Effect of temperature on growth and ingestion rates of Favella sp

This study describes the effect of temperature on the growthand ingestion rates of the tintinnid, Favella sp. cultured withthe dinoflagellate Heterocapsa triquetra. In vivo fluorescencewas used to monitor the change in density of the H. triquetrapopulation over 4- to 5-day periods in control tubes containingonly algae, and in experimental tubes containing algae and tintinnids.A ‘switchover point’ occurred in the temperaturedependency of the growth rate such that below 11.4°C, H.triquetra grew more quickly than Favella sp. and above thistemperature the situation was reversed. Ingestion rates of Favellaon H. triquetra were found to be temperature dependent in anonlinear fashion. The rate doubled (from 2.5 to 5.3 cells animal^–1h^–1) between 11.4 and 16.4°C whereas there was nochange in ingestion rates between 8.0 and 11.4°C, or between16.4 and 21.1°C.     

Antarctic moss carpets facilitate growth of Deschampsia antarctica but not its survival

The vegetation of the Antarctic tundra is dominated by mosses and lichens. Deschampsia antarctica, the Antarctic hairgrass, is one of two vascular plant species which grow along the west coast of the Antarctic Peninsula. However, little is known about its recruitment and interaction with non-vascular tundra plants. Although several authors propose that tolerance and/or competition should be the main forms of interaction between moss carpets and D. antarctica, no relevant studies exist so far. We investigated whether positive interactions are predominant at the Shetland Islands and the west coast of the Antarctic Peninsula and focussed on the role that moss carpets play in the recruitment of D. antarctica. Across the studied zone, D. antarctica showed a significant association with moss carpets, with higher frequencies as well as more and larger individuals than on bare ground. At one site, we conducted moss removal and seedlings transplant experiments to assess the relevance of the moss carpets for different life stages of hairgrass. All experimental individuals survived until the following summer whether the moss carpet was removed or not, but growth rate was significantly lower in tussocks with moss carpets removed. Likewise, tiller size was higher in plants growing in moss carpets than on bare ground. The detected positive interactions with mosses seem to be important for the expansion of D. antarctica, raising the question about their importance under future climate change scenarios.     

Protozoan growth rates in Antarctic lakes

The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057–0.384 h⁻¹), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific growth rates than HNAN (0.0029–0.0059 h⁻¹ and 0.0056–0.0127 h⁻¹, respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and 0.150 h⁻¹ for heterotrophic ciliates, 0.0143 h⁻¹ for a mixotrophic Plagiocampa species and 0.0075 h⁻¹ for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable growth rates seen within and between Antarctic lakes. Accepted: 7 December 1999     

Comparative growth rates and yields of ciliates and heterotrophic dinoflagellates

Growth rates, ingestion rates and grazer yields (grazer volumeproduced/prey volume consumed) were measured for six protozoanspecies (ciliates: Favella sp., Strombidinopsis acuminatum,Uronema sp.; heterotrophic dinoflagellates: Amphidinium sp.,Gymnodinium sp., Noctiluca scintillans) in laboratory batchculture experiments. Comparative growth data indicate that theprymnesiophyte Isochrysis galbana, the prasinophyte Mantoniellasquamata, two cryptophyte species and several autotrophic dinoflagellatespecies were suitable foods for these grazers. When grown onoptimized diets at 13C, maximum ciliate growth rates (range0.77–1.01 day^–1 uniformly exceeded maximum heterotrophicdioflagellate growth rates (range 0.41–0.48 day^–1).A compilation of published data demonstrates that this growthrate difference persists across a range of ciliate and dinoflagellatetaxa and cell sizes. Comparison of volume-specific ingestionrates and yields for the six species studied here showed thatthere was no single explanation for this growth rate disparity.Heterotrophic dinoflagellates exhibited both low ingestion ratesand, in one case, low yields; ciliates were able to achievehigher growth rates via either higher ingestion rates or higheryields, depending on ciliate species. Volume yield increasedover time throughout the exponential growth phase in nearlyall experiments, suggesting variation in response to changingfood concentrations or long-term acclimation to culture conditions.Higher maximum ciliate growth rates mean that these grazershave the potential to exercise tighter control over incipientblooms of their prey than do heterotrophic dinoflagellates.     

