Can invasive Burmese pythons inhabit temperate regions of the southeastern United States?

Understanding potential for range expansion is critical when evaluating the risk posed by invasive species. Burmese pythons (Python molurus bivittatus) are established in southern Florida and pose a significant threat to native ecosystems. Recent studies indicate that climate suitable for the species P. molurus exists throughout much of the southern United States. We examined survivorship, thermal biology, and behavior of Burmese pythons from South Florida in a semi-natural enclosure in South Carolina, where winters are appreciably cooler than in Florida, but within the predicted region of suitable climate. All pythons acclimated to the enclosure, but most died after failing to seek appropriate refugia during sub-freezing weather. The remaining snakes used refugia but died during an unusually cold period in January 2010. Although all snakes died during the study, most survived extended periods at temperatures below those typical of southern Florida and none exhibited obvious signs of disease. Our study represents a first step in evaluating the results of climate matching models and we address factors that may affect range expansion in this invasive species.     

Parasite spillover: indirect effects of invasive Burmese pythons

Identification of the origin of parasites of nonindigenous species (NIS) can be complex. NIS may introduce parasites from their native range and acquire parasites from within their invaded range. Determination of whether parasites are non‐native or native can be complicated when parasite genera occur within both the NIS’ native range and its introduced range. We explored potential for spillover and spillback of lung parasites infecting Burmese pythons (Python bivittatus) in their invasive range (Florida). We collected 498 indigenous snakes of 26 species and 805 Burmese pythons during 2004–2016 and examined them for lung parasites. We used morphology to identify three genera of pentastome parasites, Raillietiella, a cosmopolitan form, and Porocephalus and Kiricephalus, both New World forms. We sequenced these parasites at one mitochondrial and one nuclear locus and showed that each genus is represented by a single species, R. orientalis, P. crotali, and K. coarctatus. Pythons are host to R. orientalis and P. crotali, but not K. coarctatus; native snakes are host to all three species. Sequence data show that pythons introduced R. orientalis to North America, where this parasite now infects native snakes. Additionally, our data suggest that pythons are competent hosts to P. crotali, a widespread parasite native to North and South America that was previously hypothesized to infect only viperid snakes. Our results indicate invasive Burmese pythons have affected parasite‐host dynamics of native snakes in ways that are consistent with parasite spillover and demonstrate the potential for indirect effects during invasions. Additionally, we show that pythons have acquired a parasite native to their introduced range, which is the initial condition necessary for parasite spillback.     

Cold weather and the potential range of invasive Burmese pythons

The Burmese python (Python molurus bivittatus) is established in Everglades National Park and neighboring areas in south Florida. Beyond its substantial ecological impacts to native fauna in south Florida, concerns have been raised as to its potential to occupy other parts of the USA, even as far north as Washington, DC. During a recent period of cold weather, seven of nine captive Burmese pythons held in outdoor pens at our facility in north-central Florida died, or would have died absent our intervention. This cold-induced mortality occurred despite the presence of refugia with heat sources. Our findings cast doubt on the ability of free-ranging Burmese pythons to establish and persist beyond the subtropical environment of south Florida.     

Experimentally derived salinity tolerance of hatchling Burmese pythons (Python molurus bivittatus) from the Everglades,Florida (USA)

In a laboratory setting, we tested the ability of 24 non-native, wild-caught hatchling Burmese pythons (Python molurus bivittatus) collected in the Florida Everglades to survive when given water containing salt to drink. After a one-month acclimation period in the laboratory, we grouped snakes into three treatments, giving them access to water that was fresh (salinity of 0, control), brackish (salinity of 10), or full-strength sea water (salinity of 35). Hatchlings survived about one month at the highest marine salinity and about five months at the brackish-water salinity; no control animals perished during the experiment. These results are indicative of a “worst-case scenario”, as in the laboratory we denied access to alternate fresh-water sources that may be accessible in the wild (e.g., through rainfall). Therefore, our results may underestimate the potential of hatchling pythons to persist in saline habitats in the wild. Because of the effect of different salinity regimes on survival, predictions of ultimate geographic expansion by non-native Burmese pythons that consider salt water as barriers to dispersal for pythons may warrant re-evaluation, especially under global climate change and associated sea-level-rise scenarios.     

