Unnatural Selection
Unnatural Selection ->>> https://byltly.com/2tl8H0
Using a meta-analysis of previously published data, the authors compared the rates of phenotypic change in 40 populations subject to human harvesting with the rates seen in 20 systems that experienced selection from natural forces (for example, Darwin's finches) and with the rates in 25 systems that experienced other human disturbance (for example, pollution). The human-harvested organisms included fish, ungulates, invertebrates and even plants, examples of these being respectively sockeye salmon, bighorn sheep, marine snails and gingseng.
For billions of years, species have evolved by natural selection, the process by which genetic mutations that help an organism survive are passed on from one generation to the next and harmful ones are eliminated.
But natural selection takes time -- sometimes millions or even hundreds of millions of years. Humans have only been around for tens of thousands of years, but we are changing the world so much that genetic evolution simply can't keep up.
John Hawks, an anthropologist and geneticist at the University of Wisconsin, Madison, says we've created a lifestyle that is at odds with the one natural selection provided us with. Consider, for example, what ate when we were hunter gatherers, long before we started farming.
We've turned the notion of natural selection on its head. Nature isn't the only force that picks the genes that stick around -- we're doing it too. We're moving toward a time when we can routinely repair, remove or even insert genes in people.
As the authors detail in the book, adverse selection leaves policymakers in a bind. Making health insurance the same price for everyone, even for those with observable problems, can seem fair and just. But the numbers may not add up for insurers, as shown by the collapse of state-backed health insurance exchanges in New Jersey and New York that required that all customers be charged the same price.
Harvest can affect sexual selection because it tends to remove individuals with particular characteristics, such as large size or elaborate weapons from those of the breeding pool. Sexual selection can act in concert with natural selection on some of these same traits (as well as others), with complex results [e.g., Hamon and Foote (2005)]. Sexual and natural selection can act simultaneously to change the frequency of particular phenotypes, depending on the intensity of natural prebreeding mortality (e.g., through predation or disease), breeding density, and the characteristics of breeding adults (e.g., frequency-dependent selection). Because different environmental conditions and population features favor different phenotypes, natural and sexual selection can interact in complex ways in different places and at different times to affect the characteristics of successful breeders.
The objective of this chapter is to summarize the consequences of unnatural selection and sexual selection in wild populations of animals (Fig. 7.1), outline why these consequences threaten future yield and population viability, and suggest some measures to address this problem.
Recognition that exploitation of wild animals can produce evolutionary change is not new. It was recognized for fishing by the late 19th century and for hunting by the early 20th century. However, few studies have been able to clearly document evolutionary response to exploitative selection, and the possibility that exploitation-induced evolutionary change can oppose adaptive responses to natural and sexual selection has not been widely appreciated. Nevertheless, Coltman (2008) argued that rapid contemporary evolution has now been shown to occur in response to invasive species, habitat degradation, climate change, and exploitation, and he went on to say that exploitation-induced evolution may well have the most dramatic impact of any of these anthropogenic sources of selection to date. Mace and Reynolds (2001) asked why sustainable exploitation is so difficult, and pointed to limits of biological knowledge and limits of control as the 2 primary factors that cause exploitation to be such a challenge for conservation.
This form of selection is thought to oppose natural and sexual selection on these traits, and the fisheries-induced evolution that is likely to result from such selection will favor trait phenotypes among breeders that differ substantially from those targeted in fisheries (Naish and Hard, 2008). That is, fisheries-induced evolution will tend to proceed along a trajectory that is counter to one that maintains trait combinations desirable to fishermen. Exploitative selection imposed by fishing tends to reduce the frequency of desirable phenotypes through directional selection for alternative phenotypes, unlike other human-induced forms of selection, such as domestication, which often produce maladapted phenotypes indirectly by favoring alternative optima through alteration of the natural selection regime [e.g., Araki et al. (2007)].
Recreational fisheries can also bring about a genetic response to angling. However, there has been little work done in this area. Some authors have reported differences in angling vulnerability between domestic and wild strains of fish (Beukema, 1969; Biro et al., 2004). Biro and Stamps (2008) argued that behaviors such as boldness and activity, which are often correlated with growth rate, are likely to affect productivity and could respond to selective mortality. Philipp et al. (2009) reported differences in hook-and-line angling vulnerability between individual largemouth bass (Micropterus salmoides) in a wild population. The authors estimated a realized heritability of 0.15 through a 3-generation selection experiment.
