Abstract
Spiders spinning skills have fascinated mankind since ancient times. These animals owe this ability to unique appendages named spinnerets. These structures are connected to silk-producing glands and are responsible for silk extrusion and manipulation, granting spiders the ability to use the threads for functions far beyond web-building. In spite of the relevance of spinnerets, there is scarce knowledge about their development and evolution. Most research on these structures focused on their morphological aspects, or possible applications of the silk for human purposes. In this mini review, we included this literature, but our main purpose is to introduce and discuss the preeminent hypotheses on the origins of spinnerets in light of an evo-devo perspective. We present the available information on genetic pathways involved in spinneret genesis during spider’s embryonic development, evidencing the eminent need for further research in the evolution and development of spinnerets.
Highlights
The origin of silk production precedes the evolution of spinnerets (Shultz, 1987). This is supported by fossils described by Selden et al (2008) that bear spigot-like structures and were found with silk threads, but had no signs of spinneret-like appendages
As a matter of fact, the developmental study by Pechmann and Prpic (2009) has demonstrated that the posterior spinneret in Acanthoscurria geniculata presents a leg-like gene expression profile—what was interpreted as evidence of serial homology between spinnerets and legs
Clarke et al (2015) has taken this hypothesis further. They have found that a spider-specific gene duplication has occurred, and that gene families with genes that are expressed only in silk glands are more likely to retain the paralog sequences that emerged from this event
Summary
The major synapomorphy of this clade is its spinning apparatus (Wheeler et al, 2017; Wang et al, 2018), formed by silk-producing glands that lead to appendages called spinnerets, present in the fourth and fifth opisthosomal (abdominal) segments (Pechmann et al, 2010). This is supported by fossils described by Selden et al (2008) that bear spigot-like structures and were found with silk threads, but had no signs of spinneret-like appendages. As a matter of fact, the developmental study by Pechmann and Prpic (2009) has demonstrated that the posterior spinneret in Acanthoscurria geniculata presents a leg-like gene expression profile—what was interpreted as evidence of serial homology between spinnerets and legs.
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