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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

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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.

 

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This year’s edition of Advances in the Study of Behavior will be published shortly, to which Paula Stockley and I have contributed an in-depth review of male adaptations to sperm competition in rodents. The review pulls together many of the different research strands we have ourselves been working on over the past several years, covering aspects such as copulatory behaviour, sperm production, sperm allocation, sperm quality, seminal fluid and genitalia, as well as the wider context of sperm competition studies by considering topics such as cryptic female choice, sexual conflict and multivariate selection and trade-offs. We argue that allied to traditional behavioural and morphological studies, recent molecular and genome-based approaches are transforming our understanding of traits that contribute to male competitive fertilization ability, closing the gap between genotypic and phenotypic perspectives on their adaptive evolution.

Hopefully the review will be a useful synthesis of where we’ve got to with respect to understanding sperm competition in this important vertebrate model group, and can serve as a guide to where we need to go next. The advance online version can be found here.

Integrating perspectives on rodent sperm competition.
Ramm SA, Stockley P (2016)
Advances in the Study of Behavior 48, in press. 
DOI: 10.1016/bs.asb.2016.02.003

Photo credit: Joad Hughes, via Unsplash.


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).

Beethoven_sym_5_motive

Owing to its complex composition, the mixture of sperm and seminal fluid substances that comprise an ejaculate has recently been likened to a musical symphony. In a new study I conducted with former colleagues at the University of Liverpool and published this week in BMC Biology, we used proteomics techniques to ask whether male mammals can plastically adjust ejaculate composition. We discovered that the “seminal symphony” males produce indeed depends strongly upon the prevailing “social milieu”. Under more competitive conditions, males produce more sperm and a different blend of seminal fluid proteins than they do under less competitive conditions. This is presumably because high sperm numbers and large amounts of certain seminal fluid proteins enhance male competitive fertilization success, but aren’t needed when there are no competitors around, and so plasticity in ejaculate composition is selectively favoured.

Ramm SA, Edward DA, Claydon AJ, Hammond DE, Brownridge P, Hurst JL, 
Beynon RJ, Stockley P (2015) 
Sperm competition risk drives plasticity in seminal fluid composition
BMC Biology 13:87. doi: 10.1186/s12915-015-0197-2

Image credit: from Beethoven’s Symphony No. 5. Licensed under Public Domain via Wikimedia Commons.

CoolidgeLtGov… a joke about former US President Calvin Coolidge …

The President and Mrs. Coolidge were being shown [separately] around an experimental government farm. When [Mrs. Coolidge] came to the chicken yard she noticed that a rooster was mating very frequently. She asked the attendant how often that happened and was told, “Dozens of times each day.” Mrs. Coolidge said, “Tell that to the President when he comes by.” Upon being told, the President asked, “Same hen every time?” The reply was, “Oh, no, Mr. President, a different hen every time.” President: “Tell that to Mrs. Coolidge.”

(from Wikipedia entries on Calvin Coolidge and the Coolidge Effect, citing Hatfield & Walster’s A New Look At Love)

In biology, the Coolidge Effect was a term originally coined by Frank Beach to refer to the restoration of sexual activity among males that had previously reached sexual satiety when presented with a new female. More recently, that definition has tended to be broadened to encompass all forms of differential investment that males might exhibit towards novel females, and it is increasingly recognised that such investment can take on more cryptic forms. In a new paper together with Klaus Reinhold, Leif Engqvist and Albia Consul, we report one such example of strategic male investment, presenting evidence that male birch catkin bugs mate for longer with novel females.

 Reinhold K, Engqvist L, Consul A, Ramm SA (2015)
 Male birch catkin bugs vary copula duration to invest
 more in matings with novel females.
 Animal Behaviour 109:161–166. doi:10.1016/j.anbehav.2015.08.020

Image credit: Calvin and Grace Coolidge, about 1918. Public domain image from Wikimedia Commons.

We recently discovered that isolated flatworms of the species Macrostomum hystrix are capable of self-fertilization, and now we know how they do it.

In a new study published today in Proceedings of the Royal Society B, I investigated selfing behaviour in M. hystrix together with Lukas Schärer, Aline Schlatter and Maude Poirier at the University of Basel. Because the flatworms are transparent, we can look under the microscope and see where in their body sperm have been received, and thereby compare patterns of sperm transfer under outcrossing and selfing. The results were surprising: whereas outcrossing worms tend to contain most sperm in their tail, close to where fertilization occurs, isolated worms that have begun selfing have very few sperm in this region. Instead, the distribution of sperm is shifted forwards, including observing sperm in their head region, implying a rather strange insemination route: using their needle-like stylet (male copulatory organ), isolated worms apparently self-inject sperm into their own anterior body, from where these sperm then presumably swim through their body to fertilize their own eggs. Such a convoluted route is likely needed because, although all individuals of this species are hermaphrodites, there are no internal connections between their male and female reproductive systems.

What’s fascinating about this behaviour is that it means their needle-like stylet, which is thought to have evolved in the context of sexual conflict and attempting to inject sperm into a mating partner, can be facultatively deployed to inject sperm into themselves when environmental conditions dictate that this is likely to be the only route available for successful reproduction.

Image credit: Maude Poirier & Aline Schlatter. In this microscope image of the tail of the flatworm M. hystrix, the hooked structure towards the rear of the animal is the needle-like copulatory stylet used for injecting sperm into a mating partner…or into themselves.

Ramm SA, Schlatter A, Poirier M, Schärer L. 2015
Hypodermic self-insemination as a reproductive assurance strategy.
Proc. R. Soc. B 282: 20150660. doi:10.1098/rspb.2015.0660