Thermal Physiological Ecology of Drosophila mojavensis (Diptera:
Drosophilidae) in Northwest Mexico: a model of evolution of life-history
parameters.
***IMPORTANT***
If Gibbs has published his D. mojavensis thermal environment paper, this
will include the model. If not, make the modeling effort a second
paper.***
Ask the question “Why are Tmin for developmental time and T m a x for progeny
number (i) different and (ii) the values that they actually are?”, and address it with
the model.
Phrase it thusly: “It would seem that, since short generation time and high numbers
of progeny are ‘favored’ in a colonizing species such as D. mojavensis, the
optimal T r o t for each would coincide. Or, “A priori,
**********************************************************************
Really cool concept – the cycle time of the environment is longer than the life span
of the flies. A fly can be pretty certain its progeny will encounter different
thermal conditions that it has experienced.
As discussed in *** and ***, r is an appropriate fitness parameter to use in
treatment of life history evolution if
I used formula 4 in Lewontin (1965) to estimate the value of r (= intrinsic rate of
increase) for different rearing Tamb regimes (using the mean Tamb for the variable Tamb
regimes). Certainly, early in the season, when population sizes are very small and new
rots await invasion, D. mojavensis would experience conditions similar to those
encountered by a colonizing species (**potentially high r, limited competition, ?? =
"limited population pressures" (Lewontin, 1965, p. 78)**). **Under such circumstances,
with the population in the exponential growth phase, selection should favor early
reproduction (= short developmental times).**
e. Fluctuating temperatures produce constant-mass flies, so we can leave mass out of
the equation, and Developmental Time & number of flies emerging at a given
temperature become the major factors.
Predicted seasonal changes in r for the study population are presented in Figure 8.
**********************************************************************
The details of the model are presented in the Materials and Methods. We can use its
output to address the question “Why don’t the optimal temperatures for maximizing
production of progeny and mi nimizing developmental time coincide?”
-90: 23/23, 23/18 >
28/23, 28/18
>
28/28
-60: 23/18
>
23/23, 28/18
>
28/23
>
28/28
-30: 23/18
>
23/23, 28/18
>
28/23, 28/28
0: 23/18
>>
23/23
>
28/18
>
28/23,
28/28
30: 23/18, 23/23 >
28/18
>
28/23, 28/28
60: 23/23
>
23/18, 28/23, 28/28 >
28/18
90: 28/28
>
28/23
>
23/23, 28/18, 23/18
120: 28/28
>>
28/23
>
28/18
>
23/23,
23/18
135: 28/28
>>
28/23
>
28/18
>>
23/23,
23/18
1. Explicitly list the assumptions of the model:
That population pressures aren’t important (let’s see what could happen if, for
example, flies could disperse all over the place when they eclose). This
assumption is probably ok, because any female that manages to find a rot would
‘want’ her progeny’s development to be optimized.
Note that I don’t have any information on the effects of precipitation regime: do wet/dry
years affect the flies via their effect on rot conditions?
There would be two benefits to having a high r (due to short generation time) at the end
of the season: more progeny produced from a new rot that’s colonized late in the
season and ‘ability’ to take advantage of a slightly longer growing season (should it
occur).
“Most alternative combinations of developmental time and progeny number would
seem to be better -- in terms of population size at the end of the season -- if
‘summed’ over the whole growing season. However, it is unlikely that D.
mojavensis works this way.
Really moist rots are ephemeral and conditions therein deteriorate as the rot ages.
And, new rots appear. Both of these situations favor colonizing ability, and,
therefore, a high r. ”
2. The optimal genotype would produce require a short generation time & produce a big
fly, especially early in the season.
3. 51. How does r relate to individual fitness? Check Stearns, Kowalski, K** &
Stearns.
4. 52. Isn’t Reproductive Value a function of population growth rate?
5. 53. What happens to the value of r if minimum developmental time shifts
downward?
