Aleksandra Walczyńska

The Temperature–Size Rule in Lecane inermis (Rotifera) is adaptive and driven by nuclei size adjustment to temperature and oxygen combinations ☆

The evolutionary implications of the Temperature-Size Rule (TSR) in ectotherms is debatable; it is uncertain whether size decrease with temperature increase is an adaptation or a non-adaptive by-product of some temperature-dependent processes. We tested whether (i) the size of the rotifer Lecane inermis affects fecundity in a way that depends on the combination of low or high temperature and oxygen content and (ii) the proximate mechanism underlying TSR in this species is associated with nuclei size adjustment (a proxy of cell size). Small-type and large-type rotifers were obtained by culturing at different temperatures prior to the experiment and then exposed to combinations of two temperature and two oxygen conditions. Fecundity was estimated and used as a measure of fitness. Nuclei and body sizes were measured to examine the response to both environmental factors tested. The results show the following for L. inermis. (i) Body size affects fecundity in response to both temperature and oxygen, supporting a hypothesis regarding the contribution of oxygen in TSR. (ii) Large individuals are generally more fecund than small ones; however, under a combination of high temperature and poor oxygen conditions, small individuals are more fecund than large ones, in accordance with a hypothesis of the adaptive significance of TSR. (iii) The body size response to temperature is realised by nuclei size adjustment. (iv) Nuclei size changes in response to temperature and oxygen conditions, in agreement with hypotheses on the cellular mechanism underlying TSR and on a contribution of oxygen availability in TSR. These results serve as empirical evidence for the adaptive significance of TSR and validation of the cellular mechanism for the observed response.

Inter- and intraspecific relationships between performance and temperature in a cryptic species complex of the rotifer Brachionus plicatilis

AbstractThe strategy of decreasing size with increasing temperature operates at regional and phenotypic scale and presents a puzzle to researchers. In this work, we studied two aspects of the temperature–performance relationship along a temperature gradient, (i) comparing the population growth rates of three cryptic Brachionus species differing in adult size, and (ii) assessing the phenotypic plasticity of adult size, in one clone per species. The working hypotheses were that (i) the bigger the species the lower its optimal temperature for population growth, and (ii) the higher the temperature the smaller the individual within each focal species. The results showed that (i) the optimal temperature for population growth is related to species size in a manner foreseen by Bergmanns’ rule for two of the three species (the third, biggest species, performed evenly well at all temperatures examined, what could be explained by its generally eurioic character), and that (ii) the strategy of body size adjustment to environmental temperature differs between species and may depend on the level of temperature specialization. This work demonstrated the usefulness of inter- and intraspecific comparisons for studying the role of growth strategies in adaptation to temperature.

Seasonal changes in the body size of two rotifer species living in activated sludge follow the Temperature-Size Rule.

Temperature-Size Rule (TSR) is a phenotypic body size response of ectotherms to changing temperature. It is known from the laboratory studies, but seasonal patterns in the field were not studied so far. We examined the body size changes in time of rotifers inhabiting activated sludge. We hypothesize that temperature is the most influencing parameter in sludge environment, leading sludge rotifers to seasonally change their body size according to TSR, and that oxygen content also induces the size response. The presence of TSR in Lecane inermis rotifer was tested in a laboratory study with two temperature and two food-type treatments. The effect of interaction between temperature and food was significant; L. inermis followed TSR in one food type only. The seasonal variability in the body sizes of the rotifers L. inermis and Cephalodella gracilis was estimated by monthly sampling and analyzed by multiple regression, in relation to the sludge parameters selected as the most influential by multivariate analysis, and predicted to alter rotifer body size (temperature and oxygen). L. inermis varied significantly in size throughout the year, and this variability is explained by temperature as predicted by the TSR, but not by oxygen availability. C. gracilis also varied in size, though this variability was explained by both temperature and oxygen. We suggest that sludge age acts as a mortality factor in activated sludge. It may have a seasonal effect on the body size of L. inermis and modify a possible effect of oxygen. Activated sludge habitat is driven by both biological processes and human regulation, yet its resident organisms follow general evolutionary rule as they do in other biological systems. The interspecific response patterns differ, revealing the importance of taking species-specific properties into account. Our findings are applicable to sludge properties enhancement through optimizing the conditions for its biological component.

