Evolutionary Change In Timing Research Articles

Genetic and phenotypic responses to genomic selection for timing of breeding in a wild songbird

Abstract The physiological mechanisms underlying avian seasonal timing of reproduction, a life‐history trait with major fitness consequences, are not well understood. Comparing individuals that have been selected to differ in their timing of breeding may prove to be a promising in studying these mechanisms, making selection lines a valuable tool. We created selection lines for early and late timing of breeding in great tits (Parus major) using genomic selection, that is selection based on multi‐marker genotypes rather than on the phenotype. We took in nestlings (F1 generation) from wild broods of which the mother was either an extremely early (“early line”) or extremely late (“late line”) breeder. These chicks were then genotyped and, based on their “genomic breeding values” (GEBVs), we selected individuals for early and late line breeding pairs to produce the F2 generation in captivity. The F2 offspring was hand‐reared, genotyped and selected to produce an F3 generation, which were then again genotyped and selected. This way we obtained laying dates in aviaries for F1, F2 and F3 birds. We studied the genetic response to the artificial selection and found increased genetic differentiation between the early and late reproducing selection lines over generations (F1–F3), indicated by both diverging GEBVs and increased fixation indices (FST). We studied the phenotypic response to selection for birds breeding in outdoor breeding aviaries. We found that early line birds laid earlier than late line birds, and this difference increased over the generations (F1–F3), with non‐significant line effects for the F1 and F2, but highly significant line differences for the F3. We also assessed whether there was correlated selection on two traits that are potentially part of the mechanisms underlying seasonal timing: the endogenous free‐running period of the day/night clock (tau) and basal metabolic rate, but found no correlated selection. We have successfully created selection lines on seasonal timing in a wild bird species and obtained an instrument for future studies to investigate the physiological mechanisms underlying timing of breeding, and the genetic variation in these mechanisms, an essential component for evolutionary change in timing of reproduction. A free Plain Language Summary can be found within the Supporting Information of this article.

Modular evolution of DNA-binding preference of a Tbrain transcription factor provides a mechanism for modifying gene regulatory networks.

Gene regulatory networks (GRNs) describe the progression of transcriptional states that take a single-celled zygote to a multicellular organism. It is well documented that GRNs can evolve extensively through mutations to cis-regulatory modules (CRMs). Transcription factor proteins that bind these CRMs may also evolve to produce novelty. Coding changes are considered to be rarer, however, because transcription factors are multifunctional and hence are more constrained to evolve in ways that will not produce widespread detrimental effects. Recent technological advances have unearthed a surprising variation in DNA-binding abilities, such that individual transcription factors may recognize both a preferred primary motif and an additional secondary motif. This provides a source of modularity in function. Here, we demonstrate that orthologous transcription factors can also evolve a changed preference for a secondary binding motif, thereby offering an unexplored mechanism for GRN evolution. Using protein-binding microarray, surface plasmon resonance, and in vivo reporter assays, we demonstrate an important difference in DNA-binding preference between Tbrain protein orthologs in two species of echinoderms, the sea star, Patiria miniata, and the sea urchin, Strongylocentrotus purpuratus. Although both orthologs recognize the same primary motif, only the sea star Tbr also has a secondary binding motif. Our in vivo assays demonstrate that this difference may allow for greater evolutionary change in timing of regulatory control. This uncovers a layer of transcription factor binding divergence that could exist for many pairs of orthologs. We hypothesize that this divergence provides modularity that allows orthologous transcription factors to evolve novel roles in GRNs through modification of binding to secondary sites.

Mechanisms of Evolutionary Changes in Timing, Spatial Expression, and mRNA Processing in the msp130Gene in a Direct-Developing Sea Urchin, Heliocidaris erythrogramma

Developmental processes associated with skeletogenesis differ in the direct-developing sea urchin Heliocidaris erythrogrammafrom that in Heliocidaris tuberculataand other indirect-developing species. In H. erythrogramma,the differences include ingression of a much higher number of mesenchyme cells, failure of the cells to form the typical ring pattern of cells prior to the onset of skeletogenesis, a significantly reduced larval skeleton, and a delay in timing of expression of the skeletogenic cell-restricted gene msp130.We report that the heterochronic change in msp130expression is regulated at the level of transcription. By transient expression of reporter constructs containing msp130promoter regions from direct- and indirect-developing species, we found that this evolutionary change in regulation is consistent with changes in the timing of action of trans-acting factors in skeletogenic mesenchyme cells. We further used these experiments to show that the H. erythrogrammapromoter contains elements required for correct spatial expression in the primary mesenchyme cells of an indirect-developing host. We finally show that alternate processing of H. erythrogramma msp130is thus far specific to this species and not an aspect of adult skeletogenesis.

COMPARATIVE ONTOGENY OF A WILD CUCURBIT AND ITS DERIVED CULTIVAR.

Most previous studies of evolutionary modification of form in plants have focused primarily on individual organs or flowers. Few have investigated the role of evolutionary changes in timing or position at the level of whole plant ontogeny. This study compares ontogenies of the primary shoots of two subspecies of Cucurbita argyrosperma, one a cultivar and the other its wild progenitor. Differences in flowering times between these subspecies suggested that the cultivar may have evolved from the wild subspecies via heterochronic processes leading to paedomorphosis. Analyses showed that both subspecies are similar in vegetative architecture and rates of leaf production. Earlier flowering in the cultivar, both in terms of position and absolute time, appears to have arisen through progenesis. Initial observations of leaf blade morphology led to the hypothesis that paedomorphosis and gigantism also may have been involved in the evolution of leaf blade shape in the cultivar: all leaves of the cultivar are larger and visually similar in shape to early leaves of the wild subspecies. However, quantitative analysis revealed that leaves of the cultivar are neither geometrically, nor solely allometrically larger versions of early leaves of the progenitor. Leaf shape in the cultivar exhibits novel features as well as effects of allometry shared with the progenitor, hence a simple hypothesis of paedomorphic evolution of leaf shape is not supported.