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Hunting and evolution: Theory, evidence, and unknowns

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Abstract

Intense selective harvest of large mammals who carry the largest weapons may lead to an evolutionary shrinkage of those weapons. Currently, evidence suggesting evolutionary effects of harvest is limited to a few species of Bovidae and only 1 study has obtained data indicating a genetic effect. To have an evolutionary impact, harvest must be intense, persistent over time, similar over a large area without an effective source of unselected immigrants, and remove large individuals before they have a chance to breed. Many current harvest schemes do not fulfill all of these requirements, and they are unlikely to cause evolution. Before changes in weapon size over time are attributed to evolution, potential environmental sources of change, mainly density and climate, must be considered. We suggest that the role of weapon size in determining reproductive success, especially in interaction with male age, will determine whether or not intensive selective harvests may have evolutionary consequences. Age at harvest is a very important variable to consider. Changes in age structure over time may reveal underlying changes in harvest pressure or selectivity. A lack of data hampers our ability to assess the potential evolutionary effects of selective hunting. We provide a list of research hypotheses required to advance our ability to assess the evolutionary sustainability of current management practices.

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... Selective hunting has the potential to affect population dynamics 9 , and evolutionary processes; though strong evidence of artificial selection has only been found in mountain ungulates 55 . Hunter selectivity appears to be influenced by many factors, such as regulations or social preferences, perceived opportunities, or quota availability 14,53 . Particularly for bears, sex and age-specific vulnerabilities to hunting have been found in many species 50,[56][57][58] pointing to selectivity for younger, inexperienced individuals, especially males. ...
... Particularly for black bears, hunting is a primary population management tool used by many jurisdictions throughout their range. In many managed vertebrate populations, the selective pressures of human activities have raised concern regarding their long-term evolutionary consequences 2,63 ; however, robust evidence is lacking 14 . Despite this concern, hunting is an important component of many conservation programs and can provide economic and social incentives to encourage support for wildlife conservation 64,65 , including mitigating the socioeconomic and political costs of the coexistence with wildlife 66,67 . ...
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With efforts to restore large mammal populations following extirpations, it is vital to quantify how they are impacted by human activities and gain insights into population dynamics in relation to conservation goals. Our objective was to characterize cause-specific mortality of black bears (Ursus americanus) throughout their range. We first quantified cause-specific mortality for 247 black bears in one harvested and two non-harvested populations. We then simulated a small recolonizing population with and without anthropogenic mortality. Lastly, we conducted a meta-analysis of all published black bear mortality studies throughout North America (31 studies of 2630 bears). We found anthropogenic mortality was greater than natural mortality, non-harvest anthropogenic mortality (e.g. poaching, defense of property, etc.) was greater in non-harvested populations, and harvesting was one of the major causes of mortality for bears throughout their range. Our simulation indicated that removing anthropogenic mortality increased population size by an average of 23% in 15 years. We demonstrated that bears are exposed to high levels of anthropogenic mortality, and the potential for human activities to slow population growth in expanding populations. Management and conservation of wide-ranging mammals will depend on holistic strategies that integrate ecological factors with socio-economic issues to achieve successful conservation and coexistence.
... Our ancestors exhibited gender-based physical and emotional responsibilities that have potentially dictated food preferences. Men were involved in intensive labor, which imposed a need for a larger muscle mass [109] and may have prompted an enhanced appetite for meat [110]. Meat supplies ample amounts of essential amino acids (AA), namely the branched chain AA, and creatine that promote muscle growth and power, respectively. ...
... In fact, higher education, which happens over several years, is associated with enhanced neuroplasticity, typically mediated by BDNF [120]. This notion was further supported by an in vitro study describing that overexpression of BDNF is coupled specifically with enhanced hippocampal neurogenesis [121], which is linked to improvement in mental wellbeing especially in men [109]. ...
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Customization of mental health therapies needs to consider the differences in degree of brain maturity between young (18–29 years) and mature (30 years or older) adults as well as brain morphology among men and women. The aim of this study was to identify the significant dietary and lifestyle contributors to mental distress in these sub-populations. Independent repeated cross-sectional sampling was performed for over a 5-year period (2014–2019) to collect data from different populations at different time-points and seasons. A backward stepwise regression analysis was used on 2628 records. Mental distress in young women was associated with high consumption of caffeine and fast-food, and it was negatively correlated with moderate-high levels of exercise as well as frequent breakfast consumption. Mature women shared several common factors with young women; however, high fruit consumption was negatively associated with mental distress. For young men, high exercise, moderate consumption of dairy, and moderate-high intake of meat were negatively associated with mental distress. In addition, high fast-food and caffeine consumption were positively associated with mental distress in young men. For mature men, strong negative associations between higher education, moderate intake of nuts and mental distress surfaced. Our results support the need to customize dietary and lifestyle recommendations to improve mental wellbeing.
... Ungulate species can exhibit accelerated changes in weapon size in response to the selective removal of individuals with large weaponry (Festa-Bianchet, Jorgenson, & Réale, 2000;Hard & Mills, 2006;Monteith et al., 2013;Pigeon et al., 2016). Nevertheless, it remains challenging to disentangle the effects of natural processes from selective pressures of harvest, especially given that long-term data on phenotypic traits are exceedingly rare (Festa-Bianchet & Mysterud, 2018;Hundertmark et al., 1998;LaSharr et al., 2019;Monteith et al., 2013). Although the level of harvest pressure necessary to produce evolutionary changes in the size of weaponry has been examined in a theoretical context (Festa-Bianchet 2016;Mysterud, 2011), few empirical studies have directly tested the effects of harvest practices on weapon size. ...
... Research and media attention associated with the effects of harvest on wildlife over the past few decades have yielded increased interest among scientists, wildlife managers, and the public in understanding the consequences of harvest (Festa-Bianchet, 2017;Festa-Bianchet & Mysterud, 2018;Heffelfinger, 2018). Nevertheless, most research in terrestrial systems demonstrating potential evolutionary consequences of harvest has been limited to a management unit comprised of a single population of mountain sheep (Coltman et al., 2003;Pigeon et al., 2016), which makes extrapolating results from those studies to larger geographic and temporal scales difficult (but see Festa-Bianchet, . ...
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The influence of human harvest on evolution of secondary sexual characteristics has implications for sustainable management of wildlife populations. The phenotypic consequences of selectively removing males with large horns or antlers from ungulate populations have been a topic of heightened concern in recent years. Harvest can affect size of horn-like structures in two ways: (a) shifting age structure toward younger age classes, which can reduce the mean size of horn-like structures, or (b) selecting against genes that produce large, fast-growing males. We evaluated effects of age, climatic and forage conditions, and metrics of harvest on horn size and growth of mountain sheep (Ovis canadensis ssp.) in 72 hunt areas across North America from 1981 to 2016. In 50% of hunt areas, changes in mean horn size during the study period were related to changes in age structure of harvested sheep. Environmental conditions explained directional changes in horn growth in 28% of hunt areas, 7% of which did not exhibit change before accounting for effects of the environment. After accounting for age and environment, horn size of mountain sheep was stable or increasing in the majority (~78%) of hunt areas. Age-specific horn size declined in 44% of hunt areas where harvest was regulated solely by morphological criteria, which supports the notion that harvest practices that are simultaneously selective and intensive might lead to changes in horn growth. Nevertheless, phenotypic consequences are not a foregone conclusion in the face of selective harvest; over half of the hunt areas with highly selective and intensive harvest did not exhibit age-specific declines in horn size. Our results demonstrate that while harvest regimes are an important consideration, horn growth of harvested male mountain sheep has remained largely stable, indicating that changes in horn growth patterns are an unlikely consequence of harvest across most of North America.
... In bighorn sheep, males with rapidly growing horns were at risk of hunting mortality, leading to an evolutionary decrease in horn size over time ( Pigeon et al., 2016). Hunting re-distributed siring success among survivors of the hunting season and shortened the life expectancy of males that would likely have been successful breeders in its absence (Festa-Bianchet & Mysterud, 2018), thereby possibly limiting our ability to measure reproductive costs. Trophy hunting also led to a negative correlation between early development and longevity (Douhard, Festa-Bianchet, Landes, & Pelletier, 2019) because males that developed under favourable conditions were shot at a younger age, as reported in other populations of mountain sheep (Douhard, Festa-Bianchet, Pelletier, Gaillard, & Bonenfant, 2016;Hengeveld & Festa-Bianchet, 2011). ...
