The energetic cost of arousal from torpor in the marsupial Sminthopsis macroura : benefits of summer ambient temperature cycles

The costs of arousal from induced torpor were measured in the striped-faced dunnart (Sminthopsis macroura; ca. 25 g) under two experimental ambient temperature cycles. The sinusoidal-type temperature cycles were designed to evaluate the effects of passive, ambient temperature heating during arousal from torpor in these insectivorous marsupials. It was hypothesised that diel ambient temperature cycles may offer significant energy savings during arousal in animals that employ daily torpor in summer as a response to unpredictable food availability. The cost of arousal in animals in which passive, exogenous heating occurred was significantly lower than that in animals not exposed to an ambient temperature cycle. The total cost of all three phases of torpor (entry, maintenance and arousal) was almost halved when animals were exposed to an ambient heating cycle from 15 °C to 25 °C over a 24-h period. In all animals, irrespective of the experimental ambient temperature cycle employed, the minimum torpor body temperature was 17–18 °C. The body temperature (T_b) of animals exposed to exogenous heating increased from the torpor T_b minimum to a mean value of 22.59 °C before endogenous heat production commenced. This relatively small increase in T_b of ca. 5 °C through `free' passive heating was sufficient to account for the significant ca. three-fold decrease in the cost of arousal and may represent an important energetic aid to free-ranging animals. Accepted: 4 October 1998     

Confirmation of pleisiomorphic daily torpor in mammals: the round-eared elephant shrew Macroscelides proboscideus (Macroscelidea)

The characteristics of daily torpor were measured in the round-eared elephant shrew Macroscelides proboscideus (Macroscelidea) in response to ambient temperature and food deprivation. Elephant shrews are an ancient mammal order within a superordinal African clade including hyraxes, elephants, dugongs and the aardvark. M. proboscideus only employed torpor when deprived of food; torpor did not occur under an ad libitum diet at ambient temperatures of 10, 15 and 25?°C. Torpor bout duration ranged from <1?h to ca. 18?h. The times of entry into torpor were restricted to the scotophase, despite normothermic body temperature patterns indicating a rest phase coincident with the photophase. Full arousal was always achieved within the first 3?h of the photophase. When food deprived, the onset of the rest phase, and hence torpor, advanced with respect to the experimental photoperiod. The lowest torpor body temperature measured was 9.41?°C. Daily torpor in M. proboscideus confirms a pleisiomorphic origin of daily heterothermy. Torpor facilitates risk-averse foraging behaviour in these small omnivores by overcoming long-term energy shortfalls generated by the inherent variability of food availability in their semi-arid, El Niño-afflicted habitats.     

The evolution of genetic canalization under fluctuating selection

Abstract.— If the direction of selection changes from generation to generation, the ability to respond to selection is maladaptive: the response to selection in one generation leads to reduced fitness in the next. Because the response is determined by the amount of genetic variance expressed at the phenotypic level, rapidly fluctuating selection should favor modifier genes that reduce the phenotypic effect of alleles segregating at structural loci underlying the trait. Such reduction in phenotypic expression of genetic variation has been named "genetic canalization." I support this argument with a series of two- and multilocus models with alternating linear selection and Gaussian selection with fluctuating optimum. A canalizing modifier gene affects the fitness of its carriers in three ways: (1) it reduces the phenotypic consequences of genetic response to previous selection; (2) it reduces the genetic response to selection, which is manifested as linkage disequilibrium between the modifier and structural loci; and (3) it reduces the phenotypic variance. The first two effects reduce fitness under directional selection sustained for several generations, but improve fitness when the direction of selection has just been reversed. The net effect tends to favor a canalizing modifier under rapidly fluctuating selection regimes (period of eight generations or less). The third effect improves fitness of the modifier allele if the fitness function is convex and reduces it if the function is concave. Under fluctuating Gaussian selection, the population is more likely to experience the concave portion of the fitness function when selection is stronger. Therefore, only weak to moderately strong fluctuating Gaussian selection favors genetic canalization. This paper considerably broadens the conditions that favor genetic canalization, which so far has only been postulated to evolve under long-term stabilizing selection.     

Osmoregulated periplasmic glucans are needed for competitive growth and biofilm formation by Salmonella enterica serovar Typhimurium in leafy-green vegetable wash waters and colonization in mice

Osmoregulated periplasmic glucans (OPGs) are major periplasmic constituents of Gram-negative bacteria. The role of OPGs has been postulated in symbiotic as well as pathogenic host–microorganism interactions. Here, we report the role of OPGs from Salmonella enterica serovar Typhimurium during growth and biofilm formation in leafy-green vegetable wash water. The opgGH mutant strain, which was defective in OPG biosynthesis, initiated the growth at a slower rate in wash waters obtained from spinach, lettuce and green collard and severely impaired biofilm formation. The lack of OPG synthesis did not influence biofilm formation by the opgGH mutant in low-nutrient low-osmolarity laboratory media. In coculture experiments initiated with equal proportions of cells, the opgGH mutant was outnumbered by the wild-type strain under the planktonic as well as the biofilm growth conditions. The opgGH mutant strain poorly colonized mouse organs when introduced orally along with the wild-type strain. This is the first report demonstrating the role of OPGs of Salmonella in competitive colonization of biofilms, planktonic cultures and mouse organs.     

