Relatedness modulates density‐dependent cannibalism rates in Drosophila

Abstract

Cannibalism is taxonomically widespread and can have large impacts on individual fitness and population‐level processes. As such, identifying how cannibalism rates vary in response to ecological cues is important for predicting species evolution and population dynamics. In this study, we aimed to identify several eco‐evolutionary factors that affect cannibalism rate and measure how they interacted with one another. To do this, we conducted two experiments using complimentary methods to measure how cannibalism rates varied among larval Drosophila melanogaster and Drosophila simulans in response to changes in conspecific relatedness, social familiarity and density. We found that larvae were more likely to cannibalise non‐related larval victims in both species, and that this effect increased at high densities in D. simulans. We found no evidence that Drosophila larvae use social familiarity to assess relatedness. Finally, in D. melanogaster, cannibalistic larvae prefer to cannibalise larvae that are being attacked by a greater number of conspecifics, implying that cues linked to conspecific abundance encourage cooperative cannibalism. By showing that cannibalism frequency in Drosophila spp. is sensitive to relatedness and several other factors, we reveal the complex relationship between cannibalism frequency and species ecology. Also, by showing that the effect of relatedness on cannibalism frequency is density dependent, we advance the current understanding of how ecological variables interact to affect kin selection. A free Plain Language Summary can be found within the Supporting Information of this article.

The impact of intrinsic and extrinsic factors on the epidemiology of male‐killing bacteria

“…2). Intra‐brood competition over common resources is known to be a significant source of mortality for juveniles across a range of arthropod species, including fruit flies (Fisher et al 2021), dragonflies (Hopper et al 1996), earwigs (Dobler and Kölliker 2010), mantids (Fea et al 2014) and spiders (de Tranaltes et al 2022) to name but a few. Thus, our results may well be biologically plausible in suggesting that the extent to which MKB infections can provide relief from intra‐brood competition is an important determinant of their long‐term viability in response to temperature change.…”

“…Infections caused by maternally inherited bacteria occur in at least 50% of arthropod species (Weinert et al 2015, Sanaei et al 2021). As these bacteria cannot be transmitted by males, males represent evolutionary ‘dead ends' with the potential to hinder the fitness of their female siblings via costly competitive interactions (Engelstädter and Hurst 2009, Fea et al 2014, Fisher et al 2021). Thus, many maternally inherited bacterial species have evolved to kill the male embryos of their hosts, which is expected to increase female survival, presumably via reduced intra‐brood competition (Werren et al 1986, Jaenike et al 2003, Engelstädter and Hurst 2009).…”

Kin recognition in Drosophila: rearing environment and relatedness can modulate gut microbiota and cuticular hydrocarbon odour profiles

“…Kin discrimination also occurs in males, who can modulate male–male competition and female harm levels when they compete against related rivals (Carazo et al 2014, Le Page et al 2017). Recent evidence suggests that kin recognition in D. melanogaster might actually be critical for larvae, both in mediating cooperative feeding behaviour (Dombrovski et al 2017, Khodaei and Long 2019) and cannibalism (Fisher et al 2021). Remarkably, kin recognition in this species depends on both familiarity and relatedness, and is thought to rely mainly on cuticular hydrocarbons (Carazo et al 2014, Le Page et al 2017).…”

Pathways to the density‐dependent expression of cannibalism, and consequences for regulated population dynamics

“…One thing we do know is that for cannibalism to contribute to the regulation of animal population densities, it must be a density‐dependent process, generating increasing per‐capita mortality as densities rise. A large body of empirical evidence, including both observational and experimental studies, has demonstrated that this is generally true: per‐capita mortality rates from cannibalism rise, in many cases very strongly, with rising population density (Baskauf, 2003; Buddle et al, 2003; Elliott, 2004; Fincke, 1994; Fisher et al, 2021; Fox, 1975; Gillespie et al, 2020; Grosholz et al, 2021; Hannesson, 2018; Hopper et al, 1996; Houghton et al, 2017; Klotz & Wright, 2020; Moksnes, 2004; Oraze & Grigarick, 1989; Orr et al, 1990; Persson et al, 2003; Persson & Elliott, 2013; Polis, 1981; Strauss et al, 2016; Van Buskirk, 1989; Wagner & Wise, 1996; Wildy et al, 2001; Wissinger et al, 2010). These studies have, furthermore, demonstrated that there are multiple pathways through which cannibalism emerges as a density‐dependent process.…”