Journal Article

Sexual morph specialisation in a trioecious nematode balances opposing selective forces


The coexistence of diferent mating strategies, whereby a species can reproduce both by selfng and outcrossing, is an evolutionary enigma. Theory predicts two predominant stable mating states: outcrossing with strong inbreeding depression or selfng with weak inbreeding depression. As these two mating strategies are subject to opposing selective forces, mixed breeding systems are thought to be a rare transitory state yet can persist even after multiple speciation events. We hypothesise that if each mating strategy plays a distinctive role during some part of the species life history, opposing selective pressures could be balanced, permitting the stable co-existence of selfng and outcrossing sexual morphs. In this scenario, we would expect each morph to be specialised in their respective roles. Here we show, using behavioural, physiological and gene expression studies, that the selfng (hermaphrodite) and outcrossing (female) sexual morphs of the trioecious nematode Auanema freiburgensis have distinct adaptations optimised for their diferent roles during the life cycle. A. freiburgensis hermaphrodites are known to be produced under stressful conditions and are specialised for dispersal to new habitat patches. Here we show that they exhibit metabolic and intestinal changes enabling them to meet the cost of dispersal and reproduction. In contrast, A. freiburgensis females are produced in favourable conditions and facilitate rapid population growth. We found that females compensate for the lack of reproductive assurance by reallocating resources from intestinal development to mate-fnding behaviour. The specialisation of each mating system for its role in the life cycle could balance opposing selective forces allowing the stable maintenance of both mating systems in A. freiburgensis.

Attached files


Adams, Sally
Pathak, Prachi
Kittelmann, Maike
Jones, Alun R.C.
Mallon, Eamonn B.
Pires-daSilva, Andre

Oxford Brookes departments

Department of Biological and Medical Sciences


Year of publication: 2022
Date of RADAR deposit: 2022-05-17

Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 International License

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