Effect of chronic low body temperature on feeding and gut passage in a plethodontid salamander

Although feeding in some plethodontid salamander species, such as Dusky Salamanders (Desmognathus, family Plethodontidae), occurs at short-term (acute) low temperature below 5 °C, it is unknown whether feeding, digestion, and gut passage continue to occur during periods of long-term (chronic) low temperature. We performed a controlled laboratory experiment to examine the effect of several chronic low environmental temperatures on both feeding and gut passage in semiaquatic Spotted Dusky Salamanders (D. conanti). We quantified salamander feeding and defecation for different experimental groups maintained for many weeks at a constant temperature of 4, 7, 10, or 13 °C. Although feeding frequency, number of prey items consumed per feeding, and defecation frequency were significantly less for individuals at 4 °C than for individuals at 10 or 13 °C, salamanders continued to feed, defecate, and maintain body mass for 12 weeks at 4 °C. The ratio of the number of fecal pellets produced to the number of prey items consumed each week by individuals did not significantly decrease at 4 °C, which indicates gut passage was sustained at this temperature. Because both time between feeding and time between defecation were similarly affected by prolonged low temperature, the significant decrease in feeding frequency at 4 °C may depend, in part, on a decrease in digestive function and an extended time for gut passage at low temperature. We conclude that most individuals of D. conanti can feed, digest, and maintain body mass for several months at constant low temperature down to 4 °C. Our results support a growing body of data that indicate some plethodontid salamanders may acquire energy at environmental temperatures only a few degrees above freezing.     

Position dependence of hemiray morphogenesis during tail fin regeneration in Danio rerio

The fins of actinopterygian can regenerate following amputation. Classical papers have shown that the ray, a structural unit of these fins, might regenerate independent of this appendage. Each fin ray is formed by two apposed contralateral hemirays. A hemiray may autonomously regenerate and segmentate in a position-independent manner. This is observed when heterotopically grafted into an interray space, after amputation following extirpation of the contralateral hemiray or when simply ablated. During this process, a proliferating hemiblastema is formed, as shown by bromodeoxyuridine incorporation, from which the complete structure will regenerate. This hemiblastema shows a patterning of gene expression domain similar to half ray blastema. Interactions between contralateral hemiblastema have been studied by recombinant rays composed of hemirays from different origins on the proximo-distal or dorso-ventral axis of the caudal fin. Dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocianine perchlorate labeling of grafted tissues was used as tissular marker. Our results suggest both that there are contralateral interactions between hemiblastema of each ray, and that hemiblastema may vary its morphogenesis, always differentiating as their host region. These non-autonomous, position-dependent interactions control coordinated bifurcations, segment joints and ray length independently. A morphological study of the developing and regenerating fin of another long fin mutant zebrafish suggests that contralateral hemiblastema interactions are perturbed in this mutant.     

Autotomy reduces feeding, energy storage and growth of the sea star Stichaster striatus

We evaluated the effect of autotomy on feeding, energy storage and growth of juvenile Stichaster striatus kept in the laboratory for five months with a limited supply of the mussel Semimytilus algosus. Autotomy strongly decreased feeding, energy storage and growth. Intact juveniles showed a ∼ 3 fold higher feeding rate than autotomized individuals throughout the experiment. Intact juveniles also had a higher (∼ 5 fold) energy content per pyloric caeca in each arm. This was mainly due to higher lipid content, the main proximate constituent of pyloric caeca. Intact juveniles showed a greater growth rate and reached a greater size than autotomized individuals, more evident for underwater mass than radius length. The reduced capacity to feed reduced energy intake in autotomized individuals. However, low energy reserves along with low growth in autotomized sea stars, support the hypothesis that juveniles of this species allocate energy to regeneration to the detriment of growth. This was also supported by the ∼ 25% of arm length regeneration after 5 mo. Remaining small could increase risk of lethal predation, however, S. striatus may reduce predation risk by using crevices and kelp holdfasts as refuges from predators. Given the strong impact of autotomy on feeding, regeneration of arms to recover full capacity to forage and grow seems a better strategy for juvenile S. striatus, than merely growing.     

