Toxin-assisted micropredation: experimental evidence shows that contact micropredation rather than exotoxicity is the role of Prymnesium toxins

Blooms of Prymnesium parvum can severely harm fish and zooplankton, presumably through the release of allelopathic exotoxins that offer advantages for Prymnesium in its interactions with competitors and prey. We show that Prymnesium attaches to zooplankton and fish, causing mortality, whereas exposure of these organisms to Prymnesium across a permeable membrane does not cause mortality. We also show that Prymnesium exotoxins are released independently of contact toxicity only in response to experimental procedures or natural causes of stress. Our results are consistent with the idea that toxins have evolved for release during cell-to-cell contact in support of heterotrophy. The evolution of toxin-assisted micropredation would be consistent with mechanisms of natural selection favouring individual fitness as opposed to broadcast allelopathy from which the benefits are more dispersed. Research into the toxicity of Prymnesium and other harmful algal species may profit from focus on processes following physical contact with potential prey.     

Eocene isopods on electric rays: tracking ancient biological interactions from a complex fossil record

Isopod crustaceans have developed a variety of feeding strategies, which impact on their various life habits over time. Apart from morphological adaptations and the typical secondary deformations that some parasitic isopods inflict on their host's exoskeleton, traces of feeding behaviours involving isopods on their victim/food are seldom fossilized. Many of these rare occurrences consist of cases for which the degree of association between the isopods and their potential food source is unclear, or the interaction only very briefly explained (recently analysed cases excepted). There are two limiting problems in identifying the biological nature of fossilized associations: (1) direct associations of organisms preserved as ‘imprint’ (as opposed to inclusions in cherts or amber) are shaped by several taphonomic events difficult to identify (such as the time of death, burial and fossilization of the organism); (2) even in modern nature, differences within syn vivo interactions (like parasitism and micropredation) are poorly understood in marine systems. We report the occurrence of isopods associated with ancient chondrichthyans which also represent rare cases of the preservation of several fossil isopods on larger organisms. These organisms are adult electric rays of the genus ?Titanonarke Carvalho from the late Ypresian (Eocene) of the Monte Postale site, Bolca Lagerstätte, Italy. By examining: (1) the involved lineages of rays and isopods; (2) the taphonomy of the association; (3) its environmental context; and (4) biological/adaptive features; we identify this association as a selective case, either of ancient scavenging or of micropredation on specific electric rays by isopods.