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| Social
Theridiids - Phylogenetic Patterns, Processes, and Predictions |
|
Author
|
Institutions
|
|
Ingi
Agnarsson
|
George
Washington University, Washington DC |
| Smithsonian
Institution, Washington DC |
|
|
Abstract:
Theridiids are particularly interesting for studying spider
sociality. The majority of social spider species are theridiids,
and representatives of the family show the entire spectrum
of web sharing, ranging from short term maternal care (e.g.
Theridion), to periodic or permanent social behavior
(most Anelosimus, some Achaearanea and Theridion),
and kleptoparasitism (e.g. Argyrodes). Major questions
surrounding spider sociality include: the origin of quasisocial
behavior (e.g. via aggregations around abundant resources
or temporal extension of maternal care), its phylogenetic
distribution (e.g. single vs. multiple origins, origins clumped
or randomly distributed), and how different forms of web sharing
(e.g. sociality and kleptoparasitism) may be related. To investigate
such questions I present a cladistic analysis of 61 theridiid
taxa, based on 242 morphological and behavioral characters.
The resulting phylogenetic hypothesis implies the following:
1) sociality in theridiid spiders evolved as a temporal extension
of maternal care, 2) quasisociality (<10 species in total)
originated independently no less than four times within Theridiidae;
by contrast, web sharing evolved once in the diverse clade
of kleptoparasites (>200 species), 3) social instances
are non-randomly clustered among distal theridiids, suggesting
a common cause, 4) kleptoparasitism and sociality may be related
as alternative modifications of maternal care. My phylogenetic
hypothesis, furthermore, predicts that maternal care may be
much more widespread and common than currently entertained
and that social behavior will be discovered in several taxa
whose behavior is currently unknown. One such prediction was
confirmed by the discovery of the first social Anelosimus
in Africa.(Added 6/ 12 / 2003)
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| Progress
in Tetragnathid Phylogenetics with Emphasis on the "Metinae
Problem" (Araneae, Tetragnathidae) |
|
Author
|
Institution
|
| Fernando
Alvarez |
George
Washington University |
|
|
Abstract:
Simon originally defined the tetragnathid subfamily
Metinae as comprising "all forms intermediate between
Tetragnatha and Nephila"; This definition
has obscured the higher level systematics of Tetragnathidae
for more than one century. The phylogenetic relationships
of metines are crucial to understand the evolutionary history
of tetragnathid spiders. The cladistic analysis of Hormiga
et al. (1995), based on 22 taxa and 61 characters, found metines
to be paraphyletic with respect to tetragnathines, and nephilines
sister to a clade including all remaining tetragnathid taxa.
This presentation reports recent progress towards a better
understanding of the phylogenetic relationships of metines.
The cladistic analysis of a matrix of 42 species of tetragnathids
(plus nine outgroups) and 117 characters scored (morphological
and behavioral) corroborated the monophyly of Tetragnathidae,
Nephilinae and Tetragnathinae, as well as the paraphyly of
"Metinae"; (the latter represented by 16 species).
Traditional metines comprise two lineages: 'Leucaugines' and
'Metines sensu stricto.' The relationships of these
two clades and the synapomorphies that support these lineages
will be discussed. (Added 6 / 18 / 2003)
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| Running
Speed In The Wolf Spider Pirata sedentarius: Between-Sex
Variation And A Cost Of Leg Autotomy |
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Authors
|
Institutions
|
| Pasha
Apontes |
SUNY
Fredonia, Fredonia, N.Y. |
|
Christopher
A. Brown
|
Tennessee
Technological University,
Cookeville, TN |
|
|
Abstract:
Leg autotomy in spiders is a relatively common occurrence
resulting from agonistic interactions with predators or conspecifics.
While autotomy has immediate benefits, due to enhanced survival
probability, it also potentially decreases future fitness.
