Microanatomical variation of the nasal capsular cartilage in newborn primates.

The breakdown of nasal capsule cartilage precedes secondary pneumatic expansion of the paranasal sinuses. Recent work indicates the nasal capsule of monkeys undergoes different ontogenetic transformations regionally (i.e., ossification, persistence as cartilage, or resorption). This study assesses nasal capsule morphology at the perinatal age in a taxonomically broad sample of non-human primates. Using traditional histochemical methods, osteopontin immunohistochemistry and tartrate-resistant acid phosphatase procedure, the cartilage of the lateral nasal wall (LNC) was studied. At birth, matrix properties differ between portions of the LNC that ultimately form elements of the ethmoid bone and regions of the LNC that have no postnatal (descendant) structure. The extent of cartilage that remains in the paranasal parts of the LNC varies among species. It is fragmented in species with the greatest extent of maxillary and/or frontal pneumatic expansion. Conversely, greater continuity of the LNC is noted in newborns of species that lack maxillary and/or frontal sinuses as adults. Chondroclasts occur adjacent to elements of the ethmoid bone, along the margin of the nasal tectum, and/or along islands of cartilage that bear no signs of ossification. Chondroclasts are prevalent along remnants of the paranasal LNC in tamarin species (Leontopithecus, Saguinus), which have extensive frontal and maxillary bone pneumatization. Taken together, the morphological observations indicate that the localized loss of cartilage might be considered a critical event at the onset of secondary pneumatization, facilitated by rapid recruitment of chondro-/osteoclasts, possibly occurring simultaneously in cartilage and bone.

Behavioral and ecological consequences of sex-based differences in gustatory anatomy in Cebus apella.

Fungiform papillae (FPs) are the only gustatory structures on the anterior tongue. Taste buds (TBs), which are located in FPs, house taste receptors. Each TB has a taste pore (TP) by which tastants are transmitted. In humans, FP and TB densities correlate with taste sensitivity and food preferences. Females have higher FP densities than males in Homo, Pan, and Cebus. Homo, Pan, and Cebus also have larger brains, slower ontogenetic development, and higher maternal investment in offspring compared to most primates. An increase in maternal investment places intense pressure on females to 1) obtain high-quality foods, and 2) detect potential toxins at low levels. This study examines sex differences in FPs and TPs (a TB surrogate) in 11 Cebus apella to test the hypothesis that higher FP density in females may be an adaptation specific to reproductive strategies of females. Tongues were imaged using an environmental scanning electron microscope; from these images FP surface area, FP density, TP count, and TP densities were calculated. We found that there were no significant differences between males and females in the number of TPs per FP. However, we did find that females do have larger FP surface areas and higher FP densities than males. The anatomical evidence indicates that females may have greater taste sensitivity than males because females have more FP than males. Future research on food preference and selection in Cebus is expected to show sex-specific behaviors similar to those observed in Homo and Pan.

Comparative microanatomy of the orbicularis oris muscle between chimpanzees and humans: evolutionary divergence of lip function.

The orbicularis oris muscle plays a role in the production of primate facial expressions and vocalizations, nutrient intake, and in some non-human primates it is used as a prehensile, manipulative tool. As the chimpanzee (Pan troglodytes) is the closest living relative of humans, a comparison of the orbicularis oris muscle between these species may increase our understanding of the morphological specializations related to the differing functional demands of their lips and the factors responsible for their divergent evolution. To this end, this study compares the microanatomy of the mid-line upper fibers of the orbicularis oris muscle between chimpanzees and humans. A mid-line portion of the orbicularis oris muscle was harvested from the upper lips of three chimpanzee and five human cadavers. The sampled blocks included the area between the lateral borders of the nasal alar cartilages in both species. Each sample was processed for paraffin histology, sectioned and stained with a variety of protocols. Sections were examined for fiber direction and relative thickness of muscle layers. Ratios of cross-sectional connective tissue area vs. cross-sectional muscle tissue area, muscle fiber diameter and relative dermal thickness were calculated for each species. In both species, a clear pars marginalis layer was recognized, contrary to previous reports that only humans possess this layer. In chimpanzees, the relative fiber diameter and relative amount of muscle tissue (i.e. based on ratio of connective tissue area : muscle tissue area) were significantly (P < 0.05) greater than in humans. In contrast, measurements of relative dermal thickness showed that humans have a greater average dermal thickness of the upper lip than chimpanzees. Taken together, these results suggest that both human and chimpanzee orbicularis oris muscle upper fibers meet the specific functional demands associated with their divergent vocal and facial display repertoires, the development of human speech, and the use of the upper lip as a prehensile tool in chimpanzees.

