hrvatski

Utjecaj vremenskog razdoblja i prostornog širenja na genetsku varijabilnost populacije kukuruzne zlatice (Diabrotica virgifera virgiferaLeConte, Coleoptera: Chrysomelidae)

Western corn rootworm Diabrotica virgifera virgifera LeConte are a major pest of maize in corn growing regions of Croatia and Europe. Since its first introduction to Serbia, D. v. virgifera have spread into Europe and are now present in 22 European countries spanning some tens of thousands of arable land. All the factors contributing to its spread remain unknown and research into their spread is still required. Classical population genetic and geometric morphometric analyses were used to investigate populations D. v. virgifera in Croatia, Serbia, Hungary and Italy during the introduction (1996 - 2001) and establishment/spread (2002 - 2011) phases of its invasion. From the introduction phase 12 populations (256 samples) from Croatia, one population (40 samples) from Serbia, two populations (40 samples) from Hungary and three populations (60 samples) from Italy were analysed. From the establishment/spread phase 12 populations (606 samples) from Croatia, one population (45 samples) from Serbia, one population (55 samples) from Hungary and three populations (80 samples) from Italy were analysed. Populations from the USA (a combined 150 samples from: Iowa, Arizona, Illinois and Nebraska) were used for inter-continental comparative analyses. In total, D. v. virgifera individuals were analysed 1327. The first phase of the research centred upon the use of population genetics to: (1) to estimate the population genetic structure, diversity and gene flow among D. v. virgifera populations in Croatia, Serbia, Hungary and Italy ; (2) genetically monitor D. v. virgifera populations on a microgeographic scale and to establish the most likely source of D. v. virgifera in Croatia and its neighbouring countries ; and (3) to describe the invasion genetics of D. v. virgifera over space and time. The second phase of the research centred upon the use of geometric morphometrics to: (4) determine whether wing shape dimorphism varies between D. v. virgifera populations and whether these differences are sex based ; or (5) based on specific soil types ; and to explore the influence of wing shape variation on insect dispersal capabilities and invasion dynamics. Genetic structure during the introduction phase was medium (FST=0.024), while in establishment/spread phase was low (FST=0.005). After conducting a combined data analyses comparing the introduction with the establishment/spread phases, high levels of genetic structure were found (FST=0.11-0.16). However, when investigating genetic structure within an invasion and by country the results showed low to no genetic differentiation within a country regardless of invasion phase. Therefore, populations from the introduction phase was treated as a one putative population that is persisting over a large geographic area ; the same result being true for populations sampled during the establishment/spread phase. It was found that the two putative populations found during the two different phases were also found to be genetically distinct. Of all known D. v. virgifera alleles worldwide, 83% are now found in Croatia, Serbia, Hungary and Italy. This survey revealed two unique alleles and nine previously unrecorded alleles in Europe. Serbia was identified as the geographic source of D. v. virgifera in Croatia and Hungary, while the US was the source of D. v. virgifera to Italy. Bayesian cluster analysis (Structure) identified two genetic clusters that grouped southern European D. v. virgifera populations separately from US populations. However, these clusters were not neat and numerous US individuals had both European and US ancestry, suggesting bi-directional gene flow back and forth between the two continents. Period of time (number of generations) had a greater impact on D. v. virgifera genetic variation than other factors such as geographic direction of spread, spatial distance, landscape effect and plant protection. To complement the genetic data analyses conducted, geometric morphometric analyses were further used to examine the wing shape variation present in D. v. virgifera populations. Sexual dimorphism was assessed at an intercontinental geographic scale and used to find the shape characters that best distinguish groups of individuals. It was revealed that each of the populations of D. v. virgifera examined showed high levels of sex based hind wing shape dimorphism. A stronger pattern of hind wing shape variation was found in the USA than in Europe. Results showed that female D. v. virgifera have more elongated wings than males, which provides morphological evidence that long distance migration can be attributed to the females of this species. Also, geometric morphometrics was used to examine the influence of soil type on D. v. virgifera population variation. Changes in the marker’s position at 3 and 7 resulted in elongated wing shape morphotypes in areas with a chernozemic soil type, whereas changes in the marker’s position 2, 3 and 14 resulted in narrow wing shape morphotypes in area with an alluvial soil type. Finally, changes in the marker’s position at 3, 7 and 14 resulted in mixes wing shape morphotypes in areas where gley soils and ground water are prevalent. These findings showed that D. v. virgifera hind wing shape can be used to differentiate populations based on edaphic factors. The temporal and spatial genetic and geometric morphometric analyses undertaken, allowed a deeper understanding of the population dynamics of D. v. virgifera in Croatia and southern Europe. Knowledge of a pest’s invasion history (source population) on a specific area as well as the direction of its spread is important for planning future strategies for its control. The findings presented in this thesis are congruent with others who have suggested that genotypic changes are slower to manifest in a population than phenotypic changes. Therefore, geometric morphometric analysis can be used to detect the effect that various factors (e.g. resistance, changes in climatic conditions, diet) have on D. v. virgifera before classical genetics techniques can. Nevertheless, the use of both genetic and geometric morphometric techniques is important in D. v. virgifera monitoring and management and can be effectively used to detect the possible entry into Europe of control resistant variants currently only found in the USA.

Diabrotica virgifera virgifera; invazija; populacijska genetika; proširenje; FST; mikrosateliti; genetski monitoring; geometrijska morfometrija; seksualni dimorfizam; analiza oblika krila

nije evidentirano