Editing Maternal effect (section)

==Adaptive maternal effects==

Adaptive maternal effects induce phenotypic changes in offspring that result in an increase in fitness.<ref>{{cite journal | vauthors = Van Cann J, Koskela E, Mappes T, Sims A, Watts PC | title = Intergenerational fitness effects of the early life environment in a wild rodent | journal = The Journal of Animal Ecology | volume = 88 | issue = 9 | pages = 1355–1365 | date = September 2019 | pmid = 31162628 | doi = 10.1111/1365-2656.13039 | bibcode = 2019JAnEc..88.1355V | s2cid = 174808731 | url = http://urn.fi/urn:nbn:fi-fe2019120545818 }}</ref> These changes arise from mothers sensing environmental cues that work to reduce offspring fitness, and then responding to them in a way that then “prepares” offspring for their future environments. A key characteristic of “adaptive maternal effects” phenotypes is their plasticity. Phenotypic plasticity gives organisms the ability to respond to different environments by altering their phenotype. With these “altered” phenotypes increasing fitness it becomes important to look at the likelihood that adaptive maternal effects will evolve and become a significant phenotypic adaptation to an environment.

===Defining adaptive maternal effects===

When traits are influenced by either the maternal environment or the maternal phenotype, it is said to be influenced by maternal effects.  Maternal effects work to alter the phenotypes of the offspring through pathways other than DNA.<ref>{{cite journal | vauthors = Adkins-Regan E, Banerjee SB, Correa SM, Schweitzer C | title = Maternal effects in quail and zebra finches: Behavior and hormones | journal = General and Comparative Endocrinology | volume = 190 | pages = 34–41 | date = September 2013 | pmid = 23499787 | doi = 10.1016/j.ygcen.2013.03.002 }}</ref> ''Adaptive'' maternal effects are when these maternal influences lead to a phenotypic change that increases the fitness of the offspring.<ref>{{cite journal | vauthors = Leftwich PT, Nash WJ, Friend LA, Chapman T | title = Contribution of maternal effects to dietary selection in Mediterranean fruit flies | journal = Evolution; International Journal of Organic Evolution | volume = 73 | issue = 2 | pages = 278–292 | date = February 2019 | pmid = 30592536 | pmc = 6492002 | doi = 10.1111/evo.13664 }}</ref> In general, adaptive maternal effects are a mechanism to cope with factors that work to reduce offspring fitness;<ref name=Galloway>{{cite journal | vauthors = Galloway LF | title = Maternal effects provide phenotypic adaptation to local environmental conditions | journal = The New Phytologist | volume = 166 | issue = 1 | pages = 93–9 | date = April 2005 | pmid = 15760354 | doi = 10.1111/j.1469-8137.2004.01314.x | doi-access =  | bibcode = 2005NewPh.166...93G }}</ref> they are also environment specific.

It can sometimes be difficult to differentiate between maternal and adaptive maternal effects. Consider the following: Gypsy moths reared on foliage of black oak, rather than chestnut oak, had offspring that developed faster.<ref name=Spitzer>{{cite journal |vauthors=Spitzer BW |title=Maternal effects in the soft scale insect Saissetia coffeae (Hemiptera: Coccidae) |journal=Evolution |volume=58 |issue=11 |pages=2452–61 |year=2004 |pmid=15612288 |jstor=3449399 |doi=10.1554/03-642|s2cid=198152929 }}</ref> This is a maternal, ''not'' an adaptive maternal effect. In order to be an adaptive maternal effect, the mother's environment would have to have led to a change in the eating habits or behavior of the offspring.<ref name=Spitzer/> The key difference between the two therefore, is that adaptive maternal effects are environment specific. The phenotypes that arise are in response to the mother sensing an environment that would reduce the fitness of her offspring. By accounting for this environment she is then able to alter the phenotypes to actually increase the offspring's fitness. ''Maternal'' effects are not in response to an environmental cue, and further they have the potential to increase offspring fitness, but they may not.

When looking at the likelihood of these “altered” phenotypes evolving there are many factors and cues involved. Adaptive maternal effects evolve only when offspring can face many potential environments; when a mother can “predict” the environment into which her offspring will be born; and when a mother can influence her offspring's phenotype, thereby increasing their fitness.<ref name=Spitzer/> The summation of all of these factors can then lead to these “altered” traits becoming favorable for evolution.

