A sexually-selected male weapon is associated with lower inbreeding load but higher gender load in the bulb mite

Aleksandra Łukasiewicz, Małgorzata Niśkiewicz, Jacek Radwan

Evolution 2020

Is it because of sexually antagonistic effects of underlying genes?

Sexually selected traits are heritable, but not correlated with viability.

Rhizoglyphus robini – a male dimorphic species

Aggressive fighter male with a

thickened and sharply terminated third

pair of legs (sexually selected weapon)

Scrambler male with unmodified legs

Aim: estimate both the load of deleterious mutations

and gender load using inbred lines derived from

females mated with either fighter or scrambler males.

Weapon condition dependent = low load of

deleterious mutations?

BUT

may cause gender load(i.e. negative, pleiotropic effect on female fitness , e.g Harano et

al. 2010, Plesnar-Bielak et al. 2014)

Obtaining inbred lines and simultaneous male morph selection

Scramblers+

sisters

x4 generations

Fighters+

sisters

x4 generations Proportions of fighter morph in fighter and scrambler

isoclines across 4 generations of brother-sister mating.

Scramblers+

sisters

Fighters+

females from other figther

line

Scramblers+

females from other

scrambler line

Fighters+

sisters

Inbreds (F=0.5) OutbredsGeneration 4

Comparison of inbreeding and gender load between lines derived from armed fighters and unarmed scramblers

• Mutation load: comparison of fecundity of inbred

and outbred females within F- and S- lines

• Gender load: comparison of fecundity of outbred

females derived from F- and S- lines

Comparison of inbreeding and gender load between lines derived from armed fighters and unarmed scramblers

Scramblerinbreds

Fightersoutbreds

Scrambleroutbreds

Fighter inbreds

• founder morph * treatment interaction, (LMM: t = -3.096, p = 0.003)

• fecundity of outbred females derived from S-lines was significantly higher than in F-lines (LMM: t= 2.557, P= 0.019)

Comparison of inbreeding and gender load between lines derived from armed fighters and unarmed scramblers

Fighter lines Scrambler lines

Under outbreeding, genetic benefits of mating with

bearers of elaborate sexually selected traits

might be swamped by the costs of decreased fitness

of daughters due to sexually antagonistic

effect.

Comparison of inbreeding and gender load between lines derived from armed fighters and unarmed scramblers

Fighter lines Scrambler lines