Complex secretory products in the oviduct of the plethodontid salamander Bolitoglossa dofleini (Amphibia, Urodela)

The ultrastructure of the secretory granules in the cells of the subdivisions of the oviduct in the neotropical plethodontid salamander Bolitoglossa dofleini was studied by transmission electron microscopy. In addition, we applied the cationic dye Cuprolinic Blue (CB) at different electrolyte concentrations to demonstrate proteoglycans, and the pyrogallol red-copper (PR-C) method to stain proteins at the ultrastructural level. The entire oviduct is lined by a simple epithelium that contains ciliated and microvillous cells in the first subdivision, the aglandular pars recta; microvillous cells show a moderate secretory activity. The following pars convoluta is differentiated into five glandular subdivisions and the aglandular “uterine portion”. Especially in the glandular parts, the epithelium is arranged in longitudinal folds. At their crests ciliated and microvillous cells similar to those in the pars recta occur. Gland cells are crowded with secretory granules that differ in their structural complexity (with and without electron-dense spheres or masses; elaborated, homogeneous or granular matrix; spherical; distorted) along the various subdivisions. Further, as suggested by the CB-technique, the cranial subdivisions contain large amounts of sulphated proteoglycans that decrease in the caudal direction. Carboxylated proteglycans appear to be present in all subdivisions examined. Electron-dense spheres of secretory granules are largely free of CB-precipitates, but stain more or less intensely with PR-C. The ultrastructure of the pars recta, and especially the “uterine portion” indicates transporting capability. The epithelial cells of the “uterus” have coated pits and a considerable amount of lysosome-like bodies.     

Effect of dietary history and algal traits on feeding rate and food preference in the green sea urchin Strongylocentrotus droebachiensis

Feeding behaviour is influenced by a variety of factors, including nutritional requirements, the quality of available foods, and environmental conditions. We examined the effect of two factors, food morphology and dietary history, on the feeding rate and preference of the sea urchin Strongylocentrotus droebachiensis. Standardizing food shape and structure did not alter urchins' expected preference for the native kelp Laminaria longicruris over the invasive alga Codium fragile ssp. tomentosoides. However, when foods containing L. longicuris were shaped to mimic the algae, the C. fragile mimic was consumed more rapidly than the kelp mimic. Dietary history had no effect on single diet feeding rate. Urchins feeding on C. fragile consistently consumed twice as much (by mass) as those fed kelp, regardless of their previous diet. Despite higher feeding rates on C. fragile, urchins feeding on this alga were unable to compensate for its low energetic content and ingested less energy. Dietary history had a short-term effect on food preference, with urchins tending to prefer less familiar foods. Our findings suggest that urchins feed on C. fragile at a high rate, due to ease of handling and/or compensatory feeding, and that they do not a have strict preference hierarchy. Rather, food choice appears to reflect active maintenance of a mixed diet.     

Trout affect the density, activity and feeding of a larval plethodontid salamander

1. Ecologists have struggled to describe general patterns in the impacts of predators on stream prey, particularly at large, realistic spatial and temporal scales. Among the confounding variables in many systems is the presence of multiple predators whose interactions can be complex and unpredictable. 2. We studied the interactions between brook trout (Salvelinus fontinalis) and larval two‐lined salamanders (Eurycea bislineata), two dominant vertebrate predators in New England stream systems, by examining patterns of two‐lined salamander abundance in stream reaches above and below waterfalls that are barriers to fish dispersal, by measuring the effects of trout on salamander density and activity using a large‐scale manipulation of brook trout presence, and by conducting a small‐scale laboratory experiment to study how brook trout and larval two‐lined salamanders affect each other's prey consumption. 3. We captured more salamanders above waterfalls, in the absence of trout, than below waterfalls where trout were present. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish. Analysis of stomach contents from our laboratory experiment revealed that salamanders eat fewer prey with trout, but trout eat more prey in the presence of salamanders. 4. We suggest that as predators in streams, salamanders can influence invertebrate prey communities both directly and through density‐ and trait‐mediated interactions with other predators.     

