Age Structure and Life Expectancy in a Stellagama stellio (Linnaeus, 1758) Population from Kütahya, Turkey

The life history traits of the rough-tailed agama, Stellagama stellio (Linnaeus, 1758) in a population from Kütahya, Turkey were described by the skeletochronological method. From a total of 54 individuals, the mean ages ± standard deviation (SD) of males and females were calculated as 5.03 ± 2.076 years and 4.79 ± 1.584 years, respectively, and age distributions were not significantly different between sexes. The age at maturity was 2 years for both sexes. The longevity of females was 8 years, whereas for males it was 9 years. Mean snout-vent length (SVL) ± SD was 101.7 ± 9.6 mm in females and 104.9 ± 14.4 mm in males and did not significantly differ between the two sexes. We examined the sexual dimorphism of S. stellio in relation to the difference in population age structure between the sexes using the skeletochronological method. Male individuals were slightly larger than female individuals at the same age, but this difference was not statistically significant. We also estimated the maximum ages for S. stellio, which agree with other populations in Turkey.

Environmentally Modulated Repeat Evolution of Polymorphic Arctic Charr Life History Traits

Sympatric Arctic charr, Salvelinus alpinus (L. 1758), morphs have flexible but repeated life history strategies tested across five Norwegian lakes. In several Scandinavian polymorphic Arctic charr populations differentiated by their diet and habitat use, a large littoral omnivorous (LO) morph commonly cooccurs with a smaller profundal spawning (PB/PZ) morph. A third, large piscivorous (PP) morph is also known to occur within a portion of Arctic charr populations in the profundal habitat along with the PB/PZ individuals. Life history traits, such as age at maturity, growth, and diet are known to differ among coexisting morphs. Notably, the PP morph was the longest morph with the oldest age at maturity while the PB/PZ morph showed the shortest lengths overall and youngest age with LO morph being intermediate in both traits. Growth parameters differed across all the morphs. When examining growth within morph groups, the LO morph was found to have different growth across all lakes, while similar reproductive investments and different energy acquisition patterns were seen within the PB/PZ and PP morphs. These results suggest repeat evolution in several life history strategies of reproductively isolated Arctic charr sympatric morphs, notably for the first time in the PP morph, while also highlighting the importance of the local environment in modulating life history traits.

Older but not wider. Impacts of molt frequency variation on age and growth dynamics of Newfoundland & Labrador snow crab (Chionoecetes opilio) toward corroborating gastric mill 2 age estimations

Aging specimen and survey data from a heterogeneous stock range are combined to investigate effects of molt frequency variation on age and growth dynamics and efficacy of gastric mill age band estimations in snow crab. A central assumption that bands form independent of molting is examined through analyses of molt frequency variation with an overall result of support for the hypothesis that gastric mill bands form independent of molting. This is based on an applied review approach, demonstrating blind age estimation results within and across population units featuring different rates of molt frequency interruptions in context of literature-based expected outcomes of age and growth dynamics. The comprehensive analyses overall supports the ability of gastric mill bands to track chronological ages, but non-fully explained outcomes of growth delays into sexual maturity stages in males and potential estimation error in 1-3 year old crab preclude a conclusion that absolute ages are consistently tracked throughout ontogeny. The results suggest gastric mill bands continue to form during both skip-molts and after terminal molt. Despite uncertainties, the research highlights that males originating from populations where skip-molting is prominent are older reaching fishery size than previously thought (9-10 years), with tentative average estimates of 10-12 years. The study presents novel observations of size-at-age and age-at-maturity in Newfoundland & Labrador (NL) snow crab and broadens life history knowledge for the species. Along with corroborating gastric mill age band estimations, the study reveals future research streams to further help advance the discipline of aging crustaceans [247].

The influences of pre- and post-smolt captive rearing environments on growth, maturation, body size, and reproductive success of steelhead (Oncorhynchus mykiss) released as adults.

Conservation hatcheries designed to aid in recovery of imperiled fish population often implement atypical rearing and release strategies. We evaluated a conservation hatchery program for steelhead (Oncorhynchus mykiss) that hydraulically removed naturally spawned eggs, and captively reared them in different freshwater hatcheries to the smolt stage, and reared smolts in both freshwater and seawater to sexual maturity, before releasing the sexually maturing adults onto the spawning grounds. The adult steelhead added to the spawning population, accounting for most of the adults observed during snorkel observations. They produced 32% of the juvenile offspring sampled, and females were 2.9 times more successful than males. Reproductive success was positively correlated with female body size, which was influenced by pre-smolt and post-smolt rearing conditions and their effects on growth rate and age-at-maturity. Juvenile offspring of the released adults showed size and age differences from offspring of naturally returning steelhead, but exhibited very similar early marine survival rates.

Variation in body size of ringed seals (Pusa hispida hispida) across the circumpolar Arctic: evidence of morphs, ecotypes or simply extreme plasticity?

