Abstract: We use the am, an, as and the aσ geomagnetic indices to the explore a previously overlooked factor in magnetospheric electrodynamics, namely the inductive effect of diurnal motions of the Earth’s magnetic poles toward and away from the Sun caused by Earth’s rotation. Because the offset of the (eccentric dipole) geomagnetic pole from the rotational axis is roughly twice as large in the southern hemisphere compared to the northern, the effects there are predicted to be roughly twice the amplitude of those in the northern hemisphere. Hemispheric differences have previously been discussed in terms of polar ionospheric conductivities generated by solar photoionization, effects which we allow for by looking at the dipole tilt effect on the time-of-year variations of the indices. The electric field induced in a geocentric frame is shown to also be a significant factor and gives a modulation of the voltage applied by the solar wind flow in the southern hemisphere that is typically a ±30% diurnal modulation for disturbed intervals rising to ±76% in quiet times. For the northern hemisphere these are 15% and 38% modulations. Motion away from/towards the Sun reduces/enhances the directly-driven ionospheric voltages and reduces/enhances the magnetic energy stored in the tail and we estimate that approximately 10% of the effect appears in directly driven ionospheric voltages and 90% in changes of the rate of energy storage or release in the near-Earth tail. The hemispheric asymmetry in the geomagnetic pole offsets from the rotational axis is shown to be the dominant factor in driving Universal Time (UT) variations and hemispheric differences in geomagnetic activity. Combined with the effect of solar wind dynamic pressure and dipole tilt on the pressure balance in the near-Earth tail, the effect provides an excellent explanation of how the observed Russell-McPherron pattern with time-of-year F and UT in the driving power input into the magnetosphere is converted into the equinoctial F-UT pattern in average geomagnetic activity (after correction is made for dipole tilt effects on ionospheric conductivity), added to a pronounced UT variation with minimum at 02–10 UT. In addition, we show that the predicted and observed UT variations in average geomagnetic activity has implications for the occurrence of the largest events that also show the nett UT variation.

Abstract: Group-living is associated with both fitness benefits and costs for animals. In seabird colonies, spatial heterogeneity in social density and other environmental parameters may affect the quality of breeding territories. For instance, in king penguins, increased conspecific density has been correlated with increased stress hormone levels and increased energy expenditure in individual birds, suggesting a cost of colonial breeding. We unravelled the influences of early (genetic and early maternal effects) and rearing environments on chick growth trajectories, stress physiology and survival. Our results suggest that the rearing social environment (rather than biological background) can influence chicks’ phenotype, growth and survival. Especially, chicks reared in high density areas of the colony showed increased weight gain and survival probabilities. These results suggest either a difference in terms of parental quality between individual breeding at high and low social densities or a difference in chick’s competitiveness due to their early life social environment.

Abstract: Coloniality is associated with various benefits and costs for animals affecting their fitness. Breeding colonies are heterogeneous both in terms of physical and social parameters, thus, breeding territories are of different quality relative to their location within the colony. In king penguins, increased conspecific density has been correlated with increased stress level in individual birds, suggesting a cost of colonial breeding. We used a cross-fostering approach to question the relationship linking breeding location, phenotype and reproduction success. We crossfostered eggs shortly after laying within and between high-and low-density colony areas. This design allowed us to unravel the influences of early genetic and maternal effects together with rearing environments on chick growth trajectories, stress physiology and survival. We tested whether chick phenotype is determined at birth to match their early environment or if higher social density conferred an advantage for reproduction.

Abstract: Subsequent to their introduction in the 1950s, Arctic charr Salvelinus alpinus have been able to establish a self-sustaining population that has adapted to the unique conditions of the sub-Antarctic Kerguelen Islands. Here, 48 individuals (198–415 mm) were caught with gillnets and their basic biology and feeding ecology were examined using stable isotope analysis. The Lac des Fougères population split use of littoral and pelagic resources evenly, although larger fish relied more heavily on littoral production and appear to follow the size-dependent life history habitat template seen in many Scandinavian lakes where smaller sized individuals occupy the pelagic zone and larger individuals dominate the littoral habitat. In Kerguelen, Arctic charr mature at the same ages (5.6 years) as Arctic charr in both sub-Arctic and Arctic lakes. Although mortality was average in comparison to comparator sub-Arctic lakes, it was high in comparison to Arctic lakes. Maximal age (>7+) was at the lower end of the range typically seen in sub-Arctic lakes. Although they inhabit a resource-poor environment, Kerguelen Arctic charr showed no evidence of cannibalism. Thus, while Arctic charr can survive and reproduce in the relatively unproductive Kerguelen lake environments, survival and growth nevertheless appear to be traded off against survival and longevity. The uniqueness of the population location and the recency of its introduction suggest that further monitoring of the population has the potential to yield valuable insights into both the adaptability of the species and its likely responses to ongoing large-scale environmental change as represented by climate change.

Abstract: In 1954, brown trout were introduced to the Kerguelen archipelago (49°S, 70°E), a pristine, sub-Antarctic environment previously devoid of native freshwater fishes. Trout began spreading rapidly via coastal waters to colonize adjacent watersheds, however, recent and unexpectedly the spread has slowed. To better understand the ecology of the brown trout here, and why their expansion has slowed, we documented the marine habitat use, foraging ecology, and environmental conditions experienced over one year by 50 acoustically tagged individuals at the colonization front. Trout mainly utilized the marine habitat proximate to their tagging site, ranging no further than 7 km and not entering any uncolonized watersheds. Nutritional indicators showed that trout were in good condition at the time of tagging. Stomach contents and isotope signatures in muscle of additional trout revealed a diet of amphipods (68%), fish (23%), isopods (6%), and zooplankton (6%). The small migration distances observed, presence of suitable habitat, and rich local foraging opportunities suggest that trout can achieve their resource needs close to their home rivers. This may explain why the expansion of brown trout at Kerguelen has slowed.