Latitudinal but not elevational variation in blood glucose level is linked to life history across passerine birds

Macrophysiological research is vital to our understanding of mechanisms underpinning global life history variation and adaptation under diverse environments. Birds represent an important model taxon in this regard, yet our knowledge is limited to only a few physiological traits, mostly studied in temperate and Neotropical species. Here, we examined latitudinal and elevational variation in an emerging biomarker of physiological pace of life, blood glucose concentration, collected from 61 European temperate and 99 Afrotropical passerine species. Our data suggest that the slow physiological pace-of-life syndrome, indicated by lower baseline glucose level and stronger stress response, evolves convergently in lowland tropical birds across continents and is shaped by their low fecundity. In contrast, elevational variation in blood glucose levels implied a unique montane pace-of-life syndrome combining slow-paced life histories with fast-paced physiology. The observed patterns suggest an unequal importance of life history in shaping physiological adaptations associated with latitude and elevation.

Intraspecific variation in migration timing of green sturgeon in the Sacramento River system

BackgroundUnderstanding movement patterns of anadromous fishes is critical to conservation management of declining wild populations and preservation of habitats. Yet, infrequent observations of individual animals fundamentally constrain accurate descriptions of movement dynamics.MethodsIn this study, we synthesized over a decade (2006–2018) of acoustic telemetry tracking observations of green sturgeon (Acipenser medirostris) in the Sacramento River system to describe major anadromous movement patterns.ResultsWe observed that green sturgeon exhibited a unimodal in-migration during the spring months but had a bimodal distribution of out-migration timing, split between an ‘early’ out-migration (32%) group during May - June, or alternatively, holding in the river until a ‘late’ out-migration (68%), November - January. Focusing on these out-migration groups, we found that river discharge, but not water temperature, may cue the timing of migration, and that fish showed a tendency to maintain out-migration timing between subsequent spawning migration events.ConclusionsWe recommend that life history descriptions of green sturgeon in this region reflect the distinct out-migration periods described here. Furthermore, we encourage the continued use of biotelemetry to describe migration timing and life history variation, not only this population but other green sturgeon populations and other species.

Chasing the fitness optimum: temporal variation in the genetic and environmental expression of life-history traits for a perennial plant

The ability of plants to track shifting fitness optima is crucial within the context of global change, where increasing environmental extremes may have dramatic consequences to life history, fitness, and ultimately species persistence. However, to track changing conditions relies upon the complex relationship between genetic and environmental variance, where selection may favor plasticity, the evolution of genetic differences, or both depending on the spatial and temporal scale of environmental heterogeneity. Over three years, we compared the genetic and environmental components of phenological and life-history variation in a common environment for the spring perennial Geum triflorum. Populations were sourced from alvar habitats that exhibit extreme, but predictable annual flood-desiccation cycles and prairie habitats that exhibit similar, but less predictable variation in water availability. Narrow-sense heritabilities were generally higher for early life history (emergence probability) relative to later life history traits (total seed mass), indicating that traits associated with establishment within an environment are under stronger genetic control relative to later life-history fitness expressions, where plasticity may play a larger role. This pattern was particularly notable in seeds sourced from environmentally extreme, but predictable alvar habitats relative to less predictable prairie seed sources. Fitness landscapes based on seed source origin, largely characterized by varying water availability and flower production, described selection as the degree of maladaptation to the prairie common garden environment relative to seed source environment. Plants from alvar populations were consistently closer to the fitness optimum across all years. Annually, the breadth of the fitness optimum expanded primarily along a moisture gradient, with inclusion of more populations onto the expanding optimum. These results highlight the importance of temporally and spatially varying selection for the evolution of life history, indicating plasticity within perennial systems may over time become the primary mechanism to track fitness for later life history events.

Climate-induced habitat suitability intensifies fishing-induced life-history variation of a migratory long-lived fish

Intense fishing pressure and climate change are major threats to coastal fisheries. Larimichthys crocea (large yellow croaker) is a long-lived fish, which performs seasonal migrations from its spawning and nursery grounds along the coast of the East China Sea (ECS) to overwintering grounds offshore. This study used length-based analysis and habitat suitability index (HSI) model to evaluate current life-history parameters and overwintering habitat suitability of L. crocea, respectively. We compared both life-history parameters and overwintering HSI between recent (2019) and historical (between 1971 to 1982) to analyze the fishing pressure and climate change effects on the overall population and overwintering phase of L. crocea. In the context of overfishing, the length-based analysis indicated serious overfishing of L. crocea, characterized by reduced catch yield, size truncation, constrained distribution, and advanced maturation in the ECS, namely recruitment bottleneck. In the context of climate change, the overwintering HSI modeling results indicated that climate change has led to decreased sea surface temperature during L. crocea overwintering phase over the last half-century, which in turn led to area decrease and an offshore-oriented shifting of optimal overwintering habitat. The fishing-caused size truncation may constrain the migratory ability and distribution of L. crocea, subsequently led to the mismatch of the optimal overwintering habitat against climate change background, namely habitat bottleneck. Hence, while heavily fishing was the major cause of L. crocea fishery collapse, climate-induced overwintering habitat suitability may have intensified the fishery collapse of L. crocea population. It is important for management to take both overfishing and climate change issues into consideration when developing stock enhancement activities and policy regulations, particularly for migratory long-lived fish that share a similar life history to L. crocea. Combined with China’s current restocking and stock enhancement initiatives, we propose recommendations for future restocking of L. crocea in China.