Article
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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 dependence mostly involves later primiparity and lower recruitment, but rarely affects adult survival. Future research will seek to better account for heterogeneity in reproductive potential, assess cumulative reproductive costs and investigate the potential effects of fathers on maternal allocation tactics. Fitness costs of reproduction affect the evolution of life histories, morphology and population dynamics of wild species. They are key to the consequences of different forms of exploitation. The authors combine 104 population‐years of monitoring two species of mountain ungulates to show that fitness costs are mostly transferred to subsequent offspring. Les coûts de la reproduction émergent lorsque les ressources sont limitées et influencent l’évolution des stratégies d’histoire de vie. Si les femelles modifient l’allocation des ressources dans la reproduction pour mitiger ces coûts, ils peuvent aussi affecter la dynamique de population. Nous avons étudié les coûts de la reproduction chez des ongulés en Alberta, Canada. Nous avons suivi deux populations de mouflons d’Amérique (Ovis canadensis) pour 44 et 30 ans, et une de chèvre de montagne (Oreamnos americanus) pour 30 ans. Ces deux espèces sont itéropares. L’hétérogénéité dans le potentiel reproducteur des individus peut masquer les coûts en fitness liés à la reproduction. Ils sont donc plus souvent détectables à l’aide de manipulation expérimentale. Chez les espèces avec reproduction « sur capital », il est possible de contrôler pour les différences individuelles en incluant des variables liées au potentiel reproducteur telles que la masse corporelle. Les suivis à long terme permettent de détecter des coûts qui se manifestent seulement lors de conditions environnementales défavorables. Malgré les différences en potentiel reproducteur, nous avons détecté des coûts chez les femelles. Ces coûts, tels qu’une réduction en croissance ou en survie, sont presque toujours subis par les jeunes nés lors d’épisodes de reproduction subséquents. En effet, les mères priorisent leur propre maintien et leur survie. Les coûts sont supérieurs pour les femelles primipares et dans les conditions défavorables. Ils sont plus faibles pour les femelles plus lourdes et il semble que les fils soient plus coûteux que les filles. Les coûts augmentent aussi chez les femelles sénescentes qui semblent réduire leur allocation dans la reproduction. Chez les mouflons, les coûts impliquent une réduction du gain en masse et une survie plus faible des jeunes nés lors de reproductions subséquentes. Chez les chèvres de montagne, ces coûts sont accompagnés d’une réduction de la fécondité future. Chez les mâles, les coûts sont surtout influencés par l’investissement en temps et en énergie dans le rut plutôt que par le succès d’accouplement. Ces coûts devraient donc surtout dépendre de l’habileté compétitive individuelle. En absence de chasse sélective, les mâles dominants devraient avoir un fort succès reproducteur avec des coûts potentiellement plus faibles comparativement aux subordonnées. La tactique conservative adoptée par les ongulés de montagne femelles peut expliquer pourquoi les effets densité‐dépendant mènent à un retard dans l’âge à la primiparité et à un recrutement plus faible, mais affectent rarement la survie adulte. Nos recherches futures tenteront de mieux quantifier l’hétérogénéité individuelle, évalueront les coûts cumulatifs à la reproduction et investigueront l’effet potentiel des pères sur les tactiques d’allocation maternelles.
... Declining morphological trait sizes have also been associated with selective hunting pressure [25][26][27][28]; the directed removal of animals with specific traits. Yet again, the lack of sufficiently long and wellreplicated datasets complicates any systematic assessment of species' evolutionary responses to intensive trophy harvesting [29,30]. Hence, it remains debatable whether a properly managed hunting system can be used as a conservation tool for maintaining sustainability [31,32]. ...
Article
In many species, decreasing body size has been associated with increasing temperatures. Although climate-induced phenotypic shifts, and evolutionary impacts, can affect the structure and functioning of marine and terrestrial ecosystems through biological and metabolic rules, evidence for shrinking body size is often challenged by (i) relatively short intervals of observation, (ii) a limited number of individuals, and (iii) confinement to small and isolated populations. To overcome these issues and provide important multi-species, long-term information for conservation managers and scientists, we compiled and analysed 222 961 measurements of eviscerated body weight, 170 729 measurements of hind foot length and 145 980 measurements of lower jaw length, in the four most abundant Alpine ungulate species: ibex (Capra ibex), chamois (Rupicapra rupicapra), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Regardless of age, sex and phylogeny, the body mass and size of these sympatric animals, from the eastern Swiss Alps, remained stable between 1991 and 2013. Neither global warming nor local hunting influenced the fitness of the wild ungulates studied at a detectable level. However, we cannot rule out possible counteracting effects of enhanced nutritional resources associated with longer and warmer growing seasons, as well as the animals' ability to migrate along extensive elevational gradients in the highly diversified alpine landscape of this study.
... Additionally, shifts in the proportion of unique phenotypes (Wilfred 2012, Monteith et al. 2013, Rivrud et al. 2013, Coulson et al. 2018, LaSharr et al. 2019b or behavioral traits (Singer andZeigenfuss 2002, Leclerc et al. 2019) also may occur. Considerable speculation exists about the biological effects of trophy hunting, but much remains unknown (Harris et al. 2002, Festa-Bianchet and Lee 2009, Festa-Bianchet 2016, Festa-Bianchet and Mysterud 2018. ...
Article
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Reported effects of trophy harvest often are controversial. The subject is nuanced and many studies lack details necessary to place their results in context. Consequently, many studies are misunderstood or their conclusions misapplied. We propose that all dialogues about trophy hunting include a definition of how they use the term trophy, details of variables measured and why they were selected, and explanations of temporal and spatial scales employed. Only with these details can potential effects of trophy hunting be understood in context and used for management and policy decisions. © 2021 The Wildlife Society. Effects of trophy harvest often are controversial because many studies lack important details. Dialogues about trophy hunting must include a definition of how they use the term trophy, details of variables measured and why they were selected, and explanations of temporal and spatial scales employed so that potential effects of trophy hunting can be understood in context.
... In animals, selective hunting by humans is reported to result in smaller weapon (e.g., horns or antlers) size in ungulates, but such an effect has been suggested to be limited because hunted males often reproduce before they are shot. 13 Both young and adult fritillary are harvested, with smaller (younger) bulbs being sold for higher prices in the retail market. Our results show that the color of Fritillaria delavayi varies among populations and closely matches their local background, with the degree of such background matching closely following the local harvest pressure for this highly valued herb in Chinese traditional medicine. ...
Article
Color in nature mediates numerous among and within species interactions,¹ and anthropogenic impacts have long had major influences on the color evolution of wild animals.² An under-explored area is commercial harvesting, which in animals can exert a strong selection pressure on various traits, sometimes greater even than natural selection or other human activities.³,⁴ Natural populations of plants that are used by humans have likely also suffered strong pressure from harvesting, yet the potential for evolutionary change induced by humans has received surprisingly little attention.⁵ Here, we show that the leaf coloration of a herb used in traditional Chinese medicine (Fritillaria delavayi) varies among populations, with leaves matching their local backgrounds most closely. The degree of background matching correlates with estimates of harvest pressure, with plants being more cryptic in heavily collected populations. In a human search experiment, the time it took participants to find plants was greatly influenced by target concealment. These results point to humans as driving the evolution of camouflage in populations of this species through commercial harvesting, changing the phenotype of wild plants in an unexpected and dramatic way.
... Effects from harvest are most pronounced with repeated, intensive harvest and when selection occurs in both sexes (Festa-Bianchet & Mysterud, 2018). And, harvest intensity can outweigh selection as a driver of changes to genetic composition and/or induce adaptive responses in populations (Proaktor et al., 2007) and be detrimental to population genetics, and thus persistence, that is, decrease effective population size (Allendorf & Hard, 2009). ...
Article
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Harvest can disrupt wildlife populations by removing adults with naturally high survival. This can reshape sociospatial structure, genetic composition, fitness, and potentially affect evolution. Genetic tools can detect changes in local, fine-scale genetic structure (FGS) and assess the interplay between harvest-caused social and FGS in populations. We used data on 1614 brown bears, Ursus arctos, genotyped with 16 microsatellites, to investigate whether harvest intensity (mean low: 0.13 from 1990 to 2005, mean high: 0.28 from 2006 to 2011) caused changes in FGS among matrilines (8 matrilines; 109 females ≥4 years of age), sex-specific survival and putative dispersal distances, female spatial genetic autocorrelation, matriline persistence, and male mating patterns. Increased harvest decreased FGS of matrilines. Female dispersal distances decreased, and male reproductive success was redistributed more evenly. Adult males had lower survival during high harvest, suggesting that higher male turnover caused this redistribution and helped explain decreased structure among matrilines, despite shorter female dispersal distances. Adult female survival and survival probability of both mother and daughter were lower during high harvest, indicating that matriline persistence was also lower. Our findings indicate a crucial role of regulated harvest in shaping populations, decreasing differences among “groups,” even for solitary-living species, and potentially altering the evolutionary trajectory of wild populations. © 2020 The Authors. Evolutionary Applications published by John Wiley & Sons Ltd
... Hunters may select individuals to harvest based on various traits, such as body size or, for ungulates, antler or horn size or shape (e.g., Festa-Bianchet et al. 2014;Allen et al. 2018). Such selection may result in undesirable ecological or evolutionary changes in harvested populations, where selection for specific traits by hunters is strong (Langvatn and Loison 1999;Coltman et al. 2003;Mysterud 2011;Allen et al. 2018;Festa-Bianchet and Mysterud 2018). Wildlife managers should be cognizant of hunters selecting for specific traits and, if necessary, implement regulations to mitigate against undesirable changes (Festa-Bianchet 2017). ...
Article
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Hunters may select individuals to harvest based on various traits and wildlife managers need to be cognizant of these preferences so that they can mitigate for undesirable consequences of selectivity, where warranted. American black bears (Ursus americanus) vary widely in coat colour; yet there is no information on hunter selectivity for particular colourmorphs, even though such selection may occur. To test the hypothesis that hunters select non-black colourmorph black bears, I used a database of black bears killed by hunting and other sources of mortality in Yukon, Canada. I compared the percentage of black and non-black colourmorph bears hunted (n = 1664) to those killed by other causes (n = 655). I found no evidence of hunters selecting non-black colourmorph black bears disproportionate to their availability, contrary to predictions by wildlife managers. While some hunters in Yukon may prefer to harvest a non-black colourmorph black bear, several factors (multiple motivations for hunting, shooting the first animal encountered, selection for other traits [e.g., body size], or less willingness to shoot a brown bear [Ursus arctos]) or a combination thereof may result in colourmorphs being harvested in proportion to their availability.
