Some aspects of the thermal tolerance of Trichomya hirsuta (Mollusca: Bivalvia) of Eastern Australia

The upper temperature tolerance range for Trichomya hirsuta L. is described for acclimation temperatures of 10° to 32°C at 30% S. Changes in thermal resistance with time are described along with the incipient lethal temperatures. The eurythermicity for the species is 240.7 C°-squared. The ultimate upper incipient lethal temperature is 35.1°C. Definition of the incipient sublethal temperature is given, and is equal to 32°C. Diet effects are shown not to be significant in short-term lethal experiments, but indicate that unfed mussels reduce their resistance after prolonged exposure to high temperatures. Size was also shown to have no effect on resistance and tolerance. A comparison of the tolerance triangle of T. hirsuta with those of the temperate species Mytilus edulis and Mya arenaria revealed that the 24-h LT₅₀ minus 2.2 C° approximates the incipient lethal temperature. The eurythermicities of the temperate species are Mytilus edulis, 363 C°-squared; and Mya arenaria, 415 C°-squared.     

Climate heterogeneity modulates impact of warming on tropical insects

Evolutionary history and physiology mediate species responses to climate change. Tropical species that do not naturally experience high temperature variability have a narrow thermal tolerance compared to similar taxa at temperate latitudes and could therefore be most vulnerable to warming. However, the thermal adaptation of a species may also be influenced by spatial temperature variations over its geographical range. Spatial climate gradients, especially from topography, may also broaden thermal tolerance and therefore act to buffer warming impacts. Here we show that for low-seasonality environments, high spatial heterogeneity in temperature correlates significantly with greater warming tolerance in insects globally. Based on this relationship, we find that climate change projections of direct physiological impacts on insect fitness highlight the vulnerability of tropical lowland areas to future warming. Thus, in addition to seasonality, spatial heterogeneity may play a critical role in thermal adaptation and climate change impacts particularly in the tropics.     

Heat resistance of gametes of marine invertebrates in relation to temperature conditions under which the species exist

It is the purpose of this paper to elucidate the possible role of the heat resistance level of mature gametes and embryos of poikilotherms in the adaptation of a species to environmental temperature conditions. Within a species, heat resistance of gametes does not undergo any recognisable changes even in the presence of significant fluctuations in temperature. Evidence in support of this statement was obtained on gametes of invertebrates belonging to different populations of the same species collected in different seasons, and on invertebrates maintained under different temperatures. The heat resistance of gametes is correlated with the degree of thermophily of the species concerned. Species living under similar temperature conditions exhibit minimal, if any, differences in heat resistance. Hence, the heat resistance level of their gametes is a function of temperature conditions of formation and existence of the species as a whole. During the ontogenesis of poikilotherms, eggs, zygotes and early stages of embryonic development are most susceptible to heat injury. The upper thermal limit for the normal development of eggs and embryos is only 1 to 3C^o higher than the temperatures encountered under natural conditions. It is concluded that the heat resistance level of gametes and embryos represents an adjustment to temperatures at which spawning, fertilisation and earlier embryonal development occur. Temperatures which, throughout the year, exceed the upper thermal limit or remain below the lower thermal limit for the development of embryos, act as limiting factors for the species' distribution.     

Female adaptation to developmental plasticity in male calling behavior

The katydid Neoconocephalus triops exhibits in North America substantial developmental plasticity of male mating calls. The AM rate of the summer calls is significantly faster than that of the winter calls at the same temperature. In the tropics, where N. triops originated, males express only the fast summer-call phenotype. We tested two alternative hypotheses: (1) call plasticity in the population from North America evolved in response to selection by female preference after N. triops colonized North America, or (2) call plasticity evolved before N. triops expanded into North America and its expression in the novel environment led to adaptive change of female preferences. First, we tested whether call plasticity was present in tropical populations of N. triops. Tropical males expressed the winter-call phenotype when reared under winter conditions, indicating that call plasticity did not evolve in response to temperate climates. Second, we compared female preferences among temperate and tropical populations. We found that the temperature dependence of preferred AM rate was significantly steeper in temperate N. triops than in a tropical population of N. triops. Third, we compared temperature dependence of female preference of the N. triops populations to three Neoconocephalus species without call plasticity. Only temperate N. triops had significantly steeper temperature dependence than the other species. This steeper temperature dependence matched female preference to the fast summer call at high temperatures and to the slow winter call at low temperatures in temperate populations. These results support the hypothesis that female preference changed in N. triops in North America to compensate for the plasticity of male calls.     

