Testing evolutionary predictions in wild mice Pelletier, Fanie
Science (American Association for the Advancement of Science),
2019-Feb-01, 2019-02-00, 20190201, Volume:
363, Issue:
6426
Journal Article
Peer reviewed
An experimental demonstration of a “simple” evolutionary path for camouflage in nature
Four decades ago, Dougal Dixon used “thought experiments” based on evolutionary and ecological principles in his ...book
After Man
(
1
), to imagine what adaptations species may develop in a future after humans disappeared. For example, he imagined that pytherons, a group of carnivorous mammals evolved from rats, would fill the ecological niche currently occupied by seals in the polar oceans. Pytheron evolution included fin-shaped limbs and a streamlined body, better adapted for swimming. His book on “speculative evolution” is a reminder that making specific predictions about trait evolution in nature, in many cases, belongs more to science fiction than to science. Indeed, evolutionary ecology has yet to build a predictive framework that allows forecasting how genetically encoded traits may respond to known selective pressures (
2
,
3
). On page 499 of this issue, Barrett
et al.
(
4
) take advantage of recently evolved traits in wild mice (
Peromyscus maniculatus
) with known genetic architecture to experimentally simulate the ecological context and evolutionary forces that may have led to the evolution of differences in coat color according to soil color in Sand Hills, Nebraska.
Cohort effects, when a common environment affects long-term performance, can have a major impact on population dynamics. Very few studies of wild animals have obtained the necessary data to study the ...mechanisms leading to cohort effects. We exploited 42 years of individual-based data on bighorn sheep to test for causal links between birth density, body mass, age at first reproduction (AFR), longevity and lifetime reproductive success (LRS) using path analysis. Specifically, we investigated whether the effect of early-life environment on lifetime fitness was the result of indirect effects through body mass or direct effects of early-life environment on fitness. Additionally, we evaluated whether the effects of early-life environment were dependant on the environment experienced during adulthood. Contrary to expectation, the effect on LRS mediated through body mass was weak compared to the effects found via a delay in AFR, reduced longevity and the direct effect of birth density. Birth density also had an important indirect effect on LRS through reduced longevity, but only when adult density was high. Our results show that the potential long-term consequences of a harsh early-life environment on fitness are likely to be underestimated if investigations are limited to body mass instead of fitness at several life stages, or if the interactions between past and present environment are ignored.
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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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Cohort effects can be a major source of heterogeneity and play an important role in population dynamics. Silver-spoon effects, when environmental quality at birth improves future performance ...regardless of the adult environment, can induce strong lagged responses on population growth. Alternatively, the external predictive adaptive response (PAR) hypothesis predicts that organisms will adjust their developmental trajectory and physiology during early life in anticipation of expected adult conditions but has rarely been assessed in wild species. We used over 40 years of detailed individual monitoring of bighorn ewes (Ovis canadensis) to quantify long-term cohort effects on survival and reproduction. We then tested both the silver-spoon and the PAR hypotheses. Cohort effects involved a strong interaction between birth and current environments: reproduction and survival were lowest for ewes that were born and lived at high population densities. This interaction, however, does not support the PAR hypothesis because individuals with matching high-density birth and adult environments had reduced fitness. Instead, individuals born at high density had overall lower lifetime fitness suggesting a silver-spoon effect. Early-life conditions can induce long-term changes in fitness components, and their effects on cohort fitness vary according to adult environment.
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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.
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Harvest regulations commonly attenuate the consequences of hunting on specific segments of a population. However, regulations may not protect individuals from non‐lethal effects of hunting and their ...consequences remain poorly understood. In this study, we compared the movement rates of Scandinavian brown bears (Ursus arctos, n = 47) across spatiotemporal variations in risk in relation to the onset of bear hunting. We tested two alternative hypotheses based on whether behavioural responses to hunting involve hiding or escaping. If bears try to reduce risk exposure by avoiding being detected by hunters, we expect individuals from all demographic groups to reduce their movement rate during the hunting season. On the other hand, if bears avoid hunters by escaping, we expect them to increase their movement rate in order to leave high‐risk areas faster. We found an increased movement rate in females accompanied by dependent offspring during the morning hours of the bear hunting season, a general decrease in movement rate in adult lone females, and no changes in males and subadult females. The increased movement rate that we observed in females with dependant offspring during the hunting season was likely an antipredator response because it only occurred in areas located closer to roads, whereas the decreased movement rate in lone females could be either part of seasonal activity patterns or be associated with an increased selection for better concealment. Our study suggests that female brown bears accompanied by offspring likely move faster in high‐risk areas to minimize risk exposure as well as the costly trade‐offs (i.e. time spent foraging vs. time spent hiding) typically associated with anti‐predator tactics that involve changes in resource selection. Our study also highlights the importance of modelling fine‐scale spatiotemporal variations in risk to adequately capture the complexity in behavioural responses caused by human activities in wildlife.
In this study, we investigated the movement behaviour of brown bears in response to roads and human disturbances by using linear mixed‐effect models. We found that females with dependant offspring increase their movement speed when located close to roads during the bear hunting season.
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7.
Evolutionary origins for ecological patterns in space Urban, Mark C.; Strauss, Sharon Y.; Pelletier, Fanie ...
