Editing Directional selection (section)

==Examples==
=== Finch beak size ===
[[File:Darwin's finches by Gould.jpg|thumb|Darwin's finches with different sized beaks that were suited for different seed types]]
Another example of directional selection is the beak size in a specific population of [[Finch|finches]]. Darwin first observed this in the publication of his book, ''[[On the Origin of Species]],'' and he details how the size of the finches beak differs based on environmental factors. On the [[Galápagos Islands]] west of the coast of [[Ecuador]], there were groups of finches displaying different beak phenotypes.<ref>{{Cite web |last=Burrows |first=Leah |date=November 2021 |title=For Darwin's finches, beak shape goes beyond evolution |url=https://seas.harvard.edu/news/2021/11/darwins-finches-beak-shape-goes-beyond-evolution |website=Harvard School of Engineering}}</ref> In one group, the beaks ranged from large and tough to small and smooth. Throughout the wet years, small seeds were more common than large seeds, and because of the large supply of small seeds the finches rarely ate large seeds. During the dry years, neither the small or large seeds were in great abundance, and the birds trended towards eating larger seeds. The changes in diet of the finches based on the environmental wet and dry seasons affected the depth of the birds’ beaks in future generations. <ref>{{cite book |last1=Campbell |first1=Neil A. |url=https://books.google.com/books?id=9pqXQgAACAAJ |title=Biology |last2=Reece |first2=Jane B. |publisher=Benjamin Cummings |year=2002 |isbn=978-0-8053-6624-2 |edition=6th |pages=450–451}}</ref> The beaks most beneficial to the more plentiful type of seed would be selected for because the birds were able to feed themselves and reproduce.
=== Peppered moths ===
[[File:Biston betularia (4777708667).jpg|thumb|Peppered moth with dark phenotype that was positively selected for during the Industrial Revolution. ]]
[[File:-1931- Peppered Moth (Biston betularia) (49943032886).jpg|thumb|Peppered Moth with white phenotype that was negatively selected for during the Industrial Revolution.]]
A significant example of directional selection in populations is the fluctuations of light and dark phenotypes in [[Peppered moth|peppered moths]] in the 1800s.<ref>{{Cite web |title=Peppered Moth |url=https://globalchange.umich.edu/globalchange1/current/labs/Lab5_PepperedMoth/PepperedMoth.htm |access-date=2024-03-24 |website=globalchange.umich.edu}}</ref> During the industrial revolution, environmental conditions were rapidly changing with the newfound emission of dark, black smoke from factories that would change the color of trees, rocks, and other niches of moths.<ref>{{Cite web |title=Peppered Moth and natural selection |url=https://butterfly-conservation.org/moths/why-moths-matter/amazing-moths/peppered-moth-and-natural-selection |access-date=2024-03-24 |website=butterfly-conservation.org |language=en}}</ref> Before the industrial revolution, the most prominent phenotype in the peppered moth population was the lighter, speckled moths. They thrived on the light birch trees and their phenotype would provide them with better camouflage from predators. After the [[Industrial Revolution]] as the trees become darker with soot, the moths with the darker phenotype were able to blend in and avoid predators better than their white counterparts. As time went on, the darker moths were positively directionally selected for and the allele frequency began to shift due to the increase in the number of darker moths.<ref>{{Cite journal |last=Saccheri |first=Ilik J. |date=October 2008 |title=Selection and gene flow on a diminishing cline of melanic peppered moths |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=42 |pages=16212–16217 |doi=10.1073/pnas.0803785105 |doi-access=free |pmid=18854412 |pmc=2571026 |bibcode=2008PNAS..10516212S }}</ref>