Temperature as a key driver of ecological sorting among invasive pest species in the tropical Andes

Invasive species are a major threat to the sustainable provision of ecosystem products and services, both in natural and agricultural ecosystems. To understand the spatial arrangement of species successively introduced into the same ecosystem, we examined the tolerance to temperature and analyzed the field distribution of three potato tuber moths (PTM, Lepidoptera: Gelechiidae), that were introduced in Ecuador since the 1980s. We studied physiological responses to constant temperatures of the three PTM species under laboratory conditions and modeled consequences for their overall population dynamics. We then compared our predictions to field abundances of PTM adults collected in 42 sites throughout central Ecuador. Results showed that the three PTM species differed with respect to their physiological response to temperature. Symmetrischema tangolias was more cold tolerant while Tecia solanivora had the highest growth rates at warmer temperatures. Phthorimaea operculella showed the poorest physiological performance across the range of tested temperatures. Overall, field distributions agree with predictions based on physiological experiments and life table analyses. At elevations >3000 m, the most cold-tolerant species, S. tangolias, was typically dominant and often the only species present. This species may therefore represent a biological sensor of climate change. At low elevations (<2700 m), T. solanivora was generally the most abundant species, probably due to its high fecundity at high temperatures. At mid elevations, the three species co-occurred, but P. operculella was generally the least abundant species. Consistent with these qualitative results, significant regression analyses found that the best predictors of field abundance were temperature and a species x temperature interaction term. Our results suggest that the climatic diversity in agricultural landscapes can directly affect the community composition following sequential invasions. In the tropical Andes, as in other mountain ecosystems, the wide range of thermal environments found along elevational gradients may be one reason why the risks of invasion by successively introduced pest species could increase in the near future. More data on potential biological risks associated with climatic warming trends in mountain systems are therefore urgently needed, especially in developing nations where such studies are lacking.     

The nature of heat coma in Littorina littorea (Mollusca: Gastropoda)

 The nature of heat coma was examined in the edible periwinkle Littorina littorea (L.). Duration of acclimation did not influence heat-coma temperature at 12 °C, although other acclimation temperatures were important in influencing thermal tolerance, with positive shifts in coma temperature observed in response to elevated temperatures. Previous thermal history also influenced heat-coma temperatures. Individuals subjected to repeat heat-coma events on a daily basis showed significant declines (P < 0.05) in coma-temperature; in contrast individuals exposed to repeat heat-coma events on a weekly basis showed no decline in thermal tolerance. Size-effects occurred at selected sites, where decreased heat-coma temperatures were recorded in large individuals. Received: 16 August 1999 / Accepted: 13 June 2000     

Temperature and pressure tolerance of larvae of Crepidula fornicata suggest thermal limitation of bathymetric range

The extant deep-sea fauna is thought to result from recolonisation of this environment by shallow-water organisms following climate-driven mass extinctions. Planktonic larval tolerance to high pressure is considered an important preadaptation for successful deep-sea invasion. In this study, the pressure and temperature tolerance of a species without any known confamilial deep-sea relative were assessed for the first time. Early- and late-veliger larvae of the shallow-water species Crepidula fornicata were subjected to a temperature/hydrostatic pressure regime from 5 to 25 °C and from 0.1 to 40 MPa. Although early and late veliger survived pressures equivalent to 2,000 m water depth or greater at all temperatures, decreased larval activity indicated significant sublethal temperature and pressure effects. Reduced larval activity of early veliger at low temperatures suggests that the bathymetric range of this species may be thermally constrained. A mechanistic model is proposed to explain the emerging pattern of ontogenetic shifts in pressure tolerance of shallow-water benthic invertebrates.     

