Conditions for neutral speciation via isolation by distance

Abstract

The branching of new species from an ancestral population requires the evolution of reproductive isolation between groups of individuals. Geographic separation of sub-populations by natural barriers, if sustained for sufficiently long times, may lead to the accumulation of independent genetic changes in each group and to mating incompatibilities (Mayr, 2001; Fitzpatrick et al., 2009). A similar phenomenon may occur in the absence of barriers via isolation by distance if the population is distributed over large areas (de Aguiar et al., 2009; Etienne and Haegeman, 2011; Gavrilets et al., 2000). The first demonstration of this process was based on computer simulations employing agent-based models. Recently, analytical results were derived combining network theory, to model the spatial structure of the population, and an ansatz that accounts for the effect of forbidding mating between individuals that are too different genetically (de Aguiar and Bar-Yam, 2011). The main result obtained with this approach is an expression that indicates when speciation is possible as a function of the parameters describing the population. The aim of this work is to test this analytical result by comparing it with numerical simulations for a hermaphroditic population (de Aguiar et al., 2009) and for a population whose individuals are explicitly separated into males and females (Baptestini et al., 2013). We show that the analytical formula is indeed a very good overall description of the simulations and that the exponents describing dependence of the critical threshold of speciation with the parameters are in good agreement with the simulations.

Escape from the cryptic species trap: lichen evolution on both sides of a cyanobacterial acquisition event

“…For one thing, this is a contradiction in terms: invariability of a specific phenotype leaves nothing on which selection can act. Although never explicitly stated by lichenologists, evolution without phenotypic divergence would require an alternative to speciation through natural selection or imply neutral speciation (Baptestini et al 2013). Neutral speciation in lichenized fungi is a conceivable possibility but is unlikely to be common due to widespread sympatry, and would be difficult to prove.…”

Allopatry increases the balance of phylogenetic trees during radiation under neutral speciation

“…Individuals reproduce sexually in a mating range and the species definition is based on reproductive isolation. Genetic diversity, generated by recombination and mutation, correlates with the spatial dimension (of mating range) (Baptestini et al , b, Martins et al ). As a result, individuals that are far apart tend to be genetically different, forming species in spatial clusters of genetically similar individuals (de Aguiar et al , Baptestini et al ).…”

“…Genetic diversity, generated by recombination and mutation, correlates with the spatial dimension (of mating range) (Baptestini et al , b, Martins et al ). As a result, individuals that are far apart tend to be genetically different, forming species in spatial clusters of genetically similar individuals (de Aguiar et al , Baptestini et al ). Previous results using the same modelling framework (Costa et al ) have shown that the mating range significantly affects the branching tempo: larger mating ranges (when individuals use the same geographic region, corresponding to sympatry) lead to an increase in the rate of speciation throughout the radiation process.…”

Single-species fragmentation: The role of density-dependent feedback

“…Population fragmentation is characterized by critical changes in the spatial distribution of individuals, creating isolated subgroups of a given initial population. This phenomenon has important consequences for secondary processes such as epidemic spreading, species invasion [1], or also speciation [2]. Fragmentation is often attributed to landscape heterogeneity, which encompasses the spatial distribution of geographic and environmental features [3].…”