No evidence of sex ratio manipulation by Galápagos mockingbirds in response to environment

Abstract

Birds can adjust investment in reproduction by altering the sex ratios of their broods. When one sex is more costly to raise than the other, producing either more male or female offspring can lower the costs of reproduction. Biasing sex ratios can also be advantageous if the expected fitness of male versus female offspring differs. Here, we investigated whether Galápagos mockingbirds Mimus parvulus bias sex ratios in response to variation in rainfall. Female mockingbirds are smaller and thus females may reduce the costs of reproduction by biasing sex ratios in favor of female offspring. We quantified sex ratios in 131 mockingbird broods over four years with variable rainfall (2012, 2013, 2015 and 2016). We found no evidence that mockingbirds adjusted sex ratios in response to environmental conditions. Mockingbirds may not adjust sex ratios either because they lack the ability to do so, or because the costs of manipulation outweigh its benefits.

The genome sequence of the avian vampire fly (Philornis downsi), an invasive nest parasite of Darwin's finches in Galapagos

“…The major expansions of the GST family in P. downsi were observed in Delta and Epsilon subclasses (Figure 4d). Insecticides, such as permethrin, are used to experimentally manipulate P. downsi abundance in bird nests to study the effects of the parasite on the health of the birds (Fessl et al, 2010;Koop et al, 2011;Koop, Le Bohec, et al, 2013;Koop, Owen, et al, 2013;Knutie et al, 2014Knutie et al, , 2016bO'Connor et al, 2014;McNew et al, 2020;Addesso et al, 2020). Increased expression of GSTs following permethrin exposure has been documented in several insect species including oriental fruit flies (Bactrocera dorsalis) (Hu et al, 2008).…”