Two groups of morphologically and phylogenetically
closely related species of Littorina marine mollusks, the
‘obtusata’ (L. obtusata, L. fabalis) and the ‘saxatilis’ (L.
saxatilis, L. arcana, L. compressa) inhabit sympatrically
the intertidal zone of the North Atlantic. These
species are characterized by similar breeding season
and reproductive behavior, thus, the existence of
mechanisms preventing interspecific breeding and
supporting reproductive isolation might be expected.
The characteristics of a mucus trail made by a snail
during locomotion were suggested as a key cue for
a mate choice. Mucus trail chemical compositions
were analyzed for males and females of each of five
sister species and L. littorea as an outgroup using
liquid chromatography-mass spectrometry (LC-MS).
Collected from wild populations snails were placed
individually into Petri dishes and left to creep.
Mucus was collected and LC-MS-analyzed. Jaccard’s
dissimilarities coefficients based on presence-absence
data were used for samples clustering. Considerable
variation in mucus composition was revealed among
individuals of either different or the same species.
Only five compounds among 108 used for analysis
were common to all examined samples. Two of them
proved to be halogenated alkaloids of yet unknown
structure. We failed to find any differences between
mucus compositions of conspecific males, females
and immature or infected individuals in all five
species of the “obtusata” and “saxatilis” groups,
but such differences were revealed for L. littorea.
Comparative interspecies analysis showed that L.
saxatilis / L. arcana pair and L. obtusata formed the
separate sister-clusters, while L. compressa, L. fabalis
and L. littorea – a mixed cluster, outer to three species
mentioned above. Obtained results are compatible
with the hypothesis of a mucus trail as a species-
specific cue for a mate choice. This could represent
the molecular background for possible mechanisms
of prezygotic reproductive isolation in Littorina
sympatric populations. However, obtained data
of mucus chemical composition cannot explain the
copulative preference to females as mates, observed
in nature (224 copulative pairs collected from wild
populations were evaluated for conspecific mating).
This work was supported by RFBR grant 15-04-
08210 and the Research Center “Molecular and Cell
Technologies” of St. Petersburg State University.