The 'Woman in Red' effect: pipefish males curb pregnancies at the sight of an attractive female.

Proc Biol Sci. 2018 Aug 22;285(1885). pii: 20181335. doi: 10.1098/rspb.2018.1335. Cunha M1, Berglund A2, Mendes S1, Monteiro N3,4. Author information 1 CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, rua Padre Armando Quintas, 4485-661 Vairão, Portugal. 2 Department of Ecology and Genetics/Animal Ecology, Uppsala University, Uppsala, Sweden. 3 CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, rua Padre Armando Quintas, 4485-661 Vairão, Portugal nm.monteiro@icloud.com. 4 CEBIMED, Faculdade de Ciências da Saúde, Universidade Fernando Pessoa, rua Carlos da Maia 296, 4200-150 Porto, Portugal. Abstract In an old Gene Wilder movie, an attractive woman dressed in red devastated a man's current relationship. We have found a similar 'Woman in Red' effect in pipefish, a group of fish where pregnancy occurs in males. We tested for the existence of pregnancy blocks in pregnant male black-striped pipefish (Syngnathus abaster). We allowed pregnant males to see females that were larger and even more attractive than their original high-quality mates and monitored the survival and growth of developing offspring. After exposure to these extremely attractive females, males produced smaller offspring in more heterogeneous broods and showed a higher rate of spontaneous offspring abortion. Although we did not observe a full pregnancy block, our results show that males are able to reduce investment in current broods when faced with prospects of a more successful future reproduction with a potentially better mate. This 'Woman in Red' life-history trade-off between present and future reproduction has similarities to the Bruce effect, and our study represents, to our knowledge, the first documentation of such a phenomenon outside mammals. KEYWORDS: abortion; fitness; investment; male pregnancy; post-copulatory sexual selection