Christopher P. Heesy

The nocturnal bottleneck and the evolution of mammalian vision.

Evidence from the early paleontological record of mammalian evolution has often been interpreted as supporting the idea that mammals were nocturnal for most of their early history. Multiple features of extant mammal sensory systems, such as evolutionary modifications to the light-regulated circadian system, photoreceptor complement, and retinal morphology, support this nocturnal hypothesis for mammalian evolution. Here, we synthesize data on eye shape and orbit orientation in mammals as these data compare to other amniotes. Most mammals differ from other amniotes in retaining an eye design optimized for high visual sensitivity, with the requisite reduction in acuity, which is typically restricted to scotopically (i.e. low light) adapted amniotes. Mammals also possess the more convergent (similarly facing) orbits and, on average, the largest binocular visual fields among amniotes. Based on our analyses, we propose that extant mammals retain a scotopic eye design as well as expanded binocular zones as a result of their nocturnal origin. Only anthropoid primates notably differ from general mammalian patterns, and possibly have evolved an eye shape more typical of the ancestral amniote condition.

Relative Wulst volume is correlated with orbit orientation and binocular visual field in birds

In mammals, species with more frontally oriented orbits have broader binocular visual fields and relatively larger visual regions in the brain. Here, we test whether a similar pattern of correlated evolution is present in birds. Using both conventional statistics and modern comparative methods, we tested whether the relative size of the Wulst and optic tectum (TeO) were significantly correlated with orbit orientation, binocular visual field width and eye size in birds using a large, multi-species data set. In addition, we tested whether relative Wulst and TeO volumes were correlated with axial length of the eye. The relative size of the Wulst was significantly correlated with orbit orientation and the width of the binocular field such that species with more frontal orbits and broader binocular fields have relatively large Wulst volumes. Relative TeO volume, however, was not significant correlated with either variable. In addition, both relative Wulst and TeO volume were weakly correlated with relative axial length of the eye, but these were not corroborated by independent contrasts. Overall, our results indicate that relative Wulst volume reflects orbit orientation and possibly binocular visual field, but not eye size.

Mosaic Evolution of Activity Pattern, Diet, and Color Vision in Haplorhine Primates

One important component of an animal’s niche is the temporal axis, or daily activity pattern (e.g., Kronfeld-Schor et al., 2001). Numerous studies have shown that activity pattern is an important constraint on the behavior and ecology of primate species. Activity pattern is correlated with resource availability, predation pressure, social structure, mating system, and diet, among other factors. Dissimilar activity patterns, such as diurnality or nocturnality, may allow even ecologically similar species to partition their environments and thereby eliminate direct competition between them (Kronfeld-Schor and Dayan, 1999; Kronfeld-Schor et al., 2001). Nocturnal primates are often insectivorous or frugivorous, never habitually terrestrial, and tend to be solitary and cryptic or live in small, monogamous groups (Clutton-Brock and Harvey, 1977; Crook and Gartlan, 1966; Janson, 1992; Terborgh and Janson, 1986). Conversely, diurnal species are more frugivorous or folivorous, arboreal and terrestrial, and often live in larger groups with more diverse and complex social systems (Clutton-Brock and Harvey, 1977; Crook and Gartlan, 1966; Janson, 1992; Terborgh and Janson, 1986).

A novel method for comparative analysis of retinal specialization traits from topographic maps

Vertebrates possess different types of retinal specializations that vary in number, size, shape, and position in the retina. This diversity in retinal configuration has been revealed through topographic maps, which show variations in neuron density across the retina. Although topographic maps of about 300 vertebrates are available, there is no method for characterizing retinal traits quantitatively. Our goal is to present a novel method to standardize information on the position of the retinal specializations and changes in retinal ganglion cell (RGC) density across the retina from published topographic maps. We measured the position of the retinal specialization using two Cartesian coordinates and the gradient in cell density by sampling ganglion cell density values along four axes (nasal, temporal, ventral, and dorsal). Using this information, along with the peak and lowest RGC densities, we conducted discriminant function analyses (DFAs) to establish if this method is sensitive to distinguish three common types of retinal specializations (fovea, area, and visual streak). The discrimination ability of the model was higher when considering terrestrial (78%-80% correct classification) and aquatic (77%-86% correct classification) species separately than together. Our method can be used in the future to test specific hypotheses on the differences in retinal morphology between retinal specializations and the association between retinal morphology and behavioral and ecological traits using comparative methods controlling for phylogenetic effects.

Oculomotor Stability and the Functions of the Postorbital Bar and Septum

The postorbital bar and septum are circumorbital structures that are important to adaptive hypotheses for the origins of primates and haplorhines, respectively. All primates possess complete postorbital bars, bony arches formed by processes of the frontal and zygomatic bones that encompass the lateral aspect of the eye. Postorbital septa, bony walls formed by the frontal, zygomatic and alisphenoid bones, walling off the orbit from the anterior temporal fossa, are limited to tarsiers and anthropoids. Numerous functional hypotheses have been advanced for postorbital bars and septa. Many of these hypotheses can easily be rejected (Cartmill, 1970, 1972, 1980; Ravosa, 1991a,b; Ravosa et al., 2000a,b; Ross, 1994, 1995a,b, 1996, 2000, 2001; Ross and Hylander, 1996; see Heesy, 2003). Cartmill (1970, 1972, 1980; see also Collins, 1921) suggested that in therian mammals with large eyes, relatively small temporal fossae, and derived orbit

Malagasy Primate Origins: Phylogenies, Fossils, and Biogeographic Reconstructions

The geographic origin of Malagasy primates is a rich source of debate, providing a useful context for understanding effects of differing phylogenetic interpretations upon area of origin reconstructions. This study has evaluated the biogeographic implications of competing primate phylogenies in order to reconstruct the area of origin of Malagasy strepsirhines. The robusticity of biogeographic inference is examined based on sensitivity to tree topology. The results demonstrate extreme vulnerability to both out-group choice and internal tree topology, suggesting caution for area of origin interpretations from phylogenies that exclude fossil taxa. Moreover, even a single taxon can have a powerful effect upon biogeographic interpretations. Perhaps not surprisingly, it is only with greater phylogenetic resolution that a clearer understanding of the biogeographic origins of Malagasy primates will emerge.

