Eye Size at Birth in Prosimian Primates: Life History Correlates and Growth Patterns

Abstract

BackgroundPrimates have large eyes relative to head size, which profoundly influence the ontogenetic emergence of facial form. However, growth of the primate eye is only understood in a narrow taxonomic perspective, with information biased toward anthropoids.Methodology/Principal FindingsWe measured eye and bony orbit size in perinatal prosimian primates (17 strepsirrhine taxa and Tarsius syrichta) to infer the extent of prenatal as compared to postnatal eye growth. In addition, multiple linear regression was used to detect relationships of relative eye and orbit diameter to life history variables. ANOVA was used to determine if eye size differed according to activity pattern. In most of the species, eye diameter at birth measures more than half of that for adults. Two exceptions include Nycticebus and Tarsius, in which more than half of eye diameter growth occurs postnatally. Ratios of neonate/adult eye and orbit diameters indicate prenatal growth of the eye is actually more rapid than that of the orbit. For example, mean neonatal transverse eye diameter is 57.5% of the adult value (excluding Nycticebus and Tarsius), compared to 50.8% for orbital diameter. If Nycticebus is excluded, relative gestation age has a significant positive correlation with relative eye diameter in strepsirrhines, explaining 59% of the variance in relative transverse eye diameter. No significant differences were found among species with different activity patterns.Conclusions/SignificanceThe primate developmental strategy of relatively long gestations is probably tied to an extended period of neural development, and this principle appears to apply to eye growth as well. Our findings indicate that growth rates of the eye and bony orbit are disassociated, with eyes growing faster prenatally, and the growth rate of the bony orbit exceeding that of the eyes after birth. Some well-documented patterns of orbital morphology in adult primates, such as the enlarged orbits of nocturnal species, mainly emerge during postnatal development.

Relative tooth size at birth in primates: Life history correlates

“…This allows us to draw inferences about the relationship between midfacial length and developing teeth. Most variables were strongly correlated with CL (Table 2; and see Cummings, Muchlinski, Kirk et al, 2012). Therefore, residuals were calculated from a least-squares regression of dental and life history variables versus CL (e.g., relative dental volume).…”

The Chiropteran Brain Database: Volumetric Survey of the Hypophysis in 165 Species

“…Residuals can be used to demonstrate how a measurement varies “away from an expected or detected trend” (Pagel and Harvey, , p. 422). Specifically, the residuals calculated here represent deviations from best‐fit regression lines, as in numerous previous studies (e.g., Harvey et al, ; Cummings et al, ). Positive values indicate a relatively greater‐than‐expected size of a given variable.…”

Microstructure of the eye tunics, eyelids and ocular glands of the Sulawesi bear cuscus (Ailurops ursinusTemminck, 1824) (Phalangeridae: Marsupialia) based on anatomical, histological and histochemical studies

“…The eyeballs was measured according to the method described by Cummings et al (2012), Kirk (2004Kirk ( , 2006 and Lluch, Ventura, and Lopez-Fuster (2008). The axial eye diameter (from the anterior cornea to the root of the optic nerve), the maximum transverse (equatorial) eye diameter, the minimum transverse (equatorial) eye diameter, the minimum and maximum corneal diameter, the corneal thickness, the lens thickness, the aqueous humour thickness, the vitreous humour thickness and the values of six random measurements of the whole eyeball were analysed statistically and expressed as mean ± standard deviation (SD).…”