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GAPDH as a control gene to estimate genome copy number in Great Tits, with cross-amplification in Blue Tits
No full textEstimating the number of genome copies in a tissue sample can serve various purposes. For example, such an estimate serves as scaling variable when measuring telomeres with quantitative PCR. We describe the primer development and evaluation for the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene in the Great Tit Parus major, as a control gene to estimate genome copy number. We demonstrate specific amplification with negligible variation in 48 Great Tits and cross-amplification in 53 Blue Tits Cyanistes caeruleus. We conclude this primer set to be reliable for amplification of GAPDH as a reference gene for quantitative PCR analysis in Great and Blue Tits.
Population growth in a wild bird is buffered against phenological mismatch
No full textroad-scale environmental changes are altering patterns of natural selection in the wild, but few empirical studies have quantified the demographic cost of sustained directional selection in response to these changes. We tested whether population growth in a wild bird is negatively affected by climate change–induced phenological mismatch, using almost four decades of individual-level life-history data from a great tit population. In this population, warmer springs have generated a mismatch between the annual breeding time and the seasonal food peak, intensifying directional selection for earlier laying dates. Interannual variation in population mismatch has not, however, affected population growth. We demonstrated a mechanism contributing to this uncoupling, whereby fitness losses associated with mismatch are counteracted by fitness gains due to relaxed competition. These findings imply that natural populations may be able to tolerate considerable maladaptation driven by shifting climatic conditions without undergoing immediate declines.
Predicting demographically-sustainable rates of adaptation: can great tit breeding time keep pace with climate change?
No full textPopulations need to adapt to sustained climate change, which requires micro-evolutionary change in the long term. A key question is how the rate of this micro-evolutionary change compares with the rate of environmental change, given that theoretically there is a ‘critical rate of environmental change’ beyond which increased maladaptation leads to population extinction. Here, we parametrize two closely related models to predict this critical rate using data from a long-term study of great tits (Parus major). We used stochastic dynamic programming to predict changes in optimal breeding time under three different climate scenarios. Using these results we parametrized two theoretical models to predict critical rates. Results from both models agreed qualitatively in that even ‘mild’ rates of climate change would be close to these critical rates with respect to great tit breeding time, while for scenarios close to the upper limit of IPCC climate projections the calculated critical rates would be clearly exceeded with possible consequences for population persistence. We therefore tentatively conclude that micro-evolution, together with plasticity, would rescue only the population from mild rates of climate change, although the models make many simplifying assumptions that remain to be tested.
Mixotrophic organisms become more heterotrophic with rising temperature
No full textThe metabolic theory of ecology predicts that temperature affects heterotrophic processes more strongly
than autotrophic processes. We hypothesized that this differential temperature response may shift mixotrophic
organisms towards more heterotrophic nutrition with rising temperature. The hypothesis was tested
in experiments with the mixotrophic chrysophyte Ochromonas sp., grown under autotrophic, mixotrophic
and heterotrophic conditions. Our results show that (1) grazing rates on bacterial prey increased more
strongly with temperature than photosynthetic electron transport rates, (2) heterotrophic growth rates
increased exponentially with temperature over the entire range from 13 to 33 °C, while autotrophic growth
rates reached a maximum at intermediate temperatures and (3) chlorophyll contents during mixotrophic
growth decreased at high temperature. Hence, the contribution of photosynthesis to mixotrophic growth
strongly decreased with temperature. These findings support the hypothesis that mixotrophs become more
heterotrophic with rising temperature, which alters their functional role in food webs and the carbon cycle.
Soil and Freshwater and Marine Sediment Food Webs: Their Structure and Function
No full textThe food webs of terrestrial soils and of freshwater and marine sediments depend on adjacent aboveground or pelagic ecosystems for organic matter input that provides nutrients and energy. There are important similarities in the flow of organic matter through these food webs and how this flow feeds back to primary production. In both soils and sediments, trophic interactions occur in a cycle in which consumers stimulate nutrient cycling such that mineralized resources are made available to the primary producers. However, aquatic sediments and terrestrial soils differ greatly in the connectivity between the production and the consumption of organic matter. Terrestrial soils and shallow aquatic sediments can receive organic matter within hours of photosynthesis when roots leak carbon, whereas deep oceanic sediments receive organic matter possibly months after carbon assimilation by phytoplankton. This comparison has implications for the capacity of soils and sediments to affect the global carbon balance.
Determining patterns of variability in ecological communities: time lag analysis revisited
No full textAll ecological communities experience change over time. One method to
quantify temporal variation in the patterns of relative abundance of communities is
time lag analysis (TLA). It uses a distance-based approach to study temporal community
dynamics by regressing community dissimilarity over increasing time lags
(one-unit lags, two-unit lags, three-unit lags). Here, we suggest some modifications
to the method and revaluate its potential for detecting patterns of community change.
We apply Hellinger distance based TLA to artificial data simulating communities with
different levels of directional and stochastic dynamics and analyse their effects on the
slope and its statistical significance. We conclude that statistical significance of the
TLA slope (obtained by a Monte Carlo permutation procedure) is a valid criterion
to discriminate between (i) communities with directional change in species composition,
regardless whether it is caused by directional abundance change of the species
or by stochastic change according to a Markov process, and (ii) communities that
are composed of species with population sizes oscillating around a constant mean
or communities whose species abundances are governed by a white noise process.
TLA slopes range between 0.02 and 0.25, depending on the proportions of species
with different dynamics; higher proportions of species with constant means imply
shallower slopes; and higher proportions of species with stochastic dynamics or directional
change imply steeper slopes. These values are broadly in line with TLA slopes
from real world data. Caution must be exercised when TLA is used for the comparison
of community time series with different lengths since the slope depends on time series
length and tends to decrease non-linearly with it.
Effects of root herbivory on pyrrolizidine alkaloid content and aboveground plant-herbivore-parasitoid interactions in Jacobaea vulgaris
No full textThe importance of root herbivory is increasingly recognized in ecological studies, and the effects of root herbivory on plant growth, chemistry, and performance of aboveground herbivores have been relatively well studied. However, how belowground herbivory by root feeding insects affects aboveground parasitoid development is largely unknown. In this study, we examined the effects of root herbivory by wireworms (Agriotes lineatus) on the expression of primary and secondary compounds in the leaves and roots of ragwort (Jacobaea vulgaris). We also studied the effects of root herbivory on the performance of a generalist aboveground herbivore, Mamestra brassicae and its parasitoid Microplitis mediator. In contrast to what most other studies have reported, root herbivory in J. vulgaris had a strong negative effect on the total concentration of pyrrolizidine alkaloids (PAs) in shoot tissues. The composition of PAs in the shoots also changed after root herbivory. In particular, the concentration of less toxic N-oxide PAs decreased. There was no significant effect of root herbivory on PA composition and concentration in the roots. Although the concentration of PA in the leaves decreased, M. brassicae tended to grow slower on the plants exposed to root herbivory. Parasitoid performance was not affected by root herbivory, but parasitoids developed faster when the concentration of jacobine-type PAs in the foliage was higher. These results point at a putative role of individual PAs in multitrophic interactions and emphasize that generalizations about aboveground-belowground effects should be made with great caution.