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Migratory animals face costs and benefits related to traveling to another habitat and the timing of the journey. These trade-offs can be sex-specific, with male reproductive success expected to be influenced by arrival time at the breeding habitat. In this study, we examined mating success in a population of partially migrating Red-Spotted Newts (Notophthalmus viridescens viridescens (Rafinesque, 1820)). We tested the hypothesis that migrant males are at a disadvantage for spring mating opportunities compared with resident males owing to (i) later arrival time at the breeding pond and (ii) delay in developing the aquatic tail fin, which reduces their competitiveness. We measured the tail heights of successfully courting males compared with the general male population, as well as the time required for migrating males to develop tail fins. Temporally, migrant males arrived at the breeding pond before the majority of mating activity. However, we found that the time required for migrating males to acquire tail-fin heights necessary to be competitive for mating opportunities places them at a significant reproductive disadvantage compared with resident males. For partial migration to be maintained in the population, a reproductive cost for migrants could either trade off with another life-history trait or migration could be condition-dependent. Les animaux migrateurs encourent des couts et recjoivent des benefices relies aux deplacements vers un autre habitat et au calendrier de la migration. Ces compromis peuvent etre specifiques au sexe, car le succes reproductif du male est vraisemblablement affecte; par le moment de son arrivee dans l'habitat de reproduction. Notre etude examine le succes de l'accouplement dans une population de tritons verts (Notophthalmus viridescens viridescens (Rafinesque, 1820)) partiellement migratrice. Nous verifions l'hypothese selon laquelle les males migrateurs sont deesavantagees lors des occasions d'accouplement au printemps par comparaison aux males sedentaires a cause (i) de leur arrivee tardive sur l'aire de reproduction et (ii)dudelai dans le deeveloppement de leur nageoire caudale, qui reduit leur competitivite. Nous avons mesure la hauteur de la queue chez les males qui ont reussi leur cour par comparaison a la population generale de males; nous avons aussi note; le temps requis par les males migrateurs pour developper leur nageoire caudale. Les males migrateurs arrivent a l'etang de reproduction avant le maximum de l'activite; reproductrice. Cependant, le temps necessaire pour que les males migrateurs acquierent une hauteur de nageoire caudale suffisante pour etre compeetitifs lors des occasions d'accouplement les met dans une position de desavantage reproductif significatif par rapport aux males residants. Afin que la migration partielle se maintienne dans la population, le cout reproductif pour les migrateurs doit representer un compromis avec un autre trait du cycle biologique ou alors la migration doit etre dependante de la condition. [Traduit par la Redaction], Introduction In partially migratory populations of animals, a portion of the population completes a migration while the remainder stays resident in the shared habitat (Lundberg 1988). The shared habitat is [...]

The main goal of this paper is to prove that if the energy-momentum (or energy-Casimir) method predicts formal instability of a relative equilibrium in a Hamiltonian system with symmetry, then with the addition of dissipation, the relative equilibrium becomes spectrally and hence linearly and nonlinearly unstable. The energy-momentum method assumes that one is in the context of a mechanical system with a given symmetry group. Our result assumes that the dissipation chosen does not destroy the conservation law associated with the given symmetry group – thus, we consider internal dissipation. This also includes the special case of systems with no symmetry and ordinary equilibria. The theorem is proved by combining the techniques of Chetaev, who proved instability theorems using a special Chetaev-Lyapunov function, with those of Hahn, which enable one to strengthen the Chetaev results from Lyapunov instability to spectral instability. The main achievement is to strengthen Chetaev’s methods to the context of the block diagonalization version of the energy momentum method given by Lewis, Marsden, Posbergh, and Simo. However, we also give the eigenvalue movement formulae of Krein, MacKay and others both in general and adapted to the context of the normal form of the linearized equations given by the block diagonal form, as provided by the energy-momentum method. A number of specific examples, such as the rigid body with internal rotors, are provided to illustrate the results. [ABSTRACT FROM AUTHOR]