Does Size Matter Most? The Effect of Growth History on Probabilistic Reaction Norm for Salmon Maturation

Abstract

Abstract. Body size is widely believed to affect the occurrence of sexual maturation. Recent studies have used changes in the age-specific body size at which the probability of maturing is 50%, a feature of probabilistic reaction norms, to quantify purported evolution of life histories. However, body size results from a combination of growth rates during successive developmental stages. Therefore, to understand the evolution of the maturation schedule, it is necessary to comprehend the relationships among body size, growth history, and maturation schedule. We examined the relationships among body size, previous growth history, and maturation probability in chum salmon (Oncorhynchus keta). In this study, previous growth history was estimated from yearly specific growth increments that provide information describing body size. Previous growth history was found to be more closely linked to maturation probability than body size. The most recent growth condition was the most important factor affecting whether a fish matured during the subsequent breeding season. Because individuals of similar body size and same age can have different growth histories, the relationship between body size and maturation probability could be plastically modified by growth history. This may violate an assumption required to infer evolution, namely that size-related maturation trends in probabilistic reaction norms are immune to growth history.

Changes in the plasma levels of insulin-like growth factor-I from the onset of spawning migration through upstream migration in chum salmon

“…This result coincides well with the report by Morita and Fukuwaka (2006). They estimated growth history from annuli of scales in hatchery-arrived chum salmon, and showed that the recent growth rate is the most important factor for oceanic fish to determine whether mature or not mature in the subsequent spawning period.…”

Trait changes in a harvested population are driven by a dynamic tug-of-war between natural and harvest selection

“…2), supporting the view that reduced reproductive investment was not only a response to strengthening natural selection but also related to increased life expectancy. Finally, somatic body condition had a positive effect on investment (significant on gonad weight and egg number) ( Table 1), confirming that surplus energy gained before reproduction plastically affects energy allocation to reproduction (23).…”

“…Importantly, we have accounted for the plastic effect of short-term variation in growth conditions in our reaction norm approach. Indeed, in teleosts plasticity in reproductive decisions is affected by the rate of surplus energy gained during critical periods (23). In Windermere pike, energy used for reproduction in March and April is gained during the previous summer (15).…”

Marine growth patterns of southern British Columbia chum salmon explained by interactions between density-dependent competition and changing climate

“…We used the annual scale growth between the first and third winters at sea to represent cumulative early growth because Morita and Fukuwaka (2006) found that growth during the second and third year at sea best predicted the probability of maturation for chum salmon.…”