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The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

Environmental conditions during early development, from conception to sexual maturity, can have lasting consequences on fitness components. Although adult life span often accounts for much of the variation in fitness in long-lived animals, we know little about how early environment affects adult life span in the wild, and even less about whether these effects differ between the sexes. Using data collected over 45 years from wild bighorn sheep (Ovis canadensis), we investigated the effects of early environment on adult mortality in both sexes, distinguishing between natural and anthropogenic sources of mortality. We used the average body mass of yearlings (at about 15 months of age) as a yearly index of environmental quality. We first examined sex differences in natural mortality responses to early environment by censoring harvested males in the year they were shot. We then investigated sex differences in the effects of early environment on overall mortality (natural and hunting mortality combined). Finally, we used path analysis to separate the direct influence of early environment from indirect influences, mediated by age at first reproduction, adult mass and horn length. As early environmental conditions improved, natural adult mortality decreased in both sexes, although for males the effect was not statistically supported. Sex differences in the effects of early environment on adult mortality were detected only when natural and hunting mortality were pooled. Males that experienced favourable early environment had longer horns as adults and died earlier because of trophy hunting, which does not mimic natural mortality. Females that experienced favourable early environment started to reproduce earlier and early primiparity was associated with reduced mortality, suggesting a silver-spoon effect. Our results show that early conditions affect males and females differently because of trophy hunting. These findings highlight the importance of considering natural and ant

Isolation of small populations is expected to reduce fitness through inbreeding and loss of genetic variation, impeding population growth and compromising population persistence. Species with long generation time are the least likely to be rescued by evolution alone. Management interventions that maintain or restore genetic variation to assure population viability are consequently of significant importance. We investigated, over 27 years, the genetic and demographic consequences of a demographic bottleneck followed by artificial supplementation in an isolated population of bighorn sheep (Ovis canadensis). Based on a long-term pedigree and individual monitoring, we documented the genetic decline, restoration and rescue of the population. Microsatellite analyses revealed that the demographic bottleneck reduced expected heterozygosity and allelic diversity by 6.2% and 11.3%, respectively, over two generations. Following supplementation, first-generation admixed lambs were 6.4% heavier at weaning and had 28.3% higher survival to 1 year compared to lambs of endemic ancestry. Expected heterozygosity and allelic diversity increased by 4.6% and 14.3% after two generations through new alleles contributed by translocated individuals. We found no evidence for outbreeding depression and did not see immediate evidence of swamping of local genes. Rapid intervention following the demographic bottleneck allowed the genetic restoration and rescue of this bighorn sheep population, likely preventing further losses at both the genetic and demographic levels. Our results provide further empirical evidence that translocation can be used to reduce inbreeding depression in nature and has the potential to mitigate the effect of human-driven environmental changes on wild populations.

Fitness costs of reproduction are expected when resources are limited. Costs drive the evolution of life-history strategies and can affect population dynamics if females change their allocation of resources to reproduction. We studied fitness costs of reproduction in mountain ungulates in Alberta, Canada. We monitored two populations of bighorn sheep (Ovis canadensis) for 44 and 30 years, and one of mountain goats (Oreamnos americanus) for 30 years. Both species are highly iteroparous. Heterogeneity in individual reproductive potential makes fitness costs of reproduction difficult to detect and quantify without manipulations. In capital breeders, individual differences can be partly accounted for by considering body mass and other correlates of reproductive potential. Long-term monitoring can reveal costs that only manifest under stressful conditions such as disease or resource scarcity. Despite individual differences in reproductive potential, we detected fitness costs of reproduction in females. Costs, in terms of mass gain and survival, are almost entirely born by subsequent offspring, as mothers prioritize their own maintenance and survival. Costs are greater for primiparous females, decrease with increasing body mass and increase as resource availability declines, and sons are costlier than daughters. Costs may increase for senescent females that appear to reduce allocation to reproduction. In bighorn sheep, costs mostly involve reduced mass gain and lower survival of subsequent offspring. In mountain goats, costs include reductions in mass gain, subsequent fecundity and juvenile survival. In males, fitness costs derive mostly from attempts to reproduce rather than from siring success and likely depend upon individual competitiveness. In the absence of selective harvests, dominant males may enjoy high fitness and possibly lower costs compared to subordinates. The conservative reproductive tactic of mountain ungulate females likely explains why density dependenc