... Declining morphological trait sizes have also been associated with selective hunting pressure [25-28]; the directed removal of animals with specific traits. Yet again, the lack of sufficiently long and wellreplicated datasets complicates any systematic assessment of species' evolutionary responses to intensive trophy harvesting [29,30]. Hence, it remains debatable whether a properly managed hunting system can be used as a conservation tool for maintaining sustainability [31,32]. ...
Article
Full-text available
In many species, decreasing body size has been associated with increasing temperatures. Although climate-induced phenotypic shifts, and evolutionary impacts, can affect the structure and functioning of marine and terrestrial ecosystems through biological and metabolic rules, evidence for shrinking body size is often challenged by (i) relatively short intervals of observation, (ii) a limited number of individuals, and (iii) confinement to small and isolated populations. To overcome these issues and provide important multi-species, long-term information for conservation managers and scientists, we compiled and analysed 222 961 measurements of eviscerated body weight, 170 729 measurements of hind foot length and 145 980 measurements of lower jaw length, in the four most abundant Alpine ungulate species: ibex (Capra ibex), chamois (Rupicapra rupicapra), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Regardless of age, sex and phylogeny, the body mass and size of these sympatric animals, from the eastern Swiss Alps, remained stable between 1991 and 2013. Neither global warming nor local hunting influenced the fitness of the wild ungulates studied at a detectable level. However, we cannot rule out possible counteracting effects of enhanced nutritional resources associated with longer and warmer growing seasons, as well as the animals' ability to migrate along extensive elevational gradients in the highly diversified alpine landscape of this study.
... Critics of the conduct of the African hunting industry indicate that unregulated hunting may drive species' population decline (Packer et al., 2011), or may disrupt animal age-sex structures (Loveridge et al., 2007). Hunting may also lead to "unnatural selection" (Festa-Bianchet & Mysterud, 2018). A key criticism is that the funds generated by hunting do not reach the intended beneficiaries in rural areas (Nelson et al., 2013). ...
Article
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Over the past decade, trophy hunting in Africa has seen increased public and scientific interest. Much of that attention has come from outside of Africa, with little emphasis on local views. We circulated an online survey through international networks to explore demographic and regional differences in opinion regards support for African trophy hunting, trophy import bans, and outside funding of conservation estates supported by hunting. We received ∼5700 responses and found that location, demography, and conservation background influenced opinion. African and North American respondents showed (significantly) more support for trophy hunting than respondents from Europe or other areas, as did respondents with conservation backgrounds. Unlike North Americans, Africans supported external subsidies of wildlife areas presently funded by hunting. Many factors affected opinions on African hunting, but respondent location played a major role. Realistic policy on African trophy hunting should thus integrate African perspectives, in particular those of rural communities.
... Yet, hunters usually are not highly selective, often taking the first opportunity to kill a legal animal (Heffelfinger 2018) and uncertainty remains about the possibility that selective hunter harvests can have detrimental effects (Mysterud 2011). An evolutionary response requires intense selection on highly heritable traits for an extended period (Coulson et al. 2018;Festa-Bianchet and Mysterud 2018). Clearly, hunting can alter the demography of a population, thereby increasing population turnover, changing sex and age ratios, or both (Milner et al. 2007;Monteith et al. 2013Monteith et al. , 2018Hewitt et al. 2014). ...
Article
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Mammals are imperiled worldwide. Threats to terrestrial species are primarily from habitat loss or modification, and in some instances from commercial, illegal, or unregulated hunting. Terrestrial species are negatively affected throughout the tropics from deforestation. Threats to marine mammals are related to harvest, strikes in shipping lanes, pollution, and depleted levels of food resources. Hazards to marine species are pronounced in the North Atlantic Ocean, North Pacific Ocean, and oceans and seas flanking southeastern Asia. Protected areas designed to conserve mammals often are too small, too few, poorly delimited or isolated, and too unreliably supported. The new conservation science proposes that human livelihoods be considered alongside traditional preservationist perspectives. For conservation outside of protected areas to succeed, the protection of wild mammals and their habitats should result in benefit to local people, especially in rural or poor communities. Concerns about declining populations of large mammals in North America during the late 19th and early 20th centuries resulted in the institution of regulations that contributed to the recovery of many populations. Today, in North America and Europe, wild populations are thriving and legal hunting is allowed for a number of mammals, something that is less common in many developing countries, where illegal killing remains a threat to conservation. Nevertheless, populations of large mammals are resilient to regulated hunting because of density-dependent processes that result in increased reproduction, survival, and growth rates. Unfortunately, hunting is unregulated for cultural and economic reasons over much of the Earth. We are beginning to see effects of climate change and invasive species on risk of extinction for many species. The future of mammals, however, is entwined ultimately with the size, growth, and resource demands of the human population.
... Several factors can thus concur to shape horn growth, and disentangling the ecological and 29 evolutionary causes of temporal changes in weapon size may be exceptionally challenging Bianchet and Mysterud, 2018). 31 ...
Article
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The development of horns in Caprinae can be largely influenced by food-limiting factors such as population density and climate, as well as by negative evolutionary responses to size-selective harvesting. In this study, we investigated the effects of population density, environmental covariates and trophy hunting on horn development in a population of European mouflon Ovis aries musimon introduced to the Mediterranean region of Croatia in the early 1980s. The study population was subject to commercial trophy hunting on males since the mid-1980s. This allowed to analyse the temporal trend in early horn growth in 341 rams legally culled. Cohort-based linear model and analysis of deviance (ANODEV) revealed a significant negative trend in early horn growth, with a decline of ca. 10% over only 15 cohorts (1993-2007). The increase in population density (by ca. 600%) and summer temperature, selected via LASSO regression, explained about 61% and 13% of the decline in early horn growth, as revealed by the ANODEV R2. Our results suggest a prominent role of food-limiting factors in the decline of weapon size. We also found a negative relationship between age at death and early horn growth in our study population, which suggests the occurrence of hunters’ selectivity towards large horns. The effect of trophy hunting on the decline in horn size, however, is difficult to quantify. Our analysis was largely influenced by the rapid increase of mouflon density after introduction, thereby limiting the possibility to detect potential effects of hunting selection, although the large number of rams shot before 5 years of age may possibly lead to undesirable consequences of trophy hunting on mating success. To clarify the consequences of commercial trophy hunting on the mouflon population, the long-term pattern of horn growth and the age-dependent male siring success should be further investigated.
... Despite controversy associated with the evolutionary effects of harvest (Mysterud 2014;Festa-Bianchet 2016;Heffelfinger 2018), harvest strategies that result in evolutionary responses have important conservation and management implications (Kuparinen and Festa-Bianchet 2017). Unfortunately, disentangling the effects of selective harvest from selective pressures imposed by the environment (Berger 2005) is difficult without long-term data (Festa-Bianchet and Mysterud 2018). ...
Article
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Long-term datasets are becoming increasingly important for assessing population-and species-level responses to a changing environment. Programs that record morphological measurements of horns, antlers, and pronghorns were established in the early-to mid-20th century to collect biological information about animals that possess large horns, antlers, or pronghorns, which could be used to assess the effectiveness of conservation efforts for large mammals in North America. The general relevance of record books has been questioned because of the minimum size requirements for inclusion in a record book, which may mask trends when changes in the population occur. We compared trends in size of antlers, horns, and pronghorns through time using records from three records programs with different minimum size requirements to evaluate the influence of entry requirements on temporal trends. We also investigated whether horn, antler, or pronghorn size affected the probability of specimens being submitted to a records program. Only two of 17 categories exhibited less-pronounced trends in the record book with the highest size requirements for entry, and in two categories trends were more pronounced. Although societal interest in submitting eligible specimens increased slightly over time in one of six categories, the probability of voluntary entry was largely random and not affected by year of harvest or size of specimen. In contrast to previous criticisms, trends in record books should not be expected to represent the size of all males within a population. Instead, our evaluation indicates that the records programs we examined can provide a useful resource for assessing long-term changes in phenotypic characteristics of ungulates, but importantly, they represent the respective range of sizes within which each program collects data.
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Secondary sexual traits (e.g., horns and antlers) have ecological and evolutionary importance and are of management interest for game species. Yet, how these traits respond to emerging threats like infectious disease remains underexplored. Infectious pneumonia threatens bighorn sheep (Ovis canadensis) populations across North America and we hypothesized it may also reduce horn growth in male sheep. We assess the effect of pneumonia on horn size in male bighorn sheep using 12 herd datasets from across the western United States that had horn growth and disease data. Disease resulted in 12–35% reduction in increment (yearly) length and 3–13% reduction in total horn length in exposed individuals. The disease effect was prolonged when pathogens continued to circulate in sheep populations. Further, disease likely delays the age at which horns reach ¾‐curl and prevents achievement of full‐curl. This is further evidenced with 6 of the 12 herds experiencing an increase in average age at harvest following die‐off events. Management of bighorn sheep for horn size and for population maintenance has focused on factors including nutrition, environmental conditions, and genetic diversity. We demonstrate that disease plays an important role in horn size: pneumonia disease outbreak events significantly reduced horn growth in male bighorn sheep, and continued horn stunting occurred when chronically infected individuals remained present in the population.