Fate of the nasal capsular cartilages in prenatal and perinatal tamarins (Saguinus geoffroyi) and extent of secondary pneumatization of maxillary and frontal sinuses.

Development of the nasal capsule cartilages was studied in seven Geoffroy's tamarins (Saguinus geoffroyi), including one fetus, five neonates and one infant. Four additional postnatal specimens of the genus were studied (one 5-month-old and three adults) to determine the magnitude of postnatal expansion of the paranasal sinuses. Alcian blue histochemistry and osteopontin immunohistochemistry were employed in selected subadult specimens to characterize cartilage matrix. The fetal S. geoffroyi possesses a continuous nasal capsule, including a zona anularis; the primordial maxillary sinuses are surrounded by cartilage. Secondary pneumatization is in progress in all older specimens, which have sinuses that are more than twofold larger compared to that of the fetus. Results indicate that extensive ossification of the middle part of the nasal capsule (pars intermedia) is occurring in the perinatal timeframe, forming portions of the ethmoid bone. Anteriorly, the nasal capsule comprises isolated fragments in perinatal specimens, which are fewer and smaller in the infant and in a 5-month-old S. midas, and nearby multinucleate cells suggest that osteoclasts break apart these initially continuous elements. Fragments of the pars intermedia and the tectum nasi are found transiently between mucosa and the sites of secondary pneumatization. The maxillary sinus mucosa is highly vascular in most perinatal specimens. Histochemical and immunohistochemical findings show that cartilage of endochondral bones and non-ossifying parts are distinct in the perinatal time period. These results indicate that breakdown of the capsular cartilage precedes secondary pneumatization as previously suggested. There are portions of the cartilage of the recessus maxillaris and tectum nasi that transiently block mucosa from interfacing directly with bone. Vascularization may play a role in the breakdown of cartilages as well as the onset of secondary pneumatization. Since cartilage has the capacity to produce substances that trigger angiogenesis and bone resorption, further detailed characterization of the cartilage bordering sites of secondary pneumatization is merited.

Scaling of the first ethmoturbinal in nocturnal strepsirrhines: olfactory and respiratory surfaces.

Turbinals (scroll bones, turbinates) are projections from the lateral wall of the nasal fossa. These bones vary from simple folds to branching scrolls. Conventionally, maxilloturbinals comprise the respiratory turbinals, whereas nasoturbinals and ethmoturbinals comprise olfactory turbinals, denoting the primary type of mucosa that lines these conchae. However, the first ethmoturbinal (ETI) appears exceptional in the variability of it mucosal covering. Recently, it was suggested that the distribution of respiratory versus olfactory mucosae varies based on body size or age in strepsirrhine primates (lemurs and lorises). The present study was undertaken to determine how the rostrocaudal distribution of olfactory epithelium (OE) versus non-OE scales relative to palatal length in strepsirrhines. Serially sectioned heads of 20 strepsirrhines (10 neonates, 10 adults) were examined for presence of OE on ETI, rostral to its attachment to the nasal fossa wall (lateral root). Based on known distances between sections of ETI, the rostrocaudal length of OE was measured and compared to the length lined solely by non-OE (primarily respiratory epithelium). In 13 specimens, the total surface area of OE versus non-OE was calculated. Results show that the length of non-OE scales nearly isometrically with cranial length, while OE is more negatively allometric. In surface area, a lesser percentage of non-OE exists in smaller species than larger species and between neonates and adults. Such results are consistent with recent suggestions that the olfactory structures do not scale closely with body size, whereas respiratory structures (e.g., maxilloturbinals) may scale close to isometry. In primates and perhaps other mammals, variation in ETI morphology may reflect dual adaptations for olfaction and endothermy.