Palaeogeography, Palaeoclimatology, Palaeoecology 410 (2014) 126–133

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Palaeogeography, Palaeoclimatology, Palaeoecology

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What controls cannibalism in drilling gastropods? A case study onNatica tigrina

Devapriya Chattopadhyay ⁎,1, Deepjay Sarkar 1, Saurav Dutta 1, S.R. Prasanjit 1

Department of Earth Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, WB-741252, India

⁎ Corresponding author.E-mail address: devapriya@iiserkol.ac.in (D. Chattopad

1 Tel.: +91 9874155997.

http://dx.doi.org/10.1016/j.palaeo.2014.05.0370031-0182/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 16 March 2014Received in revised form 27 May 2014Accepted 30 May 2014Available online 6 June 2014

Keywords:Drilling predationCannibalismPrey selectionNaticidaeEvolutionary stable strategy (ESS)

Cannibalism is observed among the drilling gastropods in Recent and in the fossil record. However, the ecologicalfactors triggering cannibalism are not well understood. While competition over food is considered a factor toinitiate cannibalism in certain groups, it is yet to be tested for drilling gastropods.In an experiment with live naticid gastropods, Natica tigrina, we evaluated the effect of the following factors incontrolling cannibalism: 1. availability of preferred prey, 2. size ratio of predator and prey, and 3. ontogeneticstage of the predators. Cannibalism is found to be quite rarewhen preferred bivalve prey (Cardium sp.) is present.Size ratio among predator and prey is observed to play themost crucial role; cannibalism ismaximum in amixedgroup of small and large gastropods. While the incidence of cannibalism ismuch lower in groups of similar bodysize, the intensity differs with mean size. Cannibalism is relatively common in groups of larger size compared tothose of smaller size. This indicates an ontogenetic threshold in cannibalism; the naticids seem to acquire suchbehavior only at a specific ontogenetic stage.Our findings are corroborated by observed drilling pattern in the Recent shells collected from Chandipur-on-sea,India. While the preferred prey Cardium sp. has the highest drilling frequency, the shells of N. tigrina often beardrill holes; the smaller size class of Natica has the highest drilling frequency among all size classes. The smallestdrill holes inNatica are larger than those found in Cardium; this pattern indicates that theNatica are less likely toattempt a cannibalistic attack in their early ontogeny. These behavioral patterns are also reported fromaMioceneassemblage of N. tigrina from Poland (Zlotnik, 2001).It has been postulated that cannibalism should be observed in nutrient depleted conditions. However, our studydemonstrates the relative importance of other ecological factors in guiding this behavioral trait. Moreover, the on-togenetic development of cannibalistic habit is closely linked to the evolutionary stable strategy (ESS). Therefore,such factors shouldalso be taken into considerationwhile studying cannibalism in the context of drilling predation.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

The structure of ecological communities is primarily controlled bythe dynamics of the constituting populations, characterized by theintra- and inter-population interactions (Polis and Strong, 1996). Bioticinteractions, such as competition, predation, parasitism, mutualism,etc., hence play a crucial role in shaping the community structure. Can-nibalism is one of the special types of predation in which the predatorand the prey belong to the same population (Claessen et al., 2004). Itis one of themost common ecological interaction that is observed in nu-merous species from aquatic and terrestrial communities (Fox, 1975;Polis, 1981). Although, ecologists have identified potential cause andecological consequence of cannibalism, it is rarely done in deep time(but see Kelley, 1991; Kelley and Hansen, 2007). This study aims to

hyay).

shed light on causes of cannibalism in ecological community and toextend it to deep time.