不同生长环境下水稻穗伸出度的QTL分析

以十和田/昆明小白谷225个F14家系为作图群体,在云南省弥勒县(正常生长环境)、嵩明县(自然低温胁迫环境)、丽江市(自然低温胁迫环境)等3个试点不同年份共5种不同生长环境下进行了水稻主穗和分蘖穗穗伸出度的异地鉴定,并利用SSR标记对水稻穗伸出度进行了QTL分析。检测结果表明,在5种不同的生长环境下共检测到12个与水稻穗伸出度相关的QTL,分别分布于第1(2个QTLs)、2、4、6(3个QTLs)、7(3个QTLs)、9(2个QTLs)号染色体,对表型的贡献率为3.72%~22.17%。其中与主穗穗伸出度相关的QTL共11个,与分蘖穗穗伸出度相关的QTL共7个,其中6个在主穗和分蘖穗上均检测到。在与主穗穗伸出度相关的11个QTL中,q PE-7-1在4种环境下均被检测到,解释的表型变异为9.49%~22.17%;q PE-1-1、q PE-1-2、q PE-6-1和q PE-9-2 4个QTL在2种环境下均被检测到。在与分蘖穗穗伸出度相关的7个QTL中,q PE-1-2、q PE-7-1和q PE-6-1 3个QTL在2种环境中均被检测到,解释的表型变异率分别为4.35%~12.64%、13.22%~20.89%和11.49%~15.73%。     

GENETIC VARIATION AND THE EVOLUTION OF EPIGENETIC REGULATION

Epigenetic variation has been observed in a range of organisms, leading to questions of the adaptive significance of this variation. In this study, we present a model to explore the ecological and genetic conditions that select for epigenetic regulation. We find that the rate of temporal environmental change is a key factor controlling the features of this evolution. When the environment fluctuates rapidly between states with different phenotypic optima, epigenetic regulation may evolve but we expect to observe low transgenerational inheritance of epigenetic states, whereas when this fluctuation occurs over longer time scales, regulation may evolve to generate epigenetic states that are inherited faithfully for many generations. In all cases, the underlying genetic variation at the epigenetically regulated locus is a crucial factor determining the range of conditions that allow for evolution of epigenetic mechanisms.     

Fluvial response to late Quaternary climate change in NE Queensland, Australia

Samples of alluvial and colluvial deposits from the coastal plain and coastal valleys north and south of Cairns (17°S) have been dated using optically stimulated luminescence (OSL) protocols, with additional thermoluminescence (TL) and Radiocarbon assays. Coarse fanglomerates from elevated coastal terraces date back to 81 ka, but most are clustered in oxygen isotope stage three (OIS3, 64-28 ka), indicating high-energy conditions during this period. Extensive fans and terraces of finer calibre sediments are widely represented grading from coarse gravels and cobbles in proximal zones fine sand and silt in distal areas. Dates show that vertical accumulation of 10-15 m of sediment occurred between ∼ 28 and 14 ka (OIS2), after which the fans were dissected and Holocene deposits become fragmentary. A number of deposits indicating hillslope instability were successfully dated and these fall mainly into OIS3 and post 12 ka. These results are interpreted as catchment responses to Late Pleistocene climate and vegetation changes, documented elsewhere from local pollen and ocean drilling sites. Correlation with these records and with evidence for regional climate change from the Austral-Asian region is good and indicates that these changes were sufficient to transform fluvial activity and slope processes.     

Connecting local environmental sequences to global climate patterns: evidence from the hominin-bearing Hadar Formation, Ethiopia

Central to the debate surrounding global climate change and Plio-Pleistocene hominin evolution is the degree to which orbital-scale climate patterns influence low-latitude continental ecosystems and how these influences can be distinguished from regional volcano-tectonic events and local environmental effects. The Pliocene Hadar Formation of Ethiopia preserves a record of hominin paleoenvironments from roughly 3.5 to 2.2 Ma at a temporal resolution relevant to evolutionary change within hominins and other taxa. This study integrates the high-resolution sedimentological and paleontological records at Hadar with climate proxies such as marine core isotope, dust, and sapropel records. Consistent cycling observed both between and within fluvial and lacustrine depositional environments prior to 2.9 Ma at Hadar appears to be predominantly climatic in nature. In contrast a significant change in depositional facies after 2.9 Ma to sequences dominated by conglomerate cut-and-fill cycles indicates a strong tectonic signature related to regional developments in the Main Ethiopian Rift. While specific events seen in marine proxy records may have parallels in the Hadar environmental archive, their overall patterns of high versus low variability may be even more relevant. For example, periods of relatively high-amplitude climate oscillations between 3.15 and 2.95 Ma may be linked to noted size-related morphological changes within the Hadar Australopithecus afarensis lineage and a significant increase in more arid-adapted bovid taxa. Increased aridity in East Africa during this period is also indicated by peaks in eolian dust in the marine core record. Conversely, the dominant lacustrine phase at Hadar ca. 3.3 Ma coincides with the least variable period in several climate proxy records, including marine core foraminifera delta(18)O values and eolian dust concentration. This phase is also coeval with low insolation variability and a very distinct and significant long-term period of low dust percentage in circum-Africa marine cores.