New publication on cannibalism

Cyrus, A.Z., Swiggs, J., Santidrian Tomillo, P., Paladino, F. V., Peters, W. S., 2015. Cannibalism causes size-dependent intraspecific predation pressure but does not trigger autotomy in the intertidal gastropod Agaronia propatula. Journal or Molluscan Studies doi:10.1093/mollus/eyv007

Abstract: Autotomy of the foot is readily inducible in the predatory marine gastropod Agaronia propatula (Conrad,1849), but the natural trigger of the autotomy response is obscure. Since cannibalistic predation hasbeen observed in the species while interspecific predation on A. propatula has not, it was hypothesized that autotomy in A. propatula helps to defend against cannibalism.
This hypothesis was tested in the present study. In our Costa Rican study population, autotomy as well as cannibalism occurred at significant rates; morphological indicators of foot regeneration suggested that 9–23% of the animals had autotomized previously, while about 5% of all observed predation attempts were directed at smaller conspecifics. However, autotomy in response to cannibalistic aggression was neither observed in the wild, nor did experimentally induced intraspecific aggression trigger autotomy. Successful cannibals generally were large and appeared to kill smaller conspecifics by suffocation in the metapodial pouch, but even then autotomy did not occur. These results refuted the hypothesis that A. propatula autotomizes to escape cannibalism. However, the size dependence of successful cannibalism on one hand, and the size spectrum of the population on the other, enabled a semiquantitative evaluation of the size-dependent intraspecific predation pressure in the population. The analysis indicated that in A. propatula different size classes represent ‘ecological species’ with distinct trophic roles. Since large A. propatula may actually reduce the total predation pressure on their heterospecific prey by cannibalizing smaller conspecifics, this size-dependent functional differentiation increases the complexity of the food-web around these snails.

New Publication !

Sergio, F., Taferna A., De Stephanis, R., López Jiménez, L., Blas, J., Tavecchia, G., Preatoni, D., and Hiraldo, F., 2014: 'Individual improvements and selective mortality shape lifelong migratory performance'. Nature. doi:10.1038/nature13696

Billions of organisms, from bacteria to humans, migrate each year and research on their migration biology is expanding rapidly through ever more sophisticated remote sensing technologies. However, little is known about how migratory performance develops through life for any organism. To date, age variation has been almost systematically simplified into . These comparisons have regularly highlighted better migratory performance by adults compared with juveniles, but it is unknown whether such variation is gradual or abrupt and whether it is driven by improvements within the individual, by selective mortality of poor performers, or both.

Here we exploit the opportunity offered by long-term monitoring of individuals through Global Positioning System (GPS) satellite tracking to combine within-individual and cross-sectional data on 364 migration episodes from 92 individuals of a raptorial bird, aged 1–27 years old. We show that the development of migratory behaviour follows a consistent trajectory, more gradual and prolonged than previously appreciated, and that this is promoted by both individual improvements and selective mortality, mainly operating in early life and during the pre-breeding migration. Individuals of different age used different travelling tactics and varied in their ability to exploit tailwinds or to cope with wind drift. All individuals seemed aligned along a race with their contemporary peers, whose outcome was largely determined by the ability to depart early, affecting their subsequent recruitment, reproduction and survival. Understanding how climate change and human action can affect the migration of younger animals may be the key to managing and forecasting the declines of many threatened migrants.

See also at IMEDEA (CSIC-UIB) and IMEDEA Divulga here