title: Brachiopods hitching a ride: an early case of commensalism in the middle Cambrian Burgess Shale.
abstract: Ecological interactions, including symbiotic associations such as mutualism, parasitism and commensalism are crucial factors in generating evolutionary novelties and strategies. Direct examples of species interactions in the fossil record generally involve organisms attached to sessile organisms in an epibiont or macroboring relationship. Here we provide support for an intimate ecological association between a calcareous brachiopod (Nisusia) and the stem group mollusc Wiwaxia from the Burgess Shale. Brachiopod specimens are fixed to Wiwaxia scleritomes, the latter showing no signs of decay and disarticulation, suggesting a live association. We interpret this association as the oldest unambiguous example of a facultative ectosymbiosis between a sessile organism and a mobile benthic animal in the fossil record. The potential evolutionary advantage of this association is discussed, brachiopods benefiting from ease of attachment, increased food supply, avoidance of turbid benthic conditions, biofoul and possible protection from predators, suggesting commensalism (benefiting the symbiont with no impact for the host). While Cambrian brachiopods are relatively common epibionts, in particular on sponges, the association of Nisusia with the motile Wiwaxia is rare for a brachiopod species, fossil or living, and suggests that symbiotic associations were already well established and diversified by the "middle" (Series 3, Stage 5) Cambrian.
authors.affiliation: Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, SE - 752 36 Uppsala, Sweden.
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Topper
authors.affiliation: Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, SE - 752 36 Uppsala, Sweden.
authors.forename: Lars E
authors.initials: LE
authors.lastname: Holmer
authors.affiliation: 1] Department of Natural History (Palaeobiology Section), Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario. M5S2C6, Canada [2] Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S3B2, Canada.
authors.forename: Jean-Bernard
authors.initials: JB
authors.lastname: Caron
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004463:Ecology; D007448:Invertebrates / Q000502:physiology*; D008974:Mollusca / Q000502:physiology*; D013559:Symbiosis