Ontogenetic Diet Shifts Research Articles

The effects of fishing on the ontogeny of trophic position and body condition of a small-sized temperate marine fish

Using rainbow wrasse as a model species, we evaluate the impact of protection on the relationship between body size and: i) trophic position (TP), based on δ15N; and ii) body condition (BC), based on weight-at-length. We found that the biomass of the rainbow wrasse, their predators and their competitors was higher inside the no-take marine protected area (NTA) than in the area open to fishing. The TP of rainbow wrasse was higher inside the NTA but the BC was lower. A domed relationship between TP and size was observed in both areas: the TP increased with size up to 12.6 cm total length, when all individuals shifted to terminal males, and then decreased. Although other confounding environmental variables may exist, the indirect effects of fishing on competition and predation risk are the most likely explanation for the changes in TP, BC and the ontogenetic dietary shift of the rainbow wrasse.

Impacts of ontogenetic dietary shifts on the food-transmitted intestinal parasite communities of two lake salmonids.

Ontogenetic dietary shifts are common in fish and often impact trophically transmitted parasite communities. How parasite species composition and relative abundances change among size classes, and at what rate these changes occur, is rarely examined. Hosts with a broad trophic niche are potentially exposed to a large variety of parasite species. The degree of ontogenetic changes in parasite species composition versus changes in parasite abundance should suggestively differ between thropically generalist and specialist host species. In the present study, we explore ontogenetic dietary shifts and their impact on species composition and relative abundance of intestinal parasites in two sympatric salmonid fish species, Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) caught in the littoral habitat of a subarctic lake. Our results highlight a close interplay between ontogenetic dietary niche shifts and alterations in the acquisition of trophically transmitted parasites, leading to host-specific differences in the component community of parasites. Ontogenetic changes in the intestinal parasite community related to dietary niche shifts were distinct but less pronounced in Arctic charr than in brown trout due to a broader and more consistent dietary niche of the former and an ontogenetic shift toward piscivory in the latter. At the component community level, changes in parasite assemblages of both host species were driven by a faster increase in the heterogeneity of parasite relative abundance than in the compositional heterogeneity, a pattern that partly may be related to a rather species-poor parasite community of this subarctic study system. Separating compositional heterogeneity from heterogeneity in relative parasite abundance is important to understand how size-dependent variability shapes parasite communities of host populations.

A Review of Galaxias (Galaxiidae) Fossils from the Southern Hemisphere

The Galaxiidae is a Southern Hemisphere family of freshwater fish, considered to be of Gondwanan origin based on the current distribution of species in New Zealand, Australia (including Tasmania), New Caledonia, Africa, South America, and on some associated and subantarctic islands. The fossil record of galaxiids is extremely sparse and geographically restricted. The only galaxiid fossils currently known come from several Miocene lakes in southern New Zealand. They include more than 100 articulated fishes, some remarkably preserving soft parts such as eyes and skin, skulls and jaw components, and more than 200 isolated otoliths. Common coprolites and in situ preserved gut content at one site (Foulden Maar) indicate the different diets of larvae and adult fish. These discoveries reveal a diverse Galaxias fauna, the presence of lake-locked populations, ontogenetic diet shifts, and representatives of several non-migratory Galaxias lineages associated with inland streams and lakes. There are at least six Galaxias species based on macrofossils and six separate otolith-based species from varied volcanic and regional lacustrine environments. This diversity points to southern New Zealand as a centre of biodiversity and speciation in Galaxiidae in the early to late Miocene.

