Speciation Has a Spatial Scale That Depends on Levels of Gene Flow

Abstract

Area is generally assumed to affect speciation rates, but work on the spatial context of speciation has focused mostly on patterns of range overlap between emerging species rather than on questions of geographical scale. A variety of geographical theories of speciation predict that the probability of speciation occurring within a given region should (1) increase with the size of the region and (2) increase as the spatial extent of intraspecific gene flow becomes smaller. Using a survey of speciation events on isolated oceanic islands for a broad range of taxa, we find evidence for both predictions. The probability of in situ speciation scales with island area in bats, carnivorous mammals, birds, flowering plants, lizards, butterflies and moths, and snails. Ferns are an exception to these findings, but they exhibit high frequencies of polyploid and hybrid speciation, which are expected to be scale independent. Furthermore, the minimum island size for speciation correlates across groups with the strength of intraspecific gene flow, as is estimated from a meta-analysis of published population genetic studies. These results indicate a general geographical model of speciation rates that are dependent on both area and gene flow. The spatial scale of population divergence is an important but neglected determinant of broad-scale diversity patterns.

Islands as model systems in ecology and evolution: prospects fifty years after MacArthur‐Wilson

“…Accordingly, for example, it appears that 150 species of diving beetle are the product of a single colonisation event followed by speciation within the island of New Guinea (Balke et al 2007), and 1000 species of picture-winged Drosophila are the product of speciation within the Hawaiian archipelago (O'Grady et al 2011). Islands have illustrated that the factors that interact to provide conditions necessary for in situ speciation include isolation (Manceau et al 2010), age (Gillespie & Baldwin 2010) and area (Losos & Schluter 2000;Kisel & Barraclough 2010) of the region concerned, and variables often associated with area, such as topographic complexity and elevation (Whittaker et al 2008). Table 1 Under-explored or in need of revisiting: prospects for using islands to advance understanding in ecology and evolution in general.…”

“…Furthermore, larger areas imply larger population sizes, likely increasing both the number of advantageous mutations and the efficiency with which selection acts upon them (Gavrilets & Losos 2009). Several island-based studies have confirmed the importance of area in cladogenesis (Losos & Schluter 2000;Kisel & Barraclough 2010;Rabosky & Glor 2010). However, beyond Rosindell & Phillimore's (2011) test of their own predictions with island bird data, how the interplay between isolation and area influences the relative importance of anagenesis and cladogenesis largely remains to be evaluated (but see Johnson et al 2000;Valente et al 2014).…”

“…Variation in island size (e.g. owing to sea level fluctuations) affects the overall probability of speciation (Losos & Schluter 2000;Kisel & Barraclough 2010) and may therefore also affect the contributing mode(s) of speciation (Whittaker et al 2008;Losos & Ricklefs 2009). Aguil ee et al (2013) recently developed a model allowing for such variable history, in which ecological speciation includes temporary and repetitive geographical isolation.…”

Asynchrony of Seasons: Genetic Differentiation Associated with Geographic Variation in Climatic Seasonality and Reproductive Phenology

“…Because body size correlates with dispersal abilities and thus influences genetic differentiation (Kisel and Barraclough 2010), we tested the effect of species' average body mass.…”

Phylogenetic evidence from freshwater crayfishes that cave adaptation is not an evolutionary dead‐end

“…It is generally accepted that there is an interplay among dispersal ability, geographic range size, speciation, and extinction that influences a group's evolutionary success (Bilton et al. 2001; Bohonak and Jenkins 2003; Kisel and Barraclough 2010; Sukumaran et al. 2015).…”