Mitochondrial genome sequencing of marine leukemias reveals cancer contagion between clam species in the Seas of Southern Europe

ABSTRACTClonally transmissible cancers are tumour lineages that are transmitted between individuals via the transfer of living cancer cells. In marine bivalves, leukemia-like transmissible cancers, called hemic neoplasia, have demonstrated the ability to infect individuals from different species. We performed whole-genome sequencing in eight warty venus clams that were diagnosed with hemic neoplasia, from two sampling points located more than 1,000 nautical miles away in the Atlantic Ocean and the Mediterranean Sea Coasts of Spain. Mitochondrial genome sequencing analysis in tumour tissues from neoplastic animals revealed the coexistence of haplotypes from two different clam species. Phylogenies estimated from mitochondrial and nuclear markers confirmed this leukemia originated in striped venus clams and later transmitted to clams of the species warty venus, in which it survives as a contagious cancer. The analysis of mitochondrial and nuclear gene sequences supports all studied tumours belong to a single neoplastic lineage that spreads in the Seas of Southern Europe.

Characterization of Varroa destructor Mites in Cuba Using Mitochondrial and Nuclear Markers

Varroa destructor has been present in Cuba since 1996, but without the use of acaricidal infestation rates remain at very low levels. The presence of Korean haplotype mites was described in 2007, but there is no information regarding the introgression of the less virulent Japanese haplotype that could account for a low pathogenicity of the mite. In this research, we carried out molecular characterization of Cuban Varroa mites through mitochondrial DNA and hypervariable nuclear loci. We applied an alternative RFLP technique and found that all the analyzed samples corresponded to Korean haplotypes. We analyzed the three STRs loci VD112, VD114 and VD016, previously described as highly variable and found new alleles in all of them, with an absolute allele size very different to those reported worldwide. We also detected genic and genotypic differentiation between samples from two nearby locations (P=0.08). We also tested a new RFLP method for mite haplotype discrimination with an intra-reaction positive control of digestion.

Ancient divergence, a crisis of salt and another of ice shaped the evolution of the west Mediterranean butterfly Euchloe tagis

The Mediterranean region is an extremely complex hotspot where, since the Miocene, extensive geological, habitat and climate changes have taken place, alternating between warm and cold periods. These phenomena have taken a toll on the genetic composition of species, and surviving lineages have often adapted locally and diverged to the point of (complete) speciation. To study these phenomena, in this study we used one of the most enigmatic butterflies, the Portuguese dappled white, Euchloe tagis, a west Mediterranean endemic with fragmented, morphologically differentiated populations whose status have long been disputed. Even its affiliations with other Anthocharidini are largely unresolved. We used mitochondrial and nuclear markers under a phylogenetic and phylogeographical framework to evaluate its placement among relatives and population differentiation, reconstructing its evolutionary history. We found that this species had a Miocene origin ~15 Mya and was nearest to Euchloe s.s. and Elphinstonia. Its populations showed high genetic diversity but all coalesced to 5.3 Mya, when European and all but one African population diverged. Our multiple findings concerning the evolution of E. tagis through a changing, narrow habitable area might provide a more general perspective on how species survive within this hotspot of paramount importance.

Introgressive hybridization between the endangered native Bombina pachypus and the introduced B. variegata in a protected area in central Italy

Amphibians are experiencing an ascertained global decline, which causes include the introduction of alien species and the (anthropogenic) hybridization between native and exotic taxa. Detecting introductions and assessing their impact on populations of native species is crucial for amphibian conservation. We used mitochondrial and nuclear markers to reveal introgressive hybridization between the native Bombina pachypus and the exotic B. variegata (probably introduced from Albania) in a population from a protected area of central Italy. Almost all genotyped individuals were genetically admixed, showing a larger proportion of the allochthonous genome. To our knowledge, this study provides the first evidence of successful hybridization between the two species (we found both putative F1 and backcrosses), hence representing a new threat to the conservation of the endangered, Italian-endemic B. pachypus.

Biogeography and Cophylogeny of Paussus favieri(Carabidae, Paussinae) and Pheidole pallidula(Hymenoptera, Myrmicinae)

The myrmecophilous carabid beetle, Paussus favieri, has a circum-Mediterranean distribution and it is completely dependent upon its host ant Pheidole pallidula during all stages of its life history. Using molecular sequence data we inferred the phylogenies of the populations of both the beetle and its ant host to determine if there are signs of co-evolution. A total of 34 P. favieri from France, Spain, Portugal, Morocco and Tunisia and 42 Ph. pallidula workers from the same countries, plus Greece and Italy, were collected and analyzed. Many mitochondrial and nuclear markers were sequenced, but only COI was evolving fast enough to infer the population-level phylogenies of the beetles and the ants. Preliminary analyses suggest that the European populations of P. favieri are derived from a single dispersal event from Africa, while several dispersal events are suggested for Ph. pallidula. We found the topologies of host and parasite trees to be generally congruent, as would be expected if the host and parasite have had a history of co-evolution or co-divergence.