Differential reproductive plasticity under thermal variability in a freshwater fish ( Danio rerio )

Abstract

Human-driven increases in global mean temperatures are associated with concomitant increases in thermal variability. Yet, few studies have explored the impacts of thermal variability on fitness-related traits, limiting our ability to predict how organisms will respond to dynamic thermal changes. Among the myriad organismal responses to thermal variability, one of the most proximate to fitness—and, thus, a population's ability to persist—is reproduction. Here, we examine how a model freshwater fish ( Danio rerio ) responds to diel thermal fluctuations that span the species's viable developmental range of temperatures. We specifically investigate reproductive performance metrics including spawning success, fecundity, egg provisioning and sperm concentration. Notably, we apply thermal variability treatments during two ontogenetic timepoints to disentangle the relative effects of developmental plasticity and reversible acclimation. We found evidence of direct, negative effects of thermal variability during later ontogenetic stages on reproductive performance metrics. We also found complex interactive effects of early and late-life exposure to thermal variability, with evidence of beneficial acclimation of spawning success and modification of the relationship between fecundity and egg provisioning. Our findings illuminate the plastic life-history modifications that fish may undergo as their thermal environments become increasingly variable.

Thermal variability induces sex‐specific morphometric changes in zebrafish (Danio rerio)

“…We used a factorial experimental design to contrast the contributions of “early” fluctuating temperature exposure, “later” fluctuating temperature exposure, and their interaction towards variation in body shape and size (Huey et al, 1999; Massey et al, 2022). Briefly, we split clutches of fish during embryonic and larval stages, placing them in either C or F early temperature treatments until the approximate juvenile stage was reached (30 days post‐fertilization [dpf]).…”

“…We used 30 dpf to define the early ontogenetic period because it is largely recognized as the onset of the juvenile period, at which adult characteristics are defined in the absence of sexual maturity, reflecting a natural widely used timepoint for investigating early developmental effects (Bradford et al, 2022; Parichy & Kaplan, 1995). Because it is a recognized standard, this timepoint allows for comparisons with other experimental studies (e.g., Massey et al, 2022).…”

“…The fish photographed in this experiment were originally part of a larger study using the long‐term experimental treatments described herein (Massey et al, 2022) in order to ethically increase the scientific value of their use. All 2021 studies on this colony were approved by the Dalhousie University Committee on Laboratory Animals (Protocol 19‐105).…”

“…Because it is a recognized standard, this timepoint allows for comparisons with other experimental studies (e.g., Massey et al, 2022).…”

“…The fish photographed in this experiment were originally part of a larger study using the long-term experimental treatments described herein (Massey et al, 2022)…”