Plasticity and cross-tolerance to heterogeneous environments: divergent stress responses co-evolved in an African fruit fly.

Plastic adjustments of physiological tolerance to a particular stressor can result in fitness benefits for resistance that might manifest not only in that same environment but also be advantageous when faced with alternative environmental stressors, a phenomenon termed 'cross-tolerance'. The nature and magnitude of cross-tolerance responses can provide important insights into the underlying genetic architecture, potential constraints on or versatility of an organism's stress responses. In this study, we tested for cross-tolerance to a suite of abiotic factors that likely contribute to setting insect population dynamics and geographic range limits: heat, cold, desiccation and starvation resistance in adult Ceratitis rosa following acclimation to all these isolated individual conditions prior to stress assays. Traits of stress resistance scored included critical thermal (activity) limits, chill coma recovery time (CCRT), heat knockdown time (HKDT), desiccation and starvation resistance. In agreement with other studies, we found that acclimation to one stress typically increased resistance for that same stress experienced later in life. A more novel outcome, however, is that here we also found substantial evidence for cross-tolerance. For example, we found an improvement in heat tolerance (critical thermal maxima, CTmax ) following starvation or desiccation hardening and improved desiccation resistance following cold acclimation, indicating pronounced cross-tolerance to these environmental stressors for the traits examined. We also found that two different traits of the same stress resistance differed in their responsiveness to the same stress conditions (e.g. HKDT was less cross-resistant than CTmax ). The results of this study have two major implications that are of broader importance: (i) that these traits likely co-evolved to cope with diverse or simultaneous stressors, and (ii) that a set of common underlying physiological mechanisms might exist between apparently divergent stress responses in this species. This species may prove to be a valuable model for future work on the evolutionary and mechanistic basis of cross-tolerance.

Population dynamics of Eldana saccharina Walker (Lepidoptera: Pyralidae): application of a biophysical model to understand phenological variation in an agricultural pest.

Understanding pest population dynamics and seasonal phenology is a critical component of modern integrated pest-management programs. Accurate forecasting allows timely, cost-effective interventions, including maximum efficacy of, for example, biological control and/or sterile insect technique. Due to the variation in life stage-related sensitivity toward climate, insect pest population abundance models are often not easily interpreted or lack direct relevance to management strategies in the field. Here we apply a process-based (biophysical) model that incorporates climate data with life stage-dependent physiology and life history to attempt to predict Eldana saccharina life stage and generation turnover in sugarcane fields. Fitness traits are modelled at two agricultural locations in South Africa that differ in average temperature (hereafter a cold and a warm site). We test whether the life stage population structures in the field entering winter and local climate during winter directly affect development rates, and therefore interact to determine the population dynamics and phenological responses of E. saccharina in subsequent spring and summer seasons. The model predicts that: (1) E. saccharina can cycle through more generations at the warm site where fewer hours of cold and heat stress are endured, and (2) at the cold site, overwintering as pupae (rather than larvae) confer higher relative fitness and fecundity in the subsequent summer adult moths. The model predictions were compared with a large dataset of field observations from scouting records. Model predictions for larval presence (or absence) generally overlapped well with positive (or negative) scout records. These results are important for integrated pest management strategies by providing a useful foundation for future population dynamics models, and are applicable to a variety of agricultural landscapes, but especially the sugarcane industry of South Africa.

Investigating population differentiation in a major African agricultural pest: evidence from geometric morphometrics and connectivity suggests high invasion potential.

The distribution, spatial pattern and population dynamics of a species can be influenced by differences in the environment across its range. Spatial variation in climatic conditions can cause local populations to undergo disruptive selection and ultimately result in local adaptation. However, local adaptation can be constrained by gene flow and may favour resident individuals over migrants-both are factors critical to the assessment of invasion potential. The Natal fruit fly (Ceratitis rosa) is a major agricultural pest in Africa with a history of island invasions, although its range is largely restricted to south east Africa. Across Africa, C. rosa is genetically structured into two clusters (R1 and R2), with these clusters occurring sympatrically in the north of South Africa. The spatial distribution of these genotypic clusters remains unexamined despite their importance for understanding the pest's invasion potential. Here, C. rosa, sampled from 22 South African locations, were genotyped at 11 polymorphic microsatellite loci and assessed morphologically using geometric morphometric wing shape analyses to investigate patterns of population structure and determine connectedness of pest-occupied sites. Our results show little to no intraspecific (population) differentiation, high population connectivity, high effective population sizes and only one morphological type (R2) within South Africa. The absence of the R1 morphotype at sites where it was previously found may be a consequence of differences in thermal niches of the two morphotypes. Overall, our results suggest high invasion potential of this species, that area-wide pest management should be undertaken on a country-wide scale, and that border control is critical to preventing further invasions.