One possible cost of losing a leg is a reduction in burst
running speed, which may affect prey capture and predator
avoidance behaviors in wandering spiders. We examined running
speed in intact and autotomized Pirata sedentarius,
a wolf spider commonly found in moist cobble zones, from two
stream banks in New York. Autotomy was fairly common in the
field, with 18.8% and 22.2% of spiders missing at least one
leg at our two sites. Females were relatively heavier than
males and ran significantly faster. Intact spiders, both males
and females, ran significantly faster than spiders missing
a leg. We found no difference in speed between spiders which
had lost a leg in the field and spiders for which we removed
a leg in the laboratory. Heavier females ran significantly
faster than lighter females in pre-autotomy trials, but mass
did not affect female speed following autotomy. Male running
speed was unaffected by mass. Our results suggest that leg
loss is potentially costly to both male and female P. sedentarius,
and does not support the "spare leg" hypothesis
of Guffey (1998. J. Arachnol. 26: 296-302). (Added 5
/ 15 / 2003)
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| Sociality
Buffers Against Inbreeding Depression In A Subsocial Spider |
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Authors
|
Institutions
|
| Leticia
Avilés |
Dept.
of Zoology, University of British Columbia, Vancouver,
Canada |
|
Todd
Bukowski
|
Center for Insect Science, University of Arizona, Tucson,
USA. |
|
|
Abstract:
Social spiders are unusual among social organisms
in being highly inbred--males and females mature within their
natal nest and mate with each other to produce successive
generations. We hypothesize that such inbred social systems
originated under conditions where benefits of group living
were sufficiently strong to overcome inbreeding depression
in the transition from an outbred ancestral state. As a window
into such conditions, we have been exploring the fitness consequences
of group living, inbreeding, and dispersal in inbred social
and outbred subsocial species in the genus Anelosimus.
In the subsocial spider Anelosimus cf. jucundus in
southern Arizona we examined the consequences of artificially-imposed
inbreeding on various components of fitness in spiders raised
under natural conditions. We found that inbreeding depression
was only evident during the solitary phases of the spider's
life cycle. Prior to dispersing from the maternal nest, offspring
from inbred and outbred clutches did not differ in size or
survival probability. Instead, fitness during these stages
was influenced primarily by ecological and demographic factors
such as lifespan of the mother, number of siblings in the
group, and distance to a creek. Following dispersal, however,
inbred spiders developed more slowly and reached a smaller
size. We suggest that a similar buffering effect of group
living may have facilitated the origin of inbred social systems
in the genus. (Added 6 / 15 / 2003)
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| Phylogeography
of the Desert Spider, Agelenopsis aperta: Testing
Predictions Based on the Fossil Record |
|
Authors
|
Institution
|
| Nadia
A. Ayoub |
University
of Tennessee, Knoxville, TN |
|
Susan
E. Riechert
|
|
|
Abstract:
Over the past two decades phylogeographic data, or the geographic
distribution of gene lineages, has been increasingly used
to infer historical events such as population fragmentation
or range expansion. Unfortunately, most phylogeographic studies
develop post-hoc explanations for observed patterns rather
than use the genetic data to test a priori hypotheses. These
a priori hypotheses can be developed from paleoclimatic, geologic,
ecological or comparative phylogeographic data. For instance,
fossil arthropod and plant data from arid southwestern United
States during the last glacial maximum indicate that many
desert organisms were restricted to lower elevations and latitudes
than their modern day distributions. The desert spider,
Agelenopsis aperta, currently exhibits a wide range throughout
the southwestern United States but is limited to areas below
6000 feet. Based on the fossil evidence and the modern day
elevational limit of A. aperta we hypothesized that
this desert spider has been restricted to lower elevations
and latitudes during glacial maximums and has only recently
expanded its range to the modern extent. We tested this hypothesis
by comparing observed patterns of mitochondrial DNA sequence
variation to predicted patterns under various historical scenarios.
Preliminary analysis shows support for a recent range expansion
event but the evolutionary history of A. aperta populations
appears to be more complex than can be predicted from the
fossil record alone.(Added 6 / 16 / 2003)
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| What
People Think About Spiders in Russia |
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Authors
|
Institutions
|
| O.P.
Bartosh |
International Scientific Center "Arktika",
Magadan, Russia |
|
T.
A. Karpenko
|
Department
of Employment of the Population, Magadan, Russia |
|
|
Abstract:
It is rather interesting for people engaged in the study of
spiders to learn what common people know about spiders. For
this purpose, a questionnaire was developed and a statistical
investigation was made among the inhabitants of Northeast
Russia. The questionnaire was given to more than 200 people
with various levels of education, and between the ages of
15 and 65 years old.
The questionnaire
that was used included 18 multiple-choice questions. The questions
concerned the way spiders live and their physical characteristics.
The questions also examined the personal attitude, of the
person completing the questionnaire, toward spiders and their
opinion of arachnologists and others who study spiders.
