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

In the last decade and a half, advances in genetic sequencing technologies have revolutionized systematics, transforming the field from studying morphological characters or a few genetic markers, to genomic datasets in the phylogenomic era. A plethora of molecular phylogenetic studies on many taxonomic groups have come about, converging on, or refuting prevailing morphology or legacy-marker-based hypotheses about evolutionary affinities. Spider systematics has been no exception to this transformation and the inter-relationships of several groups have now been studied using genomic data. About 51 500 extant spider species have been described, all with a conservative body plan, but innumerable morphological and behavioural peculiarities. Inferring the spider tree of life using morphological data has been a challenging task. Molecular data have corroborated many hypotheses of higher-level relationships, but also resulted in new groups that refute previous hypotheses. In this review, we discuss recent advances in the reconstruction of the spider tree of life and highlight areas where additional effort is needed with potential solutions. We base this review on the most comprehensive spider phylogeny to date, representing 131 of the 132 spider families. To achieve this sampling, we combined six Sanger-based markers with newly generated and publicly available genome-scale datasets. We find that some inferred relationships between major lineages of spiders (such as Austrochiloidea, Palpimanoidea and Synspermiata) are robust across different classes of data. However, several new hypotheses have emerged with different classes of molecular data. We identify and discuss the robust and controversial hypotheses and compile this blueprint to design future studies targeting systematic revisions of these problematic groups. We offer an evolutionary framework to explore comparative questions such as evolution of venoms, silk, webs, morphological traits and reproductive strategies.

New species of the pirate spider genus Mimetus Hentz, 1832 from China with a cladistic hypothesis on their phylogenetic placement (Araneae, Mimetidae)

Five new species of mimetid spiders from China are described: Mimetus subulatus n. sp., M. clavatus n. sp., M. dentatus n. sp., M. niveosignatus n. sp. and M. uncatus n. sp. The phylogenetic placement of these new species is inferred based on a cladistic analysis of an expanded version of the morphological dataset of Benavides and Hormiga (2020). The new species form a clade that can be distinguished from other Mimetus species by the presence of a subtegular apophysis between paracymbium and subtegulum, pilose cuticular projections on the membranous part of the conductor in the male palp and by a bicameral structure of the spermathecae in females. The new species are part of a clade that includes Mimetus syllepsicus Hentz, 1832, the type species of the genus. The genus Mimetus as currently circumscribed is not monophyletic, as the clade that includes all the Mimetus species also includes the genera Australomimetus Heimer, 1986 and Anansi Benavides and Hormiga, 2017, corroborating the results of Benavides and Hormiga (2020).

Shifts in morphology, gene expression, and selection underlie web loss in Hawaiian Tetragnatha spiders

BACKGROUND

A striking aspect of evolution is that it often converges on similar trajectories. Evolutionary convergence can occur in deep time or over short time scales, and is associated with the imposition of similar selective pressures. Repeated convergent events provide a framework to infer the genetic basis of adaptive traits. The current study examines the genetic basis of secondary web loss within web-building spiders (Araneoidea). Specifically, we use a lineage of spiders in the genus Tetragnatha (Tetragnathidae) that has diverged into two clades associated with the relatively recent (5 mya) colonization of, and subsequent adaptive radiation within, the Hawaiian Islands. One clade has adopted a cursorial lifestyle, and the other has retained the ancestral behavior of capturing prey with sticky orb webs. We explore how these behavioral phenotypes are reflected in the morphology of the spinning apparatus and internal silk glands, and the expression of silk genes. Several sister families to the Tetragnathidae have undergone similar web loss, so we also ask whether convergent patterns of selection can be detected in these lineages.

RESULTS

The cursorial clade has lost spigots associated with the sticky spiral of the orb web. This appears to have been accompanied by loss of silk glands themselves. We generated phylogenies of silk proteins (spidroins), which showed that the transcriptomes of cursorial Tetragnatha contain all major spidroins except for flagelliform. We also found an uncharacterized spidroin that has higher expression in cursorial species. We found evidence for convergent selection acting on this spidroin, as well as genes involved in protein metabolism, in the cursorial Tetragnatha and divergent cursorial lineages in the families Malkaridae and Mimetidae.

CONCLUSIONS

Our results provide strong evidence that independent web loss events and the associated adoption of a cursorial lifestyle are based on similar genetic mechanisms. Many genes we identified as having evolved convergently are associated with protein synthesis, degradation, and processing, which are processes that play important roles in silk production. This study demonstrates, in the case of independent evolution of web loss, that similar selective pressures act on many of the same genes to produce the same phenotypes and behaviors.

The malkarid spiders of New Zealand (Araneae : Malkaridae)

This paper addresses the systematics of the New Zealand spiders of the family Malkaridae. Malkarids are small araneoid spiders that live primarily in the leaf litter and mosses of temperate and tropical wet forests in Australia and New Zealand, with the exception of a single species in southern South America and another in New Caledonia. We treat the New Zealand species of Malkaridae that are not members of the subfamily Pararchaeinae, a monophyletic group of 11 new species that we classify in 2 new genera (Tingotingo, gen. nov. and Whakamoke, gen. nov.) and a new subfamily (Tingotinginae, subfam. nov.). We describe, diagnose, illustrate and map the distribution of specimen records of these 11 new species of New Zealand Malkaridae: Tingotingo porotiti, sp. nov., T. pouaru, sp. nov., T. tokorera, sp. nov., T. aho, sp. nov., Whakamoke orongorongo, sp. nov.; W. tarakina, sp. nov.; W. guacamole, sp. nov.; W. hunahuna, sp. nov.; W. paoka, sp. nov.; W. heru, sp. nov.; and W. rakiura, sp. nov. We also treat the phylogenetic relationships of Malkaridae and use the results of our previous work on the molecular phylogeny of Araneoidea as the bases for the classification of the family. Tingotingo, gen. nov. and Whakamoke, gen. nov. are sister clades. Tingotinginae, subfam. nov. is the sister group of the Malkarinae plus Pararchaeinae clade. We further hypothesise and discuss the morphological synapomorphies of Malkaridae, Tingotinginae, subfam. nov. and the two new genera.