Few studies have estimated the intensity of selection that fishing exerts. Although mortality of fish caught in many fisheries tends to increase with fish size, producing negative selection differentials (Falconer and Mackay, 1996), these estimates also appear to vary substantially from place to place and over time (Handford et al., 1977; Ricker, 1981; Law and Rowell, 1993; Sinclair et al., 2002; Hindar et al., 2007; Hard et al., 2008; Hilborn and Minte-Vera, 2008) and between the sexes (Hamon et al., 2000). Kendall et al. (2009) estimated standardized selection differentials for a 60-year dataset of Bristol Bay sockeye salmon (Oncorhynchus nerka) and found that selection intensity often differed substantially between sexes of returning fish and among years, although selection was generally higher on larger fish (especially females). Hard et al. (2008) concluded that estimates of selection intensity resulting from fishing were generally modest and typically less than the few estimates of natural and sexual selection differentials that have been reported for species like Pacific salmon (Fleming and Gross, 1994; Hamon, 2005; Hamon and Foote, 2005; Ford et al., 2008). Nevertheless, even fisheries that are not highly selective are expected to produce evolutionary change if fishing mortality is high enough (Policansky, 1993).
Nevertheless, selection of this intensity is not inconsistent with estimates of natural selection in nature (Kingsolver and Pfennig, 2007) and might be sufficiently strong to produce rapid evolutionary change in many cases. In their long-term study of Windermere pike (Esox lucius) in England, Edeline et al. (2007) contrasted temporal patterns of natural and fishing selection on this species; it was the first study to relate these patterns to long-term trends in life-history characteristics of wild fish (Coltman, 2008). They estimated a substantial, fishing-induced negative selection differential on the reaction norm describing variation in gonad weight/body length, a measure of reproductive investment, in age-3 females. The temporal dynamics of life history appear to reflect the combined influences of a half century of natural and fishing selection; growth rate and reproductive investment at younger ages tended to decline during periods of higher exploitation, a pattern that diminished when fishing rates eased.
Game and especially trophy hunting generally differ from fishing in several ways. For example, key aspects of the life histories of the 2 groups of animals often differ. Game hunting often focuses on animals with relatively low reproductive output, and relatively low natural mortality rates; many fishes have higher fecundities and higher natural mortality rates than game animals. We expect that hunting selection could have a considerable effect on the evolution of adult characteristics, particularly those in prime-aged adults under sexual selection because hunting mortality is often substantially higher than natural mortality for adult game animals (Festa-Bianchet, 2003; Gaillard et al., 2003).
Virtually all hunting invokes selective elements of some kind. These elements are often associated with particular phenotypic characteristics such as body size, coat color, and weapons or ornaments such as horns and antlers. As is the case for fishing, hunting for many animals can produce the paradoxical situation of selecting against the traits that are preferred by hunters (Festa-Bianchet, 2003). Because variation in many of these traits has an appreciable genetic component (FitzSimmons et al., 1995; Hartl et al., 1995; Moorcroft et al., 1996; Lukefahr and Jacobson, 1998), such selection is likely to produce detectable evolutionary responses that reduce the ability of breeders with desirable characteristics to contribute to reproduction (Mills, 2007). Harris et al. (2002) argued that available information is sufficient to recommend hunting patterns that minimize deviations of sex- and age-specific mortality rates from natural mortality rates.
Coltman et al. (2003) used a quantitative genetic analysis of a reconstructed pedigree for a wild population of Canadian bighorn sheep to show how hunting selection affected body weight and horn size. They showed that selection was most intense against rams with high breeding values because of hunter preference for large rams with large horns, with the consequence that breeding values for both ram traits declined steeply over 35 years. Because both traits are highly heritable and positively genetically correlated (Coltman et al., 2003), continued selection against large rams with large horns is expected to directly reduce horn size with a correlated response in reduced body mass. Such selection will reduce the frequencies of these phenotypes to lower levels, with likely adverse consequences for male breeding success. Both ram weight and horn size are undoubtedly subject to sexual selection through male-male competition during the rut, but it is unclear to what extent such sexual selection can alter the rate of evolution under hunting selection because sexual selection gradients have not been estimated. However, they must be high for some heavily hunted populations, where heritabilities for traits under selection are high and observed temporal declines in breeding values for these traits are often substantial [e.g., Coltman et al. (2003)]. Garel et al. (2007) found similar patterns in morphology and life history resulting from trophy ram hunting in Europe. 59ce067264
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