A review on the potential effects of environmental and economic factors on sheep genetic diversity: Consequences of climate change

Climate change has a significant effect on the productivity of livestock including milk, meat, and reproduction. This could be attributed to the internal diversion of energy resources towards adaptive mechanisms. Among the climate change variables, thermal stress seems to be the major limiting factor in animal agriculture. A better understanding of the effects of climate change-influenced ecological factors on the genetic diversity of livestock species is warranted. Sheep is an ideal livestock species to be used in investigating environmental adaptation due to its wide range of agroecological habitats, genetic and phenotypic variability. There is a heavy reliance on sheep genetic diversity for future animal protein security, but the implications of climate change on their genetic diversity receive less attention.Here, the potential environmental factors influencing natural selection in sheep populations are presented. We argue that prolonged exposure to these factors plays a major role in influencing the development of adaptation traits in indigenous sheep breeds, consequently leading to the alteration of genetic diversity at specific loci. The factors discussed include hot temperatures (heat stress), insufficient water, low quantity and quality of forage, and prevalence of parasites, pests, and diseases. In addition, genetic diversity, some signatures of selection for adaptation and economic angles of selection are also briefly discussed.A better understanding of environmental factors influencing the genetic diversity of sheep populations will inform breeding and management programs and may offer an opportunity for greater production efficiency with low input costs.     

Demographic effects of extreme winter weather in the barn owl

Extreme weather events can lead to immediate catastrophic mortality. Due to their rare occurrence, however, the long-term impacts of such events for ecological processes are unclear. We examined the effect of extreme winters on barn owl (Tyto alba) survival and reproduction in Switzerland over a 68-year period (∼20 generations). This long-term data set allowed us to compare events that occurred only once in several decades to more frequent events. Winter harshness explained 17 and 49% of the variance in juvenile and adult survival, respectively, and the two harshest winters were associated with major population crashes caused by simultaneous low juvenile and adult survival. These two winters increased the correlation between juvenile and adult survival from 0.63 to 0.69. Overall, survival decreased non-linearly with increasing winter harshness in adults, and linearly in juveniles. In contrast, brood size was not related to the harshness of the preceding winter. Our results thus reveal complex interactions between climate and demography. The relationship between weather and survival observed during regular years is likely to underestimate the importance of climate variation for population dynamics.     

Pedigree analysis of the closed nucleus of Iranian Baluchi sheep

A study was conducted to characterise genetic diversity in the closed nucleus of Baluchi sheep using pedigree analysis. Herdbook information collected between 1979 and 2008, including pedigree records on 21,721 animals, was used to compute inbreeding and average generation intervals. Effective population size and parameters derived from probability of gene origin were computed for ewes born between 2005 and 2008 with both parents known (female reference population). The average complete generation equivalent of the female reference population was 5.47. The mean generation interval was 3.33 years in the studied period. From 1983 to 1994, the rate of increase in inbreeding was approximately 0.2% per year, but, after 1994, inbreeding did not increase as in the preceding years and had an approximately flat trend over time. The mean relationship coefficients among rams, among ewes and between rams and ewes in active animals were calculated to predict the future level of inbreeding. The effective number of founders, effective number of ancestors and founder genome equivalent of the reference population were 80, 47 and 19.5, respectively. The realised effective population size was 134 animals. The results of this study indicated that the population under study has fairly good genetic variability.     

Consequences of outbreeding on phenotypic plasticity in Drosophila mercatorum wings

A multivariate morphometric investigation was conducted on wings of two parthenogenetic Drosophila mercatorum strains and offspring (F1) of crosses between these parthenogenetic strains with highly inbred sexual individuals of the same species. The parental flies and F1 offspring were reared at three different temperatures: 20, 25, or 28°C. This design allows a comparison of completely homozygous individuals (parental generation) with identical heterozygote offspring (F1), which makes an analysis of phenotypic plasticity of morphometric traits possible, without a potentially confounding effect of genotype-environment interactions, which can increase the phenotypic variability. The same pattern of phenotypic plasticity of wing size between the homozygous parental strains and the heterozygous offspring was found in both strains with an apparent heterotic effect for wing size in the F1 at 25°C. At 20 and 28°C flies from the parental generation had the biggest wings. Phenotypic plasticity of shape was found to be strain dependent. A reduced level of developmental instability (DI) was found in the F1 as compared to the parental strain only in strain 1 reared at 20°C for the wing size and 25°C for the wing shape. For all the other treatments higher DI was found in the F1 when the difference was significant, which is suggestive of outbreeding depression. These findings are difficult to interpret since an apparent heterotic effect of size at 25°C is accompanied by higher DI (though not significant in strain 2) and complex changes in wing shape. Hence, we cannot conclude whether outbreeding lowers or increases the capacity to respond to environmental change via plastic responses and via changes of the level of DI. The degree of change of phenotypic plasticity and DI is trait specific, depending on the environment and on the genotypes which are hybridizing. Kristian Krag and Hans Thomsen have contributed equally.     