Proceedings of the National Academy of Sciences - PNAS,
07/2020, Volume:
117, Issue:
30
Journal Article
Peer reviewed
Open access
Historically, many biologists assumed that evolution and ecology acted independently because evolution occurred over distances too great to influence most ecological patterns. Today, evidence ...indicates that evolution can operate over a range of spatial scales, including fine spatial scales. Thus, evolutionary divergence across space might frequently interact with the mechanisms that also determine spatial ecological patterns. Here, we synthesize insights from 500 eco-evolutionary studies and develop a predictive framework that seeks to understand whether and when evolution amplifies, dampens, or creates ecological patterns. We demonstrate that local adaptation can alter everything from spatial variation in population abundances to ecosystem properties. We uncover 14 mechanisms that can mediate the outcome of evolution on spatial ecological patterns. Sometimes, evolution amplifies environmental variation, especially when selection enhances resource uptake or patch selection. The local evolution of foundation or keystone species can create ecological patterns where none existed originally. However, most often, we find that evolution dampens existing environmental gradients, because local adaptation evens out fitness across environments and thus counteracts the variation in associated ecological patterns. Consequently, evolution generally smooths out the underlying heterogeneity in nature, making the world appear less ragged than it would be in the absence of evolution. We end by highlighting the future research needed to inform a fully integrated and predictive biology that accounts for eco-evolutionary interactions in both space and time.
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As an important extrinsic source of mortality, harvest should select for fast reproduction and accelerated life histories. However, if vulnerability to harvest depends upon female reproductive ...status, patterns of selectivity could diverge and favor alternative reproductive behaviors. Here, using more than 20 years of detailed data on survival and reproduction in a hunted large carnivore population, we show that protecting females with dependent young, a widespread hunting regulation, provides a survival benefit to females providing longer maternal care. This survival gain compensates for the females' reduced reproductive output, especially at high hunting pressure, where the fitness benefit of prolonged periods of maternal care outweighs that of shorter maternal care. Our study shows that hunting regulation can indirectly promote slower life histories by modulating the fitness benefit of maternal care tactics. We provide empirical evidence that harvest regulation can induce artificial selection on female life history traits and affect demographic processes.
Recruitment and dispersal are important demographic rates and studying their determinants is particularly important in the current context of global anthropogenic perturbations. In birds, and ...especially for migratory species, assessing these rates is challenging because of the difficulties involved in tracking individuals beyond fledging. Here we assessed the determinants of nest box local recruitment and natal dispersal distances in a declining aerial insectivore, the tree swallow Tachycineta bicolor. We used a 16‐year dataset obtained from the long term monitoring of a population breeding within a 10 200‐km2 study system located along a gradient of agricultural intensification in southern Québec, Canada. Yearly nest box local recruitment rates ranged there in between 1.0% and 3.2%. Heavier nestlings who fledged earlier were more likely to recruit. Natal dispersal distances were generally short (mean ± SD = 12.7 ± 13.8 km) in the study system and were influenced by different factors depending on sex. Females dispersed over shorter distances when conspecific occupancy on breeding site was high, while males dispersed farther in the presence of competing house sparrows Passer domesticus and when their mother was young. Selection of breeding locations appeared to take place at multiple scales and individuals recruited in sites with characteristics similar to their natal sites. Our results provide important information concerning the factors influencing nest box local recruitment and natal dispersal dynamics of this migratory species. These factors should be considered in conservation practices for this species in order to support production of recruits in habitats favorable to their survival.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Humans have exploited wild animals for thousands of years. Recent studies indicate that harvest‐induced selection on life‐history and morphological traits may lead to ecological and evolutionary ...changes. Less attention has been given to harvest‐induced selection on behavioural traits, especially in terrestrial systems. We assessed in a wild population of large terrestrial mammals whether decades of hunting led to harvest‐induced selection on trappability, a proxy of risk‐taking behaviour. We investigated links between trappability, horn growth and survival across individuals in early life and quantified the correlations between early‐life trappability and horn growth with availability to hunters and probability of being shot. We found positive among‐individual correlations between early‐life trappability and horn growth, early‐life trappability and survival and early‐life horn growth and survival. Faster growing individuals were more likely to be available to hunters and shot at a young age. We found no correlations between early‐life trappability and availability to hunters or probability of being shot. Our results show that correlations between behaviour and growth can occur in wild terrestrial population but may be context dependent. This result highlights the difficulty in formulating general predictions about harvest‐induced selection on behaviour, which can be affected by species ecology, harvesting regulations and harvesting methods used. Future studies should investigate mechanisms linking physiological, behavioural and morphological traits and how this effects harvest vulnerability to evaluate the potential for harvest to drive selection on behaviour in wild animal populations.
We quantified among‐individual correlations in behaviour, growth and survival in a wild bighorn sheep population and assessed whether decades of size‐selective hunting led to indirect harvest‐induced selection on behaviour. We found positive among‐individual correlations between early‐life trappability, growth and survival but no correlations between early‐life behaviour and vulnerability to hunters. Our results show that correlations between behaviour, growth and life‐history traits can occur in wild terrestrial population but may be context dependent and highlight the difficulty in formulating general predictions about harvest‐induced selection on behaviour.
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