Brain organization of gorillas reflects species differences in ecology

Abstract

Gorillas include separate eastern (Gorilla beringei) and western (Gorilla gorilla) African species that diverged from each other approximately 2 million years ago. Although anatomical, genetic, behavioral, and socioecological differences have been noted among gorilla populations, little is known about variation in their brain structure. This study examines neuroanatomical variation between gorilla species using structural neuroimaging. Postmortem magnetic resonance images were obtained of brains from 18 captive western lowland gorillas (Gorilla gorilla gorilla), 15 wild mountain gorillas (Gorilla beringei beringei), and 3 Grauer's gorillas (Gorilla beringei graueri) (both wild and captive). Stereologic methods were used to measure volumes of brain structures, including left and right frontal lobe gray and white matter, temporal lobe gray and white matter, parietal and occipital lobes gray and white matter, insular gray matter, hippocampus, striatum, thalamus, each hemisphere and the vermis of the cerebellum, and the external and extreme capsules together with the claustrum. Among the species differences, the volumes of the hippocampus and cerebellum were significantly larger in G. gorilla than G. beringei. These anatomical differences may relate to divergent ecological adaptations of the two species. Specifically, G. gorilla engage in more arboreal locomotion and thus may rely more on cerebellar circuits. In addition, they tend to eat more fruit and have larger home ranges and consequently might depend more on spatial mapping functions of the hippocampus.

Temporal variation selects for diet–microbe co-metabolic traits in the gut of Gorilla spp

“…Climate change and its effect on the availability of dietary resources have been proposed to be a driving force behind hominin speciation, influencing bipedalism, cranial capacity, adaptability and cultural innovations (Behrensmeyer, 2006). Furthermore, recent reports on brain organization differences between lowland and mountain gorillas point to ecological distinctions as important driving factors (Barks et al, 2015). Here, we show that the acquisition of species-specific gut microbiome arrangements in primates may also follow a trend dependent on ecological change.…”

Erratum

“…To further address data reliability, in online supplementary Table S3 we present new comparisons of our measurements with measurements of the total brain, neocortex, striatum, cerebellum, hippocampus, and thalamus for 6 GANP brains studied in previous publications [Sherwood et al, 2004;Barks et al, 2015]. These authors, like us, measured neocortical grey matter rather than grey plus white matter combined [Sherwood pers.…”

“…C.C. Sherwood provided the unpublished volumes for individual brains from Barks et al [2015]. These volumes are not corrected for shrinkage, but shrinkage is expected to have been low [Sherwood pers.…”

“…commun.]. We compared our cerebellum volume to the sum of the two hemispheres plus vermis in Barks et al [2015]. We found good correspondence between these data for the total brain volumes (mean percent error = 3.4%, n = 6, range = 1.2 to 5.8%), neocortex volumes (mean percent error = -4.3%, n = 3, range = -1.7 to -6.4%), and cerebellum volumes (mean percent error = 2.3%, n = 6, range = -4.7 to 8.3%).…”

“…Four are comparisons of our measurements with measurements of the same scans: (1) de Viet [2009], (2) Todorov [2010], (3) Pagnotta's independent measurements for our article, and (4) the published work of Sherwood et al [2004] and Barks et al [2015]. The fifth is a com- Table S1 provides the individual-level morphological dataset including additional samples, additional brain areas (hemispheres, corpus callosum, and lateral geniculate nuclei), lateralized measurements, specimen and individual details, and the list of specimens included in the means.…”