Dispersal Reduction: Causes, Genomic Mechanisms, and Evolutionary Consequences

Abstract

Recent biological analyses indicate that secondary reduction in dispersal ability is a key driver of diversification across numerous lineages. Here we synthesise emerging data to highlight similarities regarding the causes and consequences of dispersal reduction, across taxa and ecosystems, and the diverse genomic mechanisms underpinning these shifts. Natural selection has acted on standing genetic variation within taxa to drive often rapidand in some cases parallellosses of dispersal, and ultimately geographic speciation. Dispersal reduction thus represents a nexus between adaptive and neutral diversification processes, with substantial evolutionary consequences. Recognition of links between these concepts emerging from different fields, taxa and ecosystems is transforming our understanding of the fascinating role of dispersal reduction in the formation of biodiversity.

Does migration promote or inhibit diversification? A case study involving the dominant radiation of temperate Southern Hemisphere freshwater fishes

“…Although estimated extinction rates were higher in nonmigratory galaxiids, consistent with expectations from theory and some empirical tests (Rolland et al 2014;Corush 2019), they were not sufficiently elevated to suppress overall diversification rates. Although our findings are broadly consistent with a wide variety of analyses linking high diversification rates with "dispersal reduction" (Waters et al 2020), including one study of migratory behavior in fishes (Tedesco et al 2017), they directly contrast with the conclusions of some recent empirical studies that suggested migratory behavior leads to higher diversification (Rolland et al 2014;Fuchs et al 2015;Corush 2019;Gómez-Bahamón et al 2020) or has no effect (Kennedy et al 2016). The lower diversification rates for migratory galaxiids could be explained by lower natal philopatry relative to other migratory taxa, perhaps reflecting either unpredictability of freshwater habitat quality-and hence greater benefit of straying-or lower locomotory abilities of the migratory stage in galaxiids: larvae.…”

“…We encourage future investigations of the potential interaction of dispersal ability (accurately measured) and the proximity of suitable habitats on diversification rates, in the context of the "intermediate dispersal" model. More generally, galaxiid fishes also provide a key opportunity to investigate the molecular mechanisms underlining transitions between diadromous and nondiadromous life histories, and whether the multiple transitions observed among galaxiids reflect identical mechanisms, both relative to one another, and to other fishes that have already been investigated in detail (Jones et al 2012;Michalak et al 2014;Terekhanova et al 2014;Lemopoulos et al 2018;Delgado et al 2019;Waters et al 2020).…”

“…Additionally, dispersal influences individual fitness, the colonization of new environments, levels of inbreeding and genetic variation, and the genetic divergence of populations (Frankham and Ralls 1998;Lenormand 2002). Dispersal can thus have major impacts on the rates and spatial scales of both speciation and extinction and, consequently, overall diver-sification (Kisel and Barraclough 2010;Ikeda et al 2012;Waters et al 2020). However, estimating these impacts can be problematic, given that dispersal can influence speciation and extinction in different ways (Claramunt et al 2012).…”

Ecological drivers of global gradients in avian dispersal inferred from wing morphology

“…According to speciation theory, dispersal is a key factor determining the likelihood of speciation in a given geographical area because it influences rates of gene flow across barriers 5,56 . On islands, speciation is most likely to occur when dispersal is high enough to promote island colonisation 8,33 but not so high that gene flow is too frequent 30,57 .…”

Adaptive evolution of olfactory degeneration in recently flightless insects

“…Recent analyses have highlighted that shifts in animal mobility can have drastic evolutionary consequences (63). The findings of the current study highlight not only the need for rapid olfactory processing in flying insects (2), but also that this sensory ability can be rapidly degraded when no longer required (i.e.…”