Dorsal cortex volume in male side-blotched lizards (Uta stansburiana) is associated with different space use strategies

Abstract

Spatial abilities have been associated with many ecologically-relevant behaviors such as territoriality, mate choice, navigation and acquisition of food resources. Differential demands on spatial abilities in birds and mammals have been shown to affect the hippocampus, the region of the brain responsible for spatial processing. In some bird and mammal species, higher demands on spatial abilities are associated with larger hippocampal volumes. The medial and dorsal cortices are the putative reptilian homologues of the mammalian hippocampus, yet few studies have examined the relationship between these brain areas and differential spatial use strategies in reptiles. Further, many studies in birds and mammals compare hippocampal attributes between species that utilize space differently, potentially confounding species-specific effects with effects due to differential behaviors in spatial use. Here, we investigated the relationship between spatial use strategies and medial and dorsal cortical volumes in males of the side-blotched lizard (Uta stansburiana). In this species, males occur in three different morphs, each morph using different spatial niches: large territory holders, small territory holders and non-territory holders with home ranges smaller than the territories of small territory holders. We found that large territory holders had larger dorsal cortical volumes relative to the remainder of the telencephalon compared with non-territorial males, and small territory holders were intermediate. These results suggest that some aspect of holding a large territory may place demands on spatial abilities, which is reflected in a brain region thought partially responsible for spatial processing.

Figure 1

Relationship between telencephalon volume and medial cortex volume in three morphs of male side-blotched lizards.

Figure 2

Relationship between telencephalon volume and dorsal cortex volume in three morphs of male side-blotched lizards.

Figure 3

Relative telencephalon volume + SE (least squares means from the model with snout-vent length as the covariate) across three male morph types. Orange males defend large territories (n = 9), blue males defend smaller territories (n = 8), while yellow males do not defend territories and have smaller home ranges than orange and blue males (n = 7). There was not a significant effect of morph on relative telencephalon volume.

Figure 4

Relative medial cortex volume ± SE (least squares means from the model with telencephalon volume as the covariate) across three male morph types. Orange males defend large territories (n = 9), blue males defend smaller territories (n = 8), while yellow males do not defend territories and have smaller home ranges than orange and blue males (n = 7). There was not a significant effect of morph on relative medial cortex volume, but mean values showed perfect correlation with the morph.

Figure 5

Relative dorsal cortex volume ± SE (least squares means from the model with telencephalon volume as the covariate) across three male morph types. Orange males defend large territories (n = 9), blue males defend smaller territories (n = 8), while yellow males do not defend territories and have smaller home ranges than orange and blue males (n = 7). Orange males had larger dorsal cortical volumes compared with yellow males (p = 0.017), whereas blue males were intermediate.