Work Package 2:
Climate changes and mammal evolution
10 researchers
COORDINATORS Janice Britton-Davidian (UMR 5554 CNRS) and Conrad Matthee (Department of Botany and Zoology, University of Stellenbosch)
Climate change during the Quaternary period has
been put forward as one of the main drivers of biodiversity on the African
continent. Cyclical shifts in
temperature caused major changes in vegetation and this in turn resulted in the
contraction and expansion of species ranges into potential refugia. By making use of multiple data sets
derived from various sources (genetics, behaviour and ecology) and species with
different life histories (predominantly rodents) the main focus of this work
package is to establish multiple data sets that can be used to make general
evolutionary conclusions regarding speciation of African taxa. To gain a better
holistic understanding of the factors driving speciation on the African
continent will have significant conservation implications. For example, congruent geographic
patters among lineages will point to vicariance and regions with high levels of
genetic diversity across multiple taxa can be used to define refugia. These data in turn can be analysed in
the context of paleoclimatic modelling to place conservation networks in more
optimal positions.
Project 1 : The African pygmy mouse radiation: phylogeny, chromosomes and sex determination
Participants : Frédéric Veyrunes, Janice Britton-Davidian (UMR 5554 CNRS, Montpellier), Pascale Chevret (UMR 5558 CNRS, Lyon), Terry Robinson (University of
Stellenbosch).
The diversification of the
savannah-dwelling African pygmy mice is accompanied by an extensive chromosomal
radiation involving mostly centric fusions. In South Africa, cytogenetic and
molecular analyses have so far identified two species occupying different
environments, Mus indutus (semi-arid
habitats) and M. minutoides (grasslands),
and uncovered five different chromosomal groups within the latter differing by
the number and type of centric fusions present. In addition, a new case of atypical
sex determination in mammals was discovered in M. minutoides in which a
high proportion of sex-reversed XY females were present.
The objectives of this project are
twofold. The first is to complete the chromosomal and taxonomic survey of pygmy
mice throughout South Africa. This will be achieved by implementing cytogenetic
and phylogenetic approaches in newly sampled localities and in >250
previously collected museum samples. From this study, the correlation between
chromosomal divergence (including the change in sex determination), taxonomic
diversification and Quaternary climatic changes will be tested. The second aim
involves a multidisciplinary approach on both wild and laboratory-bred animals
using a variety of cytogenomic and molecular tools: (i) to identify and
characterize the genetic basis of the sex-reversion (test the
functionality of candidate genes), (ii) to investigate the evolutionary processes involved in the formation,
fixation and persistence of this aberrant
sex determining system. A breeding program will be set up in the laboratory to measure reproductive traits and
perform behavioural analyses. The evolutionary impact of these parameters will
be explored by a computer modelling approach.
Project 2 : The
African striped mouse: A biomarker of past and present environmental changes in
southern Africa
Participants: Guila Ganem (CNRS UMR 5554
Montpellier), Neville Pillay (University
of Wits, Johannesburg),
Nico Avenant (Museum Bloemfontein)
Climate change and its effects on
habitats are unquestionably affecting life history traits and the distribution
of many living organisms. Plasticity and genetic adaptation are important
mechanisms by which species can respond to changes in their environment and, in
the context of recent rapid climate change, such responses could ameliorate the
negative consequences of this disturbance. However, the effectiveness and
generality of plasticity versus adaptive responses to rapid changes are still a
matter of scientific debate and clearly deserve further investigation, which we
propose to address in a successful African small mammal, the striped mouse. The
striped mouse has split into two species some 2.9 million years ago during a
period of marked climate oscillation, and at present its various populations
occupy much diversified environments ranging from arid to humid. The striped
mouse has recently benefited from many studies resulting in a very good understanding of its biology and on
which this study will build. Further we collaborate with other participants of
the GDRI that address the phylogeography of this genus. The specific objectives
of our project are to measure within and between populations and species
variation of two behavioural characteristics that have shown to vary in the
striped mouse and expected to be sensitive to environmental variations: social
behaviour and odour signalling, as well as a morphological marker, mandible
shape, known to be prone to plastic variations related to diet changes during
ontogenesis.
Project 3 : Phylogeny of the
rodent tribe Otomyini (groove-toothed rats) and
phylogeography of four arid-adapted species : comparison of patterns of
diversification using multiple markers
Participants: Claudine Montgelard (UMR 5175 CNRS Montpellier), Christiane Denys (MNHN, Paris), Conrad
Matthee (University of
Stellenbosch), Peter Taylor (University
of Venda)
Otomyini
currently included 23 species in 3 genera but phylogenetic relationships among
them are not yet settled. In particular monophyly of each genus is still
questioned because not recovered from numerous data (morphological, chromosomal
or molecular). Our first goal will be to obtain a well resolved phylogeny
between the different species through sequencing of multiple nuclear genes
(introns and exons).
The second objective will focus on the four
arid-adapted species endemic to South Africa (Parotomys brantsii, P. littledalei, Otomys unisulcatus, and O. sloggetti) inhabiting dry and arid
environments. Phylogeographic
patterns will first be compared between species using mitochondrial (cytochrome
b and control region) sequences. Then we will use microsatellite markers to
compare the genetic structure at the population level for the same taxa. A
genomic library is currently built for Otomys
unisulcatus using next-generation sequencing (pyrosequencing) that generate
up to one million nucleotide data in stretches of 200-350 bp long, among which
numerous microsatellites will be designed. In complement to molecules, geometric
morphometrics will be performed on the same four arid taxa to analyze
variations in shape of cranium and mandible and their covariations with some
environmental variables. Finally, morphological variations of molars will also
be analyzed on fossil specimen, allowing to investigate the past changes over
the last 5 Myr (Plio-Pliocene). We will address questions such as: are the
patterns of diversification congruent in space and time between markers and
species or specific to each species ? Did the diverse groups appear
concomitantly (paleontological and molecular dating) or not and can we identify
factors (climatic or environmental) responsible for the structure (genetic and
morphometric) observed?
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