10.5061/DRYAD.VDNCJSXSS
Henriques, Jorge
0000-0001-5463-8737
Center for Ecology, Evolution and Environmental Changes (CE3C)
Lacava, Mariángeles
University of the Republic
Guzman, Celeste
Spanish National Research Council
Gavín-Centol, Maria Pilar
Spanish National Research Council
Ruiz-Lupión, Dolores
Spanish National Research Council
De Mas, Eva
Spanish National Research Council
Magalhães, Sara
University of Lisbon
Moya-Laraño, Jordi
Spanish National Research Council
Data from: The sources of variation for individual prey-to-predator size ratios
Dryad
dataset
2020
FOS: Biological sciences
additive variance
dominance variance
maternal variance
common environmental variance
Ministry of Education and Science
https://ror.org/053pcb396
Fundação para a Ciência e a Tecnologia (Portuguese Science and
Technology Foundation):PD/BD/106059/2015
Ministerio de Educación Cultura y Deporte
https://ror.org/03nc27g21
FPU13/04933
Ministry of Economy, Industry and Competitiveness
https://ror.org/034900433
CGL2015-66192-R
Regional Government of Andalusia
https://ror.org/01jem9c82
P12-RMN-1521
2020-12-17T00:00:00Z
2020-12-17T00:00:00Z
en
68746 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
The relative body size at which predators are willing to attack prey, a
key trait for predator-prey interactions, is usually considered invariant.
However, this ratio can vary widely among individuals or populations.
Identifying the range and origin of such variation is key to understanding
the strength and constraints on selection in both predators and prey.
Still, these sources of variation remain largely unknown. We filled this
gap by measuring the genetic, maternal and environmental variation of the
maximum prey-to-predator size ratio (PPSRmax) in juveniles of the wolf
spider Lycosa fasciiventris using a paternal half-sib split brood design,
in which each male was paired with two different females and the offspring
reared in two different food environments: poor and rich. Each juvenile
spider was then sequentially offered crickets of decreasing size and the
maximum prey size killed was determined. We also measured body size and
body condition of spiders upon emergence and just before the trial. We
found low, but significant heritability (h2=0.069) and dominance and
common environmental variance (d2+4c2=0.056). PPSRmax was also partially
explained by body condition (during trial) but there was no effect of the
rearing food environment. Finally, a maternal correlation between body
size early in life and PPSRmax indicated that offspring born larger were
less predisposed to feed on larger prey later in life. Therefore, PPSRmax,
a central trait in ecosystems, can vary widely and this variation is due
to different sources, with important consequences for changes in this
trait in the short and long terms.
Spider collection Individuals of Lycosa fasciiventris were collected from
June 23rd to July 27th 2015 in four different localities within the
Almeria province (South-East Spain), in dry temporal washes (“ramblas”):
1) around Paraje las Palmerillas, Estación Experimental de Cajamar
(36.7917°N, 2.6891°O); 2) near Boca de los Frailes village (36.8036°N,
2.1386°O); 3) near Carboneras village (36.9667°N, 2.1019°O) and 4) near
Almanzora river (37.3414°N, 2.0078°O). Individuals were then kept
separately in the laboratory in a container (22 x 18 x 18 cm) with the
bottom filled with 2-3 cm of soil collected from the sampling sites. Two
wooden blocks (10 x 8 x 1 cm and 3 x 5 x 1 cm) were added to each tank to
provide shelter. Only sub-adult virgin females were used to form the
laboratory population. All individuals (adult and sub-adult males, and
sub-adult females) were fed once a week with size-matched crickets
(Gryllus assimilis; Fabricius 1775) purchased from a pet supply online
store Exofauna, Spain (available in: https://exofauna.com). Spiders had
access to water ad libitum through a 40 ml vial filled with water and
covered with cotton. Tanks were placed in a climate chamber with simulated
outdoor climatic conditions (day and night temperature cycles and
photoperiod with light fluorescent tubes of 54 W, mimicking natural
sunshine, and a relative humidity from 50 to 65%). Climatic conditions
were adjusted to the preceding weekly average conditions in the Almeria
province, with day-night temperature and light oscillations (temperature:
18.7-34.3 °C; light-dark photoperiod: 17:7-16:8 hours). Breeding design To
assess genetic, maternal and environmental variation in individual
prey-to-predator size ratio (PPSR), we performed a paternal half-sib
split-brood design (Roff 1997; Lynch and Walsh 1998), in which 52 males
(sires) were each mated with two virgin females (dams). Each week,
offspring were provided with fruit flies (Drosophila melanogaster; Meigen,
1830) originated from cultures produced in the laboratory. Flies were fed
with a nitrogen rich medium supplemented with high quality dogfood, which
highly improves spider survival (Jensen et al. 2011). Maternal families
were constituted by 12 offspring, split into two food availability
treatments, varying in the number of flies provided. Thus, 3 out of 12
offspring from each maternal family were assigned to the rich environment,
being given 3× the amount of food provided in the poor (or standard)
environment. Initially, a single fly was offered to the spiders in the
poor treatment and 3 flies in the richer treatment. This quantity was
adjusted to 3 and 9 when individuals were approximately 6 months old due
to higher food demand at that stage. After hatching, spiderlings of wolf
spiders climb to the female back and, in L. fasciiventris, remain with it
for a period of a few weeks (Parellada 1998). Due to logistic reasons, all
spiderlings were removed from the female back within one week, that is
approximately 42 ± 8 (mean ± SD) days after they hatched (age at
isolation). To estimate and control for post-hatching common environmental
effects occurring on the female back, the age at isolation was included in
all models. This variable was never significant (data not shown).