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.

Life-history genotype explains variation in migration activity in Atlantic salmon (Salmo salar).

One of the most important life-history continuums is the fast-slow axis, where fast individuals mature earlier than slow individuals. Fast individuals are predicted to be more active than slow individuals; high activity is required to maintain a fast life-history strategy. Recent meta-analyses revealed mixed evidence for such integration. Here, we test whether known life-history genotypes differ in activity expression by using Atlantic salmon (Salmo salar) as a model. In salmon, variation in Vgll3, a transcription co-factor, explains ~40% of variation in maturation timing. We predicted that the allele related to early maturation (vgll3*E) would be associated with increased activity. We used an automated surveillance system to follow ~1900 juveniles including both migrants and non-migrants (i.e. smolt and parr fish, respectively) in semi-natural conditions over 31 days (~580 000 activity measurements). Against our prediction, vgll3 did not explain variation in activity in pooled migrant and non-migrant data. However, in migrants, vgll3 explained variation in activity according to our prediction in a sex-dependent manner. Specifically, in females the vgll3*E allele was related to increasing activity, whereas in males the vgll3*L allele (later maturation allele) was related to increasing activity. These sex-dependent effects might be a mechanism maintaining within-population genetic life-history variation.

Host genomic influence on bacterial composition in the switchgrass rhizosphere

Host genetic variation can shape the diversity and composition of associated microbiomes, which may reciprocally influence host traits and performance. While the genetic basis of phenotypic diversity of plant populations in nature has been studied, comparatively little research has investigated the genetics of host effects on their associated microbiomes. Switchgrass (Panicum virgatum) is a highly outcrossing, perennial, grass species with substantial locally adaptive diversity across its native North American range. Here, we compared 383 switchgrass accessions in a common garden to determine the host genotypic influence on rhizosphere bacterial composition. We hypothesized that the composition and diversity of rhizosphere bacterial assemblages would differentiate due to genotypic differences between hosts (potentially due to root phenotypes and associated life history variation). We observed higher alpha diversity of bacteria associated with upland ecotypes and tetraploids, compared to lowland ecotypes and octoploids, respectively. Alpha diversity correlated negatively with flowering time and plant height, indicating that bacterial composition varies along switchgrass life history axes. Narrow-sense heritability (h2) of the relative abundance of twenty-one core bacterial families was observed. Overall compositional differences among tetraploids, due to genetic variation, supports wide-spread genotypic influence on the rhizosphere microbiome. Lastly, a genome-wide association study identified 1,861 single-nucleotide polymorphisms associated with 110 families and genes containing them related to potential regulatory functions. Our findings suggest that switchgrass genomic and life-history variation influences bacterial composition in the rhizosphere, potentially due to host adaptation to local environments.

Applying comparative methods to different databases: lessons from demographic analyses across mammal species

Comparative demographic analyses aim to identify axes of variation in vital rates and the factors that determine the position of species along these axes. These analyses can be performed using different primary data sets, with marked heterogeneity in data quality and structure. Whether the outcome of demographic comparative analyses depends on the database used because theoretical predictions of evolutionary ecology are not that robust and depend on the set of species analysed or because data limitation prevents the identification of the expected patterns has never been investigated. This chapter fills this knowledge gap by performing a comparative demographic analysis across mammalian species from two distinct databases (Comadre and Malddaba) that were built for different purposes. The chapter first estimates some demographic metrics for each database, analyses their allometric relationships, and compares the estimates with theoretical expectations by performing phylogenetic regressions. Using Malddaba led to stronger allometric relationships closer to the expectation than Comadre. Moreover, the contribution of dimensionless demographic metrics to axes of variation in the shape of demographic trajectories was different between databases. The findings in the chapter demonstrate the key role of age dependence in vital rates for shaping demographic tactics across mammalian species and highlight the need for carefully choosing the database and the metrics to use depending on the question asked. Instead of opposing databases, the authors’ analysis nicely illustrates that different databases could be used to address different questions about life history variation.