Ontogenetic dietary shifts in Deinonychus antirrhopus (Theropoda; Dromaeosauridae): Insights into the ecology and social behavior of raptorial dinosaurs through stable isotope analysis

The image of the highly intelligent, pack-hunting raptor has become engrained in scientific literature and popular works alike. First proposed to explain the relatively common co-occurrence of the large-bodied iguanodontian Tenontosaurus tilletti and the wolf-sized Deinonychus antirrhopus from the Lower Cretaceous of North America, a canid-like social hunting structure has become the standard depiction of dromaeosaurs in popular works over the last three decades. This reconstruction is, however, problematic largely due to the fact that highly coordinated hunting strategies are rarely observed in modern archosaurs. This has led to the alternative hypothesis that D. antirrhopus was more analogous to agonistic reptilian carnivores, like the Komodo dragon (Varanus komodoensis). Among the many differences between these two analogs is how social and asocial organisms rear their young, producing a diagnostic pattern based on the presence or absence of ontogenetic dietary changes. In order to test for dietary changes through growth, stable carbon and oxygen isotope (δ13C, δ18O) analysis was performed on tooth carbonate from small (<4.5 mm crown height) and large (>9 mm crown height) D. antirrhopus specimens from two microsites from the Lower Cretaceous Cloverly (Montana) and Antlers (Oklahoma) formations. Teeth from goniopholidid crocodylians and Tenontosaurus tilletti from the Cloverly Formation were also tested for comparison. The results show that the Cloverly goniopholidids, like their modern counterparts, went through a distinct transition in diet as they grew. The smallest teeth were the relatively most enriched in 13C (mean = −9.32‰; n = 5), the medium-sized teeth were the most-depleted in 13C (mean = −10.56‰; n = 5), and the largest teeth were intermediate (mean = −10.12‰; n = 6). These factors are characteristic of the dietary shifts seen in modern asocial reptiles. D. antirrhopus showed this same pattern in tooth samples collected from both rock units, with small teeth being the more enriched in 13C (mean = −8.99‰; n = 10) and the large teeth being more depleted in 13C (mean = −10.38‰; n = 10). These differences suggest that juvenile and adult D. antirrhopus from both formations likely consumed different prey. Hypothetical food sources, such as T. tilletti, are close to the 13C isotopic signal of adult D. antirrhopus, consistent with the hypothesized trophic relationship (predator-prey) between these two species. Juvenile D. antirrhopus had a diet more enriched in 13C, likely composed of smaller-bodied, but trophically-higher species. Taken together, these data add to the growing evidence that D. antirrhopus was not a complex social hunter by modern mammalian standards.

New insights into the trophic ecology of young white sharks (Carcharodon carcharias) in waters off the Baja California Peninsula, Mexico

White sharks (Carcharodon carcharias) are described as generalist predators, with a demonstrated ontogenetic dietary shift which occurs between subadult and adult life stages. Trophic ecology studies on white shark have been focused mainly on large and mature individuals, necessitating studies of young white shark trophic ecology to better understand their resource use. This study provides new insights into young white shark diet in the North eastern Pacific Ocean using stable isotope analysis in muscle tissues. We analyzed δ13C and δ15N values of young white shark muscle (n = 21) from Sebastian Vizcaino Bay (SBV) during 2015–2018. We found changes in prey composition across early [neonates, young-of-the-years (YOYs), juveniles] white shark life stages, with significant changes in isotopic composition throughout early ontogeny. Mixing model results indicate a high use of coastal areas for foraging, mainly for juvenile stages and the substantial contribution of pelagic preys (e.g., S. japonicus, Prionotus spp., Cynoscion spp., S. sagax, etc.) in YOYs, white shark diet also indicates an important role of offshore foraging. This change in isotopic composition likely represents the shift from the embryo’s typical maternally derived isotopic signature, incorporated in offshore foraging regions, to the postpartum isotopic composition incorporated by foraging neonates in inshore nursery habitats. This study provides relevant information regarding young white shark feeding preferences, reinforces the importance of coastal areas as critical habitat for the development and the successful foraging of this species, and also provides indirect insights on the feeding habits of the adult female of white sharks, which constitutes a baseline for further research.