Studying various aspects of predation is a challenge in deep time andcannibalism is no exception. There are only few instances where the re-cord of predation is preserved in the fossil record that can be studiedwith quantitative rigor. Drilling predator–prey system is one suchunique scenario that records important information about the behaviorof predator and prey. Consequently, the fossil record of predatory dril-ling by naticid and muricid gastropods is of key interest to thepalaeontologists (Kitchell et al., 1986; Vermeij, 1987; Kowalewski,2002; Kelley and Hansen, 2003; Harper, 2006; Chattopadhyay andBaumiller, 2010). Cannibalism is observed among the Recent muricid(Basedow, 1996; Dietl, 2003) and naticid gastropods (Kitchell et al.,1981; Gould, 2010; Huchings and Herbert, 2013). In general, naticidaefrequently shows conspecific cannibalism and confamilial predation(Gould, 2010). Confamilial predation in naticids is seen from as earlyas Cretaceous (Kelley, 1991), and its frequency increased since then(Kelley and Hansen, 2007). However, the distinction betweenconfamilial predation and conspecific cannibalism in naticidae is often

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difficult because of the similarity of drill holes among all naticidae spe-cies (Kelley, 1991; Dietl and Kelley, 2006). However, the relative abun-dance of naticid species can be used to determine likelihood ofcannibalism. The frequency of true cannibalism in naticidae variesconsiderably throughout the geological record from 1% to 35% (Kelleyand Hansen, 2007).

The causes of naticid cannibalism remained elusive. Some authorsclaimed that naticid cannibalism is caused by predator ineptitude(Paine, 1963) which is refuted by later studies (Kelley and Hansen,2007). Few other studies attributed cannibalism to unavailability ofalternative prey (Stanton and Nelson, 1980) while others refuted thisnotion (Kelley, 1991; Gould, 2010). Kojumdjieva (1974) doubted thevalidity of experimental observations and attributed such cannibalismto artificiality of laboratory conditions. In contrast, Kitchell et al.(1981) suggested that cannibalism is nothing but a predictable resultof selective predation.

Based on the previous views on cannibalism, we developed severalpredictions on the relationship between cannibalism incidence and eco-logical attributes of the prey and the cannibalistic predator.We evaluatethese hypotheses using data from experimental results and ecologicalobservation on a Recent naticid gastropod, Natica tigrina.

1. Effect of alternate prey: According to cost-benefit analysis (Kitchellet al., 1981), the prey choice of a predator is guided by energy maxi-mization. Hence we expect to see lower incidence of cannibalism inthe presence of alternative “beneficial” prey.

2. Effect of size difference among the predatory group: A possible deter-rent to cannibalism would be if the interaction is dangerous to thepredator (Dietl and Alexander, 2000; Kelley and Hansen, 2007).However, this risk will be reduced if the attacking individual ismuch larger than the prey naticid. Hence we expect to see a higherrate of cannibalism in groups where there is a large dissimilarity insize.

3. Effect of ontogenetic stage of the gastropod: Often predatory behav-iors developwith age; hence, some behaviors are only observed afterthe onset of certain ontogenetic stage (Kitchell et al, 1981; Zlotnik,2001). If cannibalism is one of such behaviors, we expect to see alower cannibalistic tendency among juvenile gastropod.

2. Materials and methods

2.1. Ecological setting

The live molluscs were collected from a tidal flat situated along theOdisha coast at Chandipur (21°27′27.01″N, 87°03′25.09″E). This areais known for its highmolluscan biodiversity characterized by 42 generaand 56 species of gastropods and bivalves (Rao et al., 1991). Two majornaticid genera, Polinices (Montfort, 1810) and Natica (Scopoli, 1777)dominate this tidal flat (Mondal et al., 2010). Das et al. (2013) reportedconfamilial predation on Natica gualterina from this tidal flat.

Fig. 1. Drilled specimens from the neontological e

Interestingly, the abundance of each species is very patchy and highlyseasonal (personal observation, 2010, 2011, 2012). We collected allthe specimens from a small patch in the tidal flat entirely dominatedby N. tigrina and Cardium sp. (Fig. 1).