An analysis of
the answers to the questionnaire has shown that 96% of the
people know that spiders are invertebrate animals. However,
only 60% know that spiders have 8 legs, the other 40% of the
people thought, that spiders have 6 legs. Almost all people
know that spiders build their webs from their own silk glands.
Only 1% has answered that spiders use the wool of animals.
The majority of the people questioned, confirmed that some
kind of spiders are dangerous to man and live in family couples.
They also approved the fact that the male spider, during the
mating period, entices the female spider to his web. Some
of the people think that spiders feed on carrion and blood.
The majority of the people participating in this study have
a positive attitude toward spiders. However, many of the women
surveyed are afraid of them and have a sense of fastidiousness.
All people consider that spiders are useful and important
animals in the natural environment, but many of them killed
spiders in their childhood. Most of the people questioned
thought that arachnologists are unusual and strange people,
however necessary to science. The results of the questionnaire
about spiders were considered interesting and unexpected.(Added
5 / 23 / 2003)
|
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| The
Effect Of Predator Hunger On Chemically-Mediated Antipredator
Responses And Survival In The Wolf Spider Pardosa milvina
(Araneae: Lycosidae) |
|
Authors
|
Institutions
|
| Ryan
D. Bell |
Susquehanna
University, Selinsgrove, PA |
|
Ann
L. Rypstra
|
Miami
University, Hamilton, OH |
| Matthew
H. Persons |
Susquehanna
University, Selinsgrove, PA |
|
|
Abstract:
The wolf spider, Pardosa milvina, exhibits antipredator
behavior when detecting silk and excreta from a larger co-occurring
wolf spider, Hogna helluo. Since the quantity and quality
of silk and excreta may vary with the hunger state of the
predator, we tested if cues from hungry vs. satiated Hogna
would influence Pardosa activity level and survival.
Pardosa activity was measured on substrata containing
chemical cues from 1) a satiated Hogna, 2) a Hogna
withheld food for 2 weeks, or 3) a control consisting of a
blank test container (N = 20/treatment). Pardosa response
was recorded on each substratum over a 30-min period using
video-tracking equipment (Videomex I). We then measured Pardosa
survival in the presence of live hungry and satiated Hogna
on each respective substrate treatment or a blank control
substrate in a fully factorial design. Results indicate
Hogna cues significantly reduced Pardosa activity
level and that Pardosa show significantly less activity
in the presence of cues from a hungry Hogna than a
satiated one. Predator hunger state and substratum type significantly
affected Pardosa survival in the presence of live Hogna.
However, cues from hungry vs. satiated Hogna resulted
in no difference in Pardosa survival nor was there
a significant interaction between Hogna hunger state
and substratum type on Pardosa survival. In summary
Pardosa can discriminate between hungry versus satiated
predators based on silk and excreta cues alone, but differences
in behavior as a result of this discrimination did not translate
into increased survival in the presence of a live predator.
(Added 5 / 14 / 2003)
|
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| Did
Bolas-Hunting Spiders Evolve Through Gradual Web Reduction? |
|
Authors
|
Institution
|
| Todd
A. Blackledge |
University
of California, Riverside, CA |
| Cheryl
Hayashi |
|
|
Abstract:
Moth hunting bolas spiders construct some of the most specialized
webs found within the Araneidae. These highly reduced webs
are thought to have evolved through a gradual reduction of
the orb web within the Cyrtarachninae, which accompanied an
increased specialization upon male moths as prey. However,
this classic evolutionary story has never been empirically
tested. We used both mitochondrial (16S and COI) and nuclear
(H3 and 18S) DNA sequence data to construct a phylogeny of
genera within the Cyrtarachninae and to test the monophyly
of these moth specialists using several putative araneid genera
as outgroups. We also compare our results with the current
phylogenetic hypothesis of araneid relationships based upon
morphology and behavior. . (Added 6 / 12 / 2003)
|
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| A
Newly Introduced Jumping Spider (Myrmarachne formicaria)
in North America |
|
Author
|
Institution
|
| Richard
Bradley |
The
Ohio State University at Marion, Ohio |
|
|
Abstract:
The large genus Myrmarachne (Araneae: Salticidae)
includes over 200 species, with representatives on each biogeographic
region except the Nearctic. A population of Myrmarachne
formicaria has been discovered in northeastern Ohio. There
is reason to believe that this species, which is widespread
in Europe, is a recent accidental introduction to this area.
