Abstract
The genus Thaumetopoea contains the processionary moths, a group of lepidopteran associated with forest trees, well known for the social behaviour of the larvae and for carrying urticating setae. The taxonomy of the genus is partly unresolved and a phylogenetic approach is lacking. The goal of this work is to produce a phylogeny for Thaumetopoea and to identify the main traits driving the evolution of this group. Eighteen mitochondrial and three nuclear genes were fully/partly sequenced. Markers were aligned and analysed singularly or in various combinations. Phylogenetic analyses were performed according to maximum likelihood and Bayesian inference methods. Trees obtained from largest data sets provided identical topologies that received strong statistical support. Three main clades were identified within Thaumetopoea and were further supported by several signatures located in the mitochondrial tRNAs and intergenic spacers. The reference topology was used to investigate the evolution of life history traits related to biogeography, host plant, ecology, and morphology. A multigenic approach allowed to produce a robust phylogenetic analysis of the genus Thaumetopoea, with the identification of three major clades linked to different ecological and life history traits. The first clade is associated with Angiosperm host plants and has a fast spring development of larvae on young foliage. The other clades have originated by one event of host plant shift to Gymnosperm Pinaceae, which implied a longer larval developmental time due to the lower nutritional quality of leaves. These clades showed different adaptations to such a constraint, the first with a switch of larval feeding to cold season (winter pine processionary moths), and the second with a retraction to high altitude and latitude and a development cycle extended over two years (summer pine processionary moths). Recent global warming is affecting all species and seems able to further shape the evolution of the group.
Highlights
Evolution and diversification of animal species often result from a number of adaptive mechanisms to the environmental conditions [1]. This is true for herbivorous insects, which are strongly dependent on both abiotic and biotic variables determining their fitness in different habitats
Host plant diversity seems to be the main source of diversification in herbivorous insects [5], as host plant shifts have been recorded in almost 50% of speciation events [6]
Solely Thaumetopoea processionea (Linnaeus, 1758) and Thaumetopoea solitaria (Freyer, 1838) belong to the Thaumetopoea genus while all the other species belong to Traumatocampa (T. apologetica Strand, 1909; T. bonjeani (Powell, 1922); T. cheela Moore, 1883; T. jordana (Staudinger, 1894); T. libanotica Kiriakoff & Talhouk, 1975; T. pinivora (Treitschke, 1834); T. pityocampa (Denis and Schiffermuller, 1755); T. wilkinsoni Tams, 1925), with the only exception of one species assigned to the new genus Heliantocampa (H. herculeana (Rambur, 1840))
Summary
Evolution and diversification of animal species often result from a number of adaptive mechanisms to the environmental conditions [1]. This is true for herbivorous insects, which are strongly dependent on both abiotic and biotic variables determining their fitness in different habitats. Host plant shifts and host plant range expansion, driven by climatic changes, can lead to further speciation events as they can increase the geographical range of insect species, creating opportunities for later geographical isolation or local adaptation to new environmental conditions [7]. Host shifts are often the result of a trade-off between host plant availability/quality and the natural enemies associated with this particular habitat [8]
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