Selection For Heat Tolerance Research Articles

Selection for heat tolerance in Atlantic salmon (Salmo salar) using reaction norms

Selection for heat tolerance is a key strategy for aquaculture to cope with the effects of climate change. Different alternatives exist to select aquatic species for heat tolerance. Here, we investigated the feasibility of applying reaction norms in summer growth of Atlantic salmon (Salmo salar) naturally exposed to diverse heat loads as a strategy to genetically improve heat tolerance. For this, summer growth of 40,044 fish from 2685 families and 21 cohorts, distributed across 14 years and 2 sites in Tasmania, was analysed under different reaction norm models (RNM), using a function of the average daily seawater temperature during the summer period (ranging from 12.8 to 19.7 °C) as the environment descriptor (heat load). RNM results unravelled substantial genotype by environment interaction for summer growth, specially between intermediate and high heat loads. Quadratic and spline linear-linear RNM outperformed linear RNM, showing a non-linear behaviour of the additive genetic effect on summer growth across different heat load gradients. The predictive ability of breeding values from RNM revealed opportunities to select for heat tolerance either for the highest heat load or for sensitivity to thermal variation (slope of RNM). Genomic-based breeding values presented better statistical properties than pedigree-based breeding values, highlighting the importance of using genomic information for a better predictive ability of heat tolerance. Genome-wide association analysis reinforced the polygenic nature of heat tolerance, indicating genomic selection as a more effective strategy to improve heat tolerance in Atlantic salmon, compared to strategies targeting specific genomic regions/genes.

Mitogenomics clarifies the position of the Nearctic magpies (Pica hudsonia and Pica nuttalli) within the Holarctic magpie radiation.

Partial separation of a peripheral population may lead to its divergence and, potentially, speciation due to genetic drift followed by selection and geographic isolation. This process may cause taxonomic uncertainty because reproductive isolation in allopatry cannot be verified directly. The two Nearctic allopatric species of magpies (Aves, Corvidae: Pica) serve as a good example of these problems. The Black-billed magpie Pica hudsonia is widely distributed in North America, whereas the Yellow-billed Magpie Pica nuttalli is endemic to a restricted range in California. Their relationships with Palearctic species have been little studied. We obtained complete mitochondrial genomes of both Nearctic magpie species, along with the Eurasian Magpie (Pica pica) and the Oriental Magpie (Pica serica), 20 mitogenomes in total. Phylogenetic analysis reveals a basal position of P. serica, and P. pica as a sister clade to the two Nearctic species. P. hudsonia and P. nuttalli form reciprocal monophyletic subclades, showing recent divergence between and within them. Our data show that the Nearctic magpie lineage diverged from the common ancestor with P. pica, with a single migration wave via the Beringia. Within the Nearctic, we hypothesize a peripatric mode of speciation among Pica taxa due to the divergence and separation of the small marginal population in California below the Sierra-Nevada mountains. Diversifying amino acid substitutions in ND4-ND5-ND6 genes along the branch leading to the New World clade may indicate selection for heat-tolerance. Considering the clear phenotypic differences between P. hudsonia and P. nuttalli, our data, showing their reciprocal monophylies and genetic distinctness, is consistent with the two-species taxonomy.

Impact of hot weather on animal performance and genetic strategies to minimise the effect