This species seems to be well established, having been found
with increasing frequency over the past three years. A resident
of Warren, Trumble County, Ohio first reported noticing this
odd ant-mimic around her residence during the summer of 2000.
The first specimen record was obtained from the same locality
on 16 August 2001. Subsequently, specimens have been found
in neighboring Portage County. The species appears to be common
in a variety of situations, including occasionally inside
buildings. (Added 6 / 17 / 2003)
|
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| Wandering
the Range: Ground-Dwelling Spiders of the Sevilleta Nwr,
New Mexico 1990-2000 |
|
Author
|
Institution
|
| Sandra
L. Brantley |
Museum
of Southwestern Biology, University of New Mexico, Albuquerque |
|
|
Abstract:
New Mexico’s climate is strongly affected by
ENSO (El Nino Southern Oscillation) events, usually resulting
in increased (El Nino) or decreased (La Nina) average winter
precipitation. Arthropods are among the fauna monitored at
the Sevilleta National Wildlife Refuge for changes in species
and abundance that may be due to ENSO. I examined data from
12 predaceous families (9 spiders, 1 scorpion, 1 solpugid
and 1 centipede) from 1990-2000 for relationships between
these groups with rainfall in general and ENSO in particular.
I used a "water year," from Oct 15 of one year to
Oct 15 of the next, which described local growing seasons
better than a calendar year. During this time there were 5
El Nino years, 2 La Nina years and 4 medial years. Arthropod
data came from species counts from pitfall traps operating
continuously since 1989 and collected at 2-month intervals.
The traps were placed in three habitat types: desert grassland,
creosotebush shrubland and pinon-juniper woodland. I used
detrended correspondence analysis (DCA) to assess how well
these generalist predators differentiated among habitats (very
well) and years (not well). I used correlation analysis to
assess the relationship for each family with precipitation
at each site. Here the independence of family responses became
clearer: at all sites gnaphosids and thomisids showed no correlation
with precipitation, but lycosids did. Responses for the corinnids
and dictynids varied by site. These assemblages were robust
over this period, suggesting that the ENSO events were not
severe enough to greatly influence community structure or
function. (Added 5 / 20 / 2003)
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| Testing
Biodiversity Theory With Ground-Dwelling Spiders: Effects
Of Productivity And Disturbance |
|
Authors
|
Institutions
|
| Chris
Buddle |
McGill
University, Montreal, Quebec |
|
Ann
Rypstra
|
Miami
University, Hamilton, Ohio |
|
|
Abstract:
Understanding what determines species diversity is a central
ecological question. We tested whether ground-dwelling spider
diversity is governed by the interaction between productivity
and disturbance, as depicted by Huston’s Dynamic Equilibrium
Model. We created circular straw mulch ‘habitat islands’
(0.5 m radius) on top of 2 x 2 m areas along a disturbance
gradient: old-growth forest floor (lowest disturbance), no-till
soybean fields, soybean fields tilled once, and soybean fields
tilled twice (highest disturbance). Productivity was manipulated
by adding compost beneath the straw mulch, which directly
increased in the primary prey of spiders (Collembola) but
did not affect spider diversity. The disturbance gradient,
however, significantly affected diversity, and the intermediate
disturbance hypothesis was supported. The forest-floor had
the lowest spider diversity, and may be a dominance-controlled
community. Patterns in soybean fields suggest the colonization-competition
trade-off may be partially responsible for patterns in spider
diversity. (Added 5 / 16 / 2003)
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| Sperm
Competition Mechanisms May Benefit Female Orb-Weaving
Spiders, Micrathena gracilis |
|
Author
|
Institution
|
| Todd
C. Bukowski |
Center
for Insect Science, University of Arizona |
|
|
Abstract:
Multiple mating by females and the ensuing sperm competition,
often selects for mechanisms that either prevent other males
from releasing sperm or that displace previous males’
sperm. Because sperm competition occurs within the female’s
reproductive tract, it is thought that females should influence
which mechanisms succeed. I show here that the socially polyandrous
but typically genetically monandrous spider, Micrathena
gracilis, accrue significant weight-gain benefits by mating
with both reproductive tracts soon after molting to adulthood.
In this species males seek out females approaching the final
molt, and females mate soon after molting. The act of mating
usually alters the female reproductive tract in ways that
effectively limits sperm release by subsequent males. I released
individually marked females of various mating histories into
an experimental forest plot in which all males had been excluded.