2.2. Specimens

For our experimental setup, we collected live N. tigrina and Cardiumsp. from tidal flat at Chandipur between December, 2012–December,2013. Once the sea water recedes during the low tide, N. tigrina shellsare found scattered in the muds of the tidal flat. These live gastropodsas well as bivalve were transferred along with the sea water and sedi-ments to plastic containers (0.5 m × 0.5 m × 0.5 m). They were latertransferred to experimental chambers. After each experiment, all thespecimens were checked for drill mark. Each drilled gastropod wasmeasured for height, width, aperture size and the outer diameter ofthe drill hole.

Dead specimens of N. tigrina and Cardium sp. were also collectedusing grid sampling from the same area during December of 2012.These were then checked for predation mark and measured.

2.3. Experimental setup

The live gastropods collected from the field were transferred to asea-water tank. We fed the gastropods with bivalves for 2–3 days. Weselected only the active gastropods for the experiment to ensure thehealthy behavior (Visaggi et al., 2013). The experiments were conduct-ed in a synthetic salt water aquarium setup housed in Ecological FieldStation, IISER Kolkata. It is comprised of multiple glass tanks (1.2 m ×0.5 m × 0.5 m) with recirculating synthetic salt water. Each tank has a10 cm thick layer of coral sand to maintain the normal drilling activityof Natica (Visaggi et al., 2013). We maintained a near constant temper-ature (24 °C to 25 °C) and chemical composition (pH, salinity) of thissystem.

2.3.1. Experimental protocolWe introduced different combinations of Natica and Cardium as re-

quired by the experimental design. The setup was monitored regularlyfor pH, salinity and temperature. Data regardingdrilling attackwere col-lected after every 5 days; we removed the dead individuals at the sameinterval. We conducted each experiment for a length of two months.

2.3.2. Experiment 1: Effect of preferred preyWe introduced equal number ofmedium (15–20 cm) sizedNatica in

two identical chambers. The number of Cardium, however, was differ-ent. One chamber had a smaller number (50) of Cardium while theother chamber had a higher concentration (200) of the same. All theCardium used in this experiment was relatively small (b7 mm).

xperiment. A) Natica tigrina. B) Cardium sp.

Table 1Differences in cannibalistic attacks between experimental treatments. All p-values are the result of Fisher's exact tests and are in boldface font when less than 0.05.

Factors Experimental groups Number of cannibalistic attacks Total number of Natica tigrina Frequency p

Preferred prey High concentration 3 65 0.05 0.04Low concentration 11 69 0.16

Dissimilarity in size Dissimilar size 7 27 0.26 0.01Similar size 10 127 0.08

Ontogenetic stage Early 4 77 0.05 0.1Late 6 50 0.12

Table 2Differences in predatory attacks between ecological groups. Except for thefirst row, all attacks are cannibalistic in nature. All p-values are the result of Fisher's exact tests and are in boldfacefont when less than 0.05.

Factors Ecological groups Number of drill holes Total number of drill holes Frequency p

Preferred prey Cardium 46 263 0.34 0.01Natica 42 383 0.11

Dissimilarity in size Dissimilar size 32 42 0.76 0.0001Similar size 10 42 0.24

Ontogenetic stage Early 8 42 0.19 0.00001Late 34 42 0.81

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2.3.3. Experiment 2: Effect of size ratioWe used three chambers with only Natica specimens for this series

of experiment. In the 1st chamber, a mixed size class of Natica waskept with an equal proportion small (b15 cm) and large (N20 cm)specimens. The 2nd chamber had all small sized Natica while the 3rdchamber had all large ones.

2.3.4. Experiment 3: Ontogenetic stageData from 2nd and 3rd chamber (described above) were used for

this experiment.

Fig. 2. Plots showing the effect of preferred prey on cannibalism. A) Experimental data showingThe grey bar represents the experimental setup with high bivalve density while the black bafrequency in various prey items. The black bar represents Cardium sp. while the grey bar reprprey and conspecific.

