Morphological and Morphometrical Variations of Selected Rotifer Species in Response to Predation: a Seasonal Study of Selected Brachionid Species from Lake Xochimilco (Mexico)

We observed different morphotypes of some species in the family Brachionidae from the seasonal plankton samples of Lake Xochimilco collected during 2002–2003. We measured the body length, width, and spine lengths (posterior and anterior spines) of Brachionus havanaensis, Keratella americana, K. cochlearis and K . tropica during the periods when the predator Asplanchna brightwellii was present in great abundance but also when it was nearly absent. In general, spines of most of the selected rotifer species were longer if A . brightwellii was abundant. Relatively, small spines were observed if the predator was rare. The body lengths of brachionid rotifers widely varied in samples with more and less abundant A. brightwellii. Morphometric data are interpreted in terms of morphological adaptations of Brachionus and Keratella in response to Asplanchna predation.