Impacts of environmental variability on desiccation rate, plastic responses and population dynamics of Glossina pallidipes.

Physiological responses to transient conditions may result in costly responses with little fitness benefits, and therefore, a trade-off must exist between the speed of response and the duration of exposure to new conditions. Here, using the puparia of an important insect disease vector, Glossina pallidipes, we examine this potential trade-off using a novel combination of an experimental approach and a population dynamics model. Specifically, we explore and dissect the interactions between plastic physiological responses, treatment-duration and -intensity using an experimental approach. We then integrate these experimental results from organismal water-balance data and their plastic responses into a population dynamics model to examine the potential relative fitness effects of simulated transient weather conditions on population growth rates. The results show evidence for the predicted trade-off for plasticity of water loss rate (WLR) and the duration of new environmental conditions. When altered environmental conditions lasted for longer durations, physiological responses could match the new environmental conditions, and this resulted in a lower WLR and lower rates of population decline. At shorter time-scales however, a mismatch between acclimation duration and physiological responses was reflected by reduced overall population growth rates. This may indicate a potential fitness cost due to insufficient time for physiological adjustments to take place. The outcomes of this work therefore suggest plastic water balance responses have both costs and benefits, and these depend on the time-scale and magnitude of variation in environmental conditions. These results are significant for understanding the evolution of plastic physiological responses and changes in population abundance in the context of environmental variability.

Evolved variation in cold tolerance among populations of Eldana saccharina (Lepidoptera: Pyralidae) in South Africa.

Among-population variation in chill-coma onset temperature (CTmin ) is thought to reflect natural selection for local microclimatic conditions. However, few studies have investigated the evolutionary importance of cold tolerance limits in natural populations. Here, using a common-environment approach, we show pronounced variation in CTmin (± 4 °C) across the geographic range of a nonoverwintering crop pest, Eldana saccharina. The outcomes of this study provide two notable results in the context of evolved chill-coma variation: (1) CTmin differs significantly between geographic lines and is significantly positively correlated with local climates, and (2) there is a stable genetic architecture underlying CTmin trait variation, likely representing four key genes. Crosses between the most and least cold-tolerant geographic lines confirmed a genetic component to CTmin trait variation. Slower developmental time in the most cold-tolerant population suggests that local adaptation involves fitness costs; however, it confers fitness benefits in that environment. A significant reduction in phenotypic plasticity in the laboratory population suggests that plasticity of this trait is costly to maintain but also likely necessary for field survival. These results are significant for understanding field population adaption to novel environments, whereas further work is needed to dissect the underlying mechanism and gene(s) responsible.

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 (ULT(90) and LLT(90) , 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 LLT(90) in all species tested except for D. pseudoobscura, D. mojavensis and D. borealis. High-temperature pretreatment only significantly increased ULT(90) in D. melanogaster, D. simulans, D. pseudoobscura and D. persimilis. LLT(90) was negatively correlated with low-temperature plasticity even after phylogeny was accounted for. No correlations were found between ULT(90) and LLT(90) or between ULT(90) and rapid heat-hardening (RHH) in ordinary regression approaches. However, after phylogenetic adjustment, there was a positive correlation between ULT(90) 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.

Propagule pressure helps overcome adverse environmental conditions during population establishment.