6. 54. Note that the simulation of the effects of shifting the minimum developmental
time downward by 5o probably makes an unrealistic assumptions about the ‘breadth’
of the developmental rate curve (it assumes that development can continue even if
T a is more than 5o above the minimum point (which our lab data don’t
support....can’t rear ’em above 34o or so, only 6 o above the developmental-rate
curve’s minimum). The results in Fig. ** (r in the wild) are therefore ‘conservative’
in that the value of r at high T a (late in the season) is probably unrealistically high.
7. 55. Also, all the simulations assume that a mean T a of 35o is an effective upper
limit for development in D. mojavensis.
8. 58. Comparison of the simulation results:
“We wished to investigate the effect of shifting the thermal ‘optimum’ for the
Developmental Time (i.e., T amb giving the minimum developmental times) and
Progeny number (the T amb resulting in the maximum number of adult progeny)
curves, assuming that each optimum could ‘evolve’ independently of the other. We
also assumed that egg-to-adult survivorship was 10%, and that females were capable
of reproduction 2 days after they eclosed (***). We used the data on T rot in Figure
** as the basis ***. We also assumed that ‘population pressures’ (Lewontin, 1965)
in the rots were not significant in terms of affecting larval/pupal development and
survival, at least compared with the rearing conditions in our laboratory experiments.
We assume that the number of surviving progeny at the end of the growing
season is an important fitness parameter. This is because the flies are entering a
phase in their annual cycle when (apparently) no reproduction or development takes
place and one or more dormant life stages survive to ‘found’ the population the
following autumn. During this phase, mortality is probably density-independent to a
great extent and survival probability depends on ‘choice’ of **hiding place**.
For the first simulation, we started the populations growing on October 1 and
calculated the number of surviving progeny at the end on the growing season (June 1
of the following year). Under this scenario, ‘genotypes’ with minimum
developmental time at 28o produced essentially the same result (final population size
ranged from 39.9 - 40.7 flies; Table **) regardless of the thermal optimum for the
Progeny Number curve. However, shifting the minimum developmental time to 23 o
markedly increased the population size, to more than 50 flies. This result would
suggest that there is strong selective pressure favoring a shift in the Developmental
Time curve optimum towards lower T am . However, this may not be the most
appropriate model to use.
Rots are ephemeral. Next we assumed that a rot last for 60 days and calculated the
number of progeny that each ‘genotype’(**) could produce in that time. Under such
circumstances, the two curves with Developmental Time minimum at 23o produce higher
Simulations to be done:
Vary the lifespan of flies with rearing T a .
Calculate total population size on May 1 for different scenarios – this probably is not
the relevant parameter; I suspect Dmoj is a colonizing species for which ability to
locate and rapidly reproduce in new rots.
Consider
varying starting time of the runs (= date when conditions become suitable in the
Fall);
varying the ending time of the runs (= date when conditions become too hot in the
Spring);
throwing in some realistic year-to-year variation in T a pattern; i.e., vary the mean
T a , the amplitude of the variation in T a (have a cold winter, a hot fall and/or
spring, etc.), the timing of cooling/warming, rapidity of cooling/warming, .
varying the length of time the rots persist, while keeping thermal regime constant
(to see if variation in precipitation regime, via its possible effect on rot
persistence, affects the simulations’ outcome)
Restrict the range of the ‘tolerance/performance curves so that the flies can’t have an
optimum at 23o or 18o and still function when T a is in the low 30’s.
Change the code for d:\tc\bin\dmoj_sim.cpp, so that it:
??Asks me to specify parameter values?? Which would those be?
Does all the calculations for Julian Date from –90 to 150 in a single pass.
Stops if the current generation can’t complete development.
Writes the output to a file (can I use long file names?).
Only lets the performance curves extend for a certain number of oC (5? 10?) above the
optimum.
Make sure that the code is stopping if current generation can’t complete
development!!
.