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m²) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio = 0.43 and Simpson’s D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (Φ _ST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.     

Climatic and geographic effects on the spatial genetic pattern of a landbird species (Alectoris rufa) on the Iberian Peninsula

Understanding the spatial pattern of genetic diversity may be pivotal to adaptive conservation management of a given taxon. The red-legged partridge (Alectorisrufa, Linnaeus 1758) is naturally widely distributed from the Mediterranean to humid temperate zones. According to a recent study, the genetic structure of this species comprises five clusters, three of which are in the Iberian Peninsula (glacial refugia). Partridge demographic expansion events and climatic shifts during Pleistocene glaciations have been used to test the hypotheses concerning Iberian red-legged partridge distribution. We tested the existence of climatic and geographic relationships on genetic diversity/distances. We employed markers from two different genetic systems, such as part of the mitochondrial DNA control region (n = 113) and 20 species-specific microsatellite DNA loci (n = 377), including climatic and geographic factors from the 14 Iberian localities where A. rufa populations were sampled. Our results showed a mitochondrial genetic diversity pattern associated with a thermic gradient, and a decrease of genetic diversity in peripheral populations that concurred with the ‘abundant centre’ hypothesis. Overall, current climatic variables reliably described genetic variation and differentiation in the red-legged partridge, which may be a result of local species adaptation.     

Fine-spotted brown trout: genetic aspects and the need for conservation

In Lake Svartavasstjønn on the Hardangervidda plateau, a fine-spotted variant of brown trout has been found. The spotted variability shows a classical Mendelian mode of inheritance. In this population genetic variability was found in LDH-5 *, MDH-3 * and MDH-3 *. The fast allele at LDH-5 * had a frequency of 0,913. This is remarkable, as this allele has been found in frequencies above 0.4 in only five out of 50 investigated populations in Norway. The genetic characteristics of brown trout from Lake Svartavasstjønn were compared with 11 other populations sampled from a broad geographical area of Norway. Among these was Lake Setningen, where fine-spotted individuals occur at low frequency. Using a cluster analysis based on eight loci found to be polymorphic in brown trout, we found no indication of a close relationship between the fine-spotted brown trout from Lake Svartavasstjønn and the population in Lake Setningen. During a field survey in 1990 we found that the reproduction of fine-spotted trout in Lake Svartavasstjønn had terminated. The fine-spotted trout represents a valuable but threatened genetic resource, and attempts are carried out to conserve it.     

Hierarchy of responses to resource pulses in arid and semi-arid ecosystems

In arid/semi-arid ecosystems, biological resources, such as water, soil nutrients, and plant biomass, typically go through periods of high and low abundance. Short periods of high resource abundance are usually triggered by rainfall events, which, despite of the overall scarcity of rain, can saturate the resource demand of some biological processes for a time. This review develops the idea that there exists a hierarchy of soil moisture pulse events with a corresponding hierarchy of ecological responses, such that small pulses only trigger a small number of relatively minor ecological events, and larger pulses trigger a more inclusive set and some larger ecological events. This framework hinges on the observation that many biological state changes, where organisms transition from a state of lower to higher physiological activity, require a minimal triggering event size. Response thresholds are often determined by the ability of organisms to utilize soil moisture pulses of different infiltration depth or duration. For example, brief, shallow pulses can only affect surface dwelling organisms with fast response times and high tolerance for low resource levels, such as some species of the soil micro-fauna and -flora, while it takes more water and deeper infiltration to affect the physiology, growth or reproduction of higher plants. This review first discusses how precipitation, climate and site factors translate into soil moisture pulses of varying magnitude and duration. Next, the idea of the response hierarchy for ecosystem processes is developed, followed by an exploration of the possible evolutionary background for the existence of response thresholds to resource pulses. The review concludes with an outlook on global change: does the hierarchical view of precipitation effects in ecosystems provide new perspectives on the future of arid/semiarid lands?     

