Reduced sexual size dimorphism in a pipefish population where males do not prefer larger females

• Within a species' distribution, populations are often exposed to diverse environmentsand may thus experience different sources of both natural and sexual selection.These differences are likely to impact the balance between costs and benefits toindividuals seeking reproduction, thus entailing evolutionary repercussions. Here, welook into an unusual population (Baltic Sea) of the broadnosed pipefish, Syngnathustyphle, where males do not seem to select females based on size and hypothesizethat this pattern may derive from a reduction in direct benefits to the male. We furtherhypothesize that if larger females do not persistently secure a higher reproductivesuccess, either through pre‐ or postcopulatory sexual selection, a decrease insexual size dimorphism in the Baltic population should be apparent, especially whencontrasted with a well‐studied population, inhabiting similar latitudes (Swedish westcoast), where males prefer larger females. We found that, in the Baltic population,variation in female quality is low. We were unable to find differences in abortion ratesor protein concentration in oocytes produced by females of contrasting sizes. Directbenefits from mating with large partners seem, thus, reduced in the Baltic population.We also found no evidence of any postcopulatory mechanism that could favorlarger mothers as embryo development was unrelated to female size. While femalesize can still be selected through intrasexual competition or fecundity selection, thepressure for large female body size seems to be lower in the Baltic. Accordingly, wefound a noticeable decrease in sexual size dimorphism in the Baltic population. Weconclude that, although far from negating the significance of other selective processes,sexual selection seems to have a decisive role in supporting pipefish sexualsize asymmetries.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

embryonic development

male pregnancy

postcopulatory selection

sexual selection

Syngnathidae

Biologi med inriktning mot zooekologi

Biology with specialization in Animal Ecology

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