Trine Bilde - Sociality in Spiders

Question 1

Lubin & Bilde 2007

Answer 1

Introduction to social spiders: 25 known spp. of 6 lineages, sociality has evolved independently over 20 times.

• Permanently social groups, no pre-mating dispersal, and inbreeding.
• Female biased sex ratio of 1m:8f
• Have evolved through subsocial route (evidenced by Settepani & Bechsgaard 2016)

Also common for these social species:

• They’re derived tip clades
• No diversification
• No known reversals to non-sociality
• A higher extinction rate

Question 2

Schneider & Bilde 2008

Answer 2

Kin-selected benefits of communal feeding - less enzymes needed per individual, efficient foraging. Benefits do not apply when foraging with non-kin.
Kin recognition may happen through cuticle hydrocarbon profiles (Grinstead et al. 2011).

Question 3

Bilde et al. 2007

Answer 3

Per capita reproduction in social spiders decreases with colony size, but the overall nest production increases, so cooperative breeding still confers a reproductive advantage.

Question 4

Stebbins 1957

Answer 4

The low effective population size caused by inbreeding overall means a low potential for adaptation, reduced ability to respond to environmental change and increased risk of extincition.
Due to inc. genetic drift and higher fixation probability of deleterious alleles because of low individual heterozygosity (Charlesworth 2003).

Question 5

Settepani et al. in review

Answer 5

We find lower individual heterozygosity in social spiders, and some of the lowest levels of population level genetic diversty in animals (despite large population census size). All in all means reduced evolutionary potential.

Question 6

? -Bilde?

Answer 6

Very preiminary evidence of epigenetic adaptation in 6sp of social spiders, with 2-5% of carbon methylation patterns inherited!