2.4. Ecological data

Dead specimens ofN. tigrina and Cardium sp. collected from field citewere used as ecological specimens for this study. The distribution ofmolluscan species is very patchy and highly seasonal in the field area.Therefore, we collected all the specimens from a 100 m2 grid in thetidal flat thatwas entirely dominated byN. tigrina and Cardium sp. Spec-imens found within sediments up to a depth of 1 cm were also consid-ered. All the specimens were then washed and checked under sortingdesk to differentiate between the drilled and the undrilled ones. Onlythe complete specimens were considered for this study. Each drilled

the difference in cannibalistic attack with difference abundance of preferred bivalve prey.r represents a low density. B) Experimental data on the difference between the drillingesents Natica tigrina. C) Ecological data showing different degree of drilling in preferred

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individual was measured for height, width, aperture size and the outerdiameter of the drill hole (OBD).

2.5. Analysis

Each drill hole on a gastropod is considered as an event of cannibal-ism; hence, the frequency of cannibalism is calculated by diving thenumber of drill holes by the total number of gastropods. For calculatingthe drilling frequency in bivalves, we used the equation proposed byKowalewski (2002) where the frequency of drilling predation is calcu-lated by dividing half of the number of drilled valves by the total num-ber of valves in the collection. Outer drill hole diameter and the size ofthe responsible Natica from our experiment are used to deduce a rela-tionship between the two.

To compare the intensity of cannibalism in various groups, we usedChi-square test. All statistical analyses were performed in PAST 2.12(Hammer et al., 2001).

3. Results

3.1. Predation record

We recorded a total of 160 drill holes of which 41 represents canni-balistic attack (Table 1). Among the ecological specimens, we found 42cannibalistic attacks out of a total of 88 drilling incidents (Table 2).

3.2. Effect of preferred prey

Our experimental data shows that the presence of bivalve prey playsan important role in controlling the intensity of cannibalism. This specif-ic prey Cardium is beneficial over Natica because of their thin shell incomparison to the smooth, thick shell of Natica of same size (personalobservation, 2013). Cannibalism is significantly lower when bivalve

Fig. 3. Plots showing the effect of size ratio of predator–prey on cannibalism. A) Experimental dresents the experimental setupwith dissimilar size of predator–preywhile the black bar represepredator size for the ecological specimens. The size ratio between predator and prey is 1 on thshowing different degree of drilling in various size groups. The grey bar represents the attacksvolved individuals are of similar size.

prey is abundant; cannibalism increases with a decreasing abundanceof bivalve prey (Fig. 2A). The overall rate of cannibalism is significantlylower than the frequency of drilling in bivalves thereby making it thepreferred prey (Fig. 2B).

Ecological data also shows a significant difference between cannibal-ism intensity and drilling intensity on bivalves. The bivalves show amuch higher drilling frequency (35%) compared to cannibalism intensi-ty (10%) (Fig. 2C).

3.3. Effect of size ratio between predator and prey

Our experimental results show that rate of cannibalism is higherwhen predator andprey size are strongly dissimilar compared to scenar-ios with similar size (Fig. 3A). This difference is statistically significant.

Ecological data also shows a similar pattern. Using the followinglength vs. OBD relationship from this experiment, we reconstructedthe size of the predator.

Predator size ðmmÞ ¼ 8:64�OBD ðmmÞ þ 5:62

While dissimilar predator–prey pair accounts for the majority (76%)of cannibalism, only a small fraction (24%) of cannibalism involves groupsof similar size (Fig. 3B and C). This difference is statistically significant.

3.4. Effect of ontogenetic stage of predator

Our experiment shows a difference between the cannibalistic activ-ity of small (b10mm) and large (N15mm) gastropods. The larger indi-viduals show a higher propensity for cannibalism compared to theyoung individuals (Fig. 4A).

