Morphological, genetical and ecological discrimination of sympatric Coastal Guinea Mastomys (Mammalia : Rodentia) species (West Africa) : implications for health and agriculture

Cytogenetic and molecular tools have shown the existence of two sibling species of the multimammate rat in Coastal Guinea : M. erythroleucus and M. huberti from Mankoutan locality. Here we present the study of the unique population of M. huberti ever recorded in Guinea, distant from 350 km from the closest locality in Senegal and representing the southernmost point of the species’ disjunct distribution. In order to clarify its ecological preferences and define its degree of sympatry with M. erythroleucus, we have searched for morphological and morphometric criteria allowing reliable identification of the species in Coastal Guinea. Discriminant Factorial Analyses (DFA) were performed on external and skull measurements for respectively 108 and 106 previously genetically typed individuals. All discriminant analyses showed that the 100 % rate of good classification is never attained. Misclassifications of 55.6 % of the specimens were obtained in the field by using external fur colour and aspect whereas the error score ranged from 4.5 to 8 % by using DFA on external measurements. Furthermore, DFA on skull measurements gave 100 % of correct classification for M. huberti - which is characterized by a smaller size - against 96.97 % for M. erythroleucus. In the same time, we were able to define the local specific habitat of each species. In Mankountan, M. huberti is never found into houses but prefers wet rice fields, while M. erythroleucus is found both in houses and cultures as well as in wet rice fields where it is found in syntopy with M. huberti at the end of the dry season. In Yerende, a hundred kilometres from Mankoutan, we only caught M. erythroleucus both in houses and fields. This study once again highlights the importance of a deep taxonomic knowledge of small mammals’ diversity for sanitary and agricultural risks evaluation but also confirms the problems of identification encountered with rodent sibling species living in sympatryLes analyses cytogénétiques et moléculaires ont mis en évidence la présence de deux espèces jumelles de Mastomys en Guinée Maritime: M. ervthroleucus et M. huberti dans la localité de Mankoutan. Il s'agit de la première étude de la seule population de M. huberti rencontrée en Guinée située à 350 km de la population la plus proche du Sénégal, à l'extrémité Sud de l'aire de distribution disjointe de l'espèce. Afin de définir ses préférences écologiques, nous avons recherché des critères morphologiques et morphométriques pour identifier les deux espèces de Mastomys afin de mieux définir leur degré de sympa-trie. Des Analyses Factorielles Discriminantes (AFD) effectuées sur les caractères externes et crâniens de 108 et 106 individus ayant fait l'objet d'analyses moléculaires (cyt.b) et /ou cytogénétiques, provenant de deux localités proches, montrent que l'on ne peut jamais discriminer avec 100 % de certitude les spécimens en 'peau' et 'crâne'. Le taux d'erreur de détermination des deux espèces atteint 55,6 % pour la coloration et l'aspect du pelage sur le terrain, il oscille entre 4,5 et 8 % en AFD sur les mesures externes. Cependant avec les mesures crâniennes traitées par AFD, les M. huberti se distinguent à 100 % par une taille légèrement plus faible, contre 96,97 % chez M. erythroleucus. Parallèlement, nous avons pu préciser l'habitat spécifique aux deux espèces dans la même localité. Ainsi, à Mankountan, M. huberti n'est jamais rencontré dans les maisons et préfère les champs de riz inondés. M. erythroleucus est présent à la fois dans les maisons et dans les champs, quelquefois dans les rizières inondés où, à la fin de la saison sèche, il se retrouve en syntopie avec M. huberti. La localité de Yerendé située à 100 km de Mankountan n'a livré que des M. erythroleucus, présents à la fois dans les maisons et les champs. Cette étude montre l'importance d'une connaissance approfondie de la systématique et de la diversité des petits mammifères nuisibles pour l'évaluation des risques sanitaires et agricoles et confirme les difficultés d'identification morphologique des espèces jumelles chez les rongeurs

Mastomys natalensis and Lassa Fever, West Africa

PCR screening of 1,482 murid rodents from 13 genera caught in 18 different localities of Guinea, West Africa, showed Lassa virus infection only in molecularly typed Mastomys natalensis. Distribution of this rodent and relative abundance compared with M. erythroleucus correlates geographically with Lassa virus seroprevalence in humans

Shrews (Mammalia, Eulipotyphla) from a biodiversity hotspot, Mount Nimba (West Africa), with a field identification key to species