Temperature ecotypes near the southern boundary of the kelp Laminaria saccharina

Effects of temperature on survival, growth, and photosynthesis were compared for two USA populations of Laminaria saccharina Lamour. One population was located in New York State, near the southern latitudinal boundary of the species in the western North Atlantic. This southern boundary population was exposed to ambient temperatures 20°C for about 6 wk each summer. The second population was located in Maine, toward the center of the latitudinal range of the species, and was rarely exposed to temperatures>17°C. sporophytes from the New York (NY) population exhibited greater tolerance of high temperature than plants from the Maine (ME) site. Juvenile sporophytes from the two sites had similar rates of survivorship and growth at temperatures below 20°C, but showed different responses at 20°C in laboratory experiments. NY plants survived and grew for 6 wk at 20°C. ME plants showed negative growth during wk 2 and 100% mortality during wk 3. NY and ME plants held in situ at the NY site during June to September, 1985, also exhibited differential survivorship when ambient temperatures exceeded 20°C. Results of photosynthesis and dark respiration measurements on NY and ME plants grown at various temperatures suggested that the high-temperature tolerance of NY plants was attributable to their ability to maintain positive daily net C-fixation at 20°C. The high-temperature tolerance of the NY plants appeared to be due to genetic adaptation and is probably crucial to the persistence of the species near its southern boundary.     

Critical thermal maxima and upper lethal temperatures for the calanoid copepods Acartia tonsa and A. clausi

Determination of the critical thermal maxima and upper lethal temperatures for Acartia tonsa Dana and A. clausi Giesbrecht revealed the relative temperature tolerance of the two species. A. tonsa exhibited a wider range of acclimation temperatures compared to A. clausi. The response of A. tonsa is related to its ubiquity in Atlantic Ocean estuaries (temperate and tropical), and its capacity to live in temperate waters throughout most of the year. Differences between upper lethal temperatures and critical thermal maxima were very narrow for A. tonsa from tropical and subtropical areas. This suggests that, in warm climates, this copepod lives close to its upper lethal temperature limits.Based in part on a dissertation submitted in partial fulfillment for the Ph.D. degree at the University of Rhode Island.     

Generalists and specialists along a latitudinal transect: patterns of thermal adaptation in six species of damselflies

Tropical organisms colonizing temperate environments face reduced average temperatures and dramatic thermal fluctuations. Theoretical models postulate that thermal specialization should be favored either when little environmental variation is experienced within generations or when among-generation variation is small relative to within-generation variation. To test these predictions, we studied six temperate species of damselflies differing in latitudinal distribution. We developed a computer model simulating how organisms experience environmental variation (accounting for diapause and voltinism) and performed a laboratory experiment assaying thermal sensitivities of growth rates. The computer model showed opposing latitudinal trends in among- and within-generation thermal variability: within-generation thermal variability decreased toward higher latitudes, whereas relative levels of among-generation thermal variability peaked at midlatitudes (where a shift in voltinism occurred). The growth experiment showed that low-latitude species were more thermally generalized than mid- and high-latitude species, supporting the prediction that generalists are favored under high levels of within-generation variation. Northern species had steeper, near-exponential reaction norms suggestive of thermal specialization. However, they had strikingly high thermal optima and grew very slowly over most of the thermal range they are expected to experience in the field. This observation is at present difficult to explain. These results highlight the importance of considering interactions between life history and environmental variation when deriving expectations of thermal adaptation.     

Selecting for Tolerance against Pathogens and Herbivores to Enhance Success of Reintroduction and Translocation

Abstract: Some species have insufficient defenses against climate change, emerging infectious diseases, and non‐native species because they have not been exposed to these factors over their evolutionary history, and this can decrease their likelihood of persistence. Captive breeding programs are sometimes used to reintroduce individuals back into the wild; however, successful captive breeding and reintroduction can be difficult because species or populations often cannot coexist with non‐native pathogens and herbivores without artificial selection. In captive breeding programs, breeders can select for host defenses that prevent or reduce pathogen or herbivore burden (i.e., resistance) or traits that limit the effects of parasitism or herbivory on host fitness (i.e., tolerance). We propose that selection for host tolerance may enhance the success of reintroduction or translocation because tolerant hosts generally have neutral effects on introduced pathogens and herbivores. The release of resistant hosts would have detrimental effects on their natural enemies, promoting rapid evolution to circumvent the host resistance that may reduce the long‐term probability of persistence of the reintroduced or translocated species. We examined 2 case studies, one on the pathogenic amphibian chytrid fungus ( Batrachochytrium dendrobatidis [Bd]) and the other on the herbivorous cactus moth ( Cactoblastis cactorum) in the United States, where it is not native. In each case study, we provide recommendations for how captive breeders and managers could go about selecting for host tolerance. Selecting for tolerance may offer a promising tool to rescue hosts species from invasive natural enemies as well as new natural enemies associated with climate change‐induced range shifts.     