Sexual selection constrains the body mass of male but not female mice

Sexual size dimorphism results when female and male body size is influenced differently by natural and sexual selection. Typically, in polygynous species larger male body size is thought to be favored in competition for mates and constraints on maximal body size are due to countervailing natural selection on either sex; however, it has been postulated that sexual selection itself may result in stabilizing selection at an optimal mass. Here we test this hypothesis by retrospectively assessing the influence of body mass, one metric of body size, on the fitness of 113 wild‐derived house mice (Mus musculus) residing within ten replicate semi‐natural enclosures from previous studies conducted by our laboratory. Enclosures possess similar levels of sexual selection, but relaxed natural selection, relative to natural systems. Heavier females produced more offspring, while males of intermediate mass had the highest fitness. Female results suggest that some aspect of natural selection, absent from enclosures, acts to decrease their body mass, while the upper and lower boundaries of male mass are constrained by sexual selection.     

Wingless promotes cell survival but constrains growth during Drosophila wing development

During animal development, organs grow to a fixed size and shape. Organ development typically begins with a rapid growth phase followed by a gradual decline in growth rate as the organ matures, but the regulation of either stage of growth remains unclear. The Wnt/Wingless (Wg) proteins are critical for patterning most animal organs, have diverse effects on development and have been proposed to promote organ growth. Here we report that contrary to this view, Wg activity actually constrains wing growth during Drosophila melanogaster wing development. In addition, we demonstrate that Wg is required for wing cell survival, particularly during the rapid growth phase of wing development. We propose that the cell-survival- and growth-constraining activities of Wg function to sculpt and delimit final wing size as part of its overall patterning programme.     

Systemic but not intraovarian concentrations of insulin-like growth factor-I are affected by short-term fasting.

To determine whether systemic and/or intraovarian concentrations of insulin-like growth factor-I (IGF-I) are affected by short-term fasting, 24 heifers were blocked by weight and, within block, were assigned to one of three treatments: fasted for 0 h (controls; n = 8), fasted for 24 h (n = 8), or fasted for 48 h (n = 8). Blood plasma was collected every 8 h from -64 h to 0 h before ovariectomy (OVEX). OVEX was performed per vagina under local anesthesia during the follicular phase of an estrous cycle (36-42 h after synchronization with prostaglandin-F2 alpha). Follicular fluid (FFL) and granulosa cells were collected individually from follicles greater than or equal to 6 mm (large), and FFL was pooled from follicles 1.0-5.9 mm (small) in diameter. Fasting did not affect (p greater than 0.20) the number (mean +/- SE) of small (52 +/- 7) or large (1.5 +/- 0.4) follicles per heifer, specific binding of 125I-hCG to granulosa cells of follicles greater than or equal to 8 mm in diameter, or concentrations of progesterone in FFL of small follicles. At OVEX, body weight was less (p less than 0.01) for 24 h- and 48 h-fasted heifers (412 +/- 7 kg and 399 +/- 7 kg, respectively) than for 0 h-fasted heifers (442 +/- 7 kg). At OVEX, plasma concentrations of IGF-I were lower (p less than 0.05) in the 48 h-fasted group (105 +/- 8 ng/ml) than in the 0 h-fasted group (140 +/- 8 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of temperature on the growth rates of halotolerant and halophilic bacteria isolated from Antarctic saline lakes

Summary The effect of temperature on the growth rates of Halomonas subglaciescola and a Halobacterium sp., halotolerant and halophilic bacteria isolated from Antarctic saline lakes, was predicted accurately by models which propose a linear relationship between temperature and the square root of the reciprocal of the growth rate. The cardinal temperatures of the strains examined were in general 5–10°C lower than those of taxonomic counterparts isolated from temperate and tropical environments. Temperature dependence data for strains of the Halobacterium sp. and annual temperature profiles of Deep Lake allowed estimation of the in situ potential for growth.     