I then followed their movements through the forest and measured
their weight gained over time. Virgin and one-side virgin
females built their webs higher above the ground and moved
more often than non-virgin females. Non-virgin females gained
weight more than three times as fast as virgin and one-side
virgin females, an effect likely mediated, in part, by reduced
foraging efficiency in the latter groups. Among non-virgin
females, those with a genetically monandrous reproductive
strategy gained more weight than females with the more rare
genetically polyandrous strategy. I suggest that the mechanism
that limits sperm release by subsequent males may underlie
the effects of mating on weight gain. (Added 6 / 18
/ 2003)
|
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| Corn
Plants Near Discrete Habitat Refugia (Small Straw Piles)
in Conventionally-Tilled Fields Show Increased Growth,
and Reduced Insect Damage |
|
Authors
|
Institution
|
| Alan
B. Cady |
Depart.
of Zoology and Depart. Botany, Miami University, Oxford,
Ohio |
| Jon
Tyson |
|
|
Abstract:
The generalist predatory arthropods (GPAs)occupying crop fields
have great potential as agents of biological control. The
endemic species comprising this predator community are finely
adapted to their specific microclimates and communities. Unfortunately,
conventional tillage and harvesting operations are cyclical
and destructive events, forcing the native generalist predator
community to re-colonize these fields each year. Supplying
discrete habitat refugia (small straw piles; 1m X 0.5m) is
a simple and inexpensive means of reducing the impact agricultural
techniques exert on populations of predatory arthropods in
agroecosystems by providing them places to live and reproduce
in the fields before the crops grow and mature. Previous experiments
with such refugia in soybeans showed these straw piles harbored
greatly increased carabid beetle and spider populations. Considering
the drier, more open growth structure of corn, it was hypothesized
that the influence of refugia in corn probably would be greater
than for soy. Experiments with straw refugia in six one-third
hectare conventionally-tilled fields found higher corn yields
and plant growth near refugia, and insect damage was less
for plants near refugia than at control sites. When larger
GPAs were excluded from refugia, plants near those sites had
similar growth and insect damage as plants near unscreened
regugia. Comparisons of soil nutrients in refugia vs. control
sites showed no significant differences, eliminating the possibility
of a "fertilizer effect" influencing corn growth
and yield. Further larger-scale tests are required. This easy
and cheap technique has potential to help farmers increase
yields with little effort and expense. (Added
6 / 12 / 2003)
|
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| A
Banding Technique For Studying Spiders In Pecan Canopies |
|
Authors
|
Institution
|
| Alejandro
Calixto |
Department
of Entomology, Texas A&M University, College Station,
TX |
|
Allen
Dean
|
|
Bill Ree |
| Lisa
Brooks |
| Marvin
Harris |
|
|
Abstract:
Corrugated cardboard band refuges were used to determine phenology
and density of spiders throughout the year on pecan foliage.
Two hundred bands (10 per tree on 20 trees, with each band
2.5"x5", folded over a twig and held by a clothespin)
were attached to the limbs at heights between 1.6- 2 m. They
were left for 7 days, collected, placed into ziplock bags
and replaced; the bags were numbered by tree and returned
to the lab where they were frozen for later analysis. In the
lab, each band was inspected and all spiders and other arthropods
were counted. A total of 20,358 spiders including 63 species
within 17 families were collected using this banding technique.