Ectothermic omnivores increase herbivory in response to rising temperature

Higher temperatures as a consequence of global climate change may considerably alter trophic interactions. Ectothermic herbivores and carnivores generally ingest more food with rising temperature as their metabolic rates increase with rising temperature. However, omnivorous ectotherms may respond in two ways: quantitatively by consuming more food and qualitatively by altering their degree of herbivory or carnivory through a diet shift. We hypothesize that rising temperature will increase herbivory of ectothermic omnivores as herbivory increases towards the equator. We tested the hypothesis in a freshwater model system in which ectothermic omnivores are prevalent, by applying two approaches, a temperature manipulation experiment and a literature study. We performed feeding trials with a juvenile aquatic ectothermic omnivore (pond snail Lymnaea stagnalis) at different temperatures ranging from 12 to 27°C, supplying them with both animal food and plant material, and directly quantified their consumption rates over time. The results showed that snails cultured at high temperatures (&gt; 21°C) increased the proportion of plant material in their diets after 17 days, which supports our hypothesis. In the literature survey, we found that rising temperature increased herbivory in multiple aquatic animal taxa, including zooplankton, amphibians, crayfish, fish and snails. This suggests that aquatic ectothermic omnivores might commonly increase herbivory with rising temperature. The mechanisms underlying this temperature‐induced diet shift are not sufficiently explained by current theories related to the physiology, metabolism and stoichiometry of omnivores. We propose to incorporate the animals’ ontogenetic development in the temperature metabolic stoichiometry hypothesis as a complementary explanation for the diet shift, namely that the diet shift could be due to faster development of the ectotherms and an earlier ontogenetic diet shift at higher temperatures. We conclude that future global warming will most likely alter food webs by increasing the top–down control of aquatic herbivores and omnivores on primary producers.

Ontogenetic diet change of hadal amphipods in the New Britain Trench revealed by fatty acid biomarker and stable isotope ratio

The hadal zone (from 6 to 11 km depth) is one of the least explored habitats on Earth, and the knowledge about trophic ecology of hadal organisms is limited. Here, we analyzed fatty acid biomarker and stable isotope ratios of the amphipod species (Alicella gigantean) collected in the New Britain Trench (8225 m depth) in the southwestern Pacific Ocean. A total of 50 samples were divided into five developmental stages according to body length (1–129 cm): Stages I (juvenile), II (sub-adult) and III/IV/V (adult). Stages III, IV and V were further divided according to sex. Mean total fatty acid content for stage I (237.7 ± 105.6 mg g-1) was significantly lower than that for stages II to V (476.4 ± 49.0 mg g-1). The δ15N (14.7–18.4‰) positively correlated with the body length, whereas the EPA/DHA (C20:5ω3/C22:6ω3) ratio (0.09–0.51) negatively correlated with the body length. These results suggested an increase of trophic level with growth. Principal component analysis (PCA) separated major fatty acids into three clusters: (1) C18:1ω9, C16:1ω7, C14:1ω5 (indicative of carrion-based diet); (2) C14:0, C15:0, isoC15:0, C16:0, C17:0, isoC17:0, anteisoC17:0, C18:1ω7, C18:0, C20:1ω9, and C22:1ω9 (bacteria/zooplankton-based diet); and (3) C20:4ω6, C20:5ω3, C22:6ω3 and C22:5ω6 (benthic fauna/algae-based diet). The PCA result revealed that stage I-individuals consumed more bacteria/zooplankton debris, stages II to IV-individuals primarily preyed on carrion, while stage V-individuals had more diverse diet (benthic fauna/algae and carrion). Female amphipods had higher proportions of monounsaturated fatty acids, lower proportions of polyunsaturated fatty acids, and higher δ15N compared to male amphipods, suggesting that female individuals rely more on carrion from higher trophic organisms. This sex-related difference, however, diminished from stage III to V. Overall, our fatty acid and stable isotope data suggest an ontogenetic diet shift for hadal amphipods that may contribute to their success in the deepest ocean.

The branchial skeleton in Aptian chanid fishes (Gonorynchiformes) from the Araripe Basin (Brazil): Autecology and paleoecological implications

Gonorynchiformes are a small, but morphologically diverse group of teleost fishes with an extensive fossil record. Most extant gonorynchiforms are efficient filter feeders, bearing long gill rakers and other morphological specializations, such as microbranchiospines and an epibranchial organ. The analyses of the gill arch of the Brazilian gonorynchiform fishes Dastilbe crandalli and Tharrias araripis from the Aptian of the Araripe Basin, Northeast Brazil, demonstrate significant morphological variation suggestive of distinct feeding habitats as well as ontogenetic dietary shifts in these closely related gonorynchiforms.