Homing of invasive Burmese pythons in South Florida: evidence for map and compass senses in snakes

Navigational ability is a critical component of an animal''s spatial ecology and may influence the invasive potential of species. Burmese pythons (Python molurus bivittatus) are apex predators invasive to South Florida. We tracked the movements of 12 adult Burmese pythons in Everglades National Park, six of which were translocated 21–36 km from their capture locations. Translocated snakes oriented movement homeward relative to the capture location, and five of six snakes returned to within 5 km of the original capture location. Translocated snakes moved straighter and faster than control snakes and displayed movement path structure indicative of oriented movement. This study provides evidence that Burmese pythons have navigational map and compass senses and has implications for predictions of spatial spread and impacts as well as our understanding of reptile cognitive abilities.     

Identifying plausible scenarios for the establishment of invasive Burmese pythons (<Emphasis Type="Italic">Python molurus</Emphasis>) in Southern Florida

Successful invasions of secretive alien species often go unrecognized until spread has exceeded the point where control or eradication is feasible. In such situations, understanding factors that contributed to establishment can be critical to preventing subsequent introductions of previously-successful invaders or ecologically similar species. The Burmese python (Python molurus bivittatus), a native to Southeast Asia, is abundant in the pet trade and is now well-established in southern Florida. Although there can be little argument that the ultimate source of Florida pythons was the pet industry, there has been limited consideration of biological support for scenarios that may have lead to their establishment. In this study we use information on python capture rates and biologically-derived population growth models to evaluate the plausibility of various scenarios for python establishment. Our results indicate that scenarios involving relatively recent establishment (post-1990) require large numbers (100–1,000) of founders or unrealistically high juvenile survivorship. Intentional simultaneous release of large numbers of pythons is unlikely and accidental release of large numbers of founders is inconsistent with the spatial and temporal pattern of pythons captures in the region. We conclude that the most parsimonious scenario for establishment of pythons in Florida involves the release of a relatively small number of founders prior to 1985. Our results demonstrate that for pythons and other species with low inherent detection probabilities, early action during incipient phases of an invasion is critical and understanding likely introduction scenarios is important for preventing similar situations from occurring elsewhere or with other species.     

The Cold European Winter of 2005–2006 Assisted the Spread and Persistence of H5N1 Influenza Virus in Wild Birds

In January 2006, a major cold spell affected Europe, coinciding with an increase of H5N1 influenza virus detected in wild birds, mostly dead mute swans, starting along the River Danube and the Mediterranean coast line. Subsequently H5N1 detections in wild birds were concentrated in central and western parts of Europe, reaching a peak in mid February. We tested the hypothesis that the geographic distribution of these H5N1 infections was modulated by the long-term wintering line, the 0°C isotherm marking the limit beyond which areas are largely unsuitable for wintering waterfowl. Given the particularly cold 2005–2006 European winter, we also considered the satellite-derived contemporary frost conditions. This brought us to select the long-term maximum rather than the mean January 0°C isotherm as the best approximation for the 2005–2006 wintering line. Our analysis shows that H5N1 detection sites were closer to the wintering line than would be expected by chance, even when the geographic distribution of water bird wintering sites was accounted for. We argue that partial frost conditions in water bodies are conducive to bird congregation, and this may have enhanced H5N1 transmission and local spread. Because the environmental virus load also would build up in these hot spots, H5N1 virus may have readily persisted during the spring, at least in cooler areas. We conclude that H5N1 introduction, spread, and persistence in Europe may have been enhanced by the cold 2005–2006 winter.     

