Environmental Effects on Temperature Stress Resistance in the Tropical Butterfly Bicyclus Anynana

BACKGROUND: The ability to withstand thermal stress is considered to be of crucial importance for individual fitness and species' survival. Thus, organisms need to employ effective mechanisms to ensure survival under stressful thermal conditions, among which phenotypic plasticity is considered a particularly quick and effective one. METHODOLOGY/PRINCIPAL FINDINGS: In a series of experiments we here investigate phenotypic adjustment in temperature stress resistance following environmental manipulations in the butterfly Bicyclus anynana. Cooler compared to warmer acclimation temperatures generally increased cold but decreased heat stress resistance and vice versa. In contrast, short-time hardening responses revealed more complex patterns, with, e.g., cold stress resistance being highest at intermediate hardening temperatures. Adult food stress had a negative effect on heat but not on cold stress resistance. Additionally, larval feeding treatment showed interactive effects with adult feeding for heat but not for cold stress resistance, indicating that nitrogenous larval resources may set an upper limit to performance under heat stress. In contrast to expectations, cold resistance slightly increased during the first eight days of adult life. Light cycle had marginal effects on temperature stress resistance only, with cold resistance tending to be higher during daytime and thus active periods. CONCLUSIONS/SIGNIFICANCE: Our results highlight that temperature-induced plasticity provides an effective tool to quickly and strongly modulate temperature stress resistance, and that such responses are readily reversible. However, resistance traits are not only affected by ambient temperature, but also by, e.g., food availability and age, making their measurement challenging. The latter effects are largely underexplored and deserve more future attention. Owing to their magnitude, plastic responses in thermal tolerance should be incorporated into models trying to forecast effects of global change on extant biodiversity

Chill-coma recovery time of <i>Bicyclus anynana</i> in relation to hardening temperature.

<p>We predicted that colder hardening temperatures increase but warmer hardening temperatures decrease cold resistance. While hardening temperature indeed affected recovery time (F_4,229 = 3.08, p = 0.0169), both high and low hardening temperatures increased recovery times (6°C = 34°C≥13°C = 27°C (control) ≥20°C; Tukey HSD after ANOVA). Given are means +1 SE. Sample sizes range between 47 and 48 per group.</p

Efecto de la posicion de la estaca, niveles de control de malezas y arreglo espacial sobre competencia entre malezas y yuca y el rendimiento de la yuca, variedad M Col 22

Research was conducted at the Centro Internacional de Agricultura Tropical (CIAT) in 1980 in order to solve the problem of low cassava yields in Loja, Ecuador, Objectives were: (1) to determine the effect of vertical and horizontal plantings of cuttings on the emergence and competitive vigor of cassava; (2) to determine the effect of 3 levels of weed control on the cost of each practice and on cassava yields; and (3) assess the effect of spatial arrangements on the competitive ability of cassava regarding weeds, keeping a constant population. A total of 3072 cuttings, of var. M Col 22 were used in a split-plot design with 12 treatments and 4 replications. Treatments were: 1 x 1 m and 0.7 x 0.7 m spacings for populations of 20,000 and 20,408 plants/ha, resp.; vertical and horizontal planting positions; and weed control: (a) weeding at 3O days; (b) 3 weedings at 3O,60, and 9O days; and (c) preemergent control + one weeding. The percentage of germination, coverage/crop and coverage/weed, yield and its components, DM and starch contents were determined. The highest av. yield (40.2 t/ha) was obtained with vertical planting in the 0.7 x0.7 m system with just one weeding. No differences were observed among yields regarding the different levels of weed control. It was concluded that a good cultural control of weeds and good yields can be obtained with var. with little or intermediate vigor if they are planted in quadratic arrangements and in high populations. (CIAT

Heat knock-down time of <i>Bicyclus anynana</i> in relation to sex, larval and adult feeding treatment.

<p>Both larval and adult food stress were expected to decrease temperature stress resistance. Indeed, adult food stress significantly reduced heat tolerance (F_1,227 = 4.9, p = 0.03), while larval food stress did not (F_1,227 = 2.2, p = 0.14; though note the significant interaction with adult starvation, cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0015284#pone-0015284-t005" target="_blank">Table 5</a>). AS: adult starvation, AC: adult control. Given are means +1 SE. Sample sizes range between 12 and 50 per group.</p

Heat knock-down time of <i>Bicyclus anynana</i> in relation to acclimation and hardening temperature.

<p>We hypothesized that warmer acclimation and hardening temperatures increase heat tolerance and vice versa. While this prediction was met for acclimation temperature (F_2,321 = 62.6, p<0.0001; 34°C>27°C>20°C; Tukey HSD after ANOVA), the effect of hardening temperature was not significant (F_2,321 = 2.2, p = 0.11). Black bars: hardened at 20°C; open bars: hardened at 27°C; hatched bars: hardened at 34°C. Given are means +1 SE. Sample sizes range between 37 and 38 per group.</p

ANCOVA results for the effects of pupal mass (covariate), acclimation treatment and age on chill-coma recovery time. Significant p-values are given in bold.

<p>ANCOVA results for the effects of pupal mass (covariate), acclimation treatment and age on chill-coma recovery time. Significant p-values are given in bold.</p

ANOVA results for the effects of light cycle and sex on chill-coma recovery time after 19 h at 1°C (A) or after 20 min at −5°C (B), and on heat knock-down time at 45°C (C).

<p>Significant p-values are given in bold.</p

ANCOVA results for the effects of pupal mass (covariate), larval feeding treatment, adult feeding treatment and sex on chill-coma recovery time (A) and heat knock-down time (B).

<p>Significant p-values are given in bold.</p

Chill-coma recovery time and mortality rates in <i>Bicyclus anynana</i>.

<p>Chill-coma recovery time (<b>A</b>, means ±1 SE) and mortality 24 h after cold exposure (<b>B</b>; in %) for 20°C- and 27°C-acclimated <i>Bicyclus anynana</i> butterflies across five induction treatments. Significant p-values, as tested by ANOVAs <b>(A)</b> and nominal logistic regressions <b>(B)</b>, are given in bold. Sexes differed in one out of ten analyses only, with females (47.5%) showing higher mortality rates than males (10.5%) when exposed for 19 h to 1°C (results not shown). Sample sizes are 39 or 40 throughout, except for recovery times in the final treatment, where sample size is only 18 and 20, respectively.</p