Skull ontogenetic variation of the coastal developmental stage of the loggerhead turtle (Caretta caretta) in the western South Atlantic Ocean

The present study aims to describe the ontogenetic changes in the skull of the loggerhead turtle, Caretta caretta by focusing on the stages of development in the western South Atlantic Ocean. Our hypothesis is based on the premise that changes in feeding habits will reflect changes in the shape and/or size of the skull. The existence of changes in skull of the loggerhead turtle were analyzed using traditional and geometric morphometrics on skulls collected from stranded individuals in the southern Brazilian coast. As a general result, a transformation pattern was observed: from younger specimens with smaller, elongated and flattened skulls towards a larger, rounded and more robust skull in older specimens. It is suggested that these skull changes are associated with the diet shift of the loggerhead turtle specimens, providing the skull with greater mechanical resistance and enabling a change in feeding strategy from soft organisms to hard-shelled preys. This result highlights the importance of southern Brazilian coast for the life cycle of the loggerhead turtle. In this region, the individuals undergo the process of ontogenetic diet shift, changing their skull shape to adapt to the newly occupied niche and ensuring the ecological success of the species.

Spatial and Temporal Trends in Diet for Pinfish (Lagodon rhomboides) from Turtle Grass (Thalassia testudinum) Beds with Contrasting Environmental Regimes in the Lower Laguna Madre, Texas

Seagrass meadows in far South Texas are dominated by turtle grass (Thalassia testudinum), and juvenile pinfish (Lagodon rhomboides) are abundant grazers of seagrass epifauna. As they grow, pinfish exhibit an ontogenetic dietary shift and begin consuming increasing amounts of plant material. In this study, contrasting environmental regimes in two seagrass meadows were examined to identify how they might affect pinfish diets, diet shifts, and growth across the growing season. The eastern site was sheltered from prevailing southeasterly winds by a barrier island, while the western site was shallower and subjected to higher wind energy and turbidity. Gut contents from 290 pinfish were quantified from May through October 2016 and multivariate analyses showed strong but overlapping separation of diets and temporal change in feeding habits. Although there were spatial and temporal differences between the two sites, a site by time interaction indicated different temporal trends. Nonetheless, ooze (amorphous detritus) and aquatic invertebrates (primarily amphipods) were the primary diet items consumed at both localities across time. Pinfish at both sites consumed seagrass, which increased in importance as the growing season progressed, although volume and consumption rate did not differ between sites. Growth rates of pinfish were similar at both sites, but pinfish from the western site were larger and fewer in number across the study. Although pinfish diets differed under different environmental regimes, they were generalist consumers in South Texas seagrass meadows with high diet variability that trended towards herbivory in late summer and fall.

Predator population size structure alters consumption of prey from epigeic and grazing food webs.

Numerous studies have found that predators can suppress prey densities and thereby impact important ecosystem processes such as plant productivity and decomposition. However, prey suppression by spiders can be highly variable. Unlike predators that feed on prey within a single energy channel, spiders often consume prey from asynchronous energy channels, such as grazing (live plant) and epigeic (soil surface) channels. Spiders undergo few life cycle changes and thus appear to be ideally suited to link energy channels, but ontogenetic diet shifts in spiders have received little attention. For example, spider use of different food channels may be highly specialized in different life stages and thus a species may be a multichannel omnivore only when we consider all life stages. Using stable isotopes, we investigated whether wolf spider (Pardosa littoralis, henceforth Pardosa) prey consumption is driven by changes in spider size. Small spiders obtained > 80% of their prey from the epigeic channel, whereas larger spiders used grazing and epigeic prey almost equally. Changes in prey consumption were not driven by changes in prey density, but by changes in prey use by different spider size classes. Thus, because the population size structure of Pardosa changes dramatically over the growing season, changes in spider size may have important implications for the strength of trophic cascades. Our research demonstrates that life history can be an important component of predator diet, which may in turn affect community- and ecosystem-level processes.