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Abstract While all models of sexual selection assume that the development and expression of enlarged secondary sexual traits are costly, males with larger ornaments or weapons generally show greater survival or longevity. These studies have mostly been performed in species with high sexual size dimorphism, subject to intense sexual selection. Here, we examined the relationships between horn growth and several survival metrics in the weakly dimorphic Pyrenean chamois (Rupicapra pyrenaica). In this unhunted population living at high density, males and females were able to grow long horns without any apparent costs in terms of longevity. However, we found a negative relationship between horn growth and survival during prime age in males. This association reduces the potential evolutionary consequences of trophy hunting in male chamois. We also found that females with long horns tended to have lower survival at old ages. Our results illustrate the contrasting conclusions that may be drawn when different survival metrics are used in analyses. The ability to detect trade‐off between the expression of male secondary sexual traits and survival may depend more on environmental conditions experienced by the population than on the strength of sexual selection.
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1. Research into global change ecology is motivated by the need to understand the role of humans in changing biotic systems. Mechanistic understanding of ecological responses requires the separation of different climatic parameters and processes that often operate on diverse spatiotemporal scales. Yet most environmental studies do not distinguish the effects of internal climate variability from those caused by external, natural (e.g. volcanic, solar, orbital) or anthropogenic (e.g. greenhouse gases, ozone, aerosols, land‐use) forcing factors. 2. We suggest extending the climatological concept of ‘Detection and Attribution’ (DA) to unravel abiotic drivers of ecological dynamics in the Anthropocene. We therefore apply DA to quantify the relative roles of natural versus industrial temperature change on elevational shifts in the outbreak epicentres of the larch budmoth (LBM; Zeiraphera diniana or griseana Gn.); the classic example of a cyclic forest defoliating insect. 3. Our case study shows that anthropogenic warming shifts the epicentre of travelling LBM waves upward, which disrupts the intensity of population outbreaks that occurred regularly over the past millennium in the European Alps. Our findings demonstrate the ability of DA to detect ecological responses beyond internal system variability, to attribute them to specific external climate forcing factors, and to identify climate‐induced ecological tipping points. 4. In order to implement the climatological concept of ‘Detection and Attribution’ successfully into modern global change ecology, future studies should combine high‐resolution paleoenvironmental reconstructions and state‐of‐the‐art climate model simulations to inform inference‐based ecosystem models.
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Although there are many examples of contemporary directional selection, evidence for responses to selection that match predictions are often missing in quantitative genetic studies of wild populations. This is despite the presence of genetic variation and selection pressures - theoretical prerequisites for the response to selection. This conundrum can be explained by statistical issues with accurate parameter estimation, and by biological mechanisms that interfere with the response to selection. These biological mechanisms can accelerate or constrain this response. These mechanisms are generally studied independently but might act simultaneously. We therefore integrated these mechanisms to explore their potential combined effect. This has implications for explaining the apparent evolutionary stasis of wild populations and the conservation of wildlife.
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Elucidating the genetic basis of fitness-related traits is a major goal of molecular ecology. Traits subject to sexual selection are particularly interesting, as non-random mate choice should deplete genetic variation and thereby their evolutionary benefits. We examined the genetic basis of three sexually selected morphometric traits in bighorn sheep ( Ovis canadensis ): horn length, horn base circumference, and body mass. These traits are of specific concern in bighorn sheep as artificial selection through trophy hunting opposes sexual selection. Specifically, horn size determines trophy status and, in most North American jurisdictions, if an individual can be legally harvested. Using between 7,994–9,552 phenotypic measures from the long-term individual-based study at Ram Mountain (Alberta, Canada), we first showed that all three traits are heritable ( h² = 0.15–0.23). We then conducted a genome-wide association study (GWAS) utilizing a set of 3,777 SNPs typed in 76 individuals using the Ovine Infinium ® HD SNP BeadChip. We found suggestive association for body mass at a single locus (OAR9_91647990). The absence of strong associations with SNPs suggests that the traits are likely polygenic. These results represent a step forward for characterizing the genetic architecture of fitness related traits in sexually dimorphic ungulates.
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The five most pervasive anthropogenic threats to biodiversity are over-exploitation, habitat changes, climate change, invasive species, and pollution. Since all of these threats can affect intraspecific biodiversity-including genetic variation within populations-humans have the potential to induce contemporary microevolution in wild populations. We highlight recent empirical studies that have explored the effects of these anthropogenic threats to intraspecific biodiversity in the wild. We conclude that it is critical that we move towards a predictive framework that integrates a better understanding of contemporary microevolution to multiple threats to forecast the fate of natural populations in a changing world.
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Management of large carnivores is among the most controversial topics in natural resource administration. Regulated hunting is a centrepiece of many carnivore management programmes and, although a number of hunting effects on population dynamics, body-size distributions and life history in other wildlife have been observed, its effects on life history and demography of large carnivores remain poorly documented. We report results from a 30-year study of brown bears (Ursus arctos) analysed using an integrated hierarchical approach. Our study revealed that regulated hunting has severely disrupted the interplay between age-specific survival and environmental factors, altered the consequences of reproductive strategies, and changed reproductive values and life expectancy in a population of the world’s largest terrestrial carnivore. Protection and sustainable management have led to numerical recovery of several populations of large carnivores, but managers and policymakers should be aware of the extent to which regulated hunting may be influencing vital rates, thereby reshaping the life history of apex predators.
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Humans commonly harvest animals based on their expression of secondary sexual traits such as horns or antlers. This selective harvest is thought to have little effect on harvested populations because offtake rates are low and usually only the males are targeted. These arguments do not, however, take the relationship between secondary sexual trait expression and animal condition into account: there is increasing evidence that in many cases the degree of expression of such traits is correlated with an animal’s overall well-being, which is partly determined by their genetic match to the environment. Using an individual-based model,we find that when there is directional environmental change, selective harvest of males with the largest secondary sexual traits can lead to extinction in otherwise resilient populations. When harvest is not selective, the males best suited to a new environment gain the majority of matings and beneficial alleles spread rapidly. When these bestadapted males are removed, however, their beneficial alleles are lost, leading to extinction. Given the current changes happening globally, these results suggest that trophy hunting and other cases of selective harvest (such as certain types of insect collection) should be managed with extreme care whenever populations are faced with changing conditions. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
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Adaptive certification is the best remaining option for the trophy hunting industry in Africa to demonstrate sustainable and ethical hunting practices that benefit local communities and wildlife conservation.
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Some ecologists suggest that trophy hunting (e.g., harvesting males with a desirable trait above a certain size) can lead to rapid phenotypic change, which has led to an ongoing discussion about evolutionary consequences of trophy hunting. Claims of rapid evolution come from the statistical analyses of data, with no examination of whether these results are theoretically plausible. We constructed simple quantitative genetic models to explore how a range of hunting scenarios affects the evolution of a trophy such as horn length. We show that trophy hunting does lead to trophy evolution defined as change in the mean breeding value of the trait. However, the fastest rates of phenotypic change attributable to trophy hunting via evolution that are theoretically possible under standard assumptions of quantitative genetics are 1–2 orders of magnitude slower than the fastest rates reported from statistical analyses. Our work suggests a re-evaluation of the likely evolutionary consequences of trophy hunting would be appropriate when setting policy. Our work does not consider the ethical or ecological consequences of trophy hunting.
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Trophy hunting, the selective removal of animals for human recreation, can contribute to conservation when appropriately managed. Yet, little is known about how harvest rates or different definitions of trophy affect age structure and trophy size in harvested animals and in survivors because no controlled studies exist. To investigate the impacts of different management regimes, we developed an individual-based model for bighorn sheep (Ovis canadensis), based on empirical data on survival from a protected population and data on horn growth from 2 populations that differed in their growth rates. One population showed slow horn growth and the other population fast horn growth. We subjected these model populations to varying harvest rates and 2 different hunting regulations: 4/5 curl and full-curl definitions of a trophy male. We found that the effect of hunting regulations depends on horn growth rate. In populations with fast horn growth, the effects of trophy hunting on male age structure and horn size were greater and the effect of a change in the definition of legal male smaller than in populations with slow growth rates. High harvest rates led to a younger age structure and smaller horn size. Both effects were weakened by a more restrictive definition of trophy male. As harvest rates increased past 40% of legal males, the number of males harvested increased only marginally because an increasing proportion of the harvested males included those that had just become legal. Although our simulation focused on bighorn sheep, the link between horn growth rate and harvest effects may be applicable for any size-selective harvest regime.
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Warming-induced range shifts along elevational and latitudinal gradients have been observed in several species from various taxa. The mobility and behavioral plasticity of large endothermic mammals, however, complicate the detection of climatic effects on their spatial distributions. Here, we analyzed 230,565 hunting locations of the four most abundant ungulate species in the European Alps: ibex, chamois, red deer, and roe deer. Year-to-year and inter-decadal range shifts toward higher elevations in Switzerland coincided with warmer, snow-free, and thus more favorable autumn conditions in the same area. The average harvest elevation of ibex, chamois, and red deer significantly increased between 1991 and 2013. Although this trend is anticipated to continue, behavioral plasticity may allow the Alpine ibex and other mountain ungulates to buffer some of the associated consequences of climate change. Our results demonstrate the utility of well-replicated hunting archives to supplement shorter but more precise monitoring data. This study also provides independent evidence of animal range shifts in response to environmental change at interannual and multi-decadal time-scales.