Human harvest can induce selection on life history and morphological traits, leading to ecological and evolutionary responses. Our understanding of harvest-induced selection on behavioral traits is, however, very limited. Here, we assessed whether hunters harvest, consciously or not, individuals with specific behavioral traits. We used long-term, detailed behavioral and survival data of a heavily harvested brown bear ( Ursus arctos ) population in Sweden. We found that hunters harvested male bears that were less active during legal hunting hours and had lower movement rates. Also, hunters harvested male and female bears that used habitats closer to roads. We provide an empirical example that individual behavior can modulate vulnerability to hunting and that hunters could exert a selective pressure on wildlife behaviors. This study increases our understanding of the complex interactions between harvest method, human behavior, and animal behavior that are at play in harvest-induced selection and provides better insight into the full effects of human harvest on wild populations.

We know little about the determinants and demographic consequences of the marked seasonal mass changes exhibited by many northern and alpine mammals. We analysed 43 years of data on individual winter mass loss (the difference between mass in early June and mass in mid-September the previous year) and summer mass gain (the difference between mass in mid-September and in early June of the same year) in adult bighorn sheep (Ovis canadensis). We calculated relative seasonal mass change as a proportion of individual body mass at the start of each season. We first examined the effects of weather and population density on relative changes in body mass. We then assessed the consequences of relative seasonal mass changes on reproduction. Mean April-May temperature was the main driver of relative seasonal mass changes: warm springs reduced both relative winter mass loss and summer mass gain of both sexes, likely partially due to a trade-off between growth rate of plants and duration of access to high-quality forage. Because these effects cancelled each other, spring temperature did not influence mass in mid-September. Mothers that lost relatively more mass during the winter had lambs that gained less mass during summer, likely because these females allocated fewer resources to lactation. Winter survival of lambs increased with their summer mass gain. In males, relative mass loss during winter, which includes the rut, did not influence the probability of siring at least one lamb, possibly indicating that greater mating effort did not necessarily translate into greater reproductive success. Our findings improve our understanding of how weather influences recruitment and underline the importance of cryptic mechanisms behind the effects of climate change on demographic traits.

Heterogeneity among individuals influences the life‐history trajectories we observe at the population level because viability selection, selective immigration and emigration processes, and ontogeny change the proportion of individuals with specific trait values with increasing age. Here, we review the two main approaches that have been proposed to account for these processes in life‐history trajectories, contrasting how they quantify ontogeny and selection, and proposing ways to overcome some of their limitations. Nearly all existing approaches to model individual heterogeneity assume either a single normal distribution or a priori known groups of individuals. Ontogenetic processes, however, can vary across individuals through variation in life‐history tactics. We show the usefulness of describing ontogenetic processes by modelling trajectories with a mixture model that focuses on heterogeneity in life‐history tactics. Additionally, most methods examine individual heterogeneity in a single trait, ignoring potential correlations among multiple traits caused by latent common sources of individual heterogeneity. We illustrate the value of using a joint modelling approach to assess the presence of a shared latent correlation and its influence on life‐history trajectories. We contrast the strengths and limitations of different methods for different research questions, and we exemplify the differences among methods using empirical data from long‐term studies of ungulates.

