Short-term dietary changes are reflected in the cerebral content of adult ring-billed gulls.

Omega-3 long-chain polyunsaturated fatty acids (n3-LCPUFAs) are produced primarily in aquatic ecosystems and are considered essential nutrients for predators given their structural role in vertebrates' cerebral tissues. Alarmingly, with urbanization, many aquatic animals now rely on anthropogenic foods lacking n3-LCPUFAs. In this study undertaken in Newfoundland (Canada), we tested whether recent or longer term diet explains the cerebral fatty acid composition of ring-billed gulls (Larus delawarensis), a seabird that now thrives in cities. During the breeding season, cerebral levels of n3-LCPUFAs were significantly higher for gulls nesting in a natural habitat and foraging on marine food (mean ± s.d.: 32 ± 1% of total identified fatty acids) than for urban nesters exploiting rubbish (27 ± 1%). Stable isotope analysis of blood and feathers showed that urban and natural nesters shared similar diets in autumn and winter, suggesting that the difference in cerebral n3-LCPUFAs during the breeding season was owing to concomitant and transient differences in diet. We also experimentally manipulated gulls' diets throughout incubation by supplementing them with fish oil rich in n3-LCPUFAs, a caloric control lacking n3-LCPUFAs, or nothing, and found evidence that fish oil increased urban nesters' cerebral n3-LCPUFAs. These complementary analyses provide evidence that the brain of this seabird remains plastic during adulthood and responds to short-term dietary changes.

The origin, connectivity, and individual specialization of island wolves after deer extirpation.

Wolves are assumed to be ungulate obligates, however, a recently described pack on Pleasant Island, Alaska USA, is persisting on sea otters and other marine resources without ungulate prey, violating this long-held assumption. We address questions about these wolves regarding their origin and fate, degree of isolation, risk of inbreeding depression, and diet specialization by individual and sex. We applied DNA metabarcoding and genotyping by amplicon sequencing using 957 scats collected from 2016 to 2022, and reduced representation sequencing of tissue samples to establish a detailed understanding of Pleasant Island wolf ecology and compare them with adjacent mainland wolves. Dietary overlap was higher among individual wolves on Pleasant Island (Pianka's index mean 0.95 ± 0.03) compared to mainland wolves (0.70 ± 0.21). The individual diets of island wolves were dominated by sea otter, ranging from 40.6% to 63.2% weighted percent of occurrence (wPOO) (mean 55.5 ± 8.7). In contrast, individual mainland wolves primarily fed on ungulates (42.2 ± 21.3) or voles during a population outbreak (31.2 ± 23.2). We traced the origin of the Pleasant Island pack to a mainland pair that colonized around 2013 and produced several litters. After this breeding pair was killed, their female offspring and an immigrant male became the new breeders in 2019. We detected 20 individuals of which 8 (40%) were trapped and killed while two died of natural causes during the 6-year study. Except for the new breeding male, the pedigree analysis and genotype results showed no additional movement to or from the island, indicating limited dispersal but no evidence of inbreeding. Our findings suggest wolves exhibit more flexible foraging behavior than previously believed, and hunting strategies can substantially differ between individuals within or between packs. Nevertheless, anthropogenic and natural mortality combined with limited connectivity to the mainland may inhibit the continued persistence of Pleasant Island wolves.

Varying Diet Composition Causes Striking Differences in Legacy and Emerging Contaminant Concentrations in Killer Whales across the North Atlantic.

Lipophilic persistent organic pollutants (POPs) tend to biomagnify in food chains, resulting in higher concentrations in species such as killer whales (Orcinus orca) feeding on marine mammals compared to those consuming fish. Advancements in dietary studies include the use of quantitative fatty acid signature analysis (QFASA) and differentiation of feeding habits within and between populations of North Atlantic (NA) killer whales. This comprehensive study assessed the concentrations of legacy and emerging POPs in 162 killer whales from across the NA. We report significantly higher mean levels of polychlorinated biphenyls (PCBs), organochlorine pesticides, and flame retardants in Western NA killer whales compared to those of Eastern NA conspecifics. Mean ∑PCBs ranged from ∼100 mg/kg lipid weight (lw) in the Western NA (Canadian Arctic, Eastern Canada) to ∼50 mg/kg lw in the mid-NA (Greenland, Iceland) to ∼10 mg/kg lw in the Eastern NA (Norway, Faroe Islands). The observed variations in contaminant levels were strongly correlated with diet composition across locations (inferred from QFASA), emphasizing that diet and not environmental variation in contaminant concentrations among locations is crucial in assessing contaminant-associated health risks in killer whales. These findings highlight the urgency for implementing enhanced measures to safely dispose of POP-contaminated waste, prevent further environmental contamination, and mitigate the release of newer and potentially harmful contaminants.