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Weaponry in ungulates may be costly to grow and maintain, and different selective pressures in males and females may lead to sex-biased natural survival. Sexual differences in the relationship between weapon growth and survival may increase under anthropogenic selection through culling, for example because of trophy hunting. Selection on weaponry growth under different scenarios has been largely investigated in males of highly dimorphic ungulates, for which survival costs (either natural or hunting-related) are thought to be greatest. Little is known, however, about the survival costs of weaponry in males and females of weakly dimorphic species. We collected information on horn length and age at death/shooting of 407 chamois Rupicapra rupicapra in a protected population and in two hunted populations with different hunting regimes, to explore sexual differences in the selection on early horn growth under contrasting selective pressures. We also investigated the variation of horn growth and body mass in yearling males (n=688) and females (n=539) culled in one of the hunted populations over 14 years. The relationship between horn growth and survival showed remarkable sexual differences under different evolutionary scenarios. Within the protected population, under natural selection, we found no significant trade-off in either males or females. Under anthropogenic pressure, selection on early horn growth of culled individuals showed diametrically opposed sex-biased patterns, depending on the culling regime and hunters’ preferences. Despite the selective bias between males and females in one of the hunted populations, we did not detect significant sex-specific differences in the long-term pattern of early growth. The relationship between early horn growth and natural survival in either sex might suggest stabilizing selection in horn size in chamois. Selection through culling can be strongly sex-biased also in weakly dimorphic species, depending on hunters’ preferences and hunting regulations, and long-term data are needed to reveal potential undesirable evolutionary consequences.
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Human activities are a major evolutionary force affecting wild populations. Selective pressure from harvest has mainly been documented for life-history and morphological traits. The probability for an individual to be harvested, however, may also depend on its behaviour. 2.We report empirical studies that examined whether harvesting can exert selective pressures on behavioural traits. 3.We show that harvest-induced selection on behavioural traits is not specific to a particular harvest method and can occur throughout the animal kingdom. 4.Synthesis and applications. Managers need to recognize that artificial selection caused by harvesting is possible. More empirical studies integrating physiological, behavioural, and life-history traits should be carried out to test specific predictions of the potential for harvest-induced selection on heritable traits using models developed in fisheries. To limit selective pressure on behaviour imposed by harvesting, managers could reduce harvest quotas or vary harvest regulations over time and/or space to reduce the strength of selection on a particular phenotype. This article is protected by copyright. All rights reserved.
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Commercial and recreational harvests create selection pressures for fitness-related phenotypic traits that are partly under genetic control. Consequently, harvesting can drive evolution in targeted traits. However, the quantification of harvest-induced evolutionary life history and phenotypic changes is challenging, because both density-dependent feedback and environmental changes may also affect these changes through phenotypic plasticity. Here, we synthesize current knowledge and uncertainties on six key points: (i) whether or not harvest-induced evolution is happening, (ii) whether or not it is beneficial, (iii) how it shapes biological systems, (iv) how it could be avoided, (v) its importance relative to other drivers of phenotypic changes, and (vi) whether or not it should be explicitly accounted for in management. We do this by reviewing findings from aquatic systems exposed to fishing and terrestrial systems targeted by hunting. Evidence from aquatic systems emphasizes evolutionary effects on age and size at maturity, while in terrestrial systems changes are seen in weapon size and date of parturition. We suggest that while harvest-induced evolution is likely to occur and negatively affect populations, the rate of evolutionary changes and their ecological implications can be managed efficiently by simply reducing harvest intensity. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences'.
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Potential evolutionary consequences of selective hunting of mammals are controversial because of limited evidence and important socio-economic impacts. Several ecological and management variables facilitate evolutionary responses to selection for horn, tusk or antler size, including strong selective hunting pressure; harvest of males with large horns, tusks or antlers before they can breed; unavailable or ineffective sources of unselected immigrants; and age-dependent relationships between horn, tusk or antler size and male mating success. Plastic responses of male horns, tusks and antlers to environment are probably more common than evolutionary changes. Evidence for evolutionary effects of selective hunting is strong for large mammals where biological characteristics and hunting regulations combine to favour them.
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The extent of heritability and predictability of phenotypic characteristics influences directional selection of a species’ phenotype by the environment or through anthropogenic selection. Heritability is often related to evolvability, whereas predictability describes the efficiency of using one characteristic to predict another. Characteristics that are highly heritable and predictable may be easily selected for or against. Discrepancy exists in previous reports of heritability estimates for antler characteristics of white-tailed deer (Odocoileus virginianus) and if antler size of young males can be used to predict antler size later in life. We assessed the level of heritability of 6 antler characteristics using captive white-tailed deer aged 2.5–5.5 years and tested if antler size of 1.5-year-old males was a reliable predictor of antler size at 3.5 years after accounting for the effects of litter size and parturition date. Antler characteristics were moderately to highly heritable, whereas 1.5-year-old antler size alone was only a moderate predictor of antler size at 3.5 years. However, predictability nearly doubled after accounting for parturition date and litter size. White-tailed deer antler characteristics are moderately to highly heritable and although hunter selection may influence long-term phenotype for some ungulates, hunter selection is unlikely to manipulate white-tailed deer population-level phenotype because predicting future antler size is inefficient and individual reproductive success is variable.
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Selective harvest may lead to rapid evolutionary change. For large herbivores, trophy hunting removes males with large horns. That artificial selection, operating in opposition to sexual selection, can lead to undesirable consequences for management and conservation. There have been no comparisons of long-term changes in trophy size under contrasting harvest pressures. We analyzed horn measurements of Stone's rams (Ovis dalli stonei) harvested over 37 years in two large regions of British Columbia, Canada, with marked differences in hunting pressure to identify when selective hunting may cause a long-term decrease in horn growth. Under strong selective harvest, horn growth early in life and the number of males harvested declined by 12% and 45%, respectively, over the study period. Horn shape also changed over time: horn length became shorter for a given base circumference, likely because horn base is not a direct target of hunter selection. In contrast, under relatively lower hunting pressure, there were no detectable temporal trends in early horn growth, number of males harvested, or horn length relative to base circumference. Trophy hunting is an important recreational activity and can generate substantial revenues for conservation. By providing a reproductive advantage to males with smaller horns and reducing the availability of desirable trophies, however, excessive harvest may have the undesirable long-term consequences of reducing both the harvest and the horn size of rams. These consequences can be avoided by limiting offtake.
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Sexual selection has a critical role in evolution and it is fundamental to identify what ecological factors drive its variation. Disentangling the ecological correlates of sexual selection over the long term, however, is challenging and has rarely been done in nature. We sought to assess how demographic changes influenced the intensity, direction, and form of sexual selection, and whether selective pressures varied with age. We tested if breeder sex ratio, number of competitors and age structure influenced selection differentials on horn length of wild bighorn rams (Ovis canadensis) of different age classes on Ram Mountain, Alberta. We used 21 years of data including a detailed pedigree, demographic parameters, and repeated morphological measurements. Sexual selection on horn length of males of all ages was directional and positive. Selection intensity increased with the number of competitors, reflecting male-male encounter rate during the rut, but was independent of breeder sex ratio or age structure. This result can also be linked to changes in population size because the number of competitors was highly correlated to total number of sheep. This demographic effect likely arises from age-dependent mating tactics. Males aged 2 to 4 years are weakly competitive and experienced stronger sexual selection as they accounted for a greater proportion of all males. Selection experienced by mature males appeared independent of demography. Our study provides a rare description of the demographic determinants of sexual selection in nature. This article is protected by copyright. All rights reserved.
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Inbreeding depression is of major concern for the conservation of threatened species, and inbreeding avoidance is thought to be a key driver in the evolution of mating systems. However, the estimation of individual inbreeding coefficients in natural populations has been challenging, and, consequently, the full effect of inbreeding on fitness remains unclear. Genomic inbreeding coefficients may resolve the long-standing paucity of data on inbreeding depression in adult traits and total fitness. Here we investigate inbreeding depression in a range of life history traits and fitness in a wild population of red deer (Cervus elaphus) in Scotland using individual inbreeding coefficients derived from dense Single-Nucleotide Polymorphism (SNP) data ([Formula: see text]). We find associations between [Formula: see text] and annual breeding success in both sexes, and between maternal inbreeding coefficient and offspring survival. We also confirm previous findings of inbreeding depression in birth weight and juvenile survival. In contrast, inbreeding coefficients calculated from a deep and comparatively complete pedigree detected inbreeding depression in juvenile survival, but not in any adult fitness component. The total effect of inbreeding on lifetime breeding success (LBS) was substantial in both sexes: for [Formula: see text] [Formula: see text], a value resulting from a half-sib mating, LBS declined by 72% for females and 95% for males. Our results demonstrate that SNP-based estimates of inbreeding provide a powerful tool for evaluating inbreeding depression in natural populations, and suggest that, to date, the prevalence of inbreeding depression in adult traits may have been underestimated.
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Parents should bias sex allocation toward offspring of the sex most likely to provide higher fitness returns. Trivers and Willard proposed that for polygynous mammals, females should adjust sex-ratio at conception or bias allocation of resources toward the most profitable sex, according to their own body condition. However, the possibility that mammalian fathers may influence sex allocation has seldom been considered. Here, we show that the probability of having a son increased from 0.31 to 0.60 with sire reproductive success in wild bighorn sheep (Ovis canadensis). Furthermore, our results suggest that females fertilized by relatively unsuccessful sires allocated more energy during lactation to daughters than to sons, while the opposite occurred for females fertilized by successful sires. The pattern of sex-biased offspring production appears adaptive because paternal reproductive success reduced the fitness of daughters and increased the average annual weaning success of sons, independently of maternal allocation to the offspring. Our results illustrate that sex allocation can be driven by paternal phenotype, with profound influences on the strength of sexual selection and on conflicts of interest between parents. This article is protected by copyright. All rights reserved
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The potential for selective harvests to induce rapid evolutionary change is an important question for conservation and evolutionary biology, with numerous biological, social and economic implications. We analyze 39 years of phenotypic data on horn size in bighorn sheep (Ovis canadensis) subject to intense trophy hunting for 23 years, after which harvests nearly ceased. Our analyses revealed a significant decline in genetic value for horn length of rams, consistent with an evolutionary response to artificial selection on this trait. The probability that the observed change in male horn length was due solely to drift is 9.9%. Female horn length and male horn base, traits genetically correlated to the trait under selection, showed weak declining trends. There was no temporal trend in genetic value for female horn base circumference, a trait not directly targeted by selective hunting and not genetically correlated with male horn length. The decline in genetic value for male horn length stopped, but was not reversed, when hunting pressure was drastically reduced. Our analysis provides support for the contention that selective hunting led to a reduction in horn length through evolutionary change. It also confirms that after artificial selection stops, recovery through natural selection is slow. This article is protected by copyright. All rights reserved.
