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Cannibalism in Holocene muricid snails in the Beagle Channel, at the extreme southern tip of South America: an opportunistic response?

Sandra Gordillo

Plain Language Abstract

This is the first record of cannibalism in Cenozoic fossil mollusks from South America. This work also explains a case of study in which cannibalism appears as a response to the absence of prey as opposed to other cases where cannibalism is seen as a mechanism of predation in order to maximize energy gain per unit foraging time.

Resumen en Español

Canibalismo en gasterópodos murícidos del Holoceno del canal Beagle, en el extremo meridional de Sudamérica: ¿un comportamiento oportunista?

En este trabajo se documenta la presencia de marcas de bioerosión en las conchas del murícido Trophon geversianus de los sedimentos marinos emergidos del Holoceno en el canal Beagle, en el extremo meridional de Sudamérica (~55ºS). La morfología de las perforaciones y datos anteriores obtenidos en laboratorio permiten atribuir esas marcas a la actividad depredadora de individuos conespecíficos, sugiriendo así la existencia de canibalismo. Parece ser que cuando el alimento es escaso y no existen presas alternativas (Tawera gayi y otros bivalvos), T. geversianus puede aumentar la frecuencia de canibalismo con objeto de compensar la pérdida de esas presas. Este comportamiento caníbal se desarrolló hace unos 4000 años como respuesta a la ausencia de bivalvos, que habrían desaparecido durante un evento hidrológico local repentino que afectó a los organismos filtradores.

PALABRAS CLAVE: canibalismo; gasterópodos murícidos; perforaciones; Holoceno; Tierra del Fuego

Traducción: Miguel Company

Résumé en Français

Cannibalisme chez les escargots muricidés holocènes dans le canal de Beagle, à la limite extrême sud de l'Amérique du Sud : une réponse opportuniste ?

Ce travail documente la présence de perçages sur des coquilles de muricidés Trophon geversianus provenant de dépôts marins holocènes élevés dans le canal de Beagle, localisés à la limite extrême sud de l'Amérique du Sud (~ 55ºS). Sur la base de la morphologie des perçages et de données acquises précédemment en laboratoire, ces trous de prédations sont attribués à la même espèce, suggérant donc du cannibalisme. Il apparait que lorsque la nourriture est rare et que la proie alternative (Tawera gayi et autres palourdes) n'est pas disponible, T. geversianus pourrait augmenter la fréquence du cannibalisme dans le but de compenser les pertes de proies bivalves. Le cannibalisme c'est donc développé il y a environ 4000 ans comme une réponse au manque de palourdes, qui auraient disparues durant un événement hydrologique local soudain qui a affecté les organismes filtreurs.

Mots clés : cannibalisme ; gasteropodes muricidés ; perçage ; holocène ; Terre de Feu

Translator: Olivier Maridet

Deutsche Zusammenfassung

Kannibalismus bei muriciden Schnecken aus dem Holozän des Beagle Channels an der äußersten Spitze von Südamerika: eine opportunistische Reaktion?

Diese Arbeit dokumentiert das Vorkommen von Bohrlöchern auf Schalen des muriciden Trophon geversianus in herausgehobenen marinen Ablagerungen aus dem Holozän im Beagle Channel, der an der äußersten südlichsten Spitze von Südamerika liegt (~ 55°S). Basierend auf der Bohrlochmorphologie und früheren Daten unter Laborbedingungen werden diese räuberischen Löcher der gleichen Art zugeschrieben, was Kannibalismus andeutet. Es sieht so aus, dass T. geversianus möglicherweise öfter Kannibalismus praktiziert um fehlende Muschelbeute zu kompensieren, wenn das Nahrungsangebot knapp ist und keine Alternativbeute (wie Tawera gayi oder andere Muscheln) vorhanden ist. Kannibalismus wurde daher ca. 4000 v. Chr. entwickelt, als eine Reaktion auf das Fehlen von Muscheln, welche möglicherweise während eines plötzlichen lokalen hydrologischen Ereignisses verschwanden bei dem die Filtrierer in Mitleidenschaft gezogen wurden.

SCHLÜSSELWÖRTER: Kannibalismus; muricide Gastropoden; Bohrlöcher; Holozän; Tierra del Fuego

Translators: Eva Gebauer

Arabic

344 arab

Translator: Ashraf M.T. Elewa

 

 

TABLE 1. Regression equations relating shell size (mm) to biovolume.

