20th International Congress of Arachnology

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76 DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Cushing
cohesive clades of S. robustus. Divergence dating analyses
suggest that these separate refugia date to the Pliocene
and that divergence between clades predates the late Pleis-
tocene glacial cycles, while diversification within clades
was likely driven by these cycles.
Keywords: sky islands, southwestern United States,
landscape genomics, isolation by environment, refugial
persistence, ddRAD-seq
Student - oral presentation
Population genomics and mitochondrial-
nuclear discordance in range expanding
populations of Argiope bruennichi
*Abhilesh Dhawanjewar1, Henrik Krehenwinkel 2
1School of Biological Sciences, University of
Nebraska-Lincoln, Lincoln, NE, USA; 2Department for
Environmental Sciences, Policy and Management,
University of California, Berkeley, CA, USA.
In the past decade, molecular markers have been increas-
ingly employed to test various phylogeographic hypotheses.
While resolving the geographic histories of many taxa,
these methods can also be used to study the behavior of
genetic markers such as mtDNA. Populations of Argiope
bruennichi have exhibited poleward range expansion into
Northern Europe in the past century. Mitochondrial and
Nuclear genome-wide analyses of the range-expanding pop-
ulations reveal the role of genomic admixture in enabling
invasive populations to adapt to novel climatic conditions.
These analyses also reveal an interesting difference between
the mitochondrial and nuclear markers. While regions of
the nuclear genome freely introgress between populations,
mitochondrial genomes show high levels of structure
between populations suggesting limited mitochondrial
introgression. While various hypotheses such as sex-biased
dispersal could lead to this apparent pattern, we propose
the role of mitochondrial-nuclear incompatibilities in
producing this discordance. These incompatibilities could
serve as targets for selection and further pave the way for
speciation. Such discordant patterns are most commonly
observed in populations undergoing hybridization fol-
lowed by a period of geographical isolation. The proficient
colonizing capabilities of spiders make them excellent
candidates for testing these hypotheses and future studies
in spiders should incorporate molecular methods to gain
insight about the evolutionary processes that govern species
delimitation and species hybridization.
Keywords: phylogeography, population genomics, mito-
nuclear discordance
Student - oral presentation
Dispersal, local density dependence,
and population stability in social spider
metapopulations
*Suzana Diniz¹, João Vasconcellos Neto¹, Leticia Avilés²
¹Departamento de Biologia Animal, Universidade
Estadual de Campinas, Caixa Postal 6109, CEP
13083-970, Campinas, SP, Brazil; ²University of
British Columbia #2370-6270 University Blvd.
Vancouver, BC V6T 1Z4, Canada.
In subdivided populations, local population stability may
depend on dispersal occurring to prevent overcrowding
and resource depletion. Social spider colonies constitute
relatively isolated local populations forming part of a
metapopulation. In the more highly social species, greater
intrinsic rates of growth and lower dispersal tendencies may
result in boom and bust colony and patch dynamics, whereas
local populations may be more stable in the less social
species with greater tendencies to disperse. We recorded the
growth, dispersal, and stability of two co-occuring social
Anelosimus spiders at Serra do Japi, Brazil. We found that
in the transitional A. jabaquara per capita fitness was not
affected by colony size, whereas in the more highly social A.
dubiosus per capita fitness was maximum at intermediate
colony sizes, but below replacement value in small and large
colonies. The more highly social species thus exhibited both
positive (Allee effect) and negative density dependence; the
less social, did not. Dispersal and extinction were inversely
correlated across species: the transitional A. jabaquara had
consistently higher dispersal, but lower extinction rates,
whereas the social A. dubiosus had the opposite pattern.
These results are consistent with the hypothesis of dispersal
as a stabilizing factor in local population dynamics.