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Male Swords and Female Preferences

1991; American Association for the Advancement of Science; Volume: 253; Issue: 5026 Linguagem: Inglês

10.1126/science.253.5026.1426

1095-9203

Jack da Silva,

Neurobiology and Insect Physiology Research

A. L. Basolo teStS the: hypothesis that, in the: swordless platytish. Xiphophonts rruu:ul4rus, female: mate choice: arises from a prc:c:xisting sensory bias (1). Basolo shows thar ti:males c::xhibir a mating pn:fi::rc:nce for males with an at:C1chc::d, arrificia.!, colored sword whc:n given a choice: bc:rwo:n thc:sc: males and males with an arrificia.!,rransparc:nr sword as a controL Because: swordlessness is the: ancc:srral sran: of the:Xiphophorus clade:, Basolo argues thar the: results of her c:xpc:rimc:nrindican: rh.ar fanale: pn:fc:rc:nce: for swords predateS the: evolurion of the: sword and concludes thar coc:volutionary modds of sc::x112l sc:lc:aion arc: inadequarc:. Basolo provides no d.irca evidence in supporr of a prc:cxi.sringfc:male:sc:nsorybias, bur rejc:a:s the: coc:volutionary hypothc:sc:s of mare-choice: evolution. Fc:male: platyfish may have: ahibited a preference: for artificially sworded males be:Cluse: thc:sc:males wc:rc:novcl (2). The: approprian: control for t:his possibility would be: males with some: other shapes aa:u:hed rhar do nor n:sc:mble:any marking on males, a blue:rriangie:, for c::x:ample:. If fc:maJ.esprefer males with a triangle: co those: withoUt, then ti:males arc:clc::arlyamaca:d ro novcl males. If t:hisresr shows that fi:malc:sarc:nor aancred co novcl males, then ir would be:nc:a:ssary co demonstran: rh.ar fc:m.alesarc:ac:raacd ro the: sword per sc: and nor the: com:cxt in which the: sword is displayai This is an importanr distinction, beaus rhing a sword co areas other than the: lower edge of the:Cludal fin. The: mOStconvincing supporr for the:sensory-bias hypothesis would come: from a dc:monsrr:u:ionthatmalc:sshow a mating ?,cf...u;ua: for fc:males bearing swords. This counrc:rinruirivc: prediction daM:s from the: hypothesis rhar a female:sc:osorybias c:volvc:s in response: co some: c:nvironmc:nal stimulus. Basolo gives the: c::x:ample: that fc:maJ.c:s may have: c:volved a search image for a favorite food and thc:n prcfc:m:d co mate with males that sporrc:d an appc:ndage resembling this food. In such a scc:nario, malc:swould be:just as liIa:1yco c:volve:the: sensory bias, as they arc: also subjc:a to sc:lc:crionto dca:cr food. The: prediaion rh.ar males pn:fc:r fc:males with swords should be:tested with a swordk:ss species whose: fc:malc:sahibit a sword ptd\:...<.ucc:, as the: swords of sworded speci~ 1~ may be: usc:d by males as an indiClror of gc:nder (3). Even if males prefc:rrc:dfanales with swords, fanale: swords would not be: e:xpc:aed to have: c:volved.,as sworded females arc: not likc:lyto have: c:xpc:riencc:da mating advanc.gc:. This is beaus<: fc:maJ.e: gc:st:1tionin thc:sc:live:-bearing spc:ciesprobably mc:ansthat females arc: the: limiting sex.. Is the: sc:nsory-bias hypothesis tenable:: One: must ask why a female:might want to mate with a male: associated with some:thing that looks good to eat. It cannOt be: argued that males with swords arc: more: easily de:tc:Cte:dby fe:malesbeause: of limitS to female: visual perce:ption; X mtU:ulatus males and males of the: sworded species X hd1eri both perform complex courrship displays at very close: range: to fc:m.ales(3, 4). Pe:rhaps some: constraint on the: dc:vclopmc:nt of nc:ural circuitry causes fc:males ro court attractive: obje:CtSeven though they provide: no information about mate: type:or quality. As pointed our by Basolo, this is nor the:same:as a novcl-male: dfc:ct, as such a hypothesis doc:s not c:xplain the: wtion of sword gc:nes in a population. Nc:vc:rthe:less, narural sc:lc:crionwould likely favor a srrarcgy of informc:d mate choice: over arbitrary mate choia:. FUrther testS of the: sensory-bias hypothesis would be: usc:ful., but the:premise: of the:hypothesis must first: be:carc:fullyexamined. JACK DA Sn..VA DqxutmDIl of Biology, McGi1I Univcsity, M~ QudJ«, H3A 1B1, Canada