View source for Biology:Haplodiploidy

{{Short description|Biological system where sex is determined by the number of sets of chromosomes}}
[[File:Haplodiploid Sex Determination in Honey Bees.svg|thumb|upright=2.0|In the Hymenoptera, the sex-determination system involves haploid males and diploid females. System for honey bee shown.]]

'''Haplodiploidy''' is a [[Biology:Sex-determination system|sex-determination system]] in which males develop from unfertilized eggs and are [[Biology:Haploid|haploid]], and females develop from fertilized eggs and are diploid.<ref>{{cite book |author1=King, R.C. |author2=Stansfield, W.D. |author3=Mulligan, P.K.  |date=2006 |title=A dictionary of genetics |url=https://archive.org/details/dictionarygeneti00king |url-access=limited |edition=7th |publisher=Oxford University Press |page=[https://archive.org/details/dictionarygeneti00king/page/n201 194] |isbn=978-0-19-530761-0}}</ref> Haplodiploidy is sometimes called [[Biology:Arrhenotoky|arrhenotoky]].

Haplodiploidy determines the sex in all members of the insect orders [[Biology:Hymenoptera|Hymenoptera]] ([[Biology:Bee|bee]]s, [[Biology:Ant|ant]]s, and [[Biology:Wasp|wasp]]s)<ref name=Grimaldi408>{{cite book |author1=Grimaldi, D. |author2=Engel M.S.  |date=2005 |title=The evolution of the insects |url=https://archive.org/details/evolutioninsects00grim_110 |url-access=limited |publisher=Cambridge University Press |isbn=978-0-521-82149-0 |page=[https://archive.org/details/evolutioninsects00grim_110/page/n422 408]}}</ref> and [[Biology:Thysanoptera|Thysanoptera]] ('thrips').<ref name=White84/> The system also occurs sporadically in some [[Biology:Spider mite|spider mite]]s, [[Biology:Hemiptera|Hemiptera]], [[Biology:Coleoptera|Coleoptera]] ([[Biology:Bark beetle|bark beetle]]s), and [[Biology:Rotifer|rotifer]]s.

In this system, sex is determined by the number of sets of [[Biology:Chromosome|chromosome]]s an individual receives. An offspring formed from the union of a [[Biology:Sperm|sperm]] and an egg develops as a female, and an unfertilized egg develops as a male. This means that the males have half the number of chromosomes that a female has, and are [[Biology:Haploid|haploid]].

The haplodiploid sex-determination system has a number of peculiarities. For example, a male has no father and cannot have sons, but he has a grandfather and can have grandsons. Additionally, if a [[Biology:Eusociality|eusocial]]-insect colony has only one queen, and she has only mated once, then the relatedness between workers (diploid females) in a hive or nest is {{3/4}}. This means the workers in such monogamous single-queen colonies are significantly more closely related than in other sex determination systems where the relatedness of siblings is usually no more than {{1/2}}. It is this point which drives the [[Philosophy:Kin selection|kin selection]] theory of how eusociality evolved.<ref name=Grimaldi465>{{cite book |author1=Grimaldi, D. |author2=Engel M.S.  |date=2005 |title=The evolution of the insects |url=https://archive.org/details/evolutioninsects00grim_110 |url-access=limited |publisher=Cambridge University Press |isbn=978-0-521-82149-0 |page=[https://archive.org/details/evolutioninsects00grim_110/page/n479 465]}}</ref> Whether haplodiploidy did in fact pave the way for the evolution of eusociality is still a matter of debate.<ref name=Hughes>{{cite journal| last=Hughes |first= W.O.H. | title=Ancestral monogamy shows kin selection is key to the evolution of eusociality | journal=Science | volume=320 | issue=5880 | pages=1213–1216 | year=2008| doi=10.1126/science.1156108 | pmid=18511689 |bibcode= 2008Sci...320.1213H |s2cid= 20388889 |display-authors=0}}</ref><ref name=eowilson>{{cite journal | author=Edward O. Wilson | title=Kin Selection as the Key to Altruism: Its Rise and Fall | journal=Social Research | year=2005 | volume=72 | issue=1 | pages=159–166 | doi=10.1353/sor.2005.0012 | jstor=40972006| s2cid=142713581 }}</ref>

