Abstract
Larvae of the cosmopolitan family Limacodidae, commonly known as “slug” caterpillars, are well known because of the widespread occurrence of spines with urticating properties, a morpho‐chemical adaptive trait that has been demonstrated to protect the larvae from natural enemies. However, while most species are armed with rows of spines (“nettle” caterpillars), slug caterpillars are morphologically diverse with some species lacking spines and thus are nonstinging. It has been demonstrated that the evolution of spines in slug caterpillars may have a single origin and that this trait is possibly derived from nonstinging slug caterpillars, but these conclusions were based on limited sampling of mainly New World taxa; thus, the evolution of spines and other traits within the family remains unresolved. Here, we analyze morphological variation in slug caterpillars within an evolutionary framework to determine character evolution of spines with samples from Asia, Australia, North America, and South America. The phylogeny of the Limacodidae was reconstructed based on a multigene dataset comprising five molecular markers (5.6 Kbp: COI, 28S, 18S, EF‐1α, and wingless) representing 45 species from 40 genera and eight outgroups. Based on this phylogeny, we infer that limacodids evolved from a common ancestor in which the larval type possessed spines, and then slug caterpillars without spines evolved independently multiple times in different continents. While larvae with spines are well adapted to avoiding generalist predators, our results imply that larvae without spines may be suited to different ecological niches. Systematic relationships of our dataset indicate six major lineages, several of which have not previously been identified.
Highlights
When similar phenotypes occur in a broadly distributed taxonomic clade, it may result from one or more processes, including inheritance from a common ancestor, adaptation to similar local environments, shared constraints, and random genetic drift (Jacobs et al, 2013; Losos, 2011; Stewart, 2007)
The evolutionary reconstruction of spines in limacodid caterpillars indi‐ cated that the ancestral state was most likely larvae with spines present from second instar to final instar (Figure 3, Node 1: FIGURE 2 Phylogenetic trees of the Limacodidae based on the combined dataset constructed with: (a) partitioned Bayesian Inference; (b) partitioned Maximum Likelihood using the GTR + Γ+I substitution model
According to the phylogeny reconstructed in this study, limaco‐ dids evolved from a common ancestor in which the larval type possessed spines from second instar to final instar, and spines were evolutionary lost or reduced in late instars multiple times—at least on four oc‐ casions (Figure 3)
Summary
Because the study of Zaspel et al (2016) was based on mainly New World taxa, the results may be de‐ rived from in situ diversification or independent colonization. It is uncertain if the evolutionary pattern of slug caterpillars is the same after including samples from different zoogeographic regions of the world. It is unclear whether the existence or loss of spines in slug caterpillars has evolved once or has evolved repeatedly and independently in different lineages and/or in different continents. Most of the taxa included in this study were reared from samples collected from Asia, but we include material from Australia, North America, and South America
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