Offspring size affects survival and subsequent reproduction in many organisms. However, studies of offspring size in large mammals are often limited to effects on juveniles because of the difficulty of following individuals to maturity. We used data from a long-term study of individually marked gray seals (Halichoerus grypus; Fabricius, 1791) to test the hypothesis that larger offspring have higher survival to recruitment and are larger and more successful primiparous mothers than smaller offspring. Between 1998 and 2002, 1182 newly weaned female pups were branded with unique permanent marks on Sable Island, Canada. Each year through 2012, all branded females returning to the breeding colony were identified in weekly censuses and a subset were captured and measured. Females that survived were significantly longer offspring than those not sighted, indicating size-selective mortality between weaning and recruitment. The probability of female survival to recruitment varied among cohorts and increased nonlinearly with body mass at weaning. Beyond 51.5 kg (mean population weaning mass) weaning mass did not influence the probability of survival. The probability of female survival to recruitment increased monotonically with body length at weaning. Body length at primiparity was positively related to her body length and mass at weaning. Three-day postpartum mass (proxy for birth mass) of firstborn pups was also positively related to body length of females when they were weaned. However, females that were longer or heavier when they were weaned did not wean heavier firstborn offspring.

Organic matter mineralization rates were measured by the accumulation of DIC + CH, in the water overlying intact cores taken from littoral and protimdal sediments of nine Quebec lakes. The variability in areal carbon mineralization is much greater within lakes than among lakes varying in trophic richness. Organic matter mineralization in littoral sediments is more variable and, on average, threefold higher than in the profundal sediments. Sixty percent of the variation in mean summer mineralization rates is explained by site depth, a surrogate variable that incorporates the effect of temperature and may also be reflecting substrate quality and(or) supply. The lakespecific characteristics most strongly correlated to the residuals of the regression with depth are catchment area-tolake area ratio (CA : LA) and water residence time. In lakes with a larger CA : LA and a shorter residence time, the amount and(or) the quality of organic matter settling to the sediments at a given depth may be reduced, resulting in the lower observed mineralization rates. Total mineralization in the sediments is, not surprisingly, greater in larger lakes but the rate per unit area is smaller, reflecting the decreased importance of the littoral zone. More than half (54-100%) of the DIC + CH, produced in the sediments is from the littoral zone. Yet, because of the large biomass in epilinmetic waters, the littoral sediments account for <20% of the sum of metabolism in the epilimnetic water column and underlying sediments. The relative importance of the sediments in metabolism in lakes is a function of both the trophy and lake morphometry. In deep lakes a smaller proportion of total respiration occurs in the sediments than in shallow lakes, and in eutrophic lakes the sediments account for a smaller proportion of total respiration than in oligotrophic lakes.

Breed. 2020. Variation in individual reproductive performance amplified with population size in a long-lived carnivore. Ecology 101(6):e03024. 10. 1002/ecy.3024

Changes in the genetic mechanisms that control sexual determination have occurred independently across the tree of life, and with exceptional frequency in teleost fishes.To investigate the genomic changes underlying the evolution of sexual determination, we sequenced a chromosome-level genome, multitissue transcriptomes, and reduced representation population data for the Atlantic halibut (Hippoglossus hippoglossus), which has an XY/XX sex determination mechanism and has recently diverged (0.9-3.8 Ma) from the Pacific halibut (Hippoglossus stenolepis), which has a ZZ/ZW system.We used frequency and coverage-based population approaches to identify a putative sex-determining factor, GSDF. We characterized regions with elevated heterozygosity and linkage disequilibrium indicating suppression of recombination across a nascent sex chromosome. We detected testis-specific expression of GSDF, the sequence of which is highly conserved across flatfishes. Based on evidence from genome-wide association, coverage, linkage disequilibrium, testis and brain transcriptomes, and sequence conservation with other flatfishes, we propose a mechanism for the recent evolution of an XY sex-determination mechanism in Atlantic halibut. Changes to the ancestral sex-determining gene DMRT1 in regulating the downstream gene GSDF probably coincided with GSDF, or a proximal regulatory element of it, becoming the primary sex-determining factor. Our results suggest changes to a small number of elements can have drastic repercussions for the genomic substrate available to sex-specific evolutionary forces, providing insight into how certain elements repeatedly evolve to control sex across taxa. Our chromosome-level assembly, multitissue transcriptomes, and population genomic data provide a valuable resource and understanding of the evolution of sexual systems in fishes. K E Y W O R D Sevolution of sex, fish, genome-wide association analyses, pleuronectiformes, sex chromosome turnover | 1687 EINFELDT ET aL.