Structure and Function of Regional Specializations in the Vertebrate Retina

Visual sensory demands vary substantially across vertebrates. Different visual sensory components have evolved to meet these sensory demands and enhance visual behavioral performance. One of these components is the retinal specialization, which is a portion of the retina with generally high ganglion cell densities, which increase spatial resolving power. Retinal specializations are relevant from a functional perspective because animals can align these “acute zones” with objects of interest within a localized region of their visual space, consequently affecting different behavioral dimensions. In this chapter, we reviewed the different types of retinal specializations found in vertebrates (retinal area , fovea, visual streak, radial anisotropy, area gigantocellularis) by discussing the different hypotheses proposed over decades to explain their function. Empirical tests on the functional properties of these different retinal specializations have been limited, which constrains our ability to understand the functional evolution of the vertebrate eye. We derive specific predictions from each of the hypotheses put forward to identify their degree of overlap. Finally, we provide some future directions as to how to test these functional hypotheses by integrating physiological and behavioral approaches. Testing these functional hypotheses will enhance our understanding of the relationship between the eye and the physical environment, and ultimately the visual ecology of vertebrates.

New adapiform primate fossils from the late Eocene of Egypt

Abstract Caenopithecine adapiform primates are currently represented by two genera from the late Eocene of Egypt (Afradapis and Aframonius) and one from the middle Eocene of Switzerland (Caenopithecus). All are somewhat anthropoid-like in several aspects of their dental and gnathic morphology, and are inferred to have been highly folivorous. Here we describe a new caenopithecine genus and species, Masradapis tahai, from the ~37 million-year-old Locality BQ-2 in Egypt, that is represented by mandibular and maxillary fragments and isolated teeth. Masradapis is approximately the same size as Aframonius but differs in having a more dramatic distal increase in molar size, more complex upper molar shearing crests, and an exceptionally deep mandibular corpus. We also describe additional mandibles and part of the orbit and rostrum of Aframonius which suggest that it was probably diurnal. Phylogenetic analyses place Masradapis either as the sister taxon of Aframonius (parsimony), or as the sister taxon of Afradapis and Caenopithecus (Bayesian methods). Bayesian tip-dating analysis, when combined with Bayesian biogeographic analysis, suggests that a common ancestor of known caenopithecines dispersed to Afro-Arabia from Europe between 49.4 and 47.4 Ma, and that a trans-Tethyan back-dispersal explains Caenopithecus’ later presence in Europe. For Masradapis: https://www.zoobank.org/urn:lsid:zoobank.org:act:41BC8459-7CCE-487F-BC59-1C34257D5C4E For Masradapis tahai: https://www.zoobank.org/urn:lsid:zoobank.org:act:C0A620AD-6FCA-4649-A980-FCA237AFE39D

Head Posture and Visual Orientation in Loris tardigradus During Locomotion on Oblique Supports

Primates moving through the trees must cope with a three-dimensional network of branches that differ in angular orientation. On oblique supports, an animal must not only avoid toppling or sliding off of a branch, it may also need to adjust its visual field orientation along the path of movement. Previous studies have found that primate quadrupeds walking on top of horizontal supports direct the orbital plane more inferiorly, whereas suspensory primates moving beneath branches direct the orbital plane more superiorly. If primates adjust the visual path to reflect substrate position, they should incline the orbital plane more on inclines than on declines. Alternatively, eye mobility within the orbits may permit collection of sufficient visual information without reorienting angular posture of the head. Lorisids are adept arboreal quadrupeds that routinely negotiate inclines and declines. We collected 150 strides of kinematic data on head postures for two adult slender lorises (Loris tardigradus) during locomotion on horizontal and oblique supports. In general, lorises adjusted head posture as predicted, directing orbits more superiorly on inclines and more inferiorly on declines. However, we observed higher angles on declines than predicted by substrate angle alone, suggesting that other locomotor and vestibular issues also influence head orientation.

Restricted access to fossils hinders claim confirmation.

SIR — Scientists and whole institutes are frequently judged by the number of citations of their papers in scientific journals, and project funding depends on it. But, as Clint Kelly and Michael Jennions note in Correspondence (‘H-index: age and sex make it unreliable’ Nature 449, 403; 2007), the context and relevance of citations are crucial in reaching this judgement. Researchers from developing nations often face another problem. In the name of local issues and the national interest, they are required to publish in national journals that rarely find a place among cited journals and have a very limited circulation abroad. For example, a study of the Thomson Scientific Essential Science Indicators (ESI) during the past five years has found that the National Geophysical Research Institute (NGRI) in Hyderabad, India, scores among the top 1% of institutions publishing in the geosciences. During this period, the NGRI had 2,338 citations of 657 papers (www.incites.com/institutions/2007menu.html). But if it had not published more than half its publications in national journals — not all of which figure in the ESI database — the NGRI could have been ranked even nearer the top. In formulating their criteria, publications from institutes and by individuals in local and national journals should also be taken into account: this could be done by assigning some weighted average. The total number of publications in national journals not counted by the ESI would then be considered and weighted in order to arrive at a more appropriate index. D. C. Mishra National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, Andhra Pradesh, India