Application of Agriculture‐Developed Demographic Analysis for the Conservation of the Hawaiian Alpine Wekiu Bug

Insects that should be considered for conservation attention are often overlooked because of a lack of data. The detailed information necessary to assess population growth, decline, and maximum range is particularly difficult to acquire for rare and cryptic species. Many of these difficulties can be overcome with the use of life table analyses and heat energy accumulation models common in agriculture. The wekiu bug (Nysius wekiuicola), endemic to the summit of one volcanic mountain in Hawaii, is a rare insect living in an environmentally sensitive alpine stone desert, where field‐based population assessments would be inefficient or potentially detrimental to natural and cultural resources. We conducted laboratory experiments with the insects by manipulating rearing temperatures of laboratory colonies and made detailed observations of habitat conditions to develop life tables representing population growth parameters and environmental models for wekiu bug phenology and demographic change. Wekiu bugs developed at temperatures only found in its environment on sunny days and required the thermal buffer found on cinder cones for growth and population increase. Wekiu bugs required approximately 3.5 months to complete one generation. The bug developed optimally from 26 to 30 °C, temperatures that are much higher than the air temperature attains in its elevational range. The developmental temperature range of the species confirmed a physiological reason why the wekiu bug is only found on cinder cones. This physiology information can help guide population monitoring and inform habitat restoration and conservation. The wekiu bug was a candidate for listing under the U.S. Endangered Species Act, and the developmental parameters we quantified were used to determine the species would not be listed as endangered or threatened. The use of developmental threshold experiments, life table analyses, and degree day modeling can directly inform otherwise unobservable habitat needs and demographic characteristics of extremely rare insects. Aplicación de Análisis Demográfico de Desarrollo Agrícola para la Conservación del Insecto Weiku Alpino Hawaiano     

Evidence of Local Adaptation in the Demographic Response of American Ginseng to Interannual Temperature Variation

Abstract: Bioclimatic envelope models of species’ responses to climate change are used to predict how species will respond to increasing temperatures. These models are frequently based on the assumption that the northern and southern boundaries of a species’ range define its thermal niche. However, this assumption may be violated if populations are adapted to local temperature regimes and have evolved population‐specific thermal optima. Considering the prevalence of local adaptation, the assumption of a species‐wide thermal optimum may be violated for many species. We used spatially and temporally extensive demographic data for American ginseng (Panax quinquefolius L.) to examine range‐wide variation in response of population growth rate (λ) to climatic factors. Our results suggest adaptation to local temperature, but not precipitation. For each population, λ was maximized when annual temperatures were similar to site‐specific, long‐term mean temperatures. Populations from disparate climatic zones responded differently to temperature variation, and there was a linear relation between population‐level thermal optima and the 30‐year mean temperature at each site. For species that are locally adapted to temperature, bioclimatic envelope models may underestimate the extent to which increasing temperatures will decrease population growth rate. Because any directional change from long‐term mean temperatures will decrease population growth rates, all populations throughout a species’ range will be adversely affected by temperature increase, not just populations at southern and low‐elevation boundaries. Additionally, when a species’ local thermal niche is narrower than its range‐wide thermal niche, a smaller temperature increase than would be predicted by bioclimatic envelope approaches may be sufficient to decrease population growth.     

Tolerance of high temperatures by some intertidal barnacles

The median lethal times of survival of the barnacles Elminius modestus, Balanus crenatus and B. balanoides, when continuously submerged at high temperatures, were determined for individuals collected in the summer and winter. In E. modestus and B. crenatus there was no seasonal change in high temperature tolerance. In B. balanoides, however, the adults were more susceptible in the winter than in the summer to temperatures a little below the upper lethal temperature. Using less comprehensive data for other British species of barnacles, it is concluded that, in general, the order of tolerance to high temperatures corresponds to the order of temperatures within the geographical and the intertidal distributions of the species. From the time-temperature-survival curves, intertidal barnacles are living closer to environmental temperatures than would be supposed on the basis of the measurement of the upper lethal temperature, which has been commonly measured for many species, but is of less ecological significance.     