Effects of ingesting mercury-containing bacteria on mercury tolerance and growth rates of ciliates

The ciliateUronema nigricans was found to acquire tolerance to mercury after being fed mercury-laden bacteria followed by exposure of washed suspensions of these ciliates to various concentrations of mercury in solution. Significant differences in percent mortality were observed for ciliates fed mercury-laden bacteria compared with control suspensions fed mercury-free bacteria. The phenomenon of acquired mercury tolerance was demonstrated within a single generation time. Ciliates fed mercury-free bacteria and subsequently exposed to increasing levels of mercury in solution showed an elevated tolerance to concentrations which, on initial testing, resulted in mortality of 83% of the ciliate population. The effect of ingesting mercury-laden bacteria on growth rate ofUronema was examined, and results showed no significant differences in growth rates of both 3- and 14-day-old cultures of protozoa that had been fed mercury-laden and mercury-free bacteria under controlled conditions.     

Discovery of ciliates reproducing in the gut of Antarctic krill

During a recent Antarctic research cruise (December 1994/February 1995), dissection of fresh Antarctic krill (Euphausia superba) on board ship revealed live motile ciliates in the gut of krill. Further observation of gut samples by scanning electron microscopy indicated that the ciliates were symbionts located within the gut. We inferred that the ciliates may have enabled the krill to digest a wider range of food items, and as a consequence, this had became an important strategy for Antarctic krill's survival in the Antarctic ecosystem. Received: 1 August 1996 / Accepted: 1 December 1996     

Enforced exercise, but not acute temperature elevation, decreases venous capacitance in the stenothermal Antarctic fish Pagothenia borchgrevinki

The venous haemodynamic response to enforced exercise and acute temperature increase was examined in the Antarctic fish Pagothenia borchgrevinki (borch) to enable comparisons with the existing literature for temperate species, and investigate if the unusual cardiovascular response to temperature changes previously observed in the borch can be linked to an inability to regulate the venous vasculature. Routine central venous blood pressure (P (cv)) was 0.08 kPa and the mean circulatory filling pressure (P (mcf); an index of venous capacitance) was 0.14 kPa. Acute warming from 0 to 2.5 and 5 degrees C increased heart rate (f (H)), while dorsal aortic blood pressure (P (da)) decreased. P (mcf) did not change, while P (cv) decreased significantly at 5 degrees C. This contrasts with the venoconstriction previously observed in rainbow trout in response to increased temperature. Exercise resulted in small increases in P (mcf) and P (cv), a response that was abolished by alpha-adrenoceptor blockade. This study demonstrates that the heart of P. borchgrevinki normally operates at positive filling pressures (i.e. P (cv)) and that venous capacitance can be actively regulated by an alpha-adrenergic mechanism. The lack of decrease in venous capacitance during warming may suggest that a small increase in venous tone is offset by a passive temperature-mediated increase in compliance.     

Thermodynamics constrains the evolution of insect population growth rates: "warmer is better"

Diverse biochemical and physiological adaptations enable different species of ectotherms to survive and reproduce in very different temperature regimes, but whether these adaptations fully compensate for the thermodynamically depressing effects of low temperature on rates of biological processes is debated. If such adaptations are fully compensatory, then temperature-dependent processes (e.g., digestion rate, population growth rate) of cold-adapted species will match those of warm-adapted species when each is measured at its own optimal temperature. Here we show that cold-adapted insect species have much lower maximum rates of population growth than do warm-adapted species, even when we control for phylogenetic relatedness. This pattern also holds when we use a structural-equation model to analyze alternative hypotheses that might otherwise explain this correlation. Thus, although physiological adaptations enable some insects to survive and reproduce at low temperatures, these adaptations do not overcome the "tyranny" of thermodynamics, at least for rates of population increase. Indeed, the sensitivity of population growth rates of insects to temperature is even greater than predicted by a recent thermodynamic model. Our findings suggest that adaptation to temperature inevitably alters the population dynamics of insects. This result has broad evolutionary and ecological consequences.     

Resource-use-related traits correlate with population turnover rates, but not stem diameter growth rates, in 29 subtropical montane tree species

