Variation in terrestrial mammalian skull morphology is known to constrain feeding performance, which in turn influences dietary habits and ultimately fitness. Among mustelids, otters have evolved two ...feeding specializations: underwater raptorial capture of prey (mouth-oriented) and capture of prey by hand (hand-oriented), both of which have likely associations with morphology and bite performance. However, feeding biomechanics and performance data for otters are sparse. The first goal of this study was to investigate the relationships between feeding morphology and bite performance among two mouth-oriented piscivores (Pteronura brasiliensis and Lontra canadensis) and two hand-oriented invertebrate specialists (Enhydra lutris and Aonyx cinerea). Since other vertebrate taxa that are mouth-oriented piscivores tend to possess longer skulls and mandibles, with jaws designed for increased velocity at the expense of biting capability, we hypothesized that mouth-oriented otters would also possess long, narrow skulls indicative of high velocity jaws. Conversely, hand-oriented otters were expected to possess short, blunt skulls with adaptations to increase bite force and crushing capability. Concomitant with these skull shapes we hypothesized that sea otters would possess a greater mandibular bluntness index, providing for a greater mechanical advantage compared to other otter species investigated. A second goal was to examine morphological variation at a finer scale by assessing variation in cranial morphology among three sea otter subspecies. Since diet varies among these subspecies, and their populations are isolated, we hypothesized that the magnitude of mandibular bluntness and concomitant mechanical advantage, as well as occlusal surface area would also vary within species according to their primary food source (fish versus hard invertebrates). Functional expectations were met for comparisons among and within species. Among species the phylogeny suggests a deeply rooted transition to alternative foraging types. Yet within foraging types alternative species were also strongly variable, suggesting either selective differences in the extent or nature of realized foraging mode, or an accumulation of non-adaptive changes during the long independent evolutionary history. At the finest scale, variation among subspecies indicates that trophic adaptation occurred rapidly, making it interesting that we happened to find both deeply and shallowly-rooted transformations associated with diet type in otter species and subspecies.
A significant uncertainty in assessments of the role of clouds in climate is the characterization of the full distribution of their sizes. Order-of-magnitude disagreements exist among observations of ...key distribution parameters, particularly power law exponents and the range over which they apply. A study by Savre and Craig (2023) suggested that the discrepancies are due in large part to inaccurate fitting methods: they recommended the use of a maximum likelihood estimation technique rather than a linear regression to a logarithmically transformed histogram of cloud sizes. Here, we counter that linear regression is both simpler and equally accurate, provided the simple precaution is followed that bins containing fewer than ∼ 24 counts are omitted from the regression. A much more significant and underappreciated source of error is how to treat clouds that are truncated by the edges of unavoidably finite measurement domains. We offer a simple computational procedure to identify and correct for domain size effects, with potential application to any geometric size distribution of objects, whether physical, ecological, social or mathematical.
A fundamental question in evolutionary biology asks whether organisms experiencing similar selective pressures will evolve similar solutions or whether historical contingencies dominate the ...evolutionary process and yield disparate evolutionary outcomes. It is perhaps most likely that both shared selective forces as well as unique histories play key roles in the course of evolution. Consequently, when multiple species face a common environmental gradient, their patterns of divergence might exhibit both shared and unique elements. Here we describe a general framework for investigating and evaluating the relative importance of these contrasting features of diversification. We examined morphological diversification in three species of livebearing fishes across a predation gradient. All species (Gambusia affinisfrom the United States of America,Brachyrhaphis rhabdophorafrom Costa Rica, andPoecilia reticulatafrom Trinidad) exhibited more elongate bodies, a larger caudal peduncle, and a relatively lower position of the eye in predator populations. This shared response suggests that common selective pressures generated parallel outcomes within three different species. However, each species also exhibited unique features of divergence, which might reflect phylogenetic tendencies, chance events, or localized environmental differences. In this system, we found that shared aspects of divergence were of larger magnitude than unique elements, suggesting common natural selective forces have played a greater role than unique histories in producing the observed patterns of morphological diversification. Assessing the nature and relative importance of shared and unique responses should aid in elucidating the relative generality or peculiarity in evolutionary divergence.
