Buffered Lugol's Iodine Preserves DNA Fragment Lengths.

Museum collections play a pivotal role in the advancement of biological science by preserving phenotypic and genotypic history and variation. Recently, contrast-enhanced X-ray computed tomography (CT) has aided these advances by allowing improved visualization of internal soft tissues. However, vouchered specimens could be at risk if staining techniques are destructive. For instance, the pH of unbuffered Lugol's iodine (I2KI) may be low enough to damage deoxyribonucleic acid (DNA). The extent of this risk is unknown due to a lack of rigorous evaluation of DNA quality between control and experimental samples. Here, we used formalin-fixed mice to document DNA concentrations and fragment lengths in nonstained, ethanol-preserved controls and 3 iodine-based staining preparations: (1) 1.25% weight-by-volume (wt/vol.) alcoholic iodine (I2E); (2) 3.75% wt/vol. I2KI; and (3) 3.75% wt/vol. buffered I2KI. We tested a null hypothesis of no significant difference in DNA concentrations and fragment lengths between control and treatment samples. We found that DNA concentration decreases because of staining-potentially an effect of measuring intact double-stranded DNA only. Fragment lengths, however, were significantly higher for buffered I2KI and control samples, which were not, themselves, significantly different. Our results implicate buffered I2KI as the appropriate choice for contrast-enhanced CT imaging of museum wet collections to safely maximize their potential for understanding genetic and phenotypic diversity.

Las colecciones de museos juegan un papel crucial en el avance de la ciencia biológica al preservar la historia y la variación fenotípica y genotípica. Recientemente, la tomografía computarizada (CT) mejorada con contraste ha facilitado estos avances al permitir una mejor visualización de los tejidos blandos internos. Sin embargo, los especímenes con vales podrían estar en riesgo si las técnicas de tinción son destructivas. Por ejemplo, el pH del yodo de Lugol sin tamponar (I2KI) puede ser lo suficientemente bajo como para dañar el ADN. Se desconoce el alcance de este riesgo debido a la falta de una evaluación rigurosa de la calidad del ADN entre las muestras de control y las experimentales. Aquí utilizamos ratones fijados en formalina para documentar las concentraciones de ADN y las longitudes de los fragmentos en controles no teñidos, preservados en etanol, y en tres preparaciones de tinción basadas en yodo: (i) 1.25% peso/volumen (wt/vol.) de yodo alcohólico (I2E), (ii) 3.75% wt/vol. I2KI, y (iii) 3.75% wt/vol. I2KI tamponado. Probamos una hipótesis nula de que no hay diferencias significativas en las concentraciones de ADN y las longitudes de los fragmentos entre las muestras de control y las de tratamiento. Encontramos que la concentración de ADN disminuye debido a la tinción, potencialmente un efecto de medir solo ADN de doble cadena intacto. Sin embargo, las longitudes de los fragmentos fueron significativamente mayores para I2KI tamponado y las muestras de control, que no fueron, ellas mismas, significativamente diferentes. Nuestros resultados implican que I2KI tamponado es la opción adecuada para la imagenología CT mejorada con contraste de colecciones húmedas de museos para maximizar de manera segura su potencial para comprender la diversidad genética y fenotípica.

Cranial Musculoskeletal Description of Black-Throated Finch (Aves: Passeriformes: Estrildidae) with DiceCT.

Synopsis Dietary requirements and acquisition strategies change throughout ontogeny across various clades of tetrapods, including birds. For example, birds hatch with combinations of various behavioral, physiological, and morphological factors that place them on an altricial-precocial spectrum. Passeriformes (=songbirds) in particular, a family constituting approximately more than half of known bird species, displays the most drastic difference between hatchling and adults in each of these aspects of their feeding biology. How the shift in dietary resource acquisition is managed during ontogeny alongside its relationship to the morphology of the feeding apparatus has been largely understudied within birds. Such efforts have been hampered partly due to the small size of many birds and the diminutive jaw musculature they employ. In this study, we used standard and diffusible iodine-based contrast-enhanced computed tomography in conjunction with digital dissection to quantify and describe the cranial musculature of the Black-throated Finch (Poephila cincta) at fledgling and adult stages. Our results reveal that in both the fledgling and the adult, cranial musculature shows clear and complex partitioning in the Musculus adductor mandibulae externus that is consistent with other families within Passeriformes. We quantified jaw-muscle sizes and found that the adult showed a decrease in muscle mass in comparison to the fledgling individual. We propose that this could be the result of low sample size or a physiological effect of parental care in Passeriformes. Our study shows that high-resolution visualization techniques are informative at revealing morphological discrepancies for studies that involve small specimens such as Passeriformes especially with careful specimen selection criteria.

A Bigger Picture: Organismal Function at the Nexus of Development, Ecology, and Evolution: An Introduction to the Symposium.

Over the past 40 years of research, two perspectives have dominated the study of ecomorphology at ontogenetic and evolutionary timescales. For key anatomical complexes (e.g., feeding apparatus, locomotor systems, sensory structures), morphological changes during ontogeny are often interpreted in functional terms and linked to their putative importance for fitness. Across larger timescales, morphological transformations in these complexes are examined through character stability or mutability during cladogenesis. Because the fittest organisms must pass through ontogenetic changes in size and shape, addressing transformations in morphology at different time scales, from life histories to macroevolution, has the potential to illuminate major factors contributing to phenotypic diversity. To date, most studies have relied on the assumption that organismal form is tightly constrained by the adult niche. Although this could be accurate for organisms that rapidly reach and spend a substantial portion of their life history at the adult phenotype (e.g., birds, mammals), it may not always hold true for species that experience substantial growth after one or more major fitness filters during their ontogeny (e.g., some fishes, reptiles). In such circumstances, examining the adult phenotype as the primary result of selective processes may be erroneous as it likely obscures the developmental configuration of morphology that was most critical to early survival. Given this discrepancy-and its potential to mislead interpretations of how selection may shape a taxon's phenotype-this symposium addresses the question: how do we identify such ontogenetic "inertia," and how do we integrate developmental information into our phylogenetic, ecological, and functional interpretations of complex phenotypes?