===African cichlids===
[[File:Labeotropheus fuelleborni in Botanic garden in Teplice (2).JPG|thumb|''Labeotropheus fuelleborni'']]
[[File:Metriaclima zebra.jpg|thumb|''Metriaclima zebra'']]
[[Cichlid|African cichlids]] are known to be a diverse fish species, with evidence indicating that they evolved extremely quickly. These fish evolved within the same habitat, but have a variety of [[Morphology (biology)|morphologies]], especially pertaining to the mouth and jaw. Experiments pertaining the cichlid jaw phenotypes was done by Albertson and others in 2003 by crossing two species of African cichlids with very different mouth morphologies. The cross between ''[[Blue mbuna|Labeotropheus fuelleborni]]'' (subterminal mouth for biting algae off rocks) and ''[[Zebra mbuna|Metriaclima zebra]]'' (terminal mouth for suction feeding) allowed for mapping of QTLs affecting feeding morphology. Using the QTL sign test, definitive evidence was used to support the existence of directional selection in the oral jaw apparatus in African cichlids. However, this was not the case for the suspensorium or skull QTLs, suggesting genetic drift or stabilizing selection as mechanisms for the speciation.<ref>{{cite journal | last1=Albertson | first1=R. C. | last2=Streelman | first2=J. T. | last3=Kocher | first3=T. D. | title=Directional selection has shaped the oral jaws of Lake Malawi cichlid fishes | journal=Proceedings of the National Academy of Sciences | volume=100 | issue=9 | date=2003-04-18 | issn=0027-8424 | doi=10.1073/pnas.0930235100 | pages=5252–5257| pmid=12704237 | pmc=154331| bibcode=2003PNAS..100.5252A | doi-access=free }}</ref> 

===Sockeye salmon===
[[File:Sockeye salmon swimming right.jpg|thumb|Sockeye Salmon]]
[[Salmon|Sockeye salmon]] are one of the many species of fish that are [[anadromous]], in which individuals migrate to the same rivers in which they were born to reproduce. These migrations happen around the same time every year, but a 2007 study shows that sockeye salmon found in the waters of the [[Bristol Bay]] in [[Alaska]] have recently undergone directional selection on the timing of migration.<ref>{{Cite journal |last=Quinn |first=Thomas P. |date=April 2007 |title=Directional selection by fisheries and the timing of sockeye salmon (Oncorhynchus Nerka) Migrations |url=https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/06-0771 |journal=Ecological Applications|volume=17 |issue=3 |pages=731–739 |doi=10.1890/06-0771 |pmid=17494392 |bibcode=2007EcoAp..17..731Q |url-access=subscription }}</ref> In this study, two populations of sockeye salmon, [[Egegik River|Egegik]] and [[Ugashik River|Ugashik]], were observed. Data from 1969–2003 provided by the [[Alaska Department of Fish and Game]] were divided into five sets of seven years and plotted for average arrival to the fishery.  After analyzing the data, it was determined that in both populations the average migration date was earlier and the populations were undergoing directional selection as a result of changing ecological conditions. The Egegik population experienced stronger selection and the migration date shifted four days. The paper suggests that fisheries can be a factor driving this selection because fishing occurs more often in the later periods of migration (especially in the Egegik district), preventing those fish from reproducing.<ref>{{cite journal | last1=Quinn | first1=Thomas P. | last2=Hodgson | first2=Sayre | last3=Flynn | first3=Lucy | last4=Hilborn | first4=Ray | last5=Rogers | first5=Donald E. | title=Directional Selection by Fisheries and the Timing of Sockeye Salmon (Oncorhynchus Nerka) Migrations | journal=Ecological Applications | publisher=Wiley | volume=17 | issue=3 | year=2007 | issn=1051-0761 | doi=10.1890/06-0771 | pmid=17494392 | pages=731–739| bibcode=2007EcoAp..17..731Q }}</ref> This discovery also goes to show that in addition to environmental changes, human behaviors can also have massive effects on the selection of species around them.<ref name=":2">{{Cite journal |last=Lin |first=J. E. |last2=Hard |first2=J. J. |last3=Naish |first3=K. A. |last4=Peterson |first4=D. |last5=Hilborn |first5=R. |last6=Hauser |first6=L. |date=May 2016 |title=It’s a bear market: evolutionary and ecological effects of predation on two wild sockeye salmon populations |url=https://www.nature.com/articles/hdy20163 |journal=Heredity |language=en |volume=116 |issue=5 |pages=447–457 |doi=10.1038/hdy.2016.3 |issn=1365-2540|pmc=4834386 }}</ref> 