Predation exerts strong selection pressure on morphological traits and is often studied in freshwater fishes. A common morphological ecophenotype driven by predation from pursuit predators is the ...predator‐associated burst speed (PABS) ecophenotype. This ecophenotype, characterized by a smaller head, smaller body, and larger caudal region, is commonly found in western mosquitofish (Gambusia affinis) residing in environments with sunfish (family Centrarchidae) predators. However, the repeatability and transferability of the PABS ecophenotype across populations have not been tested. The four objectives of this study were to (1) assess the repeatability of methods to confirm the presence of the PABS ecophenotype in independent populations, (2) test whether morphology is correlated with predator abundance, (3) assess the repeatability of utilizing a discriminant function analysis (DFA) to accurately classify fish to predator status, and (4) use a DFA to conduct a cross‐validation test of the PABS model using previously studied populations of G. affinis to predict predator status of newly studied populations. There was consistency in the occurrence of the PABS ecophenotype among populations with predators. Permuted MANOVA (PMANOVA) models fit to each dataset revealed a significant effect of collection site nested within predator status (i.e., presence or absence of predator), suggesting location‐specific variations of the PABS ecophenotype. In addition, a PMANOVA model fit to body shape as a function of predator abundance (i.e., 0, 0.1–1.0, or >1.0 predators per minute of electrofishing) revealed a significant effect of predation level in the newly studied populations, suggesting morphology differs among populations with varying predator abundances. Cross‐study validation of the DFA revealed low between‐study accuracy compared to within‐study accuracy, but elongation of the caudal region in the presence of predators was consistent across studies. Our findings ultimately suggest that although the PABS ecophenotype at studied locations provides partial predictive capacity at unstudied locations, the nature and magnitude of the PABS ecophenotype depend on environmental settings, encounter histories with predators, level of abundance of predators, or other spatially structured mechanisms.
Main conclusion
Domestication affected the abundances and diversity of maize root volatiles more than northward spread and modern breeding, and herbivore preference for roots was correlated with ...volatile diversity and herbivore resistance.
Studies show that herbivore defenses in crops are mediated by domestication, spread, and breeding, among other human-driven processes. They also show that those processes affected chemical communication between crop plants and herbivores. We hypothesized that (i) preference of the herbivore (
Diabrotica virgifera virgifera
) larvae for embryonic roots of maize (
Zea mays mays
) would increase and (ii) root volatile diversity would decrease with the crop’s domestication, northward spread to present-day USA, and modern breeding. We used Balsas teosinte (
Zea mays parviglumis
), Mexican and USA landrace maizes, and US inbred maize lines to test these hypotheses. We found that herbivore preference and volatile diversity increased with maize domestication and northward spread but decreased with modern breeding. Additionally, we found that the abundances of single volatiles did not consistently increase or decrease with maize domestication, spread, and breeding; rather, volatiles grouped per their abundances were differentially affected by those processes, and domestication had the greatest effects. Altogether, our results suggested that: the herbivore’s preference for maize roots is correlated with volatile diversity and herbivore resistance; changes in abundances of individual volatiles are evident at the level of volatile groups; and maize domestication, but not spread and breeding, affected the abundances of some green leaf volatiles and sesquiterpenes/sesquiterpenoids. In part, we discussed our results in the context of herbivore defense evolution when resources for plant growth and defense vary across environments. We suggested that variability in relative abundance of volatiles may be associated with their local, functional relevance across wild and agricultural environments.
Vibrissae (whiskers) are important components of the mammalian tactile sensory system, and primarily function as detectors of vibrotactile information from the environment. Pinnipeds possess the ...largest vibrissae among mammals and their vibrissal hair shafts demonstrate a diversity of shapes. The vibrissae of most phocid seals exhibit a beaded morphology with repeating sequences of crests and troughs along their length. However, there are few detailed analyses of pinniped vibrissal morphology, and these are limited to a few species. Therefore, we comparatively characterized differences in vibrissal hair shaft morphologies among phocid species with a beaded profile, phocid species with a smooth profile, and otariids with a smooth profile using traditional and geometric morphometric methods. Traditional morphometric measurements (peak-to-peak distance, crest width, trough width and total length) were collected using digital photographs. Elliptic Fourier analysis (geometric morphometrics) was used to quantify the outlines of whole vibrissae. The traditional and geometric morphometric datasets were subsequently combined by mathematically scaling each to true rank, followed by a single eigendecomposition. Quadratic discriminant function analysis demonstrated that 79.3, 97.8 and 100% of individuals could be correctly classified to their species based on vibrissal shape variables in the traditional, geometric and combined morphometric analyses, respectively. Phocids with beaded vibrissae, phocids with smooth vibrissae, and otariids each occupied distinct morphospace in the geometric morphometric and combined data analyses. Otariids split into two groups in the geometric morphometric analysis and gray seals appeared intermediate between beaded- and smooth-whiskered species in the traditional and combined analyses. Vibrissal hair shafts modulate the transduction of environmental stimuli to the mechanoreceptors in the follicle-sinus complex (F-SC), which results in vibrotactile reception, but it is currently unclear how the diversity of shapes affects environmental signal modulation.
