Faster juvenile growth promotes earlier sex change in a protandrous hermaphrodite (barramundi Lates calcarifer)

The relationship between growth and sexual maturation is central to understanding the dynamics of animal populations which exhibit indeterminate growth. In sequential hermaphrodites, which undergo post-maturation sex change, the size and age at which sex change occurs directly affects reproductive output and hence population productivity. However, these traits are often labile, and may be strongly influenced by heterogenous growth and mortality rates. We analysed otolith microstructure of a protandrous (i.e., male-to-female) fish (barramundi Lates calcarifer) to examine growth in relation to individual variation in the timing of sex change. Growth trajectories of individuals with contrasting life histories were examined to elucidate the direction and extent to which growth rate influences the size and age individuals change sex. Then, the relationships between growth rate, maturation schedules and asymptotic maximum size were explored to identify potential trade-offs between age at female maturity and growth potential. Rapid growth was strongly associated with decreased age at sex change, but this was not accompanied by a decrease in size at sex change. Individuals that were caught as large females grew faster than those caught as males, suggesting that fast-growing individuals ultimately obtain higher fitness and therefore make a disproportionate contribution to population fecundity. These results indicate that individual-level variation in maturation schedules is not reflective of trade-offs between growth and reproduction. Rather, we suggest that conditions experienced during the juvenile phase are likely to be a key determinant of post-maturation fitness. These findings highlight the vulnerability of sex-changing species to future environmental change and harvest

Climate change and its implications for Australia's freshwater fish

Freshwater environments and their fishes are particularly vulnerable to climate change because the persistence and quality of aquatic habitat depend heavily on climatic and hydrologic regimes. In Australia, projections indicate that the rate and magnitude of climate change will vary across the continent. We review the likely effects of these changes on Australian freshwater fishes across geographic regions encompassing a diversity of habitats and climatic variability. Commonalities in the predicted implications of climate change on fish included habitat loss and fragmentation, surpassing of physiological tolerances and spread of alien species. Existing anthropogenic stressors in more developed regions are likely to compound these impacts because of the already reduced resilience of fish assemblages. Many Australian freshwater fish species are adapted to variable or unpredictable flow conditions and, in some cases, this evolutionary history may confer resistance or resilience to the impacts of climate change. However, the rate and magnitude of projected change will outpace the adaptive capacities of many species. Climate change therefore seriously threatens the persistence of many of Australia's freshwater fish species, especially of those with limited ranges or specific habitat requirements, or of those that are already occurring close to physiological tolerance limits. Human responses to climate change should be proactive and focus on maintaining population resilience through the protection of habitat, mitigation of current anthropogenic stressors, adequate planning and provisioning of environmental flows and the consideration of more interventionist options such as managed translocations

Regional climate, primary productivity and fish biomass drive growth variation and population resilience in a small pelagic fish

International audienceEnvironmental change often combined with selective harvesting has profound and diverse impacts on marine fish populations. Unlocking the biological consequences of these effects on wild fish is notoriously challenging, especially in highly productive but naturally variable systems with uncertain futures such as Eastern Boundary current systems. Here, we developed otolith increment-based growth chronologies covering half a century (53 years) for a small pelagic fish (Atlantic horse mackerel, Trachurus trachurus) in the northern limb of the Canary current upwelling system. We used increasingly complex mixed-effects models to partition individually resolved growth variation among intrinsic (Age and Age-at-capture) and extrinsic (biotic and abiotic factors) sources in four complementary data sets: a general population chronology, and three chronologies derived from age groups that reflect ontogenetic habitat shifts. First, we investigated the timing and scale of growth phase shifts and assessed the effects of extrinsic factors on inter-annual growth variation. Second, we quantified among and within cohort growth variability over time. Our results provided strong evidence for inter-annual SST and primary productivity variation impacting on Atlantic horse mackerel growth. We also identified phase shifts in growth that point to larger ecosystem-wide changes (regime shifts), potentially driven by large-scale climatic indices, such as North Atlantic Oscillation and East Atlantic pattern. Cohort-dependent growth effects likely reflect persistent environmental influences and density dependence. Further, we found evidence for carryover effects in growth whereby a poor start in life tended to persist despite compensatory growth being observed in some individuals. We show how population productivity can be impacted by multiple, interacting environmental and biotic factors leading to potential ecosystem regime shifts. Such information is key to understand recruitment dynamics and population persistence, and will have important implications for fisheries management and to those seeking to understand the effects of large-scale climate change on marine productivity

Migration to freshwater increases growth rates in a facultatively catadromous tropical fish

Diadromy is a form of migration where aquatic organisms undergo regular movements between fresh and marine waters for the purposes of feeding and reproduction. Despite having arisen in independent lineages of fish, gastropod molluscs and crustaceans, the evolutionary drivers of diadromous migration remain contentious. We test a key aspect of the ‘productivity hypothesis’, which proposes that diadromy arises in response to primary productivity differentials between marine and freshwater habitats. Otolith chemistry and biochronology data are analysed in a facultatively catadromous tropical fish (barramundi, Lates calcarifer) to determine the effect of freshwater residence on growth rates. Individuals that accessed freshwater grew ~ 25% faster on average than estuarine residents in the year following migration, suggesting that catadromy provides a potential fitness advantage over non-catadromous (marine/estuarine) life histories, as predicted by the productivity hypothesis. Although diadromous barramundi exhibited faster growth than non-diadromous fish, we suggest that the relative reproductive success of diadromous and non-diadromous contingents is likely to be strongly influenced by local environmental variability such as temporal differences in river discharge, and that this may facilitate the persistence of diverse life history strategies within populations

Children's implicit knowledge of harmony in Western music

Three experiments examined children's knowledge of harmony in Western music. The children heard a series of chords followed by a final, target chord. In Experiment 1, French 6- and 11-year-olds judged whether the target was sung with the vowel /i/ or /u/. In Experiment 2, Australian 8- and 11-year-olds judged whether the target was played on a piano or a trumpet. In Experiment 3, Canadian 8- and 11-year-olds judged whether the target sounded good (i.e. consonant) or bad (dissonant). The target was either the most stable chord in the established musical key (i.e. the tonic, based on do, the first note of the scale) or a less stable chord. Performance was faster (Experiments 1, 2 and 3) and more accurate (Experiment 3) when the target was the tonic chord. The findings confirm that children have implicit knowledge of syntactic functions that typify Western harmony