The establishment success of a population is a function of abiotic and biotic factors and introduction dynamics. Understanding how these factors interact has direct consequences for understanding and managing biological invasions and for applied ecology more generally. Here we use a mesocosm approach to explore how the size of founding populations and the number of introduction events interact with environmental conditions (temperature) to determine the establishment success of laboratory-reared Drosophila melanogaster. We found that temperature played the biggest role in establishment success, eclipsing the role of the other experimental factors when viewed overall. Under optimal temperature conditions propagule pressure was of negligible importance to establishment success.  At adverse temperatures, however, establishment success increased with the total founding population size. This effect was considerably stronger at the cold than at the hot extreme. Whether the population was introduced all at once or by increments (changing the number of introduction events) had a negligible global effect. However, once again, a stronger effect of increasing number of introduction events was seen at adverse temperatures, with hot and cold extremes revealing opposite effects: adding flies incrementally decreased their establishment success at the hot extreme, but increased it at the cold extreme. These differing effects at hot and cold thermal extremes implies that different establishment mechanisms are at play at either extreme. These results suggest that the effort required to prevent (or conversely, to facilitate) the establishment of populations varies with the environment in ways that can be complicated but predictable.

Phenotypic plasticity of desiccation resistance in Glossina puparia: are there ecotype constraints on acclimation responses?

Phenotypic plasticity allows organisms to cope with environmental variation and may aid in the evolution of novel traits. However, whether phenotypic plasticity is beneficial, or if acclimation responses might be constrained to particular ecotypes is generally poorly explored. Here we test the beneficial acclimation hypothesis (BAH) and its alternatives for desiccation resistance to atmospheric moisture in mesic- and xeric-adapted Glossina species. Highly significant interactions among acclimation and test humidity were detected for water loss rates indicative of significant phenotypic plasticity. Ordered-factor anova was unable to reject predictions of the 'drier is better' acclimation hypothesis in xeric Glossina morsitans and mesic G. austeni. Evidence for the 'deleterious acclimation hypothesis' was found for mesic G. palpalis as expected from the moist habitats it typically occupies. By contrast, support for the 'optimal acclimation hypothesis' was found in xeric G. pallidipes. Little support for BAH was obtained in the present study, although other hypotheses, which might enhance fitness within the environments these species are typically exposed to, were supported. However, acclimation responses were not necessarily constrained to xeric/mesic ecotypes which might be expected if adaptation to a particular environment arose as a trade-off between plastic responses and living in a particular habitat. These results highlight the complexity of acclimation responses and suggest an important role for phenotypic plasticity in moderating environmental effects on evolutionary fitness in Glossina.

Gas exchange characteristics, metabolic rate and water loss of the Heelwalker, Karoophasma biedouwensis (Mantophasmatodea: Austrophasmatidae).

This study presents the first physiological information for a member of the wingless Mantophasmatodea, or Heelwalkers. This species shows cyclic gas exchange with no evidence of a Flutter period (more typical of discontinuous gas exchange in insects) and no indication that the spiracles are fully occluded during quiescent metabolism. Standard metabolic rate at 20 degrees C was 21.32+/-2.73 microl CO(2)h(-1) (mean+/-S.E.), with a Q(10) (10-25 degrees C) of 1.7. Increases in V()CO(2) associated with variation in mass and with trial temperature were modulated by an increase in burst period volume and a decline in cycle frequency. Total water loss rate, determined by infrared gas analysis, was 0.876+/-0.08 mg H(2)Oh(-1) (range 0.602-1.577, n=11) whilst cuticular water loss rate, estimated by linear regression of total water loss rate and metabolic rate, was 0.618+/-0.09 mg H(2)Oh(-1) (range 0.341-1.363, n=11). Respiratory water loss rate was therefore no more than 29% of the total rate of water loss. Both total water loss rate and estimated cuticular water loss rate were significantly repeatable, with intraclass correlation coefficients of 0.745 and 0.553, respectively.

The effect of feeding and starvation upon immunoreactive glucagon in the pancreatectomized pig.

The response of 13 pigs to total pancreatectomy was compared with the response of 9 animals to sham operation. Approximately half of each group had free access to food while the remainder received oral water only. Completeness of pancreatectomy was confirmed at autopsy, and the disappearance of insulin and the rise in blood glucose to 14-19 mmol/l. Immunoreactive glucagon (IRG) increased in fed pancreatectomized pigs from the 3rd day postoperatively to a level of 350-400% of basal values by the 8th day. There was no rise in starved pancreatectomized animals, or in either group of sham-operated animals. The rises in glucose, free fatty acids, triglycerides and ketones were similar in the two groups of pigs.

Sucralfate in the prevention of porcine experimental peptic ulceration.