Ecological data shows a similar trend with higher cannibalism bylarger gastropods compared to smaller ones (Fig. 4B). They also showa significant difference in prey preference; while the young individuals

ata showing the difference in cannibalistic attack in various size groups. The grey bar rep-nts groupswith similar size. B) Plot showing the relationship between prey and estimatede black line. The grey lines indicate 95% CI of the observed relationship. C) Ecological datawith dissimilar size of predator–prey while the black bar represents attacks where the in-

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preferentially attack bivalve prey, the larger gastropods aremore canni-balistic (Fig. 4C).

4. Discussion

4.1. Effect of preferred prey

Cannibalism is often associated with a decline in alternative prey inmany organisms (Fox, 1975; Polis, 1981, 1988). For naticids also, it issuggested that cannibalism may result from the lack of alternativeprey (Paine, 1963; Taylor, 1970). Under such conditions of food limita-tion, cannibalismmay increase because hunger increases foraging activ-ities and food deprived conspecific prey may be more vulnerable toattack. Dietl (2003) attributed cannibalism by the fasciolariid gastropodTriplofusus giganteus to increased hunger that is induced by lack of alter-native resources. Our experimental data also showed an increase in can-nibalism with the decreasing abundance of preferred bivalve prey. Inthe ecological observation, however, assemblages containing cannibal-ized naticids also include abundant drilled bivalves, suggesting that can-nibalism was not a “last resort” of starving naticid predators. However,there could be spatial patches with low concentration preferred bivalveprey that may lead to cannibalism in the natural setting.

4.2. Effect of size ratio

It is generally assumed that cannibals can capture only victims that aresmaller than some critical body size owing to morphological limitationssuch as the ability of prey to escape an attack (Christensen, 1996). The

Fig. 4. Plots showing the effect of ontogenetic stage of the predator on cannibalism. A) ExperiThe grey bar represents the experimental setup with smaller (younger) individuals while the bof drilling in various ontogenetic stages. The grey bar represents the attacks by smaller (younC) Ecological data showing the prey preference in different ontogenetic groups. The grey bar repby the larger (older) individuals. The vertical striped bars indicate the proportion of bivalve pr

upper limit to victim size is often assumed to be a fixed ratio of cannibalsize (DeAngelis et al., 1979; Cushing, 1992; Fagan and Odell, 1996;Dong and DeAngekis, 1998) but the precise relationship between canni-bal size and victim size is rarely known. These studies provide evidencethat there is also a lower limit to the victim sizes that cannibals cantake, which has been explained in terms of difficulties in the detectionand retention of very small prey (Lundvall et al., 1999), and evidencethat the capture rate reaches a maximum at an intermediate ratio ofvictim length to cannibal length (Amundsen, 1994; Lovrich andSainte-Marie, 1997; Lundvall et al., 1999). There are exceptions to thispattern of size dependence, such as larger individuals falling victim to“group cannibalism” by smaller ones (Polis, 1981). Irrespective of taxonidentity, an increasing rate in cannibalism with highly size-diamorphicprey population is predicted by theoretical modelling (Dercole andRinaldi, 2002).

Drilling predators often show a preferred size of prey that can be ex-plained from cost-benefit analysis (Kitchell et al., 1981; Chattopadhyayand Baumiller, 2009). A possible deterrent to cannibalism would be ascenario where the cannibalistic interaction proved dangerous to thepredator. Dietl and Alexander (2000) have argued that confamilialnaticid predation can be considered dangerous because the “hunted”individual may turn on its predator and become the “hunter”; a largerattacking predator could be killed by its smaller prey if the smallerprey has a larger foot or is more aggressive. Such a scenario is not likelyto occur in conspecific cannibalism. However, if a size differential existsbetween conspecifics during attempted cannibalism, the smallerindividual will be killed (Kitchell et al., 1981) without endangeringthe larger individual. In such cases, smaller naticid prey would not be

mental data showing the difference in cannibalistic attack in different ontogenetic stage.lack bar represents larger (older) individuals. B) Ecological data showing different degreeger) individuals while the black bar represents attacks by the larger (older) individuals.resents the attacks by smaller (younger) individuals while the black bar represents attacksey and the dotted bars indicate proportion of cannibalism.

