Eye morphology in cathemeral lemurids and other mammals.

University of Texas at Austin, Austin, TX 78712, USA.
Folia Primatologica (Impact Factor: 0.73). 02/2006; 77(1-2):27-49. DOI: 10.1159/000089694
Source: PubMed

ABSTRACT The visual systems of cathemeral mammals are subject to selection pressures that are not encountered by strictly diurnal or nocturnal species. In particular, the cathemeral eye and retina must be able to function effectively across a broad range of ambient light intensities. This paper provides a review of the current state of knowledge regarding the visual anatomy of cathemeral primates, and presents an analysis of the influence of cathemerality on eye morphology in the genus Eulemur. Due to the mutual antagonism between most adaptations for increased visual acuity and sensitivity, cathemeral lemurs are expected to resemble other cathemeral mammals in having eye morphologies that are intermediate between those of diurnal and nocturnal close relatives. However, if lemurs only recently adopted cathemeral activity patterns, then cathemeral lemurids would be expected to demonstrate eye morphologies more comparable to those of nocturnal strepsirrhines. Both predictions were tested through a comparative study of relative cornea size in mammals. Intact eyes were collected from 147 specimens of 55 primate species, and relative corneal dimensions were compared to measurements taken from a large sample of non-primate mammals. These data reveal that the five extant species of the cathemeral genus Eulemur have relative cornea sizes intermediate between those of diurnal and nocturnal strepsirrhines. Moreover, all Eulemur species have relative cornea sizes that are comparable to those of cathemeral non-primate mammals and significantly smaller than those of nocturnal mammals. These results suggest that Eulemur species resemble other cathemeral mammals in having eyes that are adapted to function under variable environmental light levels. These results also suggest that cathemerality is a relatively ancient adaptation in Eulemur that was present in the last common ancestor of the genus (ca. 8-12 MYA).

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    ABSTRACT: Many animals regulate their activity over a 24-h sleep-wake cycle, concentrating their peak periods of activity to coincide with the hours of daylight, darkness, or twilight, or using different periods of light and darkness in more complex ways. These behavioral differences, which are in themselves functional traits, are associated with suites of physiological and morphological adaptations with implications for the ecological roles of species. The biogeography of diel time partitioning is, however, poorly understood. Here, we document basic biogeographic patterns of time partitioning by mammals and ecologically relevant large-scale patterns of natural variation in "illuminated activity time" constrained by temperature, and we determine how well the first of these are predicted by the second. Although the majority of mammals are nocturnal, the distributions of diurnal and crepuscular species richness are strongly associated with the availability of biologically useful daylight and twilight, respectively. Cathemerality is associated with relatively long hours of daylight and twilight in the northern Holarctic region, whereas the proportion of nocturnal species is highest in arid regions and lowest at extreme high altitudes. Although thermal constraints on activity have been identified as key to the distributions of organisms, constraints due to functional adaptation to the light environment are less well studied. Global patterns in diversity are constrained by the availability of the temporal niche; disruption of these constraints by the spread of artificial lighting and anthropogenic climate change, and the potential effects on time partitioning, are likely to be critical influences on species' future distributions.
    Proceedings of the National Academy of Sciences 09/2014; 111(38). DOI:10.1073/pnas.1216063110 · 9.81 Impact Factor
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    01/2012: chapter 16: pages 306-330; Cambridge University Press.


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