In Vivo Measurements of Lung Volumes in Ringed Seals: Insights from Biomedical Imaging

Marine mammals rely on oxygen stored in blood, muscle, and lungs to support breath-hold diving and foraging at sea. Here, we used biomedical imaging to examine lung oxygen stores and other key respiratory parameters in living ringed seals (Pusa hispida). Three-dimensional models created from computed tomography (CT) images were used to quantify total lung capacity (TLC), respiratory dead space, minimum air volume, and total body volume to improve assessments of lung oxygen storage capacity, scaling relationships, and buoyant force estimates. Results suggest that lung oxygen stores determined in vivo are smaller than those derived from postmortem measurements. We also demonstrate that—while established allometric relationships hold well for most pinnipeds—these relationships consistently overestimate TLC for the smallest phocid seal. Finally, measures of total body volume reveal differences in body density and net vertical forces in the water column that influence costs associated with diving and foraging in free-ranging seals.

Investigating the Surface Area to Volume Ratio (S/V) in Bergmann's Rule

Students are almost universally interested in animals, and especially endotherms, including mammals and birds. According to Bergmann's rule, endotherms that live in colder climates at higher latitudes are larger than those living in warmer climates. As with most biological principles, hands-on investigation will provide a better understanding of why size is important in endotherm thermal regulation. One easily observable aspect of this principle is that larger organisms have a lower ratio of body surface area to total body volume. This affects how efficiently they can retain or radiate heat, which can be easily tested in the laboratory using commonly available materials. In this activity, simple models of endotherms of different sizes are used to assess the effects of body size on heat loss.

Sympathetic Renal Innervation and Resistant Hypertension

Hypertension in chronic renal disease and renovascular disease is often resistant to therapy. Understanding the pathogenic mechanisms responsible for hypertension in these conditions may lead to improved and more targeted therapeutic interventions. Several factors have been implicated in the pathogenesis of hypertension associated with renal disease and/or renal failure. Although the role of sodium retention, total body volume expansion, and hyperactivity of the renin-angiotensin-aldosterone system (RAAS) are well recognized, increasing evidence suggests that afferent impulses from the injured kidney may increase sympathetic nervous system activity in areas of the brain involved in noradrenergic regulation of blood pressure and contribute to the development and maintenance of hypertension associated with kidney disease. Recognition of this important pathogenic factor suggests that antiadrenergic drugs should be an essential component to the management of hypertension in patients with kidney disease, particularly those who are resistant to other modalities of therapy.

Gametogenic cycle of the tropical vermetids Eualetes tulipa and Dendropoma corrodens (Mollusca: Caenogastropoda: Vermetidae)

The population density, annual gametogenic cycle, and size at sexual maturity of two vermetid species, Eualetes tulipa (invasive) and Dendropoma corrodens was studied in the southern Caribbean at the Planta Centro power plant intake channel and at Punta Mayorquina, Morrocoy National Park, respectively. Minimal size of mature females of E. tulipa and D. corrodens was 5.0 and 0.7 cm in body length respectively. The gonad represented between 44 to 47% of total body length, while it represented between 15 to 18% of total body volume (for both males and females). Gonad volume was significantly related to total body volume. A significant quadratic relationship between the number of capsules and female body volume was obtained for E. tulipa, indicating that females measuring 6–10 cm in body length are those that have the highest number of egg capsules. Females larger than 11 cm have a lower fecundity in terms of brooded capsules. Gonad sections of males and females of both species showed that several gametogenesis stages are simultaneous within the same individual. In the female, germ cells, oogoniums and primary oocytes with yolk granules were observed simultaneously. In the male, the spermatogonium, primary and secondary spermatocytes, spermatids and sperm cells were also observed within one gonad. The same pattern was observed throughout the year, showing no maturation/resting period or annual cycle. The area covered by D. corrodens was about 700 m2 with a mean density of 13,000 ind/m2. The area covered by the invasive E. tulipa was at least about 1000 m2, with a density of 27,000 to 29,000 ind/m2 in the first 3 m of depth. A follow up of the E. tulipa population showed that its density is increasing in time and has doubled in 20 years. This population increment could be related to an increase in organic suspended matter as evidenced in the region.