A cattle tick collected from a university farm in El Salvador has become the country’s first documented example of gynandromorphism, a rare developmental anomaly in which a single animal displays both male and female body features. The specimen belonged to Rhipicephalus microplus, commonly known as the cattle tick, an economically important parasite of livestock. Researchers describe its body as divided asymmetrically along its length: the left side was dominated by female characteristics, while the right side carried several structures normally associated with males. The discovery offers an unusual glimpse into how sexual identity can be expressed in the bodies of arthropods—and raises questions about whether such a malformed tick can reproduce or transmit pathogens normally.

The specimen was found in October 2025 during a surveillance program run by the University of El Salvador’s Health Discovery and Investigation Center, known as CENSALUD. The team is building a national tick biorepository to identify veterinary and medically important species and to investigate the pathogens they may carry. At an experimental and practical agricultural station in San Luis Talpa, in the Department of La Paz, researchers examined 23 animals—12 cows, 10 goats and one dog—as well as one person and the surrounding environment for ticks seeking hosts. During inspection of a Holstein Brown Swiss cow, they noticed an unusual tick attached to the animal’s udder. It was removed with fine forceps and preserved in 70 percent ethanol and glycerol before being examined under a stereomicroscope.

In total, the visit produced 192 ticks, but only one showed the striking combination of male and female anatomy. The researchers identified it as R. microplus using a regional taxonomic key for hard ticks and detailed examination of its external structures. In dorsal view, a longitudinal boundary extended from the base of the capitulum—the tick’s mouthpart-bearing head region—to the posterior end of the body. The left half had a scutum, the hard dorsal shield characteristic of female cattle ticks, while the right half displayed male traits. The finding is classified as bilateral gynandromorphism, although the division was not perfectly symmetrical and the female side appeared to have expanded during feeding.

Gynandromorphism differs from ordinary sexual variation and from intersexuality. An intersexual animal may possess a mixture of male and female traits throughout its body, often because of hormonal or developmental changes. A gynandromorph, by contrast, has distinct regions whose morphology follows different sexual patterns. In a bilateral form, one side of the body is predominantly male and the other predominantly female. Other gynandromorphs show mosaic or patchwork arrangements, in which male and female cells are scattered in irregular regions. The pattern depends on when and how the developmental error occurs. A mistake during early cell division can establish large, sharply separated territories, whereas a later event may produce smaller or more complicated patches.

Several mechanisms could generate such a body plan. In animals with sex chromosomes, errors in chromosome segregation during the formation of eggs or sperm can produce cells with different genetic sex identities. An abnormal fertilization event, including the fertilization of an oocyte containing two nuclei, has also been proposed in other arthropods. Hormonal signals may contribute to the development of sexual structures, but research in other animals indicates that sex identity can sometimes be maintained autonomously by individual cells rather than imposed only by circulating hormones. The Salvadoran study did not analyze the tick’s chromosomes or genes, so it cannot determine which mechanism produced this individual. Its conclusions are morphological: the specimen’s physical structures clearly combine the two sexes.

The anatomical details were unusually informative. On the underside, an anal groove crossed slightly toward the female side, and the genital pore lay near the middle of the body. Both structures leaned toward the male side, apparently because the female half had become engorged with blood and expanded. The right side carried adanal plates, paired structures commonly seen in male ticks, while no caudal pedunculus was identified. The coxae, or leg bases, were short on the male side and bore pointed spurs on the first pair of legs. On the female side, the spurs were shorter and rounded. Spiracular plates, respiratory structures located laterally, occurred on both sides. The head region itself did not show the same division as the body: its small, hexagonal basis capituli had female-like features, with palps shorter than the hypostome, the piercing structure used during feeding.

The observation is important partly because R. microplus is not an incidental species. Cattle ticks feed on bovines and can weaken animals through blood loss and irritation, while also participating in the transmission of infectious agents. Heavy infestations can reduce growth, milk production and overall condition, and tick control is a continuing challenge for livestock producers. Yet the researchers emphasize that the presence of gynandromorphism does not automatically imply a new disease threat or a change in the species’ biology. The malformed tick was attached to a cow and had begun to feed, supporting earlier observations that at least some gynandromorphs can locate hosts and obtain a blood meal. Whether this individual could complete digestion, molt, mate or lay viable eggs remains unknown.

Previous examples show why those questions matter. Gynandromorphism has been reported in several hard-tick genera, including Amblyomma, Hyalomma and Ixodes, but records in Rhipicephalus are comparatively scarce. Earlier cases of R. microplus, formerly placed in the genus Boophilus, were described in Australia and India. One Australian specimen had female characteristics on its left side and male features on its right, but its posterior region was predominantly male rather than being cleanly divided. The Indian example carried a normal scutum together with a partial male-like conscutum positioned toward the side of the body, while its genital pore retained female characteristics. The Salvadoran tick differs in showing a more conspicuous separation between male and female traits, including a division that reaches the region of the genital pore.

The rarity of these animals is difficult to measure because unusual ticks may be overlooked or never reported. In a survey of 6,624 hard ticks from Panama, researchers found 255 specimens with morphological abnormalities, but only two were gynandromorphs. Other work in Brazil has suggested that gynandromorphism may be a relatively prominent type of anomaly, illustrating how estimates can vary with sampling methods, species composition and the care taken to inspect specimens. Local defects, such as damaged or misshapen legs, may be easier to recognize than complex sexual mosaics. The Salvadoran team therefore views its specimen not as evidence of a sudden biological shift, but as a reason to expand systematic surveillance across the country and to preserve abnormal individuals for future study.

The biological consequences could extend beyond appearance. Laboratory research on other external malformations in R. microplus has linked abnormal body structures with reduced weight, impaired feeding, lower egg production and decreased fertility. Gynandromorphism could affect these same processes, particularly if male and female parts are not coordinated during engorgement or reproduction. A divided body may also influence movement, attachment or the operation of respiratory and reproductive structures. At present, however, the study provides no direct evidence that the Salvadoran specimen transmitted a pathogen, reproduced, or suffered a measurable physiological disadvantage. The authors caution that its veterinary and public-health significance remains unresolved. More specimens, genetic analyses and controlled observations would be needed to establish whether gynandromorphs can maintain themselves in tick populations or participate in disease cycles.

The discovery also demonstrates the value of close morphological work in regions where tick diversity and disease ecology remain incompletely documented. A single animal attached to livestock revealed a developmental pattern that had never been recorded in El Salvador, even though the species is widespread and relevant to animal health. The researchers say continued collection across the country could clarify how often abnormalities occur, whether they are concentrated in particular species or environments, and whether they correlate with reproductive or epidemiological traits. For now, the half-male, half-female cattle tick is best understood as a rare natural experiment: a visible consequence of development unfolding along two sexual pathways within one tiny parasite.