Hibana sp. (27%), Trachelas mexicanus (10%),
Philodromus sp. (8%), Eris sp. (5%) and Hentzia
sp. (5%) were the most common species encountered. Spiders
are present year round. Phenology consisted of an increase
in number across the year and a reduction, but not disappearance,
during the winter. Increases in numbers were observed in September
and December suggesting an increase in "ballooning"
behavior as a response to the oncoming winter. This method
provides an efficient and inexpensive technique to study spiders
in pecan tree canopies. (Added
6 / 17 / 2003)
|
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|
Prey Selection By The Red Widow Spider (Araneae: Theridiidae)
|
|
Authors
|
Institutions
|
| James
E. Carrel |
Division
of Biological Sciences
University of Missouri-Columbia |
|
Mark
Deyrup
|
Archbold
Biological Station, Lake Placid, FL |
|
|
Abstract:
To ascertain the prey of the red widow spider, Latrodectus
bishopi, hereafter called "RWS", we collected
arthropods trapped in webs of 30 adult females located in
native oak-palmetto scrub at the Archbold Biological Station
after dawn and before dusk for 5 consecutive days in early
spring (March, 1989) and in late spring (May, 2003). We found
that RWS females in early spring fed predominantly on nocturnally
captured coleopterans (80% of prey items), but in late spring
day-active hymenopterans were added to the RWS diet. Analysis
of arthropods collected in aerial-interception traps operated
at different heights in Florida scrub in winter, summer, and
fall suggested that the predilection of RWS for beetles was
a true specialization: coleopterans comprised only between
5 and 18% of the catch. Moreover, unlike hymenopterans and
other arthropod taxa, we found significantly more beetles
in traps operated at 1.5 and 1 m elevation, where RWS webs
were located, than in traps at 0.5 m. Finally, statistical
analysis of patterns of prey captured by individual RWS females
showed that the process was infrequent (£
0.4 prey/spider/day) and random. (Added 5 / 23 / 2003)
|
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| Gastrulation
and Inversion in Spider Development |
| Authors:
R. Crystal Chaw and Steven D. Black |
|
Institution:
Kleinholz Biology Laboratories,
Reed College, Portland, Oregon
|
|
|
Abstract:
No one model of gastrulation in spiders is clearly supported
by data in the literature. In embryos of Zygiella x-notata,
we observed formation of an extracellular-matrix protrusion
not described in other species. This ‘nipple’ forms
prior to cell involution and migrates posteriorly, presumably
reflecting movements of superficial cells. Next, we identified
a distinct site of involution, the cumulus, which is a swelling
several cell layers thick that forms near the origin of the
nipple. Superficial cells move via the cumulus into the interior
as the cumulus migrates posteriorly during gastrulation. After
gastrulation is complete, the internalized cells participate
in the formation of the germ band, which is the primordium
of the ventral aspect of the spider. At this point the embryo
undergoes a massive morphogenetic movement called inversion.
The germ band splits along the ventral midline and the two
halves migrate away from each other to rest on opposite sides
at the equator. After the halves have reached their equatorial
endpoints, cells emerge from the halves to close the embryo
dorsally while a cell sheet migrates from the posterior end
of the embryo to close it ventrally. Despite being a definitive
characteristic of spider development and one of the longer
cellular migrations known in axis formation, inversion has
not been studied beyond its description. Our preliminary investigation
of possible cytoskeletal mechanisms underlying inversion used
confocal imaging of tubulin and actin, and microinjection
of microtubule and microfilament inhibitors. We demonstrate
that inversion does not continue when either system is poisoned.
(Added 4 / 24 / 2003)
|
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| Contrasting
Patterns of Genetic Structuring in Homalonychus (Homalonychidae)
from the Desert Southwest |
|
Authors
|
Institution
|
| Sarah
Crews |
Department
of Biology, San Diego State University, San Diego, CA. |
| Marshal
Hedin |
|
|
Abstract:
The genus Homalonychus includes two species
(H. selenopoides & H. theologus), both distributed
in desert habitats of southwest North America. Prior studies
indicate that H. selenopoides consists of a single
genetic lineage, but that H. theologus is separated
into two deeply-divergent mitochondrial lineages (H. theologus
"northern" and "southern"). We have compared
the population history and genetic structuring of H. selenopoides
and H. theologus "northern" using DNA sequence
data. These two lineages are very closely related, show few
apparent ecological differences, and in most places are separated
only by the narrow strip of the Colorado River, although no
apparent geographic barrier exists in the northern Mojave
Desert (vic. Death Valley). Unless landscape or regional histories
have been very different, we might expect these spider lineages
to exhibit similar patterns of genetic structuring. This expectation
is not corroborated by our data. Instead, sequence data indicate
that H. selenopoides is highly genetically-structured
across the eastern Sonoran desert. Most haplotypes are geographically
confined, and divergent from haplotypes from other sampling
sites, suggesting long-term population fragmentation. Conversely,
the H. theologus "northern" lineage shows
a mosaic population genetic structure. More southerly regions
are genetically structured, much like H. selenopoides.