Resource Availability, Sex, and Individual Differences in Exploration Drive Individual Diet Specialization.

AbstractIndividual diet specialization (IDS) is widespread and can affect the ecological and evolutionary dynamics of populations in significant ways. Extrinsic factors (e.g., food abundance) and individual variation in energetic needs, morphology, or physiology have been suggested as drivers of IDS. Behavioral traits like exploration and boldness can also impact foraging decisions, although their effects on IDS have not yet been investigated. Specifically, variation among individuals in exploratory behavior and their position along the exploration/exploitation trade-off may affect their foraging behavior, acquisition of food items, and home range size, which may in turn influence the diversity of their diet. Here, we analyzed stable carbon and nitrogen isotopes in hair of wild eastern chipmunks, Tamias striatus, to investigate the influence of individual differences in exploration on IDS. We found that exploration profile, sex, and yearly fluctuations in food availability explained differences in the degree of dietary specialization and in plasticity in stable carbon and stable nitrogen over time. Thus, consistent individual differences in exploration can be an important driver of within-population niche specialization and could therefore affect within-species competition. Our results highlight the need for a more thorough investigation of the mechanisms underlying the link between individual behavioral differences and diet specialization in wild animal populations.

Patterns of Herbivory in Neotropical Forest Katydids as Revealed by DNA Barcoding of Digestive Tract Contents.

Many well-studied animal species use conspicuous, repetitive signals that attract both mates and predators. Orthopterans (crickets, katydids, and grasshoppers) are renowned for their acoustic signals. In Neotropical forests, however, many katydid species produce extremely short signals, totaling only a few seconds of sound per night, likely in response to predation by acoustically orienting predators. The rare signals of these katydid species raises the question of how they find conspecific mates in a structurally complex rainforest. While acoustic mechanisms, such as duetting, likely facilitate mate finding, we test the hypothesis that mate finding is further facilitated by colocalization on particular host plant species. DNA barcoding allows us to identify recently consumed plants from katydid stomach contents. We use DNA barcoding to test the prediction that katydids of the same species will have closely related plant species in their stomach. We do not find evidence for dietary specialization. Instead, katydids consumed a wide mix of plants within and across the flowering plants (27 species in 22 genera, 16 families, and 12 orders) with particular representation in the orders Fabales and Laurales. Some evidence indicates that katydids may gather on plants during a narrow window of rapid leaf out, but additional investigations are required to determine whether katydid mate finding is facilitated by gathering at transient food resources.

Density-by-Diet Interactions during Larval Development Shape Adult Life History Trait Expression and Fitness in a Polyphagous Fly.

AbstractHabitat quality early in life determines individual fitness, with possible long-term evolutionary effects on groups and populations. In holometabolous insects, larval ecology plays a major role in determining the expression of traits in adulthood, but how ecological conditions during the larval stage interact to shape adult life history and fitness, particularly in nonmodel organisms, remains subject to scrutiny. Consequently, our knowledge of the interactive effects of ecological factors on insect development is limited. Here, using the polyphagous fly Bactrocera tryoni, we conducted a fully factorial design where we manipulated larval density and larval diet (protein rich, standard, and sugar rich) to gain insights into how these ecological factors interact to modulate adult fitness. As expected, a protein-rich diet resulted in faster larval development and heavier and leaner adults that were more fecund compared with the standard and sugar-rich diets, irrespective of larval density. Females from the protein-rich larval diet had overall higher reproductive rate (i.e., eggs per day) than females from other diets, and reproductive rate decreased linearly with density for females from the protein-rich diet but nonlinearly for females from the standard and sugar-rich diets over time. Surprisingly, adult lipid reserve increased with larval density for adults from the sugar-rich diet (as opposed to decreasing as in other diets), possibly because of a stress response to an extremely adverse condition during development (i.e., high intraspecific competition and poor nutrition). Together, our results provide insights into how ecological factors early in life interact and shape the fate of individuals through life stages in holometabolous insects.

Jack-of-all-trades paradigm meets long-term data: Generalist herbivores are more widespread and locally less abundant.