Changes in size and trends of North American sea duck populations associated with North Pacific oceanic regime shifts

Broad-scale multi-species declines in populations of North American sea ducks for unknown reasons is cause for management concern. Oceanic regime shifts have been associated with rapid changes in ecosystem structure of the North Pacific and Bering Sea. However, relatively little is known about potential effects of these changes in oceanic conditions on marine bird populations at broad scales. I examined changes in North American breeding populations of sea ducks from 1957 to 2011 in relation to potential oceanic regime shifts in the North Pacific in 1977, 1989, and 1998. There was strong support for population-level effects of regime shifts in 1977 and 1989, but little support for an effect of the 1998 shift. The continental-level effects of these regime shifts differed across species groups and time. Based on patterns of sea duck population dynamics associated with regime shifts, it is unclear if the mechanism of change relates to survival or reproduction. Results of this analysis support the hypothesis that population size and trends of North American sea ducks are strongly influenced by oceanic conditions. The perceived population declines appear to have halted >20 years ago, and populations have been relatively stable or increasing since that time. Given these results, we should reasonably expect dramatic changes in sea duck population status and trends with future oceanic regime shifts.     

Shifts in a Pacific Ocean Fish Assemblage: the Potential Influence of Exploitation

Abstract:  As in many regions of the world, marine fishes and invertebrates along the Pacific coast of the United States have long been subjected to overexploitation. Despite this history, however, we lack basic information on the current status of many fishes along this coastline. We used data from a quarter century of fishery-independent, coast-wide trawl surveys to study systematically the demersal fish assemblages along the U.S. Pacific coast. We documented fundamental shifts in this fish assemblage. Average fish size, across a diversity of species, has declined 45% in 21 years. There have been major shifts in the constituent species of the assemblage, with some species achieving annual population growth rates of >10% and others declining in excess of 10% per year. Annual rate of change in population size appeared to be a function of life history interacting with fishing pressure. Negative trends in population size were particularly apparent in rockfish ( Sebastes spp.). However, across all taxa examined, trends in population size were associated with size of maturity, maximum size, and growth rate. Trends in population size were associated inversely with harvest levels, but stocks that mature late tended to decline faster than would be predicted by catch rates alone. Our results are disquieting because they raise the possibility that fishing-induced phase shifts in fish communities may affect the recovery of fishes, even after the implementation of severe fishing restrictions.     

Tolerance to high temperatures and potential impact of sea warming on reef fishes of Gorgona Island (tropical eastern Pacific)

Knowledge of upper thermal-tolerance limits of marine organisms in the tropical eastern Pacific (TEP) is important because of the influence of phenomena such as El Niño and global warming, which increase sea temperature. Laboratory experiments were conducted to determine the critical thermal maximum (CTM) of reef fishes from the TEP. In 15 reef fishes of Gorgona Island (TEP) the CTM was between 34.7°C and 40.8°C. None of these CTMs was exceeded by sea temperature in the TEP during any of the strongest El Niño events in this century (32°C during El Niño 1982-1983 and 1997-1998), which indicates that all species studied here may tolerate El Niño maximum temperatures. In addition, the CTM of the least-tolerant species was 8°C above the current mean sea temperature in a wide range of latitudes in the TEP. This suggests that fishes live far from their upper thermal tolerance limits and that the current global-warming trend is still unlikely to be dangerous for these species. If sea temperature continues to increase at the current rate, in about a century sea temperature could exceed the thermal tolerance of some reef fishes and threaten them with extinction. Such risk, however, might occur sooner if the sea temperature during El Niño also increased in step with the global warming, but also because other processes involved in maintaining population, such as reproduction, can be affected at lower temperatures. The possible ability of reef fishes to adapt to increases in sea temperature is discussed.     

