Population structure and phylogeography of the Gentoo Penguin (Pygoscelis papua) across the Scotia Arc

Climate change, fisheries' pressure on penguin prey, and direct human disturbance of wildlife have all been implicated in causing large shifts in the abundance and distribution of penguins in the Southern Ocean. Without mark‐recapture studies, understanding how colonies form and, by extension, how ranges shift is challenging. Genetic studies, particularly focused on newly established colonies, provide a snapshot of colonization and can reveal the extent to which shifts in abundance and occupancy result from changes in demographic rates (e.g., reproduction and survival) or migration among suitable patches of habitat. Here, we describe the population structure of a colonial seabird breeding across a large latitudinal range in the Southern Ocean. Using multilocus microsatellite genotype data from 510 Gentoo penguin (Pygoscelis papua) individuals from 14 colonies along the Scotia Arc and Antarctic Peninsula, together with mitochondrial DNA data, we find strong genetic differentiation between colonies north and south of the Polar Front, that coincides geographically with the taxonomic boundary separating the subspecies P. p. papua and P. p. ellsworthii. Using a discrete Bayesian phylogeographic approach, we show that southern Gentoos expanded from a possible glacial refuge in the center of their current range, colonizing regions to the north and south through rare, long‐distance dispersal. Our findings show that this dispersal is important for new colony foundation and range expansion in a seabird species that ordinarily exhibits high levels of natal philopatry, though persistent oceanographic features serve as barriers to movement. </p

Mixed-effects modelling of scale growth profiles predicts the occurrence of early and late fish migrants

Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth variation can be interpreted inrelation to conspecifics’ performance. Unfortunately, assessing individual variation in growth rates is problematic undernatural conditions because subjects typically need to be marked, repeated measurements of body size are difficult to obtainin the field, and recaptures may be limited to a few time events which will generally vary among individuals. The analysis ofconsecutive growth rings (circuli) found on scales and other hard structures offers an alternative to mark and recapture forexamining individual growth variation in fish and other aquatic vertebrates where growth rings can be visualized, butaccounting for autocorrelations and seasonal growth stanzas has proved challenging. Here we show how mixed-effectsmodelling of scale growth increments (inter-circuli spacing) can be used to reconstruct the growth trajectories of sea trout(Salmo trutta) and correctly classify 89% of individuals into early or late seaward migrants (smolts). Early migrants grewfaster than late migrants during their first year of life in freshwater in two natural populations, suggesting that migrationinto the sea was triggered by ontogenetic (intrinsic) drivers, rather than by competition with conspecifics. Our studyhighlights the profound effects that early growth can have on age at migration of a paradigmatic fish migrant and illustrateshow the analysis of inter-circuli spacing can be used to reconstruct the detailed growth of individuals when these cannot bemarked or are only caught once

TRANSVERSE MOMENTUM SPECTRUM OF NEUTRAL ELECTROMAGNETIC PARTICLES PRODUCED AT THE CERN PROTON ANTI-PROTON COLLIDER

Forward shower counters equipped with position detectors able to locate to +/- 2mm have been used to measure an inclusive p_t distribution in the rapidity range 1.6&lt;|y|&lt;2.5 for neutral electromagnetic particles produced in proton-antiproton collisions at sqrt(s)=540 GeV. The covered p_t range extends up to 12 GeV/