SEXUAL DIMORPHISM IN MORPHOMETRIC AND HEMATOLOGICAL INDICES OF SYMPATRIC RATTUS NORVEGICUS AND RATTUS RATTUS POPULATIONS IN AGROECOLOGICAL ZONES OF CENTRAL PUNJAB, PAKISTAN

Abstract

Morphometric and hematological characteristics are important indicators of physiological condition, biological variation, and adaptation in wild rodents. However, these traits may vary according to species, sex, and environmental conditions. The present study evaluated sex-associated morphometric and hematological variation in sympatric populations of brown rats (Rattus norvegicus) and black rats (Rattus rattus) from agroecological areas of Sargodha, Punjab, Pakistan. A total of 65 wild rodents were collected between April and July 2024, comprising 35 brown rats and 30 black rats. Species identification was performed using a dichotomous identification key. Morphometric characteristics, including head-and-body length, head length, tail length, body weight, hind-foot length, ear length, head width, body width, body girth, eye diameter, and front-foot length, were recorded using standardized measurements. Blood samples were collected by cardiac puncture into EDTA-containing tubes, and complete blood count parameters were assessed. Differences in hematological parameters were evaluated using a two-sample t-test. Marked interspecific and sex-associated variation was observed in body size. Male brown rats had the highest mean body weight (125.9 g), followed by female brown rats (106.2 g), whereas female black rats had the lowest mean body weight (75.30 g). Brown rats generally exhibited greater body dimensions than black rats. Hematological profiles also differed between species, particularly in leukocyte distribution. Brown rats showed higher mean WBC counts (8.60 × 10³/µL) than black rats (6.77 × 10³/µL), while black rats had a higher mean lymphocyte proportion (61.0%) than brown rats (54.4%). Monocytes were markedly higher in brown rats (34.5%) than black rats (12.9%; p < 0.001). In black rats, males had significantly higher WBC counts, monocyte percentages, and eosinophil percentages than females, whereas females showed higher MCV. In brown rats, MCH differed significantly between sexes (p = 0.02), while most erythrocytic and platelet parameters showed no significant sex-related differences. The findings demonstrate substantial morphometric and hematological variation between sympatric brown and black rats and indicate that sex contributes to variation in selected blood parameters. The observed differences provide useful baseline information for understanding biological variation and physiological adaptation of free-ranging rodent populations in agroecological environments of Central Punjab.