Diet and food partitioning between juvenile of Epinephelus coioides (Perciformes: Epinephelidae) and other co-existing juvenile fishes in shallow waters of Thailand and Malaysia

This work examined diet composition of the juvenile orange-spotted grouper, Epinephelus coioides, and its trophic association with other juvenile fish species in tropical estuarine habitats during recruitment. From December 2015 to March 2016, juveniles were collected, their stomachs excised, preserved and analyzed. Small shrimps and amphipods, especially Grandidierella sp. and Elasmopus sp., were the most common food resources sharing among the most species. Epinephelus coioides predominantly ingested small shrimp, Grandidierella sp., Elasmopus sp. and fish larvae and had the greatest trophic overlap with Palatrus scapulopunctatus. Fish size, location and month significantly affected fullness indices and food items diversity in E. coioides. It is clear that the larger the size of E. coioides and its mouth opening, the larger the size of items ingested. This study confirms the ontogenetic dietary shift of juvenile E. coioides during recruitment season by starting as amphipod and small shrimp feeder and shifting to shrimp and fish larvae predator as they grow. This finding is fundamental to understanding how juvenile E. coioides cope with different conditions and its association with other co-existing species during the recruitment period.

Dietary Partitioning in Two Co-occurring Caecilian Species (Geotrypetes seraphini and Herpele squalostoma) in Central Africa.

SynopsisTrophic interactions among fossorial vertebrates remain poorly explored in tropical ecosystems. While caecilian species can co-occur, whether and how sympatric species partition dietary or other resources are largely unknown. Based on specimens collected during field surveys in southern Cameroon, we conducted a dietary analysis of two co-occurring caecilian species, Geotrypetes seraphini and Herpele squalostoma. We find a negligible overlap in the adult diets of these two species. Earthworms dominated the diet of adult G. seraphini, whereas we found that mole crickets were the most frequent prey items in adult H. squalostoma. The dietary breadth of adult G. seraphini is smaller than that of H. squalostoma, which consumes a variety of hard-bodied prey including mole crickets, cockroaches, beetles, and crabs. Juvenile diets were similar between these species and mostly contained earthworms and ants. We did not detect significant ontogenetic dietary shifts in either species, though adults generally consumed a broader diversity of prey. As adults, G. seraphini and H. squalostoma may partition prey categories by consuming soft-bodied and hard-bodied prey, respectively. Because most caecilians are likely opportunistic predators, we expect that sympatric species partition dietary resources either by preference for different soil layers or ability to consume different prey categories.

Stomach content and stable isotopes reveal an ontogenetic dietary shift of young-of-the-year scalloped hammerhead sharks (Sphyrna lewini) inhabiting coastal nursery areas

Sphyrna lewini is a placental viviparous shark that uses coastal nursery areas in Jalisco, Mexico, where pups stay 4–12 months. Changes in size or swimming speed may be reflected in diet composition. The main objectives of this study were as follows: (1) analyze the differences in trophic ecology of juvenile S. lewini from coastal nursery areas of Jalisco by sex and size, through stomach content and stable isotope analyses; and (2) analyze changes in muscle and liver δ15N and δ13C values with shark size. Samples were collected from the artisanal fishery from September 2013 to December 2016. Three size classes were compared: neonates, stretched total length (STL) ≤ 75 cm, and STL > 75 cm (75–100 cm). Bony fishes were the most important group in all size classes, and the importance of shrimps decreased with STL. Significant differences in diet composition were found between neonates and STL > 75 cm, which showed the lowest niche overlap (0.32). STL ≤ 75 cm showed the largest niche width (0.75). The δ15N muscle and liver values declined with total length, reflecting the maternal isotopic signal. No differences in liver δ13C values were observed among size classes, but larger size class showed higher muscle δ13C values. Both isotope and stomach content analyses classified all sharks as tertiary consumers, but the trophic position (TP) estimated using δ15N was higher in neonates. No significant differences in the diet and TP were observed between sexes. The liver C:N ratio decreased sharply with STL up to 55 cm, from which increased smoothly, reflecting the lipid reserves consumed during their neonatal stage.

