Aphally and imposex in Nucella lapillus from Galicia (NW Spain):incidence, geographical distribution and consequences for the biomonitoring of TBT contamination

Abstract

Males of Nucella lapillus (L.), an intertidal gastropod, can suffer from a curious genetic disorder that causes underdevelopment of the reproductive tract ['Dumpton Syndrome' [DS]). Its extreme form leads to a lack of a penis ('aphally') and an incompletely developed vas deferens (VD). DS-affected females are also recognisable by a lesser degree of masculinisation ('imposex') when exposed to tributyltin (TBT) pollution, i.e. penis development may be lacking (female 'aphally') and VD formation may be iveak. Based on the results of an extensive survey [at 56 stations) around GaLicia (NW Spain) from 1996 to 1998, it is now known that imposex is widespread and the variations shown in its development indicate that DS also occurs widely. A modified version of the Vas Deferens Sequence (VDS) schemes currently devoted to assess the intensity of masculinization of female N. lapillus is proposed. It attempts to accommodate the vanants in imposex development observed in a DS-affected population whilst remaining both simple and comparable with previously applied schemes. The proposed VDS classification solely employs VD development as a rankmg criterion so as to attain a consistent scoring of both aphallic and penis-bearing females. Irnportantly. the evidence indicates aphally need not preclude a female from being sterilized. Both males and females afflicted by DS were scattered throughout the Gaiician region, although aphaliic females were present at many sites at which DS males went unrecorded. Also, female aphally was commonly more frequent than male aphally on a per site basis. DS-affected males were very unconunon, never exceeding -20% and more frequently constituted ~10%. In contrast, aphallic females were common, reaching frequencies of 20 to 50% at some sites, although overall it also must be considered a low-frequency phenomenon. Imposex levels. overwhelmingly dominated by VDS Stage 4 , showed that TBT pollution is widespread throughout the region. However. a high degree of inter-individual variability was found at many locations. At those sites, females showing no signs of irnposex or only an early stage (i.e. VDS Stages 0 to 2) were found thriving alongside heavily afflicted individuals (VDS Stages 4 to 6). The significant association between this variability in the effects of imposex and the presence of DS strongly reinforces the interpretation of DS as a genetic disorder which lessens the effects of TBT The consequences those TBT-resistant specimens might have for the impact of TBT on the population level are discussed as well as the impact their presence might pose for the assessment of TBT pollution and its effects based on irnposex indices currently in use.

Generalized system of imposex and reproductive failure in female gastropods of coastal waters of mainland China

“…Nevertheless, Path b in the generalized scheme could still be modified to suit DS in N. lapillus without regard to a penis in Stages 5 and 6 temporarily. On the contrary, it is biased to negate the typical scheme only because it cannot fit a specific species (Barreiro et al 1999). In all, the generalized scheme was valid for all the main morphological expressions of imposex found at present (Fig.…”

“…(2) What are the criteria for proposing a scheme? Barreiro et al (1999) thought the adoption of only 1 criterion to be most reasonable. One criterion based upon vas deferens development might be valid for DS in Nucella lapillus, but not for general use even in this species.…”

“…Up to date, different criteria-dependent schemes have been proposed for the description of imposex (Axiak et al 1995, Barreiro et al 1999, Mensink et al 2002. To make a scheme more applicable for general use, 2 questions should first be clarified: (1) What is the purpose of scheme?…”

“…In the typical scheme, a penis is regarded as a conspicuous masculine character and the complete penis will be formed at least in Stage 4. However, sterility may occur in females of N. lapillus without formation of a penis (Huet et al 1996, Barreiro et al 1999.…”

“…To make the identification easy, several schemes are proposed for specific species, based on different criteria (Axiak et al 1995, Barreiro et al 1999, Mensink et al 2002. For example, Barreiro et al (1999) proposed a specific scheme for DS in Nucella lapillus solely based on vas deferens development instead of vas deferens and penis development in the typical scheme.…”