Phylogeny of study species and genome-wide pattern of molecular evolution in social and nonsocial branches. a The maximum likelihood (ML) phylogenetic tree with estimated divergence time of the 22 spider species included in the study. The ML tree was inferred from 3832 core-shared single-copy orthologs. Bootstrap values are indicated along the branches. The divergence times at the nodes were estimated using four calibrations indicated with solid black dots. Median age estimates and 95% highest posterior densities (Mya) are shown for each node. Q and P represent the Quaternary Period and the Pliocene Epoch, respectively. Four lineages of spiders are distinguished by dark columns: genera Anelosimus, Theridion, Stegodyphus and the family Sparassidae. Orange dots represent social spider species, light blue dots represent nonsocial species including prolonged subsocial, subsocial, and solitary spider species, the arrow tails represent the independent origins of sociality in spiders. Pictures of social spiders (from top to bottom) from Stegodyphus dumicola (photo credit: Noa Pinter-Wollman), Theridion nigroannulatum and Anelosimus eximius (photo credit: Leticia Avilés). b Violin plot depicting the genome-wide pattern of molecular evolution (dN/dS) between social (n = 8) and nonsocial spider (n = 14) branches across the phylogeny (horizontal bars indicate 95% CI of the means). P value was calculated by using Wilcoxon rank-sum test. Social spiders experienced convergent elevated genome-wide molecular evolution during the transition to social life. c Multi-bar plot depicting the patterns of selection experienced across sites in the genomes of social and nonsocial spiders, estimated with the Partitioned Descriptive model in RELAX. P value as calculated by using Likelihood-ratio test (LRT). The distribution of dN/dS across sites in the genomes are illustrated by three categories of dN/dS for social (orange) and nonsocial (light blue) branches. The vertical dashed line at dN/dS = 1 represents neutral evolution, bars at dN/dS > 1 represent sites experiencing positive selection, and bars at dN/dS <1 represent sites experiencing purifying selection. The arrows show the direction of change in dN/dS between nonsocial and social branches, demonstrating relaxation of purifying and positive selection associated with the transition to sociality. K < 1 indicates genome-wide relaxation of selection. Credit: Nature Communications (2022). DOI: 10.1038/s41467-022-34446-8
A team of researchers at the University of Pennsylvania, Texas Tech University, Cornell University and Australian National University has found similar genes between species of spiders that have some degree of sociability. They have published their paper in the journal Nature Communications.
Spiders are well known for living an antisocial, solo existence—most build webs alone, live on them and only interact with others of their kind when it comes time to mate. But prior research has shown that some species do exhibit some degree of sociability.
In one species, mothers were found to protect their offspring from predators, for example. Such examples are known as sub-social behaviors. Other species, such as the Australian huntsman, have been found to share meals. Such types of social behavior are better described as tolerance, the researchers note, than as demonstrations of sociability. Still, they suggest such behaviors may be indications that spiders are evolving to become more social. Doing so has made most other species more resourceful and therefore more successful.
Prior research has also shown that along with sociability comes a bigger brain. Creatures that socialize have to do all the things that nonsocial species do while getting along with others of their kind. This presents a problem for spiders, because they do not have centralized brains. Instead, they have clusters of nerves distributed throughout their bodies.
Still, prior research has shown that spiders that exhibit some degree of sociability do have more developed nervous systems than spiders that do not. In this new effort, the researchers looked for differences between social and nonsocial spiders. Their work involved comparing the genomes of 22 spider species with some degree of sociability.
They found evidence of genetic changes compared to other spiders, which allowed the spiders to be more social. This development could prove challenging for prey, the researchers note, if such social activities involve spiders teaming up to improve their hunting skills.
More information:
Chao Tong et al, Genomic signatures of recent convergent transitions to social life in spiders, Nature Communications (2022). DOI: 10.1038/s41467-022-34446-8
Citation:
Sociability genes found in some spiders (2022, November 28)
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