However, northern populations of this lineage show a pattern
of genetic structuring consistent with recent range expansion,
with a few closely-related haplotypes spread broadly over
space. This apparent N > S range expansion is most obvious
in the Mojave Desert, where the "northern" H.
theologus lineage may actually be displacing the H.
selenopoides lineage.(Added 5 / 23 / 2003)
|
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| Taxonomic
Diversity of Jumping Spiders in Trinidad and Tobago |
|
Authors
|
Institutions
|
| Bruce
Cutler |
University
of Kansas, Lawrence KS |
|
G.
B. Edwards
|
Florida
State Collection of Arthropods, Gainesville FL |
|
|
Abstract:
Trinidad and Tobago consists of two islands on the continental
shelf off the northeast coast of Venezuela. Last year we published
a list of the salticid fauna of this country (Living World,
p. 39-44, 2002), noting 117 species. The majority of specimens
were collected in the lower montane rain forest of the Northern
Range of Trinidad. More intensive collecting in other habitats
should produce more taxa. The number of species in eight salticid
subfamilies was determined. Two non-taxonomic catagories were
also enumerated, antlike and introduced species. The resulting
percentages were compared to other New World regions with
a relatively well catalogued salticid fauna. Unfortunately
no comparable species lists exist for Venezuela or the Guianas
so it is not possible to make a comparison to the nearest
continental areas. In Trinidad and Tobago the largest subfamily
is the "Freyinae" (not formally defined) with 19%
of the species, followed by the Dendryphantinae with 15% and
the Euophryines with 12%. Freyines are a speciose Neotropical
group reaching their greatest diversity in equatorial South
America. Dendryphantines are worldwide with most species in
the New World. Euophryines are another worldwide subfamily
with greatest diversity in the tropics. In comparison on the
Caribbean islands (-Trinidad and Tobago) Euophryinae are the
largest subfamily with 24% of the species. Freyines only constitute
3% of the species. The diversity of salticids of Trinidad
& Tobago more closely resembles that of mainland South
America than of the northern Caribbean. (Added 5 / 30
/ 2003)
|
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| Natural
History, Mating Behavior and Sperm Release in the Haplogyne
Glenognatha emertoni (Araneae: Tetragnathidae) |
|
Author
|
Institution
|
| Anne
Danielson-Francois |
University
of Kansas, Lawrence, KS. |
|
|
Abstract:
Glenognatha emertoni (Simon) is a small tetragnathine
orb-weaver whose habits are unknown and which has previously
been collected under rocks near streams in southern Arizona
and New Mexico. Field observations revealed that adults are
commonly found in vegetation alongside streams, rarely under
rocks, and do not emerge from their retreats until dusk. Adult
individuals and penultimate instar spiders raised to adulthood
were used to examine sperm release and mating behavior in
the laboratory. Unlike most other orb-weaving spiders studied,
the number of sperm released and overall duration of copulation
are not influenced by female mating history in Glenognatha
emertoni. Male G. emertoni release equivalent numbers
of sperm to virgin and non-virgin females, a pattern also
found in a related haplogyne spider, Tetragnatha versicolor.
Males have large ejaculates ranging from a half-million to
one-and-a-half million sperm. Males transfer more than three-quarters
of their ejaculate, on average, to females; these sperm potentially
compete with other males' sperm in the fertilization of a
clutch of approximately 15-30 eggs.(Added
5 / 20 / 2003)
|
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| Spiders
in Texas Pecans |
|
Authors
|
Institutions
|
| Allen
Dean |
Texas
A&M University, Dept. of Entomology, College Station,
TX |
|
Alejandro
Calixto,
|
Texas
Cooperative Extension, College Station, TX |
| Bill
Ree |
| Marvin
Harris |
Texas A&M University, Dept. of Entomology, College
Station, TX |
|
|
Abstract:
Spider fauna in pecan orchards has been sampled using
different collection techniques to determine relative abundance
and distribution through time. Spiders were sampled using
pitfall traps, corrugated cardboard band refuges and other
methods like hand collection. Information presented is intensive
sampling at two locations (Comanche Co. is arid and Robertson
Co. is more humid) in Texas. The most common spider species
occurring in the pecan agroecosystem, and where they were
found (trunk, leaves, nuts, ground, etc) is presented. These
predators are a significant component of the pecan agroecosystem.