Electric currents in Xenopus tadpole tail regeneration

Xenopus laevis tadpoles can regenerate tail, including spinal cord, after partial amputation, but lose this ability during a specific period around stage 45. They regain this ability after stage 45. What happens during this “refractory period” might hold the key to spinal cord regeneration. We hypothesize that electric currents at amputated stumps play significant roles in tail regeneration. We measured electric current at tail stumps following amputation at different developmental stages. Amputation induced large outward currents leaving the stump. In regenerating stumps of stage 40 tadpoles, a remarkable reversal of the current direction occurred around 12-24 h post-amputation, while non-regenerating stumps of stage 45 tadpole maintained outward currents. This reversal of electric current at tail stumps correlates with whether tails regenerate or not (regenerating stage 40—inward current; non-regenerating stage 45—outward current). Reduction of tail stump current using sodium-free solution decreased the rate of regeneration and percentage regeneration. Fin punch wounds healed normally at stages 45 and 48, and in sodium-free solution, suggesting that the absence of tail re-growth at stage 45 is regeneration-specific rather than a general inhibition of wound healing. These data suggest that electric signals might be one of the key players regulating regeneration.     

Zooid size and growth rate of the bryozoan Cryptosula pallasiana Moll in relation to temperature, in culture and in its natural environment

The size of cheilostome bryozoan zooids has been widely discussed for its potential in inferring palaeotemperatures, based on correlations between zooid size and temperature. Studies in both the natural environment and under experimental laboratory conditions have shown that an increase in temperature significantly decreases zooid size in a range of bryozoan taxa. In order to test the effect of temperature on zooid size, the cheilostome bryozoan Cryptosula pallasiana was for the first time successfully cultured under laboratory conditions. C. pallasiana was grown at 14 °C and 18 °C using Rhodomonas sp. as a food organism. Zooid size, tentacle number and growth rate were measured over a period of 26 days. For comparison, zooids from colonies of C. pallasiana collected from the natural environment were measured in winter and summer months. Results showed that colonies grown in laboratory culture had significantly longer and wider zooids at 14 °C than at 18 °C. The specific growth rate of C. pallasiana doubled from 14 °C to 18 °C. Comparison of tentacle number in culture showed a significantly higher value at lower temperatures. This may be related to differing food availability, longer polypide life spans, or a shift of energy use at colder temperatures. In nature the zooids were significantly longer in colonies sampled in July than in January, a clear difference from laboratory results. The utility of cheilostome Bryozoa as indicators of environmental change and their potential for studies of paleotemperature are highlighted.     

Apoptosis is required during early stages of tail regeneration in Xenopus laevis

The Xenopus tadpole is able to regenerate its tail, including skin, muscle, notochord, spinal cord and neurons and blood vessels. This process requires rapid tissue growth and morphogenesis. Here we show that a focus of apoptotic cells appears in the regeneration bud within 12 h of amputation. Surprisingly, when caspase-3 activity is specifically inhibited, regeneration is abolished. This is true of tails both before and after the refractory period. Programmed cell death is only required during the first 24 h after amputation, as later inhibition has no effect on regeneration. Inhibition of caspase-dependent apoptosis results in a failure to induce proliferation in the growth zone, a mispatterning of axons in the regenerate, and the appearance of ectopic otoliths in the neural tube, in the context of otherwise normal continued development of the larva. Larvae amputated during the refractory stage exhibit a much broader domain of caspase-3-positive cells, suggesting a window for the amount of apoptosis that is compatible with normal regeneration. These data reveal novel roles for apoptosis in development and indicate that a degree of apoptosis is an early and obligate component of normal tail regeneration, suggesting the possibility of the existence of endogenous inhibitory cells that must be destroyed by programmed cell death for regeneration to occur.     

