Adequate sample sizes are required for reliable Bayesian Skyline Plot demographic reconstructions.
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INSUFFICIENT LEANING
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Technical literature on skyline-plot methods notes general sampling design principles and limitations, but does not comprehensively establish specific sample size requirements for reliable demographic reconstructions.
Estimation of demographic history from nucleotide sequences represents an important component of many studies in molecular ecology. For example, knowledge of a population's history can allow us to test hypotheses about the impact of climatic and anthropogenic factors. In the past, demographic analysis was typically limited to relatively simple population models, such as exponential or logistic growth. More flexible approaches are now available, including skyline-plot methods that are able to reconstruct changes in population sizes through time. This technical review focuses on these skyline-plot methods. We describe some general principles relating to sampling design and data collection. We then provide an outline of the methodological framework, which is based on coalescent theory, before tracing the development of the various skyline-plot methods and describing their key features. The performance and properties of the methods are illustrated using two simulated data sets.
infer skyline plots from this type of data (e.g., Allen et al., 2012 ; Molfetti et al., 2013 ; Minhós et al., 2016 ). Also for microsatellite data, a composite-likelihood approach has been developed (R package VarEff, Nikolic & Chevalet, 2014 ).
Similar piecewise models to infer historical population sizes through time have been proposed in the context of population genomics (e.g., Li & Durbin, 2011 ; Terhorst, Kamm & Song, 2016 ). The methods discussed above assume a set of independent (unlinked) genetic markers. However, if a large proportion of the genome has been sequenced, the studied polymorphism are in linkage disequilibrium. Methods such as the Pairwise Sequentially Markovian Coalescent (PSMC, Li & Durbin, 2011 ) and its successors profit from the additional information of linkage disequilibrium for the inference. We will not further discuss this family of methods, as our focus here is on datasets of independent molecular markers, such as microsatellites, which remain reliable markers for low-budget projects. Note, however, the PSMC-like implementation on ABC by Boitard et al. (2016) .
The use of the skyline plot in the ABC framework was first proposed in Burgarella et al. (2012) . Here, we provide a suite of R scripts (DIYABCskylineplot) to produce approximate-Bayesian-computation skyline plots from microsatellite data and evaluate its performance on simulated pseudo-data. We show the method to be useful for detecting population decline and expansion and discuss its limits. ABC skyline plots are then built for four study cases (whale shark, leatherback turtle, Western black-and-white colobus and Temminck’s red colobus) and compared with the demographic inference obtained by an alternative full likelihood method. Methods
ABC skyline plot
For a demographic skyline plot analysis within the ABC framework, our model consisted of a single population with constant size that instantaneously changes to a new size n times through time. The parameters (from present
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