Comparative Gross Morphometry and Histomorphology of Brain and Testes in Thomas's Rope Squirrel (Funisciurus anerythrus) and Gambian Sun Squirrel (Heliosciurus gambianus)

Squirrels have attracted many interests from many scientists as a model for research. There are several species of squirrels found across the globe; however, different species are found in specific locations. This study examined the Thomas'-Rope-Squirrel (TRS) and Gambian-Sun-Squirrel (GSS), mostly found in West Africa and Central Africa. There is paucity of information on the brain and testicular morphometry in these species. Therefore, the aim of this study was to compare the gross morphometric and histological descriptions of the brain and testes between TRS and GSS. Comparing five adult males from each species, the study found that TRS had smaller brains but significantly larger testes relative to their body size compared to GSS. Brain length differed between the species, but brain width was similar. The observed macromorphological variation in size and weight of testes could be attributed to the number of seminiferous tubules and degree of cellularity within the testis of each species. The olfactory bulb and testes of both species displayed similar histological features. In the TRS, the internalplexiform-layer (IPL) was not easily differentiated from the mitral cell layer except when observed at a higher magnification. The subventricular-zone was evident in the TRS but not noticeable in the GSS. TRS showed a higher testicular cell density compared to the GSS. The findings from the present study show significant differences in body, brain and testicular weights of the two tree squirrels. The similarities observed in histological patterns of the organs further suggest conservation of features across rodent species.

Key Words: gross morphometry, histomorphology, brain, testes, tree squirrels