Diets and trophic guilds of small fishes from coastal marine habitats in western Taiwan

True grit? Comparative anatomy and evolution of gizzards in fishes

Gut morphology frequently reflects the food organisms digest. Gizzards are organs of the gut found in archosaurs and fishes that mechanically reduce food to aid digestion. Gizzards are thought to compensate for edentulism and/or provide an advantage when consuming small, tough food items (e.g., phytoplankton and algae). It is unknown how widespread gizzards are in fishes and how similar these structures are among different lineages. Here, we investigate the distribution of gizzards across bony fishes to (1) survey different fishes for gizzard presence, (2) compare the histological structure of gizzards in three species, (3) estimate how often gizzards have evolved in fishes, and (4) explore whether anatomical and ecological traits like edentulism and microphagy predict gizzard presence. According to our analyses, gizzards are rare across bony fishes, evolving only six times in a broad taxonomic sampling of 51 species, and gizzard presence is not clearly correlated with factors like gut length or dentition. We find that gizzard morphology varies among the lineages where one is present, both macroscopically (presence of a crop) and microscopically (varying tissue types). We conclude that gizzards likely aid in the mechanical reduction of food in fishes that have lost an oral dentition in their evolutionary past; however, the relative scarcity of gizzards suggests they are just one of many possible solutions for processing tough, nutrient-poor food items. Gizzards have long been present in the evolutionary history of fishes, can be found in a wide variety of marine and freshwater clades, and likely have been overlooked in many taxa.

Temporal distribution patterns of metals in water, sediment, and components of the trophic structure in a tropical coastal lagoon of the Gulf of Mexico

Trophic transfer and bioaccumulation of trace metals have a profound impact on the structure and function of coastal areas; however, the metal accumulation patterns in detritus-based food webs and the influence of climatic variability have not been thoroughly investigated. The Tampamachoco Lagoon (Gulf of Mexico) is a coastal system impacted by emissions from a thermoelectric plant. We evaluated the spatial-temporal distribution patterns of Al, Cd, Hg, Cr, Cu, and Pb in water, sediments, and in organisms categorized by trophic levels (TLs), trophic guilds, and habitat preferences. The sediments had the highest concentrations of metals with no significant differences between seasons. The indices of geo-accumulation and potential ecological risk classified sediments as "moderately contaminated", evidencing a threat to human health through consumption of detritivores and filter-feeders. The lowest TLs (filter-feeders and detritivorous) reached the maximum Metal Pollution Index in the rainy season. According to discriminant analyses of metals and species, omnivorous and zoobentivorous organisms were associated with Hg during the rainy and dry seasons; while Al, Cd, and Cu were related to low TLs, and seston was associated with Pb. Food web magnification factor analysis showed that: (a) Pb, Cu, and Cr were biodiluted as trophic levels increased; (b) Cd and Hg showed temporal biomagnification trends; (c) Al, Pb, Cu, and Cd showed significant biodilution from the lowest TL to intermediate TLs; and (d) Hg was transferred from the lowest to intermediate TLs with clear biomagnification effects.

Patterns of Phenotypic Evolution Associated with Marine/Freshwater Transitions in Fishes

Evolutionary transitions between marine and freshwater ecosystems have occurred repeatedly throughout the phylogenetic history of fishes. The theory of ecological opportunity predicts that lineages that colonize species-poor regions will have greater potential for phenotypic diversification than lineages invading species-rich regions. Thus, transitions between marine and freshwaters may promote phenotypic diversification in trans-marine/freshwater fish clades. We used phylogenetic comparative methods to analyze body size data in nine major fish clades that have crossed the marine/freshwater boundary. We explored how habitat transitions, ecological opportunity, and community interactions influenced patterns of phenotypic diversity. Our analyses indicated that transitions between marine and freshwater habitats did not drive body size evolution, and there are few differences in body size between marine and freshwater lineages. We found that body size disparity in freshwater lineages is not correlated with the number of independent transitions to freshwaters. We found a positive correlation between body size disparity and overall species richness of a given area, and a negative correlation between body size disparity and diversity of closely related species. Our results indicate that the diversity of incumbent freshwater species does not restrict phenotypic diversification, but the diversity of closely related taxa can limit body size diversification. Ecological opportunity arising from colonization of novel habitats does not seem to have a major effect in the trajectory of body size evolution in trans-marine/freshwater clades. Moreover, competition with closely related taxa in freshwaters has a greater effect than competition with distantly related incumbent species.