Insect herbivores are relatively specialized. Why this is so is not clear. We examine assumptions about associations between local abundance and dietary specialization using an 18-year data set of caterpillar-plant interactions in Ecuador. Our data consist of caterpillar-plant associations and include standardized plot-based samples and general collections of caterpillars, allowing for diet breadth and abundance estimates across spatial scales for 1917 morphospecies. We find that more specialized caterpillars are locally more abundant than generalists, consistent with a key component of the 'jack of all trades, master of none' hypothesis. As the diet breadth of species increased, generalists were not as abundant in any one location, but they had broader occupancy across the landscape, which is a pattern that could reflect high plant beta diversity and is consistent with an alternative neutral hypothesis. Our finding that more specialized species can be both rare and common highlights the ecological complexity of specialization.

Diet specialization and brood parasitism in cuckoo species.

Brood parasitism is a breeding strategy adopted by many species of cuckoos across the world. This breeding strategy influences the evolution of life histories of brood parasite species.In this study, we tested whether the degree on diet specialization is related to the breeding strategy in cuckoo species, by comparing brood parasite and nonparasite species. We measured the gradient of diet specialization of cuckoos, by calculating the Gini coefficient, an index of inequality, on the multiple traits describing the diet of species. The Gini coefficient is a measure of statistical dispersion on a scale between 0 and 1, reflecting a gradient from low to high specialization, respectively. First, we tested the strength of the phylogenetic signal of diet specialization index among cuckoo species worldwide. Then, we ran phylogenetic generalized least square (PGLS) models to compare diet specialization, distribution range, and body mass of parasitic and nonparasitic cuckoo species, considering the phylogenetic signal of data.After adjusting for the phylogenetic signal of the data and considering both, species distribution range and species body mass, brood parasitic cuckoos were characterized by higher diet specialization than nonbrood parasitic species. Brood parasitic species were also characterized by a larger breeding distribution range than nonparasitic species.The findings of this study provide an additional understanding of the cuckoos' ecology, relating diet and breeding strategies, information that could be important in conservation ecology.

Life-history genomic regions explain differences in Atlantic salmon marine diet specialization.

Animals employ various foraging strategies along their ontogeny to acquire energy, and with varying degree of efficiencies, to support growth, maturation and subsequent reproduction events. Individuals that can efficiently acquire energy early are more likely to mature at an earlier age, as a result of faster energy gain which can fuel maturation and reproduction. We aimed to test the hypothesis that heritable resource acquisition variation that covaries with efficiency along the ontogeny would influence maturation timing of individuals. To test this hypothesis, we utilized Atlantic salmon as a model which exhibits a simple, hence trackable, genetic control of maturation age. We then monitored the variation in diet acquisition (quantified as stomach fullness and composition) of individuals with different ages, and linked it with genomic regions (haploblocks) that were previously identified to be associated with age-at-maturity. Consistent with the hypothesis, we demonstrated that one of the life-history genomic regions tested (six6) was indeed associated with age-dependent differences in stomach fullness. Prey composition was marginally linked to six6, and suggestively (but non-significantly) to vgll3 genomic regions. We further showed Atlantic salmon switched to the so-called 'feast and famine' strategy along the ontogeny, where older age groups exhibited heavier stomach content, but that came at the expense of running on empty more often. These results suggest genetic variation underlying resource utilization may explain the genetic basis of age structure in Atlantic salmon. Given that ontogenetic diet has a genetic component and the strong spatial diversity associated with these genomic regions, we predict populations with diverse maturation age will have diverse evolutionary responses to future changes in marine food web structures.

Relative prey abundance and predator preference predict individual diet variation in prey-switching experiments.

Individual diet specialization appears widespread and has several ecological ramifications. Hypotheses on the causes of diet specialization generally assume prey preferences differ among predator individuals. They then predict how the magnitude of diet variation should change when ecological factors (e.g., intraspecific competition) alter prey abundances. However, the magnitude of diet variation is expected to change with prey abundances due to stochasticity in the foraging process even if all predators share the same prey preferences. Here I show that the relative prey abundance where diet variation is maximized and the magnitudes of diet variation in prey switching experiments are predicted well by a simple stochastic foraging model based only on relative prey abundances and a shared relative prey preference among predators. These results suggest that the effects of stochasticity during foraging may confound studies of individual diet specialization if these effects are not accounted for in experimental design or interpretation. Furthermore, the stochastic foraging model provides simple baseline expectations for theoretical studies on the ecological consequences of diet variation and offers a way forward on quantitative predictions of how ecological factors influence the magnitude of diet variation when stochasticity during foraging and diet specialization occur simultaneously. Last, this study highlights the continued importance of integrating stochasticity into mechanistic ecological hypotheses.

