3.2 | Variation in somatic morphology and its relationship with behavioral niche
The NMDS ordination shows the heavy influence of behavioral niche on mygalomorph somatic morphology, although evolutionary history also plays a role (Figure 2). A clear behavioral gradient can be seen, with opportunistic, web-building taxa representing one extreme of the morphological/behavioral spectrum in the bottom-left of the ordination, and burrowers and nest-builders with a trapdoor entrance representing the other, on the right. Between these two extremes lies opportunists and burrowers with open entrances (generally clustering slightly left of center), and burrowers with other entrance modifications besides a trapdoor (slightly right of center).
Clearly, many aspects of somatic morphology are strongly influenced by evolutionary history, as many major phylogenetic clades do not overlap, and the proximity of these clades to one-another is generally reflective of their phylogenetic relationships (Figure 2). For example, the Atypoidea are at the bottom of the ordination, separate from the Avicularioidea (all other Mygalomorphae), and the Crassitarsi (Nemesioidina + Theraphosoidina) and Venom Clade+ and Domiothelina form clusters. However, many of these clades are spread widely across morpho-space from left to right, reflecting the diversity of behavioral niches that their species inhabit.
Members of different clades with similar burrowing behaviors are often closer together in morpho-space than members of the same clade that behave differently, presumably reflecting the convergent evolution of morphological characters that are adapted to particular behavioral niches (e.g., see Table 2). For example, those members of the Antrodiaetidae, Actinopodidae, Stasimopidae, and Bemmeridae that are burrowers with structurally-modified burrow entrances all cluster closer to the Domiothelina than to other more closely related taxa that behave differently. Indeed, the position of taxa in morphospace often mirrors previous phylogenetic hypotheses based on morphology, for exampleAtrax (Venom clade), which has independently evolved opportunistic habits and a web-entrance, is recovered close to the Hexathelidae, the Actinopodidae (Venom Clade) cluster within the Domiothelina, and the bemmerid genera Spiroctenus andHomostola cluster closest to nemesioid and euctenizid genera respectively, mirroring their previous taxonomic positions.