In this study, we collected 226 shrew specimens originating from 16 localities on the Guinean and Liberian sides of Mount Nimba. We surveyed all major vegetation zones from 400 to 1600 m above sea level (asl), including forest and savannah habitats. We recorded 11 species, whose identifications were confirmed by genetic analyses and classical morphometrics. Furthermore, we provide cytogenetic data for five of these species. The shrew community at Mount Nimba is composed of a mix of both savannah- and forest-dependent species, which is related to the peculiar position of Mount Nimba situated at the transition between lowland rainforest to the south and Guinean woodlands to the north. We recorded 11 species of shrews in syntopy in lowland rainforest, seven in edaphic savannah and mountain forest, and five in high-altitude savannah at 1600 m asl. Based on morphometric analyses, we show that these syntopic species separate along a size axis, allowing species to occupy different ecological niches, which we speculate allows them to access different food resources. We also highlight that Crocidura theresae Heim de Balsac, 1968 from Mount Nimba has a different karyotype from that described in Côte d’Ivoire. Finally, we develop a novel identification key for shrews from Mount Nimba using external characters and standard body measurements, allowing it to be used in the field on live specimens. In total 12 shrew species are now known from Mount Nimba, which highlights its exceptional position as a tropical African biodiversity hotspot.https://sciencepress.mnhn.fr/en/periodiques/zoosystemadm2022Mammal Research InstituteZoology and Entomolog

The Impact of Human Conflict on the Genetics of Mastomys natalensis and Lassa Virus in West Africa

Environmental changes have been shown to play an important role in the emergence of new human diseases of zoonotic origin. The contribution of social factors to their spread, especially conflicts followed by mass movement of populations, has not been extensively investigated. Here we reveal the effects of civil war on the phylogeography of a zoonotic emerging infectious disease by concomitantly studying the population structure, evolution and demography of Lassa virus and its natural reservoir, the rodent Mastomys natalensis, in Guinea, West Africa. Analysis of nucleoprotein gene sequences enabled us to reconstruct the evolutionary history of Lassa virus, which appeared 750 to 900 years ago in Nigeria and only recently spread across western Africa (170 years ago). Bayesian demographic inferences revealed that both the host and the virus populations have gone recently through severe genetic bottlenecks. The timing of these events matches civil war-related mass movements of refugees and accompanying environmental degradation. Forest and habitat destruction and human predation of the natural reservoir are likely explanations for the sharp decline observed in the rodent populations, the consequent virus population decline, and the coincident increased incidence of Lassa fever in these regions. Interestingly, we were also able to detect a similar pattern in Nigeria coinciding with the Biafra war. Our findings show that anthropogenic factors may profoundly impact the population genetics of a virus and its reservoir within the context of an emerging infectious disease

Genetic Variation in a North African Rodent Pest, Meriones shawi : Microsatellite Polymorphism

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Variabilité phénotypique et génétique des Mastomys (Rodentia, Muridae) de Guinée (évolution, environnement et infection virale)

L'objectif de cette thèse est d étudier la production de phénotypes différents chez des populations sauvages d un rongeur de la sous famille des Murinae, endémique au continent africain, le genre Mastomys. Nous avons identifier des patrons de variation de la structure crânienne et déterminer l importance respective de diverses contraintes sur l évolution morphologique (contrainte génétique, contrainte environnementale liée au type d habitat ou à une infection virale par l arénavirus Lassa). La confrontation des données issues des études morphométriques, génétiques et épidémiologiques a permis de montrer que l évolution de la variation phénotypique chez Mastomys avait deux origines différentes : la modification de la sensibilité du phénotype cible aux conditions environnementales (canalisation environnementale) et génétiques (canalisation génétique). De plus, nos résultats ont révélé une instabilité développementale chez les individus infectés par le virus Lassa, survenue probablement au cours de la gestation lors de la transmission verticale du virus.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Genetic variation in a North African rodent pest, Meriones shawi: microsatellite polymorphism

Meriones shawi is an ubiquitous and endemic rodent in northern African. This species is considered as an economically important pest because it often damages crops. Moreover, the gerbillines are known to function as reservoirs for a variety of serious human epidemic diseases. Ten polymorphic microsatellite loci were identified using 454 GS-FLX Titanium pyrosequencing and a multiplex PCR assay was developed. The utility of these markers was evaluated in 30 individuals from three different Moroccan populations. Number of alleles per locus ranged from 2 to 7, with observed and expected heterozygosities ranging from 0.033 to 0.967 and from 0.033 to 0.729, respectively. Departures from Hardy-Weinberg equilibrium were observed at two loci. These markers will be useful resources for future population genetics studies for this rodent and pest-borne disease management.Key words: Meriones shawi, gerbil, rodent-borne disease, microsatellite, polymorphism

Morphological identification of sibling species: the case of West African Mastomys (Rodentia: Muridae) in sympatry

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Holocene subfossil rodents from the Lavajaza Cave, Central Highlands of Madagascar

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