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International pressure to ban trophy hunting is increasing. However, we argue that trophy hunting can be an important conservation tool, provided it can be done in controlled manner to benefit biodiversity conservation and local people. Where political, and governance structures are adequate, trophy hunting can help address the ongoing loss of species.
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Many agencies and researchers use data from harvested animals to study temporal trends in phenotype. For large mammals, complete harvest records are typically only available for the past few decades, but records of the largest trophies have been collected for over a century. To examine whether record books and data from male bighorn sheep (Ovis canadensis) harvested under a minimum-curl regulation could detect temporal trends in horn length, we simulated populations of trophy-harvested male bighorn sheep where horn length was modeled to increase, remain stable, and decrease over time. All populations experienced a simulated harvest based on a minimum horn length, but only horns in the longest 5% of the initial distribution were entered in a fictional record book. We then assessed whether monitoring of harvested and “record” males detected temporal trends. Data from selective harvest underestimated declines and initially underestimated increases, but qualitatively detected both trends. Record-book entries, however, severely underestimated increases and did not detect declines, suggesting that they should not be used to monitor population trends. When these biases are taken into account, complete trophy harvest records can provide useful biological information.
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In polygynous mating systems, reproductive skew depends on the ability of males to monopolize females, which in turn may promote the development of contrasting traits in the two sexes. Although dominant individuals normally enjoy a higher reproductive success (RS) than subordinates, the use of genetic markers has shown that behavioural observations of male mating success may not provide reliable clues of RS. We report the preliminary results of the first DNA-based paternity analysis on the Northern chamois (Rupicapra rupicapra), a scarcely dimorphic mountain ungulate described as highly polygynous, in relation to mating tactic and age. Because of sampling difficulties, the success in parentage assignment was low, and the interpretation of results requires caution. Territorial males had a greater RS than nonterritorial ones but they were unable to monopolize mating events. Age had a weak effect on paternity outcome but only males ≥ 6 years showed siring success. Although future studies are needed to assess the opportunity for sexual selection in male chamois, the concurrence of limited sexual size dimorphism, compensatory growth, unbiased sex-specific survival, RS of alternative mating tactics and, possibly, long breeding tenure, may hint at the adoption of a conservative mating strategy in this species.
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Selective harvest may lead to rapid evolutionary change. For large herbivores, trophy hunting removes males with large horns. That artificial selection, operating in opposition to sexual selection, can lead to undesirable consequences for management and conservation. There have been no comparisons of long-term changes in trophy size under contrasting harvest pressures. We analyzed horn measurements of Stone's rams (Ovis dalli stonei) harvested over 37 years in two large regions of British Columbia, Canada, with marked differences in hunting pressure to identify when selective hunting may cause a long-term decrease in horn growth. Under strong selective harvest, horn growth early in life and the number of males harvested declined by 12% and 45%, respectively, over the study period. Horn shape also changed over time: horn length became shorter for a given base circumference, likely because horn base is not a direct target of hunter selection. In contrast, under relatively lower hunting pressure, there were no detectable temporal trends in early horn growth, number of males harvested, or horn length relative to base circumference. Trophy hunting is an important recreational activity and can generate substantial revenues for conservation. By providing a reproductive advantage to males with smaller horns and reducing the availability of desirable trophies, however, excessive harvest may have the undesirable long-term consequences of reducing both the harvest and the horn size of rams. These consequences can be avoided by limiting offtake.
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Hunting by humans can be a potent driver of selection for morphological and life history traits in wildlife populations across continents and taxa. Few studies, however, have documented selection on behavioural responses that increase individual survival under human hunting pressure. Using habitat with dense concealing cover is a common strategy for risk avoidance, with a higher chance of survival being the payoff. At the same time, risk avoidance can be costly in terms of missed foraging opportunities. We investigated individual fine-scale use of habitat by 40 GPS-marked European red deer, Cervus elaphus, and linked this to their survival through the hunting season. Whereas all males used similar habitat in the days before the hunting season, the onset of hunting induced an immediate switch to habitat with more concealing cover in surviving males, but not in males that were later shot. This habitat switch also involved a trade-off with foraging opportunities on bilberry, Vaccinium myrtillus, a key forage plant in autumn. Moreover, deer that use safer forest habitat might survive better because they make safer choices in general. The lack of a corresponding pattern in females might be because females were already largely using cover when hunting started, as predicted by sexual segregation theory and the risk of losing offspring. The behavioural response of males to the onset of hunting appears to be adaptive, given that it is linked to increased survival, an important fitness component. We suggest that predictable harvesting regimes with high harvest rates could create a strong selective pressure for deer to respond dynamically to the temporal change in hunting risk. Management should consider the potential for both ecological and evolutionary consequences of harvesting regimes on behaviour.
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Abstract There is now considerable empirical evidence that evolutionary changes in many phenotypic characters, such as body mass, age at maturation, and timing of breeding, often occur in populations subject to intense harvesting over longer periods. Here, we analyze the evolutionary component of the selection due to nonselective harvesting, which will operate even under selective harvesting and may generate a large evolutionary response. If phenotype affects susceptibility to density dependence-for example, through resource limitation-then nonselective harvesting can induce evolutionary change through its effect on population density. We provide a model for evolution of a quantitative character in such a fluctuating density-dependent population, using the diffusion approximation to describe jointly the temporal changes in mean phenotype and log population size. We show how nonselective harvesting in particular generates r-selection governed by genetic variation in the strength of density regulation and the magnitude of population fluctuations. We show that r-selection caused by nonselective harvesting is proportional to the mean fraction of the population harvested. We then compare the short-term as well as the long-term evolutionary impact of nonselective harvesting for different harvesting strategies by using the mean harvest fraction for different strategies. This comparison is performed for three different harvesting strategies: constant, proportional, and threshold harvesting. The more ecologically sustainable strategies also produce smaller evolutionary changes.
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Climate and environmental change have driven widespread changes in body size, particularly declines, across a range of taxonomic groups in recent decades. Size declines could substantially impact on the functioning of ecosystems. To date, most studies suggest that temporal trends in size have resulted indirectly from climate change modifying resource availability and quality, affecting the ability of individuals to acquire resources and grow. Here, we investigate striking long-term body mass declines in juvenile Alpine chamois (Rupicapra rupicapra), within three neighbouring populations in the Italian Alps. We find strong evidence that increasing population density and warming temperatures during spring and summer are linked to the mass declines. We find no evidence that the timing or productivity of resources have been altered during this period. We conclude that it is unlikely that environmental change has driven body size change indirectly via effects on resource productivity or phenology. Instead, we propose that environmental change has limited the ability of individuals to acquire resources. This could be due to increases in the intensity of competition and decreases in time spent foraging, owing to high temperatures. Our findings add weight to a growing body of evidence for long-term body size reductions and provide considerable insight into the potential drivers of such trends. Furthermore, we highlight the potential for appropriate management, for instance increases in harvest size, to counteract the impacts of climate change on body mass.
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Human harvests can unwittingly drive evolution on morphology and life history, and these selective effects may be detrimental to the management of natural resources. Although theory suggests that harvest refuges, as sources of unselected animals, could buffer the effects of human exploitation on wild populations, few studies have assessed their efficiency. We analyzed records from >7000 trophy bighorn rams (Ovis canadensis) harvested in Alberta, Canada, between 1974 and 2011 to investigate if the movement of rams from refuges toward harvested areas reduced the effects of selective harvesting on horn size through phenotypic rescue. Rams taken near refuges had horns on average about 3% longer than rams shot far from refuges and were slightly older, suggesting migration from refuges into hunted areas. Rams from areas adjacent to and far from harvest refuges, however, showed similar declines in horn length and increases in age at harvest over time, indicating a decreasing rate of horn growth. Our study suggests that the influx of rams from refuges is not sufficient to mitigate the selective effects of sheep trophy harvest. Instead, we suggest that selective hunting of highly mobile animals may affect the genetic structure of populations that spend part of the year inside protected areas.
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Long-term data (1974–2011) from harvested bighorn rams (Ovis canadensis) in Alberta, Canada, suggested a reduction in horn size and in the proportion of trophy rams in the provincial population over time. Age at harvest increased over time, suggesting slower horn growth. Rams that experienced favorable environmental conditions early in life had rapid horn growth and were harvested at a younger age than rams with slower horn growth. Guided nonresident hunters did not harvest larger rams than residents, suggesting that few large rams were available. Resident hunter success declined in recent years. Despite an apparently stable population, successive cohorts produced a decreasing harvest of trophy rams. We suggest that unrestricted harvest based on a threshold horn size led to a decline in the availability of trophy rams. That decline is partly an inevitable consequence of selective hunting that removes larger rams. Although our analysis does not establish that evolution of smaller horns caused the observed decline in both horn size and harvest of trophy rams, we suggest that intensive trophy hunting may have artificially selected for a decrease in horn growth rate. © 2013 The Wildlife Society.