Individual relationship between aneuploidy of gill cells and growth rate in the cupped oysters Crassostrea angulata, C. gigas and their reciprocal hybrids

The Portuguese oyster, Crassostrea angulata, is taxonomically close to the Pacific oyster, C. gigas, but there are clear genetic and phenotypic differences between these taxa. Among those differences, the faster growth of C. gigas compared with C. angulata has often been observed in the field. Crosses between C. angulata and C. gigas were performed to investigate the relationship between growth variation and somatic aneuploidy at the individual level in the two taxa and their reciprocal hybrids. The different progenies were reared in Ria Formosa (Portugal) under standard farming conditions. Growth rate and survival were significantly higher in C. gigas than in C. angulata, and the hybrids showed intermediate performances. Significant differences were also observed in the proportion of aneuploid cells (PAC) and of missing chromosomes (PMC) between the two taxa, C. angulata showing the highest values. Intermediate values of PAC and PMC were observed in the hybrids, supporting additive genetic bases of these parameters. Our results also confirm the negative correlation between somatic aneuploidy and growth rate at the individual level, as previously reported in C. gigas.     

Change in the thermal biology of tadpoles of Odontophrynus occidentalis from the Monte desert, Argentina: Responses to photoperiod

We determined if the photoperiod regime affects the thermal biology of the tadpoles of Odontophrynus occidentalis from the Monte desert (Argentina). Variables measured were: selected body temperature (T_sel), critical thermal maximum (CT_max) and thermal critical minimum (CT_min). The tadpoles were acclimated to 15±2 °C for 15 days, and they were divided in three experimental groups: 24 h light, 24 h dark and 12 h/12 h light/dark. Data indicate that the photoperiod had an important effect upon the thermal biology of the Odontophrynus occidentalis tadpoles. The treatment group exposed to 24 h of light showed the highest selected temperature and thermal extremes. We suggest that changes in photoperiod may allow these organisms to anticipate the future changes in their thermal environment, as longer days usually involve higher temperatures.     

Influence of host plants on feeding, growth and reproduction of Papilio polytes (The common mormon)

We studied the feeding, growth and reproductive behaviour of Papilio polytes (common mormon butterfly) on five different host plants, Murraya koenigii, Toddalia asiatica, Glycosmis pentaphylla, Aegle marmelos and Citrus medica. The growth rate of P. polytes was fastest on M. koenigii followed by T. asiatica, C. medica, G. pentaphylla and A. marmelos. We related this to the nutrient contexts of the five plants. The plants T. asiatica and C. medica had higher water contents, which influenced the growth rate of the insect. M. koenigii was found to contain rich quantities of carbohydrate. M. koenigii, T. asiatica and C. medica were also rich in protein when compared to A. marmelos and G. pentaphylla. Total amino acid levels were comparatively higher in M. koenigii, T. asiatica, C. medica rather than A. marmelos and G. pentaphylla.     

A simple equation for describing the temperature dependent growth of free-floating macrophytes

Temperature is one of the most important factors determining growth rates of free-floating macrophytes in the field. To analyse and predict temperature dependent growth rates of these pleustophytes, modelling may play an important role. Several equations have been published for describing temperature responses of macrophytes and algae. But they are often complex or are only applicable in a limited range of temperatures. In this paper, we present a simple three-parameter equation for describing the temperature dependent growth rates of pleustophytes. The equation that we developed is tested using results from laboratory growth experiments conducted with three different species of pleustophytes (Lemna minor, Salvinia molesta and Azolla filiculoides). The equation is simple and demonstrates reliable fits (adjusted R² reaching from 0.89 to 0.95). Additionally, our equation primarily uses parameters of biological significance, resulting in estimates of useful cardinal temperatures (minimum and maximum).     

