Editing Behavioral ecology (section)

===Familial conflict===
Familial conflict is a result of trade-offs as a function of lifetime [[parental investment]]. Parental investment was defined by [[Robert Trivers]] in 1972 as "any investment by the parent in an individual offspring that increases the offspring's chance of surviving at the cost of the parent's ability to invest in other offspring".{{Citation needed|date=December 2012}} Parental investment includes behaviors like guarding and feeding. Each parent has a limited amount of parental investment over the course of their lifetime. Investment trade-offs in offspring quality and quantity within a brood and trade offs between current and future broods leads to conflict over how much parental investment to provide and to whom parents should invest in. There are three major types of familial conflict: sexual, parent–offspring, and sibling–sibling conflict.<ref name="Davies" />

====Sexual conflict====
{{Main|Sexual conflict}}
[[File:Great Tit (Parus major) (2).jpg|thumb|Great tit]]
There is conflict among parents as to who should provide the care as well as how much care to provide. Each parent must decide whether or not to stay and care for their offspring, or to desert their offspring. This decision is best modeled by [[Game theory|game theoretic]] approaches to [[evolutionarily stable strategies]] (ESS) where the best strategy for one parent depends on the strategy adopted by the other parent. Recent research has found response matching in parents who determine how much care to invest in their offspring. Studies found that parent [[great tit]]s match their partner's increased care-giving efforts with increased provisioning rates of their own.<ref>{{cite journal|last=Johnstone|first=R.A.|author2=Hinde, C.A.|title=Negotiation over offspring care--how should parents respond to each other's efforts?|journal=Behavioral Ecology|year=2006|issue=5|pages=818–827|doi=10.1093/beheco/arl009|volume=17|doi-access=free}}</ref>  This cued parental response is a type of behavioral negotiation between parents that leads to stabilized compensation. Sexual conflicts can give rise to antagonistic co-evolution between the sexes to try to get the other sex to care more for offspring. For example, in the waltzing fly ''[[Prochyliza xanthostoma]]'', ejaculate feeding maximizes female reproductive success and minimizes the female's chance of mating multiply.<ref name=":1">{{Cite journal|last1=Bonduriansky|first1=Russell|last2=Wheeler|first2=Jill|last3=Rowe|first3=Locke|date=2005-02-01|title=Ejaculate feeding and female fitness in the sexually dimorphic fly Prochyliza xanthostoma (Diptera: Piophilidae)|journal=Animal Behaviour|volume=69|issue=2|pages=489–497|doi=10.1016/j.anbehav.2004.03.018|s2cid=16357692|issn=0003-3472}}</ref> Evidence suggests that the sperm evolved to prevent female waltzing flies from mating multiply in order to ensure the male's paternity.<ref name=":1" />

====Parent–offspring conflict====
[[File:Blackbird chicks in nest.JPG|thumb|left|Blackbird chicks in a nest]]
According to [[Robert Trivers|Robert Trivers's]] theory on relatedness,{{Citation needed|date=December 2012}} each offspring is related to itself by 1, but is only 0.5 related to their parents and siblings. Genetically, offspring are predisposed to behave in their own self-interest while parents are predisposed to behave equally to all their offspring, including both current and future ones. Offspring selfishly try to take more than their fair shares of [[parental investment]], while parents try to spread out their parental investment equally amongst their present young and future young.
There are many examples of parent–offspring conflict in nature. One manifestation of this is asynchronous hatching in birds. A behavioral ecology hypothesis is known as Lack's brood reduction hypothesis (named after [[David Lack]]).{{Citation needed|date=December 2012}} Lack's hypothesis posits an evolutionary and ecological explanation as to why birds lay a series of eggs with an asynchronous delay leading to nestlings of mixed age and weights. According to Lack, this brood behavior is an ecological insurance that allows the larger birds to survive in poor years and all birds to survive when food is plentiful.<ref name="Amundsen96">{{Cite journal |last1 = Amundsen|first1 = T. |last2 = Slagsvold |first2 = T. |title = Lack's Brood Reduction Hypothesis and Avian Hatching Asynchrony: What's Next? |journal = Oikos |volume = 76 |issue = 3 |pages=613–620 |year = 1996 |doi = 10.2307/3546359 |jstor = 3546359}}</ref><ref name="Piganowski92">{{Cite journal |last = Pijanowski |first = B. C. |title = A Revision of Lack's Brood Reduction Hypothesis |journal = The American Naturalist |volume = 139 |issue = 6 |pages=1270–1292 |year = 1992 |doi = 10.1086/285386|s2cid = 84884060 }}</ref> We also see sex-ratio conflict between the queen and her workers in social [[hymenoptera]]. Because of [[haplodiploidy]], the workers (offspring) prefer a 3:1 female to male sex allocation while the queen prefers a 1:1 sex ratio. Both the queen and the workers try to bias the sex ratio in their favor.<ref>{{cite journal |last1=Trivers |first1=Robert L. |last2=Willard |first2=Dan E. |title=Natural selection of parental ability to vary the sex ratio of offspring |journal=Science |year=1976 |issue=191 |pages=90–92 |bibcode=1973Sci...179...90T |volume=179 |doi=10.1126/science.179.4068.90 |pmid=4682135|s2cid=29326420 }}</ref> In some species, the workers gain control of the sex ratio, while in other species, like ''[[Bombus terrestris|B. terrestris]]'', the queen has a considerable amount of control over the colony sex ratio.<ref>{{cite journal |author1=Bourke, A.F.G.  |author2=F.L.W. Ratnieks  |name-list-style=amp| year = 2001 | title = Kin-selected conflict in the bumble-bee ''Bombus terrestris'' (Hymenoptera: Apidae) | journal = Proceedings of the Royal Society of London B | volume = 268 |issue=1465  | pages = 347–355 | doi=10.1098/rspb.2000.1381 | pmid=11270430 | pmc=1088613}}</ref> Lastly, there has been recent evidence regarding [[genomic imprinting]] that is a result of parent–offspring conflict. Paternal genes in offspring demand more maternal resources than maternal genes in the same offspring and vice versa. This has been shown in imprinted genes like [[IGF-2|insulin-like growth factor-II]].<ref>{{cite journal |last=Haig|first=D.|author2=Graham, C.|title=Genomic imprinting and the strange case of the insulin-like growth factor-II receptor|journal=Cell|year=1991|volume=64|issue=6|pages=1045–1046|doi=10.1016/0092-8674(91)90256-x |pmid=1848481|s2cid=33682126}}</ref>