The effects of temperature and pressure acclimation on the temperature and pressure tolerance of the shallow-water shrimp Palaemonetes varians

Anthropogenic effects on marine ecosystems (e.g. hypoxia, warming) at and beyond continental margins are assumed to affect physiological and biochemical boundaries to species’ distributions, potentially leading to habitat contraction across depth. Whether or not shallow-water benthic invertebrates are capable of undergoing depth-related migrations in response to such perturbations remains largely unknown. The few studies available have focused solely on whether colonisation of deep waters may be ongoing and on the ability of shallow-water species to tolerate low temperatures and high hydrostatic pressures: two physical parameters, which are thought to limit the depth range of a species. Those studies did not consider the effects of acclimation to low temperature and, especially, acclimation to high hydrostatic pressure on pressure tolerance. We demonstrate that acclimation to both low temperature (5 °C) and to high hydrostatic pressure (10 MPa) increases the pressure tolerance within the shallow-water shrimp Palaemonetes varians. Previous studies have demonstrated the impressive temperature and pressure tolerance of this shallow-water shrimp. Here, we provide evidence that a shallow-water species may acclimate to low temperature and high pressure and show greater pressure tolerance, suggesting that shallow-water organisms may be able to rapidly—and potentially stepwise—acclimate to the low temperature and high pressure conditions typical of the deep sea. These findings are of importance for understanding phylogenetic development from shallow- to deep-water species and the processes behind past, present and future bathymetric range shifts in species.     

Thermal tolerance of early development in tropical and temperate sea urchins: inferences for the tropicalization of eastern Australia

The thermal envelope of development to the larval stage of two echinoids from eastern Australia was characterized to determine whether they fill their potential latitudinal ranges as indicated by tolerance limits. The tropical sand dollar, Arachnoides placenta, a species that is not known to have shifted its range, was investigated in Townsville, northern Australia (19°20′S, 146°77′E), during its autumn spawning season (May 2012). The subtropical/temperate sea urchin, Centrostephanus rodgersii, a species that has undergone poleward range expansion, was investigated in Sydney, southern Australia (33°58′S, 151°14′E), during its winter spawning season (August 2012). The thermal tolerance of development was determined in embryos and larvae reared at twelve temperatures. For A. placenta, the ambient water temperature near Townsville and experimental control were 24 °C and treatments ranged from 14 to 37 °C. For C. rodgersii, ambient Sydney water temperature and experimental control were 17 °C, and the treatment range was 9–31 °C. A. placenta had a broader developmental thermal envelope (14 °C range 17–31 °C) than C. rodgersii (9 °C range 13–22 °C). Both species developed successfully at temperatures well below ambient, suggesting that cooler water is not a barrier to poleward migration for either species. Both species presently live near the upper thermal limits for larval development, and future ocean warming could lead to contractions of their northern range limits. This study provides insights into the factors influencing the realized and potential distribution of planktonic life stages and changes to adult distribution in response to global change.     

Impact of minimum winter temperatures on the population dynamics of Dendroctonus frontalis.

Predicting population dynamics is a fundamental problem in applied ecology. Temperature is a potential driver of short-term population dynamics, and temperature data are widely available, but we generally lack validated models to predict dynamics based upon temperatures. A generalized approach involves estimating the temperatures experienced by a population, characterizing the demographic consequences of physiological responses to temperature, and testing for predicted effects on abundance. We employed this approach to test whether minimum winter temperatures are a meaningful driver of pestilence from Dendroctonus frontalis (the southern pine beetle) across the southeastern United States. A distance-weighted interpolation model provided good, spatially explicit, predictions of minimum winter air temperatures (a putative driver of beetle survival). A Newtonian heat transfer model with empirical cooling constants indicated that beetles within host trees are buffered from the lowest air temperatures by approximately 1-4 degrees C (depending on tree diameter and duration of cold bout). The life stage structure of beetles in the most northerly outbreak in recent times (New Jersey) were dominated by prepupae, which were more cold tolerant (by >3 degrees C) than other life stages. Analyses of beetle abundance data from 1987 to 2005 showed that minimum winter air temperature only explained 1.5% of the variance in interannual growth rates of beetle populations, indicating that it is but a weak driver of population dynamics in the southeastern United States as a whole. However, average population growth rate matched theoretical predictions of a process-based model of winter mortality from low temperatures; apparently our knowledge of population effects from winter temperatures is satisfactory, and may help to predict dynamics of northern populations, even while adding little to population predictions in southern forests. Recent episodes of D. frontalis outbreaks in northern forests may have been allowed by a warming trend from 1960 to 2004 of 3.3 degrees C in minimum winter air temperatures in the southeastern United States. Studies that combine climatic analyses, physiological experiments, and spatially replicated time series of population abundance can improve population predictions, contribute to a synthesis of population and physiological ecology, and aid in assessing the ecological consequences of climatic trends.