The relationships between species’ functional traits and their demographic life histories are central to understanding the causes of life-history diversity. A previous study identified three independent demographic axes amongst 29 broadleaved tree species: a light-demand axis, a population turnover rate (r–K) axis, and one discriminating substrate requirements for recruitment. This study evaluates the basis of life-history variation amongst the 29 species by assessing the correlation between the three demographic axes above and 14 morphological, phenological, architectural and biomass-partitioning traits. A principal components analysis of the 14 traits revealed two main axes: (1) a ‘resource capture versus conservation’ axis separated species with large and thin leaf laminas, high leaf K, P and N concentrations, light wood and small seeds from species with opposite attributes, and (2) a ‘physiognomic’ axis separated species with compound leaves, high leaf/above-ground mass ratio, and tall first branch in saplings from species with opposite attributes. Subsequent paired correlations and a Procrustes superimposition analysis showed that species with attributes typical of high capture and low conservation of resources, small seeds and short stature had faster population turnover rates (short longevity, and high mortality and recruitment rates) than species with opposite attributes. Species with compound leaves, high leaf/above-ground mass ratio, and tall first branch as saplings (physiognomic axis) tended to be more light-demanding and to have fast diameter growth rates of stems 10 cm diameter. The independence between attributes typical of resource capture or conservation and stem diameter growth rate is noteworthy; it differs from correlations often reported for saplings and could be attributed to ontogenetic changes in plant function. In addition, the clear link between attributes typical of resource capture or conservation and plant recruitment, survivorship and longevity is consistent with r–K theory and brings to light an important connection between a leading axis of plant evolutionary diversification (resource capture versus conservation) and rates of population turnover.     

Volcanic explosive eruptions of the Vesuvio decrease tree-ring growth but not photosynthetic rates in the surrounding forests

Volcanic eruptions impact the global and the hemispheric climate, but it is still unknown how and to what degree they force the climate system and in particular the global carbon cycle. In this paper, the relationships between individual eruptions (reconstructed for the past using written records), tree primary productivity (estimated using ring widths), photosynthetic rate and stomatal conductance (assessed by carbon and oxygen isotope data) are investigated, to understand the impact of volcanic eruptions on net primary production. Data from a mixed stand of Fagus sylvatica L. and Acer pseudoplatanus L. located in the area of the Vesuvio volcanic complex (Southern Italy) showed a significant decrease in ring width following each eruption. Isotope analyses indicate a change in climatic conditions after such events. Specifically, the lower oxygen isotope ratio in the tree‐ring cellulose strongly suggests an increase in relative humidity and a decrease in temperature, with the latter resulting in a strong limitation to tree‐ring growth. The carbon isotope ratio was only moderately but not significantly reduced in the years of volcanic eruption, suggesting no major changes in C fixation rates. This work is a case study on the effects of volcanic eruptions resulting in strong climatic changes on the local scale. This is an opportunity to explore the process and causal relationships between climatic changes and the response of the vegetation. Thus, we propose here a realistic model scenario, from which we can extrapolate to global scales and improve our interpretations of results of global studies.     

Within-cultivar differences in relative leaf growth rates at low temperature of onion seedlings are not heritable

Onion seedlings of two open-pollinated cultivars were grown either at a constant 10°C or outdoors in spring and were selected for high, medium or low relative leaf growth rate, R_L. Flowering plants within each R_L group were crossed using controlled pollination for the 10°C selections and as a fly-pollinated polycross for the outdoor selections. The pollen donors of the 10°C selections were also selfed. Despite the wide variation of R_L in the parent populations, there was no indication of heritability of R_L. Mean R_L was significantly lower for the progeny from self-rather than cross-pollinations as was initial leaf area and rate of seedling emergence.     

Elevated spring temperature stimulates growth, but not smolt development, in anadromous Arctic charr

Parr–smolt transformation and growth were studied in captive offspring of anadromous Arctic charr (Salvelinus alpinus) from the Hals watercourse in northern Norway (70°N), held either at a natural temperature (< 1 °C until May) or at a temperature elevated to 6 °C in late March. In mid-May, 5 weeks after the increase in photoperiod from 8:16 h light:dark to continuous light, gill Na⁺, K⁺-ATPase activity started to increase in both temperature groups, concurrent with the final development of full seawater tolerance. Temperature had no effect on the development of gill Na⁺, K⁺-ATPase activity, or on hypoosmoregulatory ability. The fish in both treatments resumed growth in mid-May, but from then on growth was faster in the elevated than in the ambient temperature group. In the former group, fish mass doubled in 6 weeks (from 65 to 137 g), and growth ceased at the time when the fish were about to complete their parr–smolt transformation. These findings show that an early vernal temperature increase advances the seasonal growth cycle, but not the parr–smolt transformation, in anadromous Arctic charr.     