Sucralfate is the first drug to be shown to prevent ulceration in bile duct-ligated pigs. Usually such ulceration is uniformly fatal. Seven pigs in each of four groups in this study received only saline, or sucralfate (1 g every six hours), famotidine (40 mg per day), or misoprostol (200 micrograms every six hours). A Foley catheter was placed into a gastrectomy after bile duct ligation. Similar groups of sham-operated pigs were also prepared. After 48 hours, all saline-, famotidine-, or misoprostol-treated pigs showed severe macroscopic ulceration, whereas only two of those treated with sucralfate showed minimal macroscopic ulceration. Until now, only highly selective vagotomy has reduced ulceration caused by bile duct ligation. The present results suggest that acid inhibition is not the only important factor in healing bile duct ligation-induced peptic ulceration.

Exchange transplantation of the liver in the pig.

An original technique is described for exchange transplantation of the liver in the pig. The procedure also allows a complete autograft to be performed with the same operative trauma as a transplant. The initial problems that were encountered, but overcome in both autografts and transplants, included difficulty with adequate perfusion of the liver in the live animals, gas gangrene resulting from hepatic arterial thrombosis in animals under 22 kg, and fear of devascularisation of the pancreas or stomach during dissection. In this series, six successful pairs of pigs were transplanted and, in three pairs, one animal showed severe rejection and early death while the other lived longer with a different response. The technique has significant immunological and economical potential.

Anorexia and weight loss in the portacaval-shunted pig.

The pig shows a marked response to end-to-side portacaval shunt. Survival is short and levels of alkaline phosphatase and cholesterol fall. This study was designed to determine the role of the reduced food intake which follows the operation upon these results. In pair-fed, sham-operated pigs, survival was short and levels of alkaline phosphatase and cholesterol also fell. Sham-operated animals fed normally did not show this response. Reduced appetite has been recorded in many experimental animals after portacaval shunt, but the cause remains to be elucidated. Encephalopathy, bacteremia, peptic ulceration, or hormonal imbalance could be implicated. Similar alteration in appetite and weight loss have not been observed in children who have been treated by portacaval shunt for glycogen storage disease or hypercholesterolemia; however, the underlying metabolic disorder or the species difference may be a contributory cause.

The prevention of peptic ulceration by highly selective vagotomy in a new peptic ulcer experimental model: the bile duct-ligated pig.

Bile duct ligation produced gross peptic ulceration of the pars esophagea of the stomach, with a 70% mortality rate from hemorrhage or perforation. The situation and histological appearance of the ulcers was identical to the peptic ulcers that occur spontaneously in pigs. Previous work has shown that these ulcers are associated with gastric hypersecretion. The technique of highly selective vagotomy was established in the pig and was shown to have no short-term adverse effects. In a group of 10 pigs, highly selective vagotomy virtually eliminated pars esophageal peptic ulceration and significantly prolonged survival after bile duct ligation. The bile duct-ligated pig experimental peptic ulcer model should be of value in studying peptic ulceration and methods of treatment. Further investigation is required to determine the cause of death in those animals in which peptic ulceration is prevented by treatment, such as highly selective vagotomy.

Subtotal cholecystectomy: for the difficult gallbladder in portal hypertension and cholecystitis.

An easy, safe, and definitive operation for the "difficult gallbladder" is described and has been termed subtotal cholecystectomy. Eighteen patients underwent subtotal cholecystectomy during a 30-month period, which constitutes approximately 7% of cholecystectomies performed at our institution. The indications were cholecystitis with severe fibrosis or inflammatory changes that prevented safe dissection in Calot's triangle in 11 patients and portal hypertension in seven patients (liver cirrhosis [two patients] and segmental portal hypertension caused by chronic pancreatitis [five patients]) to prevent massive blood loss from the gallbladder bed. The operation entails leaving the posterior wall of the gallbladder attached to the liver and securing the cystic duct at its origin from within the gallbladder with a purse string technique. The latter obviates the need for dangerous dissection in Calot's triangle. Control of bleeding from the remaining gallbladder edge is greatly facilitated by the use of a running suture after each stage of piecemeal excision of the gallbladder. All patients survived the operation and wound infection occurred in only two patients (11%). One patient required a laparotomy 1 month after surgery for adhesive small bowel obstruction related to the remaining gallbladder wall and site of a liver biopsy. No patients have so far developed postcholecystectomy symptoms (median follow-up 12.2 months; range 3 to 31 months). Subtotal cholecystectomy is a definitive operation that prevents recurrent gallstone formation, as no residual diseased gallbladder mucosa is left in continuity with the biliary system. It provides a simple, safe option in patients in whom cholecystectomy could be hazardous.

