Teratological anomalies of an adult Asiatic blue tick, Rhipicephalus microplus (Acari: Ixodidae)

Teratological anomalies occur at low frequencies in ticks. However, this phenomenon has been reported for several species of the genera Argas, Ornithodoros, Amblyomma, Dermacentor, Ixodes, Haemaphysalis, Hyalomma and Rhipicephalus (Campana-Rouget 1959a; Oliver & Delfin 1967; Siuda 1981; Labruna et al. 2002; Dergousoff & Chilton 2007; Prusinski et al. 2015; Keskin et al. 2016; Ren et al. 2016; Keskin et al. 2018). According to the most widely accepted classification system (Campana-Rouget 1959a, b), teratological changes in ticks divide into two major categories: 1) general anomalies (e.g., gynandromorphs, double monstrosities, asymmetries, gigantism and dwarfism); and 2) local anomalies. Gynandromorphisum, i.e., the presence of both male and female genotypical and phenotypical characters in adult ticks, represents the most reported teratology associated with ticks (to date over 60 natural cases; Guglielmone et al. 1999; Labruna et al. 2000; 2002; Salceda-Sánchez et al. 2020). In ticks, gynandromorphisum believed to be resulted from elimination of maternal sex chromosomes during early embryonic development (Oliver & Delfin 1967; Homsher & Yunker 1981). There are other less conclusive modes such as double fertilization, somatic crossing-over between chromosomes, partial fertilization and sex chromosome nondisjunction might have contributed to the gynandromorphisum in ticks (Oliver & Delfin 1967; Chitimia-Dobler & Pfeffer 2017). Further, Campana-Rouget (1959a) grouped morphological deformities in mouth parts, stigmas, festoons, eyes and appendages as local anomalies in ixodid ticks. In a later classification, however, Campana-Rouget (1959b) further separated appendages abnormalities as schizomélies i.e., division of the appendages/segments and meiomélies. Meomélies, defects in appendages, include symmélies (fusion of appendages), atrophies (appendages reduce in size), and ectromélies (absence of one or more legs). Such anomalies are likely caused by somatic or germinal mutations, exposure to toxic chemicals, mechanical damage, stress caused by adverse environmental conditions and feeding on a resistant host (Latif et al. 1988; Buczek 2000; Estrada-Pena 2001; Buczek et al. 2019). Local morphological anomalies can impair tick’s off-host survival, host seeking activities and successful completion of a blood meal. Further, some studies have shown that local anomalies can affect the overall body symmetry (Balinandi et al. 2018; Domínguez & Bermúdez 2020). Despite the numerous reports on teratological deformities in ticks their possible causes and ecological implications are still not clear for arthropodologists. The aim of this study was to report morphological abnormality found in economically important Rhipicephalus microplus collected from north central province of Sri Lanka. The abnormal specimen described here was recognized during a cross sectional island-wide collection of ticks infesting goats (Capra aegagrus hircus) carried out in Dry, Intermediate and Wet Zones of Sri Lanka (Diyes & Rajakaruna 2015). In total 2,628 ticks belongs to Haemaphysalis bispinosa (n=1,151), H. intermedia (n=1,157), H. cuspidata (n=4), Rhipicephalus sanguineus