Another feature of the haplodiploidy system is that recessive [[Biology:Mutation#Deleterious mutations|lethal and deleterious alleles]] will be removed from the population rapidly because they will automatically be expressed in the males (dominant lethal and deleterious alleles are removed from the population every time they arise, as they kill any individual they arise in).<ref name=White84>{{Cite journal| doi=10.1080/11250008409439455| issn=0373-4137| volume=51| issue=1–2| pages=1–23| last=White| first=Michael J.D.| title=Chromosomal mechanisms in animal reproduction| journal=Bollettino di Zoologia| year=1984}}</ref>

Haplodiploidy is not the same thing as an [[Biology:X0 sex-determination system|X0 sex-determination system]].  In haplodiploidy, males receive one half of the chromosomes that females receive, including autosomes.  In an X0 sex-determination system, males and females receive an equal number of autosomes, but when it comes to sex chromosomes, females will receive two X chromosomes while males will receive only a single X chromosome.

== Mechanisms ==

Several models have been proposed for the genetic mechanisms of haplodiploid sex-determination. The model most commonly referred to is the ''complementary allele model''. According to this model, if an individual is heterozygous for a certain [[Biology:Locus (genetics)|locus]], it develops into a female, whereas hemizygous and homozygous individuals develop into males. In other words, diploid offspring develop from fertilized eggs, and are normally female, while haploid offspring develop into males from unfertilized eggs.
Diploid males would be infertile, as their cells would not undergo [[Biology:Meiosis|meiosis]] to form sperm.  Therefore, the sperm would be diploid, which means that their offspring would be triploid.  Since hymenopteran mother and sons share the same genes, they may be especially sensitive to [[Biology:Inbreeding|inbreeding]]: Inbreeding reduces the number of different sex [[Biology:Allele|allele]]s present in a population, hence increasing the occurrence of diploid males.

After [[Biology:Mating|mating]], each fertile hymenopteran female stores [[Biology:Sperm|sperm]] in an internal sac called the [[Biology:Spermatheca|spermatheca]]. The mated female controls the release of stored sperm from within the organ: If she releases sperm as an egg passes down her oviduct, the egg is fertilized.<ref>van Wilgenburg, Ellen; Driessen, Gerard & Beukeboom, Leo W. [http://www.frontiersinzoology.com/content/3/1/1 Single locus complementary sex determination in Hymenoptera: an "unintelligent" design?] Frontiers in Zoology 2006, 3:1</ref>
Social bees, wasps, and ants can modify sex ratios within colonies which maximizes relatedness among members and generates a workforce appropriate to surrounding conditions.<ref>Mahowald, Michael; von Wettberg, Eric
[http://www.sccs.swarthmore.edu/users/99/mahowald/hymenoptera.html Sex determination in the Hymenoptera] [[Organization:Swarthmore College|Swarthmore College]] (1999)</ref> In other solitary hymenopterans, the females lay unfertilized male eggs on poorer food sources while laying the fertilized female eggs on better food sources, possibly because the fitness of females will be more adversely affected by shortages in their early life.<ref>{{Cite journal | last1=Chow | first1=A. | last2=MacKauer | first2=M. | doi=10.1006/anbe.1996.0090 | title=Sequential allocation of offspring sexes in the hyperparasitoid wasp, Dendrocerus carpenteri | journal=Animal Behaviour | volume=51 | issue=4 | pages=859–870 | year=1996 | s2cid=53192398 }}</ref><ref>{{Cite journal | last1=Van Alphen | first1=J. J. M. | last2=Thunnissen | first2=I. | doi=10.1163/002829683X00228 | title=Host Selection and Sex Allocation by Pachycrepoideus Vindemiae Rondani (Pteromalidae) as a Facultative Hyperparasitoid of Asobara Tabida Nees (Braconidae; Alysiinae) and Leptopilina Heterotoma (Cynipoidea; Eucoilidae) | journal=Netherlands Journal of Zoology | volume=33 | issue=4 | pages=497–514 | year=1982}}</ref> Sex ratio manipulation is also practiced by haplodiploid [[Biology:Ambrosia beetle|ambrosia beetle]]s, who lay more male eggs when the chances for males to disperse and mate with females in different sites are greater.<ref>{{Cite journal | last1=Peer | first1=K. | last2=Taborsky | first2=M. | doi=10.1111/j.1420-9101.2003.00687.x | title=Female ambrosia beetles adjust their offspring sex ratio according to outbreeding opportunities for their sons | journal=Journal of Evolutionary Biology | volume=17 | issue=2 | pages=257–264 | year=2004 | pmid= 15009259| doi-access=free }}</ref>