RELEVANT REFERENCES:
Trait evolution in an individual-based model of herbaceous vegetation
Warren J, Topping C
EVOLUTIONARY ECOLOGY
v. 15(#1) pp. 15-35 2001
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Univ Wales, Inst Rural Studies, Llanbadarn Fawr, Aberystwyth SY23 3AL, Ceredigion,
Wales
Univ Wales, Inst Rural Studies, Aberystwyth SY23 3AL, Ceredigion, Wales
NERI, Dept Landscape Ecol, DK-8410 Ronde, Denmark
Abstract:
Many theoretical studies of evolution are based upon the concepts of the evolutionary
stable strategy and optimal life-history solutions. An individual based model of
vegetation is used to simulate life-history evolution under two different sets of
environmental conditions. At one level the results suggest that optimal life-history
solutions do appear to evolve. At the end of the simulations the vegetation that evolved in
a fertile and uncut environment was taller, thinner and germinated later than that which
developed in a less fertile and cut habitat. However, between simulation variation was
observed to be high, particularly for the parameter regulating the timing of reproduction,
and it showed no indication of reaching fixation. When this trait was prevented from
mutating, the variances of other traits were seen to increase. Although at the population
level between simulation variation was high, some traits achieved a degree of stability
within simulations, suggesting that multiple adaptive peaks may be being approached.
However, there was little evidence of trait fixation occurring within the most abundant
'genotype'. It is considered that frequency dependent selection/Red Queen dynamics may
be acting to prevent the most abundant 'genotype' from reaching fixation. It is argued that
if such processes prevent optimal genetic solutions from being achieved then the search
for evolutionary stable strategies within the evolution of life-histories may be over
simplistic.
Reproductive effort in variable environments, or environmental variation is for the
birds
Orzack SH, Tuljapurkar S
ECOLOGY
v. 82(#9) pp. 2659-2665 SEP 2001
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Institutions:
Fresh Pond Res Inst, 64 Fairfield St, Cambridge, MA 02140 USA
Fresh Pond Res Inst, Cambridge, MA 02140 USA
Stanford Univ, Dept Biol Sci, Stanford, CA 94305 USA
Abstract:
We analyze a model of life history evolution in which there is a temporally variable cost
of reproduction. Analysis of the stochastic growth rate indicates that the optimal clutch
size in a variable environment can be substantially increased or decreased relative to the
optimal clutch size in a constant environment. This finding holds regardless of whether
the cost of reproduction varies discretely or continuously. Our results also illustrate how
two distinct optimal life histories can evolve in response to a given amount of
environmental variability. One life history pays a cost of reproduction that is relatively
fixed and small on average (by producing a small fixed clutch size); it can always
produce an optimal clutch size but is unable to exploit highly favorable environments.
The other pays a cost of reproduction that is variable and large on average (by producing
a large fixed clutch size); it cannot always produce an optimal clutch size but is able to
exploit highly favorable environments.
Reproductive asynchrony increases with environmental disturbance
Post E, Levin SA, Iwasa Y, Stenseth NC
EVOLUTION
v. 55(#4) pp. 830-834 APR 2001
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Institutions:
Penn State Univ, Dept Biol, Mueller Lab 208, University Pk, PA 16802 USA
Univ Oslo, Dept Biol, Div Zool, N-0316 Oslo, Norway
Princeton Univ, Dept Ecol & Evolutionary Biol, Princeton, NJ 08544 USA
Kyushu Univ, Fac Sci, Dept Biol, Fukuoka 8128581, Japan
Abstract:
While it is widely recognized that the manner in which organisms adjust their timing of
reproduction reflects evolutionary strategies aimed at minimizing offspring mortality or
maximizing reproductive output, the conditions under which the evolutionarily stable
strategy involves synchronous or asynchronous reproduction is a matter of considerable
discord. A recent theoretical model predicts that whether a population displays
reproductive synchrony or asynchrony will depend on the relative scales of intrinsic
regulation and environmental disturbance experienced by reproducing individuals. This
model predicts that, under conditions of negligible competition and large-scale
environmental perturbation, evolution of a single mixed strategy will result in
asynchronous reproduction. We tested this prediction using empirical data on large scale
climatic fluctuation and the annual timing of reproduction by three species of flowering
plants covering 1300-population-years and four degrees of latitude in Norway. In
agreement with model predictions, within populations of all three species reproductive
asynchrony increased with the magnitude of large-scale climatic perturbation, but bore no
relation to the strength of local density dependence. These results suggest that mixed
evolutionarily stable strategies can arise from the interplay of combinations of agents of
selection and the scale at which they operate; hence it is fruitless to associate
synchronous versus asynchronous timing with particular single factors like climate,
competition, or predation.
