Etienne, L., Rousset, F., Godelle, B. Courtiol, A., (2014).
How choosy should I be? The relative searching time predicts evolution of choosiness under direct sexual selection. Proceedings of the Royal Society B - Biological Sciences 281 (1785): Article Number: 20140190. [ISEM 2014-037] .

Most theoretical research in sexual selection has focused on indirect selection. However, empirical studies have not strongly supported indirect selection. A well-established finding is that direct benefits and costs exert a strong influence on the evolution of mate choice. We present an analytical model in which unilateral mate choice evolves solely by direct sexual selection on choosiness. We show this is sufficient to generate the evolution of all possible levels of choosiness, because of the fundamental trade-off between mating rate and mating benefits. We further identify the relative searching time (RST, i.e. the proportion of lifetime devoted to searching for mates) as a predictor of the effect of any variable affecting the mating rate on the evolution of choosiness. We show that the RST: (i) allows one to make predictions about the evolution of choosiness across a wide variety of mating systems; (ii) encompasses all alternative variables proposed thus far to explain the evolution of choosiness by direct sexual selection; and (iii) can be empirically used to infer qualitative differences in choosiness.

Orliac, M.J. Ladevèze, S. Gingerich, P.D., Lebrun, R. Smith, T. (2014).
Endocranial morphology of Palaeocene Plesiadapis tricuspidens and evolution of the early primate brain. Proceedings of the Royal Society B-Biological Sciences 281 (1781): Article Number: 20132792. [ISEM 2014-012] .

Expansion of the brain is a key feature of primate evolution. The fossil record, although incomplete, allows a partial reconstruction of changes in primate brain size and morphology through time. Palaeogene plesiadapoids, closest relatives of Euprimates (or crown-group primates), are crucial for understanding early evolution of the primate brain. However, brain morphology of this group remains poorly documented, and major questions remain regarding the initial phase of euprimate brain evolution. Micro-CT investigation of the endocranial morphology of Plesiadapis tricuspidens from the Late Palaeocene of Europe-the most complete plesiadapoid cranium known-shows that plesiadapoids retained a very small and simple brain. Plesiadapis has midbrain exposure, and minimal encephalization and neocorticalization, making it comparable with that of stem rodents and lagomorphs. However, Plesiadapis shares a domed neocortex and downwardly shifted olfactory-bulb axis with Euprimates. If accepted phylogenetic relationships are correct, then this implies that the euprimate brain underwent drastic reorganization during the Palaeocene, and some changes in brain structure preceded brain size increase and neocortex expansion during evolution of the primate brain.

Nabholz, B. Sarah, G., Sabot, F., Ruiz, M., Adam, H., Nidelet, S., Ghesquière, A., Santoni, S., David, J., Glémin, S. (2014).
Transcriptome population genomics reveals severe bottleneck and domestication cost in the African rice (O. glaberrima). Molecular Ecology 23(9): 2210-2227. [ISEM 2014-034] .

The African cultivated rice (Oryza glaberrima) was domesticated in West Africa 3000years ago. Although less cultivated than the Asian rice (O.sativa), O.glaberrima landraces often display interesting adaptation to rustic environment (e.g. drought). Here, using RNA-seq technology, we were able to compare more than 12000 transcripts between 9 O.glaberrima, 10 wild O.barthii and one O.meridionalis individuals. With a synonymous nucleotide diversity (s)=0.0006 per site, O.glaberrima appears as the least genetically diverse crop grass ever documented. Using approximate Bayesian computation, we estimated that O.glaberrima experienced a severe bottleneck during domestication. This demographic scenario almost fully accounts for the pattern of genetic diversity across O.glaberrima genome as we detected very few outliers regions where positive selection may have further impacted genetic diversity. Moreover, the large excess of derived nonsynonymous substitution that we detected suggests that the O.glaberrima population suffered from the cost of domestication’. In addition, we used this genome-scale data set to demonstrate that (i) O.barthii genetic diversity is positively correlated with recombination rate and negatively with gene density, (ii) expression level is negatively correlated with evolutionary constraint, and (iii) one region on chromosome 5 (position 4-6Mb) exhibits a clear signature of introgression with a yet unidentified Oryza species. This work represents the first genome-wide survey of the African rice genetic diversity and paves the way for further comparison between the African and the Asian rice, notably regarding the genetics underlying domestication traits.

Morin-Rivat, J., Fayolle, A., Gillet, J.F., Bourland, N., Gourlet-Fleury, S., Oslisly, R., Bremond, L., Bentaleb, I., Beeckman, H., Doucet, J-L., (2014).
New evidence of human activities during the Holocene in the low-land forests of the northern Congo basin. Radiocarbon 56(1): 209–220. [ISEM 2014-028].

In the last decade, the myth of the pristine tropical forest has been seriously challenged. In central Africa, there is a growing body of evidence for past human settlements along the Atlantic forests, but very little information is available about human activities further inland. Therefore, this study aimed at determining the temporal and spatial patterns of human activities in an archaeologically unexplored area of 110,000 km2 located in the northern Congo Basin and currently covered by dense forest. Fieldwork involving archaeology as well as archaeobotany was undertaken in 36 sites located in southeastern Cameroon and in the northern Republic of Congo. Evidence of past human activities through either artifacts or charred botanical remains was observed in all excavated test pits across the study area. The set of 43 radiocarbon dates extending from 15,000 BP to the present time showed a bimodal distribution in the Late Holocene, which was interpreted as two phases of human expansion with an intermediate phase of depopulation. The 2300–1300 BP phase is correlated with the migrations of supposed farming populations from northwestern Cameroon. Between 1300 and 670 BP, less material could be dated. This is in agreement with the population collapse already reported for central Africa. Following this, the 670–20 BP phase corresponds to a new period of human expansion known as the Late Iron Age. These results bring new and extensive evidence of human activities in the northern Congo Basin and support the established chronology for human history in central Africa.

Conéjéro, G., Noirot, M., Talamond, P., Verdeil, J.L. (2014).
Spectral analysis combined with advanced linear unmixing allows for histolocalization of phenolics in leaves of coffee trees. Frontiers in Plant Science 5(37): 1-7. [ISEM2014-029].

An imaging method using spectral analysis combined with advanced linear unmixing was used to allow histolocalization of natural autofluorescent compounds such as hydroxycinnamic acid (chlorogenic acid) and xanthone (mangiferin) in living cells and tissues (mature coffee leaves). The tested method included three complementary steps: 1/ visualization of natural autofluorescence and spectrum acquisition with a multiphoton microscope; 2/ identification of some compounds using previous information on the chemical composition of the tissue, obtained from litterature; and 3/ localization of candidate compounds by spectral imaging. The second part of the study consisted of describing the histochemical structure of leaves during their development. This revealed very fast histochemical differentiation of leaves during the first week after their emergence. Lastly, young leaves of Coffea pseudozanguebariae (PSE), C. eugenioides (EUG), C. arabica (ARA) and C. canephora (CAN) were compared. This confirmed the presence of xanthone in PSE and EUG, but especially its precise tissue localization. This also highlighted the paternal CAN origin of the leaf structure in the allotetraploid species ARA. The limits and advantages of the method without staining are discussed relative to classical epifluorescence microscopy under UV light. This non-invasive optical technique does not require pretreatment and is an effective experimental tool to differentiate multiple naturally-occuring fluorochores in living tissues.