Dairy cows in Australia and New Zealand are generally kept outdoors, making them susceptible to weather variability and in particular heat stress. In this paper, we review (1) exploiting genetic variability to improve heat tolerance, (2) genotype by environment interactions, i.e. suitability of high merit cows to weather variability and (3) how novel phenotyping and genomics can help improve heat tolerance. Selection for heat tolerance is a permanent and cumulative strategy and especially useful in grazing situations where management practices, such as cooling mechanisms, are sometimes impractical. Australia was the first country in the world to release breeding values for heat tolerance in dairy cattle nationally in 2017. The breeding value captures genetic variation in the reduction of milk production traits with rising temperature and humidity. The breeding values have been validated in independent studies (in Victoria, Australia, and California, USA), showing that thermotolerant cows maintain a lower core body temperature under hot and humid conditions. Genotype by environment interactions for traits sensitive to heat is only a concern for farms in very extreme conditions and therefore affect only a small proportion of individuals (those in the extreme 5th percentile). Heat tolerance is a complex trait in that in addition to milk traits, health and fertility may also be affected. Next-generation heat tolerance breeding values may include sensor device information in addition to changes in milk composition, or other measurable biomarkers. This is especially useful when measured in genotyped female populations. Research into novel ways of measuring heat tolerance could transform the way we select for this trait and capture more of the complexity of this trait. To be successful in this area, multi-disciplinary collaboration among animal scientists is likely to facilitate this goal. Combining genomics, traditional and novel measures of heat tolerance with intermediate metabolic biomarkers and prioritised genetic variants could be a way to capture the complexity of thermotolerance in future heat tolerance breeding values. Finally, selecting cows that are resilient to variability in weather is feasible and heat tolerance is a good example of this.

Comparative Expression Profiling and Sequence Characterization of ATP1A1 Gene Associated with Heat Tolerance in Tropically Adapted Cattle.

Simple SummaryAn understanding of the way that animals respond to heat stress is key to the development of adaptation and mitigation strategies for a changing climate. The response of mammals to heat exposure involves changes at every level of organization from molecular and cellular to systemic and behavioral. The concert of events involves many genes and gene products. The Na+/K+ ATPase ∝1 (ATP1A1), a product of the ATP1A1 gene, is important for the response to heat because it determines the activity of the Na+/K+ pump that is ubiquitous in cell membranes. It was shown recently that ATP1A1 is important in combating the oxidative stress that a cell faces and that it modulates the Src signaling pathway that is involved in the response to many stressors. Vechur cattle (dwarf Bos taurus indicus) are well known for their adaptability to the tropical heat and humidity that persists in their native state of Kerala, India. We here analyze the comparative expression profile of the ATP1A1 gene in heat-tolerant Vechur and Kasaragod (another dwarf B. t. indicus) cattle and a heat-intolerant crossbreed (B. t. taurus × B. t. indicus) and characterize the sequence of ATP1A1 mRNA in the Vechur genotype. Environmental stress and heat tolerance were measured. Expression profiling indicated that ATP1A1 was differentially expressed in the phenotypically disparate cattle breeds. A molecular evolutionary genetic analysis revealed that the divergent origin of dwarf cattle was adaptive in response to heat stress and suggests the potential use of ATP1A1 as a marker for heat tolerance.Climate change is an imminent threat to livestock production. One adaptation strategy is selection for heat tolerance. While it is established that the ATP1A1 gene and its product play an important role in the response to many stressors, there has been no attempt to characterize the sequence or to perform expression profiling of the gene in production animals. We undertook a field experiment to compare the expression profiles of ATP1A1 in heat-tolerant Vechur and Kasaragod cattle (Bos taurus indicus) with the profile of a heat-susceptible crossbreed (B. t. taurus × B. t. indicus). The cattle were exposed to heat stress while on pasture in the hot summer season. The environmental stress was quantified using the temperature humidity index (THI), while the heat tolerance of each breed was assessed using a heat tolerance coefficient (HTC). The ATP1A1 mRNA of Vechur cattle was amplified from cDNA and sequenced. The HTC varied significantly between the breeds and with time-of-day (p < 0.01). The breed–time-of-day interaction was also significant (p < 0.01). The relative expression of ATP1A1 differed between heat-tolerant and heat-susceptible breeds (p = 0.02). The expression of ATP1A1 at 08:00, 10:00 and 12:00, and the breed–time-of-day interaction, were not significant. The nucleotide sequence of Vechur ATP1A1 showed 99% homology with the B. t. taurus sequence. The protein sequence showed 98% homology with B. t. taurus cattle and with B. grunniens (yak) and 97.7% homology with Ovis aries (sheep). A molecular clock analysis revealed evidence of divergent adaptive evolution of the ATP1A1 gene favoring climate resilience in Vechur cattle. These findings further our knowledge of the relationship between the ATP1A1 gene and heat tolerance in phenotypically incongruent animals. We propose that ATP1A1 could be used in marker assisted selection (MAS) for heat tolerance.