=== Sex determination in honey bees ===
[[File:Apis mellifera (queen and workers).jpg|thumb|upright|left|[[Biology:Honey bee|Honey bee]] workers are unusually closely related to their full sisters (same father) because of their haplodiploid inheritance system.]]
In honeybees, the drones (males) are entirely derived from the queen, their mother. The diploid queen has 32 chromosomes and the haploid drones have 16 chromosomes.  Drones produce [[Biology:Sperm|sperm]] cells that contain their entire genome, so the sperm are all genetically identical except for mutations.  The male bees' genetic makeup is therefore entirely derived from the mother, while the genetic makeup of the female worker bees is half derived from the mother, and half from the father.<ref>Sinervo, Barry [http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/LEVELS.HTM Kin Selection and Haplodiploidy in Social Hymenoptera] {{Webarchive|url=https://web.archive.org/web/20110716165105/http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/LEVELS.HTM |date=2011-07-16 }} 1997</ref> Thus, if a queen bee mates with only one drone, any two of her daughters will share, on average, {{3/4}} of their genes. The diploid queen's genome is [[Biology:Chromosomal crossover|recombined]] for her daughters, but the haploid father's genome is inherited by his daughters "as is". It is also possible for a laying worker bee to lay an unfertilised egg, which is always a male.

There are rare instances of diploid drone larvae. This phenomenon usually arises when there is more than two generations of brother-sister mating.<ref>Woyka, J.; Pszczelnictwa, Zaklad; [http://jerzy_woyke.users.sggw.pl/1963_dipldrlarvae.pdf Drone Larvae from Fertilized Eggs of the Honey Bee] {{Webarchive|url=https://web.archive.org/web/20141022232521/http://jerzy_woyke.users.sggw.pl/1963_dipldrlarvae.pdf |date=2014-10-22 }} Journal of Apiculture Research, (1963), pages 19-24</ref> Sex determination in honey bees is initially due to a single locus, called the complementary sex determiner (''csd'') gene. In developing bees, if the conditions are that the individual is heterozygous for the ''csd'' gene, they will develop into females. If the conditions are so that the individual is [[Biology:Zygosity|hemizygous]] or homozygous for the ''csd'' gene, they will develop into males. The instances where the individual is homozygous at this gene are the instances of diploid males.<ref>Weinstock, George M.; Robinson, Gene E., & the Honeybee Genome Sequencing Consortium [http://www.nature.com/nature/journal/v443/n7114/full/nature05260.htm Insights into social insects from the genome of the honeybee Apis mellifera] ''Nature'', volume "'443'" (2006), pages 931-949</ref> Diploid males do not survive to adulthood, as the nurse worker bees will cannibalize the diploid males upon hatching.<ref>Santomauro, Giulia; Oldham, Neil J.; Boland, Wilhelm; Engels Wolf; [http://cat.inist.fr/?aModele=afficheN&cpsidt=16003284 Cannibalism of Diploid Drone Larvae in the Honey Bee (Apis mellifera) is Released by Odd Pattern of Circular Substance] Journal of Apiculture Research, volume "'43'" (2004), pages 69-74</ref>

While workers can lay unfertilized eggs that become their sons, haplodiploid sex-determination system increases the individual's [[Biology:Fitness|fitness]] due to indirect selection. Since the worker is more related to the queen's daughters (her sisters) than to her own offspring, helping the queen's offspring to survive helps the spread of the same genes that the worker possesses more efficiently than direct reproduction.<ref name="FosterRatnieks2001">{{cite journal |last1=Foster |first1=Kevin R. |last2=Ratnieks |first2=Francis L. W. |title=The Effect of Sex-Allocation Biasing on the Evolution of Worker Policing in Hymenopteran Societies |journal=The American Naturalist |volume=158 |issue=6 |year=2001 |pages=615–623 |doi=10.1086/323588|pmid=18707355 |s2cid=46052954 |url=http://eprints.whiterose.ac.uk/1303/1/ratinieksf8.pdf }}</ref>

