Crimson-breasted Shrike females with extra pair offspring contributed more to duets

Many socially monogamous bird species follow a genetically promiscuous reproductive strategy. Duetting birds may be an exception, as they appear to exhibit very low levels of extra pair paternity—which is thought to be connected to duetting. Duets are predicted to function either in paternity guarding or as signals of commitment to the pair bond, reciprocally reducing extra pair mating in both sexes. In this study, we used four microsatellites to document paternity loss in the Crimson-breasted Shrike (Laniarius atrococcineus), a socially monogamous subtropical duetting species. Extra pair paternity was surprisingly high, with extra pair males siring 20 % of young in 30 % of broods. Furthermore, we compared the levels of extra pair paternity of each pair to certain characteristics of their duets to test the paternity guard and the commitment hypotheses. Our results offered no support that duets function in paternity guarding, although the fact that males which had been cuckolded answered more of their female’s calls could represent an adaptation to avoid future cuckoldry. We also found no evidence for duets functioning as signal of commitment. Female vocal behaviour was in fact the reverse of that predicted: Levels of infidelity amongst social females were positively related to female answer rate of their mates’ songs. These results indicate that females may use increased answer rates as a form of manipulation, in an attempt to avoid potential costs associated with their extra pair matings.     

An approach for particle sinking velocity measurements in the 3–400?μm size range and considerations on the effect of temperature on sinking rates

The flux of organic particles below the mixed layer is one major pathway of carbon from the surface into the deep ocean. The magnitude of this export flux depends on two major processes—remineralization rates and sinking velocities. Here, we present an efficient method to measure sinking velocities of particles in the size range from approximately 3–400?μm by means of video microscopy (FlowCAM^?). The method allows rapid measurement and automated analysis of mixed samples and was tested with polystyrene beads, different phytoplankton species, and sediment trap material. Sinking velocities of polystyrene beads were close to theoretical values calculated from Stokes’ Law. Sinking velocities of the investigated phytoplankton species were in reasonable agreement with published literature values and sinking velocities of material collected in sediment trap increased with particle size. Temperature had a strong effect on sinking velocities due to its influence on seawater viscosity and density. An increase in 9?°C led to a measured increase in sinking velocities of ~40?%. According to this temperature effect, an average temperature increase in 2?°C as projected for the sea surface by the end of this century could increase sinking velocities by about 6?% which might have feedbacks on carbon export into the deep ocean.