Diet of longnose stingray Hypanus guttatus (Myliobatiformes: Dasyatidae) in tropical coastal waters of Brazil

AbstractThis study investigated the diet of longnose stingray Hypanus guttatus in the tropical waters of north-eastern Brazil. Samples were obtained from monthly sampling of artisanal fisheries from August 2007 to July 2008. A total of 258 specimens were examined, 127 females and 131 males, and stomach contents analysis suggested H. guttatus to be a generalist and opportunistic predator feeding on the most available prey in the environment. There was no significant difference in the diet composition of males and females, or between seasons. However, an ontogenetic dietary shift was observed with larger individuals having an increased proportion of molluscs in the diet, whilst smaller individuals predated primarily on small crustaceans.

Ontogenetic variation in the diet of the anuran community from a semi-arid environment in the southeastern Chihuahuan Desert.

Although ontogeny influences dietary composition and trophic niche breadth in many anurans, its effects on diet have been little analyzed in sympatric species. In this study, we analyzed interspecific and ontogenetic variation in dietary composition and trophic niche width in an anuran community from a semi-arid environment. We found a more profound effect of species identity than body size on dietary composition, with the diet of four species dominated by formicids, that of two others by coleopterans and formicids, and that of the remaining species not dominated by specific prey types. We found ontogenetic changes in dietary composition in three of four species analyzed, in which consumption of some small insects decreased as predator size increased, regardless of species. Additionally, we did not find ontogenetic change in prey number consumed in any of the four species, but prey size increased with increasing predator size in all of them. Most species exhibited a narrow trophic niche, which was even narrower in adults in three of the four species analyzed. Costello’s modified plots revealed a high variation among individuals in termite consumption in Anaxyrus punctatus, and in more prey types in Spea multiplicata. Our results suggest that this community is not size-structured, and that ontogenetic diet shifts are mainly caused by passive sampling toward prey of different sizes. Finally, comparisons with previous data revealed an interpopulation pattern, in which trophic niche width contracts as aridity increases, possibly because of an increase in interspecific competition for trophic resources.

Ontogenetic and Temporal Diet Shifts of the Invasive Asian Swamp Eel in South Florida

AbstractThe Asian Swamp Eel Monopterus albus is an introduced species in South Florida waters and is considered to be a potential threat to the native biota and ecosystems in the region. As a protogynous hermaphrodite that, under the right climatic conditions, can travel short distances over land and tolerate abrupt shifts in salinity, this species has strong invasive potential. In this study, our main goal was to evaluate the potential effects of the Asian Swamp Eel as a predator on native fishes and other biota. Our specific objectives were to (1) analyze the stomach contents of introduced Asian Swamp Eels from canals located near Everglades National Park and (2) assess the ontogenetic and temporal shifts in their consumption of prey. We dissected 752 Asian Swamp Eels (107–833 mm TL), and 46.4% (N = 349) of the samples had stomach contents for the analyses. The analyses indicated that amphipods, fishes, dragonfly nymphs, Hemiptera insects, and grass shrimp Palaemonetes were the most important prey items for Swamp Eels. Swamp Darters Etheostoma fusiforme, juvenile Asian Swamp Eels, and centrarchids were the most common fishes eaten by Swamp Eels. Ontogenetic shifts in diet were apparent, with amphipods and dipteran larvae most often observed in the stomachs of small‐ to medium‐sized Swamp Eels and fish, dragonfly nymphs, and Hemiptera insects more commonly identified in the stomachs of larger eels. The Swamp Eels also became increasingly piscivorous with size. Dragonfly nymphs and grass shrimp occurred more frequently in the Swamp Eel diets in May 2010, while the consumption of fish and amphipods increased in October 2010. Fish were the most important prey item that was consumed during the November–December 2009 period, although other prey items were relatively important during that collection period. As an opportunistic predator that consumes a wide range of prey, the Asian Swamp Eel likely has its greatest effects on native biota and ecosystems as a predator and competitor with native fishes for resources.

