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.

栖息于北部环境的春季产卵鱼类，依赖水温升高与光周期（photoperiod）延长作为繁殖启动的触发信号，因此在昼长仍较短的早春遭遇快速升温时，其受影响程度可能更为显著。本研究以驼背太阳鱼（Lepomis gibbosus）为研究对象，探究其在升温起始昼长范围为9~15小时（对应1月10日至5月22日的日历日期）下遭遇春季升温时的繁殖响应。无论是实验室可控环境还是野外自然生境，昼长小于11小时时经历早期升温的雌雄个体均表现出以下特征：1）在性腺发育（gonad development）启动前，肝脏未能启动繁殖相关的准备过程；2）繁殖分配（reproductive allocation）量显著降低。对温带鱼类已发表研究数据的分析表明，性腺发育前的肝脏发育过程在暖水性、温水性与冷水性鱼类的热生态类群（thermal guild）中广泛存在，不过肝脏发育相较于性腺发育的精确物候期，在不同物种间差异显著。综合上述研究结果，本研究表明，繁殖准备过程受抑制是早春升温导致暖水性与温水性鱼类繁殖产出降低的全新调控机制。