Holocentric chromosomes: convergent evolution, meiotic adaptations, and genomic analysis

In most eukaryotes, the kinetochore protein complex assembles at a single locus termed the centromere to attach chromosomes to spindle microtubules. Holocentric chromosomes have the unusual property of attaching to spindle microtubules along their entire length. Our mechanistic understanding of holocentric chromosome function is derived largely from studies in the nematode Caenorhabditis elegans, but holocentric chromosomes are found over a broad range of animal and plant species. In this review, we describe how holocentricity may be identified through cytological and molecular methods. By surveying the diversity of organisms with holocentric chromosomes, we estimate that the trait has arisen at least 13 independent times (four times in plants and at least nine times in animals). Holocentric chromosomes have inherent problems in meiosis because bivalents can attach to spindles in a random fashion. Interestingly, there are several solutions that have evolved to allow accurate meiotic segregation of holocentric chromosomes. Lastly, we describe how extensive genome sequencing and experiments in nonmodel organisms may allow holocentric chromosomes to shed light on general principles of chromosome segregation.

Energy-Economical Heuristically Based Control of Compass Gait Walking on Stochastically Varying Terrain

Investigation uses simulation to explore the inherent tradeoffs ofcontrolling high-speed and highly robust walking robots while minimizing energy consumption. Using a novel controller which optimizes robustness, energy economy, and speed of a simulated robot on rough terrain, the user can adjust their priorities between these three outcome measures and systematically generate a performance curveassessing the tradeoffs associated with these metrics.

Evolution of the Morphology of Bottom Walking Turtles

Ecomorphology and functional morphology are two distinct disciplines within biology that are often conflated and erroneously used interchangeably. By investigating the morphological distinctiveness of bottom-walking turtles relative to aquatic swimmers and terrestrial walkers, we can disentangle the effects of ecology and performance. Shell morphology, tail length, digit length, webbing length, and integumental differences were examined using dry and wet preserved specimens. Bottom-walkers were hypothesized to be distinct in all measurements. Instead, bottom-walkers were typically distinct from terrestrial taxa but not aquatic taxa, although for integumentary structures, only bottom-walkers were found to have significantly more integumentary structures than terrestrial turtles. This demonstrates that, despite sometimes highly differential locomotor modes, ecology, defined as habitat type, can show a stronger morphological signal than function.