Genomic and genetic methods allow investigation of how frequently the same genes are used by different populations during adaptive evolution, yielding insights into the predictability of evolution at the genetic level. We estimated the probability of gene reuse in parallel and convergent phenotypic evolution in nature using data from published studies. The estimates are surprisingly high, with mean probabilities of 0.32 for genetic mapping studies and 0.55 for candidate gene studies. The probability declines with increasing age of the common ancestor of compared taxa, from about 0.8 for young nodes to 0.1–0.4 for the oldest nodes in our study. Probability of gene reuse is higher when populations begin from the same ancestor (genetic parallelism) than when they begin from divergent ancestors (genetic convergence). Our estimates are broadly consistent with genomic estimates of gene reuse during repeated adaptation to similar environments, but most genomic studies lack data on phenotypic traits affected. Frequent reuse of the same genes during repeated phenotypic evolution suggests that strong biases and constraints affect adaptive evolution, resulting in changes at a relatively small subset of available genes. Declines in the probability of gene reuse with increasing age suggest that these biases diverge with time.

Ecological differences often evolve early in speciation as divergent natural selection drives adaptation to distinct ecological niches, leading ultimately to reproductive isolation. Though this process is a major generator of biodiversity, its genetic basis remains poorly understood. Here we investigate the genetic architecture of niche differentiation in a sympatric species pair of threespine stickleback fish by mapping the environment-dependent effects of phenotypic traits on hybrid feeding and performance under semi-natural conditions. We show that multiple, unlinked loci act largely additively to determine position along the major niche axis separating these recently diverged species. We also find that functional mismatch between phenotypic traits reduces growth of some stickleback hybrids beyond that expected from an intermediate phenotype, suggesting a role for epistasis between the underlying genes. This functional mismatch might lead to hybrid incompatibilities that are analogous to those underlying intrinsic reproductive isolation but that depend on the ecological context.

Natural selection arising from resource competition and environmental heterogeneity can drive adaptive radiation. Ecological opportunity facilitates this process, resulting in rapid divergence of ecological traits in many celebrated radiations. In other cases, sexual selection is thought to fuel divergence in mating signals ahead of ecological divergence. Comparing divergence rates between naturally and sexually selected traits can offer insights into processes underlying species radiations, but to date such comparisons have been largely qualitative. Here, we quantitatively compare divergence rates for four traits in African mormyrid fishes, which use an electrical communication system with few extrinsic constraints on divergence. We demonstrate rapid signal evolution in the Paramormyrops species flock compared to divergence in morphology, size, and trophic ecology. This disparity in the tempo of trait evolution suggests that sexual selection is an important early driver of species radiation in these mormyrids. We also found slight divergence in ecological traits among closely related species, consistent with a supporting role for natural selection in Paramormyrops diversification. Our results highlight the potential for sexual selection to drive explosive signal divergence when innovations in communication open new opportunities in signal space, suggesting that opportunity can catalyze species radiations through sexual selection, as well as natural selection.

A little over 5 years ago, the U.S. National Institutes of Health (NIH) announced the intention to develop policies to require applicants to report plans to balance male and female cells and animals in preclinical investigations. Soon thereafter, the NIH issued a request for information from the scientific community and consulted with various stakeholders. The feedback received was considered during development of policy requiring the consideration of sex as a biological variable (SABV) in NIH-funded research on vertebrate animals and humans, which went into effect for applications due on or after January 25, 2016. We identified NIH programs related to SABV and reviewed SABV-relevant scientific literature. We find that the application of SABV throughout the research process can serve as a guiding principle to improve the value of biomedical science. The NIH is engaged in ongoing efforts to develop resources to help investigators consider SABV in their research. We also provide an update on lessons learned, highlight ways that different disciplines consider SABV, and describe the opportunities for scientific discovery that applying SABV offers. We call on NIH's various stakeholders to redouble their efforts to integrate SABV throughout the biomedical research enterprise. Sex-and gender-aware investigations are critical to the conduct of rigorous and transparent science and the advancement of personalized medicine. This kind of research achieves its greatest potential when sex and gender considerations are integrated into the biomedical research enterprise in an end-to-end manner, from basic and preclinical investigations, through translational and clinical research, to improved health care delivery.