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Abstract Plants have the ability to transmit mutations to progeny that arise through both meiotic and mitotic (somatic) cell divisions. This is because the same meristem cells responsible for vegetative growth will also generate gametes for sexual reproduction. Despite the potential for somatic mutations to contribute to genetic variation and adaptation, their role in plant evolution remains largely unexplored. We conducted experiments with the bush monkeyflower (Mimulus aurantiacus) to assess the phenotypic effects of somatic mutations inherited across generations. By generating self-pollinations within a flower (autogamy) or between flowers on different stems of the same plant (geitonogamy), we tracked the effects of somatic mutations transmitted to progeny. Autogamy and geitonogamy lead to different segregation patterns of somatic mutations among stems, with only autogamy resulting in offspring that are homozygous for somatic mutations specific to that stem. This allowed us to compare average phenotypic differences between pollination treatments that could be attributed to the inheritance of somatic variants. While most experimental units showed no impacts on fitness, in some cases, we detected increased seed production, as well as significant increases in drought tolerance, even though M. aurantiacus is already well adapted to drought conditions. We also found increased variance in drought tolerance following autogamy, consistent with the hypothesis that somatic mutations transmitted between generations can impact fitness. These results highlight the potential role of inherited somatic mutations as a relevant source of genetic variation in plant evolution. 

Abstract Characterizing molecular underpinnings of plastic traits and balanced polymorphisms represent 2 important goals of evolutionary biology. Fire ant gynes (pre-reproductive queens) provide an ideal system to study potential links between these phenomena because they exhibit both supergene-mediated polymorphism and nutritional plasticity in weight and colony-founding behaviour. Gynes with the inversion supergene haplotype are lightweight and depend on existing workers to initiate reproduction. Gynes with only the ancestral, non-inverted gene arrangement accumulate more nutrient reserves as adults and, in a distinct colony-founding behaviour, initiate reproduction without help from workers. However, when such gynes overwinter in the natal nest they develop an environmentally induced lightweight phenotype and colony-founding behaviour, similar to gynes with the inversion haplotype that have not overwintered. To evaluate the extent of shared mechanisms between plasticity and balanced polymorphism in fire ant gyne traits, we assessed whether genes with expression variation linked to overwintering plasticity may be affected by the evolutionary divergence between supergene haplotypes. To do so, we first compared transcriptional profiles of brains and ovaries from overwintered and non-overwintered gynes to identify plasticity-associated genes. These genes were enriched for metabolic and behavioural functions. Next, we compared plasticity-associated genes to those differentially expressed by supergene genotype, revealing a significant overlap of the 2 sets in ovarian tissues. We also identified sequence substitutions between supergene variants of multiple plasticity-associated genes, consistent with a scenario in which an ancestrally plastic phenotype responsive to an environmental condition became increasingly genetically regulated. 

Abstract Copulations are very brief in many species, sometimes taking only seconds, but in other species, they can be quite prolonged. Potential explanations for prolonged copulations include time requirements for the transfer of sperm and/or other ejaculate substances. Ejaculate substances could function to regulate female receptivity to subsequent matings, provide nutritional nuptial gifts, or hasten egg oviposition at a potential survival cost to the female. We investigated prolonged copulation in a member of the Enchenopa binotata complex of treehoppers (Hemiptera: Membracidae), in which females rarely remate and copulation can last several hours. We assigned females to treatments in which we interrupted copulation at different times. We also included a control where copulation was not interrupted. We found that females that experienced shorter copulations were more likely to be subsequently receptive to an attractive male. We also found that few females produced offspring when they engaged in short copulations compared to those with longer copulations. We did not find any differences in female survival. Our results support the sperm transfer and receptivity regulation hypotheses. We discuss potential reasons for why these processes should take so long in a species with low female remating. 

Abstract The field of genomics has ushered in new methods for studying molecular-genetic variation in natural populations. However, most population-genomic studies still rely on small sample sizes (typically, <100 individuals) from single time points, leaving considerable uncertainties with respect to the behavior of relatively young (and rare) alleles and, owing to the large sampling variance of measures of variation, to the specific gene targets of unusually strong selection. Genomic sequences of ∼1,700 haplotypes distributed over a 10-year period from a natural population of the microcrustacean Daphnia pulex reveal evolutionary-genomic features at a refined scale, including previously hidden information on the behavior of rare alleles predicted by recent theory. Background selection, resulting from the recurrent introduction of deleterious alleles, appears to strongly influence the dynamics of neutral alleles, inducing indirect negative selection on rare variants and positive selection on common variants. Temporally fluctuating selection increases the persistence of nonsynonymous alleles with intermediate frequencies, while reducing standing levels of variation at linked silent sites. Combined with the results from an equally large metapopulation survey of the study species, classes of genes that are under strong positive selection can now be confidently identified in this key model organism. Most notable among rapidly evolving Daphnia genes are those associated with ribosomes, mitochondrial functions, sensory systems, and lifespan determination.