两种海星对三种双壳贝类的捕食选择性和摄食率

在实验室条件下,研究了多棘海盘车和海燕这两种海星对栉孔扇贝、菲律宾蛤仔和贻贝三种双壳贝类的捕食选择性和摄食率及温度的影响,测定了捕食Q₁₀温度系数。结果显示:多棘海盘车和海燕对三种贝类均可捕食,且表现出明显的捕食选择性,选择顺序依次为菲律宾蛤仔、贻贝和栉孔扇贝。海星对菲律宾蛤仔的摄食率显著高于其他两种贝类,分别为0.50和0.37个/d;对扇贝的摄食率最低,分别为0.05和0.07个/d。海星摄食率随水温升高而呈上升的趋势,总平均摄食干重分别为0.69 和0.79 g/d。水温从4.3 ℃升高到7.8 ℃多棘海盘车和海燕捕食Q₁₀系数分别为6.38和2.33,而水温从7.8 ℃升高至13.3 ℃时,Q₁₀系数没有显著升高,分别为1.13和1.22。说明水温从4.3 ℃升高时,海星捕食强度显著升高,是防御海星的重点时期。根据海星对贝类捕食的选择性,可在养殖笼内放入贻贝等低值贝类来保护扇贝,缓冲海星对扇贝的捕食,并在缓冲期间对养殖笼内的海星进行清除。     

Effects of temperature, pH and salinity on the infection of Leptolegnia chapmanii Seymour (Peronosporomycetes) in mosquito larvae

The effects of temperature, pH, and NaCl concentrations on the infectivity of zoospores of Leptolegnia chapmanii (Argentine isolate) were determined for Aedes aegypti and Culex pipiens under laboratory conditions. Zoospores of L. chapmanii were infectious at temperatures between 10 and 35 degrees C but not at 5 or 40 degrees C. At the permissive temperatures, mortality rates in young instars were much higher than in older instars and larvae of Ae. aegypti were more susceptible to L. chapmanii than larvae of Cx. pipiens. At 25 degrees C, Ae. aegypti larvae challenged with L. chapmanii zoospores resulted in 100% infection at pH levels ranging from 4 to 10. Larvae of Cx. pipiens exposed to similar pH and zoospore concentrations resulted in increasing mortality rates from 62% to 99% at pH 4 to 7, respectively, and then decreased to 71% at pH 10. Aedes aegypti larvae exposed to L. chapmanii zoospores in NaCl concentrations ranging from 0 to 7 parts per thousand (ppt) at 25 degrees C resulted in 100% mortality while mortality rates for Cx. pipiens decreases from 96% in distilled water to 31.5% in water with 6 ppt NaCl. Control Cx. pipiens larvae died when exposed at a NaCl concentration of 7 ppt. Vegetative growth of L. chapmanii was negatively affected by NaCl concentrations. These results have demonstrated that the Argentinean isolate of L. chapmanii tolerated a wide range of temperatures, pH, and salinity, suggesting that it has the potential to adapt to a wide variety of mosquito habitats.     

Effect of reverse photoperiod on in vitro regeneration and piperine production in Piper nigrum L.

In this study, a novel approach for in vitro regeneration of Piper nigrum L. has been applied in order to increase healthy biomass, phytochemicals and piperine production via reverse photoperiod (16hD/8hL). Leaf portions of the seed-derived plants were placed on an MS-medium fortified with different PGRs. Under 16hD/8hL, thidiazuron (TDZ; 4.0 mg L⁻¹) and BA (1.5 mg L⁻¹) was found to be the most effective (< 90%) in callus induction. Two concentrations (1.5, 2.0 mg L⁻¹) of the IBA produced > 80% shoots from callus cultures. Healthy shoots were transferred to rooting medium and higher percentage of rooting (< 90%) was observed on IBA (1.5 mg L⁻¹). These in vitro tissues were subjected to amino acid analysis, spectrophotometry, and HPLC. ARG, SER, THR, and TYR were the most abundant components out of 17 amino acids. Higher amino acid production was observed under normal photoperiod (16hL/8hD) than under reverse photoperiod (16hD/8hL). The highest total phenolic content (TPC; 9.91 mg/g-DW) and flavonoid content (7.38 mg/g-DW) were observed in callus cultures incubated under 16hL/8hD than other tissues incubated under 16hD/8hL photoperiod. Higher DPPH and PoMo activities were observed in tissues incubated under 16hL/8hD photoperiod, while ABTS and Fe²⁺ chelating activities were found higher in tissues incubated under reverse photoperiod. Significant quantities of piperine content were observed in all tissues except callus cultures. These results suggest that reverse photoperiod is a promising approach for callus induction, phytochemicals and piperine production for commercial applications.     

