COEXISTENCE AND HYBRIDISATION OF DIFFERENT SPECIES AND LINEAGES OF HETEROCYPRIS (CRUSTACEA, OSTRACODA) ON LAMPEDUSA ISLAND (ITALY)

We analysed the genetic structure of three populations of Heterocypris from temporary ponds on the island of Lampedusa (Italy) where both unisexual (all females) and bisexual populations were found. Population from Cavallo Bianco is made up of females only with typical morphological feature of H. incongruens. In the bisexual population from Aria Rossa adult females present a lobe-like expansion (lamella hyalina) on the posterior margin of the left valve. This is a typical morphological feature of H. barbara. In bisexual population from Vallone della Forbice both female morphotypes are syntopic. Isoenzymatic analysis shows that adult females without lamella hyalina are apomictic, whereas females with this feature are amphimictic.To evaluate the taxonomic status and the phylogenetic relationships in Heterocypris complex from Lampedusa, we used sequences of the mtDNA 16 S ribosomal subunit and sequences of the Elongation factor-1 nuclear gene. In addition, karyotype analysis was performed with Giemsa, fluorocromes and C-banding. For comparison, we analysed a clonal lineage from a parthenogenetic population from a northern Italian rice-field, individuals from a Spanish amphimictic population of H. incongruens (temporary pond of Laguna Espolla) and individuals from a Spanish bisexual population of H. barbara.Heterocypris populations from Lampedusa can be grouped into two main groups: a cluster including parthenogenetic females without lamella from Cavallo Bianco (20 chromosomes two of which unpaired), the parthenogenetic lineage of H. incongruens from northern Italy and H. incongruens from bisexual population from Spain (female 2n = 10A+10X; male 2n = 10A+5X). A second cluster including amphimictic females with lamella from Aria Rossa (female 2n = 10A+10X; male 2n = 10A+5X), parthenogenetic females without lamella and amphimictic females with lamella from Vallone della Forbice and H. barbara bisexual population from Spain. This result confirms that two species of Heterocypris coexist on Lampedusa Island: H. incongruens and H. barbara. Heterocypris incongruens parthenogenetic females from Cavallo Bianco show the typical morphological feature of the species. Within the H. barbara group, two female lineages are distinguishable according to their morphotypes and reproductive modes: amphimictic females with lamella and parthenogenetic females without lamella. These lineages are syntopic in Vallone della Forbice.Our data support the hypothesis of inter-specific hybridisation between coexisting syngamic and clonal lineages of Heterocypris. The close taxonomic association of asexual and sexual females within H. barbara cluster imply a recent origin for asexual lineages.