Incidence of Hemorrhagic Disease in White-Tailed Deer Is Associated with Winter and Summer Climatic Conditions

Hemorrhagic disease (HD) is an important vector-borne disease of white-tailed deer (Odocoileus virginianus). The objective of this study was to determine whether temperature and precipitation were associated with a measure of annual incidence of HD in white-tailed deer from Virginia. The annual percentages of deer with hoof wall growth interruptions (a clinical sign of HD) from four climate divisions in the HD endemic area of Virginia recorded during 1993–2006 were used as indicators of annual HD incidence. Pearson’s correlation coefficients between these indicators of incidence and average temperature (°F) or total precipitation (in.) for each month, as well as for winter (January–February), early summer (June–July), and late summer/fall (August–September–October) seasons were calculated. Strong direct correlations between the measure of annual HD incidence and average temperature for winter (r = 0.39, P = 0.003, n = 57), early summer (r = 0.51, P < 0.0001, n = 57), and late summer/fall (r = 0.42, P = 0.001, n = 57) were evident. There also was a strong inverse correlation between the measured annual HD incidence and June precipitation (r = −0.44, P = 0.0006, n = 57). Poisson regression models of seasonal temperatures and June precipitation to annual percentage of deer with hoof wall growth interruptions were developed. Based on Akaike’s Information Criterion with small sample size correction (AICc), the global model was selected as the top model. Higher winter and summer temperatures may increase vector capacity and competence, and lower precipitation in June may create favorable breeding sites for midges.     

Marsh rabbit mortalities tie pythons to the precipitous decline of mammals in the Everglades

To address the ongoing debate over the impact of invasive species on native terrestrial wildlife, we conducted a large-scale experiment to test the hypothesis that invasive Burmese pythons (Python molurus bivittatus) were a cause of the precipitous decline of mammals in Everglades National Park (ENP). Evidence linking pythons to mammal declines has been indirect and there are reasons to question whether pythons, or any predator, could have caused the precipitous declines seen across a range of mammalian functional groups. Experimentally manipulating marsh rabbits, we found that pythons accounted for 77% of rabbit mortalities within 11 months of their translocation to ENP and that python predation appeared to preclude the persistence of rabbit populations in ENP. On control sites, outside of the park, no rabbits were killed by pythons and 71% of attributable marsh rabbit mortalities were classified as mammal predations. Burmese pythons pose a serious threat to the faunal communities and ecological functioning of the Greater Everglades Ecosystem, which will probably spread as python populations expand their range.     

Tolerance of nonindigenous cichlid fishes (<Emphasis Type="Italic">Cichlasoma urophthalmus</Emphasis>, <Emphasis Type="Italic">Hemichromis letourneuxi</Emphasis>) to low temperature: laboratory and field experiments in south Florida

The cold tolerance of two non-native cichlids (Hemichromis letourneuxi and Cichlasoma urophthalmus) that are established in south Florida was tested in the field and laboratory. In the laboratory, fishes were acclimated to two temperatures (24 and 28°C), and three salinities (0, 10, and 35 ppt). Two endpoints were identified: loss of equilibrium (11.5–13.7°C for C. urophthalmus; 10.8–12.5°C for H. letourneuxi), and death (9.5–11.1°C for C. urophthalmus; 9.1–13.3°C for H. letourneuxi). In the field, fishes were caged in several aquatic habitats during two winter cold snaps. Temperatures were lowest (4.0°C) in the shallow marsh, where no fish survived, and warmest in canals and solution-holes. Canals and ditches as shallow as 50 cm provided thermal refuges for these tropical fishes. Because of the effect on survival of different habitat types, simple predictions of ultimate geographic expansion by non-native fishes using latitude and thermal isoclines are insufficient for freshwater fishes.     

Occurrence of Ayu (<Emphasis Type="Italic">Plecoglossus altivelis</Emphasis>) larvae in northern Vietnam

The early life history of Ayu (Plecoglossus altivelis) was investigated in the Kalong and Tien Yen River systems, northern Vietnam, which is probably the most southern distribution locality for this species, during the period of November 2010 to February 2011. A total of 248 larvae were captured in the Kalong, and none were collected in the Tien Yen. There was little difference in development between the Kalong larvae and those of P. a. altivelis and P. a. ryukyuensis. Temperatures and salinities when the larvae were collected ranged from ca. 12 to 21°C and from ca. 3.5 to 30 psu. The preflexion to flexion larvae (primarily preflexion with yolk, 5.2–12.9 mm BL) occurred in the central current from December to February, with a peak abundance in early January. The flexion to postflexion (primarily postflexion, 14.1–23.8 mm BL) larvae occurred in the bank waters from early January to late February. The larval occurrence in the Kalong was 1–2 months later than for P. a. altivelis in Japan and P. a. ryukyuensis in the Ryukyu Islands, probably because of the delay until a reasonable photoperiod for the start of spawning in the lower latitudinal region. The larvae were never collected from the sea, where the temperatures were lower than in the river and estuary in January and February, unlike in Japan.     