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considered dangerous to larger conspecific predators, obviating thispossible deterrent to cannibalism. Our experimental and ecologicaldata point to the existence of this viable ratio in predator–prey sizefor a cannibalistic attack; majority of the cannibalistic attacks demon-strates a significant deviation from a 1:1 ratio between predator–preysizes (Fig. 3B).

4.3. Effect of ontogenetic stage

It is often claimed that predatory behavior varied depending on theontogenetic stage of the predator (Polis, 1988). The same has been ar-gued specifically for naticid predators (Kitchell et al, 1981; Zlotnik,2001). Older naticids often show higher size and site-selectivity thanthe younger ones increasing the net energy gain with ontogeny(Zlotnik, 2001). The magnitude of cannibalism also seems to be depen-dent on ontogenetic stage as demonstrated by the experimental as wellas the ecological data.

4.4. Fossil data

Extending the present findings to the fossil record could be quitechallenging because the resolution of identification based on drillmarks is only up to family level. Hence, it is extremely difficult, if not im-possible, to ascertain a conspecific cannibalism in a multi-predator

Fig. 5. Plots showing the cannibalistic behavior of Natica tigrina from Korytnica Clays (Middle Mferent degree of drilling in bivalve prey (Corbula gibba) and conspecific. B) Plot different degre(younger) individualswhile the black bar represents attacks by the larger (older) individuals. C)the attacks by smaller (younger) individualswhile the black bar represents attacks by the largerdotted bars indicate proportion of cannibalism.

assemblage. Moreover, these behaviors observed in the experimentalsetting and ecological assemblages, could very well be species specific.

The study of drilling predation by naticid gastropods on molluscsfrom the Korytnica Clays (Middle Miocene, Holy Cross Mountains,Central Poland) by Zlotnik (2001) presents an excellent opportunity toextend our findings to fossil record. This study focused on drilling onthe bivalve Corbula gibba and gastropodsN. tigrina andHinia restitutiana.The characteristic feature of the drill hole and the overwhelmingly dom-inant population of naticids in the assemblage helped the author to ruleout the possibility of predation by muricids. The naticidae family inKorytnica Clays is represented by seven species belonging to six genera(Bałuk, 1995). Although, it is almost impossible to identify a naticid spe-cies on the basis of drill hole morphology (Bromley, 1981; Kowalewski,1990), the relative abundance of species shed light on the identity of thepredator. The study reveals the dominant species to be N. tigrinarepresenting 95% of all specimens of naticids. Therefore, majority ofthe drillings in N. tigrina are cannibalistic in nature. Moreover, this as-semblage also has a bivalve species that is comparable in size(b7 mm) (Zlotnik, 2001) with the bivalve species used in our study.

The study reveals a significantly higher drilling rate in thebivalveprey,C. Gibba, compared to the cannibalism (Fig. 5A). This is similar to the pat-tern that we observed in our ecological observation. As the size of drillhole for each Natica prey is not available (personal communication withZlotnik, 2013), it is not possible to test the hypothesis regarding the effect

iocene, Holy Cross Mountains, Central Poland) after Zlotnik (2001). A) Plot showing dif-e of drilling in various ontogenetic stages. The grey bar represents the attacks by smallerPlots showing the prey preference in different ontogenetic groups. The grey bar represents(older) individuals. The vertical striped bars indicate the proportion of bivalve prey and the

