Resistance and resilience of genetic and phenotypic diversity to “black swan” flood events: A retrospective analysis with historical samples of guppies

Abstract

Rare extreme “black swan” disturbances can impact ecosystems in many ways, such as destroying habitats, depleting resources, and causing high mortality. In rivers, for instance, exceptional floods that occur infrequently (e.g., so‐called “50‐year floods”) can strongly impact the abundance of fishes and other aquatic organisms. Beyond such ecological effects, these floods could also impact intraspecific diversity by elevating genetic drift or dispersal and by imposing strong selection, which could then influence the population's ability to recover from disturbance. And yet, natural systems might be resistant (show little change) or resilient (show rapid recovery) even to rare extreme events – perhaps as a result of selection due to past events. We considered these possibilities in two rivers where native guppies experienced two extreme floods – one in 2005 and another in 2016. For each river, we selected four sites and used archived “historical” samples to compare levels of genetic and phenotypic diversity before vs. after floods. Genetic diversity was represented by 33 neutral microsatellite markers, and phenotypic diversity was represented by body length and male melanic (black) colour. We found that genetic diversity and population structure was mostly “resistant” to even these extreme floods; whereas the larger impacts on phenotypic diversity were short‐lived, suggesting additional “resilience”. We discuss the determinants of these two outcomes for guppies facing floods, and then consider the general implications for the resistance and resilience of intraspecific variation to black swan disturbances.

Plasticity of Performance Curves in Ectotherms: Individual Variation Modulates Population Responses to Environmental Change

“…Increased variation of phenotypes can render the populations as a whole more resilient to change if different phenotypes are advantageous under different environmental conditions ( Schindler et al, 2015 ; Blondel et al, 2021 ). Plasticity is advantageous by buffering performance under cooler conditions, such as in winter, while fixed phenotypes perform better at high temperatures during summer.…”

Interpopulation variation of behavioural and morphological traits that affect downstream displacement of the juvenile white‐spotted charr Salvelinus leucomaenis

“…Small fish consistently had higher SH proportion than large fish in the above‐dam populations, but this trend was inconsistent in the open‐stream populations. Small fish are generally at high risk of downstream displacement owing to their poor swimming ability (Blondel et al ., 2021; Chapman & Kramer, 1991; Jowett & Richardson, 1989), thus the relationship observed in the above‐dam populations would more effectively reduce downstream displacement. Additionally, the SH proportions of above‐dam populations were higher than those of open‐stream populations across almost the entire estimated range of FLs.…”

“…Water flows that cause downstream displacement can be divided into two types: flood flows (Chapman & Kramer, 1991; Good et al ., 2001; Meffe, 1984; Sato, 2006; Weese et al ., 2011; Yamada & Wada, 2021) and flows under ordinary river conditions ( i.e ., ordinary flows; Lechner et al ., 2016; Nagel et al ., 2021; Thiesmeier & Schuhmacher, 1990). Although flood flows can cause catastrophic downstream displacement (Meffe, 1984; Sato, 2006; Weese et al ., 2011), occurrences of such downstream displacement are often trait‐dependent in riverine fishes (Blondel et al ., 2021; Chapman & Kramer, 1991; Good et al ., 2001; Meffe, 1984; Yamada & Wada, 2021). For example, smaller individuals are more likely to be displaced by strong floods from their home river section in populations of the molly Poecilia gillii (Kner 1863) (Chapman & Kramer, 1991) and the Trinidadian guppy Poecilia reticulata Peters 1859 (Blondel et al ., 2021).…”

“…Although flood flows can cause catastrophic downstream displacement (Meffe, 1984; Sato, 2006; Weese et al ., 2011), occurrences of such downstream displacement are often trait‐dependent in riverine fishes (Blondel et al ., 2021; Chapman & Kramer, 1991; Good et al ., 2001; Meffe, 1984; Yamada & Wada, 2021). For example, smaller individuals are more likely to be displaced by strong floods from their home river section in populations of the molly Poecilia gillii (Kner 1863) (Chapman & Kramer, 1991) and the Trinidadian guppy Poecilia reticulata Peters 1859 (Blondel et al ., 2021). Downstream displacement due to ordinary flows can also remove individuals with vulnerable traits from upstream populations.…”

High growth performance in the early ontogeny of an amphidromous fish, Ayu Plecoglossus altivelis altivelis, promoted survival during a disastrous river spate

“…Adult ayu that survived the 2018 flood showed significantly higher juvenile growth rates than the individuals collected before the spate, when comparing the individuals hatched in the same month. In reality, body length rather than instantaneous growth rate is most likely to be the phenotypic trait directly responsible for improved survival in extreme hydrological events (Blondel et al, 2021; Good et al, 2001; Jurajda et al, 2006; Mann & Bass, 1997), considering the positive correlation between body length and swimming ability (Tsukamoto et al, 1975).…”