An ischemic basis for biliary strictures.

Three case reports reflecting a probable ischemic basis for biliary strictures are presented. A stricture occurring after biliary-enteric anastomosis following low division of the bile duct and another after relatively low division of the bile duct are explained on the basis of the tenuous blood supply to the supraduodenal bile duct from above. It is postulated that these strictures could have been avoided had the bile duct been divided at a higher level originally and had adequate back-bleeding from the transected upper bile duct been checked prior to performing the anastomosis. The stricture in the third patient probably occurred because the damaged duct segment was used for the anastomosis. The stricture could probably also have been avoided by higher transection of the duct.

The role of U tube palliative treatment in high bile duct carcinoma.

Twenty-one patients with cholangiocarcinoma at the confluence of the main right and left hepatic ducts were referred to our professorial surgical unit between 1968 and 1982. All were evaluated, treated, and documented prospectively with follow-up to mid 1986. No lesion was deemed resectable. The U tube palliative bypass developed during the course of the study was used in 14 patients, and its role in treating high bile duct carcinoma was evaluated. Histologic confirmation of the diagnosis was obtained in 71% of patients. Seven patients received additional treatment with radical radiotherapy. The 30-day overall hospital mortality rate was 19%. The 1- and 2-year survival rates were 57% and 33%, respectively. The quality of survival was usually good. The need for centralized referral and treatment of these difficult patients is stressed. The case against radical resection for this lesion is presented. It is concluded that radical resection is seldom possible, and therefore the U tube palliative procedure is advocated in most patients.

High or low hepaticojejunostomy for bile duct strictures?

The 19 patients who underwent 22 postoperative repairs of bile duct stricture in our institution between 1973 and 1984 were evaluated to assess whether the recognition of the tenuous blood supply of the supraduodenal bile duct in 1979 had improved the results thereafter. Thirteen of these 22 operations followed a previous biliary tract repair; in 10 of the operations a low anastomosis had been performed without taking blood supply into account. Follow-up was complete and ranged from 5 to 15 years. There were no operative deaths and minimal morbidity. There were three deaths at a later time. Five of the 11 patients treated by surgery to 1979 had a clinically unsatisfactory result: recurrent strictures developed in all five patients. All but one of the eight patients receiving a high hepaticojejunostomy from 1980 had a clinically satisfactory result with no recurrent strictures. The one exception was the patient who had a second repair with separate high right and left hepatic duct anastomoses and who has ongoing symptoms from preexisting secondary sclerosing cholangitis. The results in the five high repairs performed for low strictures were particularly striking: All five were asymptomatic. This study lends support to the hypothesis of an ischemic basis for biliary strictures and to the recommendation that strictures be repaired with a high hepaticojejunostomy.

Incidence and management of complications after injection sclerotherapy: a ten-year prospective evaluation.

The incidence and management of complications of injection sclerotherapy are reviewed in 304 consecutive patients with esophageal varices followed up prospectively for a 10-year period. The 304 patients were injected on 1336 occasions. Three hundred eleven local esophageal complications occurred in 140 patients (complication rate, 23% per injection and 46% per patient). Esophageal mucosal slough, which was diagnosed by endoscopy, occurred on 250 occasions in 126 patients but did not require specific treatment. An injection site leak occurred in 25 patients, was managed conservatively, and was associated with a mortality rate of 28%. Stenosis of the esophagus was found in 32 patients, but only five patients required dilatation for relief of symptoms. Rupture of the esophagus occurred in four patients, three of whom had surgical treatment, and was associated with a mortality rate of 50%. Serious complications were more frequent with the rigid esophagoscope. An injection site leak occurred more frequently after acute sclerotherapy via the rigid esophagoscope. All four patients with rupture of the esophagus were injected electively via the rigid esophagoscope. Although the incidence of serious complications after injection sclerotherapy in this series appears acceptable, complications have been noted to be cumulative with time.