AboutZoos, Since 2008


Knowl­edge gap on the ori­gin of sex

pub­lished 04 June 2017 | mod­i­fied 04 June 2017

Though we seem to be con­vinced that sex is evo­lu­tion­ar­ily advan­ta­geous — cre­at­ing fit­ter off­spring1 — there are sig­nif­i­cant gaps in our knowl­edge on the evo­lu­tion of sex, accord­ing to a research review on sex chro­mo­somes from Lund Uni­ver­sity in Swe­den. Even after more than a cen­tury of study, researchers do not know enough about the evo­lu­tion of sex chro­mo­somes to under­stand how males and females emerge.

Sex chromosomes evolutionOverview of the dynamic evo­lu­tion of sex chro­mo­somes, illus­trated in a male het­eroga­metic sys­tem. Top left cor­ner: an auto­some pair in a her­maph­ro­dite gains a sex-​determining fac­tor that evolves to become a highly het­ero­mor­phic pair of sex chro­mo­somes, via ces­sa­tion of recom­bi­na­tion, degen­er­a­tion (a) and evo­lu­tion of dosage com­pen­sa­tion (b). This pro­gres­sion can how­ever be per­turbed by a turnover event, such as the for­ma­tion of a neo-​sex chro­mo­some © or a gain of a new sex-​determining fac­tor (d). In ©, the mod­er­ately degen­er­ated Y chro­mo­some fuses with an exist­ing auto­some, form­ing a new sex chro­mo­some pair with an old sex-​determining fac­tor. In (d), an auto­so­mal pair gains a new sex-​determining fac­tor, cre­at­ing a com­pletely new sex chro­mo­some pair. The old Y is lost. In both © and (d), the old X may even­tu­ally gain diploidy through non-​disjunction and sub­se­quently lose dosage com­pen­sa­tion, becom­ing an ordi­nary auto­some pair. Fig­ure adapted from [7]. Note that although © and (d) are shown as lead­ing to chro­mo­some turnovers, this pro­gres­sion is not inevitable. SA, sex­u­ally antag­o­nis­tic allele.
Jes­sica K. Abbott, Anna K. Nordén, Bengt Hans­son. 2017. Sex chro­mo­some evo­lu­tion: his­tor­i­cal insights and future per­spec­tives — Cre­ative Com­mons (CC BY 4.0).

Greater focus on eco­log­i­cal aspects would increase this knowl­edge, accord­ing to evo­lu­tion­ary biol­o­gists at Lund Uni­ver­sity, who have reviewed a lot of the research con­ducted in this field in the last 100 years.

Female and male bod­ies work dif­fer­ently, even though they have the same genome. One exam­ple is reproduction.

There is a form of genetic con­flict between the sexes — a con­flict in the genome itself — which we know lit­tle about”, says pro­fes­sor Bengt Hans­son at Lund University.

Together with senior lec­turer Jes­sica Abbott and doc­toral stu­dent Anna Nordén, he has read more than 100 sci­en­tific arti­cles and papers describ­ing the evo­lu­tion of sex chro­mo­somes and the genome. Together, they have iden­ti­fied two tracks that have each dom­i­nated the research since the late 19th cen­tury: empir­i­cal stud­ies and var­i­ous theories.

The review, pub­lished on 3 May in the jour­nal Pro­ceed­ings of the Royal Soci­ety B shows that the sig­nif­i­cance of ecol­ogy has not been suf­fi­ciently noted. There­fore, the biol­o­gists in Lund call for more research on how the liv­ing envi­ron­ment of a pop­u­la­tion affects the devel­op­ment and evo­lu­tion of sex chro­mo­somes. This could include fac­tors such as access to food, age vari­a­tions within a pop­u­la­tion or the con­se­quences for sex chro­mo­somes when pop­u­la­tions that have lived sep­a­rately meet and mix.

Addi­tional approaches in research will prob­a­bly lead to a much more detailed under­stand­ing of the devel­op­ment of sex chro­mo­somes and, in turn, of how females and males evolve

Jes­sica Abbott, lead author, Sec­tion for Evo­lu­tion­ary Ecol­ogy, Depart­ment of Biol­ogy, Lund University.

The research can lead to con­crete ben­e­fits. One exam­ple is releas­ing ster­ile males in pop­u­la­tions of malaria mos­qui­toes, as an attempt to limit the num­ber of mos­qui­toes in cer­tain areas.

Drugs that tar­get women or men specif­i­cally are another hot research field. Accord­ing to the biol­o­gists at Lund Uni­ver­sity, this is also an area that requires more knowl­edge on the evo­lu­tion of sex chromosomes.

(Source: Lund Uni­ver­sity press release, 29.05.2017; 1 Dar­win was right — sex­ual repro­duc­tion)

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