Correlation with a limited set of behavioral niches explains the convergence of somatic morphology in mygalomorph spiders

Abstract

Understanding the drivers of morphological convergence requires investigation into its relationship with behavior and niche space, and such investigations in turn provide insights into evolutionary dynamics, functional morphology, and life history. Mygalomorph spiders (trapdoor spiders and their kin) have long been associated with high levels of morphological homoplasy, and many convergent features can be intuitively associated with different behavioral niches. Using genus‐level phylogenies based on recent genomic studies and a newly assembled matrix of discrete behavioral and somatic morphological characters, we reconstruct the evolution of burrowing behavior in the Mygalomorphae, compare the influence of behavior and evolutionary history on somatic morphology, and test hypotheses of correlated evolution between specific morphological features and behavior. Our results reveal the simplicity of the mygalomorph adaptive landscape, with opportunistic, web‐building taxa at one end, and burrowing/nesting taxa with structurally modified burrow entrances (e.g., a trapdoor) at the other. Shifts in behavioral niche, in both directions, are common across the evolutionary history of the Mygalomorphae, and several major clades include taxa inhabiting both behavioral extremes. Somatic morphology is heavily influenced by behavior, with taxa inhabiting the same behavioral niche often more similar morphologically than more closely related but behaviorally divergent taxa, and we were able to identify a suite of 11 somatic features that show significant correlation with particular behaviors. We discuss these findings in light of the function of particular morphological features, niche dynamics within the Mygalomorphae, and constraints on the mygalomorph adaptive landscape relative to other spiders.

Microgeographic population structuring in a genus of California trapdoor spiders and discovery of an enigmatic new species (Euctenizidae: Promyrmekiaphila korematsui sp. nov.)

“…The spider infraorder Mygalomorphae (tarantulas, trapdoor spiders, and their kin) is composed of species that are generally longlived, exhibit high morphological conservation, and have simple genitalic structures. These spiders live in subterranean silk-lined burrows or funnel/sheet webs under large debris or in crevices, consistent with their fossorial morphology (Wilson et al, 2023).…”

Species delimitation with limited sampling: An example from rare trapdoor spider genus Cyclocosmia (Mygalomorphae, Halonoproctidae)

“…However, based on the non-monophyletic nature of the morphologically defined C. truncata, the genus most certainly harbours cryptic species diversity. Our results show that Cyclocosmia exhibits strong tendency for short-range endemism combined with morphological stasis (Hedin et al, 2019;Opatova et al, 2020;Wilson et al, 2023). In sedentary taxa, chromosomal rearrangements, likely creating reproduction barriers, may arise even across very short distances (Kotrbová et al, 2016) without being accompanied by morphological differentiation.…”

“…Their current family‐level distribution is linked to major continental‐level vicariate events (Godwin et al., 2018; Opatova et al., 2020; Opatova & Arnedo, 2014a) and they typically evolve in allopatry (Bond et al., 2012). Phenotype in mygalomorph spiders is strongly correlated with their behavioural niche, particularly their foraging strategy and web/burrow construction (Wilson et al., 2023). As a consequence, repeated patterns of both morphological stasis and homoplasy are present among distantly related taxa (Hedin et al., 2019; Opatova et al., 2020; Wilson et al., 2023).…”

“…Phenotype in mygalomorph spiders is strongly correlated with their behavioural niche, particularly their foraging strategy and web/burrow construction (Wilson et al., 2023). As a consequence, repeated patterns of both morphological stasis and homoplasy are present among distantly related taxa (Hedin et al., 2019; Opatova et al., 2020; Wilson et al., 2023). Morphological homogeneity is particularly common at shallow phylogenetic level, but at the same time, mygalomorphs often possess a remarkably deep intra‐specific genetic structuring (Bond et al., 2001).…”

Advances in the reconstruction of the spider tree of life: A roadmap for spider systematics and comparative studies

“…A majority of these spiders construct silk‐lined burrows mainly on the ground with some variations such as the open burrow of Acanthoscurria (Theraphosidae), tubular silk‐lined burrows with trapdoor of Actinopus (Actinopodidae), burrow with collar door of Antrodiaetus (Antrodiaetidae), purse web of Atypus (Atypidae) and the trap‐door found on tree trunks aboveground (Migidae) (Opatova et al., 2021, Wilson et al. 2023). There are >3000 mygalomorph described species classified in c .…”