====Parent–offspring conflict resolution====
Parents need an honest signal from their offspring that indicates their level of hunger or need, so that the parents can distribute resources accordingly. Offspring want more than their fair share of resources, so they exaggerate their signals to wheedle more parental investment. However, this conflict is countered by the cost of excessive begging. Not only does excessive begging attract predators, but it also retards chick growth if begging goes unrewarded.<ref>{{cite journal|last=Kilner|first=R. M.|title=A Growth Cost of Begging in Captive Canary Chicks|journal=Proceedings of the National Academy of Sciences of the United States of America |year=2001|volume=98|pages=11394–11398 |bibcode=2001PNAS...9811394K|doi=10.1073/pnas.191221798|issue=20|pmid=11572988|pmc=58740|doi-access=free}}</ref>  Thus, the cost of increased begging enforces offspring honesty.

Another resolution for parent–offspring conflict is that parental provisioning and offspring demand have actually coevolved, so that there is no obvious underlying conflict. [[Cross-fostering]] experiments in [[great tit]]s (''Parus major'') have shown that offspring beg more when their biological mothers are more generous.<ref>{{cite journal|last=Kolliker|first=M. |author2=Brinkhof, M. |author3=Heeb, P. |author4=Fitze, P. |author5=Richner, H.|title=The Quantitative Genetic Basis of Offspring Solicitation and Parental Response in a Passerine Bird with Parental Care|journal=Proceedings of the Royal Society B: Biological Sciences|year=2000|volume=267|pages=2127–2132|doi=10.1098/rspb.2000.1259|issue=1457 |pmid=11416919 |pmc=1690782}}</ref> Therefore, it seems that the willingness to invest in offspring is co-adapted to offspring demand.

====Sibling–sibling conflict====
[[File:Galápagos fur seals (4229111296).jpg|thumb|Galápagos fur seals]]
The lifetime [[parental investment]] is the fixed amount of parental resources available for all of a parent's young, and an offspring wants as much of it as possible. Siblings in a brood often compete for parental resources by trying to gain more than their fair share of what their parents can offer. Nature provides numerous examples in which sibling rivalry escalates to such an extreme that one sibling tries to kill off broodmates to maximize parental investment (''See [[Siblicide]]''). In the [[Galápagos fur seal]], the second pup of a female is usually born when the first pup is still suckling. This competition for the mother's milk is especially fierce during periods of food shortage such as an [[El Niño–Southern Oscillation|El Niño]] year, and this usually results in the older pup directly attacking and killing the younger one.<ref>{{cite journal |last=Trillmitch|first=F.|author2=Wolf, J.B.W.|title=Parent–offspring and sibling conflict in Galapagos fur seals and sea lions|journal=Behavioral Ecology and Sociobiology|year=2008|volume=62|pages=363–375 |doi=10.1007/s00265-007-0423-1 |issue=3|s2cid=41834534}}</ref>

In some bird species, sibling rivalry is also abetted by the [[wikt:asynchronous|asynchronous]] hatching of eggs. In the [[blue-footed booby]], for example, the first egg in a nest is hatched four days before the second one, resulting in the elder chick having a four-day head start in growth. When the elder chick falls 20-25% below its expected weight threshold, it attacks its younger sibling and drives it from the nest.<ref name="Drummond">{{cite journal|last=Drummond|first=H.|author2=Chavelas, C.G.|title=Food shortage influences sibling sggression in the Blue-footed Booby|journal=Animal Behaviour|year=1989|volume=37|pages=806–819|doi=10.1016/0003-3472(89)90065-1|s2cid=53165189}}</ref>

Sibling relatedness in a brood also influences the level of sibling–sibling conflict. In a study on [[passerine]] birds, it was found that chicks begged more loudly in species with higher levels of [[Promiscuity|extra-pair paternity]].<ref>{{cite journal |last1=Briskie |first1=James V. |last2=Naugler |first2=Christopher T. |last3=Leech |first3=Susan M. |title=Begging intensity of nestling birds varies with sibling relatedness |journal=Proceedings of the Royal Society B: Biological Sciences |year=1994 |volume=258 |pages=73–78 |bibcode=1994RSPSB.258...73B |doi=10.1098/rspb.1994.0144 |issue=1351|s2cid=85105883 }}</ref>