My last blog post takes us on a journey to Northern Europe (how exciting!). The taxon of interest this time is the alpine leaf beetle Oreina elongata (Coleoptera: Chrysomelidae). Most phylogeography with regards to short term evolutionary timescales consists of making inferences, based on the Quaternary climate cycles (starting 2.6 mya). Most phylogeographic study is also usually on taxa that are distributed in lowland habitats, which are isolated into refugia (areas of habitat maintained/ not changed or covered in ice). during glacial periods. In Europe these refugia were located in southern Europe, in areas like the Italian, Iberian and Balkan Peninsulas. However this beetle taxa O.elongata is found in high altitudes, and has had its range contracted post last glacial maximum. It is of interest as to weather it expanded its range during glacial periods, and gene flow occurred keeping the taxa similar morphologically and genetically. O.elongata has many isolated populations found on the Alps and Apennines at altitudes of 1200–2500 m above sea level (See Fig 1 below).
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| Map showing isolated populations on O.elongata in the Alps and Apennines mountain ranges in southern Europe |
Figure 2. Two colour morphs of the alpine leaf beetle Oriena elongata (It's third morph is a composite green/ blue colour)
These were the main questions that this paper was trying to answer, using molecular analysis. Males were analysed molecularly as the described sub-species could be identified by the genitalia. For technical aspects about the Molecular analysis refer to the Methods and Results section of this article.
1. Did O. elongata, as a representative of the high altitude fauna, survive the cold periods of the Quaternary in situ in the Alps and Apennines?
In order to infer the timescale over which differentiation is likely to have arisen, we make use of an approximate molecular dating method based on a review of published gene-specific mtDNA substitution rates to answer a further question:
2. Was divergence within O. elongata a product of the last glacial cycle or is the differentiation more ancient?
In order to infer the timescale over which differentiation is likely to have arisen, we make use of an approximate molecular dating method based on a review of published gene-specific mtDNA substitution rates to answer a further question:
2. Was divergence within O. elongata a product of the last glacial cycle or is the differentiation more ancient?
The CO1 gene region is commonly used to express polymorphism within genera and species. For this study it has shown that there is 5 distinct clades of O. elongata across its geographic range. This is a complex the authors of this paper prefer to use, compared to the 7 subspecies approach as the genetic differentiation between these different sites and populations is that high. As the polymorphism is higher than expected and 4 of the seven sub-species do not appear to be monophyletic clades (Refer to the phylogenetic tree in the paper as the image is not clear when put onto this blog post) (shared recent common ancestor). Therefore it should be required to sample these populations more intensely and determine more morphological characters that may be variable between these proposed 5 species!
It is probable that O.elongata did survive the glacial periods in situ on the Alps and Apennines. Based on the approximate dating method, along with the phylogenetic analysis and molecular clock hypothesis, O.elongata diverged long before the Last glacial maximum. The general pattern in the phylogeography is that the populations from the central Swiss Alps and northern Italy are basal, with subsequent separation of the eastern, southern (Apennines) and western extremes of the distribution, and finally a second colonization of the Apennines. Clades I and II in the Central Alps separated early and must have survived many glacial cycles in isolation from the rest of the species, perhaps in refuges within the Alps and are the basal group. This structuring is also common within plants in the area. Four refugia are proposed for alpine plants along the southwestern, southern and eastern edges of the Alps, which is what was found similar in this study of O.elongata.
This is all interesting, as during glacial periods the habitat that O.elongata could inhabit would have been substantially larger. However most of the populations have remained relatively disjoint since the major divergence of clades about 0.3 to 1.0 million years ago! Therefore it is indicative that this genus of beetles are low dispersers and there geographic range contraction during interglacial periods has lead to speciation. It's good to see the other side of the coin sometimes!
Thanks for reading!
