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16 NEWS maltatoday | SUNDAY • 14 JANUARY 2024 Gozo's alien frogs came from Turkey, genetic research shows ALIEN frogs from three fresh water locations in Gozo trace their origins to southern Anato- lia in Turkey, researchers have discovered in the wake of genet- ic tests. The study focussed on water frogs of the genus Pelophylax that is not native to Malta and was first noted in Gozo at the turn of the millennium. Researchers genetically exam- ined 17 frogs from three sepa- rate populations found in the Gozitan localities of Mġarr ix- Xini, Għajn il-Papri and Ramla Valley. The tests showed the three dis- tinct frog communities had low genetic variability that suggests they came from only one source population. Given that the three areas have no interconnecting water courses and the alien wa- ter frogs are unable to cross ar- id land, researchers believe the alien species was introduced by humans in the three localities. Genetic markers also suggest the frogs are similar to those found in southern Anatolia in Turkey, Cyprus and the Aegean Greek island of Ikaria. However, Ikaria was ruled out as a source population since genetic se- quencing of frogs on the Greek island revealed certain differenc- es from the Maltese samples. The Maltese frogs are geneti- cally similar to those in Cyprus and Turkey with researchers noting the possibility that the Cypriot frogs were also intro- duced to the island unintention- ally by humans. The study was carried out by Petr Papežík and Peter Mikulíček from the Department of Zoolo- gy at the Comenius University in Bratislava, Slovakia, Michal Benovics from the Masaryk Uni- versity in Brno, Czechia, Alan Deidun from the University of Malta and renowned pest con- troller Arnold Sciberras and Jef- frey Sciberras. The findings were present- ed in a paper titled 'Far From Home: Tracing The Origin Of Non-native Water Frogs (genus Pelophylax) In Malta By Molec- ular Markers', published in the January issue of Biological Inva- sions, a peer-reviewed journal by Springer. The researchers said that ac- cording to published data, water frogs were introduced to Ta' Sar- raflu in Gozo in the early 1990s and first recorded in April 2000. "The exact mode of their intro- duction, as well as the individual abundance within the same pop- ulations and their survival strat- egies remained unclear at the time. However, several possible hypotheses were proposed, in- cluding the introduction by local farmers or through deliberate releases from purchases made at Maltese street markets," the pa- per reads. No official importation data for Pelophylax species to the Mal- tese islands could be retrieved from archives held by Maltese environmental authorities. However, researchers said there are anecdotal reports from farm- ers based within the Ta' Sarraflu area in Gozo suggesting a delib- erate introduction of tadpoles of the species imported from Tur- key. "If confirmed, this deliberate introduction is similar to the one observed for a number of non-indigenous crustaceans (such as crayfish) within fresh- water sites around the Maltese islands," the paper says. Sampling and localities The 17 frogs were collected in the summer and autumn of 2022 and a toe clip was collected from each individual for genetic anal- ysis. Tissue samples were pre- served in ethanol and stored at -25°C. Genomic DNA was extract- ed from the toe clips and mito- chondrial and nuclear markers were used to find out the origins of the Gozitan water frogs. Mġarr ix-Xini is a gorge lo- cated along the south-western coast of Gozo. Although it does not feature a permanent water- course, its steep flanking rocky walls provide substantial shade and shelter leaving small bodies of freshwater and mud through- out most of the year along the valley floor. Għajn il-Papri is a sizeable freshwater pond excavated in clay in the 1990s as a water res- ervoir, along the southern coast of Gozo. The pond is also a haunt for the indigenous painted frog. Ramla Valley runs from the vil- lage of Nadur to the sand dune remnants at Ramla l-Ħamra, along the north coast of Gozo. During the rainy season, the watercourse within the valley reaches the sea by meandering through sand dunes and the beach. KURT SANSONE ksansone@mediatoday.com.mt A toe clip was collected from each individual frog for genetic analysis Above: The localities in Gozo where the frog samples were taken: A. Mgarr ix-Xini; B. Ghajn il-Papri; C. Ramla Valley (Photos: Arnold Sciberras) Right: Map of Gozo showing the location of the three areas from where non-native frogs were collected: 1. Mgarr ix-Xini; 2. Ghajn il-Papri; 3. Ramla Valley