Compared to the striking diversification and levels of endemism observed in many terrestrial groups within the Hawaiian Archipelago, marine invertebrates exhibit remarkably lower rates of endemism ...and diversification. Supralittoral invertebrates restricted to specific coastal patchy habitats, however, have the potential for high levels of allopatric diversification. This is the case of Ligia isopods endemic to the Hawaiian Archipelago, which most likely arose from a rocky supralittoral ancestor that colonized the archipelago via rafting, and diversified into rocky supralittoral and inland lineages. A previous study on populations of this isopod from O'ahu and Kaua'i revealed high levels of allopatric differentiation, and suggested inter-island historical dispersal events have been rare. To gain a better understanding on the diversity and evolution of this group, we expanded prior phylogeographic work by incorporating populations from unsampled main Hawaiian Islands (Maui, Moloka'i, Lana'i, and Hawai'i), increasing the number of gene markers (four mitochondrial and two nuclear genes), and conducting Maximum likelihood and Bayesian phylogenetic analyses. Our study revealed new lineages and expanded the distribution range of several lineages. The phylogeographic patterns of Ligia in the study area are complex, with Hawai'i, O'ahu, and the Maui-Nui islands sharing major lineages, implying multiple inter-island historical dispersal events. In contrast, the oldest and most geographically distant of the major islands (Kaua'i) shares no lineages with the other islands. Our results did not support the monophyly of all the supralittoral lineages (currently grouped into L. hawaiensis), or the monophyly of the terrestrial lineages (currently grouped into L. perkinsi), implying more than one evolutionary transition between coastal and inland forms. Geometric-morphometric analyses of three supralittoral clades revealed significant body shape differences among them. A taxonomic revision of Hawaiian Ligia is warranted. Our results are relevant for the protection of biodiversity found in an environment subject to high pressure from disturbances.
The American Academy of Pediatrics recommends limits on digital media use ("screen time"), citing cognitive-behavioral risks. Media use in early childhood is ubiquitous, though few imaging-based ...studies have been conducted to quantify impacts on brain development. Cortical morphology changes dynamically from infancy through adulthood and is associated with cognitive-behavioral abilities. The current study involved 52 children who completed MRI and cognitive testing at a single visit. The MRI protocol included a high-resolution T1-weighted anatomical scan. The child's parent completed the ScreenQ composite measure of media use. MRI measures included cortical thickness (CT) and sulcal depth (SD) across the cerebrum. ScreenQ was applied as a predictor of CT and SD first in whole-brain regression analyses and then for regions of interest (ROIs) identified in a prior study of screen time involving adolescents, controlling for sex, age and maternal education. Higher ScreenQ scores were correlated with lower CT in right-lateralized occipital, parietal, temporal and fusiform areas, and also lower SD in right-lateralized inferior temporal/fusiform areas, with substantially greater statistical significance in ROI-based analyses. These areas support primary visual and higher-order processing and align with prior findings in adolescents. While differences in visual areas likely reflect maturation, those in higher-order areas may suggest under-development, though further studies are needed.
Many species show replicated ecophenotypy due to recurring patterns of natural selection. Based on the presence or absence of pursuit predators, at least 17 species of fish repeatedly differentiated ...in body shape in a manner that increases burst swimming speed and the likelihood of predator escape. The predator-associated burst speed (PABS) ecophenotype is characterized by a small head and trunk and enlarged caudal region. Mechanisms promoting replicated phenotype-environment association include selection (without evolution), a single instance of adaptive evolution followed by biased habitat occupation, repeated instances of local adaptation, or adaptive phenotypic plasticity. Common garden rearing of mosquitofish, Gambusia affinis, demonstrated a likely heritable basis for PABS phenotypy, but it is unknown whether populations are otherwise genetically distinct or whether replicated ecophenotypy represents a single or replicated instances of adaptation. To genetically characterize the populations and test hypotheses of single or multiple adaptations, we characterized variation in 12 polymorphic DNA microsatellites in the previously studied G. affinis populations. Populations were genetically distinct by multilocus analysis, exhibited high allelic diversity, and were heterozygote deficient, which effects were attributed to G. affinis's shoaling nature and habitat patchiness. Genetic and phenotypic distances among populations were correlated for non-PABS but not PABS morphology. Multilocus analysis demonstrated ecophenotype polyphyly and scattered multivariate genetic structure which support only the replicated-adaptation model. As all of the diverse tests performed demonstrated lack of congruence between patterns of molecular genetic and PABS differentiation, it is likely that divergent natural selection drove multiple instances of adaptive evolution.
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