Their conservation will contribute to better biocontrol in
agricultural systems and to preserving biodiversity in the
environment. (Added 6 / 17 / 2003)
|
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| The
Effects of Size, Sex, and Reproductive Condition on Thermal
and Desiccation Stress in a Riparian Lycosid Spider (Pirata
sedentarius) |
|
Authors
|
Institutions
|
| Jill
DeVito |
Miami
University, Ohio |
|
Daniel
R. Formanowicz, Jr.
|
University
of Texas at Arlington |
|
|
Abstract:
Within a species, physiological tolerances and thermoregulatory
behaviors may vary among ontogenetic stages or between sexes.
Such different tolerances can strongly affect the ecology
and life history of a species. In a laboratory study, we tested
the hypothesis that Pirata sedentarius Montgomery 1904
are differentially susceptible to thermal/desiccation stress
by size and sex. As predicted, male adults were more susceptible
to thermal/desiccation stress than females. Unexpectedly,
however, juvenile spiders survived longer under thermal/desiccation
stress than adults. Furthermore, female adults without egg
sacs displayed a trend toward higher thermal/desiccation tolerance
than females carrying egg sacs. These results suggest that
for P. sedentarius, microhabitat preferences and/or
thermoregulatory behaviors may change over the course of development,
and may vary 1) between sexes and 2) between females with
and without egg sacs. (Added 5 / 14 / 2003)
|
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| Seismic
communication in a courting male jumping spider (Araneae:Salticidae) |
|
Authors
|
Institutions
|
| Damian
Elias |
Cornell
University |
|
Andrew
Mason
|
University
of Toronto |
| Wayne
Maddison |
University
of Arizona |
| Ronald
Hoy |
Cornell
University |
|
|
Abstract:
While research on spiders has long shown the importance of
vibrations in communication, jumping spiders (Family: Salticidae)
differ from most spiders in that they are visual "specialists",
with vision playing a prominent role in their communication
behaviour. We now show that one species of jumping spider,
Habronattus dossenus, also exhibits a surprising complexity
of signalling behaviour in the vibratory (seismic) modality.
We videotaped courtship behaviour and recorded seismic signals
of males using laser vibrometry and observed that each prominent
visual signal is accompanied by a seismic component. Using
synchronous high-speed video and laser vibrometry we observed
that only one seismic signal component was produced concurrently
with visual signals, with most signals occurring independently.
In order to test the independence of visual and seismic signal
components and identify possible sound production mechanisms,
we performed several signall manipulation experiments where
we attempted to mute males. These experiments suggest that
three independent mechanisms are used to produce seismic signals,
and that the precise temporal coordination of visual and seismic
signals is not due to a common production mechanism. The extensive
use of complex, multicomponent seismic signals orchestrated
with intricate movements of ornamented appendages adds a new
dimension to jumping spider communication.(Added 6 /
12 / 2003)
|
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| Description
Of Populations Of The Colonial Orb-Weaver Parawixia
bistriata In Different Habitats |
|
Author
|
Institution
|
| Florencia
Fernández Campón |
Department
of Ecology and Evolutionary Biology, University of Tennessee |
|
|
Abstract:
Parawixia
bistriata
(Araneidae) is a colonial orb-weaver that occurs from wet
forests to semiarid habitats in subtropical and temperate
regions of South America. In order to examine the effect of
prey levels on colony size I studied colonies under different
prey conditions in populations from the Dry and Wet Chaco
in northern Argentina (referred as dry and wet sites, respectively).
I further examine whether these differences in prey levels
were translated into any difference in development of spiders
that could affect fecundity. Censuses conducted during the
spring-summer season 2002 showed that in colonies comprised
by 6th instar individuals prey availability is not positively
correlated to colony size, but shows the opposite trend. Colony
size was larger in the dry sites, but within-habitat variation
in colony size was similar between habitat types. Life cycle
stages occurred two months later in the dry than in the wet
sites. Results from transplanted colonies suggest that this
delay in stages is due to differences in prey availability.
In contrast, mean spider mass of 6th instar individuals did
not differ between habitats. The number of eggs/sac produce
by female showed the same pattern as spider mass. When reciprocal
transplants of colonies were performed, the changes in local
conditions (most probably prey) were reflected in a larger
number of eggs/sac in colonies transplanted to wet sites,
and fewer eggs/sac in colonies transplanted to dry sites.
These results suggest that prey levels do not affect aggregation
behavior in P. bistriata in the direction showed by
other species (larger colonies under high prey conditions).
However, even though lower prey levels might be delaying development
in dry populations, native individuals from dry sites seem
to be adapted to local prey conditions and, in terms of reproduction,
are as success | |