The evolutionary ecology of life history variation in the garter snake Thamnophis
elegans
Bronikowski AM, Arnold SJ
ECOLOGY
v. 80(#7) pp. 2314-2325 OCT 1999
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Institutions:
UNIV WISCONSIN,DEPT ZOOL,432 LINCOLN DR,MADISON,WI 53706
UNIV CHICAGO,COMM EVOLUTIONARY BIOL,CHICAGO,IL 60637
UNIV CHICAGO,DEPT ECOL & EVOLUT,CHICAGO,IL 60637
Abstract:
The purpose of this study was to document the extent of variation in individual growth
rates and its fitness consequences among several populations of an indeterminate grower,
the western terrestrial garter snake Thamnophis elegans. Twenty years of mark-recapture
data and six years of laboratory breeding data provided evidence of large differences
among six populations in individual growth rates and subsequent reproductive
maturation, fecundity, and survival. Weather, diet composition, and prey availability
were examined for their effects on individual growth. Two ecotypes were revealed whose
distribution coincided with differences in prey availability. Individuals from populations
that had continuous access to prey and water across years exhibited fast growth, early
maturation, high fecundity, and low adult survival. In contrast, individuals from
populations that experienced variable prey availability exhibited slow growth, late
maturation, low fecundity, and high adult survival. This growth rate variation was
examined in the context of two competing explanations: the maximization and
optimization hypotheses. Food availability may be a primary limiting factor to growth
and subsequent life history traits, which is consistent with the maximization hypothesis.
However, negative phenotypic correlations between growth and survival and between
growth and reproduction may indicate an underlying negative genetic correlation,
consistent with the trade-off hypothesis. Field studies such as this one are useful for
documenting the patterns of life history variation that occur in nature, identifying
possible causes of such variation, and generating testable hypotheses for controlled
experiments.
Rain forest canopy cover, resource availability, and life history evolution in guppies
Grether GF, Millie DF, Bryant MJ, Reznick DN, Mayea W
ECOLOGY
v. 82(#6) pp. 1546-1559 JUN 2001
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Institutions:
Univ Calif Los Angeles, Dept Organism Biol Ecol & Evolut, Los Angeles, CA 90095
USA
Univ Calif Los Angeles, Dept Organism Biol Ecol & Evolut, Los Angeles, CA 90095
USA
USDA ARS, Mote Marine Lab, Sarasota, FL 34236 USA
Univ Calif Riverside, Dept Biol, Riverside, CA 92521 USA
Univ Calif Santa Barbara, Dept Ecol Evolut & Marine Biol, Santa Barbara, CA 93106
USA
Abstract:
Life history traits in guppies (Poecilia reticulata) vary geographically along a predator
assemblage gradient, and held experiments have indicated that the association may be
causal; guppies introduced from high predation sites to low predation sites have evolved
the phenotype associated with low predation in as few as seven generations. It has long
been recognized, however that low predation sites tend to have greater forest canopy
cover than high predation sites. Stream differences in canopy cover could translate into
stream differences in resource availability, another theoretically potent agent of selection
on life history traits. Moreover, new computer simulations indicate that the high
predation phenotype would outcompete the low predation phenotype under both mortality
regimes. Thus, predation alone may not be sufficient to explain the observed life history
patterns, Here we show that food availability for guppies decreases as forest canopy
cover increases, among six low predation streams in the Northern Range of Trinidad.