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of size ratio on cannibalism. However, the study shows the behavior ofgroups of small vs. large Natica as predators. The criterion used by thisstudy to distinguish between small and large predator is a specific valueof the drill hole diameter (1 mm) which corresponds to the Natica bodysize of 15mm; this is the cut offwe used to define small and large individ-uals in our study. Similar to our experimental and ecological findings, thisstudy finds a significantly higher level of cannibalism initiated by large in-dividuals (Fig. 5B). Moreover, it also demonstrates a shift in prey prefer-ence with ontogeny; large Natica are more cannibalistic and less likelyto drill C. gibba than small ones. In contrast, small individuals less fre-quently initiated cannibalistic attacks; their drilling effort is dominantlyconcentrated on the bivalve prey, C. gibba (Fig. 5C). This observation isagain identical to our ecological findings.

5. Implication

Cannibalism in natural communities plays amajor role in shaping upthe population structure of the interacting species in an environment(Polis, 1981). A wide variety of taxonomic group is observed to be in-volved in cannibalistic act (Fox, 1975; Elgar and Crespi, 1992). The func-tional explanation of cannibalism involves the consideration of netbenefit of the cannibalizing individual. Energetic advantage is one ofthe most important function (Polis, 1981; Hoelzer, 1992; Belles andFitzgerald, 1993; Sowig, 1997; Lindstrom, 1998; Ebensperger et al.,2000), and hence, cannibalism is considered to be an optimal foragingprocess (Dong and Polis, 1992). Cannibalism is promoted in environ-ments where food is often limited (Hopper et al., 1996; Samu et al.,1999) and it has an adaptive function (Giray et al., 2001).

Shell drilling gastropods is one of the rare examples where cannibal-ism is found in fossils record (Kitchell et al., 1981; Basedow, 1996; Dietl,2003; Gould, 2010; Huchings and Herbert, 2013) and can be studied ingeologic time scale. The causality for cannibalism is attributed to variousreasons, from being anomalous and restricted to laboratory conditions(Kojumdjieva, 1974) to rational explanations as crowding of conspecificindividuals and/or stress created due to low availability of heterospecificprey (Paine, 1963; Stanton andNelson, 1980). In this studywe addressedthree factors that might control cannibalism in a naticid species,N. tigrina. This study uses a three-fold approach to address this issue.While the experimental approach provided uswith control over the pos-sible parameters, the ecological observation helped us in assessing thereliability of the experimental result in natural setting. In addition, an in-dependent study by Zlotnik (2001) provided fossil evidences which fur-ther support our findings. Such amulti-approach strategy to understandan ecological phenomenon is quite rare.

Considered as a unique evolutionary endpoint in terms of survivalamong the intraspecific interaction (Nishimura and Isoda, 2004), canni-balism among groups has survived and often increased over geologictime as documented by the fossil record (Kelley and Hansen, 2007).Due to its successful propagation through time, the act of cannibalisticbehavior by individuals of a population has its own evolutionary signif-icance. Using mathematical modelling, cannibalism has been demon-strated to be an evolutionary stable strategy (ESS) that helps toregulate the population dynamics (Reed and Stenseth, 1984; Dercoleand Rinaldi, 2002; Nishimura and Isoda, 2004). Moreover, such studiesalsopredict theunequal level of cannibalism in size/age-structured pop-ulations as a requirement of ESS. This prediction is corroborated by ourcurrent findings. Using experimental and paleoecological data, we wishto study the evolutionary effect of cannibalism as an evolutionary stablestrategy (ESS) in greater detail.

Acknowledgment

The comments of P. Kelley and G. P. Dietl significantly improved thearticle.M. Zlotnik provided uswith important information about the de-tails of Miocene naticids of Korytnica Clays. We are thankful to Raja forhis help in acquiring live specimens. We are also thankful to Mr. Sanjay

Gosh for his support in aquarium maintenance. This work is funded byStartup Grant, Academic and Research grant and Graduate StudentFellowship of Indian Institute of Science Education and Research(IISER) Kolkata and INSPIRE fellowship.

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