20th International Congress of Arachnology

119

DENVER MUSEUM OF NATURE & SCIENCE

REPORTS

No. 3, July 2, 2016

social and epidemiological dynamics.

Keywords: behavior, bacterial transmission, social

network analysis, social spider

Student - oral presentation

Riparian tetragnathids rely heavily on

aquatic subsidies in a tropical urban

watershed

*Sean P. Kelly, Elvira Cuevas, Alonso Ramírez

Universidad de Puerto Rico, Departamento de Biología,

Río Piedras P.O. Box 23360 San Juan, PR 00931-3360

spkelly.84@gmail.com

Some taxa of tetragnathid spiders are considered special-

ists of aquatic ecosystems and are major consumers of

emerging aquatic insects. However, little is known about

how urbanization may have indirect effects on riparian

spider assemblages due to changes in prey communities

along urban stream gradients. We predicted that due to

the loss of terrestrial primary productivity in more urban-

ized areas there will be less terrestrial prey available

and riparian tetragnathids would rely more heavily on

aquatic insects as a major energy source. Six study sites

were selected along the Río Piedras watershed that flows

through the center of San Juan, Puerto Rico. These six

sites represent individual subwatersheds and form a

gradient of increasing urbanization according to percent

vegetation in each subwatershed. To conduct stable isotope

dietary analyses, we collected samples of basal resources

for aquatic and terrestrial food webs, primary consumers

and two species of tetragnathids (

Leucauge argyra

and

Tetragnatha boydi

T. boydi

are generally nocturnal and

are known to be aquatic ecosystem specialists, while

argyra

are more diurnal and are not exclusive to aquatic

ecosystems. Utilizing Bayesian mixing models we found

that the proportion of aquatic insects in the diet of ripar-

ian tetragnathids increased along the urban gradient

from ~50% in the less urbanized areas of the watershed

to ~95% at the most urbanized sites. There was not a

large difference in the diets of the two species, although

boydi

overall was found to consume greater proportions

of aquatic insects. These findings support our prediction

that in heavily urbanized areas riparian tetragnathids

rely more on aquatic insects as their primary food source.

Therefore, impacts to urban stream ecosystems could have

strong indirect effects on riparian spiders, such as changes

in insect prey abundance and diversity, along with the pos-

sible bioaccumulation of aquatic contaminants.

Keywords: dietary analysis, riparian tetragnathids,

stable isotopes, urbanization

Student - Oral presentation

Next generation sequencing of gut content

to study niche ecology in spiders

Susan Kennedy

, Henrik Krehenwinkel

, Rosemary

Gillespie

, Stanislav Pekar

Dept. of Environmental Science, Policy, and Manage-

ment University of California - Berkeley 130 Mulford

Hall #3114 Berkeley, CA 94720-3114 USA;

Depart-

ment of Botany and Zoology, Masaryk University,

Kotlá

ská 267/2, 611 37 Brno, Czech Republic

fourjaws@berkeley.edu

Dietary studies in spiders have historically been dif-

ficult due to the infrequency of observing predation

events; the fact that spiders consume prey in liquid

form, leaving no parts for morphological identification;

and the limitations of traditional barcoding methods,

which have not always been able to distinguish spiders

from their closely related arthropod prey without the

use of blocking primers. However, recent methodologi-

cal innovations and advances in sequencing technology

have enabled powerful and detailed studies of spider gut

contents using metagenomics. We developed a protocol

for extracting, amplifying and sequencing high yields of

prey DNA from spiders’ guts using an Illumina platform

and without the need for blocking primers. Using the

agelenid spider

Hololena adnexa

, we tested several

variables in the extraction process and used the results to

create an optimized protocol. This protocol recovers prey

DNA at a higher proportion of the total yield than has

been previously obtainable. It also addresses the problem

of secondary predation by substantially decreasing the

detection of secondarily consumed prey. The assemblage

of prey we recovered from

H. adnexa

closely resembles

the findings of previous observational studies, supporting

International Congress of Arachnology