Streams with less canopy cover received more photosynthetically active light and
contained a larger standing crop of algae (the primary food of guppies), as measured by
algal pigment:, (chlorophylls and carotenoids) on both natural cobble and artificial tile
substrates, but did not contain a greater biomass of guppies (per square meter of
streambed). Consequently, algae availability for guppies (in micrograms of algal
pigments per milligram of guppy) increased with decreasing canopy cover. The biomass
of guppies and algae both decreased after a series of floods, with no net effect on algae
availability. Field mark-recapture studies revealed that female and juvenile guppies grew
faster. and that the asymptotic size of mature males was larger, in streams with less
canopy cover. Canopy cover explained 84% of the variation among streams in algae
availability which, in turn, explained 93% of the variation in guppy growth rates.
Laboratory "common garden" experiments indicated that the stream differences in growth
and adult male size in the field were largely environmental (nongenetic). These results
strongly suggest that stream differences in canopy cover result in consistent stream
differences in food availability, independent of predation. Our preliminary data indicate
that some life history traits (offspring size and litter size) vary genetically along the
canopy cover gradient, among low predation streams, in the same direction a's along the
predation gradient. Another recent study shows that food availability is higher at high
predation sites than at low predation sires, partly as an indirect effect of predators
reducing guppy densities. Further research is required to disentangle the direct effects of
predation from those of resource availability in the evolution of life histories.
The effects of pond duration on the life history traits of an ephemeral pond
crustacean, Eulimnadia texana
Marcus V, Weeks SC
HYDROBIOLOGIA
v. 359 pp. 213-221 DEC 30, 1997
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Institutions:
UNIV AKRON,DEPT BIOL,AKRON,OH 44325
Abstract:
We examined the relationship between pond duration and life history characters of the
clam shrimp Eulimnadia texana, a species inhabiting ephemeral ponds in southwestern
North America. Since the shrimp live in temporary habitats, we predicted that there
should be high selection pressure on life history characteristics associated with rapid
development (e.g., fast growth, early maturity, etc.), rather than selection for increased
longevity. Pond duration was estimated using a combination of average monthly rainfall
and pond size (surface to volume ratio). Shrimp that live in smaller ponds thigh surface to
volume ratio) in areas with low average rainfall should, on average, experience a shorter
total time available for development than those in larger ponds or in areas of higher
rainfall. These shrimp should have an earlier age at maturity, reduced longevity, lower
fecundity, and faster growth. Five replicate populations of clam shrimp were collected as
cysts from five ponds. These shrimp were raised in a common garden experiment in the
laboratory. Daily measurements of growth and egg production were taken and ages at
maturity and death were recorded. Shrimp from areas with higher average rainfall had
slower growth, higher fecundity, greater longevity, and an earlier age at maturity than
those from areas with lower average rainfall. If average rainfall is an accurate measure of
pond duration, then the first three of these life history traits differ in the directions
expected. However, age at maturity varied in a manner opposite to that expected, being
earlier in the ponds with longer duration. Surface to volume ratio was not helpful in
further resolving differences in these life history characters.
Evolution of intrinsic growth and energy acquisition rates. II. Trade-offs with
vulnerability to predation in Menidia menidia
Lankford TE, Billerbeck JM, Conover DO
EVOLUTION
v. 55(#9) pp. 1873-1881 SEP 2001
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Institutions:
SUNY Stony Brook, Marine Sci Res Ctr, Stony Brook, NY 11794 USA
SUNY Stony Brook, Marine Sci Res Ctr, Stony Brook, NY 11794 USA
SUNY Stony Brook, Dept Ecol & Evolut, Stony Brook, NY 11794 USA
Abstract:
The Atlantic silverside (Menidia menidia) exhibits countergradient latitudinal variation
in somatic growth rate along the East Coast of North America. Larvae and juveniles from
high-latitude populations display higher intrinsic rates of energy consumption and growth
than genotypes from low-latitude populations. The existence of submaximal growth in
some environments suggests that trade-offs must counter the oft-cited theoretical benefits
of energy and growth maximization (e.g., "bigger is better,'' "faster is better") in the
immature life stages. We hypothesized that energy and growth maximization trades off
against investment in defense from predators. We conducted laboratory selection
experiments to compare vulnerability to predation of silversides from: (1) fast-growing
northern (Nova Scotia, NS) versus slow-growing southern (South Carolina, SC) source
populations; (2) phenotypically manipulated fast-growing versus moderately-growing NS
fish; and (3) recently fed versus unfed NS and SC fish. Tests involved fish drawn from
common-garden environments and were conducted by subjecting mixed-treatment
schools of size-matched silversides to natural, common piscine predators. NS silversides
suffered significantly higher predation mortality than SC silversides. Parallel results were
found in phenotypic manipulation of growth: NS silversides reared on a fast-growth
trajectory (similar to1.0 mm/day) were significantly more vulnerable to predation than
those growing at a moderate rate (similar to0.5 mm/day). Food consumption also
affected vulnerability to predators: Silversides with large meals in their stomachs suffered
significantly higher predation mortality than unfed silversides. Differences in predation
vulnerability were likely due to swimming performance, not attractiveness to predators.