Does sexual segregation occur during the nonbreeding period? A comparative analysis in spatial and feeding ecology of three Calonectris shearwaters.

Sexual segregation (SS) is widespread among animal taxa, with males and females segregated in distribution, behavior, or feeding ecology but so far, most studies on birds have focused on the breeding period. Outside this period, the relevance of segregation and the potential drivers of its persistence remain elusive, especially in the marine environment, where animals can disperse over vast areas and are not easily observed. We evaluated the degree of SS in spatio-temporal distribution and phenology, at-sea behavior, and feeding ecology during the nonbreeding period among three closely related shearwaters: Scopoli's, Cory's, and Cape Verde shearwaters (Calonectris diomedea, C. borealis, and C. edwardsii, respectively). We tracked 179 birds (92 males and 87 females) from 2008 to 2013 using geolocation-immersion loggers and collected the 13th secondary remige (molted in winter) for stable isotope analyses as a proxy of trophic level and diet. The global nonbreeding distribution did not differ between sexes for the three species, but one specific nonbreeding area was visited only by males. Cory's shearwater males remained in areas closer to the colony in a larger proportion compared to females and returned earlier to the colony, probably to defend their nests. Males presented a slightly lower nocturnal flying activity and slightly (but consistently) higher isotopic values of δ13C and δ15N compared to females. These differences suggest subtle sexual differences in diet and a slightly higher trophic level in males, but the extent to which sexual dimorphism in bill size can determine them remains unclear. Our study showed that SS in ecological niche in seabirds can persist year-round consistently but at a different extent when comparing the breeding and nonbreeding periods. Based on our findings, we propose that SS in these seabird species might have its origin in an ecological specialization derived from the different roles of males and females during reproduction, rather than from social dominance during the nonbreeding period.

Altered trophic interactions in warming climates: consequences for predator diet breadth and fitness.

Species interactions are central in predicting the impairment of biodiversity with climate change. Trophic interactions may be altered through climate-dependent changes in either predator food preferences or prey communities. Yet, climate change impacts on predator diet remain surprisingly poorly understood. We experimentally studied the consequences of 2°C warmer climatic conditions on the trophic niche of a generalist lizard predator. We used a system of semi-natural mesocosms housing a variety of invertebrate species and in which climatic conditions were manipulated. Lizards in warmer climatic conditions ate at a greater predatory to phytophagous invertebrate ratio and had smaller individual dietary breadths. These shifts mainly arose from direct impacts of climate on lizard diets rather than from changes in prey communities. Dietary changes were associated with negative changes in fitness-related traits (body condition, gut microbiota) and survival. We demonstrate that climate change alters trophic interactions through top-predator dietary shifts, which might disrupt eco-evolutionary dynamics.

Can Isogroup Selection of Highly Zoophagous Lines of a Zoophytophagous Bug Improve Biocontrol of Spider Mites in Apple Orchards?

Zoophytophagous predators provide benefits in agroecosystems when feeding on pests, but they can also cause crop damage. Optimizing the use of zoophytophagous predators as biocontrol agents would require improving pest control and/or limiting damage. Populations of a zoophytophagous species can be composed of a mix of individuals diverging in their level of diet specialization. Consequently, depending on their level of zoophagy, individuals would vary widely in the benefits and risks they provide to pest management. We tested the hypothesis that manipulating the composition of the population of a zoophytophagous insect, the mullein bug, Campylomma verbasci (Hemiptera: Miridae), towards an increased zoophagy would increase their net benefit in an apple orchard. We compared the inherent benefits and risks of two different isogroup lines of mullein bug that genetically differed in their level of zoophagy. In spring, when damage occurs, both strains infrequently punctured apple fruit, which rarely lead to damage and therefore represented a low risk. During summer, only the highly-zoophagous line impacted the spider mite population, while the lowly-zoophagous line did not differ from the control treatments. We concluded that manipulating the composition of the zoophytophagous predator population provided extra net benefits that improved pest control.

Chance and predictability in evolution: The genomic basis of convergent dietary specializations in an adaptive radiation.

