Rapid adaptive radiation of Darwin's finches depends on ancestral genetic modules

Recent adaptive radiations are models for investigating mechanisms contributing to the evolution of biodiversity. An unresolved question is the relative importance of new mutations, ancestral variants, and introgressive hybridization for phenotypic evolution and speciation. Here, we address this issue using Darwin's finches and investigate the genomic architecture underlying their phenotypic diversity. Admixture mapping for beak and body size in the small, medium, and large ground finches revealed 28 loci showing strong genetic differentiation. These loci represent ancestral haplotype blocks with origins predating speciation events during the Darwin's finch radiation. Genes expressed in the developing beak are overrepresented in these genomic regions. Ancestral haplotypes constitute genetic modules for selection and act as key determinants of the unusual phenotypic diversity of Darwin's finches. Such ancestral haplotype blocks can be critical for how species adapt to environmental variability and change

Ecological adaptation in European eels is based on phenotypic plasticity

The relative role of genetic adaptation and phenotypic plasticity is of fundamental importance in evolutionary ecology [M. J. West-Eberhard, Proc. Natl. Acad. Sci. U.S.A. 102 (suppl. 1), 6543-6549 (2005)]. European eels have a complex life cycle, including transitions between life stages across ecological conditions in the Sargasso Sea, where spawning occurs, and those in brackish and freshwater bodies from northern Europe to northern Africa. Whether continental eel populations consist of locally adapted and genetically distinct populations or comprise a single panmictic population has received conflicting support. Here we use whole-genome sequencing and show that European eels belong to one panmictic population. A complete lack of geographical genetic differentiation is demonstrated. We postulate that this is possible because the most critical life stages-spawning and embryonic development-take place under near-identical conditions in the Sargasso Sea. We further show that within-generation selection, which has recently been proposed as a mechanism for genetic adaptation in eels, can only marginally change allele frequencies between cohorts of eels from different geographic regions. Our results strongly indicate plasticity as the predominant mechanism for how eels respond to diverse environmental conditions during postlarval stages, ultimately solving a long-standing question for a classically enigmatic species

Data from: Geographic and host-mediated population genetic structure in a cestode parasite of the three-spined stickleback

Comparative studies of genetic diversity and population structure can shed light on the ecological and evolutionary factors that influence host–parasite interactions. Here we examined whether geography, time and genetic variation in Alaskan three-spined stickleback (Gasterosteus aculeatus Linneaus) hosts shape the population genetic structure of the diphyllobothridean cestode parasite Schistocephalus solidus (Müller, 1776). Host lineages and haplotypes were identified by sequencing the mitochondrial cytochrome b gene, and host population structure was assessed by Bayesian clustering analysis of allelic variation at 11 microsatellite loci. Parasite population structure was characterized according to allelic variation at eight microsatellite loci. Mantel tests and canonical redundancy analysis were conducted to evaluate the proportion of parasite genetic variation attributable to time and geography vs. host lineage, haplotype, and genotypic cluster. Host and parasite population structure were largely discordant across the study area, probably reflecting differences in gene flow, environmental influences external to the host, and genomic admixture among host lineages. We found that geography explained the greatest proportion of parasite genetic variation, but that variation also reflects time, host lineage, and host haplotype. Associations with host haplotypes suggest that one parasite genotypic cluster exhibits a narrower host range, predominantly infecting the most common host haplotypes, whereas the other parasite cluster infects all haplotypes equally, including rare haplotypes. Although experimental infection trials might prove otherwise, distributional differences in hosts preferentially infected by S. solidus could underlie the observed pattern of population structure

Mantel Tests.

<p>Microsatellite based estimates of genetic differentiation (linearized F_ST) compared to (a) Euclidian distance between lakes, (b) Euclidian distance between lakes distance by streams without Hall and Pollard lakes to account for sample size variation, and (c) distance by streams, and (d) distance by streams without Hall and Pollard lakes.</p

The genomic basis and environmental correlates of local adaptation in the Atlantic horse mackerel (Trachurus trachurus)

Abstract Understanding how populations adapt to their environment is increasingly important to prevent biodiversity loss due to overexploitation and climate change. Here we studied the population structure and genetic basis of local adaptation of Atlantic horse mackerel, a commercially and ecologically important marine fish that has one of the widest distributions in the eastern Atlantic. We analyzed whole‐genome sequencing and environmental data of samples collected from the North Sea to North Africa and the western Mediterranean Sea. Our genomic approach indicated low population structure with a major split between the Mediterranean Sea and the Atlantic Ocean and between locations north and south of mid‐Portugal. Populations from the North Sea are the most genetically distinct in the Atlantic. We discovered that most population structure patterns are driven by a few highly differentiated putatively adaptive loci. Seven loci discriminate the North Sea, two the Mediterranean Sea, and a large putative inversion (9.9 Mb) on chromosome 21 underlines the north–south divide and distinguishes North Africa. A genome–environment association analysis indicates that mean seawater temperature and temperature range, or factors correlated to them, are likely the main environmental drivers of local adaptation. Our genomic data broadly support the current stock divisions, but highlight areas of potential mixing, which require further investigation. Moreover, we demonstrate that as few as 17 highly informative SNPs can genetically discriminate the North Sea and North African samples from neighboring populations. Our study highlights the importance of both, life history and climate‐related selective pressures in shaping population structure patterns in marine fish. It also supports that chromosomal rearrangements play a key role in local adaptation with gene flow. This study provides the basis for more accurate delineation of the horse mackerel stocks and paves the way for improving stock assessments

