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Macrostomum

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One of the main reasons I began working on Macrostomum flatworms is because they are so plastic, dynamically adjusting investment into reproductive traits according to the prevailing social environment. However, we’ve recently discovered that one species we’re keeping in the lab, Macrostomum pusillum, isn’t really plastic at all. That was initially puzzling, but we now think it’s for a very good reason. Rather than preferring to outcross like its close relatives, our recent experiments would seem to suggest that M. pusillum individuals instead prefer to self-fertilise their eggs with their own sperm. That means they don’t really have to plastically respond to their social environment, because that social environment isn’t particularly relevant to how they gain fitness.

Having the option to self is one major advantage of being a hermaphrodite, of course. Even so, it is not straightforward that selfing should evolve, because selfed offspring are often less fit, suffering from inbreeding depression. By forcing worms to self or giving them the option to outcross, we found no evidence for differential inbreeding depression (suggesting the worms may not be outcrossing even when they have the chance), nor did we find any evidence for plasticity in the age that worms begin producing hatchlings, their relative investment in making sperm versus making eggs, or the speed at which sperm are produced (all of which we would have expected under preferred outcrossing, based on what we know from other Macrostomum species). The next step will be to perform direct genetic tests for selfing, but for now our new working hypothesis is that the amazing diversity in Macrostomum sexual biology extends to a novel dimension, namely that some worms prefer to mate with another individual in order to reproduce, whereas others prefer to do it all by themselves.

Congratulations to lab member Athina Giannakara, who performed the study. The paper has just been published in the Journal of Experimental Biology here. (JEB were kind enough to feature my recent work on a hypodermically self-inseminating relative of M. pusillum, so the journal felt like a natural choice.)

Giannakara A, Ramm SA. 2017.
Self-fertilization, sex allocation and spermatogenesis kinetics
in the hypodermically-inseminating flatworm Macrostomum pusillum
Journal of Experimental Biology, doi: 10.1242/jeb.149682

 

Photo credit: Athina Giannakara

2016-06-11 18.53.54

Just emerging from a busy teaching period, it was as ever a pleasure this year to welcome first another enthusiastic group of Bachelor students to our upper-level undergraduate course on “Key Concepts in Evolutionary Ecology”, followed by another excellent set of Master students taking our module “Evolution of Behaviour”. The Master module – which Klaus Reinhold and I teach together – focuses on bushcricket behavioural ecology, and our aim is to try to pack in the full scientific “experience”, from developing a hypothesis and designing an experiment to test it, then actually conducting the experiment and analysing the results, through to finally presenting the research in a paper and oral presentation (all in 6 weeks!). The highlight is a two-week trip to central Greece, where we conduct the experiments the students have designed in the field. It was a brilliant trip this year, undoubtedly enhanced through various guest researchers joining us (thanks all!). Today is the last day of the module, and I’m very much looking forward to the students’ presentations of their work in the final symposium this afternoon.

A few other recent lab developments:

First, a very warm, if slightly belated, welcome to Ekin Demir, an intern student studying in Ankara who is joining the lab over the summer. During her visit, Ekin will work together with Bahar, myself and our collaboration partner Claudia Fricke in Münster on a spermatogenesis project.

Second, speaking of Münster, the lab was well represented at the Insect Reproductive Molecules meeting there this week. Well done to Bahar, Michael, Yumi and Ekin for your contributions and thanks very much to Claudia and her team for putting together an excellent meeting (and for inviting us even though we don’t work on insects!). Some fascinating discussion of seminal fluid-mediated effects and various other reproductive phenomena in Drosophila, beetles, snails and flatworms, and a really friendly and open atmosphere (despite all the talk of Brexit in the coffee breaks!).

And finally, my aim of blogging about papers as we publish them has slipped a bit, so to catch up, I’m delighted to report that an experimental evolution study in Macrostomum lignano led by Tim Janicke has just come out in Journal of Evolutionary Biology, plus two review articles. The first is a chapter I wrote together with Lukas Schärer on sex in hermaphrodites for the Encyclopedia of Evolutionary Biology, and the second is my take on why flatworms are an interesting model group for studying various aspects of sexual diversity, commissioned for a forthcoming special issue of Molecular Reproduction & Development dedicated to Hermaphrodites.

Janicke T, Sandner P, Ramm SA, Vizoso DB, Schärer L (2016)
Experimentally evolved and phenotypically plastic responses to 
enforced monogamy in a hermaphroditic flatworm
Journal of Evolutionary Biology. http://doi.org/10.1111/jeb.12910

Schärer L, Ramm SA (2016) 
Hermaphrodites
The Encyclopedia of Evolutionary Biology. Vol 2, p. 212-224. 
http://doi.org/10.1016/B978-0-12-800049-6.00160-8

Ramm SA (2016)
Exploring the sexual diversity of flatworms: Ecology, evolution,
and the molecular biology of reproduction.
Molecular Reproduction and Development. http://doi.org/10.1002/mrd.22669

 

Photo: our field site in Paleokastro, central Greece.

 


Our latest experimental results in Macrostomum lignano flatworms demonstrate that individuals are able to produce sperm faster under conditions of higher sperm competition, presumably contributing to stronger sperm competitiveness. The findings are important because they imply that the speed of spermatogenesis is not a fixed property of a species or a genotype, but rather a malleable parameter that varies according to the prevailing environmental conditions. Whether or not other animals are capable of modulating the speed of spermatogenesis in this manner is currently unknown, but it could be that speeding up and slowing down spermatogenesis based on sperm competition cues is a taxonomically widespread – but until now largely overlooked – mechanism underlying phenotypic plasticity in sperm production.

The paper is based on experiments conducted by Athina Giannakara for her Master Thesis with me here in Bielefeld,  in collaboration with Lukas Schärer in Basel, and has just been published in BMC Evolutionary Biology.

Sperm competition-induced plasticity in the speed of spermatogenesis.
Giannakara A, Schärer L, Ramm SA (2016)
BMC Evolutionary Biology 16: 60. doi: 10.1186/s12862-016-0629-9

Picture: Detail from Fig. 1 in Giannakara et al. (2016).

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12736466_10154596915937729_2017208733_n…for another year. Thanks to all of the participants for lots of fun and fascinating discussion on matters hermaphroditic at SHOW 2016 last week, and a special thank you to the ZiF for hosting us, and the team here – Bahar, Michael, Yumi & Athina – for all the hard work behind-the-scenes to make it happen. (Photo credit: Bahar)