The evolution of pedicellariae in echinoids: an arms race against pests and parasites

Abstract

Coppard, S.E., Kroh, A. and Smith, A.B. (2010). The evolution of pedicellariae in echinoids: an arms race against pests and parasites. —Acta Zoologica (Stockholm) 00:1–24. Sea urchins (Echinoidea) have evolved a diverse array of jawed appendages termed pedicellariae to deter pests and predators. Pedicellarial structure and function are reviewed and their distribution mapped in 75 extant genera. Using a phylogeny of echinoids at family level constructed from 353 skeletal characters scored across 162 extant and fossil taxa, the evolution of pedicellarial form and function is reconstructed. For much of the Palaeozoic echinoids possessed a very restricted pedicellarial armament. By the early Mesozoic a diverse array of pedicellarial types had become established, implying that the threat from predators and pests markedly increased at this time. Since the Triassic, echinoids have continued to improve their defensive capability by evolving more effective venom delivery in globiferous pedicellariae, developing spatulate‐tips and curved blades for a more efficient grab in tridentate pedicellariae, and stouter, more robust valves with a stronger bite in ophicephalous pedicellariae to disable and remove ectoparasites. However, pedicellarial types are shown to be particularly prone to subsequent secondary loss, especially among infaunal echinoids, and thus have higher homoplasy levels than other phylogenetically useful skeletal structures.

Global patterns in the effects of predator declines on sea urchins

“…larger test sizes at higher latitudes Ebert ). In this study the species that were strongly impacted by consumers exhibit a diversity of traits, including variation in test size (small, Echinometra mathaei , and large, Centrostephanus rodgersii ), spine length (short, Paracentrotus lividus , and long, Diadema savignyi ), behaviour (hiding, Echinometra viridis , and exposed, Tripneustes gratilla ) and chemical defence (present, Diadema setosum , and absent, Heliocidaris erythrogramma ; Coppard et al , Lawrence ). Investment in costly physical and chemical defences may be a reflection of intense consumer pressure and there is evidence that increased biotic interactions in the tropics has led to decreased palatability in marine sponges (Ruzicka and Gleason ), seaweeds (Bolser and Hay ) and terrestrial plants (Coley and Aide , but see Moles et al ).…”

“…To contrast the effects of predator manipulation across major habitat types, we categorised experiments into coral reefs, rocky reefs or seagrass beds. Depth was recorded as deep water provides potential prey refuge via reduced predator contact (Coppard et al ). Experimental sites were allocated to biogeographical realms (as defined by Spalding et al ) to test whether latitudinal patterns were consistent across regions of differing biota, evolutionary history and historical isolation.…”

Morphology and ecological setting of the basal echinoid genus Rhenechinus from the early Devonian of Spain and Germany

“…They are three−bladed and rest either on a small basal element or di− rectly onto a tubercle. Ophicephalous and globiferous pedi− cellariae, which have been reported from some Carbonifer− ous taxa (Geis 1936;Coppard et al 2012), are wanting. This supports the view that ophicephalous and globiferous pedi− cellariae evolved only in archaeocidarids.…”

Asterozoan pedicellariae and ossicles revealed from the Middle Ordovician of Baltica

“…Although parasites have not left an extensive body fossil record, the trace fossils left by inferred parasites together with the directly observable pests, is sufficient to be traced back to the Cambrian (Conway Morris 1981). Thus the finds of pedicellariae could also be regarded as an indication of much higher faunal diversity than it is evident from the fossilizable faunal record, and perhaps also the presence of parasitic interactions in the ecosystem (Conway Morris 1981;Coppard et al 2012). …”