Our findings demonstrate that maximization of energy intake and growth rate engenders
fitness costs in the form of increased vulnerability to predation.
Phenotypic plasticity in colonizing populations of Drosophila subobscura
Pegueroles G, Mestres F, Argemi M, Serra L
GENETICS AND MOLECULAR BIOLOGY
v. 22(#4) pp. 511-516 DEC 1999
Institutions:
UNIV BARCELONA,FAC BIOL,DEPT GENET,AV DIAGONAL 645,E-08071
BARCELONA,SPAIN
UNIV BARCELONA,FAC BIOL,DEPT GENET,E-08071 BARCELONA,SPAIN
Abstract:
The phenotypic plasticity of some quantitative traits of two colonizing populations of
Drosophila subobscura (Davis and Eureka, California) was studied. Temperature effects
and the effect of rearing in the laboratory were studied. Laboratory rearing during four
generations at 18 degrees C significantly increased the wing and tibial length. This
increase was similar to that obtained when the flies were reared at 13 degrees C during
two generations. The low temperature environment can be considered more stressful for
females than for males, as shown by the increase of phenotypic variance. The two
populations analyzed had great phenotypic plasticity in spite of the genetic bottleneck
during the colonization event. Our study shows that keeping flies for a relatively short
time in the laboratory significantly changes some quantitative traits, emphasizing the
need to analyze flies immediately after collecting them in order to obtain reliable
estimates for the analysis of these traits in natural populations.
Landscape dynamics and evolution of colonizer syndromes: interactions between
reproductive effortand dispersal in a metapopulation
Ronce O, Perret F, Olivieri I
EVOLUTIONARY ECOLOGY
v. 14(#3) pp. 233-260 2000
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Institutions:
Univ Montpellier, Inst Sci Evolut, Pl Eugene Bataillon, F-34059 Montpellier 05, France
Univ Montpellier, Inst Sci Evolut, F-34059 Montpellier 05, France
Abstract:
The evolutionary consequences of changes in landscape dynamics for the evolution of
life history syndromes are studied using a metapopulation model. We consider in turn
the long-term effects of a change in the local disturbance rate, in the maximal local
population persistence, in habitat productivity, and in habitat fragmentation. We examine
the consequences of selective interactions between dispersal and reproductive effort by
comparing the outcome of joint evolution to a situation where the species has lost the
potential to evolve either its reproductive effort or its dispersal rate. We relax the
classical assumption that any occupied site in the metapopulation reaches its carrying
capacity immediately after recolonization. Our main conclusions are the following: (1)
genetic diversity modifies the range of landscape parameters for which the
metapopulation is viable, but it alters very little the qualitative evolutionary trends
observed for each trait within this range. Although they are both part of a
competition/colonization axis, reproductive effort and dispersal are not substitutable
traits: their evolution reflects more directly the change in the landscape dynamics, than a
selective interaction among them. (2) no general syndrome of covariation between
reproductive effort and dispersal can be predicted: the pattern of association between the
two traits depends on the type of change in landscape dynamics and on the saturation
level. We review empirical evidence on colonizer syndromes and suggest lines for further
empirical work.