Transport of brine shrimps via the digestive system of migratory waders: dispersal probabilities depend on diet and season
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Waterbirds are known to disperse invertebrate propagules that survive gut passage, but there is very little information about how the probability of dispersal changes at different times of the annual cycle when birds move in different directions, or how it is affected by changes in diet. We studied internal transport of brine shrimp Artemia cysts by migratory waders in the Odiel saltworks in south-west Spain. Viable cysts of parthenogenetic Artemia were abundant in the faeces and regurgitated pellets of redshank Tringa totanus, pellets of spotted redshank T. erythropus, and faeces of black-tailed godwit Limosa limosa during spring and/or autumn migrations in 2001–2002, but were not recorded during winter. Godwits did not produce pellets, and spotted redshank faeces were not sampled. Significant correlations between the number of cysts in a pellet or faecal sample and the proportion of that sample constituted by Artemia adults suggested that most cysts were ingested while in the ovisacs of gravid females. The proportion of cysts destroyed during digestion increased when accompanied by harder food items or grit, and when fewer cysts were ingested. The median number of intact cysts was higher in redshank faeces than in their pellets, but cysts extracted from pellets were more likely to hatch. A higher proportion of redshank pellets contained Artemia cysts in spring than in autumn, but more redshank migrated through the area in autumn. Significantly fewer cysts were recorded in redshank pellets in winter than in spring or autumn. Our results confirm that there is potential for long-distance dispersal of Artemia cysts via waders during both northwards (spring) and southwards (autumn) migrations.
KeywordsBrine Shrimp Spring Migration Autumn Migration Artemia Cyst Artemia Population
This study has been partially funded by the Spanish R&D National Plan (projects BOS2003-02846 and CGL2004-03719). The first author was supported by a Ph.D. grant from the Ministerio de Ciencia y Tecnología and an I3P postgraduate grant from the Consejo Superior de Investigaciones Científicas. The Consejería de Medio Ambiente, Junta de Andalucía and Aragonesas Industrias y Energía S.A. provided permission to work in the saltworks. J.C. Rubio provided logistical support and advice. J. Figuerola and anonymous referees provided valuable comments on the manuscript.
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