The coexistence of multiple eco-phenotypes in independently assembled communities makes island adaptive radiations the ideal framework to test convergence and parallelism in evolution. In the radiation of the spider genus Dysdera in the Canary Islands, species diversification occurs concomitant with repeated events of trophic specialization. These dietary shifts, to feed primarily on woodlice, are accompanied by modifications in morphology (mostly in the mouthparts), behaviour and nutritional physiology. To gain insight into the molecular basis of this adaptive radiation, we performed a comprehensive comparative transcriptome analysis of five Canary Island Dysdera endemics representing two evolutionary and geographically independent events of dietary specialization. After controlling for the potential confounding effects of hemiplasy, our differential gene expression and selective constraint analyses identified a number of genetic changes that could be associated with the repeated adaptations to specialized diet of woodlice, including some related to heavy metal detoxification and homeostasis, the metabolism of some important nutrients and venom toxins. Our results shed light on the genomic basis of an extraordinary case of dietary shift convergence associated with species diversification. We uncovered putative molecular substrates of convergent evolutionary changes at different hierarchical levels, including specific genes, genes with equivalent functions and even particular amino acid positions. This study improves our knowledge of rapid adaptive radiations and provides new insights into the predictability of evolution.

Asymmetrical habitat coupling of an aquatic predator-The importance of individual specialization.

Predators should stabilize food webs because they can move between spatially separate habitats. However, predators adapted to forage on local resources may have a reduced ability to couple habitats. Here, we show clear asymmetry in the ability to couple habitats by Eurasian perch-a common polymorphic predator in European lakes. We sampled perch from two spatially separate habitats-pelagic and littoral zones-in Lake Erken, Sweden. Littoral perch showed stronger individual specialization, but they also used resources from the pelagic zone, indicating their ability to couple habitats. In contrast, pelagic perch showed weaker individual specialization but near complete reliance on pelagic resources, indicating their preference to one habitat. This asymmetry in the habitat coupling ability of perch challenges the expectation that, in general, predators should stabilize spatially separated food webs. Our results suggest that habitat coupling might be constrained by morphological adaptations, which in this case were not related to genetic differentiation but were more likely related to differences in individual specialization.

Breath rate of passerines across an urbanization gradient supports the pace-of-life hypothesis and suggests diet-mediated responses to handling stress.

The pace-of-life hypothesis predicts no impact of urbanization on stress responses. Accordingly, several studies have been inconsistent in showing differences in breath rate (BR), a proxy of acute stress responses to handling in passerines, between rural and urban areas. However, this evidence is limited to a single bird species and a limited geographic region (SW Europe). No study addressed whether this pattern is also apparent in other species or regions, such as in tropical environments, or whether it is dependent on the level of diet specialization, given that diet restriction and change influence stress responses. Here, we tested whether there were differences in BR between habitats and diet groups using eight highly diverse passerine assemblages experiencing different levels of anthropogenic disturbance (i.e., natural, rural, and urban locations) in SW China. We predicted that insectivores and herbivores (frugivores, nectarivores, and seed-eating species) would show higher BR than omnivores. We also predicted no differences in BR among habitat types. BR was a moderately repeatable trait, which showed a negative relationship with body mass and a positive relationship with the time of the day. We also recorded a relatively strong phylogenetic bias in the expression of this trait. Confirming our predictions, our results showed no differences in BR among natural, rural, and urban locations. Similarly, within species, there were no differences in BR between rural and urban locations. However, we also found that herbivores showed higher BR than omnivores. Overall, our results provide support to the pace-of-life hypothesis, but suggest acute stress responses can be diet-mediated, which may help to explain the marked decline of specialized trophic guilds around the world in response to anthropogenic disturbance.

Protective role of the vulture facial skin and gut microbiomes aid adaptation to scavenging.

BACKGROUND: Vultures have adapted the remarkable ability to feed on carcasses that may contain microorganisms that would be pathogenic to most other animals. The holobiont concept suggests that the genetic basis of such adaptation may not only lie within their genomes, but additionally in their associated microbes. To explore this, we generated shotgun DNA sequencing datasets of the facial skin and large intestine microbiomes of the black vulture (Coragyps atratus) and the turkey vulture (Cathartes aura). We characterized the functional potential and taxonomic diversity of their microbiomes, the potential pathogenic challenges confronted by vultures, and the microbial taxa and genes that could play a protective role on the facial skin and in the gut. RESULTS: We found microbial taxa and genes involved in diseases, such as dermatitis and pneumonia (more abundant on the facial skin), and gas gangrene and food poisoning (more abundant in the gut). Interestingly, we found taxa and functions with potential for playing beneficial roles, such as antilisterial bacteria in the gut, and genes for the production of antiparasitics and insecticides on the facial skin. Based on the identified phages, we suggest that phages aid in the control and possibly elimination, as in phage therapy, of microbes reported as pathogenic to a variety of species. Interestingly, we identified Adineta vaga in the gut, an invertebrate that feeds on dead bacteria and protozoans, suggesting a defensive predatory mechanism. Finally, we suggest a colonization resistance role through biofilm formation played by Fusobacteria and Clostridia in the gut. CONCLUSIONS: Our results highlight the importance of complementing genomic analyses with metagenomics in order to obtain a clearer understanding of the host-microbial alliance and show the importance of microbiome-mediated health protection for adaptation to extreme diets, such as scavenging.

