
  12. 12. Divergence Gerbillinae / Deomyinae Divergence Acomys / Lophuromys 1st mention of Gerbilliscus Divergence Gerbillus / Sekeetamys Molecular datation using fossils calibration Estimated dates: Divergence Sekeetamys- Gerbillus: - 6,5MYA Miocène. Plio. Pleist. subgenus Hendecapleura subgenus Gerbillus subgenus Monodia subgenus Dipodillus Emergence of Hendecapleura: - 5,1 MYA Emergence of Gerbillus: - 4,1 MYA Emergence of Dipodillus: - 3,6 MYA Emergence of mostly Gerbillus species: Pleistocène (except. G. poecilops & G. campestris) Outgroups
  13. 13. Reconstruction of ancestral distribution areas subgenus Gerbillus subgenus Dipodillus subgenus Monodia subgenus Hendecapleura Outgroups Evolutionary history of subfamily (Gerbillinae) and Gerbillus genus mainly inAfrica very few dispersions events in Gerbillus , probably from Africa to Asia (G. cheesmani, G. nanus, G. poecilops)
  14. 14. The IUCN Red List of Threatened Species. Version 2016-2. <www.iucnredlist.org>. Downloaded on 20 November 2016 How this will help us to better understand G. nanus – G. amoenus evolution of distribution area? G. nanus sibling species G. amoenus
  15. 15. Specimens from Israël and Pakistan Specimens from Mauritania, Mali and Lybia G. nanus G. amoenus 1st Results of complete cytochrome b sequences (Ndiaye et al. 2013) obtained from fresh samples K2P genetic distance between 2 clades of « G. nanus » (sensu lato) = 0,065 MLtree ➔ hypothesis of an asian species (G. nanus) and an african species (G. amoenus?) Africa Asia
  16. 16. Afghanistan* Egypte* Niger Mauritanie Testing previous hypothesis using partial cytochrome b sequences of old specimen collection (Field Museum, Chicago; Ndiaye et al. 2016b) Gerbillus nanus Gerbillus amoenus A sampling of 6 species including 6 specimens of G. amoenus (From Egypt) and 4 specimens of G. nanus (from Pakistan and d’Afghanistan) collected from 1918 and 1965 Africa Israël Pakistan* Asia
  17. 17. G. nanus G. amoenus G. amoenus G. nanus Molecular data suggested biogeographical revisions G. amoenus and G. nanus = vicariant species on both sides of the red Sea, differentiated since 1,4 +/- 0,7MA (through Sinaï/Negev from West to East) But a question about possible synonymy of G. garamantis (The « Algerian » gerbil, 2n = 54, described from Ouargla) with G. amoenus (2n = 52): If synonymy, G. garamantis should be the correct name (anteriority rule); if not, both species are represented in North Africa.
  18. 18. Sibling species find in Senegal due to Integrative taxonomy G. henleyi known to occur in Senegal since 1980 BUT Samples firstly identify like G. henleyi were too different (molecular) Use of various methods sampling small Gerbillus with hairless plantar soles (subgenus Hendecapleura) from sahelien area G. henleyi G. nancillus 2n = 52 2n = 56 Ndiaye et al. 2014
  19. 19. G. henleyi G. nancillus ! Suggesting (1) the extension of the distribution area and (2) one more Gerbillus species in Senegal small mammals diversity A: PCAon body measurements B: PCA on skull measurements C: DA on skull measurements
  20. 20. Conclusions • Gerbillus = very interesting group to study arid areas • Incomplete Systematic which is important and preliminary to all other studies (ecology, physiology, biogeography…) • Importance of good sampling for better interpretation • Importance to combine methods for better diagnosis from collections/Museum withspecimens methods ==> Very important to complete • Use of adequate sampling
  21. 21. Perspectives Why are we doing all this work upstream…? • like biological invasions in WestAfrica • with several biological pests of cereal crops (G. nigeriae) or market gardeners (Tuta absoluta) with consequences in Food security, trade… ==> JEAI- IBAO • Describe and better understand the modalities of these bio-invasions ==> can affect real biodiversity in Saharo-sahelian area More applied Sciences !!!

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