Biology subjects

Bolnick, D.

Publications and source records attributed to Bolnick, D..

4 recordsLinked to original sources

bioRxiv2017

Adaptive plasticity generates microclines in threespine stickleback male nuptial color

Adaptive phenotypic divergence is typically studied across relatively broad spatial scales (continents, archipelagos, river basins) because at these scales we expect environmental differences to be strong, and the homogenizing effect of gene flow to be weak. However, phenotypic plasticity and phenotype-dependent habitat choice are additional mechanisms that could also drive adaptation across spatially variable environments. We present evidence for apparently adaptive phenotypic variation across surprisingly small spatial scales (<2 vertical meters) in the threespine stickleback. We find that male breeding coloration varies as a function of the lakes optical-depth gradient, and these small-scale clines ( microclines) appear to be an adaptive response to ambient light gradients, as male color changes predictably in the opposite direction ( countergradient) to ambient light spectral shifts. Using visual models and field enclosure experiments, we show that these microclines result from phenotypic plasticity that maintains male conspicuousness. Our results show that adaptive phenotypic clines can exist across small spatial scales, because phenotypic plasticity rapidly generates repeatable trait-environment correlations despite the overwhelming opportunity for gene flow. Furthermore, these results provide strong evidence that phenotypic plasticity in nuptial coloration is an important mechanism for adjusting the conspicuousness of a visual signal to conspecifics.

evolutionary biology↗

bioRxiv2017

Gene Expression Stasis And Plasticity Following Migration Into A Foreign Environment

Selection against migrants is key to maintaining genetic differences between populations linked by dispersal. Yet, migrants are not just passively weeded out by selection. Migrants may mitigate fitness costs by proactively choosing among available habitats, or by phenotypic plasticity. We previously reported that a reciprocal transplant of lake and stream stickleback (Gasterosteus aculeatus) found little support for divergent selection. We revisit that experiment to test whether phenotypic plasticity in gene expression may have helped migrants adjust to unfamiliar habitats. We measured gene expression profiles in stickleback via TagSeq and tested whether migrants between lake and stream habitats exhibited a plastic response to their new environment that allowed them to converge on the expression profile of adapted natives. We report extensive gene expression differences between genetically divergent lake and stream stickleback, despite gene flow. But for many genes, expression was highly plastic. Fish transplanted into the adjoining habitat partially converged on the expression profile typical of their new habitat. This suggests that expression plasticity may soften the impact of migration. Nonetheless, lake and stream fish differed in survival rates and parasite infection rates in our study, implying that expression plasticity is not fast or extensive enough to fully homogenize fish performance.

evolutionary biology↗

bioRxiv2017

The role of gene expression in the recent evolution of resistance in a model host parasite system

Damage by parasites is a perpetual challenge for hosts, often leading to the evolution of elaborate mechanisms of avoidance, immunity, or tolerance. Host resistance can evolve via changes in immune protein coding and/or expression. Heritable population differences in gene expression following infection can reveal mechanisms of immune evolution. We compared gene expression in infected and uninfected threespine stickleback (Gasterosteus aculeatus) from two natural populations that differ in their resistance to a native cestode parasite, Schistocephalus solidus. Genes in both the innate and adaptive immune system were differentially expressed as a function of host population, infection status, and their interaction. These genes were enriched for loci controlling immune functions that we independently verified differ between host populations, or in response to infection. For instance, populations differ strongly in reactive oxygen (ROS) production, and we observed corresponding differences in expression of ROS-affecting loci. Differentially expressed genes also were involved in fibroblast activation, B-cell activation, and leukocyte trafficking. Coexpression network analysis identified two distinct immune processes contributing to stickleback resistance; several modules of genes are correlated with parasite survival while a different set of modules are correlated with suppression of cestode growth. Comparison of networks between populations showed resistant fish have a dynamic expression profile while susceptible fish are static. In summary, recent evolutionary divergence between two vertebrate populations has generated population-specific gene expression responses to parasite infection, which reveal a few immune modules likely to separately affect cestode establishment, and growth.

evolutionary biology↗

bioRxiv2016

NATURAL SELECTION ON MHC IIB IN PARAPATRIC LAKE AND STREAM STICKLEBACK: BALANCING, DIVERGENT, BOTH, OR NEITHER?

Major histocompatibility (MHC) genes encode proteins that play a central role in vertebrates adaptive immunity to parasites. MHC loci are among the most polymorphic in vertebrates genomes, inspiring many studies to identify evolutionary processes driving MHC polymorphism within populations, and divergence between populations. Leading hypotheses include balancing selection favoring rare alleles within populations, and spatially divergent selection. These hypotheses do not always produce diagnosably distinct predictions, causing many studies of MHC to yield inconsistent or ambiguous results. We suggest a novel strategy to distinguish balancing versus divergent selection on MHC, taking advantage of natural admixture between parapatric populations. With divergent selection, immigrant alleles will be more infected and less fit because they are susceptible to novel parasites in their new habitat. With balancing selection, locally-rare immigrant alleles will be more fit (less infected). We tested these contrasting predictions using threespine stickleback from three replicate pairs of parapatric lake and stream habitats. We found numerous positive and negative associations between particular MHC II{beta} alleles and particular parasite taxa. A few allele-parasite comparisons supported balancing selection, others supported divergent selection between habitats. But, there was no overall tendency for fish with immigrant MHC alleles to be more or less heavily infected. Instead, locally rare MHC alleles (not necessarily immigrants) were associated with heavier infections. Our results illustrate the complex relationship between MHC II{beta} allelic variation and spatially varying multi-species parasite communities: different hypotheses may be concurrently true for different allele-parasite combinations.

evolutionary biology↗