Isogroup Selection to Optimize Biocontrol Increases Cannibalism in Omnivorous (Zoophytophagous) Bugs.

Zoophytophagous insects can substitute animals for plant resources when prey is scarce. Many arthropods feed on conspecifics to survive in these conditions. An individual's tendency for cannibalism may depend on its genotype along with its diet specialization, in interaction with the availability of alternative food resources. We compared two isogroup lines of the zoophytophagous mullein bug, either specialized on animal or on plant diets, that were generated to improve biocontrol. We predicted that: (1) bugs from the prey-specialized line would show higher levels of cannibalism than bugs from the pollen-specialized line, and (2) both lines would decrease cannibalism levels in the presence of their preferred resource. Under laboratory conditions, large nymphal instars had 24 hours to feed on smaller instars, in the absence of additional resources, or with either spider mites or pollen present. Cannibalism was reduced by the availability of both prey and pollen, although prey had a lower effect than pollen. The intensity of cannibalism was always higher in the prey-specialized line than in the pollen-specialized line, regardless of the availability of supplemented resources. The pollen-specialized line had decreased cannibalism levels only when pollen was available. These results indicate that cannibalism is a potentially regulating force in the prey-specialized line, but not in the pollen-specialized line.

De novo transcriptome assemblies of four xylem sap-feeding insects.

Background: Spittle bugs and sharpshooters are well-known xylem sap-feeding insects and vectors of the phytopathogenic bacterium Xylella fastidiosa (Wells), a causal agent of Pierce's disease of grapevines and other crop diseases. Specialized feeding on nutrient-deficient xylem sap is relatively rare among insect herbivores, and only limited genomic and transcriptomic information has been generated for xylem-sap feeders. To develop a more comprehensive understanding of biochemical adaptations and symbiotic relationships that support survival on a nutritionally austere dietary source, transcriptome assemblies for three sharpshooter species and one spittlebug species were produced. Findings: Trinity-based de novo transcriptome assemblies were generated for all four xylem-sap feeders using raw sequencing data originating from whole-insect preps. Total transcripts for each species ranged from 91 384 for Cuerna arida to 106 998 for Homalodisca liturata with transcript totals for Graphocephala atropunctata and the spittlebug Clastoptera arizonana falling in between. The percentage of transcripts comprising complete open reading frames ranged from 60% for H. liturata to 82% for C. arizonana. Bench-marking universal single-copy orthologs analyses for each dataset indicated quality assemblies and a high degree of completeness for all four species. Conclusions: These four transcriptomes represent a significant expansion of data for insect herbivores that feed exclusively on xylem sap, a nutritionally deficient dietary source relative to other plant tissues and fluids. Comparison of transcriptome data with insect herbivores that utilize other dietary sources may illuminate fundamental differences in the biochemistry of dietary specialization.

Mitogenomes and relatedness do not predict frequency of tool-use by sea otters.

Many ecological aspects of tool-use in sea otters are similar to those in Indo-Pacific bottlenose dolphins. Within an area, most tool-using dolphins share a single mitochondrial haplotype and are more related to each other than to the population as a whole. We asked whether sea otters in California showed similar genetic patterns by sequencing mitogenomes of 43 otters and genotyping 154 otters at 38 microsatellite loci. There were six variable sites in the mitogenome that yielded three haplotypes, one found in only a single individual. The other two haplotypes contained similar percentages (33 and 36%) of frequent tool-users and a variety of diet types. Microsatellite analyses showed that snail specialists, the diet specialist group that most frequently used tools, were no more related to each other than to the population as a whole. The lack of genetic association among tool-using sea otters compared with dolphins may result from the length of time each species has been using tools. Tool-use in dolphins appears to be a relatively recent innovation (less than 200 years) but sea otters have probably been using tools for many thousands or even millions of years.