Dispersal evolution in currents: spatial sorting promotes philopatry in upstream patches

Abstract

Substantial literature is devoted to understanding dispersal evolution, but we lack theory on how dispersal evolves when populations inhabit currents. Such theory is required for understanding connectivity in freshwater and marine environments; moreover, many animals, fungi and plants rely on wind‐based dispersal, but the effects of currents on dispersal evolution in these organisms is unknown. We develop an individual‐based model for evolution of dispersal probability along a linear environment with a unidirectional current. Even a slight current substantially reduces overall emigration probability compared to no current. Under stronger currents, emigration can be drastically reduced, especially in the upstream patches. When introducing rare long‐distance dispersal that is not subject to the current, higher emigration probabilities evolve and the spatial variability in emigration propensity along the stream is reduced. Our results provide an alternative solution to the long debated ‘drift paradox' concerning the loss of individuals from upstream populations due to advective forces. A combination of natural selection and spatial sorting generates and maintains downstream gradients in dispersal propensity, where individuals from upstream populations tend to be substantially more philopatric. This is likely to have major implications for ecological and genetic connectivity that will impact effective management strategies for populations inhabiting currents.

Phenotype‐dependent downstream dispersal under ordinary flow conditions in juvenile white‐spotted char

“…Therefore, further studies, including common‐garden experiments and field experiments using natural streams, are needed to validate our evolutionary hypothesis. Despite these limitations, the present study is a pioneering attempt to consider the downstream dispersal of riverine organisms as a sorting pressure (see also Allgayer et al, 2021; Yamada & Wada, 2021). This perspective could contribute to a better understanding of the evolution of riverine organisms in future studies.…”

“…For this reason, sorting pressures are generally not regarded to have a cumulative effect (Lee, 2011). However, in riverine systems, recent studies have shown that sorting pressures caused by downstream dispersal can be cumulative (Allgayer et al, 2021). Allgayer et al (2021) examined individual‐based evolutionary models that included selection pressures from natural selection and sorting pressure and found that cumulative sorting pressure can swamp natural selection and drive evolutionary changes that reduce dispersal tendencies in upstream populations.…”

“…However, in riverine systems, recent studies have shown that sorting pressures caused by downstream dispersal can be cumulative (Allgayer et al, 2021). Allgayer et al (2021) examined individual‐based evolutionary models that included selection pressures from natural selection and sorting pressure and found that cumulative sorting pressure can swamp natural selection and drive evolutionary changes that reduce dispersal tendencies in upstream populations. Therefore, knowledge of sorting pressures caused by downstream dispersal should be important for gaining a better understanding of the evolution of riverine organisms.…”

Contrasted propensity for waterborne and airborne dispersal between two closely related semi‐aquatic spider species

“…Long‐distance dispersal seems of primary importance for the sustainability and conservation of threatened species (Trakhtenbrot et al, 2005). Combining dispersal information, mark‐recapture and landscape genetic or genomic (reviewed by Manel et al, 2003; Manel & Holderegger, 2013) in models like the one developed by Allgayer et al (2021) would permit to understand population dynamics of Dolomedes along streams. Ultimately, the gene flow and population dynamic might be threatened by habitat fragmentation and loss of interconnected wetlands due to limited propensity for long‐distance dispersal, especially for D. plantarius .…”

Scaling up and down: movement ecology for microorganisms

“…Connections between these microbiological studies and the broader study of range size and expansion may be important for extending existing theory to microorganisms and for generating new hypotheses about how populations spread in a spatial context [60,72]. In addition to affecting spatial patterns, intraspecific movement heterogeneity may have important implications for evolutionary dynamics [73,74], by modifying gene flow or through the evolution of motility itself if intraspecific motility differences have a heritable genetic component.…”