Integral projection models (IPMs) are extremely flexible tools for ecological and evolutionary inference. IPMs track the distribution of phenotype in populations through time, using functions describing phenotype-dependent development, inheritance, survival and fecundity. For evolutionary inference, two important features of any model are the ability to (i) characterize relationships among traits (including values of the same traits across ages) within individuals, and (ii) characterize similarity between individuals and their descendants. In IPM analyses, the former depends on regressions of observed trait values at each age on values at the previous age (development functions), and the latter on regressions of offspring values at birth on parent values as adults (inheritance functions). We show analytically that development functions, characterized this way, will typically underestimate covariances of trait values across ages, due to compounding of regression to the mean across projection steps. Similarly, we show that inheritance, characterized this way, is inconsistent with a modern understanding of inheritance, and underestimates the degree to which relatives are phenotypically similar. Additionally, we show that the use of a constant biometric inheritance function, particularly with a constant intercept, is incompatible with evolution. Consequently, current implementations of IPMs will predict little or no phenotypic evolution, purely as artefacts of their construction. We present alternative approaches to constructing development and inheritance functions, based on a quantitative genetic approach, and show analytically and through an empirical example on a population of bighorn sheep how they can potentially recover patterns that are critical to evolutionary inference.

The development of male secondary sexual characters such as antlers or horns has substantial biological and socio‐economic importance because in many species these traits affect male fitness positively through sexual selection and negatively through trophy hunting. Both environmental conditions and selective hunting can affect horn growth but their relative importance remains unexplored. We first examined how a large‐scale climate index, the Pacific Decadal Oscillation (PDO), local weather and population density influenced both absolute and relative annual horn growth from birth to three years of male bighorn sheep Ovis canadensis over 42 years. We then examined the relative influence of environmental conditions and evolution mainly driven by trophy hunting on male horn length at three years of age. Horn growth was positively influenced by low population density and warm spring temperature, suggesting that ongoing climate change should lead to larger horns. Seasonal values of PDO were highly correlated. Horn growth increased with PDO in spring or summer at low density, but was weak at high density regardless of PDO. The interaction between population density and PDO in spring or summer accounted for a similar proportion of the observed annual variation in horn growth (32% or 37%) as did the additive effects of spring temperature and density (34%). When environmental conditions deteriorated, males allocated relatively more resources to summer mass gain than to horn growth, suggesting a conservative strategy favoring maintenance of condition over allocation to secondary sexual characters. Population density explained 27% of the variation in horn length, while evolutionary effects explained 9% of the variance. Thus, our study underlines the importance of both evolution and phenotypic plasticity on the development of a secondary sexual trait.

Recent studies suggest that evolutionary changes can occur on a contemporary time scale. Hence, evolution can influence ecology and vice-versa. To understand the importance of eco-evolutionary dynamics in population dynamics, we must quantify the relative contribution of ecological and evolutionary changes to population growth and other ecological processes. To date, however, most eco-evolutionary dynamics studies have not partitioned the relative contribution of plastic and evolutionary changes in traits on population, community, and ecosystem processes. Here, we quantify the effects of heritable and non-heritable changes in body mass distribution on survival, recruitment, and population growth in wild bighorn sheep (Ovis canadensis) and compare their importance to the effects of changes in age structure, population density, and weather. We applied a combination of a pedigree-based quantitative genetics model, statistical analyses of demography, and a new statistical decomposition technique, the Geber method, to a long-term data set of bighorn sheep on Ram Mountain (Canada), monitored individually from 1975 to 2012. We show three main results: (1) The relative importance of heritable change in mass, non-heritable change in mass, age structure, density, and climate on population growth rate changed substantially over time. (2) An increase in body mass was accompanied by an increase in population growth through higher survival and recruitment rate. (3) Over the entire study period, changes in the body mass distribution of ewes, mostly through non-heritable changes, affected population growth to a similar extent as changes in age structure or in density. The importance of evolutionary changes was small compared to that of other drivers of changes in population growth but increased with time as evolutionary changes accumulated. Evolutionary changes became increasingly important for population growth as the length of the study period considered increased. Our results hi