The fitness effects of a pale mutant in the aposematic seed bug Lygaeus simulans indicate pleiotropy between warning coloration and life history

Conspicuous warning colours that signal chemical or other defences are common in the natural world. For instance, such aposematic warning patterns of red-and-black or yellow-and-black are common among insect taxa, particularly in the order Hemiptera, often forming the basis of Batesian and/or Müllerian mimicry rings. In addition, it has been repeatedly noted that colour polymorphisms or mutants that influence pigmentation can show pleiotropy with other behavioural, physiological or life-history traits. Here we describe a pale mutant of the seed bug Lygaeus simulans that appeared in our lab population in 2012, which differs in colour to the wild-type bugs. Through multigenerational experimental crosses between wild-type and pale mutant L. simulans, we first show that the pale phenotype segregates as a single Mendelian locus, with the pale allele being recessive to the wild-type. Next, we show (1) that there is a large heterozygous advantage in terms of fecundity, (2) that pale females suffer reduced longevity, and (3) that pale males have increased body length compared to wild-type homozygotes. Our data therefore suggest that the colour locus is pleiotropic with a number of life-history traits, opening the door for a more complete genetic analysis of aposematic colouration in this species. In addition, this phenotype will be useful as a visible genetic marker, providing a tool for investigating sperm competition and other post-copulatory drivers of sexual selection in this species.