Sofía Casasa

Current Research

The Casasa Lab studies the evolution of developmental mechanisms and their role shaping phenotypic diversity. We are particularly interested in how organismal development responds to environmental factors. The lab takes an integrative approach that includes genetics, genomics, developmental biology, ecology and behavior to understand the mechanisms and evolution of phenotypic plasticity. By using Onthophagus horned beetles and Pristionchus nematodes our goal is to understand phenotypic plasticity at multiple levels of biological organization.

Onthophagus horned beetles are a model system for studying the intersection of ecology with evolutionary developmental biology. These beetles exhibit an extreme form of developmental plasticity, polyphenism. Low nutrition males develop as small, hornless individuals, whereas high nutrition males develop as large, horned individuals. Horns in large males are used as weapons to gain access to females. Hornless males instead use a sneaker tactic, bypassing large males to gain access to females. Our research using horned beetles seeks to understand: 1) what are the genetic and genomic mechanisms regulating plastic horn development and their evolution? And, 2) what are the mechanisms regulating behavioral plasticity, how are they integrated with morphological plasticity, and how do they evolve?

The nematode Pristionchus pacificus is a model for developmental plasticity. Species in the family Diplogastridae are characterized by a mouth polyphenism in response to starvation and crowding. Under low food availability and crowding, individuals develop a wide mouth morphology (“eurystomatous”), with moveable teeth that enable them to prey on other nematodes. In contrast, under high food availability and low population densities individuals develop a narrow-mouth morphology (“stenostomoatous”) that feeds on bacteria and develops faster than their predatory counterpart. The predatory morphology is novel and only present in Diplogastridae (closely related outgroups such as Caenorhabditis elegans are microbivorous). Pristionchus nematodes are diverse in reproductive mode (male and female vs. hermaphrodites) and sexual dimorphism. Some species exhibit polyphenism mostly in females or hermaphrodites, whereas others display polyphenism in both sexes. Our research using predatory nematodes seeks to understand:1) how is the sexual dimorphism regulated and how do these mechanisms evolve? And, 2) what are the mechanisms that regulate predatory and microbivore behaviors, and how do they evolve?

Current Publications

• Casasa S*, Katsougia E*, Ragsdale EJ 2023. A Mediator subunit imparts robustness to a polyphenism decision. Proceedings of the National Academy of Sciences. 120: e2308816120 https://doi.org/10.1073/pnas.2308816120
• Casasa S, Biddle JF, Koutsovoulos GD, Ragsdale EJ 2021. Polyphenism of a novel trait integrated rapidly evolving genes into ancestrally plastic networks. Molecular Biology and Evolution. 38: 331-343
• Casasa S, Zattara EE, Moczek AP 2020. Nutrition-responsive gene expression
  and the developmental evolution of insect polyphenism. Nature Ecology & Evolution. 4: 970-978
• Casasa S, Moczek AP 2019. Evolution of, and via, developmental plasticity:
  insights through the study of scaling relationships. Integrative and Comparative Biology. 59(5): 1346-1355
• Schwab DB*, Casasa S*, Moczek AP 2019. On the reciprocally causal and
  constructive nature of developmental plasticity and robustness. Frontiers in Genetics. 9: 735
  (* equal contribution)
• Casasa S, Moczek AP 2018. Insulin signaling’s role in mediating tissue-specific
  nutritional plasticity and robustness in the horn-polyphenic beetle Onthophagus taurus. Proceedings of the Royal Society of London, Series B. 285: 20181631
• Casasa S, Moczek AP 2018. The role of ancestral phenotypic plasticity in
  evolutionary diversification: population density effects in the horned beetle Onthophagus taurus. Animal Behaviour. 137: 53-61
• Schwab DB, Casasa S, Moczek AP 2017. Evidence for developmental niche
  construction in dung beetles: effects on growth, scaling, and reproductive success. Ecology Letters. 20: 1353-163