The well-documented Floridian 'Gulf/Atlantic' marine genetic disjunction provides an influential example of vicariant cladogenesis along a continental coastline for major elements of a diverse nearshore fauna. We are engaged in a two-part study that aims to place this disjunction into a regional Caribbean Basin phylogenetic perspective using the scorched mussel Brachidontes exustus as an exemplar. Our first step, documented here, is to thoroughly characterize the genetic structure of Floridian scorched mussel populations using mitochondrial (mt) and nuclear markers. Both sets of markers recovered the expected disjunction involving sister clades distributed on alternate flanks of peninsular Florida and lineage-specific mt molecular clocks placed its origin in the Pliocene. The two sister clades had distinct population genetic profiles and the Atlantic clade appears to have experienced an evolutionarily recent bottleneck, although plots of the relative estimates of N through time are consistent with its local persistence through the last Ice Age Maximum. Our primary novel result, however, was the discovery that the Gulf/Atlantic disjunction represents but one of three cryptic, nested genetic discontinuities represented in Floridian scorched mussel populations. The most pronounced phylogenetic split distinguished the Gulf and Atlantic sister clades from two additional nested cryptic sister clades present in samples taken from the southern Florida tropical marine zone. Floridian populations of B. exustus are composed of four cryptic taxa, a result consistent with the hypothesis that the Gulf/Atlantic disjunction in this morphospecies is but one of multiple latent regional genetic breakpoints.
An efficient and accurate computational approach is proposed for optimal attitude control of a rigid body. The problem is formulated directly as a discrete time optimization problem using a Lie group variational integrator. Discrete necessary conditions for optimality are derived, and an efficient computational approach is proposed to solve the resulting two point boundary value problem. The use of geometrically exact computations on SO(3) guarantees that this optimal control approach has excellent convergence properties even for highly nonlinear large angle attitude maneuvers. Numerical results are presented for attitude maneuvers of a 3D pendulum and a spacecraft in a circular orbit.
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