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Direct effects of climate change on animal physiology, and indirect impacts from disruption of seasonal synchrony and breakdown of trophic interactions are particularly severe in Arctic and Alpine ecosystems. Unravelling biotic from abiotic drivers, however, remains challenging because high-resolution animal population data are often limited in space and time. Here, we show that variation in annual horn growth (an indirect proxy for individual performance) of 8043 male Alpine ibex (Capra ibex) over the past four decades is well synchronised among eight disjunct colonies in the eastern Swiss Alps. Elevated March to May temperatures, causing premature melting of Alpine snowcover, earlier plant phenology and subsequent improvement of ibex food resources, fuelled annual horn growth. These results reveal dependency of local trophic interactions on large-scale climate dynamics, and provide evidence that declining herbivore performance is not a universal response to global warming even for high-altitude populations that are also harvested.
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Many deer populations in Europe and North America have increased in abundance over the last decades. The increasing populations potentially entail both ecological and economic challenges and opportunities, but in practice we still know little about the extent to which these opportunities are being exploited in different management systems. The Norwegian red deer population has increased in density and expanded rapidly since the 1950s. Traditionally, red deer hunting has been undertaken by the local landowner and his relatives and friends. The present large population raises the question whether attracting other hunters could provide a higher economic return for the landowners and, if so, if they are interested in providing such hunting opportunities. We designed a survey to learn more about the landowners, both with respect to the present level of hunting income as well as economic costs of, for example, forest and agricultural damage; we also sought to understand their interest in increasing their income from red deer hunting and potential obstacles to realizing such an increased economic benefit. The results indicate that landowners on average think that red deer populations on their land result in higher costs than income but are nevertheless satisfied with the way things are. This highlights that increased numbers of deer need not automatically lead to more income for landowners and that the potential for income may be hindered by cultural factors such as reluctance to allow access to non-local hunters.
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Environmental change, including global warming, can lead to directional changes over time in phenotypic traits such as sex- and age-specific body mass. We evaluated the potential short-term effects of a series of hot and dry springs and early summers on mass of yearling chamois (Rupicapra rupicapra) in 2 populations in the western Alps. Yearling mass decreased in both populations over the study period, but much of this decline seemed to originate from a sharp drop in 2003, after which body mass remained low. Our analysis suggested that this decrease was caused by the additive effects of warm springs and summers over the first 2 years of life. The mass of adult chamois also decreased over time. These results suggest that ongoing warming in the Alps could be a selective pressure on the life history and reproductive strategies of wild ungulates.
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Sexual selection, through intra-male competition or female choice, is assumed to be a source of strong and sustained directional selection in the wild. In the presence of such strong directional selection, alleles enhancing a particular trait are predicted to become fixed within a population, leading to a decrease in the underlying genetic variation. However, there is often considerable genetic variation underlying sexually selected traits in wild populations, and consequently, this phenomenon has become a long-discussed issue in the field of evolutionary biology. In wild Soay sheep, large horns confer an advantage in strong intra-sexual competition, yet males show an inherited polymorphism for horn type and have substantial genetic variation in their horn size. Here we show that most genetic variation in this trait is maintained by a trade-off between natural and sexual selection at a single gene, relaxin-like receptor 2 (RXFP2). We found that an allele conferring larger horns, Ho(+), is associated with higher reproductive success, whereas a smaller horn allele, Ho(P), confers increased survival, resulting in a net effect of overdominance (that is, heterozygote advantage) for fitness at RXFP2. The nature of this trade-off is simple relative to commonly proposed explanations for the maintenance of sexually selected traits, such as genic capture ('good genes') and sexually antagonistic selection. Our results demonstrate that by identifying the genetic architecture of trait variation, we can determine the principal mechanisms maintaining genetic variation in traits under strong selection and explain apparently counter-evolutionary observations.
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1.Patterns of male reproductive allocation provide insight into life‐history characteristics. The trade‐offs associated with resource and female group defense are well‐defined. However, less is understood about trade‐offs in species that practice scramble‐competition polygyny, where successful strategies may favor competitive mate‐searching rather than contest competition and fighting. 2.White‐tailed deer (Odocoileus virginianus) practice scramble‐competition polygyny where solitary males search for and assess receptivity of females scattered across the landscape. Physically mature males are expected to do most of the breeding because of the high energetic costs of reproduction and high social status. However, young males may collectively sire one‐third of offspring. To gain a better understanding of trade‐offs associated with scramble‐competition polygyny, we quantified metrics associated with reproductive effort and success. 3.We quantified changes in body mass of harvested males, energetic costs of locomotion based on movements of GPS radio‐collared males, and timing of reproduction via temporal genetic parentage assignments. 4.Young males (1.5 and 2.5 years old) sired offspring, but their mating success was mainly limited to peak rut, when most females were in estrus. Furthermore, multiple paternity was common, indicating opportunistic reproduction. Reproductive effort, indexed by body mass loss, was highest in prime‐age males (5.5‐6.5 years old). Surprisingly, young and post‐prime males also exhibited significant body mass loss, indicative of investment in reproductive effort. Movement rates increased 2 to 4‐fold during rut as a function of mate‐search activities, but cost of locomotion would cause only about one‐third of observed body mass loss. Because males are capital breeders, we infer most of body mass loss is due to reduced foraging. 5.In scramble‐competition polygyny, the repeated location of potential mates and assessment of their estrous status appear to be important constituents of male mating strategies. Therefore mating success may be influenced by time management and spatial memory, and not based solely on social dominance. Thus, reproductive effort should be greater for individuals capable of reducing time foraging. For those that cannot, opportunistic mating opportunities may arise when operative adult sex ratios are low. Our analyses reveal valuable insight into the trade‐offs associated with scramble‐competition polygyny. This article is protected by copyright. All rights reserved.
Article
1.Selective hunting can affect demographic characteristics and phenotypic traits of the targeted species. Hunting systems often involve harvesting quotas based on sex, age and/or size categories to avoid selective pressure. However, it is difficult to assess if such regulations deter hunters from targeting larger ‘trophy’ animals with longer horns that may have evolutionary consequences. 2.Here, we compile 44′088 annually resolved and absolutely dated measurements of Alpine ibex (Capra ibex) horn growth increments from 8′355 males, harvested between 1978 and 2013, in the eastern Swiss Canton of Grisons. We aim to determine if male ibex with longer horns were preferentially targeted, causing animals with early rapid horn growth to have shorter lives, and whether such hunting selection translated into long‐term trends in horn size over the past four decades. 3.Results show that medium‐ to longer‐horned adult males had a higher probability of being harvested than shorter‐horned individuals of the same age, and that regulations do affect the hunters’ behaviour. Nevertheless, phenotypic traits like horn length, as well as body size and weight, remained stable over the study period. 4.Though selective trophy hunting still occurs, it did not cause a measurable evolutionary response in Grisons’ Alpine ibex populations; managed and surveyed since 1978. Nevertheless, further research is needed to understand if phenotypic trait development is co‐influenced by other, potentially compensatory factors that may possibly mask the effects of selective, long‐term hunting pressure. This article is protected by copyright. All rights reserved.
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The autumn has to a large extent been neglected in the climate effect literature, yet autumn events, e.g. plant senescence and animal migration, affect fitness of animals differently than spring events. Understanding the how variables including plant phenology influence timing of autumn migrations is important to gain a comprehensive understanding of the full annual cycle of migratory species. Here we use 13 years of data from 60 male and 168 female red deer (Cervus elaphus) to identify triggers of autumn migration. We relate the timing of autumn migration to environmental variables like snow fall, temperature and plant phenology (NDVI), and to onset of hunting, sex and migration distance. Severe weather has been suggested as the main trigger of autumn migration, but we found that the majority of the individuals had left the summer range well before snow fall (80.3%) and frost (70.5%), and also before the peak deterioration in forage quality (71.9%). Declining temperatures were associated with a higher daily migration potential. Onset of hunting showed the largest effect on migration potential, with a marked increase during the first days of hunting. Individuals still present in the summer range when snow fall, frost or peak forage deterioration occurred showed a significantly higher migration potential around these events. Males were less responsive to environmental cues, suggesting rutting activity, starting earlier in males, initiate movement prior to such conditions. Also, individuals with longer migration distances had a higher migration potential late in the season, than individuals with shorter migration distances. Our study shows that factors beyond weather and plant phenology, such as onset of hunting, may be important triggers of autumn migration. Severe weather and forage deterioration were important triggers for the individuals experiencing this, suggesting a hierarchical response to environmental cues. The trade-off between staying longer in the summer range and increased energy expenditures if surprised by severe weather is asymmetric, and leaving well in advance can be seen as a risk adverse tactic. This article is protected by copyright. All rights reserved.
Article
Studies of marked free-ranging ungulates have provided major contributions to ecology, evolution, and conservation. We focus on research areas where these studies have been particularly important: the role of individual differences in population dynamics, temporal changes in factors limiting populations, variation in reproductive success, quantitative genetics in the wild, population management, and conservation. We underline some strengths and limitations of these studies and call for more research on populations subjected to hunting, coexisting with large predators, and living in tropical or arid environments. Long-term research on ungulates requires long-term commitment, funding, access to study areas where animals can be monitored, and, usually, support from government agencies. Logistical difficulties limit the number of these important studies.
