Comparative non-metric and morphometric analyses of rats at residential halls of the University of Benin campus, Nigeria

Background: In mammals and across rat species, the variation in conformation is markedly observed in the head and the variation in the shape of the head is mostly determined by the shape of the skull. Hence comparative topographic analysis and morphometry is a veritable tool in precise categorization of peri-domestic rats and species identification. Methods: Killed rodents around residential dwellings of students on campus were collected and measurements taken of external morphology. Thirty-one external head and corporal parameters; and 40 cranial measurements respectively were obtained. Topographic features and specific anatomical landmarks measured were matched using congruent anatomical landmarks and compared to referenced standard measurements. Results: External morphometry suggests that all retrieved samples were more closely related to the species Rattus rattus. However, craniodental analysis of captured rats reveals variations from the mean of typical R. rattus. In comparison with Mastomys natalensis, the mean averages of the rat species were perceptibly different for only two of the parameters viz palatine fissure length (PL) (p = 0.039) and distance between interparietal bone (DP) (p = 0.06). In contrast, the mean of whole length of skull (WL), length of diastema (PI), length of nasal bone (NL), length of frontal bone (LF) and occipital width (OH) were significantly different from that of R. rattus with p values of 0.047, 0.036, 0.048, 0.032 and 0.034 respectively. Conclusion: This study focuses on peridomestic rat’s identification within the University campus based on morphometry, providing unique landmarks for differentiation between Mastomys, Mus, Rattus and other rat species with emphasis on the need for more comprehensive investigation, categorization and morphometric profiling of rat population in Nigeria. Metric data generated for rat profiling in Nigeria is pivotal for a more comprehensive strategy for prevention of Lassa fever. Keywords: External morphometry, Craniodental morphometry, Lassa fever, Peridomestic rat, Mastomy