The ringed seal is a small phocid seal that has a northern circumpolar distribution. It has long been recognized that body size is variable in ringed seals, and it has been suggested that ecotypes that differ in size exist. This study explores patterns of body size (length and girth) and age-at-maturity across most of the Arctic subspecies’ range using morphometric data from 35 sites. Asymptotic lengths varied from 113 to 151 cm, with sites falling into five distinct size clusters (for each sex). Age-at-maturity ranged from 3.1 to 7.4 years, with sites that had early ages of sexual maturity generally having small length-at-maturity and small final body length. The sexes differed in length at some sites, but not in a consistent pattern of dimorphism. The largest ringed seals occurred in western Greenland and eastern Canada, and the smallest occurred in Alaska and the White Sea. Latitudinal trends occurred only within sites in the eastern Canadian Arctic. Girth (with length and season accounted for) was also highly variable but showed no notable spatial pattern; males tended to be more rotund than females. Genetic studies are needed, starting with the “giants” at Kangia (Greenland) and in northern Canada to determine whether they are genetically distinct ecotypes. Additional research is also needed to understand the ecological linkages that drive the significant regional size differences in ringed seals that were confirmed in this study, and also to understand their implications with respect to potential adaptation to climate change.

Applications

By affecting age-specific survival and fecundity, human-induced disturbances affect life history. This has potential to affect r max with negative consequences for species viability and persistence. Several types of assessments are used to classify vulnerability to extinction, exploitation, and climate change. When information on r max is unavailable, vulnerability assessments often rely on life-history correlates of r max. These have included generation time, age at maturity, maximum size, longevity, fecundity, natural mortality, and individual growth rate. Empirical research indicates that links with r max are strong for some traits, such as age at maturity and body size, but weak for others, such as fecundity. In addition to assessments of declining species, efforts have been made to identify life-history correlates of the rate and uncertainty in species recovery. Persistence and stability can be strengthened by the magnitude of life-history variation. The greater the variability in life history within and among, the greater the resistance and resilience of populations and species.

Genetic coupling of life-history and aerobic performance in juvenile Atlantic salmon

1. The physiological underpinnings of life history adaptations in ectotherms are not well understood. Theories suggest energy metabolism influences life history variation via modulation of resource acquisition. However, the genetic basis of this relation and its dependence on ecological conditions, such as food availability, have rarely been characterized, despite being critical to predicting the responses of populations to environmental changes. 2. The Atlantic salmon (Salmo salar) is an emerging wild model species for addressing these questions; strong genetic determination of age-at-maturity at two unlinked genomic regions (vgll3 and six6) enables the use of complex experimental designs and tests of hypotheses on the physiological and genetic basis of life-history trait variation. 3. In this study, we crossed salmon to obtain individuals with all combinations of late and early maturation genotypes for vgll3 and six6 within full-sib families. Using more than 250 juveniles in common garden conditions, we tested (i) whether metabolic phenotypes (i.e., standard and maximum metabolic rates, and absolute aerobic scope) were correlated with the age-at-maturity genotypes and (ii) if high vs. low food availability modulated the relationship. 4. We found that salmon with vgll3 early maturation genotype had a higher aerobic scope and maximum metabolic rate, but not standard metabolic rate, compared to salmon with vgll3 late maturation genotype. This suggests that physiological or structural pathways regulating maximum oxygen supply or demand are potentially important for the determination of age-at-maturity in Atlantic salmon. 5. Vgll3 and six6 exhibited physiological epistasis, whereby maximum metabolic rate significantly decreased when late maturation genotypes were present concurrently in both loci compared to other genotype combinations. 6. The growth of the feed restricted group decreased substantially compared to the high food group. However, the effects of life-history genomic regions were similar in both feeding regimes, indicating a lack of genotype-by-environment interactions. 7. Our results indicate that aerobic performance of juvenile salmon may affect their age-at-maturity. The results may help to better understand the mechanistic basis of life-history variation, and the metabolic constrains on life-history evolution.

Evolution in salmon life-history induced by direct and indirect effects of fishing

Understanding the drivers of evolution is a fundamental aim in biology. However, identifying the evolutionary impacts of human activities, both direct and indirect, is challenging because of lack of temporal data and limited knowledge of the genetic basis of most traits1. Atlantic salmon is a species exposed to intense anthropogenic pressures during its anadromous life cycle. Previous research has shown that salmon age at maturity has evolved towards earlier maturation over the last 40 years, with an 18% decrease in the allele associated with late maturation at the large-effect vgll3 locus; but the drivers of this change remain unknown. Here, we link genetic and phenotypic changes in a large Atlantic salmon population with salmon prey species biomass in the Barents Sea, temperature, and fishing effort in order to identify drivers of age at maturity evolution. We show that age at maturity evolution is associated with two different types of fisheries induced evolution acting in opposing directions: an indirect effect linked with commercial harvest of a salmon prey species (capelin) at sea (selection against late maturation), and a direct effect due to temporal changes in net fishing pressure in the river (surprisingly, selection against early maturation). Although the potential for direct and indirect evolutionary effects of fishing have been acknowledged, empirical evidence for induced changes at the genetic level has been lacking. As capelin are primarily harvested to produce fish meal and oil for aquaculture, we hereby identify an indirect path by which Atlantic salmon aquaculture may negatively affect wild populations.