Landscape Genetics of <i>Schistocephalus solidus</i> Parasites in Threespine Stickleback (<i>Gasterosteus aculeatus</i>) from Alaska

<div><p>The nature of gene flow in parasites with complex life cycles is poorly understood, particularly when intermediate and definitive hosts have contrasting movement potential. We examined whether the fine-scale population genetic structure of the diphyllobothriidean cestode <i>Schistocephalus solidus</i> reflects the habits of intermediate threespine stickleback hosts or those of its definitive hosts, semi-aquatic piscivorous birds, to better understand complex host-parasite interactions. Seventeen lakes in the Cook Inlet region of south-central Alaska were sampled, including ten in the Matanuska-Susitna Valley, five on the Kenai Peninsula, and two in the Bristol Bay drainage. We analyzed sequence variation across a 759 bp region of the mitochondrial DNA (mtDNA) cytochrome oxidase I region for 1,026 <i>S</i>. <i>solidus </i> individuals sampled from 2009-2012. We also analyzed allelic variation at 8 microsatellite loci for 1,243 individuals. Analysis of mtDNA haplotype and microsatellite genotype variation recovered evidence of significant population genetic structure within <i>S</i>. <i>solidus</i>. Host, location, and year were factors in structuring observed genetic variation. Pairwise measures revealed significant differentiation among lakes, including a pattern of isolation-by-distance. Bayesian analysis identified three distinct genotypic clusters in the study region, little admixture within hosts and lakes, and a shift in genotype frequencies over time. Evidence of fine-scale population structure in <i>S</i>. <i>solidus</i> indicates that movement of its vagile, definitive avian hosts has less influence on gene flow than expected based solely on movement potential. Observed patterns of genetic variation may reflect genetic drift, behaviors of definitive hosts that constrain dispersal, life history of intermediate hosts, and adaptive specificity of <i>S</i>. <i>solidus </i>to intermediate host genotype.</p></div

Sampling and Diversity.

<p>NP: total number of parasites sequenced or genotyped; NP(2009–2012): number of parasites per year; NH: total number of hosts; NH(>7/host): number of hosts with greater than 7 parasites; NP(>7/host): number of parasites in hosts with greater than 7 parasites; Hap D: haplotype diversity in lake; Pairwise D: pairwise differences among haplotypes; Nucleotide D: nucleotide diversity among haplotypes; k: effective number of haplotypes; Ho: observed heterozygosity; He: expected heterozygosity; N alleles: average number of alleles over 8 loci; I: Shannon’s Information Index; R: average rarefied allelic richness across loci.</p><p>Sampling and Diversity.</p

Summary of AMOVA Results.

<p>Summary of AMOVA Results.</p

Data from: Invasion of the Hawaiian Islands by a parasite infecting imperiled stream fishes

Points of origin and pathways of spread are often poorly understood for introduced parasites that drive disease emergence in imperiled native species. Co-introduction of parasites with non-native hosts is of particular concern in remote areas like the Hawaiian Islands, where the introduced nematode Camallanus cotti has become the most prevalent parasite of at-risk native stream fishes. In this study, we evaluated the prevailing hypothesis that C. cotti entered the Hawaiian Islands with poeciliid fishes from the Americas, and spread by translocation of poeciliid hosts across the archipelago for mosquito control. We also considered the alternative hypothesis of multiple independent co-introductions with host fishes originating from Asia. We inferred conduits of introduction and spread of C. cotti across the archipelago from geographic patterns of mtDNA sequence variation and allelic variation across 11 newly developed microsatellite markers. The distribution of haplotypes suggests that C. cotti spread across the archipelago following an initial introduction on O'ahu. Approximate Bayesian Computation modeling and allelic variation also indicate that O'ahu is the most likely location of introduction, from which C. cotti dispersed to Maui followed by spread to the other islands in the archipelago. Evidence of significant genetic structure across islands indicates that contemporary dispersal is limited. Our findings parallel historical records of non-native poeciliid introductions and suggest that remediating invasion hotspots could reduce the risk of infection in native stream fishes, which illustrates how inferences on parasite co-introductions can improve conservation efforts by guiding responses to emerging infectious disease in species of concern

A multispecies BCO2 beak color polymorphism in the Darwin's finch radiation

Carotenoid-based polymorphisms are widespread in populations of birds, fish, and reptiles,(1) but generally little is known about the factors affecting their maintenance in populations.(2) We report a combined field and molecular-genetic investigation of a nestling beak color polymorphism in Darwin's finches. Beaks are pink or yellow, and yellow is recessive.(3) Here we show that the polymorphism arose in the Galapagos half a million years ago through a mutation associated with regulatory change in the BCO2 gene and is shared by 14 descendant species. The polymorphism is probably a balanced polymorphism, maintained by ecolog- ical selection associated with survival and diet. In cactus finches, the frequency of the yellow genotype is correlated with cactus fruit abundance and greater hatching success and may be altered by introgressive hybridization. Polymorphisms that are hidden as adults, as here, may be far more common than is currently recognized, and contribute to diversification in ways that are yet to be discovered