Spiderlings were carefully collected from the female back with the help of
a paintbrush. We took 12 spiderlings from each female and placed them
separately in cylindrical containers (5 cm height and 6 cm diameter). Each
container had the bottom covered with filter paper, providing a substrate
for both locomotion and absorption of excreta, inside the growth chamber.
Filter papers were checked weekly and replaced if necessary. A plastic tip
was inserted at the bottom of the container, filled with cotton connected
to a reservoir, providing water ad libitum to spiders by capillarity
(Moskalik and Uetz 2011). The 1248 spiderling containers were then
randomly arranged within the growth chamber to ensure that individuals
belonging to the same family were spatially interspersed. This allowed
mitigating possible common environmental effects after spiderling
isolation from their mothers. Morphometry Body components were divided
between structural body size (carapace width; Hagstrum 1971) and body
condition (residuals of abdomen width on carapace width; (Jakob et al.
1996). Body condition reflects energy and nutrient storage independently
on the size of the spider and thus reflects hunger level (Moya-Laraño et
al. 2008). Structural body size may reflect the strength to subdue prey
(e.g., Moya-Laraño et al. 2002). Both carapace and abdomen width were
measured at their widest point. Body size and body condition were measured
in two instances: after individuals were taken from their mothers and
isolated, and immediately before the trials for acceptance. Morphometric
measurements were taken to the nearest 0.1 mm with a dissection microscope
(Leica MZ125). While structural body size measured at the time of trial
was needed to calculate prey-to-predator size ratio, body condition at the
time of the trial was used to control for the hunger state of each
spiderling (i.e. its motivational state). These traits were also measured
early in life and used to calculate genetic and maternal correlations, to
test how maternal investment in both offspring body size and condition
could affect behavioural patterns of the spiders later in life. Prey
acceptance This experiment aimed to measure the maximum relative size of a
prey cricket (Gryllus assimilis) that a spider accepted, considering a
range of cricket lengths (in mm) decreasing from 5× to 1× (in units of 1)
the carapace width of the spider. For that, we placed them in experimental
arenas where each spider was offered crickets in a decreasing order of
relative size until it subdued and killed a cricket. The response
variable, prey-to-predator size ratio (PPSR) is the ratio at which the
spider attacks and kills the cricket. This measure corresponds to the
maximum PPSR (PPSRmax) at which predators kill their prey and the larger
the relative size of the prey killed, the higher the PPSR. Spiders were
measured in blocks of 17 ± 5 (mean ± SD) individuals. Each block was
defined as the experimental batch of individuals assessed in each day.
Although this cricket species does not occur in the study site, L.
fasciiventris is able to effectively prey on it, and a similar species
with similar body size, Gryllus bimaculatus, is highly abundant in the
collection area (Moya-laraño personal observation). As it was not feasible
to collect G. bimaculatus in numbers enough to carry out this study, we
used G. assimilis individuals from an established laboratory population.
Note that this approach allowed testing the response of spiders that were
naive to this prey, as all spiders had been fed with Drosophila to that
point. Thus, this approach minimized environmental variation due to
potential effects of previous experiences with cricket prey. In the
trial, we used crickets with a length that differed from the target PPSR
(5×, 4×, 3×, 2× or 1× of the width of the spider carapace) by less than
0.2 units. Crickets were weighted, and their length determined from a
calibration curve, previously generated with the weight and length of 40
crickets: L = 3.22 + 0.32log(M); R2 = 0.99; p < 0.0001; where L is
cricket body length (in mm) and M is cricket body mass (in mg). Mass was
measured to the nearest 0.1 mg using a high precision scale (Mettler
Toledo XP26). None of the crickets were used in more than one trial. To
standardize hunger levels across individuals, spiders were left to starve
for seven days before being tested, similarly to other studies (Persons
and Rypstra 2000). As it was not possible to standardize age across
trials, individuals were randomly assigned to each trial. Spider age at
the time of each measurement (331 ± 30 days old, mean ± SD) was recorded
and later controlled for in the statistical analysis as a covariate (see
below). A single spider and one cricket were placed inside the arena (7.5
cm diameter), in opposite sides, within enclosed inverted plastic vials (3
cm diameter). Then, both vials were gently lifted simultaneously, and
crickets and spiders were allowed to interact for 6 minutes. If the
cricket was not captured and subdued, the spider was enclosed in the vial
and the cricket was removed. Spiders were then left to recover in the vial
for 30 minutes until a new cricket from the next immediately lower size
was presented (lower PPSR). Trials ended as soon as the spider attacked
and killed a cricket or if the spider did not catch the smallest (1×)
cricket.
Data used to assess the sources of variation of the maximum
prey-to-predator size ratio (PPSRmax) in juveniles of the wolf spider
Lycosa fasciiventris using a paternal half-sib split brood design.