A geographically variable model of hemlock woolly adelgid spread

The hemlock woolly adelgid (HWA) (Adelges tsugae) has spread through the range of eastern hemlock (Tsuga canadensis) leaving dead hemlock trees in its wake. We combined county and previously unavailable township level infestation records with geographic variables including plant hardiness zone, elevation, forest cover type, urbanization, precipitation, temperature, and hemlock range in a geographic information system to build models linking HWA spread to the structure and characteristics of the environment. We explored the connections between site variables and spread rate using quantile regression, Tobit regression, a parametric model for heterogeneous error variance, and classification and regression tree modeling. The results show that since 1990 HWA has spread at a rate closer to 12.5 km/yr rather than the 20–30 km/yr previously estimated, however spread rates vary significantly with environmental variables. County-based data show a faster rate of range expansion in the south, 15.6 km/yr, and very slow spread in the northern part of the current range of HWA. The rate of spread based on township records for Pennsylvania and north is 8.13 km/yr. Our study suggests that HWA spreads more slowly in colder areas, with a mean minimum temperature of  − 26.1°C (plant hardiness zone 5B) delineating areas of slower range expansion. HWA also spreads more slowly during cold years, those with lower than average mean January temperatures. Our analysis demonstrates the value of quantile regression, Tobit regression, and classification and regression tree models for understanding the spread of invasive, exotic insects.     

Incubation behavior of king eiders on the coastal plain of northern Alaska

Incubating birds balance their energetic demands during incubation with the needs of the developing embryos. Incubation behavior is correlated with body size; larger birds can accumulate more endogenous reserves and maintain higher incubation constancy. King eiders (Somateria spectabilis) contend with variable and cold spring weather, little nesting cover, and low food availability, and thus are likely to rely heavily on endogenous reserves to maintain high incubation constancy. We examined the patterns of nest attendance of king eiders at Teshekpuk and Kuparuk, Alaska (2002–2005) in relation to clutch size, daily temperature, and endogenous reserves to explore factors controlling incubation behavior. Females at Kuparuk had higher constancy (98.5 ± 0.2%, n = 30) than at Teshekpuk (96.9 ± 0.8%, n = 26), largely due to length of recesses. Mean recess length ranged from 21.5 to 23.7 min at Kuparuk, and from 28.5 to 51.2 min at Teshekpuk. Mean body mass on arrival at breeding grounds (range; Teshekpuk 1,541–1,805, Kuparuk 1,616–1,760), and at the end of incubation (Teshekpuk 1,113–1,174, Kuparuk 1,173–1,183), did not vary between sites or among years (F < 1.1, P > 0.3). Daily constancy increased 1% with every 5°C increase in minimum daily temperature (β _min = 0.005, 95% CI 0.002, 0.009). Higher constancy combined with similar mass loss at Kuparuk implies that females there met foraging requirements with shorter recesses. Additionally, females took more recesses at low temperatures, suggesting increased maintenance needs which were potentially ameliorated by feeding during these recesses, indicating that metabolic costs and local foraging conditions drove incubation behavior.     