Growing Environment and Heat Treatment Effects on Intra- and Interspecific Pollination in Chile Pepper (Capsicum spp.)

Heat tolerance is important for the sustainable production of many crops, including chile pepper. Tolerance to high temperature is complex and involves various component traits, with pollen viability being among the most important. in vitro pollen assays for heat tolerance have been widely used in chile pepper; however, associations between the pollen treatment and pollination have not been widely explored. The objectives of this study were to validate the utility of in vitro heat stress pollen characterization through in vivo pollination during summer and winter seasons and to evaluate the cross-compatibility among wild and domesticated species to initiate introgression population development. Seven entries of wild and domestic Capsicum species grown during the summer and winter seasons were used to evaluate pollination success rate. Pollen was either used directly or treated at 38 °C for four hours before making reciprocal self- and cross-pollination among all the entries. Significant associations between in vitro pollen treatment and pollination success rate during summer and winter seasons were identified. Heat treatment was a greater contributor to variability than the growing environment, which validates previous reports on the usefulness of studying pollen in vitro in selection for heat tolerance. Accessions of the wild progenitor C. annuum var glabriusculum, PBC 1969 and PBC 1970, were identified as a potential heat-tolerant source for use in breeding and future research. This work provides a basis for future research in exploring additional heat tolerance components as well as for the development of phenotyping assays for pollen or other floral traits.

PSIII-12 Genetic analysis of heat tolerance in Holsteins using test-day production records and satellite-based meteorological data

Abstract Heat stress in dairy cattle is an existing issue in temperate regions that can cause reduced milk production, impaired fertility, and mortality. Genetic selection for heat tolerance using test-day production records and weather station data is a potential mitigation strategy. However, weather stations can have temporal data gaps and a low spatial resolution, which reduces the number of herds that can be incorporated into an analysis. The objectives for this study include: (1) compare satellite-based meteorological data from the NASA POWER database to weather station records in Ontario and Quebec, (2) evaluate the effects of heat stress on Canadian Holsteins, and (3) assess breeding value estimates for heat tolerance in the same population. Daily estimates of ambient temperature, dewpoint temperature, relative humidity, and wind speed from 481 weather stations in Ontario and Quebec were compared to the parameters estimated by the NASA POWER project using an ordinary least squares regression. The coordinates of herds in Ontario and Quebec were estimated using their addresses and Google Maps Geocoding. The best weather data for each herd location will be incorporated into two random regression animal models to analyze three test-day production traits: milk, fat, and protein yield. The first model will be used to estimate general and specific additive genetic merits over the thermal gradient. The second model will estimate the traditional additive genetic merit. In conclusion, this study explores the use of satellite estimated meteorological parameters in addition to or alternatively to weather station data in heat tolerance studies, quantifies the sensitivity of Canadian dairy cattle to heat stress, and evaluates if genetic selection for increased heat tolerance in Canadian dairy herds is possible.

Putative Markers associated with Grain weight under Terminal Heat Stress in Bread-Wheat (Triticum aestivum L.)

Terminal heat tolerance is an important breeding target in wheat. Methods of selection for heat tolerance in wheat are limited. The most common approach is the evaluation of yield in nurseries grown under heat stress. The objective of this study was to estimate inheritance of heat tolerance and the grain character in bread wheat by combining molecular marker analysis. The tolerance in bread wheat using a cross between genotypes that were identified previously were utilized to identify SSR markers that are linked to traits associated with terminal heat tolerance. Grain wt. was used as a measure of heat tolerance because this trait was highly correlated with tolerance levels of genotypes. Genotypes WH730 and RAJ4014 were used as tolerant and sensitive parents respectively for generating mapping populations against the study of terminal heat stress respectively. A Recombinant Inbred Line (RIL) mapping population derived from the heat sensitive genotype RAJ4014 and heat tolerant genotype WH730 was evaluated for the heat stress over two years in a replicated trial under timely sown (TS) and late sown (LS) field conditions. The parental lines were screened with approximately 300 SSR (μsatellite) markers out of which about 20% showed polymorphism. Parents and their Recombinant inbred lines (RILs) screened by microsatellite markers for finding allelic variation. Xgwm48, Xgwm55 and Xcfd29 are three markers suggested an application of marker-assisted selection for wheat improvement under terminal heat tolerance.

