The taxonomy of some British Littorina species, with notes on their reproduction (Mollusca: Prosobranchia)

Abstract

The rough periwinkle Littortnu scrxutilis is considered, in current literature. to consist of various sympatric "subspecies" and "varieties". These, it has been suggested, are incipient species and are evidence for sympatric speciation.This paper shows that in Wales the "saxatilis" aggregate consists of four separate. fully sympatric species: L. rudis. putufu, nigrolineuru and neglecta. Differences between these species include proportions, sculpture and size of the shell, range of colour patterns. the anatomy of the genitalia, and isozyme patterns. The possible evidence for incipient species is discussed and rejected.The diversity of penis form amongst the British winkles is remarkable, and it is suggested that in these sympatric species the structure of the penis could be of importance in species recognition.The four species occupy different zones on the shore and three certainly differ also in their methods of reproduction: L. rudir is ovoviviparous and contains embryos throughout the year, purulu is ovoviviparous but contains embryos only in winter, nigrolineuzu is oviparous. The reproduction and dispersal methods of all British winkles are reviewed. The evidence available supports the view that non-planktonic dispersal is an adaptation which, in species whose shell colour varies considerably from one locality to another, enables each population to become adapted to its local environmental. conditions. Ovoviviparity occurs in high3hore non-planktonic species, and may be an adaptation to avoid the dangers of egg desiccation.Planktonic dispersal is found in species whose shell d o u r docs not vary as much as in non-planktonic ones. In these species, it is argued that a common planktonic pool enables a rapid re-colonization in the case of local decrease in population numbers, and also the rapid dispersal of successful mutations.

A GTT microsatellite repeat motif and differentiation between morphological forms of Littorina saxatilis: speciation in progress?

“…These have sometimes been regarded as separate species, e.g. Maton (1797) described the thick shelled animals as L. rudis, and whilst a variety of synonyms have been attributed to the higher shore form (see Reid 1996), L. patula has been widely used (see Heller 1975). However, later work, particularly on shell, radula and penis morphology, led to Raffaelli (1979) concluding that these represent morphological variants of L. saxatilis, and this has become the accepted opinion (Reid 1996).…”

Littorina neglecta Bean, a morphological form within the variable species Littorina saxatilis (Olivi)?

“…This taxon is a member of the L. saxatilis species complex, and it has been separated as a distinct species mainly on shell morphology, e.g. shell form, size at maturity, shell ornamentation and colour pattern, and the morphology of the penis (Heller, 1975;Fish & Sharp, 1985).…”

“…Hannaford Ellis (1984) states that it is hard to recognize those individuals of L. neglecta, which do not have the shell colour pattern usually typical of the species (a dark band running into the aperture). She also states that the penis characteristics used by Heller (1975), are invalid for distinguishing between L. neglecta and L. rudis, (= L. saxatilis see Janson, 1985), at least outside Anglesey.…”

“…As no character has so far been reported which is diagnostic of L. neglecta, our study is based on a comparison of samples from the barnacle zone (mid-shore) and the littoral fringe (high-shore), and we assume, following earlier descriptions of the ecology of the species (e.g. Heller, 1975;Hannaford Ellis, 1980;Fish & Sharp, 1985) that, if present, L. neglecta will be more or less confined to the barnacle zone, while L. saxatilis sensu stricto will dominate in the littoral fringe.…”

“…For example, some authors describe L. neglecta as having a short blunt spire (Hannaford Ellis, 1980;Fretter & Graham, 1980), while James (1968) describes the subspecies L. saxatilis neglecta as having 'a tall to very tall spire'. L. neglecta is generally said to have a smooth shell (James, 1968;Raffaelli, 1982;Hannaford Ellis, 1980;Fish & Sharp, 1985), but Heller (1975) states that the shell may range from smooth to heavily ridged. The characters which seem to be the most generally accepted as those of L. neglecta (see e.g.…”