Spatial patterns of demography and genetic processes across the species' range: Null hypotheses for landscape conservation genetics

Compared with populations near the core of aspecies' range, edge populations tend to becharacterized by low density and high temporalvariation. Based on empirical studiesquantifying this pattern, we show thateffective population size (N _e)could be 2 to 30 times greater near the coreof the species' range than near the edge ofthe range. Hence, the rate of genetic driftmay be 2 to 30 times greater near the edge ofthe range. Despite these strong spatialpatterns in N _e, empirical findingsindicate that peripheral populations sometimeshave less but sometimes have more geneticdiversity than core populations. Our analysisindicates that this variation can be explainedby uncertainty in spatial patterns ofmigration rates. Nevertheless, our analysis:(1) provides a framework or null hypothesis forempirically assessing how spatial patterns ofmigration or selection influence large-scalespatial patterns of genetic diversity, (2)highlights the potential importance ofcontemporary processes, such as spatialpatterns in N _e (cf. historicalphenomena, such as range expansion) in thedevelopment and maintenance of large-scalespatial patterns in genetic diversity, and (3) provides new context for understanding the conservation value and vulnerability of peripheralpopulations. The conservation ofecological/evolutionary processes requiresunderstanding large scale spatial patterns ofdemographic and genetic processes such as thatdescribed here.     

Elevated CO2 ameliorates birch response to high temperature and frost stress: implications for modeling climate-induced geographic range shifts

Despite predictions that both atmospheric CO₂ concentrations and air temperature will rise together, very limited data are currently available to assess the possible interactive effects of these two global change factors on temperate forest tree species. Using yellow birch (Betula alleghaniensis) as a model species, we studied how elevated CO₂ (800 vs. 400 μl l⁻¹) influences seedling growth and physiological responses to a 5°C increase in summer air temperatures (31/26 vs. 26/21°C day/night), and how both elevated CO₂ and air temperature during the growing season influence seedling ability to survive freezing stress during the winter dormant season. Our results show that while increased temperature decreases seedling growth, temperature-induced growth reductions are significantly lower at elevated CO₂ concentrations (43% vs. 73%). The amelioration of high-temperature stress was related to CO₂-induced reductions in both whole-shoot dark respiration and transpiration. Our results also show that increased summer air temperature, and to a lesser degree CO₂ concentration, make dormant winter buds less susceptible to freezing stress. We show the relevance of these results to models used to predict how climate change will influence future forest species distribution and productivity, without considering the direct or interactive effects of CO_2. Received: 5 June 1997 / Accepted: 16 December 1997     

Evolutionary age and risk of extinction in the global avifauna

Species at high risk of extinction are not distributed at random among higher taxa. Here we demonstrate that there is a positive relationship between the proportion of species in a taxon which are considered to be threatened and the evolutionary age of that taxon, both for the global avifauna and the avifauna of the New World. The potential mechanisms and consequences of the relationship are examined.     

Trait variability and stress: canalization, developmental stability and the need for a broad approach

Trait variability (particularly fluctuating asymmetry) may provide a general measure of environmental stress applicable across taxa but consistent empirical support is lacking. Historically, stress effects were considered to act independently on trait canalization, developmental noise and trait size. However, in trait comparisons these processes are often assumed to be associated. Here we reconsider this issue and implications for detecting stress effects using trait variability. Published studies that consider multiple environments report little association between the effects of environmental variation on trait canalization and on developmental noise measured as fluctuating asymmetry, sug-gesting that environmental effects often act independently on these processes. To further test the usefulness of trait variability as an indicator of stress, comparisons across environ-ments should take a broad approach and report on several measures of trait variability, rather than focusing on only one index of fluctuating asymmetry as is commonly done.     

Major Histocompatibility Complex Variation in the Endangered Crested Ibis Nipponia nippon and Implications for Reintroduction

The major histocompatibility complex (MHC), with its extraordinary levels of genetic variation, is thought to be an essential aspect of the ability of an organism to recognize different parasites and pathogens. It has also been proposed to regulate reproductive processes in many aspects. Here we examine the genetic variation of the second exon of the MHC class II B genes of the crested ibis, an endangered species known to descend from just two breeding pairs rediscovered in 1981. Only five alleles are identified by single-strand conformation polymorphism (SSCP) analysis of 36 samples taken from both wild and captive populations, and a comparatively low level of divergence between MHC alleles is observed. We suggest that representative sampling of individuals with most of the different MHC allele genotypes to constitute a founder population, together with the monitoring of the pathogen status of candidate sites before release, is of great importance for raising the success rate of reintroduction for the crested ibis.     

