Asymmetric Isolation and the Evolution of Behaviors Influencing Dispersal: Rheotaxis of Guppies above Waterfalls

Abstract

Populations that are asymmetrically isolated, such as above waterfalls, can sometimes export emigrants in a direction from which they do not receive immigrants, and thus provide an excellent opportunity to study the evolution of dispersal traits. We investigated the rheotaxis of guppies above barrier waterfalls in the Aripo and Turure rivers in Trinidad-the later having been introduced in 1957 from a below-waterfall population in another drainage. We predicted that, as a result of strong selection against downstream emigration, both of these above-waterfall populations should show strong positive rheotaxis. Matching these expectations, both populations expressed high levels of positive rheotaxis, possibly reflecting contemporary (rapid) evolution in the introduced Turure population. However, the two populations used different behaviors to achieve the same performance of strong positive rheotaxis, as has been predicted in the case of multiple potential evolutionary solutions to the same functional challenge (i.e., "many-to-one mapping"). By contrast, we did not find any difference in rheotactic behavior above versus below waterfalls on a small scale within either river, suggesting constraints on adaptive divergence on such scales.

Reproductive benefits associated with dispersal in headwater populations of Trinidadian guppies (Poecilia reticulata)

“…We also note that while upstream dispersal can be interpreted as active, downstream movement could be either active or passive. There were no other strong biases in up-versus downstream dispersal, consistent with previous studies of P. reticulata dispersal (Crispo et al, 2006;Croft et al, 2003) and findings of positive rheotaxis in this system (Blondel et al, 2020). As a whole, these data suggest that guppy dispersal is often active, raising questions about the environmental and individual triggers of this behaviour.…”

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

“…First, guppies and other stream fishes have evolved adaptations to cope with the effects of periodic high‐water velocities. Behavioural mechanisms include hiding, maintaining their position in the stream, or orientating quickly and efficiently against the flow as evidenced in guppies (Blondel, Klemet‐N’Guessan, et al, 2020; Blondel, Paterson, et al, 2020) and other fishes (David & Closs, 2002; Meffe, 1984). Adaptations can also be evident in life history traits, where organisms synchronize reproduction events in season with low flow probability (Lytle & Poff, 2004).…”

“…This resistance might be only “apparent,” such as if the disturbance was not actually that severe (see above), although this seems unlikely because of the observed dramatic demographic effects (Weese et al, 2011; personal observation). Hence, resistance was more likely due to mechanisms guppies have evolved that resist displacement from their home sites, including the avoidance of high current and the evolution of positive rheotaxis (Blondel, Klemet‐N’Guessan, et al, 2020; Blondel, Paterson, et al, 2020) . By contrast, phenotypic variation was not as resistant as genetic variation – which might be due to several factors.…”

“…In short, guppy population structure is strongly determined by abiotic physical features that limit gene flow in the upstream direction. At the same time, gene flow in the downstream direction is limited by biotic factors, especially the general tendency of guppies to show positive rheotaxis, where they orient and swim upstream in a current (Blondel et al, 2020; Blondel et al, 2020; Mohammed et al, 2012). Yet this biotic resistance to the effects of water flow are sensitive to rare perturbations, such as stream capture events and human‐mediated introductions (Becher & Magurran, 2000; Blondel et al, 2019).…”

Rheotaxis Response Based on Sexual Dimorphism in the Green Swordtail Fish, Xiphophorus hellerii

“…In the species, Melanotaenia australis, the abundance of superficial neuromasts that function to facilitate rheotaxis (body orientation into currents) in each body region varies greatly and varies between populations and individuals (Spiller et al, 2017). Several studies have shown that populations of guppies (Poecilia reticulata) above barrier waterfalls in the Aripo and Turure rivers in Trinidad show positive rheotaxis (Blondel et al, 2020).…”