Environmental stress maintains trioecy in nematode worms

Abstract

Sex is determined by chromosomes in mammals but it can be influenced by the environment in many worms, crustaceans and vertebrates. Despite this, there is little understanding of the relationship between ecology and the evolution of sexual systems. The nematode Auanema freiburgensis has a unique sex determination system in which individuals carrying one X chromosome develop into males while XX individuals develop into females in stress-free environments and self-fertile hermaphrodites in stressful environments. Theory predicts that trioecious populations 42 Kanzaki et al., 2017). Auanema is a recently described nematode genus with two trioecious species, 43A. rhodensis and A. freiburgensis (Kanzaki et al., 2017) and is distantly related to the trioecious 44 Heterorhabditis sp. (Strauch et al., 1994). 45 3 In this article, we develop a new mathematical model to study how the flexible sex determi-46

Digest: Three sexes from two loci in one genome: A haploid alga expands the diversity of trioecious species*

“…If trioecy in P. starrii is in fact stable, stability must reflect different forces than other systems, for instance, in Auanema , where trioecy may be adaptive because environmental female‐versus‐hermaphroditic sex determination facilitates response to likely mate availability (Anderson et al. 2020). One promising avenue is that P. starrii trioecy could be maintained through environmental heterogeneity, as proposed for some plants (Fleming et al.…”

“…Adding to P. starrii's potential as a model for understanding sexual system evolution, the two interacting loci open up the possibility that selection can act separately on male-versushermaphrodite and female-versus-nonfemale loci. If trioecy in P. starrii is in fact stable, stability must reflect different forces than other systems, for instance, in Auanema, where trioecy may be adaptive because environmental female-versus-hermaphroditic sex determination facilitates response to likely mate availability (Anderson et al 2020). One promising avenue is that P. starrii trioecy could be maintained through environmental heterogeneity, as proposed for some plants (Fleming et al 1998), though what specific environmental features could be important remains to be seen.…”

Chromatin-associated effectors of energy-sensing pathways mediate intergenerational effects

“…Invertebrate model systems, such as the nematode Caenorhabditis elegans, have been instrumental in revealing some of the mechanisms of inter-and transgenerational inheritance (Miska andFerguson-Smith, 2016, Perez andLehner, 2019). The free-living nematode Auanema freiburgensis is an attractive new animal model system for studying the mechanisms of inheritance of parental effects (Kanzaki et al, 2017, Zuco et al, 2018, Anderson et al, 2020. This is because the assays for studying the mechanisms of inheritance of parental effects in A. freiburgensis are fast and easy to perform due its short generation time (~4 days at 20 °C) and easy-to-distinguish morphologies in the offspring.…”