Abstract
Geographical isolation, selection and genetic drift can cause the geographical diversification of populations and lead to speciation. Land snail species in the genus Trochulus show overlaps in geographical ranges as well as in morphology, but genetic data do not always support the species-level taxonomy based on morphological characters. Such a group offers an excellent opportunity to explore the processes involved. We have addressed the problem by determining the status of the restricted endemic T. graminicola within the larger context of Trochulus taxonomy. We used an integrated approach based on morphological features, ecological preferences and two molecular markers: mitochondrial COI sequences and microsatellites. Comparison of these results demonstrated: (i) conchological distinction of T. striolatus and T. sericeus; (ii) anatomical, ecological and genetic differentiation of T. graminicola and (iii) concordance between morphological characters and mtDNA markers in T. striolatus. Moreover, our data showed an intricate evolutionary history within the genus Trochulus, which can be best explained by: (i) recent or ongoing gene flow between taxa or (ii) their large ancestral polymorphism. Both of these hypotheses suggest that diversification within this group of snails has occurred relatively recently. The mismatches between species defined on morphology and on molecular genetics indicate the complexity of the processes involved in the diversification of this genus.
Highlights
Determining the causes of difficulties in delimiting species in many taxa has proved hard
The first of these two species demonstrated a moderate overlap of variation ranges with T. sericeus and T. graminicola, while T. coelomphala formed an overlapping subset with T. graminicola
umbilicus diameter (U/D) may be a discriminant character for T. graminicola compared to T. striolatus, T. hispidus and T. sericeus because the differences were statistically significant (Kruskal–Wallis test: p < 0.05)
Summary
Determining the causes of difficulties in delimiting species in many taxa has proved hard. To explain the speciation process, different evolutionary mechanisms have been proposed such as: rapid and recent phylogenetic divergence, introgression, high phenotypic plasticity, ongoing differentiation of varieties and partial barriers to gene flow between ecotypes [1]. The uncertainty and controversy about species recognition are mostly related to four different. Ongoing Speciation and Gene Flow in Trochulus Species Complex
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