Batches of worker bees are short lived and are constantly being replaced by the next batch, so this [[Philosophy:Kin selection|kin selection]] is possibly a strategy to ensure the proper working of the hive. However, since queens usually mate with a dozen drones or more, not all workers are full sisters. Due to the separate storage of drone sperm, a specific batch of brood may be more closely related than a specific batch of brood laid at a later date. However, many other species of bees, including bumblebees, such as ''Bombus terrestris'', are [[Biology:Monandrous|monandrous]].<ref name="Baer">{{cite journal |author1=Baer, B. |author2=P. Schmid-Hempel | year=2001 | title=Unexpected consequences of polyandry for parasitism and fitness in the bumblebee, ''Bombus terrestris'' | journal=Evolution | volume=55 | issue=8 | pages=1639–1643 | doi=10.1554/0014-3820(2001)055[1639:ucopfp]2.0.co;2 | pmid=11580023}}</ref> This means that sisters are almost always more related to one another than they would be to their own offspring, thus eliminating the conflict of variable relatedness present in honeybees.<ref>{{cite book| author= Davies, Nicholas B., John R. Krebs and Stuart A. West. |year=2012| title=An Introduction to Behavioral Ecology| publisher=Wiley-Blackwell|pages=371–375}}</ref>

=== Sex determination in [[Biology:Chalcidoidea|chalcidoid wasps]] ===
In wasps of the genus ''[[Biology:Nasonia|Nasonia]]'', a non-CSD method of sex determination has been documented. The most recent accepted model for this non-CSD system is called Maternal Effect Genomic Imprinting Sex Determination (MEGISD). This model involves a masculinizing/virilizing maternal effect gene that “imprints upon” the cytoplasmic component of oocytes, and an “unimprinted” paternal contribution (in female offspring) that provides a counter effect to [[Biology:Virilization|virilization]] and allows for female development to occur. Since all diploid eggs become female (due to the factor originating in the male genetic contribution that prevents masculinization), this differs from CSD in that under CSD, diploid eggs can become males if they are homozygous or hemizygous.<ref>Zou, Yuan et al. “A chimeric gene paternally instructs female sex determination in the haplodiploid wasp Nasonia.” Science 370 (2020): 1115 - 1118.</ref>

== Relatedness ratios in haplodiploidy ==

Relatedness is used to calculate the strength of [[Philosophy:Kin selection|kin selection]] (via Hamilton's rule).<ref name=Hamilton>{{cite book | last=Hamilton | first=W. D. | title=Narrow roads of gene land : the collected papers of W.D. Hamilton | publisher=W.H. Freeman/Spektrum | location=Oxford New York | year=1996 | isbn=978-0-7167-4530-3 }}</ref> The haplodiploidy hypothesis proposes that the unusual {{3/4}} relatedness coefficient amongst full haplodiploid sisters is responsible for the frequency of evolution of eusocial behavior in hymenopterans.<ref name="kiniskey">{{cite journal |author1=Kevin R. Foster |author2=Tom Wenseleers |author3=Francis L.W. Ratnieks | title=Kin selection is the key to altruism | journal=Trends in Ecology & Evolution | volume=21 | pages=57–60 | year=2006 | issue=2 | doi=10.1016/j.tree.2005.11.020|pmid=16701471 |url=https://lirias.kuleuven.be/handle/123456789/69591 }}</ref>  A eusocial worker helping her mother birth more sisters propagates more of her own genes than had she reproduced herself.