Germination rate and sporeling development of Chondracanthus chamissoi (Rhodophyta, Gigartinales) varies along a latitudinal gradient on the coast of Chile

Chondracanthus chamissoi (C. Agardh) Kützing is an economically important red seaweed with an extended latitudinal distribution along the south-east Pacific. Here we report on the seasonal in vitro germination of carpospores and tetraspores from four populations distributed from 27 to 41° S on the Chilean coast. Our results show that both types of spores exhibited a different physiological behavior related to the geographic origin of the specimens. Germination occurred throughout the year for both spore types in the four populations. However, for the northern locations (Calderilla, La Herradura and Puerto Aldea) germination was higher in spring, while for the southern location (Lechagua), germination was higher in summer. The growth rate of carposporelings and tetrasporelings varied seasonally in all locations studied, with higher growth in spring. Among all, carposporelings from Lechagua specimens reached the highest growth rates (9.3 ± 0.2% d⁻¹). However, spores from Herradura and P. Aldea had a good germination and SGR in all seasons and would be good candidates to start spores-based cultivation of this valuable resource in Chile.     

Novel gain-of-function alleles demonstrate a role for the heterochronic gene lin-41 in C. elegans male tail tip morphogenesis

To gain an understanding of the genes and mechanisms that govern morphogenesis and its evolution, we have analyzed mutations that disrupt this process in a simple model structure, the male tail tip of the rhabditid nematode C. elegans. During the evolution of rhabditid male tails, there have been several independent changes from tails with rounded tips ("peloderan", as in C. elegans) to those with pointed tips ("leptoderan"). Mutations which produce leptoderan (Lep) tails in C. elegans thus identify candidate genes and pathways in which evolutionary changes could have produced leptoderan tails from peloderan ancestors. Here we report that two novel, gain-of-function (gf) alleles of lin-41 have lesions predicted to affect the N-terminus of the RBCC-domain LIN-41 protein. Both gf alleles cause the tail tip of adult males to retain the pointed shape of the juvenile tails, producing a Lep phenotype that looks like the tails of leptoderan species. Consistent with its role in the heterochronic pathway, we find that lin-41 governs the timing and extent of male tail tip morphogenesis in a dose-dependent manner. Specifically, the Lep phenotype results from a heterochronic delay in the retraction and fusion of the tail tip cells during L4 morphogenesis, such that retraction is not completed before the adult molt. Conversely, we find that tail tip morphogenesis and cell fusions begin precociously at the L3 stage in the reduced-function lin-41 mutant, ma104, resulting in over-retracted male tails in the adult. Because modulated anti-LIN-41 RNAi knockdowns in the gf mutants restore wild-type phenotype, we suggest that the leptoderan phenotype of the gf alleles is due to a higher activity of otherwise normal LIN-41. Additionally, the gf allele is suppressed by the wild-type allele, suggesting that LIN-41 normally regulates itself, possibly by autoubiquitination. We speculate that small changes affecting LIN-41 could have been significant for male tail evolution.     

Piwi positive cells that line the vasculature epithelium, underlie whole body regeneration in a basal chordate

The colonial tunicate Botrylloides leachi can regenerate functional adults from minute vasculature fragments, in a poorly understood phenomenon termed Whole Body Regeneration (WBR). Using Piwi expression (Bl-Piwi), blood cell labeling and electron microscopy, we show that WBR develops through activation, mobilization and expansion of ‘dormant’ cells which normally line the internal vasculature epithelium of blood vessels. Following a mechanical insult, these cells express Bl-Piwi de novo, change morphology and invade niches of the vasculature lumen, where they proliferate and differentiate, regenerating a functional organism. Mitomycin C treatments and siRNA knockdown of Bl-Piwi result in deficient cells incapable of expanding or differentiating and to subsequent regeneration arrest. Last, we find similar transient mobilization of Piwi⁺ cells recurring every week, as part of normal colony development, and also during acute environmental stress. This recurrent activation of Piwi⁺ cells in response to developmental, physiological and environmental insults may have enabled the adaptation of colonial tunicates to the imposed varied conditions in the marine, shallow water environment.