 

Species

Size (mm) vs. biovolume (ml)

r

Tawera gayi

Ln Y = 3,21 Ln X - 9,24; X= shell length

0.91

Trophon geversianus

Ln Y= 2,29 Ln X – 5,41; X = shell width

0.97

 

TABLE 2. Relative abundance of predators and their potential prey in different sites located on the Beagle Channel. Trophon geversianus specimens with drillholes were only found in site 1. In the other sites specimens with drillholes were always bivalves.

 

Sites

This study

(site 1)

R.Ovando

(site 2)

Gable

(70 km east)

Ensenada

(5 km east)

Age

ca. 4000 yr

(Not dated)

4425+/-55

4790+/-100

Modern

Prey

35% Trophon

94% Tawera

96,38% Tawera, Mytilus

97,8% Mytilus

Predator

65% Trophon

6% Trophon

3,6% Trophon,

Xymenopsis

2,2% Trophon

N

20

180

138

141

Trophon

Predation

Intraguild

Interguild

Interguild

Interguild

Competition

Regime

High

Low

Low

Low

 

FIGURE 1. Location map showing the sampling site situated on the northern coast of the Beagle Channel. 1. The maps on the left side show the position of the studied area in southern South America. 2. The aerial photography (1:20.000) shows the area affected by the Holocene marine transgression. Radiocarbon dates were previously performed for Sites 1 and 2. Trophon geversianus shells with drillholes were recovered from the left part in Site 1.

 figure1

FIGURE 2. Landscape evolution of the studied area during the Holocene. 1. Glacilacustrine conditions after deglaciation during the early Holocene. 2. Sea transgression/regression during the middle Holocene. 3. The landscape during the late Holocene. 4. Animated landscape evolution (using Blender 2.64) (click on image to run animation).

 figure 2

Figure 2.4

FIGURE 3. Holocene Trophon geversianus shells with drillholes attributed to conspecifics from the Cormoranes Archipelago (Beagle Channel). 1. CEGH-UNC 25410. 2. CEGH-UNC 25411. 3-4. CEGH-UNC 25412. 5. CEGH-UNC 25413. 6. CEGH-UNC 25414. 7. CEGH-UNC 25415. 8. CEGH-UNC 25416. Scales= 1 cm.

 figure 3

FIGURE 4. A Trophon geversianus specimen (See also Figure 3.1.) in 3D created using photoshop. The form of the drillhole is easier to interpret in 3D. This photograph was made using anaglyph techniques, which combine two photographs one in red and the other in cyan (blue+green) color. Three-dimensional red-cyan glasses are recommended to view this image correctly.

 figure 4

FIGURE 5. Drilled and non-drilled Trophon geversianus shells in three size classes. Size classes (shell width): I, 20.00-29.99 mm; II, 30.00-39.99 mm; III, 40.00-49.99 mm.

 figure 5

FIGURE 6. Larger and smaller predators with respect to their prey.

 figure 6

FIGURE 7. The relationship between predation time in days and borehole depth (thickness of the shell); r=0.88683; p (uncorr)= 0.0014349

 figure 7

FIGURE 8. The relationship between predation time in days and biovolume as an indicator of biomass. r=0.58915; p (uncorr)= 0.095.

figure 8

 

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authorCentro de Investigaciones en Ciencias de la Tierra
Consejo Nacional de Investigaciones Científicas y Técnicas – Universidad Nacional de Córdoba (CICTERRA, CONICET-UNC)
Centro de Investigaciones Paleobiológicas (CIPAL)
Facultad de Ciencias Exactas
Físicas y Naturales
Universidad Nacional de Córdoba. Av. Vélez Sársfield 1611
X5016GCA Córdoba
Argentina

Sandra Gordillo is an Argentinean researcher at CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas). She graduated and defended her PhD thesis at the National University of Córdoba and received postdoctoral training at the University of Saskatchewan, Canada (1997-1998). Her research focuses on Quaternary mollusk shells, mainly in comparison to their extant relatives. She has participated in paleontological fieldwork mainly in Argentinean Patagonia and in southern Chile. She has also been involved in fieldwork in New Zealand and on Antarctic expedition. In 2011 she obtained a DAAD-CONICET grant for a scientific visit to the AWI Bremerhaven in Germany. Her interests are related to faunistic changes on different time scales and to the understanding of the palaeoenvironmental history of Quaternary molluscs in southern South America and Antarctica. In this context, she is especially interested in biotic interactions recorded on shells, mainly as predation marks such as drillholes. She is also currently involved in arquaeomalacology in cooperation with archaeologists from Argentina. She has authored and co-authored around 50 articles on taphonomy, systematics, paleoecology, paleobiogeography and paleoenvironmental reconstruction based on Quaternary molluscs. For more information please see http://grupomalacologiacicterra.blogspot.com.ar/