X-ray imaging as a time-saving, non-invasive technique for diet analysis

Beckmann, Melanie C.; Gilliam, James F.; Langerhans, R. Brian

doi:10.1016/j.fishres.2014.05.015

Cited by 7 publications

(8 citation statements)

References 16 publications

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“…We inspected each image for the occurrence (presence/absence) and number of molluscs within the stomach. Previous work demonstrated the feasibility of this technique for detection of hard-shelled prey, such as molluscs (Beckmann et al, 2015). Because direct stomach-content analysis of a subset of fish revealed that snails smaller than 1 mm shell length were rarely detected by x-ray imaging, our estimates provide lower bounds for the frequency of molluscivory in G. holbrooki, capturing cases of particularly dense mollusc shells (see Figure 3).…”

Section: Field Survey Of Molluscivory In Gambusia Holbrookimentioning

confidence: 82%

“…Because direct stomach-content analysis of a subset of fish revealed that snails smaller than 1 mm shell length were rarely detected by x-ray imaging, our estimates provide lower bounds for the frequency of molluscivory in G. holbrooki, capturing cases of particularly dense mollusc shells (see Figure 3). Moreover, because x-ray imaging could not unequivocally determine which stomachs were empty and which contained prey items (Beckmann et al, 2015), our estimate of percent occurrence of molluscivory was calculated as the number of fish with snails in their stomachs divided by the total number of fish examined (rather than the total number of fish with prey items in their stomach).…”

Section: Field Survey Of Molluscivory In Gambusia Holbrookimentioning

confidence: 99%

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Consuming Costly Prey: Optimal Foraging and the Role of Compensatory Growth

et al. 2021

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Some prey are exceptionally difficult to digest, and yet even non-specialized animals may consume them—why? Durophagy, the consumption of hard-shelled prey, is thought to require special adaptations for crushing or digesting the hard shells to avoid the many potential costs of this prey type. But many animals lacking specializations nevertheless include hard-bodied prey in their diets. We describe several non-mutually exclusive adaptive mechanisms that could explain such a pattern, and point to optimal foraging and compensatory growth as potentially having widespread importance in explaining costly-prey consumption. We first conducted a literature survey to quantify the regularity with which non-specialized teleost fishes consume hard-shelled prey: stomach-content data from 325 teleost fish species spanning 82 families (57,233 stomach samples) demonstrated that non-specialized species comprise ~75% of the total species exhibiting durophagy, commonly consuming hard-shelled prey at low to moderate levels (~10–40% as much as specialists). We then performed a diet survey to assess the frequency of molluscivory across the native latitudinal range of a small livebearing fish, Gambusia holbrooki, lacking durophagy specializations. Molluscivory was regionally widespread, spanning their entire native latitudinal range (>14° latitude). Third, we tested for a higher frequency of molluscivory under conditions of higher intraspecific resource competition in Bahamian mosquitofish (Gambusia spp.). Examining over 5,300 individuals, we found that molluscivory was more common in populations with higher population density, suggesting that food limitation is important in eliciting molluscivory. Finally, we experimentally tested in G. holbrooki whether molluscivory reduces growth rate and whether compensatory growth follows a period of molluscivory. We found that consumption of hard-shelled gastropods results in significantly reduced growth rate, but compensatory growth following prior snail consumption can quickly mitigate growth costs. Our results suggest that the widespread phenomenon of costly-prey consumption may be partially explained by its relative benefits when few alternative prey options exist, combined with compensatory growth that alleviates temporary costs.

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Section: Field Survey Of Molluscivory In Gambusia Holbrookimentioning

confidence: 82%

Section: Field Survey Of Molluscivory In Gambusia Holbrookimentioning

confidence: 99%

Consuming Costly Prey: Optimal Foraging and the Role of Compensatory Growth

et al. 2021

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“…Specifically, we dissected each fish, removed reproductive tissues, and examined the gut under a stereo microscope for the presence of a conspecific that had been eaten. For the invasive populations, we assessed cannibalism by capturing a digital x‐ray image of each fish in the lateral perspective using a custom‐built digital x‐ray unit comprising a micro‐focus x‐ray source (Hamamatsu L6731‐01) and a digital x‐ray detector (PaxScan 2520E) housed in a lead‐shielded cabinet (e.g., see Beckmann et al, 2015; Langerhans et al, 2021). We inspected each image for the presence/absence of fish within the guts: consumed fish were visible in the x‐ray images due to their dense otoliths, vertebrae, and skulls (body outline also often visible).…”

