of the project: Over the course of evolution, species often become divided into subgroups, and members of different subgroups may become unable to produce healthy offspring with each other. Instead, the offspring can be sick or sterile or even die before reaching adulthood. At that point, scientists consider these subgroups to be different species. When they die, their deaths result from mistakes made during development, and the goal of this project is to determine whether there are general rules that explain why these hybrid offspring die when and how they do. Perhaps these mistakes are idiosyncratic, with each individual dying in its own way. Perhaps hybrids between two species die in one way but hybrids between two others die in a different way. Or perhaps, within a group of related species, the same pattern of when and how hybrids die is repeated over and over because some parts and phases of development are more sensitive to disruption than others. To test which of these is the case, this project will use a group of related roundworms which look very similar but whose hybrid offspring tend to die as embryos. This investigation of species incompatibility will also form the basis for two hands-on science modules aligned with the California secondary school biology standards. In one students will test for themselves whether different species can mate, and in the other they will trap roundworms in the wild and use their DNA to identify the species or to discover that they are new to science.
: As species separate during evolution, incompatibilities at the genome level can accumulate and ratchet the process forward. These incompatibilities often play out during development and render hybrid offspring inviable or infertile. The developmental biology of this process is relatively little studied. Recent advances in microscopy have made it possible to quantitatively and comprehensively measure key aspects of development in real time in an increasing range of organisms. This capacity makes it possible to test hypotheses about the variability of the cellular processes that construct organisms, to compare these both within and between species, and to dissect exactly what is disrupted when development goes wrong. Through a combination of systematic crosses, high-resolution 4D microscopy of developing embryos, and targeted measurements of gene expression, this project will test three primary hypotheses about the developmental biology of hybrid inviability using the Caenorhabditis roundworm genus as a model system. These nematodes are ideal for this kind of study because their normal development is stereotyped and repeatable, different species will often mate with each other even though their embryos die, and the genus includes at least two species pairs that are in the process of speciating and remain partially interfertile. The study will determine when and how hybrid embryos tend to die, where and when the first defects in development appear, whether these defects are caused by abnormal cell movement or by abnormal cell fate decisions, and whether these patterns are systematic across the genus or idiosyncratic for each embryo or species pair.
Statement of Merit Review,
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
