S4-1

Possible evolutionary constraints by developmental robustness

Naoki Irie¹, Yui Uchida², Masahiro Uesaka², Haiyang Hu³, Philipp Khaitovich⁴, Cynthia A. Bradham⁵, Shigeru Kuratani⁵, Wen Wang⁶, Jr-Kai Yu⁷, Guojie Zhang⁸

¹University of Tokyo, Japan
²RIKEN, Japan
³China Pharmaceutical University, China
⁴Skolkovo Institute of Science and Technology, Russia
⁵Boston University, USA
⁶Chinese Academy of Science, China
⁷Academia Sinica, Taiwan
⁸Copenhagen University, Denmark

Phenotypes are not freely changeable during evolution, and some phenotypes appears to be a lot more conservative than other phenotypes, such as basic anatomical feature (or body plan) in animal. What makes this differences in phenotypic evolution? Extended modern synthesis, including natural selections and random effects by genetic drift are the major explanations provided for this question, however, classical arguments insisted that developmental constraints could also be one of the factors, limiting the phenotypic diversification. By focusing on body plan in chordates, which are strictly conserved phenotype through more than 550 million years, we have tested if developmental robustness (or canalization) could be one of the factors limiting the diversification of animal bodyplan. Based on our recent transcriptomic-based study, we found possible contribution of pleiotropic constraints at regulatory level behind this conservative feature of animal bodyplan. Specifically, we found that genes expressed in bodyplan establishing phase of vertebrates is intensively recruited to other biological processes, and the degree of the recruitment not only correlated with essentiality for normal development, but also showed positive correlation with their evolutionary conservation. Re-utilization of existing genes has long been known to facilitate evolutionary diversification (e.g., creating novel traits etc.), however, our findings imply that gene re-utilization has a double-edged sword effect toward evolution, limiting effect on the diversification. These results imply that the more complex regulatory system the organisms have, the more constrained (or less evolvable) they become. We will also talk about our recent findings over the potential relationship between robustness of developmental system and evolvability.

S4-2

Toward prediction and control of microbial evolution: Analysis of phenotypic constraints in laboratory evolution

Chikara Furusawa^1,2

¹Center for Biosystems Dynamics Research, RIKEN
²Universal Biology Institute, The University of Tokyo

Biological systems change their state in order to adapt and evolve to changing environmental conditions. However, despite the recognition of the importance of clarifying the adaptive and evolutionary capabilities of organisms, research on the evolvability and plasticity of organisms remains at a qualitative level. To clarify how evolutionary processes are constrained in high-dimensional phenotypic and genotypic space, we performed laboratory evolution under various (>100) stress environments and analyzed phenotypic and genomic sequence changes [1,2]. These comprehensive analyses revealed that changes in expression are restricted to low-dimensional dynamics, while diverse genomic changes contribute to similar phenotypic changes. To further analyze the nature of the evolutionary constraints, we performed computer simulations of adaptive evolution using a simple cellular model. Again, we found that changes in cell state in adaptation and evolution are generally restricted to low-dimensional dynamics [3]. Based on these results, we would like to discuss the nature of phenotypic plasticity and constraints in bacterial evolution and possible strategies to predict and control evolutionary dynamics. References: [1] S. Suzuki, T. Horinouchi, and C. Furusawa, Nature Comm., 5:5792 (2014) [2] T. Maeda et al, Nature Comm., 11:5970 (2020) [3] C. Furusawa and K. Kaneko, Phys. Rev. E, 97(4-1):042410 (2018)

S4-3

Mean-scaled evolvability: new results and challenges

Christophe Pelabon¹

¹NTNU, Institute of Biology

Evolvability is the ability of organisms to evolve. On a short timescale, evolvability corresponds to the ability of a population to respond to directional selection and it depends on the amount of additive genetic variance. However, the classical standardization of additive variance by the total phenotypic variance to yield heritability has hampered our ability to understand variation in evolvability and to further test hypotheses about genetic constraints. When measured as mean-scaled additive variance, evolvability can be readily compared across traits, environments, populations, or species. Here, we will first review new insights that this measure of evolvability provides to understand variation in evolvability. We also show that this measure of evolvability provides a better metric, independent of selection, to link micro- and macroevolution. Finally, we present some limitations and challenges that remain for measuring meaningfully evolvability of ecologically important traits.

S4-4

Interspecific niche competition increases morphological diversity in multi-species microbial communities

Xiao-Lin Chu^1,2, Quan-Guo Zhang², Angus Buckling¹, Meaghan Castledine¹

¹University of Exeter
²Beijing Normal University

Intraspecific competition for limited niches has been recognized as a driving force for adaptive radiation, but results for the role of interspecific competition have been mixed. Here, we report the adaptive diversification of the model bacteria Pseudomonas fluorescens in the presence of different numbers and combinations of four competing bacterial species. Increasing the diversity of competitive community increased the morphological diversity of focal species, which is caused by impeding the domination of a single morphology. Specifically, this pattern was driven by more diverse communities being more likely to contain key species that compete with the derived dominating morphotype. Our results suggest that sympatric adaptive radiation is driven by the presence or absence of niche-specific competitors.

S4-5

The role of developmental bias in the diversification of bat molars

Alexa Sadier¹, Sharlene Santana², Karen Sears¹

¹UCLA
²UW

One long-standing question in evolutionary biology is why some phenotypes are frequently realized while other theoretically possible ones seemingly never are? This paradox has commonly been hypothesized to be caused by constraints on developmental processes that can bias or favor the expression of certain phenotypes. However, while this idea has received considerable interest as of late, it has never been demonstrated experimentally using a wide range of species, mainly because the eco-evo-devo field was lacking the tools to investigate variation of developmental programs in non-model organisms. To fill this gap, we use the dramatic diversity of bat teeth as a natural experiment. We study how the inherent structure of the tooth GRNs can both bias and facilitate evolution by testing if the modular structure of GRNs can explain both the conservation and the incredible diversity of molar shape seen in bats. To do so, by using integrative approaches mixing anatomical, developmental and modeling experiments, we identify core and sub-modules of the tooth GRN and link them to morphological variation.