Research

Sex and dispersal abandon different ships

Many organisms exhibit a correlation between sexual reproduction and dispersal. Aphid females develop wings when they reproduce sexually, whereas they do not have any when parthenogenetically having daughters. Cnidarian polyps can produce more polyps asexually but these are always close by, whereas sexual production of the next polyp generation is tied to the medusa stage which involves dispersal. Many plants produce stolons/runners which vegetatively make more ramets, but sexual production of seeds is tied to dispersal. There are pathogenic fungi which can asexually colonise their current host, but must have an episode of sexual reproduction to jump hosts. The diversity of examples above suggests a general explanation transcending phylogenetic boundaries, and I am interested in why such correlations emerge between reproductive modes and dispersal lifestyles.

This question is sharpened when one considers that sex and dispersal are both ways of responding to an environmental stress – abandoning a sinking ship. The question then arises of why an organism should invest in both (thus leading to the above correlation), instead of investing all its resources in making one of the two more efficient. There are many ways by which this question can be answered, and one is to show that sex and dispersal respond to different patterns of selective pressures, and that different sinking ships demand different evolutionary responses. This is the current focus of my work, with Hanna Kokko and Yagmur Erten.

Endosymbiosis and the evolutionary transitions in individuality

The evolution of life, from molecular replicators to human societies, can be viewed as a sequence of diversifications punctuated by major events known as evolutionary transitions in individuality. In each of these transitions, initially autonomous – and potentially unrelated – individuals come together over evolutionary time to give rise to a more complex, higher-level entity. The common structure that underlies these transitions is one of group formation, conflicts of interest arising between the members of this group, followed by the mediation of this conflict. I am interested in understanding – both in these historical cases and more abstractly – the factors that lead to the emergence of higher levels of individuality.

Eukaryogenesis is a prototypical example of a between-species transition, and endosymbiosis, more generally, is central to the origins of many complex biological systems. It has, however, received much less theoretical attention than the “fraternal” i.e. within-species evolutionary transitions such as those underlying the origins of multicellularity and eusociality. Why do only some symbioses undergo a full transition, and how does the host-symbiont relationship change during this process? During my master’s thesis, together with Chaitanya Gokhale and Pete Czuppon, I studied the evolution of the traits underlying two emergent collective-level properties of an endosymbiosis: host and symbiont survival as a collective (“mutual dependence”) and the level of synchronised reproduction (“reproductive cohesion”). Our results shed light on three aspects of endosymbioses: coevolution between the host and symbiont, coevolution between dependence and cohesion, and ultimately on the opportunity of undergoing an evolutionary transition.
This work resulted in a manuscript currently under review. It can be found on biorXiv here: https://doi.org/10.1101/2023.07.17.549359

Antibiotic-mediated interactions and stability in microbial communities

The coexistence observed in diverse microbial communities presents a fundamental puzzle for ecology. Studies tackling questions framed as a “diversity paradox” like above have been around for a long time, and many bodies of work have arisen as potential resolutions, such as those focused on the effects of migration, eco-evolutionary feedbacks, priority effects, etc. An especially interesting one asks whether (and if so which) patterns of interactions between species can themselves give rise to community stability. The questions here have also become much more specific over time, incorporating the effects of spatial structure, higher-order interactions, etc. I am interested in understanding to what extent biotic interactions are necessary/sufficient to explain observed patterns of diversity.

There are many observations that make coexistence a priori unlikely, but a big one is that many microbes wield antimicrobial weapons against each other. With Prateek Verma and Chaitanya Gokhale, I worked on analysing the ecological consequences of interacting via such antibiotics and other chemicals that degrade them. Our analysis of various interaction graphs involving antibiotic production, resistance, and degradation revealed that a certain producer-sensitive-degrader (PSD) motif in the interaction graph is critical for coexistence. Using individual-based simulations, we also explored its role in spatially structured populations, and our findings provide a deeper understanding of the interaction patterns that drive diversity in complex microbial communities. This work with resulted in a preprint currently under review. It can be found on biorXiv here: https://doi.org/10.1101/2023.02.15.528676