Quantifying selection in evolving populations using time-resolved genetic data

Methods which uncover the molecular basis of the adaptive evolution of a population address some important biological questions. For example, the problem of identifying genetic variants which underlie drug resistance, a question of importance for the treatment of pathogens, and of cancer, can be understood as a matter of inferring selection. One difficulty in the inference of variants under positive selection is the potential complexity of the underlying evolutionary dynamics, which may involve an interplay between several contributing processes, including mutation, recombination and genetic drift. A source of progress may be found in modern sequencing technologies, which confer an increasing ability to gather information about evolving populations, granting a window into these complex processes. One particularly interesting development is the ability to follow evolution as it happens, by whole-genome sequencing of an evolving population at multiple time points. We here discuss how to use time-resolved sequence data to draw inferences about the evolutionary dynamics of a population under study. We begin by reviewing our earlier analysis of a yeast selection experiment, in which we used a deterministic evolutionary framework to identify alleles under selection for heat tolerance, and to quantify the selection acting upon them. Considering further the use of advanced intercross lines to measure selection, we here extend this framework to cover scenarios of simultaneous recombination and selection, and of two driver alleles with multiple linked neutral, or passenger, alleles, where the driver pair evolves under an epistatic fitness landscape. We conclude by discussing the limitations of the approach presented and outlining future challenges for such methodologies.

Multi-environment Selection of Small Sieve Snap Beans Reduces Production Constraints in East Africa and Subtropical Regions

Small-sieve snap beans (Phaseolus vulgaris L.) are an important source of income for smallholder farmers in East Africa. In this region as well as in other tropical and subtropical environments, common bean rust, caused by Uromyces appendiculatus (Pers.:Pers.), and heat stress reduce the yield and quality of snap beans. Small-sieve rust-resistant snap beans and that are heat-tolerant were developed using heat-tolerant snap bean breeding lines that had broad-spectrum rust resistance conditioned by the combination of the Andean Ur-4 and Mesoamerican Ur-11 genes. The Ur-4 and Ur-11 rust gene combination confers resistance to 90 races of the hypervariable pathogen from different parts of the world, including East Africa, that are maintained at Beltsville, MD. Four breeding lines each having the combination of the two rust genes were crossed in a 4 × 5 diallel mating design with five susceptible small-sieve cultivars to give 20 F1 hybrids. The hybrid combinations were advanced through the F2, F3, and F4 generations with selection for heat tolerance, rust resistance, and pod quality to develop lines combining these traits. Twenty F5 breeding lines that had the combination of these traits were selected and evaluated in East Africa at four field sites selected on the basis of differences in altitude, climate, and virulence diversity of the bean rust pathogen and in Puerto Rico at a field site characterized by high temperatures. There was a significant positive correlation between ranks of heat stress influenced yield components (seeds per pod and total yield) at the hot field site and the controlled high-temperature (32/27 °C) greenhouse. Four of the breeding lines developed, L5, L9, L13, and L17, combined heat tolerance and rust resistance in the desired plant type with high yield and good pod quality. These lines are the first known small-sieve snap beans with the combination of traits for heat tolerance and broad-spectrum rust resistance conferred by the Ur-4 and Ur-11 genes. These results demonstrate ability to combine heat tolerance and rust resistance as important traits for adaptation of specific market classes of common bean to tropical and subtropical environments through targeted selection of multiple traits in controlled environments.