Evaluation of food competition and resource partitioning of recruiting fish with permanent residents in a seagrass habitat

ABSTRACT Recruiting King George whiting Sillaginodes punctatus were studied to assess the potential for food competition with permanent resident fish species in a nursery habitat. Marine migrant post larval S. punctatus (<60 mm TL) consumed primarily harpacticoid copepods and had high (>0.6) diet overlap with permanent resident fish species Favonigobius leteralis and Stigmatopora nigra. Food electivity index indicated that S. punctatus juveniles preferred harpacticoid copepods and amphipods, while juvenile Heteroclinus adelaide and Gymnapistes marmoratus migrating to the nursery habitat targeted larger prey such as amphipods. Preference for larger prey by H. adelaide and G. marmoratus species coupled with differences in prey composition in the stomach was due to mouth size and feeding habits, resulting in different food preferences to S. punctatus. The whiting showed an ontogenetic shift in diet with early settlers (>60 mm TL) consuming less copepods and more amphipods, while previous year recruits (>120 mm TL) consumed polychaete worms. This study indicates that competition for food resources between the new recruiting S. punctatus juveniles and permanent resident juveniles is reduced through differences in temporal and spatial feeding behaviours, mouth morphology, and ontogenetic shift in prey consumption.

Diet-related selectivity of macroplastic ingestion in green turtles (Chelonia mydas) in the eastern Mediterranean

Understanding the drivers of key interactions between marine vertebrates and plastic pollution is now considered a research priority. Sea turtles are primarily visual predators, with the ability to discriminate according to colour and shape; therefore these factors play a role in feeding choices. Classification methodologies of ingested plastic currently do not record these variables, however here, refined protocols allow us to test the hypothesis that plastic is selectively ingested when it resembles the food items of green turtles (Chelonia mydas). Turtles in the eastern Mediterranean displayed strong diet-related selectivity towards certain types (sheet and threadlike), colours (black, clear and green) and shapes (linear items strongly preferred) of plastic when compared to the environmental baseline of plastic beach debris. There was a significant negative relationship between size of turtle (curved carapace length) and number/mass of plastic pieces ingested, which may be explained through naivety and/or ontogenetic shifts in diet. Further investigation in other species and sites are needed to more fully ascertain the role of selectivity in plastic ingestion in this marine vertebrate group.

Ontogenetic Dietary Shifts and Microscopic Tooth Wear in Western Chimpanzees

Microscopic tooth wear studies on primates have largely focused on interspecific dietary comparisons, while few have addressed intraspecific variations such as those among age groups. Here, we examined to what extent dietary shifts during ontogeny can be revealed from microscopic tooth wear in a western chimpanzee population using 3D surface texture (3DST) analysis. To this end, we analyzed feeding observation data of 14 chimpanzees of the Taї National Park (Ivory Coast) and matched them to 3DST data analyzed on two wear facets (f9, f3) of deciduous fourth premolars and permanent molars of 41 specimens (infants, juveniles, adolescents, adults) of the same population. We expected to find an age-dependent increase in texture complexity resulting from the more frequent consumption of seeds and insects in older compared to younger individuals. Furthermore, we expected the introduction of phytolith-producing plants to the diet of post-weaned individuals to result in many small and parallel-orientated 3DST features in juveniles, adolescents and adults compared to infants. We found that the 3DST pattern did not mirror the observed increase in dietary breadth from infants to adults. However, we found that age-dependent differences in the consumption of phytolith-producing plants were reflected to some extent in the 3DST pattern: infants and adolescents who spent more time feeding on phytolith-producing plants than older individuals had more parallel orientated 3DSTs with higher peaks, while adults had flatter and more randomly orientated 3DST features. Our results suggest that phytoliths as small abrasive particles may be of greater importance for the 3DST formation than food categories such as fruits, leaves or seeds. However, compared to the variation in the feeding data, 3DST results show only little variation among age groups. We conclude that 3DST does not explicitly reflect ontogenetic dietary changes in chimpanzees. Rather, other factors, such as individual- or sex-based feeding habits as well as seasonal variation in dust accumulation, may be of greater importance for 3DST formation.