Effects of temperature,salinity and composition of the dinoflagellate assemblage on the growth of Gambierdiscus carpenteri isolated from the Great Barrier Reef

Increases in reported incidence of ciguatera fish poisoning (hereafter ciguatera) have been linked to warmer sea temperatures that are known to trigger coral bleaching events. The drivers that trigger blooms of ciguatera-causing dinoflagellates on the Great Barrier Reef (GBR) are poorly understood. This study investigated the effects of increased temperatures and lowered salinities, often associated with environmental disturbance events, on the population growth of two strains of the potentially ciguatera-causing dinoflagellate, Gambierdiscus carpenteri (NQAIF116 and NQAIF380). Both strains were isolated from the central GBR with NQAIF116 being an inshore strain and NQAIF380 an isolate from a stable environment of a large coral reef aquarium exhibit in ReefHQ, Townsville, Australia. Species of Gambierdiscus are often found as part of a mixed assemblage of benthic toxic dinoflagellates on macroalgal substrates. The effect of assemblage structure of dinoflagellates on the growth of Gambierdiscus populations has, however, not been explored. The study, therefore investigated the growth of G. carpenteri within mixed assemblages of benthic dinoflagellates. Population growth was monitored over a period of 28 days under three salinities (16, 26 and 36) and three temperature (24, 28 and 34 °C) conditions in a fully crossed experimental design. Temperature and salinity had a significant effect on population growth. Strain NQAIF380 exhibited significantly higher growth at 28 °C compared to strain NQAIF116, which had highest growth at 24 °C. When strain NQAIF116 was co-cultured with the benthic dinoflagellates, Prorocentrum lima and Ostreopsis sp., inhibitory effects on population growth were observed at a salinity of 36. In contrast, growth stimulation of G. carpenteri (strain NQAIF116) was observed at a salinity of 26 and particularly at 16 when co-cultured with Ostreopsis-dominated assemblages. Range expansion of ciguatera-causing dinoflagellates could lead to higher frequency of reported ciguatera illness in populated temperate Australian regions, outside the tropical range of the GBR. Therefore, the findings on salinity and temperature tolerance of two strains of G. carpenteri indicates potential adaptability to different local environmental conditions. These are baseline data for future investigations into the potential southward range expansion of ciguatera-causing dinoflagellates originating from the GBR.     

Variability and correlations in muskmelon in relation to the cultivation method

Summary Six fruit characters have been measured in 23 cultivars of Cucumis melo, representing a wide geographical range. Plants were grown both in the greenhouse and in the field. When the 23 cultivars were analyzed together, the largest component of variance was found between cultivars under both growth conditions, suggesting the existence of large genetic diversity for all the characters studied. Generally, variance between plants within cultivars was less than or equal to variance between fruits within plant. This indicates that environmental variation is the most important part of the variation within cultivars. Correlations between pairs of characters at cultivar, plant and fruit levels were calculated from the variance-covariance components. In the majority of paired traits, the correlation values indicated that genetic and environmental factors may act in the same direction.     

Problems of sampling and inference in the study of fluctuating dental asymmetry

Randomly distributed or “fluctuating” dental asymmetry has been accorded evolutionary meaning and interpreted as a result of environmental stress. However, except for congenital malformation syndromes, the determinants of human crown size asymmetry are still equivocal. Both a computer simulated sampling experiment using a combined sample size of N = 3000, and the requirements of adequate statistical power show that sample sizes of several hundred are needed to detect population differences in dental asymmetry. Using the largest available sample of children with defined prenatal stresses, we are unable to find systematic increases in crown size asymmetry. Given sampling limitations and the current inability to link increased human dental asymmetry to defined prenatal stresses, we suggest that fluctuating dental asymmetry is not yet established as a useful and reliable measure of general stress in human populations.     

The perils of climate change: In utero exposure to temperature variability and birth outcomes in the Andean region

The discussion on the effects of climate change on human activity has primarily focused on how increasing temperature levels can impair human health. However, less attention has been paid to the effect of increased climate variability on health. We investigate how in utero exposure to temperature variability, measured as the fluctuations relative to the historical local temperature mean, affects birth outcomes in the Andean region. Our results suggest that exposure to a temperate one standard deviation relative to the municipality’s long-term temperature mean during pregnancy reduces birth weight by 20 g. and increases the probability a child is born with low birth weight by a 0.7 percentage point. We also explore potential channels driving our results and find some evidence that increased temperature variability can lead to a decrease in health care and increased food insecurity during pregnancy.