For example, if both individuals intend to donate sperm but avoid (potentially costly) sperm receipt, mating interests are incompatible.
It has been suggested that such conflicts could be resolved by a mechanism called sperm trading, where both partners accept both mating roles and trade one type of gametes, e.g. Michiels (2007): Precopulatory stabbing, hypodermic injections and unilateral copulations in a hermaphroditic sea slug. [full text] Anthes N, Putz A, Michiels NK (2006): Sex role preferences, gender conflict and sperm trading in simultaneous hermaphrodites: a new framework .
Gavrilets (eds.) The Genetics and Biology of Sexual Conflict.
Population density and group size effects on reproductive behavior in a simultaneous hermaphrodite.
The scattered distribution across the animal phylogeny indicates that alternative forms of gender expression are rather flexible and may be repeatedly gained and lost across evolutionary time scales. [free full text] The bulk of our research aims at understanding how sexual selection shapes the evolution and expression of hermaphrodite mating strategies (and beyond).
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eggs, against access to the respective gametes of the partner. Animal Behaviour Volume: 72, Issue: 1, Pages: 1-12, [full text] Anthes N, Putz A, Michiels NK (2005): Gender trading in a hermaphrodite. (2016): Darwinian sex roles confirmed across the animal kingdom. Koene JM, Pförtner T, Michiels NK (2005): Piercing the partner's skin influences sperm storage in earthworms.
Using manipulative experiments in the sea slug genus we have shown that conditional reciprocity may indeed exist, even though the costs and benefits involved remain to be studied. Current Biology 15: R792-R793, [full text] Janicke T., Häderer I.
Work in progress in collaboration with Philippe Jarne & Joris Koene. Anthes (2009): Accessory male investment can undermine the evolutionary stability of simultaneous hermaphroditism. Broadly, these targets refer to (i) the necessity that copulating individuals need to agree on who is taking the male or female sexual role during mating ('gender conflict'), (ii) the individual decision about the amount of resources invested in male versus female reproduction ('sex allocation'), and (iii) the option to self-fertilise. (2012): Female Fitness Optimum at Intermediate Mating Rates under Traumatic Mating. Michiels NK, Koene JM (2006): Sexual selection favours harmful mating in hermaphrodites more than in gonochorists. (1998): Mating conflicts and sperm competition in simultaneous hermaphrodites.
Sex allocation theory is a powerful approach to understand the conditions that favor the evolution and stability of simultaneous hermaphroditism. It has been suggested that, since hermaphrodites may be inherently motivated to engage in mating, pre-copulatory barriers may be weak. Functions, diversity, and evolution of traumatic mating. Integrative and Comparative Biology 46: 473-480 [full text] Michiels NK, Newman LJ (1998): Sex and violence in hermaphrodites.
This means that apart from bits of rhizome being washed down rivers, it can only get around by being moved around in contaminated soil.