Novel and disappearing climates in the global surface ocean from 1800 to 2100.

Marine ecosystems are experiencing unprecedented warming and acidification caused by anthropogenic carbon dioxide. For the global sea surface, we quantified the degree that present climates are disappearing and novel climates (without recent analogs) are emerging, spanning from 1800 through different emission scenarios to 2100. We quantified the sea surface environment based on model estimates of carbonate chemistry and temperature. Between 1800 and 2000, no gridpoints on the ocean surface were estimated to have experienced an extreme degree of global disappearance or novelty. In other words, the majority of environmental shifts since 1800 were not novel, which is consistent with evidence that marine species have been able to track shifting environments via dispersal. However, between 2000 and 2100 under Representative Concentrations Pathway (RCP) 4.5 and 8.5 projections, 10-82% of the surface ocean is estimated to experience an extreme degree of global novelty. Additionally, 35-95% of the surface ocean is estimated to experience an extreme degree of global disappearance. These upward estimates of climate novelty and disappearance are larger than those predicted for terrestrial systems. Without mitigation, many species will face rapidly disappearing or novel climates that cannot be outpaced by dispersal and may require evolutionary adaptation to keep pace.

The Importance of Genetic Redundancy in Evolution.

Genetic redundancy has been defined in many different ways at different levels of biological organization. Here, we briefly review the general concept of redundancy and focus on the evolutionary importance of redundancy in terms of the number of genotypes that give rise to the same phenotype. We discuss the challenges in determining redundancy empirically, with published experimental examples, and demonstrate the use of the C-score metric to quantify redundancy in evolution studies. We contrast the implicit assumptions of redundancy in quantitative versus population genetic models, show how this contributes to signatures of allele frequency shifts, and highlight how the rapid accumulation of genome-wide association data provides an avenue for further understanding the prevalence and role of redundancy in evolution.

Phytobiomes are compositionally nested from the ground up.

Plant-associated microbes are critical players in host health, fitness and productivity. Despite microbes' importance in plants, seeds are mostly sterile, and most plant microbes are recruited from an environmental pool. Surprisingly little is known about the processes that govern how environmental microbes assemble on plants in nature. In this study we examine how bacteria are distributed across plant parts, and how these distributions interact with spatial gradients. We sequenced amplicons of bacteria from the surfaces of six plant parts and adjacent soil of Scaevola taccada, a common beach shrub, along a 60 km transect spanning O'ahu island's windward coast, as well as within a single intensively-sampled site. Bacteria are more strongly partitioned by plant part as compared with location. Within S. taccada plants, microbial communities are highly nested: soil and rhizosphere communities contain much of the diversity found elsewhere, whereas reproductive parts fall at the bottom of the nestedness hierarchy. Nestedness patterns suggest either that microbes follow a source/sink gradient from the ground up, or else that assembly processes correlate with other traits, such as tissue persistence, that are vertically stratified. Our work shines light on the origins and determinants of plant-associated microbes across plant and landscape scales.

Stability of underdominant genetic polymorphisms in population networks.

Heterozygote disadvantage is potentially a potent driver of population genetic divergence. Also referred to as underdominance, this phenomena describes a situation where a genetic heterozygote has a lower overall fitness than either homozygote. Attention so far has mostly been given to underdominance within a single population and the maintenance of genetic differences between two populations exchanging migrants. Here we explore the dynamics of an underdominant system in a network of multiple discrete, yet interconnected, populations. Stability of genetic differences in response to increases in migration in various topological networks is assessed. The network topology can have a dominant and occasionally non-intuitive influence on the genetic stability of the system.