Morphological Abnormalities and Biological Effects in the Porto Alegre Strain of <scp> <i>Rhipicephalus microplus</i> </scp>

ABSTRACT Rhipicephalus microplus is a widespread tick species causing significant economic losses and transmitting pathogens to cattle. The R. microplus populations utilized in tick research are frequently maintained under laboratory conditions for many years. Despite this, morphological abnormalities developed in laboratory‐maintained strains remain underexplored. Here, we analyzed the Porto Alegre (POA) strain, maintained under controlled conditions for nearly four decades, assessing external and internal morphological abnormalities across generations and their impact on biological parameters. We identified a low frequency (~0.9%) of diverse external malformations, predominantly idiosomal asymmetries, accompanied by histological gut alterations indicative of cellular dysfunction. Malformed ticks exhibited significantly reduced body weight, oviposition, and fertility compared to normal individuals. These abnormalities were not heritable but persisted sporadically, suggesting multifactorial origins. Our findings indicate that morphological malformations impair feeding efficiency and reproductive capacity, potentially limiting the fitness of affected ticks. This study enhances understanding of morphological variation in R. microplus and its biological implications and will inform strain maintenance and tick biology research.