The phenotypic changes that arise from adaptive maternal effects are a result of the mother sensing that a certain aspect of the environment may decrease the survival of her offspring. When sensing a cue the mother “relays” information to the developing offspring and therefore induces adaptive maternal effects. This tends to then cause the offspring to have a higher fitness because they are “prepared” for the environment they are likely to experience.<ref name=Galloway/> These cues can include responses to predators, habitat, high population density, and food availability<ref name=squirrels>{{cite journal | vauthors = Dantzer B, Newman AE, Boonstra R, Palme R, Boutin S, Humphries MM, McAdam AG | title = Density triggers maternal hormones that increase adaptive offspring growth in a wild mammal | journal = Science | volume = 340 | issue = 6137 | pages = 1215–7 | date = June 2013 | pmid = 23599265 | doi = 10.1126/science.1235765 | bibcode = 2013Sci...340.1215D | s2cid = 206548036 }}</ref><ref name=seedbeetle>{{cite journal | vauthors = Fox CW, Thakar MS, Mousseau TA |title=Egg Size Plasticity in a Seed Beetle: An Adaptive Maternal Effect |journal=The American Naturalist |volume=149 |issue=1 |year=1997 |pages=149–63 |jstor=2463535 |doi=10.1086/285983|bibcode=1997ANat..149..149F |s2cid=85194061 }}</ref><ref>{{cite journal | vauthors = Van Buskirk J | title = Phenotypic lability and the evolution of predator-induced plasticity in tadpoles | journal = Evolution; International Journal of Organic Evolution | volume = 56 | issue = 2 | pages = 361–70 | date = February 2002 | pmid = 11926504 | doi = 10.1554/0014-3820(2002)056[0361:PLATEO]2.0.CO;2 | jstor = 3061574 | s2cid = 198152866 }}</ref>
 
The increase in size of Northern American red squirrels is a great example of an adaptive maternal effect producing a phenotype that resulted in an increased fitness. The adaptive maternal effect was induced by the mothers sensing the high population density and correlating it to low food availability per individual. Her offspring were on average larger than other squirrels of the same species; they also grew faster. Ultimately, the squirrels born during this period of high population density showed an increased survival rate (and therefore fitness) during their first winter.<ref name=squirrels/>

===Phenotypic plasticity===

When analyzing the types of changes that can occur to a phenotype, we can see changes that are behavioral, morphological, or physiological. A characteristic of the phenotype that arises through adaptive maternal effects, is the plasticity of this phenotype. [[Phenotypic plasticity]] allows organisms to adjust their phenotype to various environments, thereby enhancing their fitness to changing environmental conditions.<ref name=Galloway/> Ultimately it is a key attribute to an organism's, and a population's, ability to adapt to short term environmental change.<ref>{{cite journal |vauthors=Nussey DH, Wilson AJ, Brommer JE |title=The evolutionary ecology of individual phenotypic plasticity in wild populations |journal=Journal of Evolutionary Biology |volume=20 |issue=3 |pages=831–44 |year=2007 |pmid=17465894 |doi=10.1111/j.1420-9101.2007.01300.x |s2cid=18056412 |doi-access=free }}</ref><ref>{{cite journal |vauthors=Garland T, Kelly SA |title=Phenotypic plasticity and experimental evolution |journal=The Journal of Experimental Biology |volume=209 |issue=Pt 12 |pages=2344–61 |year=2006 |pmid=16731811 |doi=10.1242/jeb.02244 |doi-access=free |bibcode=2006JExpB.209.2344G }}</ref>

Phenotypic plasticity can be seen in many organisms, one species that exemplifies this concept is the seed beetle ''Stator limbatus''. This seed beetle reproduces on different host plants, two of the more common ones being ''Cercidium floridum'' and ''Acacia greggii''. When ''C. floridum'' is the host plant, there is selection for a large egg size; when ''A. greggii'' is the host plant, there is a selection for a smaller egg size. In an experiment it was seen that when a beetle who usually laid eggs on ''A. greggii'' was put onto ''C. floridum'', the survivorship of the laid eggs was lower compared to those eggs produced by a beetle that was conditioned and remained on the ''C. florium'' host plant. Ultimately these experiments showed the plasticity of egg size production in the beetle, as well as the influence of the maternal environment on the survivorship of the offspring.<ref name=seedbeetle/>

===Further examples of adaptive maternal effects===

In many insects:
* Cues such as rapidly cooling temperatures or decreasing daylight can result in offspring that enter into a dormant state. They therefore will better survive the cooling temperatures and preserve energy.<ref name=adaptivesignificance>{{cite journal |vauthors=Mousseau TA, Fox CW |title=The adaptive significance of maternal effects |journal=Trends in Ecology & Evolution |volume=13 |issue=10 |pages=403–7 |year=1998 |pmid=21238360 |doi=10.1016/S0169-5347(98)01472-4 |bibcode=1998TEcoE..13..403M }}</ref>
* When parents are forced to lay eggs on environments with low nutrients, offspring will be provided with more resources, such as higher nutrients, through an increased egg size.<ref name=seedbeetle/>
* Cues such as poor habitat or crowding can lead to offspring with wings. The wings allow the offspring to move away from poor environments to ones that will provide better resources.<ref name=adaptivesignificance/>