1School of Physical Therapy, Slippery Rock University, 2Department of Anthropology, University of Pittsburgh, 3Department of Biology, Slippery Rock University, 4Department of Anatomy and Neurobiology, University of Kentucky, 5Department of Anthropology, University of Texas at Austin, 6Center for Functional Anatomy & Evolution, Johns Hopkins University School of Medicine
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Primates have large eyes relative to head size. Based on studies of humans and macaques, eye growth is described as most rapid in prenatal and early postnatal ontogeny. To better understand the pattern of eye growth across the primate order, we measured transverse eye diameter (TD) in thirty-eight infant primates (17 strepsirrhine species and Tarsius syrichta). Data were used to investigate the proportional size of the eye (using ratios and residuals) among primates, and to examine the correlation of TD with life history variables. Most variables were strongly correlated with cranial length (CL), and residuals from CL (“relative TD”) were calculated with least squares regressions. For most species, the infant TDs are more than half of published adult values, suggesting that a substantial amount of growth in diameter occurs prenatally. Two exceptions include Nycticebus and Tarsius (infant/adult TD ratios are 0.33 and 0.44, respectively). Relative TD is uncorrelated with relative body mass (residuals of perinatal relative to adult body mass), but is significantly (p < 0.005) correlated with relative gestation length (R=0.67) and relative weaning age (R=0.56). However, when phylogeny is considered (PGLS), only the correlation with relative gestation length remains significant. Our findings reveal relative perinatal eye size is positively correlated with relative gestation length. In this sense, TD growth follows a pattern of brain growth in primates. Moreover, the majority of growth in TD occurs prenatally for most primates. In Nycticebus and Tarsius, however, eyes grow less prenatally and compensate with a greater extent of postnatal growth.
This study was supported by NSF grants EF-0905606 and BCS-0959438.