The objectives of this project is to: 1) collect and rear fruit flies from different species of Lebanese thistles (Asteraceae: Carduae) and identify new fruit fly-thistle associations; 2) determine the phylogeny of the non-frugivorous tephritids associated with thistles in Lebanon; 3) determine whether specialist tephritids evolved from generalist species.
ألانجازات المحققة Achievements -
Fifty one fruit fly-thistle associations were collected during the duration of the project, of which 15 associations are new to Lebanon. All the associations new to Lebanon will be published in a manuscript currently in preparation.
The method for extracting DNA from flies, amplifying three mitochondrial genes using PCR, and sequencing the amplified genes was optimized. At least two flies representing each collected association were sequenced.
A preliminary phylogenetic tree for all the collected associations was generated. As some associations previously reported in the literature were not collected yet (The thistles were collected but no flies emerged.), the phylogeny will be completed upon future collection seasons. The evolution of specialization will be tested when a comprehensive phylogeny is generated.
A major problem encountered during the study was that the weather in 2010 and more so in 2011 was rather unpredictable. Many of the thistles we were interested in collecting bloomed earlier than expected and their flowering period lasted shorter than usual. This shift in flowering phenology of the host thistles yielded a shift in emergence time of many of the fruit flies we were interested in collecting. We consequently missed the chance of collecting several fly-thistle associations.
Two achievements are worth noting:
1. We have previously published on host race formation in the generalist Chaetostomella cylindrica (Partially funded by LNCSR; Colin Smith, PI). In this study, we sequenced flies emerging from almost all plant hosts of this species. We have previously focused on two common hosts. The results of this study confirm our previous hypothesis that the Onopordum associated flies are distinct from the rest of the host populations, suggesting they might be a distinct cryptic species. These results will be published in a separate paper.
2. We analyzed all host associations of two other generalists, Terellia serratulae and Acanthiophilus helianthi.
a. In the case of T. serratulae, one host seems to be very distinct from the other host races. The paper has been recently submitted and is under review. However, the relationship among the other host races needs further investigation.
b. As for A. helianthi, our preliminary results confirm that it behaves as a typical generalist. It would however be difficult to understand host race formation in this species without further ecological and genetic studies.
آفاق البحث Perspectives -
In addition to finalizing the phylogeny of Lebanese flower head infesting tephritids, we plan to address several research questions, which arose from this study:
Resouce utilization in Terellia serratulae: This is important to resolve the observed intraspecific variations among the different populations.
Biology and ecology of the generalist tephritid Acanthiophilus helianthi: This is important to explain the observed size variation among the collected specimens associated with different hosts, but not genetically distinct.
Knio, K., M. S. Al-Zein, N. Sayar, S. Haddad and C. Smith. 2010. Host race formation in flower-head infesting tephritids in Lebanon. 14th Evolutionary Biology Meeting, University of EGEE, Marseilles, France. 21-24 September, 2010.
Knio, K., M. S. Al-Zein, N. Sayar, S. Haddad and C. Smith. 2012. Flower-head infesting tephritids in Lebanon: specialization and host race formation. University of Balamand. 17 January 2012
Haddad, S. G., Smith, C. S., Knio, K. M. 2012. Genetic and morphometric variation as evidence for host race formation in Terellia serratulae (Diptera: Tephritidae). Manuscript under review.
During 2010-2012, 25 species of thistles were collected from various sites in Lebanon. Fifty one fruit fly-thistle associations were found, 15 of which were recorded to occur for the first time in Lebanon. Methods for extracting DNA from the collected flies, amplifying three mitochondrial genes using PCR, and sequencing the amplified genes were developed and optimized. These yielded a preliminary phylogenetic tree for all the collected associations. The study revealed important finding on three generalist species of tephritids.
The polyphagous fruit fly, Terellia serratulae, which exploits hosts belonging to three genera of thistles (Carduus, Cirsium, and Picnomon), revealed significant morphometric and genetic variations among the different host populations. The most useful predictors in distinguishing adults associated with the different host plants were wing width and head length, in addition to ovipositor length for females. Mitochondrial DNA sequencing revealed genetic differentiation among the different populations of T. serratulae with the Picnomon acarna- associated population being most distinct. Sequencing a region of the mtND1 gene revealed 19 single nucleotide polymorphisms (SNPs) and 9 haplotypes, whereas sequencing a region of the mtCOXI gene revealed 24 SNPs and 7 haplotypes. Surprisingly, haplotype sequences of flies emerging from P. acarna showed a sequence divergence of over 3% for both COXI and ND1 genes. Therefore, the Lebanese T. serratulaepopulation associated with P. acarna most likely constitutes a distinct host race.
Another generalist species, Chaetostomella cylindrica, showed genetic variations among the different host associated populations. The Onopordum-associated population could be distinguished genetically and morphometrically from the rest of the host associations. This suggests that the Onopordum associated population might be a new cryptic species.
Preliminary results on a third generalist species, Acanthiophilus helianthi, revealed little genetic divergence between the different host plant associations, and seems to behave as a true generalist having many generations per year and high flexibility for host exploitation.
Future studies will focus on collecting more tephritids and finding new tephritid-thistle associations and shedding more light on host formation in the Lebanese fruit flies.