Section: Methodsmentioning

confidence: 99%

Resource competition explains rare cannibalism in the wild in livebearing fishes

Riesch

Araújo

Bumgarner

et al. 2022

Ecology and Evolution

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Cannibalism, the act of preying on and consuming a conspecific, is taxonomically widespread, and putatively important in the wild, particularly in teleost fishes. Nonetheless, most studies of cannibalism in fishes have been performed in the laboratory. Here, we test four predictions for the evolution of cannibalism by conducting one of the largest assessments of cannibalism in the wild to date coupled with a mesocosm experiment. Focusing on mosquitofishes and guppies, we examined 17 species (11,946 individuals) across 189 populations in the wild, spanning both native and invasive ranges and including disparate types of habitats. We found cannibalism to be quite rare in the wild: most populations and species showed no evidence of cannibalism, and the prevalence of cannibalism was typically less than 5% within populations when it occurred. Most victims were juveniles (94%; only half of these appeared to have been newborn offspring), with the remaining 6% of victims being adult males. Females exhibited more cannibalism than males, but this was only partially explained by their larger body size, suggesting greater energetic requirements of reproduction likely play a role as well. We found no evidence that dispersal‐limited environments had a lower prevalence of cannibalism, but prevalence was greater in populations with higher conspecific densities, suggesting that more intense resource competition drives cannibalistic behavior. Supporting this conclusion, our mesocosm experiment revealed that cannibalism prevalence increased with higher conspecific density and lower resource levels but was not associated with juvenile density or strongly influenced by predation risk. We suggest that cannibalism in livebearing fishes is rare in the wild because preying on conspecifics is energetically costly and only becomes worth the effort when competition for other food is intense. Due to the artificially reduced cost of capturing conspecifics within confined spaces, cannibalism in captive settings can be much more frequent.

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“…In addition, radiography can sometimes provide a noninvasive way to investigate diet (Schumacher and Toal, 2001;Erlacher-Reid et al, 2013;Beckmann et al, 2015). Mineral opaque material in the gastrointestinal tract is apparent in several of the iguanas (Figures 1a,b).…”

Section: Anatomical Observationsmentioning

confidence: 99%

“…Radiography is an established and clinically important way to assess bone integrity and health through the visualization of bones and internal organs (Mitchell, 2002;Banzato et al, 2013;Thrall, 2018), and can also sometimes be used to non-invasively investigate diet (Banzato et al, 2013;Erlacher-Reid et al, 2013;Beckmann et al, 2015). Despite these advantages, the large size of conventional radiography equipment has typically precluded imaging live marine vertebrates in the field.…”

Section: Introductionmentioning

confidence: 99%

Field-Based Radiographic Imaging of Marine Megafauna: Marine Iguanas (Amblyrhynchus cristatus) as a Case Study

et al. 2018

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Effective conservation of marine megafauna requires a thorough understanding of the ecology, physiology, population dynamics, and health of vulnerable species. Assessing the health of large, mobile marine animals poses particular challenges, in part because the subjects are difficult to capture and restrain, and in part because standard laboratory and diagnostic tools are difficult to apply in a field setting. Radiography is a critically important diagnostic tool used routinely by veterinarians, but it has seldom been possible to image live marine vertebrates in the field. As a first step toward assessing the feasibility of incorporating radiography into studies of vulnerable species in remote locations, we used portable radiographic equipment to acquire the first digital internal images of living marine iguanas, Amblyrhynchus cristatus, an iconic lizard endemic only to the Galápagos Islands of Ecuador. The radiographic machinery was powered by batteries and performed well on a rocky beach environment of an uninhabited island, despite high heat and humidity. The accuracy of radiographic measurements was validated by computing a snout-vent length (SVL) using bone dimensions and comparing this to standard measurements of SVL made externally with a tape measure. These results demonstrate the feasibility of using radiography to study animals in remote sites, a technique that may prove useful for a variety of physiological, ecological, and biomechanical studies in which reliable measurements of skeletal and soft-tissue dimensions must be acquired under challenging field conditions. Refinements are discussed that will help the technology reach its full potential in field studies.

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X-ray imaging as a time-saving, non-invasive technique for diet analysis

Cited by 7 publications

References 16 publications

Consuming Costly Prey: Optimal Foraging and the Role of Compensatory Growth

Consuming Costly Prey: Optimal Foraging and the Role of Compensatory Growth

Resource competition explains rare cannibalism in the wild in livebearing fishes

Field-Based Radiographic Imaging of Marine Megafauna: Marine Iguanas (Amblyrhynchus cristatus) as a Case Study

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