In normal [[Biology:Sexual reproduction|sexual reproduction]], the father has two sets of chromosomes, and [[Biology:Chromosomal crossover|crossing over]] takes place between the [[Biology:Chromatid|chromatid]]s of each pair during the [[Biology:Meiosis|meiosis]] which produces the [[Biology:Sperm|sperm]]. Therefore, ''the sperms are not identical'', because in each chromosome of a pair there will be different [[Biology:Allele|allele]]s at many of the [[Biology:Locus (genetics)|loci]]. But when the father is haploid ''all the sperms are identical'' (except for a small number where gene mutations have taken place in the germ line). So, all female offspring inherit the male's chromosomes 100% intact. ''As long as a female has mated with only one male'', all her daughters share a complete set of chromosomes from that male. In Hymenoptera, the males generally produce enough sperm to last the female for her whole lifetime after a single mating event with that male.<ref name=Hamilton/>

Relatedness coefficients in haplodiploid organisms are as follows, assuming that a female has only mated once. These ratios apply, for example, throughout a bee hive, unless some laying workers produce offspring, which will all be males from unfertilised eggs: in that case, average relatedness will be lower than shown.

:{| class="wikitable" style="text-align:center"
|+ '''Shared gene proportions in haplo-diploid sex-determination system relationships'''
|-
! Sex
! style="width:100px;"| Female
! style="width:100px;"| Male
|-
! Daughter
| {{1/2}}
| 1
|-
! Son
| {{1/2}}
| {{N/A}}
|-
! Mother
| {{1/2}}
| 1
|-
! Father
| {{1/2}}
| {{N/A}}
|-
! Sister
| {{3/4}}
| {{1/2}}
|-
! Brother
| {{1/4}}
| {{1/2}}
|-
! Maternal Aunt
| {{frac|3|8}}
| {{3/4}}
|-
! Maternal Uncle
| {{frac|1|8}}
| {{1/4}}
|-
! Paternal Aunt
| {{1/4}}
| {{N/A}}
|-
! Paternal Uncle
| {{1/4}}
| {{N/A}}
|-
! Niece (sister's daughter)
| {{frac|3|8}}
| {{1/4}}
|-
! Niece (brother's daughter)
| {{1/4}}
| {{1/2}}
|-
! Nephew (sister's son)
| {{frac|3|8}}
| {{1/4}}
|}

Under this assumption that mothers only mate once, sisters are more strongly related to each other than to their own daughters. This fact has been used to explain the [[Biology:Evolution of eusociality#Haplodiploidy/Kin selection|evolution of eusociality in many hymenopterans]]. However, colonies which have workers from multiple queens or queens which have mated multiple times will have worker-to-worker relatedness which is less than worker-to-daughter relatedness, such as in ''[[Biology:Melipona scutellaris|Melipona scutellaris]]''.

==See also==
* [[Biology:Green-beard effect|Green-beard effect]]
* [[Biology:Ploidy|Ploidy]]
* [[Biology:Pseudo-arrhenotoky|Pseudo-arrhenotoky]]
* [[Biology:Sexual differentiation|Sexual differentiation]]
* [[Biology:Worker policing|Worker policing]]
* [[Biology:X chromosome|X chromosome]]
* [[Biology:Y chromosome|Y chromosome]]

==References==
{{Reflist|30em}}

==Bibliography==
* {{cite journal | last1=Beye | first1=Martin | display-authors=0   | year=1999 | title=Unusually high recombination rate detected in the sex locus region of the honey bee (''Apis mellifera'') | url=http://www.genetics.org/cgi/content/full/153/4/1701 | journal=Genetics | volume=153 | issue=4| pages=1701–1708 | doi=10.1093/genetics/153.4.1701 | pmid=10581277 | pmc=1460844 }}
* {{cite journal | last1=Wu | first1=Z. | display-authors=0   | year=2005 | title=Single-locus complementary sex determination absent in Heterospilus prosopidis (Hymenoptera: Braconidae) | journal=Heredity | volume=95 | issue=3| pages=228–234 | doi=10.1038/sj.hdy.6800720 | pmid=16077738| doi-access=free }}
* {{cite journal | last1=Ratnieks | first1=Francis | year=1988 | title=Reproductive harmony via mutual policing by workers in eusocial hymenoptera | journal=American Naturalist | volume=132 | issue=2| pages=217–236 | doi=10.1086/284846 | jstor=2461867| s2cid=84742198 }}

{{Eusociality}}
{{Sex determination and differentiation}}

{{DEFAULTSORT:Haplodiploid Sex-Determination System}}
[[Category:Sex-determination systems]]
[[Category:Hymenoptera]]

{{Sourceattribution|Haplodiploidy}}