Structure of winter groundfish feeding guilds in Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords

The contents of 1056 stomachs were included in a trophic-guild analysis to document separation amongst 16 groundfish species inhabiting Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords in Prince William Sound, Alaska and to determine the relative contribution of C. pallasii and G. chalcogrammus to that separation. A total of five multi-species feeding guilds and one outlier species were determined through multivariate analyses. Major gradients of trophic separation spanned from invertebrates (mostly shrimps, crabs and unidentified decapods) to fishes (mostly unidentified fishes, C. pallasii and G. chalcogrammus) a pattern that was influenced by intra and interspecific differences in predator lengths. While C. pallasii and G. chalcogrammus were important to the overall guild structure, within-guild similarities were consistently highest due to unidentified fishes. In general, larger predators consumed the largest C. pallasii and G. chalcogrammus, with the smaller-on-average predators consuming smaller C. pallasii and fewer or smaller G. chalcogrammus. Regardless of guild inclusion, groundfishes primarily consumed pre-recruit C. pallasii and G. chalcogrammus (i.e., younger than age 3 years fishes), which has the potential to negatively influence recruitment of these forage fishes to the adult, spawning population.

Pharyngeal Jaws Converge by Similar Means, Not to Similar Ends, When Minnows (Cypriniformes: Leuciscidae) Adapt to New Dietary Niches

Convergent evolution is at the forefront of many form-function studies. There are many examples of multiple independent lineages evolving a similar morphology in response to similar functional demands, providing a framework for testing hypotheses of form-function evolution. However, there are numerous clades with underappreciated convergence, in which there is a perceived homogeneity in morphology. In these groups, it can be difficult to investigate causal relationships of form and function (e.g., diet influencing the evolution of jaw morphology) without the ability to disentangle phylogenetic signal from convergence. Leuciscids (Cypriniformes: Leuciscidae; formerly nested within Cyprinidae) are a species-rich clade of fishes that have diversified to occupy nearly every freshwater trophic niche, yet are considered to have relatively low morphological diversity relative to other large freshwater clades. Within the North American leuciscids, many genera contain at least one herbivore, insectivore, and larvaphage. We created 3D models from micro-computed tomography scans of 165 leuciscid species to measure functionally relevant traits within the pharyngeal jaws of these fishes. Using a published phylogeny, we tested these metrics for evolutionary integration, phylogenetic signal, and correlation with diet. Measurements of the pharyngeal jaws, muscle attachment areas, and teeth showed strong positive evolutionary correlation with each other and negative evolutionary correlation with measurements of the inter-ceratobranchial ligament (ICB ligament). Using diet data from published literature, we found extensive dietary convergence within Leuciscidae. The most common transitions we found were between herbivorous and invertivorous taxa and between insectivore types (aquatic vs. terrestrial). We document a trade-off in which herbivorous leuciscids have large teeth, short ICB ligaments, and large muscle attachment areas, whereas insectivorous leuciscids showed the opposite pattern. Inverse patterns of morphological integration between the ICB ligament the rest of the pharyngeal jaw correspond this dietary trade-off, which indicates that coordinated evolution of morphological traits contributes to functional diversity in this clade. However, these patterns only emerge in the context of phylogeny, meaning that the pharyngeal jaws of North American leuciscids converge by similar means (structural changes in response to dietary demands), but not necessarily to similar ends (absolute phenotype).