1,893 research outputs found
Toxicity of pesticides adsorbed to suspended sediment to larval fish in the Cedar River
How do suspended sediment and pesticides introduced into Iowa streams and rivers by erosion of agricultural soil affect warm water fish? This study looks at how chlorpyrifos, a widely used pesticide, and suspended sediment interact with each other in river water and their effects on the survival of larval walleye
Senescence in duckweed: age-related declines in survival, reproduction, and offspring quality
Sherpa Romeo yellow journal (pre-print only, accepted for publication)As they grow old, most organisms experience progressive physiological deterioration
resulting in declining rates of survival and reproduction â a seemingly maladaptive
phenomenon known as senescence.
Although senescence is usually defined with respect only to survival and reproduction, a
third component of fitness, offspring quality, may also decline with age. Few studies,
however, have assessed age-related changes in offspring quality using measures that truly reflect fitness.
In a controlled environment, we tested for age-related declines in three demographic
components of fitness (survival, reproduction, and offspring quality) in Lemna minor, a
small aquatic plant in the subfamily Lemnoideae (the duckweeds) with a short lifespan and rapid rate of asexual reproduction. Our primary measure of offspring quality, the intrinsic rate of increase, more closely approximates fitness than measures used in previous studies such as size, lifespan, and total reproductive output.
We observed strong age-related declines in all three components of fitness: old plants
had lower rates of survival and reproduction, and produced lower-quality offspring than
younger plants. Theoretical and empirical research on the evolutionary biology of senescence should
devote more attention to offspring quality. This often unrecognized component of fitness
may change with age â as we have shown in L. minor â and may be shaped by, and feed
back into, the same evolutionary forces that give rise to senescence
A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor)
Sherpa Romeo yellow journal (pre-print only; accepted for publication)Classic theories on the evolution of senescence make the simplifying assumption that all
offspring are of equal quality, so that demographic senescence only manifests through
declining rates of survival or fecundity. However, there is now evidence that, in addition to
declining rates of survival and fecundity, many organisms are subject to age-related
declines in the quality of offspring produced (i.e. parental age effects). Recent modelling
approaches allow for the incorporation of parental age effects into classic demographic
analyses, assuming that such effects are limited to a single generation. Does this âsingle generationâ assumption hold? To find out, we conducted a laboratory study with the aquatic
plant Lemna minor, a species for which parental age effects have been demonstrated
previously. We compared the size and fitness of 423 lab-cultured plants (asexually-derived
ramets) representing various birth orders, and ancestral âbirth-order genealogiesâ. We
found that offspring size and fitness both declined with increasing âimmediateâ birth order
(i.e. birth order with respect to the immediate parent), but only offspring size was affected
by ancestral birth order. Thus, the assumption that parental age effects on offspring fitness
are limited to a single generation does in fact hold for L. minor. This result will guide
theorists aiming to refine and generalise modelling approaches that incorporate parental age effects into evolutionary theory on senescence
Offspring of older parents are smaller-but no less bilaterally symmetrical-than offspring of younger parents in the aquatic plant Lemna turionifera
Open access provided under the terms of the Creative Commons Attribution LicenseOffspring quality decreases with parental age in many taxa, with offspring of older parents exhibiting reduced life span, reproductive capacity, and fitness, compared to offspring of younger parents. These âparental age effects,â whose consequences arise in the next generation, can be considered as manifestations of parental senescence, in addition to the more familiar age- related declines in parent- generation survival and reproduction. Parental age effects are important because they may have feedback effects on the evolution of demographic trajectories and longevity. In addition to altering the timing of offspring life-history milestones, parental age effects can also have a negative impact on offspring size, with offspring of older parents being smaller than offspring of younger parents. Here, we consider the effects of advancing parental age on a different aspect of offspring morphology, body symmetry. In this study, we followed all 403 offspring of 30 parents of a bilaterally symmetrical, clonally reproducing aquatic plant species, Lemna turionifera, to test the hypothesis that successive offspring become less symmetrical as their parent ages, using the âContinuous Symmetry Measureâ as an index. Although successive offspring of aging parents older than one week became smaller and smaller, we found scant evidence for any reduction in bilateral symmetryYe
Competitive intransitivity, population interaction structure, and strategy coexistence
Sherpa Romeo green journal. Permission to archive accepted author manuscriptIntransitive competition occurs when competing strategies cannot be listed in a hierarchy, but rather
form loops â as in the game Rock-Paper-Scissors. Due to its cyclic competitive replacement, competitive
intransitivity promotes strategy coexistence, both in Rock-Paper-Scissors and in higher-richness communities. Previous work has shown that this intransitivity-mediated coexistence is strongly
influenced by spatially explicit interactions, compared to when populations are well mixed. Here, we
extend and broaden this line of research and examine the impact on coexistence of intransitive
competition taking place on a continuum of small-world networks linking spatial lattices and regular
random graphs. We use simulations to show that the positive effect of competitive intransitivity on
strategy coexistence holds when competition occurs on networks toward the spatial end of the
continuum. However, in networks that are sufficiently disordered, increasingly violent fluctuations in
strategy frequencies can lead to extinctions and the prevalence of monocultures. We further show that
the degree of disorder that leads to the transition between these two regimes is positively dependent
on population size; indeed for very large populations, intransitivity-mediated strategy coexistence may
even be possible in regular graphs with completely random connections. Our results emphasize the
importance of interaction structure in determining strategy dynamics and diversity
Fitness declines toward range limits and local adaptation to climate affect dispersal evolution during climate-induced range shifts
Sherpa Romeo yellow journal (pre-print only, accepted for publication)Dispersal
ability
will
largely
determine
whether
species
track
their
climatic
niches
during
climate
change,
a
process
especially
important
for
populations
at
contracting
(low-Âlatitude/low-Âelevation)
range
limits
that
otherwise
risk
extinction.
