20th International Congress of Arachnology

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The evolution of sociality in animals is frequently associated
with a shift from outcrossing to inbreeding. This suggests
that short-term benefits outweigh costs of inbreeding. Over
evolutionary time, inbreeding populations experience a
severe reduction in effective population size increasing the
rate of genetic drift and accelerating loss of genetic diversity.
This process predicts reduced evolutionary potential and ele-
vated extinction risk. Empirical evidence for the evolutionary
dead end hypothesis comes mainly from phylogenetic analy-
ses; quantitative estimates of genome-wide diversity in
species with contrasting mating systems are scarce. We
tested the combined effects of sociality and mating system
on genome wide diversity using a comparative RAD sequenc-
ing approach. Our analysis included multiple populations
of each of three independent sister-species pairs of social
inbreeding and subsocial outcrossing Stegodyphus spiders
and a subsocial outgroup. Genetic diversity in the social
species was extraordinarily low: heterozygosity and within
population genetic diversity were 6–10 fold lower in inbreed-
ing compared to outcrossing species, and demographic
modelling revealed a tenfold reduction in effective popula-
tion size of inbreeding populations. Species-wide genetic
diversity depends on population divergence and viability of
genetic lineages. Population genomic patterns were con-
sistent with high lineage turnover, which homogenizes the
genetic structure that builds up between inbreeding popula-
tions, ultimately depleting genetic diversity at the species
level. Indeed, species-wide genetic diversity of social species
was 5-8 times lower than that of subsocial species, and
amongst the lowest estimated for any species. This severe loss
of genome-wide diversity is likely to affect all social inbreed-
ing species, limiting their evolutionary potential as predicted
by the evolutionary dead end hypothesis.
Keywords: mating systems, inbreeding, comparative pop-
ulation genomics, sociality, social spiders, Stegodyphus
Oral presentation
Obscure features of Solifugae: compara-
tive morphology of the lateral eyespots
Tharina L. Bird1,2, Sierra Little2
1Botswana International University of Science and
Technology (BIUST), P/Bag 16, Palapye, Botswana;
2Colorado State University, Fort Collins, CO 80523-
1177, USA
Lateral eyes in Arachnida are presumed plesiomorphic.
Photosensitive areas without lenses placed laterally on
the prosoma were recorded for various arachnid orders
(e.g. Ricinulei, Scorpiones, Shizomida) and their homol-
ogy with lateral eyes are generally assumed. The presence
of lateral eyespots in the anterolateral propeltidial lobes
of Solifugae (solifuges, sunspiders, false spiders) are
often overlooked and even their basic external mor-
phology is little known. This is notwithstanding their
potential importance within the Arachnida towards
interordinal, and within the Solifugae towards intraor-
dinal, phylogenetic relationships. In this study, eyespots
were examined in representative of major Solifugae taxa.
Eyespots were generally easily distinguishable either in
lateral view, ventral view, or both. Broad trends in eyespot
configuration were found at family level, especially
regarding number and relative placement, but also to an
extend in shape, size and reflectiveness.
Keywords: comparative morphology, homology, photo-
sensitive, lateral eyes
Poster presentation
Termite-eating spiders (Ammoxenidae:
Ammoxenus): distribution and coexistence
of cryptic species
Tharina L. Bird1,2, Christopher Bird3, John Irish4,
A.S. Dippenaar-Schoeman5
1Department of Biological Sciences and Biotechnology,
Botswana International University of Science and
Technology (BIUST), Private Bag 16, Palapye, Botswana;
2Department of Arachnology, National Museum of Namibia,
P.O. Box 1203/ Robert Mugabe Av. 59, Windhoek, Namibia;
3Geospace International, P.O. Box 7782, Lynnwood Ridge,
0040, South Africa; 4Namibia Biodiversity Database,
Windhoek, Namibia; 5Biosystematics:
Arachnology, ARC–Plant Protection Research Institute,
Private Bag X134, Queenswood, 0121, South Africa
50 DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Cushing