Abstract
Caterpillars of the silk moth genus Hyalophora (Lepidoptera; Saturniidae) construct multilayered cocoons that function as overwintering housing during the pupal to adult developmental period. While all cocoons share the primary function of protecting the developing moth, cocoons spun by different Hyalophora silk moth species vary significantly in architectural features and in the level of intraspecific cocoon-type polymorphism. We compared the cocoons of Hyalophora species found throughout North America and investigated the evolution of architectural variation. We first characterized and compared the architectural features of cocoons at all three cocoon sections (outer envelope, inner envelope, and the intermediate section that separates them), and found that variation in the outer envelope underlies the differences in architecture between cocoons. Phylogenetic analysis indicates ancestral polymorphic architecture (both “baggy” and “compact” morphs), with diversification within Hyalophora for both monomorphic “compact” cocoons, and increased intermediate space and silk in “baggy” lineages. The evolution of these traits suggests a potential functional role for the different cocoon architectural forms.
Highlights
Individuals from many diverse taxa have evolved to build structures that house and protect the individual from environmental stress
We used the cocoons of different species within Hyalophora (H. cecropia, H. columbia, H. euryalus, and H. cf gloveri) and that of a hybrid (H. “kasloensis”), as a model to examine the evolution of architecture and dimorphism in animal construction (Fig. 2a,b)
We found that the cocoons spun by the different Hyalophora groups were architecturally different at the level of the outer envelope
Summary
Individuals from many diverse taxa have evolved to build structures that house and protect the individual from environmental stress. The cocoons spun by silk moth species in the genus Hyalophora (Lepidoptera; Saturniidae) are examples of structures that can protect individuals against adverse environmental conditions[4,5,6]. Cecropia moth caterpillars (H. cecropia), for example, produce a multilayered cocoon with an intermediate space between the layers filled with silk[6,10,11] This intermediate space and silk, combined with two distinct morphs (baggy and compact) appears to mitigate environmental stochasticity during pupal development. We conducted a phylogenetic analysis to determine how different architectural features and the existence of multiple cocoon morphologies have evolved within the genus Together, these results inform on whether the diverse cocoon architectures in Hyalophora are consistent with a strategy for dealing with environmental conditions during the pupal developmental period prior to adult eclosion
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