Editing Volvox (section)

=== Reproduction ===

''Volvox'' is facultatively sexual and can reproduce both sexually and asexually. In the lab, asexual reproduction is most commonly observed; the relative frequencies of sexual and asexual reproduction in the wild is unknown. The switch from asexual to sexual reproduction can be triggered by environmental conditions<ref name="pmid14667362" /> and by the production of a sex-inducing pheromone.<ref>{{Cite journal |last=Hallmann |first=Armin |year=2003 |title=Extracellular Matrix and Sex-Inducing Pheromone in Volvox |journal=International Review of Cytology |volume=227 |pages=131–182 |doi=10.1016/S0074-7696(03)01009-X |pmid=14518551 |isbn=978-0-12-364631-6}}</ref> Desiccation-resistant diploid [[zygote]]s are produced following successful fertilization.

An [[asexual reproduction|asexual]] colony includes both somatic (vegetative) cells, which do not reproduce, and large, non-motile ''[[Gonidium|gonidia]]'' in the interior, which produce new colonies asexually through repeated division. In [[sexual reproduction]] two types of [[gamete]]s are produced. ''Volvox'' species can be [[monoecious]] or [[dioecious]]. [[Male]] colonies release numerous sperm packets, while in female colonies single cells enlarge to become oogametes, or eggs.<ref name="Kirk" /><ref name="Powers">{{cite journal |last=Powers |first=J. H. |date=1908 |title=Further studies in ''Volvox'', with descriptions of three new species |journal=[[Transactions of the American Microscopical Society]] |doi=10.2307/3220908 |jstor=3220908 |volume=28 |pages=141–175}}</ref>

Kirk and Kirk<ref name="pmid3941891">{{cite journal |last1=DL |first1=Kirk |last2=Kirk |first2=MM |date=1986 |title=Heat shock elicits production of sexual inducer in Volvox |journal=Science |pmid=3941891 |doi=10.1126/science.3941891 |volume=231 |issue=4733 |pages=51–4 |bibcode=1986Sci...231...51K}}</ref> showed that sex-inducing pheromone production can be triggered in [[somatic cell]]s by a short [[heat shock]] given to asexually growing organisms. The induction of sex by heat shock is mediated by [[oxidative stress]] that likely also causes oxidative DNA damage.<ref name="pmid14667362">{{cite journal |last1=Nedelcu |first1=AM |last2=Michod |first2=RE |date=2003 |title=Sex as a response to oxidative stress: the effect of antioxidants on sexual induction in a facultatively sexual lineage |journal=Proc. Biol. Sci. |pmid=14667362 |pmc=1809951 |doi=10.1098/rsbl.2003.0062 |volume=270 |issue=Suppl 2 |pages=S136–9}}</ref><ref name="pmid15306305">{{cite journal |last1=Nedelcu |first1=AM |last2=Marcu |first2=O |last3=Michod |first3=RE |date=2004 |title=Sex as a response to oxidative stress: a twofold increase in cellular reactive oxygen species activates sex genes |journal=Proc. Biol. Sci. |pmid=15306305 |pmc=1691771 |doi=10.1098/rspb.2004.2747 |volume=271 |issue=1548 |pages=1591–6}}</ref> It has been suggested that switching to the sexual pathway is the key to surviving environmental stresses that include heat and [[drought]].<ref name="Amon">{{cite journal |last1=Amon |first1=P |last2=Haas |first2=E |last3=Sumper |first3=M |date=1998 |title=The sex-inducing pheromone and wounding trigger the same set of genes in the multicellular green alga Volvox |journal=Plant Cell |pmid=9596636 |pmc=144025 |doi=10.2307/3870664 |volume=10 |issue=5 |pages=781–9 |jstor=3870664}}</ref> Consistent with this idea, the induction of sex involves a [[signal transduction]] pathway that is also induced in ''Volvox'' by wounding.<ref name="Amon" />