Wednesday, November 26, 2014

Weevil diet

The weevil  species Centricnemus leucogrammus lives predominantly in European dry-hot (xerothermic) habitats and steppes. The species was probably more widespread during the Pleistocene glaciations, while its current distribution is limited to what some call 'warm-stage refugia.' Their habitats in central and eastern
Europe sustain very high biodiversity of plants and insects. Unfortunately, these analogs of the Eurasian steppes are seriously threatened as a result of their already patchy distribution combined with human induced transformation and degradation.

Our little friend, the weevil, is a polyphagous insect that over the past years has been used as a model species understand the phylogeography and conservation genetics of xerothermic beetle species. Earlier research showed that weevil populations cluster into geographically separated clades. A Polish colleague was interested if such genetically and geographically distinct units are also ecologically separated. Not much is known about the composition of the beetle's diet and data collection by direct observation is severely limited. The colleague decided to used DNA Barcoding to overcomes these limitations:

The objective was to compare standard ABI Sanger sequencing with new high throughput sequencing (Illumina MiSeq) technique and the two selected plant barcodes (rbcL gene and trnL intron) in terms of the identification of host plant composition for the selected beetle species.

Not surprisingly the next generation sequencing (in this case Illumina) provided more exhaustive results than the Sanger method. The latter identified about 30% less genera present in the diet of Centricnemus leucogrammus. Moreover, the study shows that the two-locus approach (rbcL and trnL) provided good results useful for host plant identification, at least at the genus level. I am a little hesitant to call this a barcoding approach (as the author does) because only one marker is actually an agreed upon standard locus. It would be interesting to find out how matK does, or even ITS which has been proposed as third plant barcode by a number of researchers.

Direct observations either in the field or in laboratory trials identified 9 genera the beetles feed on. This study identified 30 plant taxa as host plants for our weevil, 25 of which have xerothermic representatives in central and eastern Europe. Other plants are either frequent on xerothermic turfs or similar habitats, ruderal or simply widespread. A comparison of host plant composition among distant populations also revealed that the species did not feed uniformly across its range which indicates some ecological adaptation within these distinct populations.

These findings, beside broadening basic knowledge on the use of barcoding and sequencing techniques for host plant identifications in insect populations, can have implications for conservation studies and strategies for rare and endangered species. Precise identification of feeding preferences and behavior could be very important for planning conservation and management of populations and habitats. Without detailed data about host plants, it would be impossible to efficiently protect some herbivorous species and whole insect assemblages. This should be especially important for habitats sustaining very rich flora and fauna, such as the xerothermic habitats of central and eastern Europe.

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