Extinction and naticid predation of the bivalve Chione von Mühlfeld in the Late Neogene of Florida
Plain Language Abstract
The Theory of Escalation, more commonly known as the Biological Arms Race, claims that one of the more important driving factors in long-term evolution is the presence of biological enemies. Animals respond to their predators by developing better defensive strategies and structures. Predators on the other hand continue to improve their own strategies. This type of interaction is preserved well in the fossil record, where one can see the traces of successful and unsuccessful predation preserved on fossilized skeletons (unsuccessful predation is of course very important; without it, there would be no evolutionary arms race!). The result of these interactions over long periods of time is the development of diffuse coevolutionary relationships between predators and prey, the dynamics of which are still poorly understood. This paper examines what happens to such a relationship when it is disrupted by a mass extinction, and one of the prey species is replaced by a very similar, but subtly different relative.
The setting is the Pliocene-Recent of Florida. This region suffered a mass extinction of molluscs and other marine invertebrates during the Pliocene, caused mainly by the oceanographic effects of the uplift of the Isthmus of Panama (approximately 3.1 mya). Gastropod predators of the family Naticidae, present in those waters, prey upon other shelled animals by drilling holes through the shells. Naticids generally have well developed behaviors for handling prey species, being very specific as to the size of prey selected, as well as the location of drilling on the prey's shell. We described this relationship between Pliocene naticids and a species of marine clam, Chione erosa. Chione erosa unfortunately went extinct at the end of the Pliocene, but was replaced by a close relative from neighboring waters, Chione cancellata. When Chione cancellata first appeared in Floridian waters, naticid predators decreased the size of prey taken, due possibly to subtle morphological differences between Chione erosa and Chione cancellata. Nevertheless, as time passed, prey size selection increased, but Chione cancellata has apparently responded by evolving significantly thicker shells (as a deterrent to successful drilling). In summary, the paper demonstrates that mass extinctions and subtle but significant morphological differences can play a critical role in our views of evolution and escalation.
Resumen en Español
Extinción y depredación por natícidos del bivalvo Chione von Mühlfeld en el Neógeno de Florida
Una discontinuidad morfométrica entre las especies del bivalvo Chione durante la extinción Plio-Pleistocena en Florida, sugiere que la especie C. erosa del Plioceno fue reemplazada por la especie inmigrante C.cancellata. La llegada de C. cancellata al ecosistema de Florida, cambió la dinámica de la depredación por natícidos sobre Chione. Cuando C. cancellata apareció en Florida no mostraba mayor grado de reforzamiento que su predecesora C. erosa. Sin embargo, el tamaño relativo de las presas seleccionadas por los depredadores natícidos, disminuyó claramente. Más tarde, del Pleistoceno a la Actualidad, el tamaño relativo de las presas seleccionadas volvió a crecer, pero C. cancellata reaccionó aumentando mucho el espesor relativo de la concha. Estos tipos de interacciones proporcionan una evidencia directa de la desaparición de los sistemas depredador-presa debido a las extinciones en masa y a la intensificación microevolutiva de las características antidepredatorias.
PALABRAS CLAVE: Depredación, perforaciones, natícidos, Chione, extinción
Traducción: Prof. Jenaro L. García-Alcalde, Depto. de Geología, Universidad de Oviedo, c/ Arias de Velasco s/n, E-33005 Oviedo
Résumé en Français
L'EXTINCTION ET LA PRÉDATION NITICIDE DU BIVALVE CHIONE VON MÜHLFELD DANS LE TARDI-NÉOGENE DE LA FLORIDE
Une discontinuité morphométrique entre les espèces du bivalve Chione lors d'une extinction Plio-Pléistocène en Floride suggère que l'espèce Pliocène C. erosa fut remplacée par l'immigrant C. cancellata. Ici, nous démontrons que l'immigration de C. cancellata a eu pour effet d'altérer l'écosystème Floridien en changeant la dynamique de la prédation naticide de Chione. Lors de sa première apparition en Floride, C. cancellata ne demontrait guerre plus d'escalation que son prédecesseur C. erosa. Cependant, il s'est produit une chute significative de la taille relative des proies selectionnées par les naticides. La taille des proies s'est par la suite augmentée au cours du Pléistocene et du Récent, mais en revanche, il s'est produit un épaississement significatif des coquillages de C. cancellata. Ces patternes d'interactions indiquent une rupture des relations prédateur-proie par l'extinction, et l'escalation microévolutif des traits anti-prédateurs.
MOTS CLÉS: Prédation, forage, naticide, Chione, extinction
Deutsche Zusammenfassung
Aussterben und Beweidung der Muschel Chione von Mühlfeld durch Naticiden im späten Neogen von Florida
Eine morphometrische Diskontinuität zwischen Arten der Gattung Chione während eines Plio-Pleistozänen Aussterbeereignisses in Florida weist auf einen Ersatz der Art C. erosa durch die eingewanderte C. cancellata hin. Wir zeigen hier, dass die Einwanderung von C. cancellata in das ökosystem Floridas die Dynamik der naticiden Beweidung von Chione verändert hat. Während ihres Erstauftretens in Florida hat C. cancellata keinen gröferen Grad von Eskalation als ihre Vorgängerin C. erosa gezeigt. Die relative Grösse der von naticiden Räubern bevorzugten Beute nahm allerdings bedeutend ab. Die bevorzugte Beutegrösse nahm danach im Pleistizän bis heute zu, worauf C. cancellata mit einer deutlich zunehmenden relativen Schalendicke reagierte. Diese Muster einer Interaktion schaffen direkte Evidenz für eine Störung im Räuber-Beute System durch Massenaussterben und die mikroevolutionäre Eskalation von Schutzmechanismen gegen fressfeinde.
Italiano
L'ESTINZIONE E LA PREDAZIONE DA PARTE DI NATICIDI DEL BIVALVE CHIONE VON MÜHLFELD NEL NEOGENE SUPERIORE DELLA FLORIDA
Una discontinuità morfometrica tra le specie del bivalve Chione durante un'estinzione Plio-Pleistocenica in Florida suggerisce che la specie Pliocenica C. erosa sia stata sostituita dalla specie di nuova immigrazione C.cancellata. In questo lavoro mostriamo che l'immigrazione di C. cancellata nell'ecosistema della Florida ha modificato le dinamiche di predazione da parte dei naticidi su Chione. Alla sua prima apparizione in Florida, Chionecancellata non mostrava un maggior numero di strategie e strutture difensive rispetto al suo predecessore C. erosa. Tuttavia le dimensioni relative delle prede dei naticidi diminuirono significativamente. Queste ripresero poi a crescere di nuovo durante il Pleistocene fino al Quaternario, ma C. cancellata ha reagito accrescendo significativamente lo spessore relativo del suo guscio. Questi tipi di interazione forniscono una prova diretta dell'interruzione dei sistemi predatore-preda in seguito ad estinzioni di massa e dell'intensificazione micro-evolutiva di tratti anti-predatori.
Parole chiave: Predazione, perforazione, naticida, Chione, estinzione
Traduzione: Alessandro Grippo, Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740