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Whether intensive harvesting alters the behavioural repertoire of exploited fishes is currently unknown, but plausible. We extend a fish life-history model to account for boldness as a personality trait that affects foraging intensity, which affects energy intake and risk from predation and fishing gear. We systematically investigate life-history and behavioral trait evolution along the boldness-timidity axis in response to the full range of common selectivity and exploitation patterns in fisheries. In agreement with previous studies we find that any type of harvesting selects for fast life histories and that merely elevated, yet unselective, fishing mortality favors boldness. We also find that timid-selective fishing (which can be expected in selected species targeted by active gear types) selects for increased boldness. By contrast, increased timidity is predicted when fishing targets bolder individuals common to passive gears, whether in combination with selection on size or not. Altered behavior caused by intensive harvesting should be commonplace in nature, which can have far-reaching ecological, evolutionary and managerial impacts. Evolution of timidity is expected to strongly erode catchability, which will negatively affect human well-being and influence the reliability of stock assessments that rely on fishery-dependent data.
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Empirical evidence strongly indicates that human exploitation has frequently led to rapid evolutionary changes in wild populations, yet the mechanisms involved are often poorly understood. Here we applied a recently developed demographic framework for analysing selection to data from a 20-year study of a wild population of moose, Alces alces. In this population, a genetic pedigree has been established all the way back to founders. We demonstrate harvest-induced directional selection for delayed birth dates in males and reduced body mass as calf in females. During the study period, birth date was delayed by 0.81 days per year for both sexes, while no significant changes occurred in calf body mass. Quantitative genetic analyses indicated that both traits harboured significant additive genetic variance. These results show that selective harvesting can induce strong selection which oppose natural selection. This may cause evolution of less favourable phenotypes that become maladaptive once harvesting ceases. This article is protected by copyright. All rights reserved.
Article
Harvesting of wild populations can cause the evolution of morphological, behavioral, and life history traits that may compromise natural or sexual selection. Despite the vulnerability of large mammals to rapid population decline from harvesting, the evolutionary effects of harvesting on mega-fauna have received limited attention. In elephants, illegal ivory harvesting disproportionately affects older age classes and males because they carry large tusks, but its' effects on tusk size for age or tusk size for stature are less understood. We tested whether severe historical elephant harvests eliminated large tuskers among survivors and whether elephants born thereafter had smaller tusks. Adjusting for the influence of shoulder height – a metric strongly correlated with body size and age and often used as a proxy for age – we compared tusk size for elephants sampled in 1966–1968, prior to severe ivory harvesting in the late 1970s and early 1980s, with tusk size of survivors and elephants born during population recovery in the mid-1990s. In a regional population, tusk length declined by ˜21% in male and by ˜27% in female elephants born during population recovery, while tusk length declined by 22% in males and 37% in females among survivors. Tusk circumference at lip declined by 5% in males but not in females born during population recovery, whereas tusk circumference reduced by 8% in male and by 11% in female survivors. In a single subpopulation, mean tusk length at mean basal tusk circumference declined by 12.4% in males and 21% in females. Tusk size varied between elephant social groups. Tusk homogeneity within social groups and the often high genetic similarity within social groups suggest that tusk size may be heritable. Our findings support a hypothesis of selection of large tuskers by poachers as a driver of the decline in tusk size for age proxy and contemporary tusk evolution in African elephants.
Article
Autumn has to a large extent been neglected in the climate effect literature, yet autumn events, e.g., plant senescence and animal migration, affect fitness of animals differently than spring events. Understanding how variables including plant phenology influence timing of autumn migrations is important to gain a comprehensive understanding of the full annual cycle of migratory species. Here we use 13 yr of data from 60 male and 168 female red deer (Cervus elaphus) to identify triggers of autumn migration. We relate the timing of autumn migration to environmental variables like snow fall, temperature, and plant phenology (NDVI), and to onset of hunting, sex, and migration distance. Severe weather has been suggested as the main trigger of autumn migration, but we found that the majority of the individuals had left the summer range well before snow fall (80.3%) and frost (70.5%), and also before the peak deterioration in forage quality (71.9%). Declining temperatures were associated with a higher daily migration potential. Onset of hunting showed the largest effect on migration potential, with a marked increase during the first days of hunting. Individuals still present in the summer range when snow fall, frost, or peak forage deterioration occurred showed a significantly higher migration potential around these events. Males were less responsive to environmental cues, suggesting rutting activity, starting earlier in males, initiate movement prior to such conditions. Also, individuals with longer migration distances had a higher migration potential late in the season than individuals with shorter migration distances. Our study shows that factors beyond weather and plant phenology, such as onset of hunting, may be important triggers of autumn migration. Severe weather and forage deterioration were important triggers for the individuals experiencing this, which suggests a hierarchical response to environmental cues. The trade-off between staying longer in the summer range and increased energy expenditures if surprised by severe weather is asymmetric, and leaving well in advance can be seen as a risk-averse tactic.
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The identification of genes influencing fitness is central to our understanding of the genetic basis of adaptation and how it shapes phenotypic variation in wild populations. Here, we used whole genome resequencing of wild Rocky Mountain bighorn sheep (Ovis canadensis) to > 50 fold coverage to identify 2.8 million SNPs and genomic regions bearing signatures of directional selection (i.e., selective sweeps). A comparison of SNP diversity between the X chromosome and the autosomes indicated that bighorn males had a dramatically reduced long term effective population size compared to females. This likely reflects a long history of intense sexual selection mediated by male-male competition for mates. Selective sweep scans based on heterozygosity and nucleotide diversity revealed evidence for a selective sweep shared across multiple populations at RXFP2, a gene that strongly affects horn size in domestic ungulates. The massive horns carried by bighorn rams appear to have evolved in part via strong positive selection at RXFP2. We identified evidence for selection within individual populations at genes affecting early body growth and cellular response to hypoxia; however these must be interpreted more cautiously as genetic drift is strong within local populations and may have caused false positives. These results represent a rare example of strong genomic signatures of selection identified at genes with known function in wild populations of a non-model species. Our results also showcase the value of reference genome assemblies from agricultural or model species for studies of the genomic basis of adaptation in closely related wild taxa. This article is protected by copyright. All rights reserved.
Conference Paper
Conservation science is often interested in predicting the future state of populations living in variable environments. Behavioral ecology is often interested in understanding individual behavior in terms of adaptive strategies for dealing with variable ecological, social, or phenotypic states. To the extent that individual behavior is strategic, predictable in different environments, and has population-level consequences, the study of behavior can advance the predictive goals of conservation. Mating system studies, via data on variation in individual reproductive success, have most frequently been applied to conservation in the estimation of effective population size and prediction of genetic trajectories of single populations. However, mating strategy may also influence dispersal, gene flow, and genetic trajectories at spatial scales involving many populations. Mating competition within populations and dispersal will often have opposing effects on effective population size. Future studies of mating systems might aid conservation (i) in evaluating the genetic effects of mating strategy at different spatial scales, and (ii) by providing, in place of point estimates, descriptions of the way in which variation in lifetime reproductive success and population dispersal pattern change in reaction to environmental variation. Such information may allow conservation science to provide better guidance regarding the appropriate spatial scale of habitat protection and restoration and effective strategies for reserve design and re-design.
Article
Trophy hunting in ungulates may favour individuals with smaller horns. A decrease in horn/antler size may jeopardize the conservation potential of hunting areas, which would be a major concern in Africa where hunting zones represent over half of the total area of protected lands. We investigated horn length trends of harvested male impalas Aepyceros melampus, greater kudus Tragelaphus strepsiceros and sable antelopes Hippotragus niger, from 1974 to 2008 in Matetsi Safari Area, Zimbabwe. Horn length declined by 4% in impalas, partly because male harvest age decreased. In greater kudus, surprisingly, horn length increased by 14%, while mean age of harvested male greater kudus increased during the study period. Reduced hunting pressure on this species during the study may have allowed males to live longer and to grow longer horns before being harvested. Horn length declined by 6% in sable antelopes, independent of age, suggesting that trophy hunting selected male sable antelopes with smaller horns through time, provided that horn length is heritable. Hunting pressure and trophy value were higher for sable antelopes than for impalas and greater kudus. Accordingly, the decline of horn length in this species was more pronounced. More valuable trophy species, such as sable antelopes, require special attention because they may be exposed to higher hunting pressure, and are therefore more likely to experience a decrease in horn size.
Article
Understanding factors affecting antler size, and the extent to which harvesting is selective for these traits, is important in order to address management strategies aimed to minimize the risk of negative evolutionary consequences. In an Alpine study area, we compared the phenotypic quality and the antler size of 2,725 male roe deer hunted in two regions differing for winter harshness and habitat quality, and evaluated whether the selective behaviour of recreational hunters was influenced by phenotypic quality and antler size. Antler length and antler circumference relative to both body mass and jaw length were larger in the region with more favourable climate and habitat conditions, indicating that here roe deer were able to allocate more resources to antler growth. The analysis of the temporal trends of harvest bags suggested that hunters did not select roe deer for their body mass or size, but instead for antler size. This resulted also in a preference for sub-adult and adult age classes, while yearlings were culled reluctantly, especially in the region where antlers were smaller. Our results indicate that environmental heterogeneity may influence the relative investment in antler growth. In this way, it may interact with the hunters’ preferences increasing the risk that recreational hunting of roe deer, which is a widespread practice in many European countries, might result in alteration of male age structure and possibly in directional artificial selection.