Life stage dependent responses to desiccation risk in the annual killifish Nothobranchius wattersi

Abstract

To assess whether the annual killifish Nothobranchius wattersi responds plastically to a desiccation risk and whether this response is life stage dependent, life-history traits such as maturation time, fecundity and life span were experimentally measured in N. wattersi that were subjected to a drop in water level either as juveniles, as adults or both as juveniles and adults. Fish that were exposed to simulated pool drying as juveniles did not show changes in reproductive output or life span. Adults reacted by doubling short term egg deposition at the cost of a shorter lifespan. Overall, these results suggest that annual fish species can use phenotypic plasticity to maximize their reproductive output when faced with early pond drying, but this response appears to be life-stage specific. In addition to frogs and aquatic insects, phenotypic plasticity induced by forthcoming drought is now also confirmed in annual fishes and could well be a common feature of the limited number of fish taxa that manage to survive in this extreme environment.

Squeezing out the last egg—annual fish increase reproductive efforts in response to a predation threat

“…Yet, no such trade‐off was found between exposed and control females, as fish in both treatments died at the same rates. This contradicts earlier findings on N. wattersi that were exposed to cues that signal desiccation risk (Grégoir et al., 2017), but is in line with the results of previous studies on N. furzeri , where female egg deposition was shown to decrease in the absence of males (Graf, Cellerino, & Englert, 2010). As to why such differences are found between studies remains unclear.…”

“…In Nothobranchius killifish, lifespan may be linked to the typical lengths of the inundations that they experience in their local habitat (Terzibasi Tozzini et al., 2013; Terzibasi et al., 2008). In addition, Nothobranchius may still retain some flexibility in dealing with impending pond drying as it has been shown that desiccation risk simulated by means of a drop in water level resulted in a plastic increase in egg deposition at the cost of a shorter lifespan (Grégoir et al., 2017). In this study, we test whether Nothobranchius killifish can produce similar plastic life history responses when exposed to predation risk rather than desiccation risk.…”

“…Hence, any further metabolic acceleration to mature at an even younger age might be physiologically unfeasible. In support, the congeneric N. wattersi also shows no developmental acceleration in response to a drop in water level (Grégoir et al., 2017), suggesting that such an acceleration might indeed be impossible. Secondly, as a consequence of the time stress experienced in the natural habitat, all individuals probably mature as soon as possible, even in the presence of a predator.…”

“…While the potential for phenotypic plasticity in the postembryonic life stages of Nothobranchius killifish has been demonstrated (Grégoir et al., 2017; Valenzano, Terzibasi, Cattaneo, Domenici, & Cellerino, 2006; Valenzano, Terzibasi, et al., 2006; Vrtílek & Reichard, 2015), the response of juvenile and adult individuals to predation risk by riverine fish is currently unknown. In other toothcarps, maturation could be plastically accelerated at the expense of somatic growth to increase the chances of reproductive success before being predated upon (Reznick, 1990).…”

“…Similarly, we expect a higher fecundity in exposed fish, so that potential reproductive output is maximized before being predated upon, as previously also suggested for guppies (Dzikowski et al., 2004). Similarly to what was found for N. wattersi in response to desiccation risk (Grégoir et al., 2017), we expect that any potential upregulation in maturation time or reproductive effort entails costs, such as a shorter lifespan or smaller adult body size.…”