The impact of the 2008 cold spell on mortality in Shanghai, China

No prior studies in China have investigated the health impact of cold spell. In Shanghai, we defined the cold spell as a period of at least seven consecutive days with daily temperature below the third percentile during the study period (2001–2009). Between January 2001 and December 2009, we identified a cold spell between January 27 and February 3, 2008 in Shanghai. We investigated the impact of cold spell on mortality of the residents living in the nine urban districts of Shanghai. We calculated the excess deaths and rate ratios (RRs) during the cold spell and compared these data with a winter reference period (January 6–9, and February 28 to March 2). The number of excess deaths during the cold spell period was 153 in our study population. The cold spell caused a short-term increase in total mortality of 13 % (95 % CI: 7–19 %). The impact was statistically significant for cardiovascular mortality (RR?=?1.21, 95 % CI: 1.12–1.31), but not for respiratory mortality (RR?=?1.14, 95 % CI: 0.98–1.32). For total mortality, gender did not make a statistically significant difference for the cold spell impact. Cold spell had a significant impact on mortality in elderly people (over 65 years), but not in other age groups. Conclusively, our analysis showed that the 2008 cold spell had a substantial effect on mortality in Shanghai. Public health programs should be tailored to prevent cold-spell-related health problems in the city.     

Intense cold and mortality in Castile-La Mancha (Spain): study of mortality trigger thresholds from 1975 to 2003

Studies on temperature–mortality time trends especially address heat, so that any contribution on the subject of cold is necessarily of interest. This study describes the modification of the lagged effects of cold on mortality in Castile-La Mancha from 1975 to 2003, with the novelty of also approaching this aspect in terms of mortality trigger thresholds. Cross-correlation functions (CCFs) were thus established with 15 lags, after application of ARIMA models to the mortality data and minimum daily temperatures (from November to March), and the results for the periods 1975–1984, 1985–1994 and 1995–2003 were then compared. In addition, daily mortality residuals for the periods 1975–1989 and 1990–2003 were related to minimum temperatures grouped in 2°C intervals, with a cold threshold temperature being obtained in cases where such residuals increased significantly (p < 0.05) with respect to the mean for the study period. A cold-related mortality trigger threshold of −3°C was obtained for Ciudad Real for the period 1990–2003. The significant number of lags (p < 0.05) in the CCFs declined every 10 years in Toledo (5–2–0), Cuenca (4–2–0), Albacete (4–3–0) and Ciudad Real (3–2–1). This meant that, while the trend in cold-related mortality trigger thresholds in the region could not be ascertained, it was possible to establish a reduction in the lagged effects of cold on mortality, attributable to the improvement in socio-economic conditions over the study period. Evidence was shown of the effects of cold on mortality, a finding that renders the adoption of preventive measures advisable in any case where intense cold is forecast.     

Life cycle,population dynamics,growth and production of <Emphasis Type="Italic">Abra segmentum</Emphasis> (Mollusca,Bivalvia) at low salinities in a Mediterranean lagoon

Aspects of the biology of Abra segmentum were investigated at low salinities in a Mediterranean coastal lagoon (Monolimni Lagoon, Northern Aegean Sea). Monthly samples were collected during the period from February 1998 to January 1999. Recruitment occurred from mid-spring to early autumn (0.3–5.7 psu) and recruits grew during summer and autumn (1.2–5.7 psu), while a major part vanished during next autumn, displaying a maximum life span of about 20 months. A positive correlation was found between the percentage of individuals having a shell length of ≤3.5 mm and temperature; age group 0 showed a growth rate of 0.97 mm per month, and the largest individual collected had a 19.76 mm shell length. The population density sharply increased during late spring (0.3–1.2 psu); this increase was followed by a decline during summer and, afterwards, a gradual increase up to late autumn. Secondary production calculated by the size–frequency method gave a mean annual density (n) of 3,357 individuals m⁻², a mean annual biomass (B) of 21.98 g DW m⁻², an annual production (P) of 73.72 g DW m⁻² and a P:B ratio of 3.35. A comparison of the present data with available data of A. segmentum populations from higher salinity habitats revealed that this bivalve in the study area showed a life history pattern similar to that of other populations of the species and a comparatively high growth rate, maximum body size, n, B, P and P:B ratio. Our findings suggest that the studied aspects of A. segmentum biology could not be markedly affected by low salinities.     