=== Bears hunting sockeye salmon ===
[[File:Caviar drips out of pink sockeye salmon hunted by big brown bear (53161193868).jpg|thumb|Bear hunting sockeye salmon]]
Studies carried out in Little [[Togiak Lake]] in Alaska, indicate that bear [[predation]] has a significant impact on sockeye salmon populations, especially in shallow streams. Bears often focus on larger male salmon and tend to prefer those that have just arrived at the spawning grounds, particularly in smaller streams where they can catch them more easily. This predation may accelerate the aging of salmon by favoring later arrivals. Additionally, the impact of predation varies among different salmon populations based on their habitat and density; it tends to be more selective in areas where fish are readily accessible. While high levels of bear predation can occur, healthy salmon populations usually maintain strong reproductive potential, although the effects are more pronounced when populations are low. Overall, these dynamics illustrate how bear predation affects salmon behavior and life cycles, influencing their evolutionary processes.<ref name=":2" />  

=== Large Felids ===
This study examines the role of lineage-specific directional selection on body size evolution in felids, revealing that several species, including those in the ''[[Panthera]]'' genus (lions, tigers, leopards, jaguars, snow leopards), the cheetah, and the puma, exhibit evidence of directional selection favoring larger body mass. These larger body sizes are likely linked to hunting large prey and solitary hunting strategies, which favor physical strength and size. Conversely, the clouded leopard did not show evidence of directional selection for body size, suggesting different ecological pressures, and the jaguarundi showed no clear selection for smaller size despite being smaller than its relatives. These findings highlight that body size evolution in felids is not uniform and is strongly influenced by ecological factors such as prey size and hunting behavior. The study concludes that directional selection for increased body size is likely associated with the need for larger predators to capture large prey, and solitary hunting may accelerate this selection, although the evolutionary paths for different felid lineages can vary considerably.<ref>{{Cite journal |last=Harano |first=Tomohiro |last2=Kutsukake |first2=Nobuyuki |date=2023-03-01 |title=Way to big cats: Directional selection in body size evolution in living felids |url=https://link.springer.com/article/10.1007/s10914-022-09639-z |journal=Journal of Mammalian Evolution |language=en |volume=30 |issue=1 |pages=97–108 |doi=10.1007/s10914-022-09639-z |issn=1573-7055|url-access=subscription }}</ref>

=== Soapberry Bugs ===
[[File:Red Shouldered Bug, Ant, Mum.jpg|thumb|''Jadera Haematoloma'']]
[[Soapberry bug|Soapberry Bugs]] (''[[Jadera haematoloma]]'') primarily feed on seeds produced by plants of the [[Sapindaceae]] family. These soapberry bugs use their beaks to feed on the seeds within the fruits of these plants, so it is crucial that their beak size is long enough to reach the seeds from the exterior of the fruits. However, the distance from the exterior of the fruit to the seed can vary. Scott Carroll and Christin Boyd (1992) conducted an experiment where they would observe how three newly introduced plant species introduced to North America that were colonized by these soapberry bugs would affect the natural selection of the insect’s beak length. Each new plant species hosted fruits of different sizes compared to the native hosts. They found that there was indeed a close correlation between the radius of the fruit and the length of the beak. There was a positive directional selection for larger beaks when the radius of the fruit was larger, and there was a positive directional selection for smaller beaks when the radius of the fruit was smaller. To confirm that these differences were caused by genetic differences and not through phenotypic plasticity, Carroll raised young soapberry bugs from the populations based on the introduced plant species and found that their beak length was retained when they were developed on the alternative host. <ref>{{Cite journal |last=Carroll |first=Scott P. |last2=Boyd |first2=Christin |date=1 August 1992 |title=HOST RACE RADIATION IN THE SOAPBERRY BUG: NATURAL HISTORY WITH THE HISTORY |url=https://academic.oup.com/evolut/article/46/4/1052/6870325 |journal=Evolution |language=en |volume=46 |issue=4 |pages=1052–1069 |doi=10.1111/j.1558-5646.1992.tb00619.x |issn=0014-3820}}</ref>