We
investigate
whether
dispersal
evolution
at
contracting
range
limits
is
facilitated
by
two
processes
that
potentially
enable
edge
populations
to
experience
and
adjust
to
the
effects
of
climate
deterioration
before
they
cause
extinction:
a)
climate-Ââinduced
fitness
declines
toward
range
limits,
and
b)
local
adaptation
to
a
shifting
climate
gradient.
We
simulate
a
species
distributed
continuously
along
a
temperature
gradient
using
a
spatially
explicit,
individual-Ââ
based
model.
We
compare
range-Ââwide
dispersal
evolution
during
climate
stability
vs.
directional
climate
change,
with
uniform
fitness
vs.
fitness
that
declines
toward
range
limits
(RLs),
and
for
a
single
climate
genotype
vs.
multiple
genotypes
locally
adapted
to
temperature.
Dispersal
decreased
toward
stable
RLs
when
range-Ââwide
fitness
was
uniform,
but
increased
when
fitness
declined
toward
RLs,
due
to
highly
dispersive
genotypes
maintaining
sink
populations
at
RLs,
increased
kin
selection
in
smaller
populations,
and
an
emergent
fitness
asymmetry
that
favoured
dispersal
in
low-Ââquality
habitat.
However,
this
initial
dispersal
advantage
at
low-Ââfitness
RLs
did
not
facilitate
climate
tracking,
as
it
was
outweighed
by
an
increased
probability
of
extinction.
Locally-Ââadapted
genotypes
benefited
from
staying
close
to
their
climate
optima;
this
selected
against
dispersal
under
stable
climates
but
for
increased
dispersal
throughout
shifting
ranges,
compared
to
cases
without
local
adaptation.
Dispersal
increased
at
expanding
RLs
in
most
scenarios,
but
only
increased
at
the
range
centre
and
contracting
RLs
given
local
adaptation
to
climate
Reasoning from connectives and relations between entities
This article reports investigations of inferences that depend both on connectives between clauses, such as or else, and on relations between entities, such as in the same place as. Participants made more valid inferences from biconditionalsâfor instance, Ann is taller than Beth if and only if Beth is taller than Cathâthan from exclusive disjunctions (Exp. 1). They made more valid transitive inferences from a biconditional when a categorical premise affirmed rather than denied one of its clauses, but they made more valid transitive inferences from an exclusive disjunction when a categorical premise denied rather than affirmed one of its clauses (Exp. 2). From exclusive disjunctions, such as Either Ann is not in the same place as Beth or else Beth is not in the same place as Cath, individuals tended to infer that all three individuals could be in different places, whereas in fact this was impossible (Exps. 3a and 3b). The theory of mental models predicts all of these results
A Keck/HIRES Doppler Search for Planets Orbiting Metal-Poor Dwarfs. I. Testing Giant Planet Formation and Migration Scenarios
We describe a high-precision Doppler search for giant planets orbiting a
well-defined sample of metal-poor dwarfs in the field. This experiment
constitutes a fundamental test of theoretical predictions which will help
discriminate between proposed giant planet formation and migration models. We
present here details on the survey as well as an overall assessment of the
quality of our measurements, making use of the results for the stars that show
no significant velocity variation.Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical
Journa
A review of the McMorran diet for rearing lepidoptera species with addition of a further 39 species
Sherpa Romeo blue journalResearch on cutworms led us to explore the use of the McMorran diet to rear lepidopteran species, mainly
Noctuidae, under laboratory conditions. We documented the development of 103 lepidopteran species, including
39 species not previously reported in the literature, to be reared on this diet. Given its low cost, ease of preparation,
and wide speciesâ acceptance, this diet provides a powerful tool for facilitating Lepidoptera and other
insects rearing and research in the laboratory.Ye
A review of diapause and tolerance to extreme temperatures to dermestids (Coleoptera)
Sherpa Romeo green journal. Permission to archive accepted author manuscript.Numerous species in Family Dermestidae (Coleoptera) are important economic pests of stored
goods of animal and vegetal origin, and museum specimens. Reliance on chemical methods for
of control has led to the development of pesticide resistance and contamination of treated
products with insecticide residues. To assess its practicality as an alternate method of control,
we review the literature on the tolerance of dermestids to extreme hot and cold temperatures.
The information for dermestid beetles on temperature tolerance is fragmentary, experimental
methods are not standardized across studies, and most studies do not consider the role of
acclimation and diapause. Difficulties in determining the diapause status of dermestid larvae
may explain the lack of studies. The few studies that do examine these factors show that they
can greatly increase tolerance to cold temperatures. The use of extreme temperatures will
need to target the most tolerant life stage, which for dermestids at cold temperatures will
potentially be the cold-acclimated individuals in diapause. The development of effective
protocols will be facilitated by studies that clearly and completely describe experimental and
statistical methods, consider factors (life-stage, acclimation, diapause) that increase tolerance
to extreme temperatures, and assess the mortality at various temperatures to develop
mathematical models
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