Interpopulation differences in several adult phenotypic traits suggest that New Zealand (NZ) chinook salmon (Oncorhynchus tshawytscha) are evolving into distinct populations. To further investigate this hypothesis, we compared egg sizes, fecundities, and early development rates of chinook from two NZ streams. The two NZ study populations differed in size-adjusted egg weight and gonadosomatic index, but not in size-adjusted fecundity. Egg weight, fecundity, and gonadosomatic index values for both NZ populations were different than values for chinook from Battle Creek, California, the population regarded as the ancestral NZ stock. In contrast, there was little evidence of divergence in juvenile development. Time to hatching did not differ between the two NZ study populations and heritability estimates were small with large standard errors. Evidence of a small difference in alevin growth rate may have represented an effect of yolk conversion mechanics related to egg size. Despite the similarity in development rates under shared conditions, modeling based on temperature records suggests that emergence dates in the two NZ streams may differ by 4-6 weeks, yielding significant phenotypic differences.Résumé : L'existence de différences entre populations en ce qui a trait à plusieurs caractères phénotypiques adultes laisse penser que le saumon quinnat (Oncorhynchus tshawytscha) de Nouvelle-Zélande (N.-Z.) est en train d'évoluer de façon à former des populations distinctes. Pour vérifier cette hypothèse, nous avons comparé les tailles des oeufs, les fécondités et les taux de développement dans les premiers stades de quinnats de deux cours d'eau de la N.-Z. Nous avons observé des différences entre les deux populations étudiées au chapitre du poids des oeufs corrigé selon la taille et de l'indice gonadosomatique, mais pas au chapitre de la fécondité corrigée selon la taille. Les valeurs de poids des oeufs, de fécondité et d'indice gonadosomatique des deux populations étaient différentes des valeurs obtenues chez le quinnat du ruisseau Battle, en Californie, lequel formerait le stock ancestral du quinnat de la N.-Z. Par ailleurs, on dispose de peu d'indices d'une divergence dans le développement des juvéniles. Le délai d'éclosion était le même chez les deux populations de la N.-Z., et les estimations d'héritabilité étaient faibles, avec de fortes erreurs-types. Les données montrant l'existence d'une petite différence dans le taux de croissance des alevins pourraient s'expliquer par la mécanique de conversion du vitellus en rapport avec la taille de l'oeuf. Malgré la similitude des taux de développement dans des conditions similaires, la modélisation fondée sur les données de température laisse penser que les dates d'émergence dans les deux cours d'eau de la N.-Z. peuvent différer de 4 à 6 semaines, ce qui témoigne de différences phénotypiques importantes.[Traduit par la Rédaction] Kinnison et al. 1953

Spawning date is a crucial life history trait in fishes, linking parents to their offspring, and it is highly heritable in salmonid fishes. We examined the spawning dates of coho salmon Oncorhynchus kisutch and chinook salmon O. tshawytscha at the University of Washington (UW) Hatchery for trends over time. We then compared the spawning date patterns with the changing thermal regime of the Lake Washington basin and the spawning patterns of conspecifics at two nearby hatcheries. The mean spawning dates of both species have become earlier over the period of record at the UW Hatchery (since the 1950s for chinook salmon and the 1960s for coho salmon), apparently because of selection in the hatchery. Countering hatchery selection for earlier spawning are the increasingly warmer temperatures experienced by salmon migrating in freshwater to, and holding at, the hatchery. Spawning takes place even earlier at the Soos Creek Hatchery, the primary ancestral source of the UW populations, and at the Issaquah Creek Hatchery. Both species of salmon have experienced marked shifts towards earlier spawning at Soos Creek and Issaquah Creek hatcheries despite the expectation that warmer water would lead to later spawning. Thus, inadvertent selection at all three hatcheries appears to have resulted in progressively earlier spawning, overcoming selection from countervailing temperature trends.

A unique feature of sex in Crassostrea oysters is the coexistence of protandric sex change, dioecy, and hermaphroditism. To determine whether such a system is genetically controlled, we analyzed sex ratios in 86 pairmated families of the Pacific oyster, Crassostrea gigas Thunberg. The overall female ratios of one-, two-, and threeyear-old oysters were 37%, 55%, and 75%, respectively, suggesting that a significant proportion of oysters matured first as males and changed to females in later years. Detailed analysis of sex ratios in factorial and nested crosses revealed significant paternal effects, which corresponded to two types of sires. No major maternal effects on sex were observed. Major genetic control of sex was further indicated by the distribution of family sex ratios in two to four apparently discreet groups. These and other data from the literature are compatible with a single-locus model of primary sex determination with a dominant male allele (M) and a protandric female allele (F), so that MF are true males and FF are protandric females that are capable of sex change. The rate of sex change of FF individuals may be influenced by secondary genes and/or environmental factors. Strong maternal and weak paternal effects on sexual maturation or time of spawning were also suggested.

A unique feature of sex in Crassostrea oysters is the coexistence of protandric sex change, dioecy, and hermaphroditism. To determine whether such a system is genetically controlled, we analyzed sex ratios in 86 pair-mated families of the Pacific oyster, Crassostrea gigas Thunberg. The overall female ratios of one-, two-, and three-year-old oysters were 37%, 55%, and 75%, respectively, suggesting that a significant proportion of oysters matured first as males and changed to females in later years. Detailed analysis of sex ratios in factorial and nested crosses revealed significant paternal effects, which corresponded to two types of sires. No major maternal effects on sex were observed. Major genetic control of sex was further indicated by the distribution of family sex ratios in two to four apparently discreet groups. These and other data from the literature are compatible with a single-locus model of primary sex determination with a dominant male allele (M) and a protandric female allele (F), so that MF are true males and FF are protandric females that are capable of sex change. The rate of sex change of FF individuals may be influenced by secondary genes and/or environmental factors. Strong maternal and weak paternal effects on sexual maturation or time of spawning were also suggested.

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