The underestimated role of temperature–oxygen relationship in large‐scale studies on size‐to‐temperature response

Abstract The observation that ectotherm size decreases with increasing temperature (temperature‐size rule; TSR) has been widely supported. This phenomenon intrigues researchers because neither its adaptive role nor the conditions under which it is realized are well defined. In light of recent theoretical and empirical studies, oxygen availability is an important candidate for understanding the adaptive role behind TSR. However, this hypothesis is still undervalued in TSR studies at the geographical level. We reanalyzed previously published data about the TSR pattern in diatoms sampled from Icelandic geothermal streams, which concluded that diatoms were an exception to the TSR. Our goal was to incorporate oxygen as a factor in the analysis and to examine whether this approach would change the results. Specifically, we expected that the strength of size response to cold temperatures would be different than the strength of response to hot temperatures, where the oxygen limitation is strongest. By conducting a regression analysis for size response at the community level, we found that diatoms from cold, well‐oxygenated streams showed no size‐to‐temperature response, those from intermediate temperature and oxygen conditions showed reverse TSR, and diatoms from warm, poorly oxygenated streams showed significant TSR. We also distinguished the roles of oxygen and nutrition in TSR. Oxygen is a driving factor, while nutrition is an important factor that should be controlled for. Our results show that if the geographical or global patterns of TSR are to be understood, oxygen should be included in the studies. This argument is important especially for predicting the size response of ectotherms facing climate warming.

Bioenergetic strategy of a xylem-feeder

To understand the efficiency of energy flow through an organism living in a nutrient poor environment, the bioenergetics of a xylem-feeding beetle Aredolpona rubra was investigated. The larvae of different ages were kept at a constant high, constant low and seasonally variable temperature or in agar plates and agar+nitrogen plates. Bioenergetic parameters were measured during the course of 1 year. The results showed (i) a very strong influence of food moisture on the bioenergetic parameters of A. rubra, (ii) the influence of temperature depends on whether it is fluctuating or constant, (iii) opposite mechanisms regulate growth in a shortage of water and at a suboptimal temperature: in the former case, consumption does not change while the metabolic rate decreases, and at a suboptimal temperature the metabolic rate is dictated by temperature and the consumption rate is altered and (iv) a nitrogen-rich diet results in a decreased metabolic rate, suggesting the existence of energetically costly adaptations to low quality wood as a food source. The study results have broad implications for environmental influences on insect life histories.

Interaction Between a Bacterivorous Ciliate Aspidisca cicada and a Rotifer Lecane inermis: Doozers and Fraggles in Aquatic Flocs

Activated sludge is a semi-natural habitat composed of macroaggregates made by flocculating bacteria and inhabited by numerous protozoans and metazoans, creating a complicated interactome. The activated sludge resembles the biological formation of naturally occurring floc habitats, such as “marine snow.” So far, these two types of habitat have been analyzed separately, despite their similarities. We examined the effect of a bacterivorous ciliate, Aspidisca cicada, on the quality of the macroaggregate ecosystem by estimating (i) the floc characteristics, (ii) the proliferation of other bacterivores (rotifers), and (iii) the chemical processes. We found that A. cicada (i) positively affected floc quality by creating flocs of larger size; (ii) promoted the population growth of the rotifer Lecane inermis, an important biological agent in activated sludge systems; and (iii) increased the efficiency of ammonia removal while at the same time improving the oxygen conditions. The effect of A. cicada was detectable long after its disappearance from the system. We therefore claim that A. cicada is a very specialized scavenger of flocs with a key role in floc ecosystem functioning. These results may be relevant to the ecology of any natural and engineered aggregates.

What may a fussy creature reveal about body/cell size integration under stressful conditions?

There is a growing amount of empirical evidence on the important role of cell size in body size adjustment in ambient or changing conditions. Though the adaptive significance of their correspondence is well understood and demonstrated, the proximate mechanisms are still in a phase of speculation. We made interesting observations on body/cell size adjustment under stressful conditions during an experiment designed for another purpose. We found that the strength of the body/cell size match is condition-dependent. Specifically, it is stronger under more stressful conditions, and it changes depending on exposure to lower temperature vs. exposure to higher temperature. The question whether these observations are of limiting or adaptive character remains open; yet, according to our results, both versions are possible but may differ in response to stress caused by too low vs. too high temperatures. Our results suggest that testing the hypotheses on body/cell size match may be a promising study system for the recent scientific dispute on the evolutionary meaning of developmental noise as opposed to phenotypic plasticity.