Aging and retinoid X receptor agonists on masculinization of female Pomacea canaliculata, with a critical appraisal of imposex evaluation in the Ampullariidae

Ampullariidae are unique among gastropods in that females normally show a primordium of the copulatory apparatus (CApp). The aims of this study were (a) to quantitatively evaluate the development and growth of the female CApp with age; (b) to compare the effects of RXR and PPARy agonists in adult females of known age and (c) to explore the effect of masculinizing RXR agonists on the expression of RXR in the CApp. It was found that the CApp grows and develops with age. A significant increase in penile sheath length (PsL) and also in a developmental index (DI) was observed in 7-8 months old females, as compared with 4-5 months old ones. A reported endogenous agonist of RXR, 9-cis retinoic acid (9cis-RA), as well as two organotin compounds, tributyltin (TBT) and triphenyltin (TPT) which have been also reported to bind to RXR, were injected and its masculinizing effects were measured. Also, the effect of a PPARy agonist, rosiglitazone, was studied. All studied RXR agonists, but not the PPAR gamma agonist, were effective in increasing PsL, penile length (PL) and DI. Finally, the expression of the RXR in the CApp was studied (Western blot) in control, TBT, TPT, and 9cis-RA treated females. A significantly increased expression of RXR was only observed after 9cis-RA treatment. It is concluded that (a) development and growth of the CApp is significantly affected by female age; (b) reported RXR agonists, but not a PPARy agonist, cause female masculinization of young females. An appraisal of previous studies of female masculinization in the Ampullariidae has also been made and it is emphasized that the masculinizing effect of aging should be considered, particularly when interpreting field data.