Membrane fluidity and fatty acid comparisons in psychrotrophic and mesophilic strains of Acidithiobacillus ferrooxidans under cold growth temperatures

Psychrotrophic strains of Acidithiobacillus ferrooxidans have an important role in metal leaching and acid mine drainage (AMD) production in colder mining environments. We investigated cytoplasmic membrane fluidity and fatty acid alterations in response to low temperatures (5 and 15°C). Significant differences in membrane fluidity, measured by polarization (P) of 1,6-diphenyl-1,3,5-hexatriene (DPH), were found where the psychrotrophic strains had a significantly more rigid membrane (P range = 0.41–0.45) and lower transition temperature midpoints (T _m = 2.0°C) and broader transition range than the mesophilic strains (P range = 0.38–0.39; T _m = 2.0–18°C) at cold temperatures. Membrane remodeling was evident in all strains with a common trend of increased unsaturated fatty acid component in response to lower growth temperatures. In psychrotrophic strains, decreases in 12:0 fatty acids distinguished the 5°C fatty acid profiles from those of the mesophilic strains that showed decreases in 16:0, 17:0, and cyclo-19:0 fatty acids. These changes were also correlated with the observed changes in membrane fluidity (R ² = 63–97%). Psychrotrophic strains employ distinctive modulation of cytoplasmic membrane fluidity with uncommon membrane phase changes as part of their adaptation to the extreme AMD environment in colder climates.     

Survival of Rumex obtusifolius L. in an unmanaged grassland

Survival of broad-leaved dock (Rumex obtusifolius) plants exposed to grass (mainly Festuca rubra and Elymus repens) competition in unmanaged grassland in Central Europe was investigated. Individual plants (n = 244) were marked in a 35 × 28 m experimental plot divided into 20 quadrats. The mortality of the dock plants was recorded twice a year, and plant size (number of flowering stems) recorded for 8 years (2000–2007). Half of the plants died within 4 years and 4% survived to the end of the experiment. On average, winter mortality (October–April, 60%) was greater than summer mortality (May–September, 40%) but both varied between years. The plants decreased in size as they approached death. The survival of dock plants in particular quadrats was negatively correlated with the biomass of grass roots and rhizomes. Intensity of below-ground competition and possibly water deficiency contributed most to dock mortality.     

Diapause development in the chestnut weevilCurculio elephas

Larval diapause development in the chestnut weevilCurculio elephas (Coleoptera, Curculionidae) was studied in the laboratory at different temperatures. The results proved that exposure to low temperatures (3–6°C) in the period December–February is not required to complete diapause. The diapause is terminated in December and from January on, the larvae can initiate post-diapause morphogenesis in the laboratory, if temperatures allow it. In the field developmental rates are negligible during winter cold (4–6°C) and only after March morphogenesis can proceed with no interruption until adult emergence. Diapause and post-diapause quiescence contribute to individual synchronization for initiation of development. The observed spread of adult emergence was 30 days in the laboratory. This variability produced during post-diapause development may be a response to annual variation in the phenology of the chestnuts.     

Effects of meal size, clutch, and metabolism on the energy efficiencies of juvenile Burmese pythons, Python molurus

We explored meal size and clutch (i.e., genetic) effects on the relative proportion of ingested energy that is absorbed by the gut (apparent digestive efficiency), becomes available for metabolism and growth (apparent assimilation efficiency), and is used for growth (production efficiency) for juvenile Burmese pythons (Python molurus). Sibling pythons were fed rodent meals equaling 15%, 25%, and 35% of their body mass and individuals from five different clutches were fed rodent meals equaling 25% of their body mass. For each of 11–12 consecutive feeding trials, python body mass was recorded and feces and urate of each snake was collected, dried, and weighed. Energy contents of meals (mice and rats), feces, urate, and pythons were determined using bomb calorimetry. For siblings fed three different meal sizes, growth rate increased with larger meals, but there was no significant variation among the meal sizes for any of the calculated energy efficiencies. Among the three meal sizes, apparent digestive efficiency, apparent assimilation efficiency, and production efficiency averaged 91.0%, 84.7%, and 40.7%, respectively. In contrast, each of these energy efficiencies varied significantly among the five different clutches. Among these clutches production efficiency was negatively correlated with standard metabolic rate (SMR). Clutches containing individuals with low SMR were therefore able to allocate more of ingested energy into growth.