Heat stress in food legumes: evaluation of membrane thermostability methodology and use of infra-red thermometry

Heat tolerance in 45 chickpea, lentil, and faba bean genotypes was investigated during 2007/2008 and 2008/2009 at Alexandria Agriculture Research Station, Alexandria, Egypt, using screening methods employing the membrane thermostability technique. Threshold temperature to be used in screening for heat tolerance at germination was also investigated for each crop. Temperatures, responsible for 50% germination were 40, 33.5, and 29°C for chickpea, faba bean, and lentil, respectively. Germination percent under high temperature varied significantly (P ≤ 0.05) amongst genotypes. Germination percentage ranged from 4.8 to 71.6, 39.2 to 90.0, and 4.8 to 68.6, in chickpea, lentil, and faba bean, respectively. Differences were significant (P ≤ 0.05) among faba bean and chickpea genotypes. Membrane relative injury (RI%) showed significant (P ≤ 0.05) variability among the genotypes and ranged from 10.57 to 58, 5.2 to 61.7, and 15.7 to 52.7 in chickpea, lentil, and faba bean, respectively. Canopy temperature was measured to evaluate heat avoidance in tested genotypes. Infra-red thermometry was used to measure canopy temperature and the gradient of canopy to ambient air temperature (∆TC-A) in moisture stressed and unstressed treatments. Canopy temperature, leaf water potential (LWP) and leaf water content were affected by the level of soil moisture. Genotypes were able to bring their canopy temperatures to levels lower than ambient air temperatures but the differences were not significant. A heat stress index (HSI) were computed relating the ∆TC-A in moisture stressed to unstressed treatments. Regression of leaf water potential (LWP) and the heat stress index (HSI) was significant (P ≤ 0.05) in faba bean genotypes in the stressful environment. The results of the present investigation emphasize the efficiency of membrane thermostability technique in selection for heat tolerance in early stages of growth in food legumes.

Effectiveness of in vitro selection for agronomic characters in potato

Effectiveness of in vitro selection for agronomic characters was studied by finding correlation coefficients between in vitro and in vivo performance of 22 potato genotypes. Evaluation was performed under eight in vitro and two in vivo conditions. Genotypic differences were highly significant for various characters under all in vitro and in vivo conditions. Error mean squares were much lower in in vitro experiments than in in vivo experiments. In vitro selection was found to be highly effective for tuber colour, stem pigment and number of eyes, and moderately effective for average tuber weight, plant vigour and foliage senescence under specific conditions. The results also indicated the possibility of in vitro selection for heat tolerance. For tuber yield and number of tubers, effectiveness of in vitro selection was low to very low, because differences in phenotypic expressions of genotypes were much enlarged under in vitro conditions compared to under in vivo conditions. Correlation coefficients for certain characters were better when in vitro conditions were closer to in vivo conditions. To improve the efficiency of in vitro selection, there is perhaps a need to simulate and identify the in vitro conditions under which genotypic differences are reflected in phenotypes more realistically as they are expressed under in vivo conditions.

Evaluation of parents and selection for heat tolerance in the early generations of a potato (Solanum tuberosum L.) breeding program

Potato cultivars (Solanum tuberosum L.) were evaluated for their capacity to form tubers under high temperature conditions (heat tolerance). In an experiment conducted in the hot summer season in the field and in experiments conducted under controlled environments in glasshouses, differences in tolerance to heat were noted among the various genotypes. Although heat tolerance tended to be associated with earliness in maturation, differences in the response to high temperatures were observed in genotypes of the same maturity class. Progeny of the cultivars Desiree and Cara, and hybrid progeny of Cara x Desiree and of Blanka x Cara were screened for heat tolerance in controlled environments in glasshouses. Long photoperiod delayed tuberization but high temperatures strongly inhibited tuber formation, which was 4% in the progeny of Desiree, <2% in the progeny of Cara and of Cara x Desiree, and ca. 16% in progeny of Blanka x Cara. For seedlings that did not form tubers in the hot glasshouse but were subsequently transferred to the cool glasshouse, tuberization was much enhanced and clones selected through this dual procedure exhibited tolerance to heat in the first conal year. The results of this study indicate that: (a) tolerance to heat is associated with earliness; however, differences in the response to heat exist among late-maturing cultivars; (b) tolerance to heat, as assessed by the capacity to form tubers under high temperatures, is genetically controlled, and the timing of tuberization might be independent of the rate of tuberization in hybrid progeny; (c) the incidence of heat tolerance in progeny population is correlated with the relative tolerance of the parents; and (d) the dual selection procedure is an efficient approach for the selection of heat-tolerant clones.