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Abstract Populations across a species’ range may be locally adapted, and failure to recognize this variation can lead to inaccurate predictions of their resilience or vulnerability to climate change. Because life history traits are directly linked to fitness, life history theory can serve as a useful framework for evaluating how populations within species may respond to rapid environmental change. However, relatively few studies quantify multiple life history traits and their tradeoffs across many populations, especially in marine taxa. Here, we used a 10-month laboratory experiment to quantify a suite of reproductive traits in populations spanning the strongest latitudinal temperature gradient in the world’s coastal oceans. We examined reproductive traits in wild-captured adults exposed to simulated local conditions for 7 native Atlantic and 4 introduced Pacific populations of the marine predatory gastropodUrosalpinx cinerea. Our data reveals that reproductive season length, the number of reproductive attempts, and annual fecundity unimodally peaked at mid-latitude populations, the species’ range-center. Introduced populations had comparably few spawning attempts and low fecundity despite a longer reproductive period in a less seasonal environment. We then conducted a second experiment quantifying thermal tolerance of developing embryos from 3 native populations, which revealed high sensitivity to temperature at early life stages but weak population differentiation. Taken together, our data reveal stark differences in reproduction that appear to reflect “fast” and “slow” paced lifestyles, which may maximize fitness by spreading the risk of reproductive failure over a single season or lifetime. Our results indicate that warm range-edge populations are highly vulnerable to warming, as low embryonic thermal tolerance may shorten the spawning season and warming is likely to reduce fecundity. This study highlights heterogeneity in life history traits across marine populations that may underlie differential vulnerability to climate warming. Open research statementAll data and code will be publicly available via Figshare and the NSF Biological and Chemical Oceanography Data Management Office (BCO-DMO). 

Understanding how latitudinal temperature variation shapes local adaptation of life history strategies is crucial for predicting future responses to warming. Contrasting predictive frameworks explain how growth and other life history traits may respond to differing selective pressures across latitude. However, these frameworks have rarely been explored within the context of fluctuating environmental temperatures across longer (i.e., seasonal) time scales experienced in nature. Furthermore, consequences of growth differences for other aspects of fitness, including reproductive output, remain unclear. Here, we conducted a long-term (17-month) simulated reciprocal transplant experiment to examine local adaptation in two populations of the predatory marine snail Urosalpinx cinerea separated by 8.6 degrees latitude (1000 km). We reared F1 offspring under two seasonally fluctuating temperature regimes (warm and cold, simulating field thermal conditions experienced by low and high latitude populations, respectively), quantifying temporal patterns in growth, maturation, and reproductive output. We identified striking divergence in life-history strategies between populations in the warm regime, with offspring from the low latitude population achieving greater growth in their first year, and high reproductive output coupled with reduced growth in their second year. In contrast, the high latitude population grew slower in their first year, but eventually attained larger sizes in their second year, at the expense of reduced reproductive output. Responses were consistent with this in the cold regime, although growth and reproductive output was reduced in both populations. Our data provides support for adaptive divergence across latitude consistent with the Pace-of-Life hypothesis, with the low latitude population selected for a fast-paced life characterized by rapid development and early reproduction. In contrast, the high latitude population exhibited slower growth and delayed maturation. Our results highlight the potential limitations of short-term comparisons of growth without considering processes over longer time scales that may exhibit seasonal temperature variation and ontogenetic shifts in energy allocation and imply a radical reshaping of physiological performance and life history traits across populations under climate change.