Basal cold but not heat tolerance constrains plasticity among Drosophila species (Diptera: Drosophilidae)

Thermal tolerance and its plasticity are important for understanding ectotherm responses to climate change. However, it is unclear whether plasticity is traded‐off at the expense of basal thermal tolerance and whether plasticity is subject to phylogenetic constraints. Here, we investigated associations between basal thermal tolerance and acute plasticity thereof in laboratory‐reared adult males of eighteen Drosophila species at low and high temperatures. We determined the high and low temperatures where 90% of flies are killed (ULT₉₀ and LLT₉₀, respectively) and also the magnitude of plasticity of acute thermal pretreatments (i.e. rapid cold‐ and heat‐hardening) using a standardized, species‐specific approach for the induction of hardening responses. Regression analyses of survival variation were conducted in ordinary and phylogenetically informed approaches. Low‐temperature pretreatments significantly improved LLT₉₀ in all species tested except for D. pseudoobscura, D. mojavensis and D. borealis. High‐temperature pretreatment only significantly increased ULT₉₀ in D. melanogaster, D. simulans, D. pseudoobscura and D. persimilis. LLT₉₀ was negatively correlated with low‐temperature plasticity even after phylogeny was accounted for. No correlations were found between ULT₉₀ and LLT₉₀ or between ULT₉₀ and rapid heat‐hardening (RHH) in ordinary regression approaches. However, after phylogenetic adjustment, there was a positive correlation between ULT₉₀ and RHH. These results suggest a trade‐off between basal low‐temperature tolerance and acute low‐temperature plasticity, but at high temperatures, increased basal tolerance was accompanied by increased plasticity. Furthermore, high‐ and low‐temperature tolerances and their plasticity are clearly decoupled. These results are of broad significance to understanding how organisms respond to changes in habitat temperature and the degree to which they can adjust thermal sensitivity.     

Rainfall,but not temperature,negatively affects the growth of Blue Tit Cyanistes caeruleus nestlings

Capsule: Growth trajectories of Blue Tit Cyanistes caeruleus nestlings differed between sexes and were negatively affected by rain but not by temperature during the linear growth phase (LGP).

Aims: To model the growth trajectories of Blue Tit nestlings and to identify the main ecological factors affecting them.

Methods: Sixty-five nestling Blue Tits from a population in northern Italy were weighed at regular intervals and sexed using molecular genetic techniques. The LGP period was identified and analysed to test for the influence of age, sex, hatching date, brood size, temperature and rainfall on individual daily growth rates during the LGP.

Results: Growth curves showed no pre-fledging mass loss. Body mass differed between the sexes, with males being 5% heavier than females at the pre-fledging stage. Daily growth rates during the LGP were higher for males and on non-rainy days, while they were not affected by other factors.

Conclusion: The higher daily growth rate observed in males during the LGP may determine the extent of sexual size dimorphism at the pre-fledging stage. Susceptibility of growth trajectories to environmental conditions was limited to rainfall and was similar in the two sexes. This contrasts with findings from previous studies, which found sex-biased environmental sensitivity of Blue Tit nestlings.     

Helpers increase long-term but not short-term productivity in cooperatively breeding long-tailed tits

Helpers at the nest in the cooperative breeding system of long-tailedtits Aegithalos caudatus exhibit kin preference in their helpingbehavior. The aim of this study was to use multivariate analysesto investigate whether helpers accrue indirect fitness benefitsthrough their cooperation by increasing the productivity ofrelatives. All birds started each season breeding independentlyin pairs, but birds that failed in their own breeding attemptoften redirected their care to help another pair provision theiroffspring. About half of all broods had one or more helpers,86% of which were male. Provisioning rates increased and therewas a corresponding increase in the mass of nestlings withinbroods as the number of helpers increased. Helpers had no significantshort-term effect on productivity because nest predation, nestlingsurvival, and brood size were unaffected by the presence ofhelpers. However, in the long term helpers had a highly significanteffect on the recruitment of fledglings, the positive effectof helpers being linear within the range of helper numbers thatwe observed. We found no evidence to suggest that these resultswere confounded by the effects of individual or habitat quality.We conclude that long-tailed tits accrue indirect fitness benefitsby helping kin. Nevertheless, the inclusive fitness benefitfrom helping is substantially lower than that of independentbreeding, showing that helpers are making the best of a badjob.