The timing of spring warming shapes reproductive effort in a warm-water fish: the role of mismatches between hepatic and gonadal processes

Spring-spawning fishes native to northern environments rely on both increasing temperature and lengthening photoperiod to cue reproduction and may thus be particularly sensitive to rapid warming earlier in the year while day lengths remain short. We investigated the reproductive response of pumpkinseed sunfish Lepomis gibbosus to spring warming commencing at a range of day lengths (9 – 15 hours), corresponding to various calendar days (January 10 – May 22). In both the laboratory and field, both male and female fish that experienced early warming while day lengths were <11 hours: 1) failed to initiate reproductive preparation in the liver before gonad development began, and 2) had reduced reproductive allocation. Analysis of published data on temperate fishes suggested that liver development prior to gonad development is widespread across warm-, cool-, and cold-water thermal guilds, though the precise phenology of liver relative to gonad development appears to vary widely among species. Together, our results point toward dampened reproductive preparation as a novel mechanism mediating reduced reproductive output in both warm- and cool-water fish following earlier spring warming.
Methods
Data were collected from lethal samples of pumpkinseed either from laboratory experiments or field collections. All measurements were collected within 4 hours of fish euthanization. All euthanized fish were kept on ice and collected with appropriate animal care protocol approvals and animal collections permits (see manuscript for more information). The attached data file includes unprocessed raw data (organ and fish masses). Indices followed by a "1" (GSI1 = GSI; LSI1 = HSI) were calculated as indicated in the manuscript. Indices without a "1" were calculated without removing the mass of the indexed organ from fish wet weight (e.g., LSI = HSI = WETLIVWT / WETBODWT*100).