How Female-Female Competition Affects Male-Male Competition: Insights into Postcopulatory Sexual Selection from Socially Polyandrous Species.

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AbstractSexual selection is a major driver of trait variation, and the intensity of male competition for mating opportunities has been linked with sperm size across diverse taxa. Mating competition among females may also shape the evolution of sperm traits, but the effect of the interplay between female-female competition and male-male competition on sperm morphology is not well understood. We evaluated variation in sperm morphology in two species with socially polyandrous mating systems, in which females compete to mate with multiple males. Northern jacanas (Jacana spinosa) and wattled jacanas (J. jacana) vary in their degree of social polyandry and sexual dimorphism, suggesting species differences in the intensity of sexual selection. We compared mean and variance in sperm head, midpiece, and tail length between species and breeding stages because these measures have been associated with the intensity of sperm competition. We found that the species with greater polyandry, northern jacana, has sperm with longer midpieces and tails as well as marginally lower intraejaculate variation in tail length. Intraejaculate variation was also significantly lower in copulating males than in incubating males, suggesting flexibility in sperm production as males cycle between breeding stages. Our results indicate that stronger female-female competition for mating opportunities may also shape more intense male-male competition by selecting for longer and less variable sperm traits. These findings extend frameworks developed in socially monogamous species to reveal that sperm competition may be an important evolutionary force layered atop female-female competition for mates.





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Lipshutz, Sara E, Samuel J Torneo and Kimberly A Rosvall (2023). How Female-Female Competition Affects Male-Male Competition: Insights into Postcopulatory Sexual Selection from Socially Polyandrous Species. The American naturalist, 201(3). pp. 460–471. 10.1086/722799 Retrieved from

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Sara E Lipshutz

Assistant Professor of Biology

Our research focuses on the evolution of behavior across weird and wonderfully diverse species of birds. This work bridges “muddy boots” experimental fieldwork with a variety of molecular and computational approaches in genetics, genomics, neuroscience, and endocrinology. We have several research foci:  


1. Female perspectives in biology. Cultural biases shape our predictions for how and why animals behave the way they do, and female animals have historically been neglected in biological research. We study the evolution of female competition across diverse avian species, ranging from social polyandry to monogamy in shorebirds and songbirds. Critically, hypotheses derived from studying males (i.e. testosterone focus) do not explain interspecific variation in female aggression. We use population genomic and transcriptomic data to evaluate the proximate causes and ultimate consequences of female competition.  


2. Global change biology. In the age of the Anthropocene, animals are facing evolutionary unprecedented environmental changes. Sensory pollutants like anthropogenic noise and artificial light at night can alter animal physiology, behavior, and ecology on a rapid timescale. Behavior flexibility and adaptation may lead the way in helping animals respond to novel challenges. We investigate why some individuals and species may be better prepared to face global change.  

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