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  • Evolutionary Biology

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Dr. Steven Ramm

Dr. Steven Ramm

+49 521 106-2719

Research Interests

My overarching research aim is to integrate organismal and molecular perspectives on adaptive evolution and plasticity, with a particular focus on male fertility traits such as spermatogenesis and seminal fluid. I am involved in a number of collaborative projects on a range of different taxa, but employ as my main model system a group of simultaneously hermaphroditic marine flatworms in the genus Macrostomum. This enables me to also study the impact of simultaneous hermaphroditism on the evolutionary dynamics of sexual selection and sexual conflict, and to study the causes and consequences of mating system transitions between outcrossing and selfing. I have been particularly interested in how all of these traits are impacted by variation in environmental conditions, testing for adaptive plasticity in response to social factors such as sexual competition and mate availability, and, increasingly, abiotic factors such as temperature and salinity under predicted climate change.

Reflecting my integrative approach,we employ a range of different methods to study these questions. One major focus is on gaining a mechanistic understanding using different molecular and imaging approaches in the lab (e.g. transcriptomics, RNAi, transgenics, in situ hybridisation, immunocytochemistry), whilst on the other hand we seek to elucidate the ecological and evolutionary context in which traits lined to sexual selection, sex allocation and selfing arise, combining controlled laboratory experiments (behavioural and fitness assays, experimental evolution) with field sampling of natural populations

Current Projects

The evolutionary ecology of spermatogenesis

Evolutionary biologists have long been interested in the effects of sperm competition on the evolution of relative testis size, because of its obvious effect on male sperm production capacity. However, sperm competition likely affects many other aspects of sperm production beyond testis size, and our understanding of the relationships between different sperm production parameters is rudimentary at best. A major motivation of my current research programme is therefore to understand in what ways and under what circumstances males can vary sperm production independently of testis size; how phenotypic plasticity in sperm production is achieved; and to test for genetic constraints on the evolution of sperm traits.

The functional and evolutionary genetics of seminal fluid

I have a long-standing interest in the function and rapid evolution of the other major aspect of the male ejaculate, seminal fluid proteins, stemming from my earlier research on mammals, and from current projects investigating seminal fluid-mediated effects in flatworms and snails. In flatworms, we have recently defined variation in the seminal fluid transcriptome as a major component of male allocation. We are now examining how the knockdown of specific seminal fluid proteins affects fitness through physiological and behavioural manipulation of mating partners.

Evolutionary transitions between outcrossing and selfing

Where precisely a hermaphroditic species resides on the outcrossing-to-selfing spectrum has profound consequences for micro- and macro-evolutionary processes, making the study of plasticity and transitions in reproductive mode a key question in evolutionary biology. However, although well-studied in plants, the causes and consequences of regular selfing in hermaphroditic animals are comparatively much less well explored, and we currently lack good model systems amenable to both field and laboratory studies. We are currently developing multiple Macrostomum species as models for studying selfing and its evolutionary consequences, having found substantial variation in mating systems within the genus ranging from obligate outcrossing to mixed mating or even preferential selfing.

Fertility under climate change

How animals cope with systematically changing and more variable environmental conditions is a key concern under climate change. A major question is how climate change will impact fertility, and the knock-on consequences this will have for population viability and biodiversity. One mechanism that potentially allows organisms to deal with variability in environmental conditions is phenotypic plasticity, whereby a single genotype can produce different phenotypes suited to different environments. On longer timescales, local adaptation may lead to a permanent shift in relevant reproductive traits and restore full fertility. We have begun developing Macrostomumas a potentially highly suitable model organism to study these questions, and thereby hope to answer to what extent phenotypic plasticity and local adaptation can mitigate the negative consequences of climate change on animal fertility.

Note for potential students/postdocs

If you’re interested in these or related questions and would like to discuss opportunities to join the lab, please get in touch!

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