Media Releases

Male guppies ensure successful mating with genital claws

July 24, 2013

TORONTO, ON – Some males will go to great lengths to pur­sue a female and take extreme mea­sures to hold on once they find one that inter­ests them, even if that affec­tion is unre­quit­ed. New research from evo­lu­tion­ary biol­o­gists at the Uni­ver­si­ty of Toron­to shows that the male gup­py grows claws on its gen­i­tals to make it more dif­fi­cult for unre­cep­tive females to get away dur­ing mat­ing.

Gen­i­talia dif­fer great­ly in ani­mal groups, even among sim­i­lar species – so much so that even close­ly relat­ed species may have very dif­fer­ent gen­i­talia. The rea­sons for these dif­fer­ences are unclear but sex­u­al con­flict between males and females may be a source. Sex­u­al con­flict occurs when the fit­ness inter­ests of males and females dif­fer, which is root­ed in dif­fer­ences in egg and sperm sizes. Males invest less than females in repro­duc­tion because sperm is cheap to pro­duce, and larg­er eggs are most cost­ly to make. This dif­fer­ence results in a con­flict in which males are inter­est­ed in mat­ing with as many females pos­si­ble while females are more selec­tive with their mates.

The researchers exam­ined the role of a pair of claws at the tip of the gonopodi­um of the male gup­py (Poe­cil­ia retic­u­la­ta) – essen­tial­ly the fish’s penis.

“Our results show that the claws are used to increase sperm trans­fer to females who are resist­ing mat­ings,” says Lucia Kwan, PhD can­di­date in U of T’s Depart­ment of Ecol­o­gy and Evo­lu­tion­ary Biol­o­gy and lead author of a paper pub­lished this week in Biol­o­gy Let­ters. “This sug­gests that it has evolved to ben­e­fit males at the expense of females, espe­cial­ly when their mat­ing inter­ests dif­fer.”

The researchers test­ed two ideas for the func­tion of the claws – one for their role in secur­ing sperm in place at the tip of the gonopodi­um just before it is insert­ed into the female, the oth­er for grasp­ing unre­cep­tive or resis­tant females dur­ing mat­ing to aid in sperm trans­fer. For the lat­ter, Kwan, for­mer grad­u­ate stu­dent Yun Yun Cheng and fac­ul­ty mem­bers Helen Rodd and Locke Rowe used a phe­no­typ­ic engi­neer­ing approach. They sur­gi­cal­ly removed the pair of claws from one set of males and com­pared the amount of sperm trans­ferred by them with a group of males who hadn’t been declawed after they had all mat­ed with recep­tive or unre­cep­tive females.

“Clawed males trans­ferred up to three times more sperm to unre­cep­tive females com­pared to declawed males,” says Kwan. “The claw has evolved to ben­e­fit the males at the expense of females, and impli­cates sex­u­al con­flict between the sex­es in the diver­si­fi­ca­tion of the gen­i­talia in this fam­i­ly of fish. This pro­vides sup­port that this impor­tant selec­tive force is behind an evo­lu­tion­ary pat­tern that evo­lu­tion­ary biol­o­gists have been try­ing to unrav­el for over a cen­tu­ry.”

The results of the study are described in a paper titled “Sex­u­al con­flict and the func­tion of gen­i­tal­ic claws in gup­pies (Poe­cil­ia retic­u­la­ta)” pub­lished this week in Biol­o­gy Let­ters. The research was fund­ed by Nat­ur­al Sci­ences and Engi­neer­ing Research Coun­cil of Cana­da (NSERC) schol­ar­ships to Kwan and Cheng, NSERC grants to Rodd and Rowe, and Cana­da Research Chair fund­ing to Rowe.

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Note to media: Vis­it for images relat­ed to the research study described here.
For more infor­ma­tion, con­tact:

Lucia Kwan
Depart­ment of Ecol­o­gy and Evo­lu­tion­ary Biol­o­gy
Uni­ver­si­ty of Toron­to

Sean Bet­tam
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to